DE1905958A1 - Process for improving the bond strength of a copper foil with a matt surface - Google Patents

Description

It is known in the T _e chnilc in that the binder · strength of a copper foil by the formation 'of a matte surface on at least one side of the. \ said slide can improve. For example, in U.S. Patent 3,328,275, there is an electrochemical

For education
Treatment / a dendritic copper electrodeposition on a surface of the foil described, whereby the bonding behavior of the foil with respect to a suitable substrate is improved. The resulting product is said to be particularly suitable for use in the manufacture of printed electronic circuits. ^v

Similarly, U.S. Patent 3,220,897 discloses a method of forming a nodularized or spherulitic copper electrodeposition a surface of a copper foil, which similarly improve the bonding behavior of the foil is intended to make them particularly useful for the production of printed electronic circuits.

Although working methods like those mentioned. Patents, which are described, serve to improve the bonding strength of a copper foil, a problem has been observed in connection with the named products in that their bonding strength tends to deteriorate when the substrate to which the treated foil is bonded is exposed to high temperatures, (eg 177 ⁰ C (350 ⁰ P) and above), is exposed for longer periods of time. Since printed circuits, which such a copper foil is incorporated /

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not sIde / at such high temperatures for long periods of time this deterioration in bond strength posed a considerable problem.

According to the invention, the problem of the deterioration in the bonding strength of a copper foil becomes complete Plating-the matte surface of the copper foil with one Metal, which at elevated temperatures essentially compared to the substrate, bound to the said film is to be, is chemically inert, dissolved, but such a coating essentially does not change the original Bond strength of the copper foil to the substrate causes.

Accordingly, an essential purpose of the invention is the creation of a novel method for improving the bond strength of the matt surface of a copper foil in the V / e that the bond strength in the course of prolonged exposure a laminate or a layer arrangement that such a copper library contains, at elevated temperatures not decreasing. Another important purpose of the invention is to provide a novel method for improving the Bond strength at high temperature of a copper foil by coating the matt surface of this foil with a metal, that is essentially chemically inert to the substrate at elevated temperatures and that at more complete Coverage of the above-mentioned matt surface has essentially no change in the bond strength of the above-mentioned mats Surface causes during its binding to the substrate.

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Yet another important purpose of the invention is that To create a tough method for improving the bond strength of a copper foil that is an electrochemically formed one has a matt surface, by coating this' matt surface, preferably by electrochemical means, with a metal which at elevated temperatures compared to "a substrate to be bonded to the said copper foil is inert, but the coating will have essentially no change in initial or initial bond strength the said matt surface causes.

Another object of the invention is to provide a novel one Copper foil, and a layer containing this foil arrangement, this film having improved bond strength under prolonged conditions of elevated temperatures urfer has retention of the initial bond strength. The basic starting material used in carrying out the method according to the invention is one Copper foil, - preferably in the form of an elongated sheet. Albeit rolled or electrodeposited obtained copper foil can be used, the latter becomes preferred, although the particular form of copper foil employed does not form part of the invention.

To improve the bond strength of the copper foil the film is first subjected to a treatment that is more effective Way a roughening of at least one of its surfaces is used., This surface with a matt surface finish remains, the binding behavior of which is improved compared to the untreated film.

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Suitable treatment for this purpose is described, for example, in the aforementioned U.S. patents, to which reference is hereby made. As indicated above, in both of these patents there is a. procedure for the electrochemical formation of a matt copper deposit on at least one of the surfaces of a copper foil. In any case, the matt head deposit thus formed exists from a microcrystalline deposit that has a powdery texture. As the procedure to form this microcrystalline copper electrodeposition does not form part of the invention, it is sufficient to rely on the working methods described in the patents mentioned Refer to 2U.

According to the invention, this is initially done treated copper foil on its? treated or matte surface coated with a metal that is opposite to the substrate to which the treated copper foil is finally bound is to be chemically inert. This metal is sufficient on the matte surface of the copper foil Extent applied to completely cover this matte surface, but with a sufficiently small thickness, see above that the coating has essentially no decrease in the bond strength of the copper foil during its bond to the Brings substrate to form a layer arrangement. This feature can be extremely effective through Electrodeposition of a metal coating on the matt surface of the copper foil can be achieved, with the electrodeposition in an amount of about 0.2 to 1.0 g / m 2 Polienoberflache is applied. On the other hand, you can, albeit

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less effective, different ways of applying the Metal coating, e.g. vapor deposition or the like ... χ -

Any metal / that is functional and convenient to the matte surface of the copper foil can be deposited to the aforementioned extent of thickness and that opposite the desired substrate on which the foil is to be bound, is chemically inert, is in connection, useful with the invention. The preferred metal for this purpose is nickel. Other metals that are used can include cobalt, chromium, stainless steel, etc., Of these three, cobalt and chromium are preferred as these can be deposited by electrodeposition, although a metal such as stainless steel, without difficulty by means of vapor deposition procedures or the like. upset can be.

As indicated above, according to the invention not only the creation of a novel process for the production of a copper foil with an improved bond strength at high temperature and a copper foil produced thereafter, but also the creation of laminates or layer arrangements, comprising such copper foils bonded to a suitable substrate As can be seen, the particular substrate used in this layer arrangement will vary depending on the purpose for which the laminate is intended and the conditions of use or working conditions under which such laminate is used

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will. Particularly suitable substrates which make the laminate suitable for use in the formation of printed circuits include non-flexible supports such as Teflon-impregnated glass fibers (Teflon, trade name for polytetrafluoroethylene), KeI-F-impregnated glass fibers ( ¹¹ KeI-F ", trade name for particular fluorocarbon products including polymers of trifluorochloroethylene and certain MischpAyinerisaten) or the like .. Flexible substrates include polyimides such as see which are known under the designations "Kapton" and ¹¹ H-FiIm "(both materials cherish up by du Pont, are Polyimide resins formed by condensing pyromellitic anhydride with an aromatic diamine). -

The one used to form the treated copper foil to the substrate adhesives used are; those that are commonly used for the specific application can be used, whereby "FEP" (an I-fluorinated ethylene propylene resin in the form of a copolymer of tetrafluoroethylene and hexafluoropropylene with properties similar to Teflon) for Teflon and KeI-F is particularly suitable and common epoxy resins are useful for the other materials. The procedure "for tying the copper foil to the substrate is carried out in a conventional manner and does not form part of the invention. details such bonding is disclosed, for example, in U.S. Patent J. 328 275.

. . The most convenient way to apply the metal coating on the matte surface of the copper foil consists in

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that one passes the copper foil through an electrolyte in the manner and using a device as described in US patent specification ....... (US patent application Serial No. ^ 21 OkQ (196 * 0) , incorporated herein by reference. The system described in this US patent includes the use of plate anodes, the copper foil being passed in serpentine fashion in the vicinity of such anodes, and by suitable contact between "the copper foil" and conductive rolls or rollers When the copper foil is passed through the system with the matt surface and the foil facing the active surface of the anodes, the metal to be coated on this matt surface is made up of the electrolyte applied by means of electrodeposition.

Practice of the invention is as follows with respect to the electrodeposition of nickel on the matte Surface of a copper foil explained in more detail using examples.

Example 1 "-" '■

A roll of 28.35 g (1 ounce) of copper foil was used in this experiment, which had a matt surface in the form of a microcrystalline powdery! Copper electrodeposition of the type commonly used e.g. ^B. in U.S. Patent 3,220,897.

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The copper was replaced by a nickel ion containing Electrolytes in an electrolytic cell of the type specified above, as in particular in the US patent (U.S. Patent Application Serial No. 421,049 described is headed. The electrolyte used for this purpose consisted of a Woods-type chloride bath in which the Bath volume of 4 ^ 4 liters (115 gals) from 109 kg (240 lbs.) Nickel chloride and 54.8 liters (14.5 g as) hydrochloric acid had been. Two separate runs were carried out, with the conditions in each experiment as given below was.

Attempt a request B HCl (g / l) 120 120 Ni (g / l) 64 "64 Temperature (' ⁰ C) 21.1-22.2 21.1-22.2 ( ⁰ F) (70 - 72) (70 - 72) Speed of
Copper foil
vm / min)
(ft./min.)
Dwell time (sec.) 1.20
(4)
57 1.20
(4)
57 Current (A) 450-475 200 Current density _p
(A / 9.3 dnr) (A / ft.) 45-47.5 20th

The copper foil became serpentine through the electrolyte guided in the manner described above, the matt surface of the film being the active surfaces of the Anodes (which were formed from soluble nickel sheets)

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opposite. At the end of experiments A and B, the nickel-coated film was bonded to an epoxy resin-impregnated fiberglass support in the usual way. The epoxy resin was in the "east-stage uses and was cured in contact with the covered nickel surface of the film under a pressure of about 35 kg / cm (500 psi) at about 166-171 ⁰ C (330 to 340 ° F) The final laminate thickness was about 1.587 mm (1/16 in.) * With the film fc being about 0.038 mm (0.0015 in.) Of that total thickness.

The laminate so formed was then 12.7 mm wide strips (one-half inch) cut and then subjected to bending · "" strength tests in the following manner: On an initial attempt (the results of which are listed in Table I below as "Initial Peel" are) the copper from the glass cloth carrier in a 5.08 cm (2 inches) per minute in vertical dimensions Direction to the layer arrangement detached. The required Force for peeling or peeling the copper the backing was read on a force meter and measured in kilograms of force (lbs). This reading has been doubled to maintain the peel strength for every 2.54 cm (inch) width of the laminate »

A second bond strength test (identified as "Condition B" in Table I below) was carried out in the same manner as the "Initial Peel" - except that before the copper was peeled from the carrier in the manner indicated, the laminate in an oil bath at 260 ° C (500 ⁰ F) for 10 sec.

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was exposed. However, the copper was peeled off in the carrier at room temperature.

(Indicated in Table I below with "after 7 days at 150 ⁰ C") at a third bond strength test, the force required was to peel the copper from the carrier in the same way as in connection with the examination of the "initial separation" Amendment measured, that the laminate was first exposed to a temperature of 15O ⁰ C for 7 days, whereby the measurement was carried out again at room temperature. To obtain more meaningful results, two separate samples from each of Trials A and B were used, with the samples from Trial A being labeled "Al" and "A-2" in Table I below and those from Trial B " BI "and" B-2 "are indicated.

The results thereby obtained are shown below Table I listed ..

Table I. 9.4 condition
.) kß / 2.54cm B.
(lbs./in. ' After 7 days
at 150 ^° C 10.0 Initial
Peel off
k _K / 2.54cm (lbs./in, 9.6 4.45 9.8 4.54 11.6 A-I 4.26 10.6 4.26 9.4 5.26 10.8 A-2 4.35 9Λ 4.54 10.0 4.9 10.4 BI 4.8 4.17 9.2 4.72 B-2 4.26

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From the above results it can be seen that, although the bond strength of the samples in three cases of the four samples from the experiment titled "Condition B" decreased, the bond strength in all four samples the long exposure to an elevated temperature increased, which was completely in contrast to what was due to the previous Expertise would have been expected.

Example 2

The second series of attempts was varied among Conditions carried out again using the Woods-type chloride bath described in Example 1. the Conditions under which the tests were carried out, were as follows:

HCl (g / liter) Ni (g / liter) temperature ( ⁰ C)

Speed of the ^{T /} "sheet

m / min)

.ftV / min)
Dwell time (sec.)

Current (A)

Current density _o

(k / 9.3 dm ² ) (A / ft-Λ)

Attempt a Attempt B 12o 120 64 64 21.1-22.2 21.1-22.2 (70 - 72) Λ (70 - 72) 2.40
⁽ § ^}
28.5 2.40
(8th)
28.5 1000 500 100 50

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The nickel-plated copper foil was bonded to the epoxy resin-impregnated glass cloth as in Example 1 and as in Example 1 with a width of 12.7 mm (one-half inch) Cut strips. The bond strength tests were carried out in the manner described in Example 1 and the results obtained are summarized in Table II below.

Table II

Initial condition B After ¹ J days

seek detachment ■ at 150 ^° C

kg / 2.54cm - (lbs./in.) kg / 2.54cm (lbs./in.) kg / 2 _t 54cm (Ibs4n.)

A-I 4.54 10.0 4.26 9.4 4.99 11.0

A-2 4.45 '9.8 x 4.45 9.8 4.65 10.2

BI 4.35 . 9.6 4.45 '9.8 5.08 11.2

B-2 4.72 10.4 4.54 10.0 5.08 11.2

Although here too the bond strength decreased in two of the four samples and substantially in the other two samples remained constant in the test under "Condition B", the exposure of the samples resulted in aäiönte Temperature! constant for a longer period of time to an increase in the bond strength in a striking way, which was contrary to the expectation.

From the foregoing it can be seen that according to the invention, considerable advantages through the grant a significantly improved bond strength at high temperature can be created on copper foils. It is

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this improved bond strength is believed to increase. - " results in a significant proportion from the fact that the metal coating on the matte surface of the copper "foil isolates the matte surface from the substrate, that a chemical interaction between the substrate and the matte. Surface, which in turn leads to a reduction the bond strength of such a surface would be prevented. At the same time, however, the thickness of the metal coating is kept sufficiently low so that the coating does not significantly affect the initial bond strength of the matt surface while it is being bonded to the substrate decreased. ·

As used herein, "essentially without; Decrease in the bonding strength of said matt surface "means a loss in bonding strength of less than about 0.45 kg per 2.54 cm (1 pound / in.),

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Claims (12)

Claims (T) A method for improving the bonding strength of a copper foil with a matt surface from a microcrystalline powder-like copper electrodeposition which, if bonded to a carrier substrate, loses its bonding strength during prolonged exposure to elevated temperatures, characterized in that the matt surface is coated with a metal which is substantially chemically inert to said substrate, the coating of the metal completely covering said matt surface and being of a thickness such that the coating causes essentially no decrease in the bond strength of said matt surface as it is bonded to the substrate. 2. The method according to claim 1, characterized in that the metal coating by electrodeposition on the called matt surface applies. 3. The method according to claim 1 or 2, characterized in that that a coating of nickel, cobalt, chromium or stainless steel is applied as a metal coating. K. Method according to one of Claims 1 to 5, characterized in that the metal coating consists of nickel. 5. The method according to any one of claims 1 to 4, characterized 'ρ indicates that about 0.2 to 1.0 g of metal per m the matt surface applies as a coating. 90983471272 6. The method according to any one of claims 1 to 5, characterized in that «a nickel coating by electrodeposition on the matt surface in an amount of ett
brings. from about 0.2 to I ₁ Og Depending of the matte surface Open m 7. Copper foil »which has at least one surface improved bond strength properties at high Has temperature when bonded to a carrier substrate, thereby characterized by having a matte finish a microcrystalline powdery copper electrodeposition completely covered with a metal coating which is substantially chemically inert to the substrate, the metal coating being such Thickness has that there is essentially no decrease in the bond strength of the matt surface mentioned Relation to the substrate when it is bonded to the substrate. "-.._ 8. copper foil mch claim 7 * characterized in that the metal coating made of nickel, cobalt, or chromium stainless steel. 9 «copper foil according to claim 7 or 8, characterized in that The metal coating consists of nickel. 10. copper foil according to any one of claims J to 9, characterized in that the metal coating has been applied to said matt surface by electrodeposition. 909834/1272 11. Copper foil according to one of claims 7 Ms 10, characterized in that the metal coating in one Extent of about 0.2 to 1.0 g per m of the matt surface is available. 12. Copper foil according to one of claims 7 to H * characterized by having an electrodeposited kickel coating in an amount of about 0.2 to 1.0 g of nickel per m of said matt surface having. IJ. Laminate or layered arrangement that the Copper foil according to claim 7 and comprising a carrier substrate, being the metal-coated matte surface of the copper foil is bound to the substrate. 903834/1232