JP5017991B2 - Printed wiring boards, electronic devices - Google Patents

Description

  The present invention relates to a printed wiring board, and more particularly to a structure of a printed wiring board on which rigid parts such as BGA (Ball Grid Array), LGA (Land Grid Array), and a butt lead package are mounted.

  Generally, in a mobile device product in which a CSP (Chip Size Package) having excellent mounting efficiency as an LSI is mounted on a printed wiring board by soldering, there is a drop of the product, a key press, etc. At that time, mechanical stress is generated in the soldering portion due to twisting or bending, and stress is generated in the solder connection portion of the corner portion of the CSP by applying this mechanical stress to the printed wiring board. The details of this situation are described below.

  FIG. 1 is a basic structural diagram of a conventional printed wiring board, and FIG. 2 is an explanatory diagram of problems of the conventional printed wiring board. In FIG. 1, 1 is a printed wiring board, 2 is a substrate, 3 is a footprint, 4 is a BGA ball, 5 is a component, 6 is a solder resist, and 7 is a through hole. FIG. 1A is a plan view showing a layout of a footprint 3 at a corner of a printed wiring board, a through hole 7 and the like, and FIG. 1B is a cross-sectional view of the printed wiring board 1 between plan views. For convenience of explanation, the BGA ball 4 and the component 5 are also shown in the sectional view for reference, but in the plan view (a), it is 3 (4), and the BGA ball 4 is mounted on the footprint 3. It shows that. When the BGA ball 4 in FIG. 1 is close to the corner of the printed wiring board 1, the BGA ball 4 is easily subjected to a force due to an external force, and the footprint 3 bends in the same direction as the printed wiring board 1 according to the external force received by the substrate 2. This is a structure in which cracks are likely to occur in the joint surface between the substrate 2 and the footprint 3 or between the footprint 3 and the BGA ball 4.

  Therefore, as a countermeasure against the fact that the solder joint is easily broken when a large force is applied near the corner of the printed wiring board 1, which is a problem of the conventional printed wiring board of FIG. The conventional technique of this improvement method will be described with reference to FIG. 2A is a plan view of the printed wiring board 1, FIG. 2B is a detailed view of the corner portion, and FIG. 2C is a cross-sectional view. As shown in FIGS. 2 (a) and 2 (b), the footprint 3 is provided with a footprint extended outside the corner in the vicinity of the corner. The footprint extended outward is set to 8, and thereafter, it is distinguished from other circular footprints 3. In the figure and subsequent drawings, the same parts are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 2 (c), when a large force is applied near the corner of the printed wiring board 1, the force acts directly between the substrate 2 and the BGA ball 4 close to the component mounting surface, and the component If the printed wiring board 1 bends in the direction opposite to the mounting surface, that is, in the downward direction of the cross-sectional view, there is a risk that the solder will be peeled off. If the plate 1 is bent, there is a risk of breaking the solder joint. In this case, although the bonding strength between the base material 2 and the footprint 8 is slightly improved due to the reinforcing effect of the footprint 8 as compared with the conventional substrate structure before improvement, when a large external force is applied, The problem that an electrical failure is likely to occur along with physical destruction when subjected to various external forces and impacts on the printed wiring board 1 is not essentially solved.

In Patent Document 1, a reinforcing pad of a chip size package (CSP) has a structure that is rounded so as to follow a predetermined portion of a contact surface with a CSP main body portion of a solder ball, so that the mounting surface has It is described that it is possible to reduce the peeling of the solder balls as a result of no sharp corners and mechanical stress concentration. In Patent Document 2, a circular shape, a rectangular shape, a fishing shape, or the like is formed in the vicinity of the outermost periphery of the connection land formed in a grid pattern on the back surface of the module substrate, and an area that is more than three times the area of one connection land It is described that connection reliability can be improved for mounting on a printed circuit board by using a module part provided with a reinforcing land. However, the reinforcement method provided on the printed circuit board of any of these documents is not sufficient, and there is no technology that can sufficiently cope with a CSP component having a rigid terminal.
JP 2002-237549 A (page 1-2, FIG. 1) JP-A-8-139233 (page 1-2, FIG. 1)

  As described above, in the conventional printed wiring board structure, since the footprint is bonded to the board, the solder joints remain as they are when the printed wiring board falls or is inserted into or removed from the shelf. Will be received. For this reason, when the amount of deflection is large, the force applied to the solder joint exceeds the solder joint force, resulting in destruction of the solder joint. Fracture extends so that the crack enters from the outer end of the solder joint to the inside, and this is called a crack. Such cracks are a serious problem that affects the circuit operation of the printed circuit board. It is an object of the present invention to provide a printed wiring board structure that avoids / relaxes thermal and mechanical stress applied to a solder joint even when the printed wiring board is bent.

  In the present invention, in order to achieve the above object, the footprint is created by making a space between the footprint 8 and the printed wiring board 1 slightly wider than the area to be soldered of the footprint 8 extending outside the corner near the corner. 8 has a structure having a spring property. More specifically, a through hole is provided in a substrate below the footprint 8, a recess is provided in the substrate surface below the footprint 8, a cushioning material made of a material serving as a cushion is provided in the provided space, or a foot used for bonding The substrate side of the print 8 is partly separated from the substrate, and the structure in which the footprint 8 and the printed wiring board 1 in this area are intentionally not partly bonded is used to relieve stress.

  According to the printed wiring board structure of the present invention, a large and hard ceramic BGA that is weak against the deflection of the printed wiring board is not problematic in terms of reliability, and the range of component adoption is widened. Large ceramic modules can also be commercialized. On the other hand, the solder joints will not break even under conditions that are more severe than the current drop impact, vibration, temperature environment, etc., so there is an effect that the range of applicable products is widened and the use environment of the products themselves is also eased. .

  FIG. 3 shows the basic structure of the present invention. 3A is a plan view of the printed wiring board 1, FIG. 3B is a detailed view of a corner portion thereof, and FIG. 3C is a cross-sectional view thereof. In FIG. 2, when the BGA 4 is set as the starting point, the footprint 8 extends in the direction toward the outside of the component. On the other hand, as shown in FIGS. As shown in FIG. 3C, the footprint 8 and the printed wiring board 1 are slightly wider than the solder-bonded area of the footprint 8 and toward the outside of the component. By creating a space between the footprints 8, the footprint 8 can be made springy. Thereby, even when the printed wiring board 1 bends, the footprint 8 can be kept parallel to the component, and the stress is relieved. With this structure, as shown in FIG. 3C, even when the printed wiring board 1 is bent upward in the cross-sectional view where the solder is peeled off, it is not peeled off, and the lower part in the cross-sectional view where the solder is crushed. Even when the printed wiring board bends in the direction, the stress on the footprint 8 is relieved so as not to be affected by crushing. The footprint 8 is desirably thicker than the normal footprint 3 so as to have a spring property.

  Specific examples of the present invention will be described below with reference to the drawings. In FIGS. 4 to 6, the left side is a plan view and the right side is a cross-sectional view as in FIG. FIG. 4 shows an embodiment in which a through hole 11 is provided that is slightly wider than the area to be soldered of the footprint 8 extending outward near the corner and through which the printed wiring board 1 penetrates. A through hole 11 is formed in the base material 2 under the footprint 8 which also serves as a reinforcement under the right BGA ball 4 shown in the cross-sectional view of FIG. If you take it wider than it is.

  FIG. 5 shows an embodiment in which the printed wiring board 1 is provided with a recess 13 which is similarly a little wider than the area of the footprint 8 to be soldered. The shape, width, and depth of the recess should be wider than the footprint. When the depth is almost zero, it can be considered that the footprint 8 and the printed wiring board 1 are not bonded, and this is also considered to be the same structure.

  FIG. 6 shows an embodiment in which a cushioning material 14 is provided on the printed wiring board 1 and is slightly wider than the area where the footprint 8 is soldered. The shape, width, thickness and material of the cushioning material should be wider than the footprint 8.

  Next, the manufacturing method of the printed wiring board 1 of this invention is demonstrated with FIG. In FIG. 7, the footprint 3 is bonded to the base material 2 with the adhesive 9, and is in a semi-finished state. At this stage of manufacturing the substrate, the component 5 and the BGA ball 4 are not present, but are shown for reference. It is shown. In FIG. 7 (a), a hole is drilled from the back side of the substrate, and a through hole 11 is provided under the footprint 8 in the lower part of the BGA ball 4 at the outermost corner of the printed wiring board 1. is there. In FIG. 7B, a soluble material 12 which is dissolved by a solvent is embedded in the lower part of the BGA ball 4 of the base material 2 immediately below the footprint 8, and the printed wiring board 1 is dissolved by dissolving with a solvent. The printed wiring board 1 having a structure in which the recess 13 is provided is manufactured.

In FIG. 7 (c), the elastic cushioning material 14 is originally embedded in the lower part of the BGA ball 4 of the base material 2 immediately below the footprint 8, and the impact or deflection is made of an elastic material. The printed wiring board 1 having a structure using a buffer material to be absorbed is manufactured. In FIG. 7D, the adhesive neutralizing agent 15 is applied to the footprint 8 so that the lower part of the BGA ball 4 of the base material 2 immediately below the footprint 8 is in an unadhered state. It is a manufacturing method of the printed wiring board 1 which produced | generated the part 16. FIG. In this case, the manufacturing method is different from that shown in FIG. 7B. However, as shown in Appendix 7 below, in the structure provided with the recess 13 shown in FIG. It can also be said.
(Appendix 1)
In a printed wiring board having a substrate and an electronic component that are electrically bonded to each other, a structure that is used for bonding the substrate and the electronic component and the footprint disposed on the surface of the substrate is partially separated from the substrate. A printed wiring board characterized by the above.
(Appendix 2)
An electronic apparatus comprising the printed wiring board according to appendix 1.
(Appendix 3)
A method for manufacturing a printed wiring board having the partially separated structure according to appendix 1.
(Appendix 4)
The printed circuit board according to the supplementary note 1, wherein the partially separated structure is wider than an area where the footprint is electrically joined, and has a through hole in the substrate below the footprint. .
(Appendix 5)
The printed circuit board according to the supplementary note 1, wherein the partially separated structure is a structure that is wider than an area where the footprint is electrically joined and has a concave portion on the substrate surface below the footprint. .
(Appendix 6)
The partially separated structure according to appendix 1, wherein the footprint is wider than an area where the footprint is electrically joined, and is a structure in which a buffer material is embedded in the substrate surface below the footprint. Wiring board.
(Appendix 7)
The printed circuit board according to claim 1, wherein the partially separated structure is a structure that is wider than an area where the footprint is electrically joined and is not bonded to the substrate below the footprint. .
(Appendix 8)
The printed wiring board according to any one of appendices 1 to 5, wherein the electrical connection between the substrate and the electronic component is a solder joint or a conductive resin joint.
(Appendix 9)
The method of manufacturing the printed wiring board according to appendix 4, wherein a hole is drilled from the back side of the substrate at a lower surface portion of the footprint in a lower portion of the BGA ball in the vicinity of a corner of the printed wiring board. A printed wiring board manufacturing method, wherein a through-hole is provided in a distribution board.
(Appendix 10)
The method of manufacturing the printed wiring board according to appendix 5, wherein a material that can be dissolved by a solvent is embedded in the lower surface portion of the footprint in the lower part of the BGA ball near the corner of the printed wiring board. A method for producing a printed wiring board, wherein the printed wiring board is provided with a recess by melting in a solvent.
(Appendix 11)
The manufacturing method of the printed wiring board according to appendix 6, wherein an elastic cushioning material is embedded in a surface of the substrate in a lower surface portion of the footprint in a lower portion of the BGA ball near a corner of the printed wiring board. What is claimed is: 1. A printed wiring board manufacturing method, comprising:
(Appendix 12)
The manufacturing method of the printed wiring board according to appendix 7, wherein an adhesive neutralizing material is applied to a lower surface side surface of the footprint in a lower portion of the BGA ball in the vicinity of a corner of the printed wiring board, A method of manufacturing a printed wiring board, wherein a lower part of a BGA ball of the substrate is in an unbonded state.

Basic structure of a conventional printed wiring board Illustration of problems with conventional printed wiring boards Illustration of the basic structure of the present invention Structure diagram when the through hole of the embodiment of the present invention is provided Structure diagram when the dent of the embodiment of the present invention is provided Structure diagram when the cushioning material of the embodiment of the present invention is provided Explanatory drawing of the manufacturing method of the printed wiring board of this invention

Explanation of symbols

1 Printed wiring board 2 Base material 3 Footprint 4 BGA ball
5 Parts 6 Solder resist 7 Through hole 8 Footprint extended outside the corner 9 Adhesive 10 Copper foil 11 Through hole 12 Soluble material 13 Recess 14 Buffer material 15 Adhesive neutralizer 16 Non-adhesive part

Claims (5)

A substrate on which electronic components are mounted;
A plurality of first footprints formed on the substrate and bonded to terminals of the electronic component;
A through hole formed in a lower portion of the second footprint disposed near a corner of the substrate among the plurality of first footprints ;
The second footprint is
An adhesion part adhered to the substrate;
A position that is spaced apart from the substrate and directly above the through-hole, and a bonding portion that is bonded to the terminal;
The printed circuit board according to claim 2 , wherein the second footprint is arranged such that the adhesive portion is disposed on a center side of the electronic component and the joint portion is disposed on an outer edge side of the electronic component. 2. The printed wiring board according to claim 1, wherein a hole outer shape of the substrate surface of the through hole is larger than an outer shape of a joint portion of the second footprint. A substrate on which electronic components are mounted;
A plurality of first footprints formed on the substrate and bonded to terminals of the electronic component;
Of the plurality of first footprints, comprising a recess formed in the lower portion of the second footprint disposed in the vicinity of the corner of the substrate ,
The second footprint is
An adhesion part adhered to the substrate;
A position that is spaced apart from the substrate and directly above the recess, and a joint that is joined to the terminal;
The printed circuit board according to claim 2 , wherein the second footprint is arranged such that the adhesive portion is disposed on a center side of the electronic component and the joint portion is disposed on an outer edge side of the electronic component. 4. The printed wiring board according to claim 3, wherein an outer shape of the substrate surface of the concave portion is larger than an outer shape of a joint portion of the second footprint. A substrate on which an electronic component is mounted, a plurality of first footprints formed on the substrate and bonded to terminals of the electronic component, and a corner vicinity of the substrate among the plurality of first footprints A through hole or a recess formed in the lower part of the second footprint disposed in
The second footprint has an adhesive portion that is bonded to the substrate, and a joint portion that is spaced from the substrate and is located directly above the through hole or the recess and is bonded to the terminal. And
Arrangement of the second footprint, said adhesive part toward the center of the electronic component is arranged, Ru is the joint disposed on the outer edge side of the electronic component
Electronic device comprising a call.

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