CA1269596A - Chip mounting device and chip carrier mounting device - Google Patents
Chip mounting device and chip carrier mounting deviceInfo
- Publication number
- CA1269596A CA1269596A CA000539855A CA539855A CA1269596A CA 1269596 A CA1269596 A CA 1269596A CA 000539855 A CA000539855 A CA 000539855A CA 539855 A CA539855 A CA 539855A CA 1269596 A CA1269596 A CA 1269596A
- Authority
- CA
- Canada
- Prior art keywords
- solder
- tape
- support
- preform
- molten
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/0001—Technical content checked by a classifier
- H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
Landscapes
- Electric Connection Of Electric Components To Printed Circuits (AREA)
Abstract
ABSTRACT
A chip carrier mounting device includes a retaining member having a predefined pattern of apertures in which are positioned preforms of joint-forming material such as solder. The preform retains its general configuration after the interconnection or soldering process to form a resilient joint which is more capable of withstanding stress, strain and fatigue. The joint-forming material may be a filled solder composition or a supported solder which substantially maintain their physical shape when the solder is molten, or a conductive elastomer.
A chip carrier mounting device includes a retaining member having a predefined pattern of apertures in which are positioned preforms of joint-forming material such as solder. The preform retains its general configuration after the interconnection or soldering process to form a resilient joint which is more capable of withstanding stress, strain and fatigue. The joint-forming material may be a filled solder composition or a supported solder which substantially maintain their physical shape when the solder is molten, or a conductive elastomer.
Description
~U~64 ~2~i~P5~6 This is a divisional of copending Canadian Patent Application Serial No. 457,810 filed on June 29, 1984 by Raychem Corporation.
This invention relates to electrical interconnections, and to methods, devices and materials for forming such interconnections. More particularly, the invention is directed to methods, devices and materials for attaching electronic components, especially chips ~r chip carrier packages, to each other or to supporting substrates, such as circuit boards.
The microelectronics industry is steadily moving toward the use of large chips and chip carrier packages ~O (CCP) which have connection pads on the faces and/or edges.
These are generally used where there are limitations with the use of dual inline packages (DIP). The number of ~ connections on the most popular packages can range f~om 64 ; to 156. Chip carrier packages can be produced with leads attached (leaded~ or they can be leadless.
Leaded CCPs can be soldered directly onto printed cir-cuit boards (PCB) or printed wire boards (PWB)~ Leadless CCPs can be soldered onto ceramic boards or installed into connectors. However, with glass/epoxy printed circuit boards ~o or printed wire boards, leadless CCPs are usually mounted into connectors which are in turn mounted on the PCBs because o~ the effect of the different thermal expansion coefficients of the materials involved when subjected to temperature fluctuations~ These connectors are complex to manufacture ~o and costly to use. As used herein "electrically conductive elements" is intended to include CCP, PCB, PWB and other electronic or electrical components.
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'' A5 the CCP technology improve and their reliability increases, more emph~sis iB directed to ~olderin~ the~e ; packag0s directly onto t~Ei PCBs to ~ske more use of the board ~pa~e~ and di~pensing with the connectors ~ven though the use of connector~ per~its replacement of ~ulty CCPi.
The ro~t of conventional connectors relative to the C08t of the CCPi can be disproportionately high. Thi~ i8 8 strong incentive to use CCPs without connector~.
However, the direct soldering of CCPs on PCBs without the use of connectors iB associated with a number of problems.
(1) The variation of the surface flatness and non-parallel contours between the CCP and the boards produces vHrying sol~er joint heights. (2) The solder ~ill have a tendency to wick o.ut of the joint area into crevices or ~astellations in the CCP9 thus "starving" the joint are~. (3) ~old elloy-ing with the solder ~ill produce ambrittlement of the Btaryedll joint. (4) Differential thermal e~pansion between ~` ~ the CCP and the board will fr~ctur~ a thin aolder joint due to the high shear strains in the joint~ (5) 8ridging ;~ ~o between joints may occur if exce3s solder is present or if the distance between the jointe i8 small. ~S) Solder looation toleranceR are small and getting smaller yet with . ~ .
~; ~ incr~asing packaging density, ~ith e typical connection :~ p~d hsving ~ width o~ O.:D12 inehes and a O.D22-inch cienter-~5 to-center spacing~ ~7) Flux remoYal from the space between ~:~ the CCP and the PCB and ~ubsequent in~pection thersof. (8) ~; The sol:der p~stes used to attsch the CCP will produce loose solder balls which cEuse electrical problems.
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' ~ ~ MPOB64 Different ~olutiDns h~ve be~n pr~o~ed for the fore-going problems. Th~ proper positioning of R prodBtermined quantity of solder may be achieved with the use of ~older preforms spaced on B carrier or template in the locations corresponding to the points where the solder joint~ are to be formed. Example~ of this technique ~ay be found in U.S.
Patents 3,320,658, issued to Bolda et al; 3,396,B94, issued t~ Ellis; ~,472~365, issued to Tiedems; 3,719,9B~, i8 ued to 5teitzg 3,744912g, i~sued to Dewey; 4,209,B9~, issued to Dyce et al.; and 49216,350j.i~sued to Reid.
Other examples of solder p~cks and solder preforms are in U.S. Patent Nos. 3,040,119 to Granzow; 3,535~769 to Gold~chmid; 3,750,265 to Cushman; 4,099,615 to Lemke et al~
~nd 4,142,286 to Knuth et ~1. U.S. P~tent No. 3,9B2,320 to Buchoff et al. disclo~es electrically conductive connectors constructed from non-conductive and conductive el~stomers.
Although the foregoing techniques provide for the cor-rect placement of a predetermined qu~ntity of solder or other ~uitsble joint-forming materi~l, snd with the proper
This invention relates to electrical interconnections, and to methods, devices and materials for forming such interconnections. More particularly, the invention is directed to methods, devices and materials for attaching electronic components, especially chips ~r chip carrier packages, to each other or to supporting substrates, such as circuit boards.
The microelectronics industry is steadily moving toward the use of large chips and chip carrier packages ~O (CCP) which have connection pads on the faces and/or edges.
These are generally used where there are limitations with the use of dual inline packages (DIP). The number of ~ connections on the most popular packages can range f~om 64 ; to 156. Chip carrier packages can be produced with leads attached (leaded~ or they can be leadless.
Leaded CCPs can be soldered directly onto printed cir-cuit boards (PCB) or printed wire boards (PWB)~ Leadless CCPs can be soldered onto ceramic boards or installed into connectors. However, with glass/epoxy printed circuit boards ~o or printed wire boards, leadless CCPs are usually mounted into connectors which are in turn mounted on the PCBs because o~ the effect of the different thermal expansion coefficients of the materials involved when subjected to temperature fluctuations~ These connectors are complex to manufacture ~o and costly to use. As used herein "electrically conductive elements" is intended to include CCP, PCB, PWB and other electronic or electrical components.
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'' A5 the CCP technology improve and their reliability increases, more emph~sis iB directed to ~olderin~ the~e ; packag0s directly onto t~Ei PCBs to ~ske more use of the board ~pa~e~ and di~pensing with the connectors ~ven though the use of connector~ per~its replacement of ~ulty CCPi.
The ro~t of conventional connectors relative to the C08t of the CCPi can be disproportionately high. Thi~ i8 8 strong incentive to use CCPs without connector~.
However, the direct soldering of CCPs on PCBs without the use of connectors iB associated with a number of problems.
(1) The variation of the surface flatness and non-parallel contours between the CCP and the boards produces vHrying sol~er joint heights. (2) The solder ~ill have a tendency to wick o.ut of the joint area into crevices or ~astellations in the CCP9 thus "starving" the joint are~. (3) ~old elloy-ing with the solder ~ill produce ambrittlement of the Btaryedll joint. (4) Differential thermal e~pansion between ~` ~ the CCP and the board will fr~ctur~ a thin aolder joint due to the high shear strains in the joint~ (5) 8ridging ;~ ~o between joints may occur if exce3s solder is present or if the distance between the jointe i8 small. ~S) Solder looation toleranceR are small and getting smaller yet with . ~ .
~; ~ incr~asing packaging density, ~ith e typical connection :~ p~d hsving ~ width o~ O.:D12 inehes and a O.D22-inch cienter-~5 to-center spacing~ ~7) Flux remoYal from the space between ~:~ the CCP and the PCB and ~ubsequent in~pection thersof. (8) ~; The sol:der p~stes used to attsch the CCP will produce loose solder balls which cEuse electrical problems.
' ~, .
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. : :
' ~ ~ MPOB64 Different ~olutiDns h~ve be~n pr~o~ed for the fore-going problems. Th~ proper positioning of R prodBtermined quantity of solder may be achieved with the use of ~older preforms spaced on B carrier or template in the locations corresponding to the points where the solder joint~ are to be formed. Example~ of this technique ~ay be found in U.S.
Patents 3,320,658, issued to Bolda et al; 3,396,B94, issued t~ Ellis; ~,472~365, issued to Tiedems; 3,719,9B~, i8 ued to 5teitzg 3,744912g, i~sued to Dewey; 4,209,B9~, issued to Dyce et al.; and 49216,350j.i~sued to Reid.
Other examples of solder p~cks and solder preforms are in U.S. Patent Nos. 3,040,119 to Granzow; 3,535~769 to Gold~chmid; 3,750,265 to Cushman; 4,099,615 to Lemke et al~
~nd 4,142,286 to Knuth et ~1. U.S. P~tent No. 3,9B2,320 to Buchoff et al. disclo~es electrically conductive connectors constructed from non-conductive and conductive el~stomers.
Although the foregoing techniques provide for the cor-rect placement of a predetermined qu~ntity of solder or other ~uitsble joint-forming materi~l, snd with the proper
2~ dimensioning of the carrier or template~ cufficiently small qua~tities of solder can be positioned on close sp~cing between centers, these proposals do not address the problem of hi~h shear strains in the solder joints.
As noted above, among the factors considered in forming ~5 acceptable electricsl connections between the CCP and the ~B is that the connect~ons mu~t be ~ble to withstand ~tre~ses developed due to the effect of temperature fluctua-tions and the difference~ in thermal expsnsion coefficients between the moteri~l of the CCP and the substr~te or circuit board on which it i8 mounted. ~hus, a CCP may be ~ade of a cersmic material and the circuit board may be made of an epoxy-gless composition, snd when subjected tD ~levsted te~perature~ these ~lement~ will expand at dif~erent r~tes, inducing ~tre8~e8 in the connections.
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~Z~59~ MP OB 64 Even if the materi~:ls uaed in the CCP ond the oirouit board h~ve ther~al expansion ooef`ficients whieh are close in val~le to minimize the differential expansion ef~ect~l heating/
cooling eycle~ which result ~qhen power i8 bpplied acros3 the ~CP induce a temperature differential between the CCP ~nd the PCB to produce stresses in the joint , lt i8 ~ell known, and as summarized belo~, that if the solder joint iB formed into.~ "long" colu~n configuration in which the height of the o~lumn i8 much greEIter th~n the dia~et~r or transverse dimension of the ~oint, le88 atre~s i~ induced in the joint snd consequently the joint has greater reliability and longer life.
In the patent to Krall, U.S. No. 3,921,2e5, a method is described for joining microminiature component~ to e carrying ~tructure in which the height of the eloctrical connections may be adjustsd during original joining of thR
com~onent to the oarrying struoture or in a two-step solder r~flow pro~es~.
In U.S. Patent No. 4,412,642 to Fisher le~dless chip csrriers are convertsd to ~cast-le~ded chip oarriers" by molding high m~lting point lead~ to the chip carrier.
~ddition~l example~ of ~ethods and devices for interconnecting chip.carriers and bo~rds ~re chown in U . S. Patent Nos.
As noted above, among the factors considered in forming ~5 acceptable electricsl connections between the CCP and the ~B is that the connect~ons mu~t be ~ble to withstand ~tre~ses developed due to the effect of temperature fluctua-tions and the difference~ in thermal expsnsion coefficients between the moteri~l of the CCP and the substr~te or circuit board on which it i8 mounted. ~hus, a CCP may be ~ade of a cersmic material and the circuit board may be made of an epoxy-gless composition, snd when subjected tD ~levsted te~perature~ these ~lement~ will expand at dif~erent r~tes, inducing ~tre8~e8 in the connections.
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~Z~59~ MP OB 64 Even if the materi~:ls uaed in the CCP ond the oirouit board h~ve ther~al expansion ooef`ficients whieh are close in val~le to minimize the differential expansion ef~ect~l heating/
cooling eycle~ which result ~qhen power i8 bpplied acros3 the ~CP induce a temperature differential between the CCP ~nd the PCB to produce stresses in the joint , lt i8 ~ell known, and as summarized belo~, that if the solder joint iB formed into.~ "long" colu~n configuration in which the height of the o~lumn i8 much greEIter th~n the dia~et~r or transverse dimension of the ~oint, le88 atre~s i~ induced in the joint snd consequently the joint has greater reliability and longer life.
In the patent to Krall, U.S. No. 3,921,2e5, a method is described for joining microminiature component~ to e carrying ~tructure in which the height of the eloctrical connections may be adjustsd during original joining of thR
com~onent to the oarrying struoture or in a two-step solder r~flow pro~es~.
In U.S. Patent No. 4,412,642 to Fisher le~dless chip csrriers are convertsd to ~cast-le~ded chip oarriers" by molding high m~lting point lead~ to the chip carrier.
~ddition~l example~ of ~ethods and devices for interconnecting chip.carriers and bo~rds ~re chown in U . S. Patent Nos.
3.~73,4Bl to Lins et el.~ 3,6BO,lgB to Wood, 3,811,186 to ~5 Larnerd et al. ~nd 4,179,B02 to 30shi et ~1. Other methods of atteching eleetronic co~pon~nts, include the pin solder :~ :terminals of U.S. Pat~nt No. 3,750,252 to Lendm~n and the ollapsed springc of U.S. Patent No. 3,616,532 to 8eck.
OSh~r exemples of 301dering chip carriers to bo~rds include 31~ U. 5 . Pst~nt Nos. 3 ,392 ,442 to Napier et ~1., 3 ,401,126 tD
;`Mill~r ~t al., 3~4Z9,040 to Miller, 3,355,D78 to Smith, ~ 3,B59,723 to Ho~er et al. ~nd 3,61149B32 to Ch~nce et ~1.
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~ he abov~ disclosure~ ~ddress the problem of connections which ~st be able to ~ithstand the ~tree~e3 From thermal oyolea, none disclose a ~Dtisfactory ~olution ~hi~h both ~nlves the problem and i suit~ble for reliable msnufacturing proce~es.
In the ~bove diaclosuP~s the solder used i5 conventional solder which r~adily flows when molten. The flow i8 u8U~lly uf a capillary nature when the ~older i~ on a ~ettable surface~ ~uch ~8 a pre-tinned contact lead. Such conventional ~Q solder has a high surface tension tending to make the molten solder form balla when un ~ non-wettable ~urface or when positioned on n sm~ll ares of wett~ble surface, ~uch ss an : el~ctrical oDntact psd, and ~urrounded by a ncn wettable surface, such 88 ~pOXy ~oard or ceramic sub3trate. When the mass of the solder is too grest fDr the ~v~ilable wett~ble ~ urface, the solder will ~low ~cross the non-wettable -~ eurf~ces and m~y bridge nearby electrical contaot~.
Solder hss been used in verious forms and oompositions fer a variety of purp~ses as illustrated in U.S. Patent Nos.
1,281,126 to Bevan, 1,291,B7B to Hess, 1~564,335 to Feldkamp, 2,431~611 to Dur~t, 3,163,50~ to Konr~d et al., 3,467,765 to Gr-~ft, 3,605,902 and 3,638,734 to Ault, 3,900,153 to Beerwerth ~t al., ~nd 4,290,195 to Rippere.
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It is a primary object of the present invention to pro-vide a device and a method for the precise placement of a predetermined quantity of material for the formation of a solder-type connection between electrically-conductive elements.
Another object of the invention is to provide a connection~forming material which will sufficiently retain its shape at melting temperatures to form structural and electrical connection between electrically conductive elements, Another object of the invention is to provide an appara-tus and a method of the foregoing type for the placement of a connection-forming material having a predefined configuration.
Another object of the invention is to provide an appara-tus and a method of the foregoing type for the placement of aconnection-forming material preform having a height dimension greater than its transverse dimension.
Yet another object of the invention is to provide an apparatus and a method of the foregoing type for the formation of solder-type connections which are resilient and better able to withstand fatigue or repetitive thermal cycling.
Still another object of the invention is to provide an apparatu6 and a method of the foregoing type for the simultane-ous formation of a plurality of resilient solder-type connec-ti~ns between a plurality of parallel-disposed electrically-conductive elements.
A further object of the invention is to provide an apparatus and a method to attach an electronic component to a circuit board.
Yet a further object of the invention is to accurately ~ aligo the CCP uith the PWB.
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A specific object of the present invention and that of the parent Canadian Application Serial No. 457,810 is to provide apparatus, materials and methods to attach an electronic component to a circuit board with resilient solder joints which are better able to withstand thermal cycling/fa-tigue stresses, to accommodate dimensional irregularities in the components, the circuit board and the conductive elements thereon and to enable higl~ speed, high reliability manufacture of electronics component - circuit board devices~
The joint forming material of the parent invention may be a filled solder composition or a supported solder, which will retain its shape upon the solder melting or reflowing. As used herein the term "filled solder~' means a solder material which contains a filler which prevents a shape of the filled solder from changing substantially in dimensions when the temperature of a preformed shape of the filled solder is raised to or above the melting point of the solder. The filler comprises discrete particles or filaments which are solid at temperatures at which the solder is molten. The filler is present in an amount suffi-cient to substantially maintain the preformed shape of the filled solder when the solder is molten. The filler may be particulate po~der or filaments such as discreet len~ths of wire or may be a mesh ,' ;~
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`~.f or "~ool" of continuous or intern~ixæd fila~nents. P~eferably the fill~r is electrioslly conductive and Isost pre~erably is a metal. The QmOunt of ~iller present is that which is sufficient to maintain the pre~ormed shape of the filled solder~ such as a column, when the solder is melted or reflow~d. Ihe amo~nt i5 generally from about 20Z by weight to about 80~ by ~eight based on the total weight of the solder-filler ~ixture, preferably from about 25~ to about 7~, more preferably from about 30~ to about 60~, and most lo preferably ~rom about 35Z to about 4~0~.
As used herein the te~m "supported solder" means a solder preform shape which is supported by a support strand or tape which is disposed about the outside of the solder preform shape. The support strand or tape must be solid at temperatures at which the solder is molten and is disposed about the outside of the preform shape in a pattern whereby the shape of the solder is substantially maintained through the surface tension of the solder when the solder is molten.
The pattern in which the support strand or tape is disposed and the spacing, angles, etc. of the pattern will depend on the cross-sectional dimension of the solder preform shape, on the height of the preform shape and on the solder composition due to its apparent surface tension relative to the support strand or tape material. The pattern may be a spiral wrap of ~5 tape or wire, a braid of wire or the like, wherein the spacing, for example between the spiral wraps will be gp-v-erned by the above factors. In gener~l, the supported solder shape will be a column type shape suitable for ~; connecting electrically conductive elements.
~o As used herein the term `'column" means a shape which c~n form g connertion between electrically conductive elements. In general the shape will be cylindrical where the length or height of the column is grester than its cross-sertion di~ension berause thi- ~onfig~rstion provides : .
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~, '- ' ' 1~6~5~ MPOB64 ease of ~anufacture and interconnect flexibility for thermal expansion of the electrically conductivlE elements. ~he column may be straight~ curved, S-shaped, C-shaped, spiraled, etc. The term "column~ also used herein to include 5 shapes wherein the length or height is less than the cross-sectional dimension and ~ny cross~section shape suitable for connecting electrically conductive elements where the distsnce between the elements is greater than the distance used for conventional capilary flow soldering. The "col~mn"
lo need not be of uniform cross-section dimension, but May vary for flexibility or other ressons, e.g. an hour-glass shape.
As used herein the term "solder" means any conventional or specifically formulated material for forming connection between elements by melting ~nd freezing. Solders are well known as exempli~ied by the Kirk-~thmer Encyclopedia of Chemical Technclogy, 3rd Edition ~19B3), Vol. 21, pages 342-355.
As used herein, the term "spertures" means holes in or through the retsining member. Usually the holes will extend through the retaining member so that the preform of joint-forming material may be plsced therein and be exposed ; at both ends or have both ends extending from the retaining member to form a connection with an electrically conductive 'e'lement. However, the apertures may be holes in the side or L5 edge of the retaining member ~hich receive a portion of the preform and hold the preform for proper positioning to form sn electrical interconnect. These various configurations are illustrated heiein.
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The various aspects of the present invention may be summarized as follows.
According to one aspect, the invention provides a solder comprising: solder; and disposed in the solder a filler comprising discrete particles or filaments which are solid at a temperature at which the solder is molten, which are present in an amount of from 20% to 80% by weight based on the total weight of the solder-filler mixture, and which are of sufficient size and density substantially to maintain the solder in a preformed shape when the solder is molten.
According to another aspect, the invention provides a solder column for forming electrical connections comprising:
solder; and disposed in the solder a filler comprising discrete particles or filaments which are of a material which is solid at a temperature at which the solder is molten, and which are present `~ in an amount sufficient substantially to maintain the column-like shape when the solder is molten.
According to yet another aspect, the invention provides a solder column for forming electrical connections comprising:
solder; and disposed about the outside of the solder a support strand or tape which is of a material which is solid at a tempera-ture at which the solder is molten, and which is disposed about the outside of the solder in a pattern whereby the column-like ~;~ shape of the solder is substantially maintained when the solder is molten.
According to still another aspect, the invention pro-` vides a method of making a columnar solder preform, which . ~ .
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comprises:
(a~ providing a solder wire; and (b) providiny a support strand or tape disposed about the outside of the solder wire such that the shape of the preform is substantially maintained by surface tension when the solder is molten, the material of the support strand or tape being solid at a temperature at which the solder is molten.
According to a further aspect, the invention provides a method of making a columnar solder preform, which co~prises:
(a) providing a preformed support in the form of a spiral wrap or a braid of a strand or tape, (b) immersing the support in molten solder which is at a temperature at which the material of the support is substantially solid; so that solder fills the support; and (c) removing the support from the molten solder;
the support being such that solder is substantially maintained wlthln it when molten by surface tension.
According -to a final aspect, the invention provides an assembly of at least two electrically conductive elements, each having at least one contact, and a columnar solder preform which extends between the contacts forming an electrical connection between them, the preform comprising a support in the form of a spiral wrap or braid o~ a strand or tape J and a quantity of solder within the support, the support being such that the solder is substantially maintained within it when molten by surface tension~
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~ ~ MP0864 Various embodiments of the presen~ i~vention will now be described by way of example with reference to the accompanying drawings in which:
Figr 1, labeled Prior Art, represents, on an enlarged scale, a solder joint between a chip device and a circuit board formed in accordance with existing techniques;
Fig. 2 is a showing similar to Fig. 1, illustrating a joint formed with the column-type connection;
Fig. 3A is a representation of the column of Fig. 2 as a cantilevered beam fixed at one end and showing the force acting on it for the purposes of considering the ; resultant displacement and stresses;
Fig. 3B is a representation of the column of Fig. 2 :~ as a beam fixed at one end and guided at the other and deformed as a result of the relative movement of its ends;
Fig. 4 is a perspective view of one embodiment of the preform placement device of the present invention showing a plurality of column-type solder preforms mo~nted in a retaining member in the form of a perimeter type carrier element;
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Fig. 5 is an elevational view showing one of the column preforms illustrated in Fig. 4;
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~13-Fig. 6 is a cross-sectional view along line ~-6 in Fi~. 5 showing a column preform containing a filler to maintain it~ col~mn-type shape;
Fig. 7 is an elévational cross-section showing the preform placement device of Fig. 4 positioned between two structures to be joined, prior to the soldering of the connections;
Fig. 8 is a showing as in Fig. 7, after the solder connections have been formed and the retaining member of the preform placement device has been removed;
Fig. 9 shows another embodiment of the present invention;
Fig. 10 is an elevational view, in section, showing the placement device of Fig. 9 in position after the solder joints have been formed;
Fig. llA-C show alternative configurations of the solder prefvrms useable in connection with the present invention;
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Figs. 12 and 13 show additional configurations for the solder preforms as well as alternative aperture configurations in the retaining member; and Figs. t4A-D show embodiments of supported solder columns - of this invention wherein Fig. 14C shows column after the solder joints have been formed and the retaining member ~: removed.
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. . ~ , , In the ~es~ript~on herein, the solder iDining of a chip ~arrier package, which is re~erred to hereafter as a "chip device" or a "chip carrier", and a circuit board is used as an illustrative application of the present invention. The joining of other electronic components is also comprehended, and the invention may be employed wherever and whenever a solder connection of i~creased reliability and longer life is desired.
Referring to the drawings, and more particularly to Fig. 1, a joint or connection made 'in accordance with techniques known in the prior art is shown formed between a chip device 10 and a circuit board 12. The chip device 10 has a plurality of electrical contacts which may be disposed along its edge.
Only one contact area is shown for the sake of simplicity.
The circuit board 12 has a plurality of complementary contact areas on its surface ~only one shown). The circuit board 12 may be a printed circuit board (PCB) or a printed wire board (PWB), and may be referred to hereinafter simply as a ~board"
~; or "circuit board." In a known fashion, the chip device will be disposed above the surface of the circuit board such that - the contact areas are vertically aligned and mechanically and/or ' electrically joined, such as with a solder connection. In the illustration of Fig. 1, the opposed, facing surface of the chip device 10 and the circuit board 12 is provided with a layer 14 of conductive material, such as copper, and these layers ~re interconnected with a suitable solder composition 16, which may be of known tin-lead alloy.
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As noted above, a s~ld~r connection 5uch as shown in Fig. 1 is subjected to s~resses in~uced by thermal and mechan~cal forces. These stresses are the result of strains produced by mechanical deformation, differences in temperature between the chip device and the printed circuit board and/or differen-- ces in the thermal coefficients of expansion between the chip device and ~he PCB. For example, ~hermal stresses may result from power cycling even when the materials of the chip device and circuit board do not exhibit any differences in the coefficient of thermal expansion, but because of the power applied to the chip device, a temperature diEferential exists bet~een the chip device and the circui~ board.
It can be seen that as the connection is subjected to repeated heating and cooling cycles, it will ultimately fail due to fatigue, and the connection will fail earlier if the stresses induced therein are high. Therefore, to prolong the life of the ~oint and to increase its reliability, the resultant stresses therein should be reduced. In order to determine how the stresses can be reduced, the factors governing the creation of the stresses in the joint should be considered.
- In Fig. 2 a column type connection 18 is illustrated and Figs~ 3A and 3~ illustrate the relationship between the deflection F for a given column of height H and diameter D for a given forces F. As will be apparent, the column t~p~-connection will have a longer life due to better withstanding of~stresses. The selection of hei~ht and diameter will be determined by a number of factors of -~ size and materials. A detailed finite element analysis of similar joint structures was presented by E. A. Wilsonr ., ~ .
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` `'` '' '' Honeywell, Phoenix, Arizona, and E. P. Anderson, Honeywell, Bloomington, Minnesota, in their paper entitled "An Analytical Investigation into Geometric Influence on Integrated Circuit Bump Strain," which was presented at the 33rd Electronic Components Conference, May 16 18, 1983, in Orlando, Florida IProceedings page 320-327). This analysis confirms the advantages of columnar structures.
It is understood that by reducing the peak stresses as described above in a repeti-tive loading situation, the number of cycles required to produce failure is greatly increased.
From the foregoing evaluations, it can be seen that the life of the solder joints can be increased substantially by a relatively s~all increase in solder joint height. Likewise, a reduction in solder joint diameter will extend the life of the solder joints. A concomittant advantage in using joints of in-creased height and/or reduced diameter is the opportunity for increased packing density. The foregoing evaluations are helpful ln predlcting the general properties and performance to be expected from the devices and methods of this invention. However, it is a1so helpful to verify performance properties by empirical testing of the devices of this invention.
The foregoing advantages of reduced stresses and extended life in the solder joints and the opportunity for increased packing density are-incorporated in the present inven-, ~ tion which provides a device for the precise positioning of solder preform of slender cylindrical shapes at predefined locations. In the embodiment of the invention illustrated in Fig. 4, the interconnectlon preform placement device 20 ' .
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~P~a6 . -17-includes a ret~ining member 22 o~ ~lectric~lly nonconductive materisl h~ing a ~onfiguration ~nd size ~ub~tantislly the 8ame as the chip carrier f~r whi h the prefarm placement device i~ u3~d in mo~nting the chip carrier on 8 3uit~ble substrat~, such aa a circuit board. The holder 22 has a central cut-out Z4 to form-~ perimeter or bordering portion in which ~re Rp~ed et predetermin~d locati~ns a plurslity of holos 26 which receive preforms 28 of solder in the shepe of slender cylindrieel columns, such ~ sh~wn in Fig. 5.
~0 The ret~ining member m~y ~150 herein be referred to e9 a "holder."
~ The location and positioning of the holes 26 on the re-: tsining ~ember 22 ~re determined by the spac~ng of the con-ductive contscts disposed on the edge of the chip cerrier tD
~5 be ~ounted1 Gener~lly, the height of e~ch solder preform 28 . ~ill ba aomewhat taller than the thickness of the ret~ining ; ~ember 22 auch thot the upper and lower edge portion~ of each aolder preform 2~ will extend above the corre~ponding surfaces of the retaining member, ~nd in uae these exposed surf~ces : ~O will make physical contsct with the corresponding conductive p~ds on the chip carrier and on the circuit board~
hile not pecifically ~hown in Fig. 4, the preform plsce-ment device i8 provided with appropriate meanY for properly locating and orienting the reteining member 22 with respect to 2s the chip carrier ond the circuit bDard 80 that the conductiYe pad3 on the chip c~rrier, the conductive p~ds on the circuit ~ board and the column solder pre~orm~ ere properly ~ligned~
Such locating ~eane are kn~wn, and m~y include a chQmfered oorner which m~te~ with ~ similerly-configured ~urfscP on .
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the ohip carrier. One cr ~ore of the corners m~y h~ve an indexing notch~ Additionelly~ alignment pins may be provided on the bottom ~urf~ce ~f the ret~ining member 22, sr hDles to accept pin~ ~hioh regi~ter ~ith positioning hole~
provid0d on ths circuit board. A combination of s~ch pnsitioning techniques ~ay be incorporated into the holder 2~.
It i~ possibls to v~r~ the composition of the ~older ~aterial ~uch that the solder preform will give or rompress under the weight of the chip carrier to be mounted. This compressibility of the solder preform i8 important becau~e the chip carrier ~nd the circuit board are typically not truly flat 80 that the length~ of the solder columns must chsnge during the soldering proces~ to eccommodate the~e irregularitie~.
The retaining member 22 may be made from any suitable materiAl, and prefer~bly is of an electrically-nonconductive .material. The material may be a ~ingle sheet or lay0r of desired thicknes~, or may be 9 lamin~te of 8 plurality of 20 thin sheet~ or lsyers of suitable meterisl or may be A
~lurolity of elements which form a sheet-like structure~
Such material ~ould include, but is not limited to, glass matt and high-temperatur0 polymerio materials such B9 Ultem~(Ultem is a trademark of General Electric Company.).
~5 The m~terial nf the retaining ~ember 22 should be sufficiently rigid and temperature-re~ist~nt to maintsin the solder ~ preform's position during the soIdering procea~.
-~ Preferably there ~re t~o cstegorie~ of reteining member~, those th~t are removable and those thet beco~e a ~o perm~nent part of the interconnection. The remov~ble type could be dissolvable, fr~ngible, ~egmented, or defDrmable without harming the prefor~. The permanent ar nonremovable ., .
type can be p~ive or can perfQrm electric~l, mech~nical ~nd/or therm~l functions. The removable type cen therefore ~;
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be destroye~ by dis301Ying or breaking apsrt. Th~ 9108s ~stt e~bodiment can be phy~ic~lly pulled away in ~hole or pieoe by piece. ~he Ulte~ materi~l csn be dissolved by ~ell-known chemical ~esn~ without harmirlg the preform or electrical ly conductive elements.
It is ~ithin the scope of the invention to makP a aegmented retsining member that can be ~tripped away aFter interconnection. The retaining me~ber 22 in Figure 4 can be provided with lines of weakness ~r cuta æs iehown Bt 29 in ~o ph~ntom line. In thie ~sy, the retaining ~ember 2~ may be removed in one or ~ore pieces end directions. The retaining member may el80 originally be made from individual elements as will be discussed later.
Thus it con be eeen that the removsble retaining member ~5 may also be conductive such a8 an aluminum foil in order to maintain the position of the preforms during interconnection.
It is important that ~uch 8 ret~ining member not bDnd to the prefor~ during the process.
Finelly, the reteining member cQn be mede from a thin heet nf ~older material which could melt end flow into the ~older-like pref~rms during the soldering procs~s.
The reteining member which remains in place should be generally nonconductive and relatively flexible 80 that it doe~ not interFere with the motion of the preform columns.
~5 Additionslly, it may provide ~n impedence-metched interconnec-~ tion if it is o combinetion of conductive ~nd dielectric mate-;~ rial ~o that it provides ~ trensmissiDn line or microstrip offect, or s coaxi~l type shield eround the preforms.
In another ~mbodi~ent the reteining member could be made from ~ noncondutive materisI ~hich, ho~ever, becDmes conduc-tive ~hen ~ specific voltage threshold is exceeded, this ShreshDld being just ~bove the normal operating voltage of the `::
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-2~-~ircuit. Thi~ type of' ret~i~ing member ~ould provide protec-tion to the chip device by ahorting DUt any potenSially dam~-ging tr~nsi0nt overvoltage ~hieh m~y result from electro-~tatic di~charge or other electrical f~ults.
In 30me ~pplications, it ~y be desir~ble to m~ke the retaining member from a ~terial which exhibits heat-recovery.
T.his type of retaining member could be reinforced ~ith gla~s fibPr or the like ts control ~t~ coef~icient of thermal expan-3inn, but locally the holes which are provided for ret~ining the ~older-like oolumns could be fabricated B0 ea to ountract in diameter during soldering and thereby extrude the solder column up to neet the CCP ~nd PWB.
Although the retaining member has been ~hown to position only interconnection preform~ in Figures 4 snd 7-10, it i8 under~tood that other element~ ~ould al80 be pnsitioned by the retaining member ~nd attached to the chip devire and board. A
heat-sink device could be csrried in the central opening of the retaining ~ember oF Figure 4 and bondsd to the CCP and PWB
during soldering. 5imilarly~ ~ vibration damper, structural reinforcement9 or a Peltier type cooler could be po3itioned ~nd attached to the CCP ~nd the PWB. Al~o, fln electricfll ground plane could be positioned near the interconn,ection preforms to benefioially ~odi~y their electronic impedence ehar,~.cteristic~ similar to ~ microstrip board trace.
Figure 4 shows 8 square periphersl srrsy of intercon-n~ction~. However, other p~tterns or arrBy~ could ~130 be ac-oomplished by this invention. Any m~trix of intercon-nections on ~ regular rectiline~r form~t could be provided.
Non-rectilinesr or psrtially filled arrsy~ c~uld olso be prov~ded.
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lf the interconnection3 are arranged suffici~ntly ~lo~e together, a random-type interconnection 8y8tem could be produced. In this type of syRtem, since the intercon-nection density i~ much higher than the density of the pads o~ ~he ~CP Qnd PWB~ then ~tatistic~:Lly there will ~lways be ~t lea~t one interconnecting preform loe2ted between each pad set to be interconneet~d. The arr~ngement of the interconnection~ i8 completely random in this type of holder sy~tem. This type of retaining member mcy ideally be msde from a plur~lity o~ element~ bonded together, esch hAving at least one ~perture therethrough. The elements, such as 31 shown in phantom in Fig. 4, ~ay be of uniform or random cross-~ection in order that they msy be efficiently b~ndled and permanently or temporarily joined together such lS as by fusion or proper adhesive materisl to form n sheet-like ~tructure. In ~uch n bundled configuration the reteining . member elements may be formed by continuously extruding the - retaining member material over the preform, cutting the extruded composite into discrete pieces, bundling the ~ 20 axi~lly-aligned pieces and prafer~bly joining the ret~ining :~ member ~aterial nnd then ~licing the assembly st right angles to the axial alignment to make a preform placement device.
Also ~hown in the configuration shown in Fig. 4, the retaining member 22 csn be ideally stamped from 8 sheet of ~ateriAl, or othsrwi~e cut from sheet material. Quite pos-~ibly the ret~ining member f~bricating proeess would provide for the oimultaneous eta~ping of the holder ~hape and the central cut-out 24 ~nd form~tion of the properly_spaced 3~ hole~ 26~ and insertion ~f the solder preforms into the holes. Of course, it is pos3ibIe that the production of the retoining member 22 c~n be ~chieved in ~ sequence of steps .
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in ~ h the ~ ining ~ember with it~ cut-out end orienta-tion a~rfsces i8 st~ped ~ro~ a ~heet ~aterial, ~nd aubsequent techniqu~s are ~sed to form the hol~ into which the solder preforms ~re inserted. Other ~anuf~cturing ~ethods such as molding or in~ert molding ~re within the seope of the invention.
The retaining member ~2 m~y be fabricated ~rom a ~heet or a l~minate of he~t recover~ble m~terial, whereby the retainlng member is ~tamped from the m~teri~l sheet, the holes formed D therein, Rnd the solder preforms positioned within the holes.
~ubsequently, the reteining member i8 he~ted to a temperature sufficient to oause the ~aterial to recover such that the diameters o~ the holes 26 are reduced, but ~t a temperature below the melting point of the solder preforms. Ihe use of a heat~recoverable material ~or the retsining 22 affords the odvantages that the holes csn be form~d to a predefined ~hape, ~uch 88 ~n hourglsss, with vsrying diameters, such that the diameter of the middle section is smaller thsn the diameter at the ends. These holes would be expanded to a unifor~
~o diameter l~rger than the diameter of the preform~ so that the preforms car~ be more readily positioned in the holes, after which the ret~ining member 22 i8 heat-recovered, causing each hole to constrict to r size ~ubstantially identical to the diameter of the preform, thus securely gripping the preform within the retaining member. Furthermore, the use of a heat-rec-o-Yerable materi~l sffords the sdvantsge that in ~se, when heat i~ applied to effect the sDlder joint, such ~s by a ~older reflD~ process, the ~irm gripping o~ the solder pre-froms by the heat-recovered ret~ining member material will ~o i~p~rt the origin~l hourglass sh~pe of the holes to the preform, thus improving the flexibility of the ~olumn-type joints, Dnd in turn reducing the ~tresses ~nd improving the relinbility of the joints.
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~ t i~ D posaib~e to further control the ulti~ate con-figur~tion of the solder joint by the u~e Df ~ he~t-recoverable ~teri~l in th~ retaining me~ber 22. This can be ~chieved by p~rtially recovering the material, causing the holes to securely ~rip the pref~rms. ~hen, during the soldering process, su~ficient heat i8 applied to cause the material of the retaining ~ember to further recover, thereby further decre~ing the dismeter of the holes to apply a con~trictive force onto the moltsn or ~oftsned preForm. Thiæ will have o a ten~ency to produce column joint~ of height greater than the thickneRs of the retaining ~ember 22.
While the ret~ining member 22 has been shown in F:lgure
OSh~r exemples of 301dering chip carriers to bo~rds include 31~ U. 5 . Pst~nt Nos. 3 ,392 ,442 to Napier et ~1., 3 ,401,126 tD
;`Mill~r ~t al., 3~4Z9,040 to Miller, 3,355,D78 to Smith, ~ 3,B59,723 to Ho~er et al. ~nd 3,61149B32 to Ch~nce et ~1.
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~ he abov~ disclosure~ ~ddress the problem of connections which ~st be able to ~ithstand the ~tree~e3 From thermal oyolea, none disclose a ~Dtisfactory ~olution ~hi~h both ~nlves the problem and i suit~ble for reliable msnufacturing proce~es.
In the ~bove diaclosuP~s the solder used i5 conventional solder which r~adily flows when molten. The flow i8 u8U~lly uf a capillary nature when the ~older i~ on a ~ettable surface~ ~uch ~8 a pre-tinned contact lead. Such conventional ~Q solder has a high surface tension tending to make the molten solder form balla when un ~ non-wettable ~urface or when positioned on n sm~ll ares of wett~ble surface, ~uch ss an : el~ctrical oDntact psd, and ~urrounded by a ncn wettable surface, such 88 ~pOXy ~oard or ceramic sub3trate. When the mass of the solder is too grest fDr the ~v~ilable wett~ble ~ urface, the solder will ~low ~cross the non-wettable -~ eurf~ces and m~y bridge nearby electrical contaot~.
Solder hss been used in verious forms and oompositions fer a variety of purp~ses as illustrated in U.S. Patent Nos.
1,281,126 to Bevan, 1,291,B7B to Hess, 1~564,335 to Feldkamp, 2,431~611 to Dur~t, 3,163,50~ to Konr~d et al., 3,467,765 to Gr-~ft, 3,605,902 and 3,638,734 to Ault, 3,900,153 to Beerwerth ~t al., ~nd 4,290,195 to Rippere.
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It is a primary object of the present invention to pro-vide a device and a method for the precise placement of a predetermined quantity of material for the formation of a solder-type connection between electrically-conductive elements.
Another object of the invention is to provide a connection~forming material which will sufficiently retain its shape at melting temperatures to form structural and electrical connection between electrically conductive elements, Another object of the invention is to provide an appara-tus and a method of the foregoing type for the placement of a connection-forming material having a predefined configuration.
Another object of the invention is to provide an appara-tus and a method of the foregoing type for the placement of aconnection-forming material preform having a height dimension greater than its transverse dimension.
Yet another object of the invention is to provide an apparatus and a method of the foregoing type for the formation of solder-type connections which are resilient and better able to withstand fatigue or repetitive thermal cycling.
Still another object of the invention is to provide an apparatu6 and a method of the foregoing type for the simultane-ous formation of a plurality of resilient solder-type connec-ti~ns between a plurality of parallel-disposed electrically-conductive elements.
A further object of the invention is to provide an apparatus and a method to attach an electronic component to a circuit board.
Yet a further object of the invention is to accurately ~ aligo the CCP uith the PWB.
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A specific object of the present invention and that of the parent Canadian Application Serial No. 457,810 is to provide apparatus, materials and methods to attach an electronic component to a circuit board with resilient solder joints which are better able to withstand thermal cycling/fa-tigue stresses, to accommodate dimensional irregularities in the components, the circuit board and the conductive elements thereon and to enable higl~ speed, high reliability manufacture of electronics component - circuit board devices~
The joint forming material of the parent invention may be a filled solder composition or a supported solder, which will retain its shape upon the solder melting or reflowing. As used herein the term "filled solder~' means a solder material which contains a filler which prevents a shape of the filled solder from changing substantially in dimensions when the temperature of a preformed shape of the filled solder is raised to or above the melting point of the solder. The filler comprises discrete particles or filaments which are solid at temperatures at which the solder is molten. The filler is present in an amount suffi-cient to substantially maintain the preformed shape of the filled solder when the solder is molten. The filler may be particulate po~der or filaments such as discreet len~ths of wire or may be a mesh ,' ;~
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`~.f or "~ool" of continuous or intern~ixæd fila~nents. P~eferably the fill~r is electrioslly conductive and Isost pre~erably is a metal. The QmOunt of ~iller present is that which is sufficient to maintain the pre~ormed shape of the filled solder~ such as a column, when the solder is melted or reflow~d. Ihe amo~nt i5 generally from about 20Z by weight to about 80~ by ~eight based on the total weight of the solder-filler ~ixture, preferably from about 25~ to about 7~, more preferably from about 30~ to about 60~, and most lo preferably ~rom about 35Z to about 4~0~.
As used herein the te~m "supported solder" means a solder preform shape which is supported by a support strand or tape which is disposed about the outside of the solder preform shape. The support strand or tape must be solid at temperatures at which the solder is molten and is disposed about the outside of the preform shape in a pattern whereby the shape of the solder is substantially maintained through the surface tension of the solder when the solder is molten.
The pattern in which the support strand or tape is disposed and the spacing, angles, etc. of the pattern will depend on the cross-sectional dimension of the solder preform shape, on the height of the preform shape and on the solder composition due to its apparent surface tension relative to the support strand or tape material. The pattern may be a spiral wrap of ~5 tape or wire, a braid of wire or the like, wherein the spacing, for example between the spiral wraps will be gp-v-erned by the above factors. In gener~l, the supported solder shape will be a column type shape suitable for ~; connecting electrically conductive elements.
~o As used herein the term `'column" means a shape which c~n form g connertion between electrically conductive elements. In general the shape will be cylindrical where the length or height of the column is grester than its cross-sertion di~ension berause thi- ~onfig~rstion provides : .
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~, '- ' ' 1~6~5~ MPOB64 ease of ~anufacture and interconnect flexibility for thermal expansion of the electrically conductivlE elements. ~he column may be straight~ curved, S-shaped, C-shaped, spiraled, etc. The term "column~ also used herein to include 5 shapes wherein the length or height is less than the cross-sectional dimension and ~ny cross~section shape suitable for connecting electrically conductive elements where the distsnce between the elements is greater than the distance used for conventional capilary flow soldering. The "col~mn"
lo need not be of uniform cross-section dimension, but May vary for flexibility or other ressons, e.g. an hour-glass shape.
As used herein the term "solder" means any conventional or specifically formulated material for forming connection between elements by melting ~nd freezing. Solders are well known as exempli~ied by the Kirk-~thmer Encyclopedia of Chemical Technclogy, 3rd Edition ~19B3), Vol. 21, pages 342-355.
As used herein, the term "spertures" means holes in or through the retsining member. Usually the holes will extend through the retaining member so that the preform of joint-forming material may be plsced therein and be exposed ; at both ends or have both ends extending from the retaining member to form a connection with an electrically conductive 'e'lement. However, the apertures may be holes in the side or L5 edge of the retaining member ~hich receive a portion of the preform and hold the preform for proper positioning to form sn electrical interconnect. These various configurations are illustrated heiein.
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~ 26775-71D
The various aspects of the present invention may be summarized as follows.
According to one aspect, the invention provides a solder comprising: solder; and disposed in the solder a filler comprising discrete particles or filaments which are solid at a temperature at which the solder is molten, which are present in an amount of from 20% to 80% by weight based on the total weight of the solder-filler mixture, and which are of sufficient size and density substantially to maintain the solder in a preformed shape when the solder is molten.
According to another aspect, the invention provides a solder column for forming electrical connections comprising:
solder; and disposed in the solder a filler comprising discrete particles or filaments which are of a material which is solid at a temperature at which the solder is molten, and which are present `~ in an amount sufficient substantially to maintain the column-like shape when the solder is molten.
According to yet another aspect, the invention provides a solder column for forming electrical connections comprising:
solder; and disposed about the outside of the solder a support strand or tape which is of a material which is solid at a tempera-ture at which the solder is molten, and which is disposed about the outside of the solder in a pattern whereby the column-like ~;~ shape of the solder is substantially maintained when the solder is molten.
According to still another aspect, the invention pro-` vides a method of making a columnar solder preform, which . ~ .
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comprises:
(a~ providing a solder wire; and (b) providiny a support strand or tape disposed about the outside of the solder wire such that the shape of the preform is substantially maintained by surface tension when the solder is molten, the material of the support strand or tape being solid at a temperature at which the solder is molten.
According to a further aspect, the invention provides a method of making a columnar solder preform, which co~prises:
(a) providing a preformed support in the form of a spiral wrap or a braid of a strand or tape, (b) immersing the support in molten solder which is at a temperature at which the material of the support is substantially solid; so that solder fills the support; and (c) removing the support from the molten solder;
the support being such that solder is substantially maintained wlthln it when molten by surface tension.
According -to a final aspect, the invention provides an assembly of at least two electrically conductive elements, each having at least one contact, and a columnar solder preform which extends between the contacts forming an electrical connection between them, the preform comprising a support in the form of a spiral wrap or braid o~ a strand or tape J and a quantity of solder within the support, the support being such that the solder is substantially maintained within it when molten by surface tension~
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~ ~ MP0864 Various embodiments of the presen~ i~vention will now be described by way of example with reference to the accompanying drawings in which:
Figr 1, labeled Prior Art, represents, on an enlarged scale, a solder joint between a chip device and a circuit board formed in accordance with existing techniques;
Fig. 2 is a showing similar to Fig. 1, illustrating a joint formed with the column-type connection;
Fig. 3A is a representation of the column of Fig. 2 as a cantilevered beam fixed at one end and showing the force acting on it for the purposes of considering the ; resultant displacement and stresses;
Fig. 3B is a representation of the column of Fig. 2 :~ as a beam fixed at one end and guided at the other and deformed as a result of the relative movement of its ends;
Fig. 4 is a perspective view of one embodiment of the preform placement device of the present invention showing a plurality of column-type solder preforms mo~nted in a retaining member in the form of a perimeter type carrier element;
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Fig. 5 is an elevational view showing one of the column preforms illustrated in Fig. 4;
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~13-Fig. 6 is a cross-sectional view along line ~-6 in Fi~. 5 showing a column preform containing a filler to maintain it~ col~mn-type shape;
Fig. 7 is an elévational cross-section showing the preform placement device of Fig. 4 positioned between two structures to be joined, prior to the soldering of the connections;
Fig. 8 is a showing as in Fig. 7, after the solder connections have been formed and the retaining member of the preform placement device has been removed;
Fig. 9 shows another embodiment of the present invention;
Fig. 10 is an elevational view, in section, showing the placement device of Fig. 9 in position after the solder joints have been formed;
Fig. llA-C show alternative configurations of the solder prefvrms useable in connection with the present invention;
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Figs. 12 and 13 show additional configurations for the solder preforms as well as alternative aperture configurations in the retaining member; and Figs. t4A-D show embodiments of supported solder columns - of this invention wherein Fig. 14C shows column after the solder joints have been formed and the retaining member ~: removed.
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. . ~ , , In the ~es~ript~on herein, the solder iDining of a chip ~arrier package, which is re~erred to hereafter as a "chip device" or a "chip carrier", and a circuit board is used as an illustrative application of the present invention. The joining of other electronic components is also comprehended, and the invention may be employed wherever and whenever a solder connection of i~creased reliability and longer life is desired.
Referring to the drawings, and more particularly to Fig. 1, a joint or connection made 'in accordance with techniques known in the prior art is shown formed between a chip device 10 and a circuit board 12. The chip device 10 has a plurality of electrical contacts which may be disposed along its edge.
Only one contact area is shown for the sake of simplicity.
The circuit board 12 has a plurality of complementary contact areas on its surface ~only one shown). The circuit board 12 may be a printed circuit board (PCB) or a printed wire board (PWB), and may be referred to hereinafter simply as a ~board"
~; or "circuit board." In a known fashion, the chip device will be disposed above the surface of the circuit board such that - the contact areas are vertically aligned and mechanically and/or ' electrically joined, such as with a solder connection. In the illustration of Fig. 1, the opposed, facing surface of the chip device 10 and the circuit board 12 is provided with a layer 14 of conductive material, such as copper, and these layers ~re interconnected with a suitable solder composition 16, which may be of known tin-lead alloy.
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As noted above, a s~ld~r connection 5uch as shown in Fig. 1 is subjected to s~resses in~uced by thermal and mechan~cal forces. These stresses are the result of strains produced by mechanical deformation, differences in temperature between the chip device and the printed circuit board and/or differen-- ces in the thermal coefficients of expansion between the chip device and ~he PCB. For example, ~hermal stresses may result from power cycling even when the materials of the chip device and circuit board do not exhibit any differences in the coefficient of thermal expansion, but because of the power applied to the chip device, a temperature diEferential exists bet~een the chip device and the circui~ board.
It can be seen that as the connection is subjected to repeated heating and cooling cycles, it will ultimately fail due to fatigue, and the connection will fail earlier if the stresses induced therein are high. Therefore, to prolong the life of the ~oint and to increase its reliability, the resultant stresses therein should be reduced. In order to determine how the stresses can be reduced, the factors governing the creation of the stresses in the joint should be considered.
- In Fig. 2 a column type connection 18 is illustrated and Figs~ 3A and 3~ illustrate the relationship between the deflection F for a given column of height H and diameter D for a given forces F. As will be apparent, the column t~p~-connection will have a longer life due to better withstanding of~stresses. The selection of hei~ht and diameter will be determined by a number of factors of -~ size and materials. A detailed finite element analysis of similar joint structures was presented by E. A. Wilsonr ., ~ .
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` `'` '' '' Honeywell, Phoenix, Arizona, and E. P. Anderson, Honeywell, Bloomington, Minnesota, in their paper entitled "An Analytical Investigation into Geometric Influence on Integrated Circuit Bump Strain," which was presented at the 33rd Electronic Components Conference, May 16 18, 1983, in Orlando, Florida IProceedings page 320-327). This analysis confirms the advantages of columnar structures.
It is understood that by reducing the peak stresses as described above in a repeti-tive loading situation, the number of cycles required to produce failure is greatly increased.
From the foregoing evaluations, it can be seen that the life of the solder joints can be increased substantially by a relatively s~all increase in solder joint height. Likewise, a reduction in solder joint diameter will extend the life of the solder joints. A concomittant advantage in using joints of in-creased height and/or reduced diameter is the opportunity for increased packing density. The foregoing evaluations are helpful ln predlcting the general properties and performance to be expected from the devices and methods of this invention. However, it is a1so helpful to verify performance properties by empirical testing of the devices of this invention.
The foregoing advantages of reduced stresses and extended life in the solder joints and the opportunity for increased packing density are-incorporated in the present inven-, ~ tion which provides a device for the precise positioning of solder preform of slender cylindrical shapes at predefined locations. In the embodiment of the invention illustrated in Fig. 4, the interconnectlon preform placement device 20 ' .
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~P~a6 . -17-includes a ret~ining member 22 o~ ~lectric~lly nonconductive materisl h~ing a ~onfiguration ~nd size ~ub~tantislly the 8ame as the chip carrier f~r whi h the prefarm placement device i~ u3~d in mo~nting the chip carrier on 8 3uit~ble substrat~, such aa a circuit board. The holder 22 has a central cut-out Z4 to form-~ perimeter or bordering portion in which ~re Rp~ed et predetermin~d locati~ns a plurslity of holos 26 which receive preforms 28 of solder in the shepe of slender cylindrieel columns, such ~ sh~wn in Fig. 5.
~0 The ret~ining member m~y ~150 herein be referred to e9 a "holder."
~ The location and positioning of the holes 26 on the re-: tsining ~ember 22 ~re determined by the spac~ng of the con-ductive contscts disposed on the edge of the chip cerrier tD
~5 be ~ounted1 Gener~lly, the height of e~ch solder preform 28 . ~ill ba aomewhat taller than the thickness of the ret~ining ; ~ember 22 auch thot the upper and lower edge portion~ of each aolder preform 2~ will extend above the corre~ponding surfaces of the retaining member, ~nd in uae these exposed surf~ces : ~O will make physical contsct with the corresponding conductive p~ds on the chip carrier and on the circuit board~
hile not pecifically ~hown in Fig. 4, the preform plsce-ment device i8 provided with appropriate meanY for properly locating and orienting the reteining member 22 with respect to 2s the chip carrier ond the circuit bDard 80 that the conductiYe pad3 on the chip c~rrier, the conductive p~ds on the circuit ~ board and the column solder pre~orm~ ere properly ~ligned~
Such locating ~eane are kn~wn, and m~y include a chQmfered oorner which m~te~ with ~ similerly-configured ~urfscP on .
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the ohip carrier. One cr ~ore of the corners m~y h~ve an indexing notch~ Additionelly~ alignment pins may be provided on the bottom ~urf~ce ~f the ret~ining member 22, sr hDles to accept pin~ ~hioh regi~ter ~ith positioning hole~
provid0d on ths circuit board. A combination of s~ch pnsitioning techniques ~ay be incorporated into the holder 2~.
It i~ possibls to v~r~ the composition of the ~older ~aterial ~uch that the solder preform will give or rompress under the weight of the chip carrier to be mounted. This compressibility of the solder preform i8 important becau~e the chip carrier ~nd the circuit board are typically not truly flat 80 that the length~ of the solder columns must chsnge during the soldering proces~ to eccommodate the~e irregularitie~.
The retaining member 22 may be made from any suitable materiAl, and prefer~bly is of an electrically-nonconductive .material. The material may be a ~ingle sheet or lay0r of desired thicknes~, or may be 9 lamin~te of 8 plurality of 20 thin sheet~ or lsyers of suitable meterisl or may be A
~lurolity of elements which form a sheet-like structure~
Such material ~ould include, but is not limited to, glass matt and high-temperatur0 polymerio materials such B9 Ultem~(Ultem is a trademark of General Electric Company.).
~5 The m~terial nf the retaining ~ember 22 should be sufficiently rigid and temperature-re~ist~nt to maintsin the solder ~ preform's position during the soIdering procea~.
-~ Preferably there ~re t~o cstegorie~ of reteining member~, those th~t are removable and those thet beco~e a ~o perm~nent part of the interconnection. The remov~ble type could be dissolvable, fr~ngible, ~egmented, or defDrmable without harming the prefor~. The permanent ar nonremovable ., .
type can be p~ive or can perfQrm electric~l, mech~nical ~nd/or therm~l functions. The removable type cen therefore ~;
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be destroye~ by dis301Ying or breaking apsrt. Th~ 9108s ~stt e~bodiment can be phy~ic~lly pulled away in ~hole or pieoe by piece. ~he Ulte~ materi~l csn be dissolved by ~ell-known chemical ~esn~ without harmirlg the preform or electrical ly conductive elements.
It is ~ithin the scope of the invention to makP a aegmented retsining member that can be ~tripped away aFter interconnection. The retaining me~ber 22 in Figure 4 can be provided with lines of weakness ~r cuta æs iehown Bt 29 in ~o ph~ntom line. In thie ~sy, the retaining ~ember 2~ may be removed in one or ~ore pieces end directions. The retaining member may el80 originally be made from individual elements as will be discussed later.
Thus it con be eeen that the removsble retaining member ~5 may also be conductive such a8 an aluminum foil in order to maintain the position of the preforms during interconnection.
It is important that ~uch 8 ret~ining member not bDnd to the prefor~ during the process.
Finelly, the reteining member cQn be mede from a thin heet nf ~older material which could melt end flow into the ~older-like pref~rms during the soldering procs~s.
The reteining member which remains in place should be generally nonconductive and relatively flexible 80 that it doe~ not interFere with the motion of the preform columns.
~5 Additionslly, it may provide ~n impedence-metched interconnec-~ tion if it is o combinetion of conductive ~nd dielectric mate-;~ rial ~o that it provides ~ trensmissiDn line or microstrip offect, or s coaxi~l type shield eround the preforms.
In another ~mbodi~ent the reteining member could be made from ~ noncondutive materisI ~hich, ho~ever, becDmes conduc-tive ~hen ~ specific voltage threshold is exceeded, this ShreshDld being just ~bove the normal operating voltage of the `::
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-2~-~ircuit. Thi~ type of' ret~i~ing member ~ould provide protec-tion to the chip device by ahorting DUt any potenSially dam~-ging tr~nsi0nt overvoltage ~hieh m~y result from electro-~tatic di~charge or other electrical f~ults.
In 30me ~pplications, it ~y be desir~ble to m~ke the retaining member from a ~terial which exhibits heat-recovery.
T.his type of retaining member could be reinforced ~ith gla~s fibPr or the like ts control ~t~ coef~icient of thermal expan-3inn, but locally the holes which are provided for ret~ining the ~older-like oolumns could be fabricated B0 ea to ountract in diameter during soldering and thereby extrude the solder column up to neet the CCP ~nd PWB.
Although the retaining member has been ~hown to position only interconnection preform~ in Figures 4 snd 7-10, it i8 under~tood that other element~ ~ould al80 be pnsitioned by the retaining member ~nd attached to the chip devire and board. A
heat-sink device could be csrried in the central opening of the retaining ~ember oF Figure 4 and bondsd to the CCP and PWB
during soldering. 5imilarly~ ~ vibration damper, structural reinforcement9 or a Peltier type cooler could be po3itioned ~nd attached to the CCP ~nd the PWB. Al~o, fln electricfll ground plane could be positioned near the interconn,ection preforms to benefioially ~odi~y their electronic impedence ehar,~.cteristic~ similar to ~ microstrip board trace.
Figure 4 shows 8 square periphersl srrsy of intercon-n~ction~. However, other p~tterns or arrBy~ could ~130 be ac-oomplished by this invention. Any m~trix of intercon-nections on ~ regular rectiline~r form~t could be provided.
Non-rectilinesr or psrtially filled arrsy~ c~uld olso be prov~ded.
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lf the interconnection3 are arranged suffici~ntly ~lo~e together, a random-type interconnection 8y8tem could be produced. In this type of syRtem, since the intercon-nection density i~ much higher than the density of the pads o~ ~he ~CP Qnd PWB~ then ~tatistic~:Lly there will ~lways be ~t lea~t one interconnecting preform loe2ted between each pad set to be interconneet~d. The arr~ngement of the interconnection~ i8 completely random in this type of holder sy~tem. This type of retaining member mcy ideally be msde from a plur~lity o~ element~ bonded together, esch hAving at least one ~perture therethrough. The elements, such as 31 shown in phantom in Fig. 4, ~ay be of uniform or random cross-~ection in order that they msy be efficiently b~ndled and permanently or temporarily joined together such lS as by fusion or proper adhesive materisl to form n sheet-like ~tructure. In ~uch n bundled configuration the reteining . member elements may be formed by continuously extruding the - retaining member material over the preform, cutting the extruded composite into discrete pieces, bundling the ~ 20 axi~lly-aligned pieces and prafer~bly joining the ret~ining :~ member ~aterial nnd then ~licing the assembly st right angles to the axial alignment to make a preform placement device.
Also ~hown in the configuration shown in Fig. 4, the retaining member 22 csn be ideally stamped from 8 sheet of ~ateriAl, or othsrwi~e cut from sheet material. Quite pos-~ibly the ret~ining member f~bricating proeess would provide for the oimultaneous eta~ping of the holder ~hape and the central cut-out 24 ~nd form~tion of the properly_spaced 3~ hole~ 26~ and insertion ~f the solder preforms into the holes. Of course, it is pos3ibIe that the production of the retoining member 22 c~n be ~chieved in ~ sequence of steps .
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in ~ h the ~ ining ~ember with it~ cut-out end orienta-tion a~rfsces i8 st~ped ~ro~ a ~heet ~aterial, ~nd aubsequent techniqu~s are ~sed to form the hol~ into which the solder preforms ~re inserted. Other ~anuf~cturing ~ethods such as molding or in~ert molding ~re within the seope of the invention.
The retaining member ~2 m~y be fabricated ~rom a ~heet or a l~minate of he~t recover~ble m~terial, whereby the retainlng member is ~tamped from the m~teri~l sheet, the holes formed D therein, Rnd the solder preforms positioned within the holes.
~ubsequently, the reteining member i8 he~ted to a temperature sufficient to oause the ~aterial to recover such that the diameters o~ the holes 26 are reduced, but ~t a temperature below the melting point of the solder preforms. Ihe use of a heat~recoverable material ~or the retsining 22 affords the odvantages that the holes csn be form~d to a predefined ~hape, ~uch 88 ~n hourglsss, with vsrying diameters, such that the diameter of the middle section is smaller thsn the diameter at the ends. These holes would be expanded to a unifor~
~o diameter l~rger than the diameter of the preform~ so that the preforms car~ be more readily positioned in the holes, after which the ret~ining member 22 i8 heat-recovered, causing each hole to constrict to r size ~ubstantially identical to the diameter of the preform, thus securely gripping the preform within the retaining member. Furthermore, the use of a heat-rec-o-Yerable materi~l sffords the sdvantsge that in ~se, when heat i~ applied to effect the sDlder joint, such ~s by a ~older reflD~ process, the ~irm gripping o~ the solder pre-froms by the heat-recovered ret~ining member material will ~o i~p~rt the origin~l hourglass sh~pe of the holes to the preform, thus improving the flexibility of the ~olumn-type joints, Dnd in turn reducing the ~tresses ~nd improving the relinbility of the joints.
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~ t i~ D posaib~e to further control the ulti~ate con-figur~tion of the solder joint by the u~e Df ~ he~t-recoverable ~teri~l in th~ retaining me~ber 22. This can be ~chieved by p~rtially recovering the material, causing the holes to securely ~rip the pref~rms. ~hen, during the soldering process, su~ficient heat i8 applied to cause the material of the retaining ~ember to further recover, thereby further decre~ing the dismeter of the holes to apply a con~trictive force onto the moltsn or ~oftsned preForm. Thiæ will have o a ten~ency to produce column joint~ of height greater than the thickneRs of the retaining ~ember 22.
While the ret~ining member 22 has been shown in F:lgure
4 ~s a perimeter conFigur~tion, it i8 possible th~t the retaining member csn be a layer of ~aterial without ~ny out-outs therein, and in which the nece~sary number of solder preforms are properly locsted throughout the entire ~ ~urf~ce of the retaining member ~8 nece~sitated by the : number, looation and configuratisn of the conductive pad~ to be joined.
The preforms 28 ~ay be made of sny suit~ble joint Forming m~teri~l, such ~s ~older, filled solder, ~upported solder or conductive elsstomer materiel which wll at lesst p~rtially melt or ~often then adhere to an electric~lly conductive element when contacted therewith ~nd coo1ed.
The preform~ can be produced by any suitable technique, 3uch A8 b-y---the oontinuous extru~ion of the ~older m~terial thr~ugh appropriate-sized die~ snd cutting the extrud~te to the proper lengths. The preforms m~y be molded. Filled solder i8 u3ed to ~intain the columnar configur~tion during the solder~ng process; particles of metallic or ncn-metallic aterial may be embedded in the solder pre~orm~, ~uch 0s '' .
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shown in Fig. 6 For examp~e, discreite pieces 30 of metallic material 5 such as pieces of copper, may be embedded in the solder preforms by mixing the particles in the composition prior to extr~sion7 ~nd then extruding the mixt~re in a known f~hion. ~s ahown in Fig. 6~ the discrete particles may be ~ligned along the longitudinal 8XiS of the extrudate.
This alignment c~n be achieved with appropriate techniques, such ns the ~pplication of a magnetic force during the extrusion process, or simp~y by the shearing and other ~o forces applied by the extruder on the extruding material.
The particles mixed into the ~older should have a melting point above the melting point o~ the solder, and good metallurgical, mechanical and electrical properties.
In addition to copper, discussed above, Fillers could include nickel, iron, ~nd metsl-coated high-temperature polymer or glass films with a high espect ratio. These materials could be discrete particles or continuous lengths with 8 slngle strsnd or many strands in each preform.
Solder could completely coat the strands or fibers, or could Xo be deposited only at the ends of inherentIy conductive fibers~ Additionally, the interconnection bonding agent or solder could be added in a separate operation. Thus, continuous conductors or fiber bundles coùld be retained by t~e retaining member and then attachment would be accomplished ~5 by immer~ing the assembly in molten solder which will wick an~ wet the components and make the electrical and mechanical interconnection.
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~ dditionally, the p~rti~le~ in the filled ~older may be oriented in ~ny other de~ir~ble nlignment, ~nd the rel~tive content of the psrticles in the solder preforms, ~8 well QS
the ~ize ~ the p~ticles r~l~tive to the height of each preform, csn be tailored to the requirement~ of the joints to be for~ed. Furthermore, ~he ~urfaces of the solder preforms ~ay be coated with 8 suitable flux, or the flux msy be coated only on the end portions of.ths pre~or~ ~o that during the soldering proceæa the flux will coat the respective cont~ot areas on the oonductive pads to ~nsure proper flow of the 001dPr. The flux m~y æl30 be incorporated ~ithin the preform.
The use of the preform placement device 20 in mounting a chip carrier 32 to a suit~ble substrate, ~uch ~8 a circuit board 34, iB illu~trsted in Figs. 7 and B. The ret~ining member 22, ~ith the sol~er preform 2~ secured therein, is positioned between the lower ~urf~ce of the chip carrier 32 ~nd the oppo~ing upper surface of the circuit board 34, and properly loc~ted 80 that the snd portions of ~ach solder preform 28 m~ke contact ~ith the conductive contacts on the 2~ chip carrier ~nd the conductlng land on the circuit board ~4.
~ Means may be provided For aligning or orienting the chip - carrier 32 relative to the circuit board 34, such a8 by providing ori~ntation hole~ 36 in the chip carrier which ~re vertically ~ligned ~ith oorresponding holes 3~ in the ~5 GirCuit board end hDles 39 in the pr~form placement devic~
by inserting pins through the eligned holes 36, 3~ and 39. Other alignment or orienting me9n8 can be used. After ~ thz soldering process, the ends of the colu~n solder preforms ;~ 2~ ~re ~ecurely bonded tc thsir respective condu~tive DntaCts ~nd l~nd~ on the chip carrier ~2 ~nd the circuit boerd }4, aa shown in Fig. B.
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Fi~ure 4 illu~tr~te~ e ~at ~temped retaining member but, ~f cour~e, the holder eould be formed by et~mping~
folding or molding in~o ~ cup shaped s~ructure into ~hich ~h2 ~CP could be accur~tely plcced. Detznt features could be provided a~ pres~ure-sensitive or hot-melt adhe6ives ~ould be pro~ided ~ithin the rstaining meinber sa th~t the ohip e~rrier eould be prea~sembled to the CCP before application to the PWB. This subassembly could then be locnted to the PWB u~ing fixtures, pick and pl~ce equipment, elignment features ~uch as holes or pins, or the like.
Adhesives or pinfi could be provided in the center ~urf~ces o~ thi~ retaining member as di~cu~ed e~rlier with respect to Fagure 4 to maintain po~iticn during the ~oldering or reflowing operation.
~5 Figure 4 illustretes a single retaining member but, of cours~9 these components could c~nveniently be ~upplied oonRected together like a bandolier for convenient assembly packeging and ~pplication.
During the soldering or reflowing process, it i~
underst20d thot suitsble ~ean~ will be utilized to maintain good cont~cts bet~een the oonductive elements on the chip c~rrier 32 and the circuit b~rd ~4 until the ioint has ~olidified. Techniques for meintaining this cont~ct ~re known. Another technique ~or providing this retaining force : ~S .i8 chown in Fi~s. 9 and 10 ~nd esn be incorporated into the ret~ining member ~or the 801der pr~forms.
A~ shown in Fig. 9, ~n illustrative number of solder preforms 28 ore dispo~ed in holes prDvided in the ret~ining ~e~ber 40 which is made from ~ l~yer of heat-recov`er&ble ~o material, and e~ch gurfuce ie formed with a depre~sion or recess 42. Form~tiDn of the re e~s 42 ceu~0~ the opposite ~urface nf the ret~ining member to be raised in ~ correspond-ingly-shaped protrusion or bump 44. The elev~ted planar , ~ ' , ,:
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-2~-surf~ce of the pro~ru~ion 44 i8 c~ated ~ith a ~uit~ble ~dhe-sive 46. ~he r2ce~aes 4~ and the protrusion~ 44 ~n be con-voniently for~ad by c 8tamping OpBratiOn in ~hich appropri-~tely-shaped dies are presaed onto the opposed 8urfsce3 of the holder 409 ~eusing recesses 42 to be formed in one sur-face and forcin9 the m~terial out in the form of protrusion 44 Dn the other surface, as ~hown more clearly in the cross-~ection of Fig. 10.
Once ~pplied between the chip csErier 32 and the circuit io boerd 34 9 the end portions of e~ch solder preform~ 28 m~ke contact with the conductive elements 1~ ~nd 12 on the chip carrier and circuit bo~rd, and the adhesive 46 on the sur-f~ces nf the protrusion3 44 make contact, re3pectively, with the opposed surfaces of the chip carrier and the circuit bo~rd, thus holding the chip ccrrier to the circuit board.
During the ~ldering proces3, the upplicat.ion of heat causes the heat-recDverable material of the retaining me~ber 40 to recover in ~ known ~a hi~n, cau~ing the recesse~ 42 and the protrusions 44 to revert to the f~at configur~tion of the ~o retsining me~ber, thu3 pulling the chip carrier 32 to~ard - the circuit board 34 and cau ing the solder to wet the contact element~ on each re~pective device.
The ~hspe at the rece~ae3 ~nd protru~ion~ ~ho~n in Figs.
9 ~nd 10 ere illustrative only; other configurations may be equally suitable. The trapezoidal configuration of the ~ece~3e~ 42 and protrusions 44 shown in the drawings are ; particularly advantageous in thet they provide ~ relatively rge fl~t~surf~ce onto ~hich the cdhesive 46 may be applied, ~nd the form of the reces3e~ ~nd protrusions c~n be easily de in the retaining member 4a. In u~e, the l~rge-area adhe~ive layers prcvide 8 ~trong gripping ~orro to the `~ re~pective surf~ces of the chip csrrier ~2 and the circuit board 34~ ~nd the contractivs ~orce produced by the recover-ing m~terial of the retaining member 40 exertB 8uf~icient ' .:
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~:~9~i -foree to pull the chip csrrier down teward the ~ir~uit board 34. The shapeR ~l~o aid in venting bet~een chip ~nd board.
ObYiously, ~dhesive c~n be put ~s ~ell on flat ret~ining mem-bers, without any protrusions9 simply to secure the deYice S on the bosrd and the CCP on the d~vice ~with or ~ithout hest-shrinking) or for vibrsticn damping, etc., as discussed earlier.
Although the ~older pre~orms considered thus f~r h~ve been of ~lender cylindrical configurations, other o gh~pes ere equally ~uitable, depending upon the requirements of the mounting. Preforms ~ith BqUare~ hexagGnal cr other ~hapes of cross-~ections can be u~ed.
Furthermore, some examples of other configurations are shown in Fig~. 11A-C, Fig. 12 ~nd Fig~ 13. The S-nhnpe of the preforms shown in Figs. 11A-C prDvide~ joint~ of greater flexibility which permit relatively large displ~cements between the chip carrisr 32 snd the circuit board 34 without inducing undue stresses in the fixed portions of the joint.
With the reverse S-shape preform 4B shown in Fig. 11A, a ~ subst~ntially l~rge contact ares is af~orded et the upper : portions Df. the prefcrm making cont~ct with the conductive pads 10 snd 12 on the chip carrier 32 and the circuit board 34. The preform 48 i8 supported by two parallel-disposed .~ holder l~ers S0 and 52.
2~ The 5-sh~ped preform 54 of Fig. 11~ affords the same ~dvantages as the prefor~ 48 of Fig. 11A end, ~dditionally, provides two probe areas P and P which may be used to test for electrical continuity of the connection. This configuretion ~s perticulsrly ~dvsntageous ~hen u~ed ~ in ~aking connection~ slong the periphery of the chip ~; carrier when the contact~ ~re spaced elong the edges o~ the chip carri~r innsmuch a8 the probe areas sre re~dily access-ible. As with the prefnrm 4B, the preform 54 is aupported `
-~9- 26775-71 V
by parallel-disposed retaining member layers 50 and 52. In fabricating the preforms 48 and 54 and positioning them into the retaining members 50 and 52, the preforms are initially straight elements which are inserted into the corresponding, vertically aligned holes in the retaining member layers 50 and 52 and the ends are bent into the configuration shown in Figs~ llA and llB.
The S-shaped preform 56 shown in Fig. llC is provided in a single retaining member layer 58 having a thickness substan-tially greater than the individual retaining member layers 50 and 52 shown in Figs. llA and llB. Otherwise, the preform 56 affords the same advantages as the preforms 48 and 54.
The preform 60 shown in Fig. 12 is of C-shape configur-ation which is suitably attached along the edge of the retaining member 58 by element 61 being inserted into the aperture in member 58. Due to its uni~ue conEiguration the C-shape preform 60 is most advantageously used when disposed along the peripheral edges of the retaining member 58. The preform 60 provides a very substantial joint surface which may be used to test for lectrical ;` continuity between the chip carrier 32 and the circuit board 34.
Although the preforms have been generally described as being made of filled solder the preforms may also be made from : :~
supported solder or from a continuous length of conductive material such as wire with filled solder or supported solder material located at the ends thereof for interconnection purposes. In some methods the preforms may be solder or conductive elastomer. These materials may also be a continuous strand of conductive material with filled solder or suppor~ed solder column located at the ends thereof for interconnection purposes as will be appreciated with ;
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For maximum flexibility and resilience between the chip carrier 32 and the circuit board 34, the coiled spring , : ~
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MP0~64 -3~--~confi~uration 62 ~h~n in Fig. 13 î~ id~al. ~he preform 62 ~ould be readily formed by sxtruding the filled ~older co~po~ition as a continuoua extrudate, forming it into ~
coiled configur~tion of ~uit~ble ~pring msterial of de~ired di~mete~ and length~ nnd appropristely holding each spring prefor~ within the ret~ining ~mber 58. The degres of reailience ~ffDrded by the preform fi2 oan be controlled in ~ubstantislly the ~sme fsshion th~t the parameters regulating the performsnce of conven~ipnal springs ere controlled, such as oontrolling the diametric 8ize8 of each turn of the spring, the length of the spring and th~ dismeter of the extrudate from which the spring i8 made. The spring configuration could also be made from a supported solder disclosed horein.
Since each solder preform i8 individu~lly pl~ced in s given location, the preform configuratlon can be tailored ~ to meet the specific requirements of a psrticular joint.
; Thus, for ex~mple, the diameter and/or height of the eylindrical preform at certnin locations c~n be different from the pr~forms at other locations to meet the specific n~ed~ of the joint being formed. Conceivably, each joint may be unique snd mey incorporate ~ different solder preform.
Additionally, it i8 possible to co~bine different preform configuration~9 such as combining the cylindric~l pre~orms with ~ny of the preform3 ~hown in Figs. 1t-13 tD meet the ~pëclfic needs for re3ilience and stress reduction in one or ore particuler solder ~oints.
-; Fig. 14 show~ ~o~e exa~plss of the supported solder preform embodiment of this inv~ntion. Fig. 14A sho~ a ~o ~older column supported by ~ire ~trands in the form of s wire breid 72. Fig. 14~ ~hows the ~olumn ~upported by ~ ~ire str~nd ~2 wrapped around the column in a spir~l f~shion. In the ~ire braid and the ~pir~l ~ire wrap e~bodimen~s, the diameter ~f the eolumn and the ~p~cing between the wires are ~5 aeleet~d ~o th~t the surf~ce tension of the ~older used ,:
, ,, ~
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` '~ -. ~ ., : ' ,, relotive to th~ wire us~d ~ill maintain the ~ub~tsntially columnar ah~p2 of ths sDlder ~hen ~olten, Fig. 14B showa a ~upport~d solder oolunn 91 u~ing ~ met~l tnpe or ribbon 92. Fig. 14C shows the 3upported solder column sfter the connection h~ been ~nde ~herein it can be sBen that the cDlumn sh~pe of the ~upported solder has been substanti~lly ~aintained ~hile the solder formPd fillet~ 94 at interconnect pads 10 ~nd 121 The solder in the supported solder column flow8 ~lightly to form the fillets ~nd the colu~n scts a8 a ~o reservoir of solder which i~ slightly depleted 8~ 6een ~t ~illet 95 between the tape support. This characteristic of the supported solder columna provides manufacturing proceRs advantages ~8 ~11 as columns of improved ~lexibility. An example of ~uch a tape found particularly useful For interconnect l$ pads sp~ced on 0~050 inch centers i8 a copper tape 0.003 inch thick end 0.013 inch wide wrapped around a salder column 0.020 to 0.025 inch in diamete~ with 0~008 ts 0.01 inch ~pace between wraps of the tape. It should be noted thst the suppDrted solder columns may be ~ade using filled 20 ~older in p1ace oF the conYentionsl ~older.
~ he suppDrted aolder can be made by applying the upport ~trand or tape to the outside of e column of solder, e.g. a solder wire. In this method support strands c~n be braided ~r ~rapped around a solder wire and the wr~pped 2s solder wire thsn cut into length to for~ column~ of a d¢sir¢d dimension usefui in this ~nvention. Similarly ~thl tape oan be wrapped around t~e ~older ~ire ~nd the wr~pped ~older ~ire cut to de~ired length~. The supported solder can al80 be m~de by dipping the pre~ormed ~upport;
uch as ~ wire brnid or ~ ~piroled wire or tape, in molten ~older tc fill the interior ~psce in the support ~ith ~older then ~olidifying the ~older. This method c~n likewi~e be done in long 8~Ction8 which sre then cut to lengths required to form the columns u~eful in this inventiGn. In thiE; fashion the 35 supported solder columns cen be formed in situ in the reteining , ' ~
` .~ ' ' ' .
~ember o~ thi~ inv~ntion. For ~x~mple, ~ ~pir~l ~etsl tcpe can be placed in the epertures of the retsining member then ~illed with ~olten ~older, ~uch a in wave soldering oper~t~Dn? then oool~d. The s~pported ~solder column in the reteining ~esn6 ~ill then function in for~ing interconne~tion~
from which the ret~ining ~eans can be rlemoved if desired~
The form~tion of supported solder columns in situ oould ~180 be done simultaneously ~ith as~embling the electrioally conductive elements~ whereby the ~older ~upport such 8S ~
lo cpir~l metel t~pe, in the retaining me~ns is filled ~nd the connections formed at the end~ of the supported ~oldEr column sll in one soldering operstion. It h~s been found th~t in ~ome case~ when ~ solder wire is wrapped with a tape, it is useful to reflow the solder then cut the desired length columns for u6e in this invention end thereby discard ~ny portions thereof th~t ~ay not have sufficient solder therein.
The interconnectiDn preform placement device o~ the pre-~ent invention provides ~ unique and conveni~nt technique Zo for eccur~t.ely positioning e plurality o~ preforms between a chip c~rrier and 8 circuit board to which the carrier is mounted. The use of cylindric~l column preforms of solder result~ in solder joint~ of low bending stif~ness.and hence low ~he~r stres~es, which contribute to high fstigue resist-~S ance in the joints._._lhe u~e of the column-~haped preform in the present invention ensure~ th~t the desir~ble oolumn ~nfigurations will be ret~ined during the snldering process and th~t the Formed solder joint~ will be of column ~hepe h~v ing low shear ~tresses di~tributed therethrough.
In ~ddition to-the e~bodiment of ~i98. 9 ~nd 1~ de6-crib~d ebove, the interconnectiOn preform pl~cement device ' ; :~ .., , - .
'` ~ . :,:
, ,: .,.. , ,.,,.. . : :
.; .: .. ,;:;~ ; :
.
-~3-~y h~ve a layer of pres~ure-~ensitive edhesive on it~
0urfaces, with or ~ithout a "rele~se" paper or co~er. This ~dhesive ~ill MBintain the device on ~he c~rcuit boQrd and the chip package on the device during hsndling prior to the oldering ~r reflowing prnce~3. The adhesive i~ ~pplied in ~uch ~ w~y as not to interfere with the sold~ring or re~lowing :: process.
The retaining member may be m~de of a suitable high-temperature material capsble of sustaining the heat applied ; lo during the coldering or refl~wing proces~ snd be of ~n electric~lly insulating materi~l to be left in pl~ce ~Fter soldering to provide an electrical insulator and an ~nvironmental ~eal. AlternativEly, the retaining member may be made of material which is he~t-soluble, chemically soluble, or ~ disintegr~ble such th~t after ~olderin~ the ret~ining member : can be dissolved or disint~gr~ted end removed from the ounting to provide clearance for flux removal, for instance, or for other procedures to c~mplete the in~tall~tiDn.
It will bE appreciated that ~hile this invention has ~: 20 been illugtra~ed by embodiments of sl2nder cylindrical column, the devices, erticle~, methods cnd composition o~
;~ this invention are equally useful to form connections between electrically conductive element~ ~here the joint forming matérial need not bé sn elongate column but can be a disk, 2S ~fer or other configuration where the ~idth is greater th~n thc l~ngth ~r height, ~uch as in applic~tions where ~: ~omp&ct spacing or current speed i8 more import~nt th~n therm~l cycling~ It will ~180 be appreci~ted that this ~: invention is useful with other conventional proce~ing . ~ methods, for ex~mple, the interconnect points on the :~
.
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~P~64 -3~-~lectrically conductive element~ or the el~ds of the p~cfDrms can be coated, fDr exe~ple, by 8 g~reening process~ ~ith a 801der ~re~m to enh~nce the formatiDn or efficiency of the connection.
The concepts ~mbodied in the present invention may be sd~pted for use in attaching ~ ehip to ~ chip carrier or a chip directly to a circuit bo~rd, or to ~ttach leaded CCP~ or hybrid thick-film-t~pe chip carrie~s to circuit bo~rd~. Multiple preform plscement devices or larger-scale o placement devices c2n ~ccommodate the simultsneous boncling of numerou~ chip carrier packages. Further, the interconnec-tion preform pl~cement device m~y be placed between two circuit board~ to interconnect verticAlly the conductive p~d6 of bo~rds.
~ hile preferred embodiments of the invention heve been illustr~ted ~nd described, it will be ~ppreciated thst v~ristions there~rom may be made without dep~rting from the scope of the invention es defined in the nppended clsims.
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The preforms 28 ~ay be made of sny suit~ble joint Forming m~teri~l, such ~s ~older, filled solder, ~upported solder or conductive elsstomer materiel which wll at lesst p~rtially melt or ~often then adhere to an electric~lly conductive element when contacted therewith ~nd coo1ed.
The preform~ can be produced by any suitable technique, 3uch A8 b-y---the oontinuous extru~ion of the ~older m~terial thr~ugh appropriate-sized die~ snd cutting the extrud~te to the proper lengths. The preforms m~y be molded. Filled solder i8 u3ed to ~intain the columnar configur~tion during the solder~ng process; particles of metallic or ncn-metallic aterial may be embedded in the solder pre~orm~, ~uch 0s '' .
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shown in Fig. 6 For examp~e, discreite pieces 30 of metallic material 5 such as pieces of copper, may be embedded in the solder preforms by mixing the particles in the composition prior to extr~sion7 ~nd then extruding the mixt~re in a known f~hion. ~s ahown in Fig. 6~ the discrete particles may be ~ligned along the longitudinal 8XiS of the extrudate.
This alignment c~n be achieved with appropriate techniques, such ns the ~pplication of a magnetic force during the extrusion process, or simp~y by the shearing and other ~o forces applied by the extruder on the extruding material.
The particles mixed into the ~older should have a melting point above the melting point o~ the solder, and good metallurgical, mechanical and electrical properties.
In addition to copper, discussed above, Fillers could include nickel, iron, ~nd metsl-coated high-temperature polymer or glass films with a high espect ratio. These materials could be discrete particles or continuous lengths with 8 slngle strsnd or many strands in each preform.
Solder could completely coat the strands or fibers, or could Xo be deposited only at the ends of inherentIy conductive fibers~ Additionally, the interconnection bonding agent or solder could be added in a separate operation. Thus, continuous conductors or fiber bundles coùld be retained by t~e retaining member and then attachment would be accomplished ~5 by immer~ing the assembly in molten solder which will wick an~ wet the components and make the electrical and mechanical interconnection.
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~ dditionally, the p~rti~le~ in the filled ~older may be oriented in ~ny other de~ir~ble nlignment, ~nd the rel~tive content of the psrticles in the solder preforms, ~8 well QS
the ~ize ~ the p~ticles r~l~tive to the height of each preform, csn be tailored to the requirement~ of the joints to be for~ed. Furthermore, ~he ~urfaces of the solder preforms ~ay be coated with 8 suitable flux, or the flux msy be coated only on the end portions of.ths pre~or~ ~o that during the soldering proceæa the flux will coat the respective cont~ot areas on the oonductive pads to ~nsure proper flow of the 001dPr. The flux m~y æl30 be incorporated ~ithin the preform.
The use of the preform placement device 20 in mounting a chip carrier 32 to a suit~ble substrate, ~uch ~8 a circuit board 34, iB illu~trsted in Figs. 7 and B. The ret~ining member 22, ~ith the sol~er preform 2~ secured therein, is positioned between the lower ~urf~ce of the chip carrier 32 ~nd the oppo~ing upper surface of the circuit board 34, and properly loc~ted 80 that the snd portions of ~ach solder preform 28 m~ke contact ~ith the conductive contacts on the 2~ chip carrier ~nd the conductlng land on the circuit board ~4.
~ Means may be provided For aligning or orienting the chip - carrier 32 relative to the circuit board 34, such a8 by providing ori~ntation hole~ 36 in the chip carrier which ~re vertically ~ligned ~ith oorresponding holes 3~ in the ~5 GirCuit board end hDles 39 in the pr~form placement devic~
by inserting pins through the eligned holes 36, 3~ and 39. Other alignment or orienting me9n8 can be used. After ~ thz soldering process, the ends of the colu~n solder preforms ;~ 2~ ~re ~ecurely bonded tc thsir respective condu~tive DntaCts ~nd l~nd~ on the chip carrier ~2 ~nd the circuit boerd }4, aa shown in Fig. B.
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Fi~ure 4 illu~tr~te~ e ~at ~temped retaining member but, ~f cour~e, the holder eould be formed by et~mping~
folding or molding in~o ~ cup shaped s~ructure into ~hich ~h2 ~CP could be accur~tely plcced. Detznt features could be provided a~ pres~ure-sensitive or hot-melt adhe6ives ~ould be pro~ided ~ithin the rstaining meinber sa th~t the ohip e~rrier eould be prea~sembled to the CCP before application to the PWB. This subassembly could then be locnted to the PWB u~ing fixtures, pick and pl~ce equipment, elignment features ~uch as holes or pins, or the like.
Adhesives or pinfi could be provided in the center ~urf~ces o~ thi~ retaining member as di~cu~ed e~rlier with respect to Fagure 4 to maintain po~iticn during the ~oldering or reflowing operation.
~5 Figure 4 illustretes a single retaining member but, of cours~9 these components could c~nveniently be ~upplied oonRected together like a bandolier for convenient assembly packeging and ~pplication.
During the soldering or reflowing process, it i~
underst20d thot suitsble ~ean~ will be utilized to maintain good cont~cts bet~een the oonductive elements on the chip c~rrier 32 and the circuit b~rd ~4 until the ioint has ~olidified. Techniques for meintaining this cont~ct ~re known. Another technique ~or providing this retaining force : ~S .i8 chown in Fi~s. 9 and 10 ~nd esn be incorporated into the ret~ining member ~or the 801der pr~forms.
A~ shown in Fig. 9, ~n illustrative number of solder preforms 28 ore dispo~ed in holes prDvided in the ret~ining ~e~ber 40 which is made from ~ l~yer of heat-recov`er&ble ~o material, and e~ch gurfuce ie formed with a depre~sion or recess 42. Form~tiDn of the re e~s 42 ceu~0~ the opposite ~urface nf the ret~ining member to be raised in ~ correspond-ingly-shaped protrusion or bump 44. The elev~ted planar , ~ ' , ,:
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-2~-surf~ce of the pro~ru~ion 44 i8 c~ated ~ith a ~uit~ble ~dhe-sive 46. ~he r2ce~aes 4~ and the protrusion~ 44 ~n be con-voniently for~ad by c 8tamping OpBratiOn in ~hich appropri-~tely-shaped dies are presaed onto the opposed 8urfsce3 of the holder 409 ~eusing recesses 42 to be formed in one sur-face and forcin9 the m~terial out in the form of protrusion 44 Dn the other surface, as ~hown more clearly in the cross-~ection of Fig. 10.
Once ~pplied between the chip csErier 32 and the circuit io boerd 34 9 the end portions of e~ch solder preform~ 28 m~ke contact with the conductive elements 1~ ~nd 12 on the chip carrier and circuit bo~rd, and the adhesive 46 on the sur-f~ces nf the protrusion3 44 make contact, re3pectively, with the opposed surfaces of the chip carrier and the circuit bo~rd, thus holding the chip ccrrier to the circuit board.
During the ~ldering proces3, the upplicat.ion of heat causes the heat-recDverable material of the retaining me~ber 40 to recover in ~ known ~a hi~n, cau~ing the recesse~ 42 and the protrusions 44 to revert to the f~at configur~tion of the ~o retsining me~ber, thu3 pulling the chip carrier 32 to~ard - the circuit board 34 and cau ing the solder to wet the contact element~ on each re~pective device.
The ~hspe at the rece~ae3 ~nd protru~ion~ ~ho~n in Figs.
9 ~nd 10 ere illustrative only; other configurations may be equally suitable. The trapezoidal configuration of the ~ece~3e~ 42 and protrusions 44 shown in the drawings are ; particularly advantageous in thet they provide ~ relatively rge fl~t~surf~ce onto ~hich the cdhesive 46 may be applied, ~nd the form of the reces3e~ ~nd protrusions c~n be easily de in the retaining member 4a. In u~e, the l~rge-area adhe~ive layers prcvide 8 ~trong gripping ~orro to the `~ re~pective surf~ces of the chip csrrier ~2 and the circuit board 34~ ~nd the contractivs ~orce produced by the recover-ing m~terial of the retaining member 40 exertB 8uf~icient ' .:
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~:~9~i -foree to pull the chip csrrier down teward the ~ir~uit board 34. The shapeR ~l~o aid in venting bet~een chip ~nd board.
ObYiously, ~dhesive c~n be put ~s ~ell on flat ret~ining mem-bers, without any protrusions9 simply to secure the deYice S on the bosrd and the CCP on the d~vice ~with or ~ithout hest-shrinking) or for vibrsticn damping, etc., as discussed earlier.
Although the ~older pre~orms considered thus f~r h~ve been of ~lender cylindrical configurations, other o gh~pes ere equally ~uitable, depending upon the requirements of the mounting. Preforms ~ith BqUare~ hexagGnal cr other ~hapes of cross-~ections can be u~ed.
Furthermore, some examples of other configurations are shown in Fig~. 11A-C, Fig. 12 ~nd Fig~ 13. The S-nhnpe of the preforms shown in Figs. 11A-C prDvide~ joint~ of greater flexibility which permit relatively large displ~cements between the chip carrisr 32 snd the circuit board 34 without inducing undue stresses in the fixed portions of the joint.
With the reverse S-shape preform 4B shown in Fig. 11A, a ~ subst~ntially l~rge contact ares is af~orded et the upper : portions Df. the prefcrm making cont~ct with the conductive pads 10 snd 12 on the chip carrier 32 and the circuit board 34. The preform 48 i8 supported by two parallel-disposed .~ holder l~ers S0 and 52.
2~ The 5-sh~ped preform 54 of Fig. 11~ affords the same ~dvantages as the prefor~ 48 of Fig. 11A end, ~dditionally, provides two probe areas P and P which may be used to test for electrical continuity of the connection. This configuretion ~s perticulsrly ~dvsntageous ~hen u~ed ~ in ~aking connection~ slong the periphery of the chip ~; carrier when the contact~ ~re spaced elong the edges o~ the chip carri~r innsmuch a8 the probe areas sre re~dily access-ible. As with the prefnrm 4B, the preform 54 is aupported `
-~9- 26775-71 V
by parallel-disposed retaining member layers 50 and 52. In fabricating the preforms 48 and 54 and positioning them into the retaining members 50 and 52, the preforms are initially straight elements which are inserted into the corresponding, vertically aligned holes in the retaining member layers 50 and 52 and the ends are bent into the configuration shown in Figs~ llA and llB.
The S-shaped preform 56 shown in Fig. llC is provided in a single retaining member layer 58 having a thickness substan-tially greater than the individual retaining member layers 50 and 52 shown in Figs. llA and llB. Otherwise, the preform 56 affords the same advantages as the preforms 48 and 54.
The preform 60 shown in Fig. 12 is of C-shape configur-ation which is suitably attached along the edge of the retaining member 58 by element 61 being inserted into the aperture in member 58. Due to its uni~ue conEiguration the C-shape preform 60 is most advantageously used when disposed along the peripheral edges of the retaining member 58. The preform 60 provides a very substantial joint surface which may be used to test for lectrical ;` continuity between the chip carrier 32 and the circuit board 34.
Although the preforms have been generally described as being made of filled solder the preforms may also be made from : :~
supported solder or from a continuous length of conductive material such as wire with filled solder or supported solder material located at the ends thereof for interconnection purposes. In some methods the preforms may be solder or conductive elastomer. These materials may also be a continuous strand of conductive material with filled solder or suppor~ed solder column located at the ends thereof for interconnection purposes as will be appreciated with ;
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-29a- 26775-71 respect to Figures 11-13.
For maximum flexibility and resilience between the chip carrier 32 and the circuit board 34, the coiled spring , : ~
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MP0~64 -3~--~confi~uration 62 ~h~n in Fig. 13 î~ id~al. ~he preform 62 ~ould be readily formed by sxtruding the filled ~older co~po~ition as a continuoua extrudate, forming it into ~
coiled configur~tion of ~uit~ble ~pring msterial of de~ired di~mete~ and length~ nnd appropristely holding each spring prefor~ within the ret~ining ~mber 58. The degres of reailience ~ffDrded by the preform fi2 oan be controlled in ~ubstantislly the ~sme fsshion th~t the parameters regulating the performsnce of conven~ipnal springs ere controlled, such as oontrolling the diametric 8ize8 of each turn of the spring, the length of the spring and th~ dismeter of the extrudate from which the spring i8 made. The spring configuration could also be made from a supported solder disclosed horein.
Since each solder preform i8 individu~lly pl~ced in s given location, the preform configuratlon can be tailored ~ to meet the specific requirements of a psrticular joint.
; Thus, for ex~mple, the diameter and/or height of the eylindrical preform at certnin locations c~n be different from the pr~forms at other locations to meet the specific n~ed~ of the joint being formed. Conceivably, each joint may be unique snd mey incorporate ~ different solder preform.
Additionally, it i8 possible to co~bine different preform configuration~9 such as combining the cylindric~l pre~orms with ~ny of the preform3 ~hown in Figs. 1t-13 tD meet the ~pëclfic needs for re3ilience and stress reduction in one or ore particuler solder ~oints.
-; Fig. 14 show~ ~o~e exa~plss of the supported solder preform embodiment of this inv~ntion. Fig. 14A sho~ a ~o ~older column supported by ~ire ~trands in the form of s wire breid 72. Fig. 14~ ~hows the ~olumn ~upported by ~ ~ire str~nd ~2 wrapped around the column in a spir~l f~shion. In the ~ire braid and the ~pir~l ~ire wrap e~bodimen~s, the diameter ~f the eolumn and the ~p~cing between the wires are ~5 aeleet~d ~o th~t the surf~ce tension of the ~older used ,:
, ,, ~
:. , ... .
` '~ -. ~ ., : ' ,, relotive to th~ wire us~d ~ill maintain the ~ub~tsntially columnar ah~p2 of ths sDlder ~hen ~olten, Fig. 14B showa a ~upport~d solder oolunn 91 u~ing ~ met~l tnpe or ribbon 92. Fig. 14C shows the 3upported solder column sfter the connection h~ been ~nde ~herein it can be sBen that the cDlumn sh~pe of the ~upported solder has been substanti~lly ~aintained ~hile the solder formPd fillet~ 94 at interconnect pads 10 ~nd 121 The solder in the supported solder column flow8 ~lightly to form the fillets ~nd the colu~n scts a8 a ~o reservoir of solder which i~ slightly depleted 8~ 6een ~t ~illet 95 between the tape support. This characteristic of the supported solder columna provides manufacturing proceRs advantages ~8 ~11 as columns of improved ~lexibility. An example of ~uch a tape found particularly useful For interconnect l$ pads sp~ced on 0~050 inch centers i8 a copper tape 0.003 inch thick end 0.013 inch wide wrapped around a salder column 0.020 to 0.025 inch in diamete~ with 0~008 ts 0.01 inch ~pace between wraps of the tape. It should be noted thst the suppDrted solder columns may be ~ade using filled 20 ~older in p1ace oF the conYentionsl ~older.
~ he suppDrted aolder can be made by applying the upport ~trand or tape to the outside of e column of solder, e.g. a solder wire. In this method support strands c~n be braided ~r ~rapped around a solder wire and the wr~pped 2s solder wire thsn cut into length to for~ column~ of a d¢sir¢d dimension usefui in this ~nvention. Similarly ~thl tape oan be wrapped around t~e ~older ~ire ~nd the wr~pped ~older ~ire cut to de~ired length~. The supported solder can al80 be m~de by dipping the pre~ormed ~upport;
uch as ~ wire brnid or ~ ~piroled wire or tape, in molten ~older tc fill the interior ~psce in the support ~ith ~older then ~olidifying the ~older. This method c~n likewi~e be done in long 8~Ction8 which sre then cut to lengths required to form the columns u~eful in this inventiGn. In thiE; fashion the 35 supported solder columns cen be formed in situ in the reteining , ' ~
` .~ ' ' ' .
~ember o~ thi~ inv~ntion. For ~x~mple, ~ ~pir~l ~etsl tcpe can be placed in the epertures of the retsining member then ~illed with ~olten ~older, ~uch a in wave soldering oper~t~Dn? then oool~d. The s~pported ~solder column in the reteining ~esn6 ~ill then function in for~ing interconne~tion~
from which the ret~ining ~eans can be rlemoved if desired~
The form~tion of supported solder columns in situ oould ~180 be done simultaneously ~ith as~embling the electrioally conductive elements~ whereby the ~older ~upport such 8S ~
lo cpir~l metel t~pe, in the retaining me~ns is filled ~nd the connections formed at the end~ of the supported ~oldEr column sll in one soldering operstion. It h~s been found th~t in ~ome case~ when ~ solder wire is wrapped with a tape, it is useful to reflow the solder then cut the desired length columns for u6e in this invention end thereby discard ~ny portions thereof th~t ~ay not have sufficient solder therein.
The interconnectiDn preform placement device o~ the pre-~ent invention provides ~ unique and conveni~nt technique Zo for eccur~t.ely positioning e plurality o~ preforms between a chip c~rrier and 8 circuit board to which the carrier is mounted. The use of cylindric~l column preforms of solder result~ in solder joint~ of low bending stif~ness.and hence low ~he~r stres~es, which contribute to high fstigue resist-~S ance in the joints._._lhe u~e of the column-~haped preform in the present invention ensure~ th~t the desir~ble oolumn ~nfigurations will be ret~ined during the snldering process and th~t the Formed solder joint~ will be of column ~hepe h~v ing low shear ~tresses di~tributed therethrough.
In ~ddition to-the e~bodiment of ~i98. 9 ~nd 1~ de6-crib~d ebove, the interconnectiOn preform pl~cement device ' ; :~ .., , - .
'` ~ . :,:
, ,: .,.. , ,.,,.. . : :
.; .: .. ,;:;~ ; :
.
-~3-~y h~ve a layer of pres~ure-~ensitive edhesive on it~
0urfaces, with or ~ithout a "rele~se" paper or co~er. This ~dhesive ~ill MBintain the device on ~he c~rcuit boQrd and the chip package on the device during hsndling prior to the oldering ~r reflowing prnce~3. The adhesive i~ ~pplied in ~uch ~ w~y as not to interfere with the sold~ring or re~lowing :: process.
The retaining member may be m~de of a suitable high-temperature material capsble of sustaining the heat applied ; lo during the coldering or refl~wing proces~ snd be of ~n electric~lly insulating materi~l to be left in pl~ce ~Fter soldering to provide an electrical insulator and an ~nvironmental ~eal. AlternativEly, the retaining member may be made of material which is he~t-soluble, chemically soluble, or ~ disintegr~ble such th~t after ~olderin~ the ret~ining member : can be dissolved or disint~gr~ted end removed from the ounting to provide clearance for flux removal, for instance, or for other procedures to c~mplete the in~tall~tiDn.
It will bE appreciated that ~hile this invention has ~: 20 been illugtra~ed by embodiments of sl2nder cylindrical column, the devices, erticle~, methods cnd composition o~
;~ this invention are equally useful to form connections between electrically conductive element~ ~here the joint forming matérial need not bé sn elongate column but can be a disk, 2S ~fer or other configuration where the ~idth is greater th~n thc l~ngth ~r height, ~uch as in applic~tions where ~: ~omp&ct spacing or current speed i8 more import~nt th~n therm~l cycling~ It will ~180 be appreci~ted that this ~: invention is useful with other conventional proce~ing . ~ methods, for ex~mple, the interconnect points on the :~
.
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~P~64 -3~-~lectrically conductive element~ or the el~ds of the p~cfDrms can be coated, fDr exe~ple, by 8 g~reening process~ ~ith a 801der ~re~m to enh~nce the formatiDn or efficiency of the connection.
The concepts ~mbodied in the present invention may be sd~pted for use in attaching ~ ehip to ~ chip carrier or a chip directly to a circuit bo~rd, or to ~ttach leaded CCP~ or hybrid thick-film-t~pe chip carrie~s to circuit bo~rd~. Multiple preform plscement devices or larger-scale o placement devices c2n ~ccommodate the simultsneous boncling of numerou~ chip carrier packages. Further, the interconnec-tion preform pl~cement device m~y be placed between two circuit board~ to interconnect verticAlly the conductive p~d6 of bo~rds.
~ hile preferred embodiments of the invention heve been illustr~ted ~nd described, it will be ~ppreciated thst v~ristions there~rom may be made without dep~rting from the scope of the invention es defined in the nppended clsims.
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Claims (25)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A solder composition comprising:
solder; and disposed in the solder a filler comprising discrete particles or filaments which are solid at a temperature at which the solder is molten, which are present in an amount of from 20%
to 80% by weight based on the total weight of the solder-filler mixture, and which are of sufficient size and density substantial-ly to maintain the solder in a preformed shape when the solder is molten.
solder; and disposed in the solder a filler comprising discrete particles or filaments which are solid at a temperature at which the solder is molten, which are present in an amount of from 20%
to 80% by weight based on the total weight of the solder-filler mixture, and which are of sufficient size and density substantial-ly to maintain the solder in a preformed shape when the solder is molten.
2. A solder composition according to claim 1 wherein the filler comprises metal particles or filaments.
3. A solder composition according to claim 2 wherein the metal comprises copper.
4. A solder column for forming electrical connections com-prising:
solder; and disposed in the solder a filler comprising discrete particles or filaments which are of a material which is solid at a temperature at which the solder is molten, and which are present in an amount sufficient substantially to maintain the column-like shape when the solder is molten
solder; and disposed in the solder a filler comprising discrete particles or filaments which are of a material which is solid at a temperature at which the solder is molten, and which are present in an amount sufficient substantially to maintain the column-like shape when the solder is molten
5. A solder column according to claim 4 wherein the filler comprises a metal powder or filament.
6. A solder column according to claim 4 wherein the filler comprises lengths of metal wire.
7. A solder column for forming electrical connections comprising:
solder; and disposed about the outside of the solder a support strand or tape which is of a material which is solid at a temperature at which the solder is molten, and which to disposed about the outside of the solder in a pattern whereby the column-like shape of the solder is substantially maintained when the solder is molten.
solder; and disposed about the outside of the solder a support strand or tape which is of a material which is solid at a temperature at which the solder is molten, and which to disposed about the outside of the solder in a pattern whereby the column-like shape of the solder is substantially maintained when the solder is molten.
8. A solder column according to claim 7 wherein the support comprises a metal wire or a metal tape.
9. A solder column according to claim 7 wherein the support strand or tape is disposed about the solder wire in the form of a spiral wrap.
10. A solder column according to claim 7 wherein the support strand or tape is disposed about the solder wire in the form of a braid.
11. A method of making a columnar solder preform, which comprises, (a) providing a solder wire; and (b) providing a support strand or tape disposed about the outside of the solder wire such that the shape of the preform is substantially maintained by surface tension when the solder is molten, the material of the support strand or tape being solid at a temperature at which the solder is molten.
12. A method as claimed in claim 11, which includes the step of heating the preform, after the support strand or tape has been applied, so as to cause the solder to flow.
13. A method as claimed in claim 11, in which the support strand or tape is disposed about the solder wire in the form of a spiral wrap.
14. A method as claimed in claim 13, in which the support strand or tape is so disposed by wrapping the strand or tape around the wire.
15. A method as claimed in claim 11, in which the support strand or tape is disposed about the solder wire in the form of a braid.
16. A method as claimed in claim 15, in which the support strand or tape is so disposed by braiding the strand or tape around the wire.
17. A method as claimed in claim 11, which includes the step of cutting the preform into pieces after the support strand or tape has been applied.
18. A method of making an assembly of solder preforms which comprises the steps of providing a retaining member having apertures therein for receiving respective solder preforms, and positioning solder preforms made by the method claimed in claim 11 in the apertures.
19. A method of melting a columnar solder preform, which comprises:
(a) providing a preformed support in the form of a spiral wrap or a braid of a strand or tape, (b) immersing the support in molten solder which is at a temperature at which the material of the support is substantially solid; to that solder fills the support; and (c) removing the support from the molten solder;
the support being such that solder is substantially maintained within it when molten by surface tension.
(a) providing a preformed support in the form of a spiral wrap or a braid of a strand or tape, (b) immersing the support in molten solder which is at a temperature at which the material of the support is substantially solid; to that solder fills the support; and (c) removing the support from the molten solder;
the support being such that solder is substantially maintained within it when molten by surface tension.
20. A method as claimed in claim 19, which includes the step of cutting the preform into pieces after the support strand or tape has been applied.
21. A method of making an assembly of solder preforms, which comprises the steps of providing a retaining member having apertures therein form receiving respective solder preforms, and positioning solder preforms made by the method claimed in claim 19 in the apertures.
22. A method as claimed in claim 19, which includes the step of forming the support.
23. An assembly of at least two electrically conductive elements, each having at least one contact, and a columnar solder preform which extends between the contacts forming an electrical connection between them, the preform comprising a support in the form of a spiral wrap or braid of a strand or tape, and a quantity of solder within the support, the support being such that the solder is substantially maintained within it when molten by surface tension.
24. An assembly as claimed in claim 23, in which one of the elements is a circuit board.
25. An assembly as claimed in claim 23, in which one of the elements is a chip carrier.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000539855A CA1269596A (en) | 1983-06-30 | 1987-06-16 | Chip mounting device and chip carrier mounting device |
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/509,684 US4664309A (en) | 1983-06-30 | 1983-06-30 | Chip mounting device |
| US06/610,077 US4705205A (en) | 1983-06-30 | 1984-05-14 | Chip carrier mounting device |
| US610,077 | 1984-05-14 | ||
| CA000457810A CA1226679A (en) | 1983-06-30 | 1984-06-29 | Chip mounting device and chip carrier mounting device |
| CA000539855A CA1269596A (en) | 1983-06-30 | 1987-06-16 | Chip mounting device and chip carrier mounting device |
| US509,684 | 1990-04-13 |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000457810A Division CA1226679A (en) | 1983-06-30 | 1984-06-29 | Chip mounting device and chip carrier mounting device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1269596A true CA1269596A (en) | 1990-05-29 |
Family
ID=27167453
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000539855A Expired - Lifetime CA1269596A (en) | 1983-06-30 | 1987-06-16 | Chip mounting device and chip carrier mounting device |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1269596A (en) |
-
1987
- 1987-06-16 CA CA000539855A patent/CA1269596A/en not_active Expired - Lifetime
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |