GB2030176A - Copper foil suitable for use in making printed circuits - Google Patents

Abstract

A copper foil having multiple layers thereon is provided by electrodepositing an arsenic-containing copper layer thinly on at least one surface of a copper foil; further electrodepositing thinly thereon, a treated layer consisting of zinc and tin or consisting of an alloy of at least one of zinc and tin together with copper; and causing the metals of the respective layers to diffusion- permeate e.g. by heating through each other to thereby form alloy compositions in the vicinities of the boundaries of the respective layers. The resulting copper foil for printed circuits is superior in the adhesion-retainability between the respective treated layers. The foil may be first electrodeposited with a fine particulate copper layer, then a smooth copper layer, prior to the arsenic-containing copper layer. The outermost layer may be treated with a chromate (e.g. chromium electroplated) or an organic anti-oxidising agent.

Description

SPECIFICATION Copper foil suitable for use in making printed circuits This process related to the production of copper foil, particularly useful for printed-circuit use.

Various processes have been proposed for surface-treating copper foils. For example, an electrodeposition-treatment process has been carried out for doubling the specific surface area of the film. Various such processes have been proposed such as simply, powdery plating belonging to burned plating, and a two-step treating process intended to prevent the powdery depositformed in the above-mentioned process from falling off. In this process a so-called smooth plating is applied onto the above-mentioned plating, at a limiting current density or less.Other processes include a process of applying a suspension of synthetic resins in place of the above-mentioned burned plating, for improving adhesion properties, and a process involving adding a coloured salt of metals such as arsenic, antimony, bismuth, etc to a copper-plating solution to thereby impart a finely roughened surface, and certain modifications of the foregoing processes.

A A process involving electrodepositing an alloy layer composed mainly of brass onto the surface of a copper foil has also been proposed, in order to avoid faults caused by the physical or compiex-chemical transfer of copper to the organic base material. This results in so-called "lamination staining", which often occurs during the indispensable etching of the copper clad laminate.

Recently, however, as the application fields of printed circuit boards have been broadened so that high performances are required, it has come to be required besides their flame-proof property that deterioration of peel strength after a long period of heating is small. According to the Underwriter's Laboratory, (so-called UL Standards which have a world-wide authority), a peel strength of 21b/inch after heat-treatment for 56 days at 153 C, is required.

In addition, copper foil with high residual strength after a long period of heating was recently come to be required not only for the above-mentioned reasons but also for practical reasons, in the production of printed circuits. In the preparation of multilayer laminates, a two-surface sheet which will later constitute an inner layer is laminated by a hot press, and subjected to various circuit-processings such as circuit formation, drilling or punching, through-hole plating, etc. Thereafter outer layer materials are further placed thereon, followed by hot pressing. When the lamination is carried out twice or three times, heat under pressure over several hours is exerted on the copper foil. This gives the same results as when heating in the temperature range defined in the U.L.Standards is repeated several times, and hence the heating conditions are entirely different from the conventional conditions at 2600C for from several seconds to several tens of seconds in the open atmosphere.

In the production of these multilayer laminated boards, apart from the retention of adhesion thereof to the laminating organic base, the adhesion between the respective metal layers, such as between copper foil and secondarily electrodep osited layers, the respective copper layers are alloy layers, has often come to be required in the surface-electrodepositing treatment of copper foil by way of a multiple electrodeposition, as an effect under heat and pressure.

This invention provides a process for producing a treated copper foil which process comprises electrodepositing an arsenic-containing copper layer onto the surface of a copper foil, and electrodepositing onto the said layer a layer of at least two of zinc, tin and copper. The foil is then preferably subjected to a treatment so as to cause the metals of the two said layers to diffuse into each other.

We have noted that the heat stability of metal interfaces is related to the two above mentioned problems, i.e. the heat stabilities are a long period of the respective secondarily electrodeposited multilayers and of the organic laminating matrix. We have made various studies aimed at positive inhibition of the transfer of copper which tends to transfer thermally and physically or complex-chemically from copper foil to the base organic material during heating for long periods, e.g. at the time of heating starting from that at about 1700C for one hour in the press lamination, to that over 56 days according to UL Standards. Our studies have also been aimed at the retention of adhesion between layers at the time of subjecting copper and copper-based alloy layers to an overlaying electrodeposition-treatment a number of times.As a result we have found that as for the former aim, a three-component alloy layer consisting of three layers of tin, zinc and an alloy formed by their diffusion is very effective as a barrier against transfer of copper from the surface to be adhered, to the organic base, from the point of view of heat stability for long periods. We have also found that, as for the latter aim, if arsenic is used, which has been abhored in the electrorefining of copper for many years because it gives a rough surface or a surface layer which is difficult to deal with thermally, then good adhesion of copper layers between each other and between copper layer and copper alloy layer are retained.

Based on this finding, we have made studies for obtaining a copper foil satisfying the requirements of UL Standards and multilayer laminates, i.e. the requirements under which adhesion and lamination onto printed circuit boards having a high peel strength after a long period of heating.

As a result we have discovered that in the case of the laminated structure of the above-mentioned three-component alloy layer and arsenic-containing copper layer, a synergistic effect is exhibited in addition to the desired effect.

The present invention exhibits a remarkable effectiveness when a multiple stage overlaying electrodeposition of two layers or more is continuously applied onto the surface of a copper foil, which is later adhered to an organic base. When the process is used at the same time as a specific surface area-increasing electrodeposition treatment wherein an electrodeposited copper layer is obtained by overlaying electrodeposition a number of times, the adhesion of the respective electrodeposited layers is reinforced by an intervening layer containing a trace of arsenic.Furthermore, it is also possible to apply this in combination with techniques for inhibiting lamination spots such as stain, spot, transfer, etc at the time of preparing printed circuits, developed by a physical or complex-chemical transfer of copper which is caused by a hot contact bonding of secondarily electrodeposited copper layers being active and having a large specific surface area, direcly onto a laminating base organic material, in the lamination. Thus is can be used for example, in conjunction with a technique previously proposed by the present inventors, in Japanese Patent Publication No 74537/1977, wherein a binary alloy electrodeposited layer is applied onto a copper foil, followed by heating to form a tertiary alloy layer, a technique proposed in the gazette of Japanese Patent Publication No 111428/1977, etc.Furthermore, it is possible to achieve the survival of peel strength after a long period of heating which has not always been stably effected by way of overlaying of these techniques, alone, without harming the effectiveness obtained by a combination of these techniques. Thus, it has become possible to broaden the application fields of copper clad laminates such as an application to heat-resistant bases, and also improve the reliability in case where it is employed as an inner copper foil of multilayer, multiple circuit laminates.

An embodiment of the invention will now be described with reference to the accompanying drawings, which is a schematic view of a production line for carrying out the process of the present invention.

The apparatus comprises a first stage electrodeposition vessel I where copper plating is carried out for forming a finely particulate roughened surface on the surface of a copper foil. It is possible to adhere the copper foil more tightly onto the base by way of surface-roughening. However, the first stage electrodeposited layer and a second stage electrodeposited layer as mentioned below may be applied if required, and can be omitted depending on the surface condition of the copper foil. The copper foil 1 is negatively charged by a contact roll 2 and has its surface purified in an acid-washing vessel 3. Numeral 4 shows an anode, and copper foil passes through an electrolyte while directing the surface thereof to be electrodeposited to the anode 4. The anodes 4 are connected to separate electric sources in each vessel.At this stage, the foil is treated generally at a current density in the vicinity of the limiting one or higher than that, to impart a finely particulate surface and thereby increase the specific surface area.

For example, in the case of acidic copper sulfate bath, it is possible to select the following conditions: CuS04 (in terms of copper) 12-20g/l(as Cu) H2SO4 45-1 20g11 Solution temperature 22-35 C Current density (based on cathodic 6-18A/dm2 surface area, in average) Passing time 8.25 sec.

Copper foil 1 having passed through the first stage electrodeposition vessel I passes through squeeze rolls 5 and enters a second stage electrodeposition vessel II, while maintaining a liquid film having a minimal thickness, for preventing its oxidation. The treatment at the second stage electrodeposition step is a smooth copper plating layer carried out to prevent the first stage electrodeposited layer which is intended to roughen the surface of the copper foil, from falling off when the foil is handled in the subsequent respective treating steps. The second stage is thus a thin plating to an extent that the roughened surface is maintained.As for the plating conditions of composition of the plating bath, current density, etc the following example can be selected: CuS04 (in terms of copper) 40-85g/l (as cu) H2SO5 40-1 20g/l Solution temperature 36-55 C Current density (based on cathodic 12-30A/dm2 surface area, in average) Passing time 10-25 sec.

In the first stage, since the amount of material electrodeposited is greatly influenced by the current density, it is necessary to pay attention to the presence of trace amounts of transition valence impurities such as iron, chromium, arsenic, etc as well as to the bath composition and the electrodeposition conditions.

In the second stage, the acceptable conditions are quite broad, and electrodeposition at a limiting current density or lower, imparting a smooth plating onto the plane may be sufficient.

The copper foil having left the second stage bath enters a third stage electrodeposition vessel Ill, while superflows solution is removed by squeezing on squeeze rolls 5 so that the amount of solution carried over is not so much as to cause large variations to the composition of the subsequent bath. In the third stage electrodeposition vessel, an arsenic-containing copper layer is deposited. This improves adhesion of the copper foil and various electrodeposited layers. For this purpose, an arsenic-containing solution is prepared in advance.

For example, arsenious acid may be employed as an arsenic source. This is used in the form of an aqueous solution obtained by dissolving it in an aqueous solution of sodium hydroxide, to prevent the generation of harmful arsine gas (AsH3).

Examples of the bath composition and electrodeposition conditions for the third stage bath are as follows: CuS04 7-lOg/I (as Cu) H2SO4 20-70g/l Arsenic-containing solution 0.05-0.5g/l (as As) added Solution temperature 18.22 C Average current density (based on cathodic surface area) 4-6A/dm2 Residence time 5-20 sec.

The arsenic-containing copper layer applied in the third stage electrodeposition step is applied with the object that the arsenic contained therein diffuse into the roughened surface copper layer as well as into a fourth electrodeposited layer to be formed on the arsenic-containing copper layer at the subsequent stage, whereby integration of the arsenic-containing copper layer with the above-mentioned upper and lower layers is effected. Accordingly, the thickness of the arsenic-containing copper layer need not be large, and a thickness such that the layer contains a sufficient amount of arsenic to diffuse will be adequate.However, it should be noted that even when the bath conditions and electrodeposition conditions are regulated to within the above-mentioned ranges, the amount of arsenic in the arsenic-containing third layer is not dictated only by the bath and electrodeposition conditions. Instead if deviates to some extent depending on the surface condition of the copper layer, and is greatly different from the analytical value obtained by a comparable test in a beaker for example, using only this electrodeposition layer.

The thickness of the arsenic-containing copper layer maybe judged by its colour. The colour of the arsenic-containing copper layer varies from a colour almost unchanged from that of the electrodeposited copper layer alone, under certain conditions when thickness is small, to a black appearance resulting from the fact that, as the thickness of the arsenic-containing copper layer increases, the acicular substance on the surface of the layer protrudes so much from the surface that it falls down. It is not necessary for the arsenic-containing copper layer to be so thick that this latter appearance is seen. The properties of the layer are quite adequate if the colour is within the range from a grey-brown colour in which considerably copper colour remains, to a pale chocolate colour, then the object of the third electrodeposition layer is fully attained.

In the above description, a case where the arsenic-containing copper layer as a third electrodeposited layer is applied onto the two first and second secondarily electrodeposited layers has been discussed. However, depending on the object and kind of printed circuit boards, and aiming at only the survival of peel strength after a long time heating, the arsenic-containing copper layer may be electrodeposited directly onto the surface of copper foil, omitting the first layer or both the first and second layers. In this case, however, it is desirable to have the arsenic-containing copper layer had a surface-roughening function at the same time, in place of the surface-roughening of copper foil, and electrodepositthe arsenic-containing copper layer till a thickness corresponding to pale brown color is given.When the layer has a thickness such an extent, an acicular projection grows on the surface, resulting in a remarkable effectiveness of making better the adhesion thereof onto copper foil as well as a fourth stage alloy layer as mentioned below.

The copper foil having left the third stage electrodeposition vessel Ill is washed with a sufficient amount of water on both the surfaces thereof in a water-washing vessel 6 and further washed on both the surfaces thereof by means of water-washing nozzles, in order to avoid mixing of the arsenic-containing solution into a reducible metal bath at the succeeding stage, and thereafter enters a fourth stage electrodeposition vessel lv. If an arsenic source is present herein, there is a danger that arsine gas is generated in an acidic reducible atmosphere, and hence a sufficient water-washing is necessary.

The fourth stage electrodeposition vessel IV is an electrodeposition bath vessel for preparing a zinc-tin mixture pre-alloying layer which later diffuse into the arsenic-containing copper layer as a ground to form an alloy layer, at the time of the succeeding drying of copper foil, application and drying of an adhesive, and further, laminating press adhesion, etc.

As for the treatment in the fourth stage electrodeposition vessel IV, the following processes based on two technical ideas may be considered, taking into acount an adptability of copper foil to the opposed laminate, through a delicate nuance in the use, which may be regarded as an affinity between the both The first is directed to a process of electrodepositing an alloy layer, aiming mainly at completely inhibiting the transfer of copper, and the second is directed to a process of thinly applying alloy layers onto both the surfaces of copper foil, for having the layers had a rust-proof function at the same time.

The electrodeposition according to the first process may be carried out under the following electrodeposition conditions: ZnSO4 (in terms of Zn) 0.8 - 2.0 g/l (as Zn) Sn(SO4)2 (in terms of Sn) 0.05 - 1.0 g/l (as Sn) K4P207 3H2O 20 - 40 g/l PH 10.7-11.5 Solution temperature 40 - 48 C Current density (based on cathodic surface area, in average) 0.5 - 5.5 A/dm2 Passing time 10 - 25 sec.

In addition, tin (II) sulfate may be substituted for tin (IV) sulfate, and zinc and tin may be employed in the form of pyrophosphate.

In the case according to the first process, since it is necessary for the layer to have a thickness sufficient for inhibiting the transfer of copper with certainty, a thickness corresponding to a pale grey color to such an extent that copper color as a ground is see-through is selected, while the layer thickness is judged, noting the colour change of itself as a standard.

In the case according to the second process, the following electrodeposition conditions may be employed: ZnSO4 (in terms of Zn) 0 - 2.5 g/l (as Zn) SnSO4 (in terms of Sn) 0.1 - 2.5 g/l (as Sn) K4P207 15-50g/l PH 10.5-11.7 Solution temperature 40 - 48 C Current density (treated surface side of copper foil) 0.3 - 3 A/dm2 (luster surface side, i.e. shiny side) 0.05 - 2 A/dm2 Passing time 1 - 10 sec.

In addition, the substitutions of zinc salt and tin salt may be the same as those in the first process. Further the current density may be selected and decided within the above-mentioned conditions, depending on the specific surface areas of both the surfaces, the amount of electricity supplied and the diffusion of Zn - Sn into the copper surface at the succeeding step and the appearance at that time.

The fourth stage electrodeposition vessel IV of the drawing illustrates a case where a thin electrodeposition treatment is applied onto both the surfaces, for having the layer had a rust-proof function at the same time, and an anode 7 is provided at the center of the vessel.

In order to prevent the surface-treated copper foil from oxidation and discolation during steps which are indispensable for producing printed circuit boards, such as an adhesive-coating step and a laminating step succeeding to the above-mentioned surface-treatment of copperfoil, and during the storage periods between the respective steps, it is necessary to apply a rust-proof treatment onto the above-mentioned surface-treated copper foil. Thus, succeeding to the fourth stage electrodeposition step, a fifth stage electrodeposition step is provided aiming at rust-prevention. If the above-mentioned second process is employed in the fourth stage electrodeposition step, it is, of course, unnecessary to carry out the fifth stage treatment. However, for enhancing the rust-proof effectiveness, the fifth stage treatment may be successively carried out.As for the rust-proof process, a conventional process using organic antioxidants such as triazoles, pyrazolones, imidazoles, silane coupling agents, etc. may be employed, but preferably an overlapping rust-proof process employing a chromate, as a fifth stage treating step, is combined with the above-mentioned fourth stage electrodeposition step, resulting in a synergistic effect of rust-prevention by means of Zn-Sn which have permeated and are remaining, together with the chromate. Thus a very effective rust-proof performance can be obtained. In carrying out the fifth stage chromate treatment, the copper foil subjected to the fourth stage treatment is washed with water in advance to sufficiently prevent bringing of impurities into the fifth stage treatment.

As for the process for chromate treatment, a process of merely immersing the foil in anhydrous chromic acid may be employed. Alternatively a process by way of electrodeposition may be also employed. In case where it is immersed in anhydrous chromic acid, the following immersion conditions may be employed: Anhydrous chromic acid 0.3 - 3 g/l Liquid-passing time 10 - 20 sec.

On the other hand, in the case of chromate treatment through electrodeposition, the following electrodeposition conditions may be employed: Anhydrous chromic acid 0.2 - 0.6 g/l Current density 0.02 - 0.2 A/dm2 Passing time 5 - 15 sec When both the surfaces of the copper foil are subjected to a cathodic treatment under the above-mentioned electrodeposition conditions, it is possible to apply a sufficient rust-proof treatment onto the fourth stage electrodeposited layer.

The final step of the surface-treatment of copper foil succeeding to the above-mentioned fifth stage electrodeposition step is steps of water-washing, sqeezing and drying. The final washing water is preferably deionized water, particularly water freed of chlorine ion.

For energy-saving at the drying step, an air knife 9 or squeeze rolls 5 are employed, followed by drying.

As for the drying process, it is preferable to employ hot air after purification. In particular when the copper foil is dried at a temperature of 60 -- 1200C for 30 seconds or longer, and thereby during this step, the electrodeposited layer of Zn-Sn as the fourth stage layer begins to diffuse and form an alloy to a certain extent, stabilized results are obtained at subsequent storage and steps. Numerals 10, 11 and 12 show a heater, a cooling fan and a take-up roll, respectively.

The practice of the present invention is not limited to the above-mentioned five stage layer treatment.

If the resulting product is a copper foil having multiple, additionally electrodeposited layers, obtained by electrodepositing an arsenic-containing copper layer directly onto the surface of a copper foil or onto the surface of a copper foil subjected to one stage or two or more stages copper layer electrodeposition treatments, and then electrodepositing onto the surface of the resulting copper foil, a plating layer consisting of zinc and tin or an alloy of at least one of zinc and tin with copper, and after naturally allowed to stand or heated, having at least an arsenic-containing copper layer intervened between copper layer and copper-based alloy, then the tightnesses between these various metal layers are retained and the object of the present invention is attained.

The present invention will be illustrated below by way of Examples.

Example 1 Employing a continuously surface-treating apparatus by which a copper foil having a width of 1.1 m and a nominal thickness of 1 ounce/sq ft (35 ) is supplied, treatments of the first stage to the fifth stage were sucessively carried out.

The treating conditions are as follows: Composition of the firststage bath CuS04 (in terms of Cu) 14 g/l (as Cu) H2SO4 65 gel Bath temperature 26 + 1 C The foil is passed through the bath and electrodeposited at an average current density on the cathodic surface, of 12 A/dm2 for about 13 seconds, and then sent to the second electrodeposition vessel.

Composition of the second stage bath CuSO4 (in terms of Cu) 50 g/l (as Cu) H2SO4 70 g/l Bath temperature 48 + 1 C The foil is passed through the electrodeposition vessel and electrodeposited at an average current density on the cathodic surface, of 15A/dm2for 17 seconds, and then via squeeze rolls, sent to the third stage electrodeposition vessel, where three conditions shown in Table I were employed.

Table 1 Experimental No. 1- A l-B i-C Cu concentration 8 gel 9 9.5 (in terms of Cu) H2SO4 (g/l) 33 g/l 44 48 As-containing solution 0.08 g/l 0.2 0.4 (in terms of As) Bath temperature ( C) 21 + 0.5 C 19 + 0.5 C 18 + 0.5 C Cathodic current density 5.5 5 4.5 (A/dm2) Passing time through 17 13 7 electrode (sec.) The copper foil having left the third stage electrodeposition vessel was sent to the fourth stage electrodeposition vessel, via light squeeze rolls, a shower water bath, a water-washing vessel and a shower water bath.

As comparative examples, the copper foils subjected to the 1 -A, B and C treatments were subjected directly to a chromate treatment, respectively, without entering the fourth stage electrodeposition vessel.

These comparative examples are named 1-A-(O), 1-B-(O) and 1-C-(O), respectively. The others were subjected to the fourth stage layer et se treatments under the same conditions.

The composition conditions of the fourth stage bath were as follows: ZnSO4 (in terms of Zn) 1.5 g/l (as Zn) SnSO4 (in terms of Sn) 0.6 g/l (as Sn) K4P207 34 g/l Bath temperature 46 C ~ 1 C pH measured bya pH meterwas 10.9.

Electrodeposition treatment was carried out at an average cathodic current density of 4.5 A/dm2 for 13 seconds. As a result, an electrodeposition amount (presumed to be 0.05 -0.15 Fm just after the coating) in which the presence of this layer was clearly visible was obtained. After this fourth stage treatment, the resulting foil was subjected to immersion in a water-washing vessel and shower water-washing and then rust-proof treatment on both the surfaces.

Composition of the fifth stage bath Anhydrous chromic acid 2.5 g/l Bath temperature 200C * 10C Fourth stage treated surface current 0 Luster surface Cathodic current density 0.03 Aldm2 The resulting foil was passed through squeeze rolls, and then introduced into a water-washing zone where it was water-washed with one stage service water, then sufficiently water-washed with deionized water on both the surfaces, and squeezed with rolls, and thereafter sent to a drying zone. The small amount of residual or moisture absorbed after squeezing was further blown off by hot air at 60 - 650C from an air knife.The resulting foil was passed through a drying zone with an infrared ray heater and force convection, at an ambient temperature of 100"C, for one minute and 20 second. After completely dried therein, it was air-cooled by a slow fan and then taken up on a coil.

Separately as a comparative example, a copper foil having ommited the third stage electrodeposition alone was prepared. This comparative example is named 1-(O).

The respective copper foils obtained according to an above-mentioned process were subjected to press adhesion at 1700C for one hour under a pressure of 17 kg/cm2, empolying a commercial impregnated glass cloth FR-4 grade for glass epoxy base to prepare copper clad laminates, which were then subjected to evaluation tests. The respective initial peel strengths, peel strengths after heating on solder bath at 260 C for 20 seconds, transfers at the time of measurement of initial peel strength, stain conditions after etching and changes in peel strength each two weeks during 56 days at 1 530C are shown in Table 2.

The Table shows that as for the performances generally required in the standards for usual copper clad laminates, even products having omitted the stages of the present invention can attain almost the same level as that of the above-mentioned performances, but as for the survival of peel strength after a long time heating, the products of the present invention are peerless.

Table 2 Evaluation table of foils of present invention of Example 1 and comparative samples Comparison of treatments Peel strength after a long time heat resistance at 153 C (kg/cm) Initial Stain Peel After After After After 1st 2nd 3rd 4th Rust- peel Transfer after strength 2 weeks 4 weeks 6 weeks 8 weeks stage stage stage stage Proof strength etching after (14 days) (28 days) (42 days) (56 days) (kg/cm) solder float at 260 C -20 seconds (kg/cm) 1 - (0) 0 0 # (1) 0 2.12 none none 2.14 1.34 0.43 < 0.1 -01 - A 0 0 (A) (1) 0 2.06 none none 2.00 1.16 0.80 0.71 0.57 1 - B 0 0 (B) (1) 0 2.14 none none 2.06 1.26 0.99 0.90 0.69 1 - C 0 0 (C) (1) 0 2.30 none none 2.10 1.12 0.83 0.69 0.51 nearly 1 - A - (O) 0 0 (A) / 0 2.21 none slight 2.28 1.10 0.32 < 0.1 -01 - B - (O) 0 0 (B) / 0 2.38 yes slight 2.34 1.26 0.35 < 0.1 -01 - C - (O) 0 0 (C) / 0 2.42 considerable slight 2.30 0.96 0.28 < 0.1 -0- Example 2 Atreated copper foil was obtained with the same samples and under the same conditions as in Example 1 except that the fourth stage electrodeposition conditions alone were varied to the following bath composition and electrodeposition conditions: The fourth stage bath composition was as follows: ZnSO4 (in terms of Zn) 1.0 gIl SnSO4 (in terms of Sn) 0.9gel K2P207 21 g/l The bath temperature was 420C and pH was adjusted to 11.2.Into this bath were introduced copper foils washed with water (shower and immersion in vessel) after the third stage, which were then subjected to a rust-proof Sn-Zn layer electrodeposition onto the treated surfaces and luster surfaces, at a current density (in average, on the cathodic surface) of 1.1 A/dm2/one side surface and for an electrode-passing time of about 3 seconds. The samples thus obtained were named 2-A, 2-B and 2-C, respectively, corresponding to the third stage treating conditions. Separately as a comparative example, an experiment having omitted the third stage electrodeposition treatment alone was carried out.

The resulting sample was named 2-(0).

The respective copper foils were laminated onto the same laminating base as in Example 1 and subjected to the same tests as in Example 1. The results are shown in Table 3.

As apparent from Table 3, the effectiveness of the present invention does not depend on the thickness of the fourth layer, but results from a synergistic effect of the arsenic-containing copper layer as the third layer and the plating layer as the fourth layer.

Table 3 Evalution table of foils of present invention of Example 2 and comparative sample Peel strength after a long time heat Comparison of treatments resistance at 153 C (Kg/cm) 1st 2nd 3rd 4th Rust- Initial Stain Peel After After After After stage stage stage stage Proof peel Transfer after strength 2 weeks 4 weeks 6 weeks 8 weeks strength etching after (14 days) (28 days) (42 days) (56 days) (Kg/cm) solder float at 260 C 20 seconds (Kg/cm) 2 - A 0 0 (A) (2) 0 2.03 none none 2.09 1.28 0.76 0.68 0.45 2 - B 0 0 (B) (2) 0 2.05 none none 2.06 1.31 0.72 0.65 0.51 2 - C 0 0 (C) (2) 0 2.07 none none 2.03 1.20 0.68 0.62 0.43 2 - (0) 0 0 / (2) 0 2.00 none none 1.95 1.10 0.28 < 0.1 -0- Example 3 An electrolyzed copper foil (thickness : 35 C, average width: 1.1 m) was unwound from a coil, passed over an electric contact roll for supplying electricity and subjected to electrodeposition, providing the cathode on the side of the roughened surface (not surface) and employing the following bath composition: CuSO4 (in terms of Cu) 9 g/l (as Cu) H2SO4 19 g/l Added solution containing arsenic (in terms of As) 0.3 g/l (as As) Bath temperature 18 C The foil was passed through the bath at a cathodic current density of 4.3 A/dm2 for 13 seconds. The resulting copper foil was passed through squeeze rolls, sufficiently washed with shower water to remove even a trace of As and then passed through a tin-zinc alloy electrodeposition vessel.

The electrodeposition bath for a plating layer as the fourth layer was as follows: ZnSO4 (in terms of Zn) 2.2 g/l (as Zn) SnSO4 (in terms of Sn) 0.9 g/l (as Sn) Bath temperature 45 f 2 C The foil was subjected to electrodeposition on both the surfaces at a cathodic current density of 1.3 A/dm2, for about 7 seconds. The resulting layer had a function as a rust-proof layer at the same time.

The foil was then washed with water in a water-washing vessel and a water shower to flow away superfluous Zn salt, etc. (electrodeposited metal tin does not dissolve away during the dissolving out of Zn), hydroextracted with an air knife, and then passed through a force convection drying zone (employing a usual infrared ray heater and at an atmospheric temperature of 110 C) for one minute and 30 seconds, followed by cooling with cold air and take-up on a coil. The resulting foil is named 3-A 3-B is a product obtained by adding 2.5 9/1 of anhydrous chromic acid to the water-washing vessel to overlap a chromate rust-proof function.Further, Comparative sample (3) is a product obtained by applying the arsenic-containing copper layer electrodeposition treatment alone, omitting the plating layer and soon immersed in a 1 % solution of benzotriazole which is famous as an anti-discoloring agent, for 15 seconds, followed by washing with water and drying.

Comparative sample (4) is a product obtained by applying the chromate rust-proof treatment employed in the case of the above-mentioned 3-B, in place of the triazole rust-inhibiting agent of the above-mentioned Comparative sample (3). Onto the copper foils thus obtained were applied commercial adhesives which were most suitable to each of them, made by M company and E company, followed by drying to obtain copper foils with adhesives, from which laminates were prepared with prepregs for FR-2 and FR-3. The resulting products were subjected to similar test to that of Example 1. The results are shown in Table 4.

As apparent from Table 4, even when the present invention is applied directly onto the surface of an untreated, electrolyzed copper foil, its effectiveness is fully exhibited.

Table 4 Evaluation results of foils of present invention of Example 3 and simplified type example and comparative samples comparison of treatements Kind of Transfer suitable Stain Initial Solder Peel Peel strenght after 1st 2nd 3rd 4th Rust- adhesive after peel Blester strenght a long time heat stage stage stage stage prof etching strenght (sec) after resistance at 153 C (Kg/cm) Solder float at 8 days 16 days 32 days 260 C 5 seconds Present 1.73/ 35 1.78 0.96 0.45 < 0.2 invention / / (D) (2) / E none none 1.76 / / / / / 3 - A > 60 1.73 1.10 0.75 0.35 Present 1.81 30 1.73 0.75 0.35 > 0.1 invention / / (D) (2) 0 E none none / / / / / / 3 - B 1.78 > 60 1.70 0.96 0.62 0.28 Comparative 1.78 35 1.73 0.28 - 0 - - 0 sample slight / / / / / (3) / / (D) / BTA M Considerable 1.81 > 60 1.70 0.45 0.35 Comparative 1.83 40 1.81 0.62 - 0 sample / / / / / - 0 (4) / / (D) / 0 E none a few 1.76 > 60 1.73 0.70 0.32

Claims (12)

1. A process for producing a treated copper foil, which process comprises electrodepositing an arsenic-containing copper layer onto the surface of a copper foil, and electrodepositing onto the said layer a layer of at least two of zinc, tin and copper.

2. A process as claimed in claim 1, and including the further step of treating the treated copper foil so as to cause the metals of the two said layers to diffuse into each other.

3. A process as claimed in claim 2, wherein the said diffusion-treatment comprises heating the copper foil to a temperature of at least 1 00'C.

4. A process as claimed in any one of claims 1 to 3, further comprising the step of treating the outermost layer with a chromate or aii organic anti-oxidising agent.

5. A process as claimed in any one of the preceding claims, wherein the treatment therein defined is carried out on both sides ol lhe foil.

6. A process as claimed in any one of claims 1 to 5, wherein the layer of at least two of zinc, tin and copper consists of at least 10% tin, the balance being zinc.

7. A process as claimed in any one of claims 1 to 6, including the step of pre-treating the foil before deposition of the arsenic-containing layer, so as to electrodeposit thereon a finely particulate copper layer, and a smooth copper layer over the finely particulate copper layer.

8. A process as claimed in claim 1 for producing a treated copper foil substantially as hereinbefore described in any one of the foregoing specific Examples.

9. A copper foil produced by a process as claimed in any one of the preceding claims.

10. A laminate comprising an insulating support having bonded thereto a foil as claimed in claim 9.

11. A process for producing a printed circuit comprising etching a laminate as claimed in claim 10.

12. A copper foil for printed circuits, consisting of a copper foil and multiple, additionally electrodeposited layers comprising an arsenic-containing copper layer electrodeposited onto at least one of the surfaces of said copper foil to be treated, and a plating layer consisting of zinc and tin or an alloy of at least one of zinc and tin with copper, electrodeposited directly onto said arsenic-containing copper layer, the metals which constitute the respective layers of said multiple, additionally electrodeposited layers having compositions in which the metals diffuse through each other.