PROCESS FOR PRODUCING COPPER-CLAD LAMINATE

Abstract: This new process consists of the following five steps. (1) pretreatment of a planar conductive base material, (2) formation by electrolysis on the planar conductive base material of a surface of copper foil at least several microns thick, (3) roughening this surface, (4) laminating the copper foil together with the conductive base material on an insulating base material and tightly integrating the assembly by application of pressure and heat, (5) peeling off the conductive base material. For the electrolysis of step (2) the negative electrode planar conductive base material is sepd. from the positive electrode planar copper foil by a distance of 3-30 mm., and the surface of copper foil is formed by high speed plating under a liquid contacting speed of 2.6-20.0 m/sec. and at a current density of 0.15-4.0 A/cm2. This liquid contacting speed can be obtd. by flowing the electrolysis soln. between the two electrodes or by rotating the negative electrode round the positive electrode. In step (3) the surface of the foil can be brought into contact with an acidic electrolysis soln. contg. copper ion and nitrate ion. Then the surface is chromium-treated. A highly pure metal film may be provided between the conductive base material and the copper foil. When the highly pure metal film has a thickness of 0.1-3.0 micron only the conductive base material is peeled off in step (5). When the thickness of the highly pure metal film is 70-250 micron it is peeledoff together with the conductive base material.

Description: Technical Field The present invention relates to a process for producing a copper-clad laminate adapted for the manufacture of a very thin copper-clad laminate with a thickness of 10 µm or less. Background Art As a conventional method of producing printed circuit boards, there is the so-called etching method in which a copper foil with a thickness of 18 µm to 35 µm or more is bonded to the surface of an insulating substrate, made of e.g. phenol or glass-epoxy resin, for lamination, the surface of the copper foil is masked with use of a resist, such as a photoresist, printing resist, etc., and undesired portions of the foil surface except conductor circuits are removed by etching. According to this etching method, however, the copper foil must have a thickness of 18 µm or more in order to stand a tensile force, bending force, etc., which are physically applied during processes after the production of the copper foil, including surface treatment, cutting, and lamination on the insulating substrate. In forming a so-called fine pattern having a conductor spacing of about 130 µm or less, therefore, an etchant acts on the lateral faces of conductors for so long a period of time that the lateral faces fail to be straight in shape, thus lowering the quality of products. In consequence, it is difficult for the etching method to cope satisfactorily with the recent tendency toward high-density versions of printed circuit boards. As means for settling these problems of the etching method, copper-clad laminates are conventionally known which are manufactured by the so-called transfer method. Examples of such copper-clad laminates are disclosed in Japanese Patent Publication No. 55-24141, Japanese Patent Publication No. 55-32239 (U.S. Pat. No. 4,053,370), Japanese Patent Publication No. 57-24080, Japanese Patent Publication No. 57-39318, Japanese Provisional Patent Publication No. 60-147192, etc. In a process (hereinafter referred to as belt transfer process) for producing copper-clad laminates disclosed in Japanese Patent Publication No. 55-24141, Japanese Patent Publication No. 55-32239 (U.S. Pat. No. 4,053,370), Japanese Patent publication No. 57-24080, and Japanese Patent Publication No. 57-39318, a copper-clad laminate is produced in the following manner. A thin, electrically conductive metal belt, which slides on the outer peripheral surface of a metallic rotating drum or a cathode portion of a horizontal plating apparatus is used as a cathode. The metal belt is transported while being kept at a predetermined distance from an insoluble anode. A plating solution is supplied compulsorily between the metal belt and the anode at high speed, thereby electrolytically forming a copper foil on the surface of the metal belt. After an insulating substrate, having a bonding agent previously applied thereto, is adhered to the copper foil, the insulating substrate and the copper foil are peeled from the metal belt. Thus, the copper-clad laminate is completed. Adapted for high-speed plating, the belt transfer process has the advantage that it permits very fast formation of the copper foil and continuous production of the copper-clad laminates. However, the belt transfer process is subject to the following drawbacks. During a peeling step in which the insulating substrate, having the copper foil transferred thereto, is peeled from the metal belt, part of the copper foil may not be able to be transferred to the insulating substrate, due to the difference between the strength of adhesion between the copper foil and the metal surface and that between the insulating substrate and the copper foil, and other causes. For the same reason, moreover, the copper foil may swing or be deformed during the transfer and peeling steps, thereby causing such defects as wrinkling, breakage, bruises, cracks etc. Using the metal belt as the electrically conductive substrate, moreover, the belt transfer process has a defect such that the metal belt, if having a substantial width, undulates as its travels, so that it is difficult to maintain a fixed distance between the metal belt and the anode. Therefore, the thickness of the copper foil, which is electrolyzed on the metal belt, varies according to location, thereby lowering the yield. Thus, the belt transfer process does not permit the use of a wide metal belt, and can be improved only limitedly in productivity. In the so-called reel-to-reel system disclosed in Japanese Patent Publication No. 57-24080, for example, a metal belt of stainless steel on a reel is wound therefrom by means of another reel. With this arrangement, the surface of the stainless-steel plate is liable to suffer flaws, soiling, or other damages. If work is suspended to remove soil or flaws on the plate, the formation of the copper foil, in its turn, is spoiled. Thus, according to the reel-to-reel system, the work (line) cannot readily be suspended even when the stainless steel surface suffers soiling, flaws, or other damages. This results in an increase in fraction defective, reduction in working efficiency, etc. If stainless steel is used for the metal belt, moreover, inevitable physical or electrochemical defects, such as pores, exist on the surface of the metal belt. According to the belt transfer process, the copper foil is electrolytically precipitated in a direct manner on the surface of the metal belt with such defects, and is therefore liable to suffer pinholes. Such a situation is particularly important to high-density conductor circuit boards with a copper circuit width of 100 µm or less and a circuit interval of 100 µm or less. A method (hereinafter referred to as conventional transfer method) of producing conductor circuit boards disclosed in Japanese Provisional Patent Publication No. 60-147192, mentioned before, comprises a step (Fig. 19(a)) of forming a thin metal layer on a metal substrate, a step (Fig. 19(b)) of roughening the surface of the thin metal layer, a step (Fig. 19(d)) of forming the copper foil by plating the surface of the thin metal layer, a step (Fig. 19(e)) of peeling the thin metal layer and the copper foil together from the substrate and transferring them to an insulating substrate, and a step (Fig. 19(f)) of removing the transferred thin metal layer by etching. This conventional transfer method has the advantage over the aforementioned belt transfer process in that the copper foil can be transferred easily and securely in the following manner. A thin metal layer of about 1 to 10 µm is previously formed on the metal substrate, and the resulting structure, along with the copper foil, is transferred to the insulating substrate. The surface of the thin metal layer is roughened by chemical etching, using a mixed solution of cupric chloride and hydrochloric acid. By doing this, good adhesion of the copper foil plating film to the thin metal layer can be maintained. However, the conventional transfer method indispensably requires the step of roughening the surface of the thin metal layer after forming the thin metal layer on the substrate in the aforesaid manner. This roughening process takes much time, thus exerting a bad influence on the improvement of productivity, and constituting a hindrance to the simplification of manufacturing processes. In an alternative prior art process for producing a copper-clad laminate, copper is deposited, by electroplating, to the surface of a carrier made of an aluminum foil 40 to 60 µm thick, thus forming a copper foil with a thickness of 5 to 10 µm. Then, an insulating substrate is bonded to the surface of the copper foil for lamination, and the carrier is removed chemically by means of an acid or alkali, or is separated mechanically. In another prior art process, a copper ingot, for example, is rolled into a copper foil with a thickness of about 3 µm by means of a multistage rolling mill, and the copper foil is pressure-bonded to an insulating substrate. In the former process, however, a complicated step is required for the removal of the aluminum-foil carrier, and the aluminum foil cannot be reused. Thus, the efficiency of production is low, and the material cost is high. In the latter process, on the other hand, the rolling method for the manufacture of the copper foil is used in place of the plating method in the aforementioned belt transfer process. Like the plating method, in this case, the rolling method causes wrinkling, cracks, dents, deformation, or other defects in the copper foil. Meanwhile, in order to improve the adhesion between the copper foil and the insulating substrate, the surfaces of the copper foil must have a predetermined roughness. Disclosure of the invention The object of the present invention is to provide a process for producing a copper-clad laminate with a very thin copper foil thereon, which is high in productivity and permits minimized equipment and installation space therefor, and which is adapted for the manufacture of a printed circuit board with a high-density circuit pattern. In order to achieve the above object, the inventors hereof conducted various researches, and obtained the following findings. The so-called high-speed plating method is needed to attain high productivity with use of minor production equipment and a narrow installation space. Electrolytic plating conditions for the high-speed plating method were able to be determined which provide a plated surface of a required roughness without requiring a special surface-roughening process. A copper foil can be transferred easily and securely to an insulating substrate after it is formed on the surface of a conductive substrate by the so-called single-plate pressing. More specifically, in a process for producing a copper-clad laminate according to the present invention, a planar, electrically conductive substrate, for use as a cathode, and a planar anode are spaced at an interelectrode distance of 3 to 30 mm from each other. An electrolytic solution is supplied to these electrodes so that the electrolytic solution comes into contact with the electrodes at a solution contact speed of 2.6 to 20.0 m/sec, thereby electroplating the electrodes under the condition of a current density of 0.15 to 4.0 A/cm². Thus, a copper foil with a thickness of 10 µm or less is formed on the surface of the conductive substrate. After the surface of the copper foil is roughened, an insulating substrate and the conductive substrate are laminated and pressure-bonded together, with thus formed copper foil therebetween, with use of heat. Thereafter, the copper foil and the insulating substrate are peeled together from the conductive substrate. Preferably, in the aforementioned steps of production, a high-purity metal film with a thickness of 0,1 to 3 µm is formed on the surface of the conductive substrate in advance of the formation of the copper foil, and it is peeled off together with the copper foil. Preferably, in the aforementioned steps of production, furthermore, a high-purity metal film with a thickness of 70 to 250 µm is formed on the surface of the conductive substrate in advance of the formation of the copper foil, and it is peeled off with the high-purity metal film left on the surface of the conductive substrate. The following three points are effects which can be claimed for the use of the above described high-purity metal film between the single-plate conductive substrate and the copper foil. (1) The conductive-substrate single plate, with the interposition of the high-purity metal film, is superposed on the insulating substrate, and the resulting structure is pressurized and heated for a predetermined period of time by means of a press. After the structure solidifies as a laminate, the single plate and the high-purity metal film can be separated from each other with a peeling strength of 70 to 120 g/cm. Thus, transfer lamination can be accomplished easily without entailing change of dimensions or defective appearance. (2) Even after the surface of the single-plate conductive substrate (e.g., stainless steel) is fully polished chemically and physically, ingredients in the substrate may slip off due to nonmetallic inclusions in the substrate or electrochemical defects thereof, or intermetallic compounds, segregations, pores, etc., may remain on the substrate surface. These defects cannot be fully offset in an economical manner. The high-purity metal film of the present invention can offset these defects of the substrate, so that pinholes cannot be produced. Thus, a circuit substrate having a fine pattern with a width of 100 µm or less can be manufactured easily and at low cost. (3) After the high-purity metal film and the copper foil are formed on the single-plate conductive substrate, the resulting structure is transferred to the insulating substrate for lamination in a step of pressure bonding with heat. In doing this, a B-stage bonding agent of resin applied to or impregnated into the insulating substrate melts and is urged to flow out to the peripheral surface of the single-plate conductive substrate during the processes of its gelling and solidification. Since the high-purity metal film is extended to the peripheral portion of the single-plate conductive substrate so as to cover its surface, however, the overflown solidified resin remains on the high-purity metal film. In the steps of transfer lamination and separation, therefore, the resin can be easily separated from the boundary (interface) between the single-plate conductive substrate and the high-purity metal film. Thus, the resin can never adhere or stick to the single-plate conductive substrate. Brief Description of the Drawings Fig. 1 is a process flow chart for illustrating manufacturing steps of a process for producing a copper-clad laminate according to the present invention; Fig. 2 is a process flow chart for illustrating alternative preferred manufacturing steps of the process for producing a copper-clad laminate according to the present invention; Fig. 3 is a process flow chart for illustrating further alternative preferred manufacturing steps of the process for producing a copper-clad laminate according to the present invention; Fig. 4 is a sectional view of the copper-clad laminate in a step (S2) of copper electroforming shown in Fig. 1; Fig. 5 is a sectional view of the copper-clad laminate in a step (S4) of transfer lamination shown in Fig. 1; Fig. 6 is a sectional view of the copper-clad laminate in a step (S5, S26) of peeling off an electrically conductive substrate shown in Figs. 1 and 3; Fig. 7 is a sectional view of the copper-clad laminate in a step (S12, S22) of forming a high-purity metal film shown in Figs. 2 and 3; Fig. 8 is a sectional view of the copper-clad laminate in a step (S13, S23) of copper electroforming shown in Figs. 2 and 3; Fig. 9 is a sectional view of the copper-clad laminate in a step (S15, S25) of transfer lamination shown in Figs. 2 and 3; Fig. 10 is a sectional view of the copper-clad laminate in a step (S17) of peeling off an electrically conductive substrate shown in Fig. 2; Fig. 11 is a front sectional view showing an arrangement of a high-speed plating apparatus of a horizontal type; Fig. 12 is a side view of the high-speed plating apparatus of Fig. 11; Fig. 13 is a sectional view taken along line XIII-XIII of Fig. 12; Fig. 14 is a sectional view taken along line XIV-XIV of Fig. 13; Fig. 15 is a front sectional view showing an arrangement of a high-speed plating apparatus of a vertical type; Fig. 16 is a cutaway front view showing an arrangement of a high-speed plating apparatus of a rotary type; Fig. 17 is a top view of a housing shown in Fig. 16; Fig. 18 is a bottom view of the housing shown in Fig. 16; and Fig. 19 is a process flow chart for illustrating manufacturing steps of a prior art process for producing a copper-clad laminate. Best Mode of Carrying Out the invention Referring now to Figs. 1 to 10, steps of manufacturing a copper-clad laminate according to the present invention will be described. An electrically conductive substrate 2 used to effect the process of the invention is formed from a rigid single plate, e.g., a planar conductive material of a suitable size, having the maximum effective dimensions of 1,220 by 1,020 mm and a thickness ranging from 1 to 10 mm. Preferably, the material of the conductive substrate 2 is resistant to electrolytic corrosion and chemicals used in a plating step. Examples of such a material include a stainless-steel plate (e.g., hardened SUS-630 as one of the best examples), nickel plate, titanium or titanium-alloy plate, copper or copper-alloy plate, etc. Dirt and oxide film on the surface of conductive substrate 2 are removed, and the surface is pretreated for a necessary roughness (Step S1 of Fig. 1). Preferably, the surface of the conductive substrate 2 is ground within a roughness range of 0.08 to 0.23 µm. The surface roughness of the conductive substrate 2 is set so as to provide an adhesion such that a copper foil 6 can be peeled off easily in a step (Step S5 of Fig. 1) of peeling the copper foil 6 and conductive substrate 2 from each other, as mentioned later. Thus, the adhesion force at the interface between the conductive substrate 2 and the copper foil 6 is smaller than that at the interface between the copper foil 6 and an insulating substrate 10, as mentioned later. When using a stainless-steel plate as the conductive substrate 2, the conductive substrate 2 is immersed, for example, in a 80 to 100 ml/l sulfuric acid solution at 60 to 70 °C, for 10 to 30 minutes, to be descaled. Then, after rinsing, the substrate 2 is immersed, for removal of smut, in a room-temperature solution of 60 to 100 ml/l nitric acid of mixed with acidic solution of 30 g/l ammonium bifluoride, for 10 to 30 minutes. Subsequently, after rinsing, the substrate 2 is subjected to 1 to 2 minutes of cathode-electrolytic degreasing in an electrolytic solution of 20 to 50 g/l sodium phosphate and 50 g/l sodium hydroxide, under the electrolytic conditions of an electrolytic-solution temperature ranging from room temperature to 40 °C and a current value of 3 to 8 A/dm². Although the surface of the conductive substrate 2 is roughened chemically in the aforesaid roughening step, it may alternatively be roughened mechanically by wet sand blasting (liquid honing) or the like, after it is cleaned chemically. When using a nickel plate as the conductive substrate 2, the substrate 2 is subjected to 1 to 2 minutes of cathode-electrolytic degreasing in an electrolytic solution of 20 to 50 g/l sodium phosphate mixed with 50 g/l sodium hydroxide, under the electrolytic conditions of an electrolytic-solution temperature ranging from room temperature to 40 °C and a current value of 3 to 8 A/dm², for example. Then, after rinsing, the substrate 2 is immersed, for surface roughening, in a 1 to 10 g/l hydrogen fluoride solution of 50 °C or a 150 ml/l hydrochloric acid solution of 50 °C, for 1 to 10 minutes. Subsequently, after rinsing, the substrate 2 is washed in warm water at 40 to 60 °C. When using a titanium or titanium-alloy plate as the conductive substrate 2, the substrate 2 is immersed, for alkaline degreasing, in a 20 to 50 g/l sodium phosphate solution of 50 to 60 °C, for 3 to 5 minutes, for example. Then, after rinsing, the substrate 2 is immersed in a 25 % hydrofluoric acid (HF) solution and a 75 % nitric acid (HNO₃) solution to be etched chemically for surface roughening. When using a copper or copper-alloy plate as the conductive substrate 2, the substrate 2 is subjected to 30 seconds to 2 minutes of cathode-electrolytic degreasing in an electrolytic solution of 20 to 50 g/l sodium phosphate, under the electrolytic conditions of an electrolytic-solution temperature of 50 to 60 °C and a current value of 3 to 10 A/dm², for example. Then, after rinsing, the substrate 2 is washed in a 1 to 10 g/l hydrogen fluoride of a temperature lower than room temperature, for 30 seconds to 2 minutes, and then in water. Subsequently, the pre-treated conductive substrate 2, for use as a cathode 1, is opposed to an anode 14 at a predetermined distance (3 to 30 mm) therefrom, and the copper foil 6 is precipitated electrolytically (Step S2 of Fig. 1; Fig. 4) on the conductive substrate 2 by the so-called high-speed plating. The electrolytic solution used for the high-speed plating may be a copper sulfate plating solution whose metallic copper content ranges from 0.20 to 2.0 mol/l, preferably, from 0.35 to 0.98 mol/l, and whose sulfuric acid content ranges from 50 to 220 g/l. To ensure the uniformity of plating, CUPPORAPID Hs (trade name) produced by LPW Co., Ltd., West Germany, is added to the copper sulfate solution at the rate of 1.5 ml/l. Alternatively, an ordinary plating solution, such as a copper pyrophosphate solution, may be used. Also, the current density, solution contact speed with respect to the electrodes, and electrolytic solution temperature are set to 0.15 to 4 A/cm², 2.6 to 20 m/sec, and 45 to 70 °C, preferably 60 to 65 °C, respectively. If the plating solution temperature is lower than 45 °C, the moving speed of copper ions is lowered, so that polarized layers are liable to be formed on the surfaces of the electrodes. Thus, the plating deposition speed is lowered. If the solution temperature exceeds 70 °C, on the other hand, the evaporation loss of a plating solution increases, so that the concentration of the solution becomes unstable. Also, the increase of the solution temperature puts restrictions on equipment. By adjusting the current density and the solution contact speed with respect to the electrodes to the aforementioned predetermined conditions, the copper foil 6 is deposited on the surface of the conductive substrate 2 at a deposition speed of 25 to 100 µm per minute. Thus, copper-electroforming can be performed at an efficiency 20 to 200 times as high as that of the conventional plating method, ensuring very deep practical significance. Moreover, deposited copper particles can be made very fine, so that the copper foil 6 can enjoy an elongation percentage of 16 to 25 % without losing its tensile strength. This elongation percentage is 1.5 to 2 times the elongation percentage of a copper foil formed by the conventional plating method (or equal to or higher than that of a rolled annealed copper foil), so that a very soft copper foil can be produced. Thus having a property equivalent to that of a rolled annealed copper foil, the produced copper foil can be used particularly effectively for a flexible substrate which requires high bending capability. Moreover, the surface grains of the produced copper foil 6 can be reduced in average grain size to a very fine level of 3.0 to 7.5 µm. Accordingly, protuberant precipitates formed in the subsequent roughening (electroplating) step can also be made very fine. When the thickness of the copper foil 6 reaches a predetermined thickness (e.g., 2 µm to <10 µm), in the copper electroforming step, the electric supply and the supply of the plating solution are stopped. After rinsing, the copper foil 6 is subjected to electroplating for continued roughening (Step S3 of Fig. 1). The electroplating conditions for this electroplating step for roughening includes a current density of 0.25 to 0.85 A/cm², interelectrode distance of 26 to 50 mm, and electrolytic solution-electrode contact speed of 0.1 to 0.8 m/sec. The electrolytic solution used, which is not specified in particular, may be a mixed solution of 80 to 150 g/l copper sulfate (CuSO₄·5H₂O), 40 to 80 g/l sulfuric acid (H₂SO₄), and 25 to 50 g/l potassium nitrate, for example. By this roughening process, the protuberant precipitates are adhered to the rough surface of the copper foil 6. The average particle size of the protuberant precipitates ranges from 1 to 5 µm, and the adhesion to an insulating substrate 10 mentioned later is improved greatly. After the roughening process described above, if the surface of the copper foil 6 is further chromate-treated, the affinity between copper and resin in the insulating substrate 10 increases. Further, the peeling strength naturally increases, and the heat resistance (e.g., soldering heat resistance) of the copper foil 6 also increases by 15 % or thereabout. More specifically, in this chromate treatment, the copper foil 6 is immersed in a 0.7 to 12 g/l potassium bichromate solution at normal temperature for 5 to 45 seconds, or treated with a commercially available electrolytic chromating solution. Subsequently, the conductive substrate 2, which is formed with the copper foil 6 in the aforesaid manner, is stacked on the insulating substrate 10 with the interposition of the copper foil 6, and is pressure-bonded thereto with heat (Step S4 of Fig. 1; Fig. 5) by means of a hot press. Both organic and inorganic materials, such as glass, epoxy resin, phenol resin, polyimide resin, polyester resin, aramid resin, etc, may be used for the insulating substrate 10. Also available are materials which are obtained by enameling the surface of a conductive material, such as iron or aluminum, or by oxidizing the surface of aluminum for alumilite treatment, for insulation. In general, the copper foil 6 is heated and pressurized, and is bonded to a prepreg in a semihardened state (B-stage) which is obtained by impregnating glass cloth or the like with epoxy resin. At this time, the copper foil 6 is adhered and transferred integrally and directly to the insulating substrate 10. Despite its low physical strength, therefore, the copper foil 6 will never be subject to defects in quality, such as wrinkling, cracks, etc. Then, after the insulating substrate 10 is heated and solidified, the conductive substrate 2 is peeled (Step S5 of Fig. 1; Fig. 6) from the copper foil 6, which is transferred to the insulating substrate 10. At this time, the force of adhesion between the copper foil 6 and the insulating substrate 10 is greater than that between the conductive substrate 2 and the copper foil 6, so that the conductive substrate 2 is separated from the copper foil 6 at the interface between them, and the copper foil 6 is adhered integrally to the insulating substrate 10. After the end of the steps described above, the surface of the conductive substrate 2, for use as the cathode, is polished and activated. Thereafter, the conductive substrate 2 can be repeatedly subjected to the above described steps. Among steps of production according to another embodiment of the present invention, a step of forming a high-purity metal film 5 on the surface of the planar conductive substrate 2 is added after the end of a pretreatment (Step S11 of Fig. 2) of the conductive substrate 2. Also in this case, the conductive substrate 2, for use as the cathode 1, is opposed to the anode 14 at a predetermined distance (6 to 30 mm) therefrom, and the high-purity metal film 5 is electrolytically precipitated (Step S12 of Fig. 2; Fig. 7) on the conductive substrate 2 by high-speed plating, in the same manner as aforesaid. Copper or nickel may be suitably used as a material for the high-purity metal film 5, which is deposited to a thickness of 0.1 to 3 µm on the surface of the conductive substrate 2. Precipitation of copper as the high-purity metal film 5 requires high-speed plating conditions such that the cathode is rotated, or the electrolytic solution is supplied compulsorily between fixed electrodes, so that a plating solution of 45 to 70 °C causes a turbulent flow on the surface of the cathode, that is, an interelectrode distance of 3 to 30 mm and an electrode-solution contact speed of 2.6 to 20.0 m/sec are obtained. Preferably, in this case, a copper sulfate plating solution or copper pyrophosphate solution, for example, is used as the plating solution, a current of cathode-current density of 0.15 to 4.0 A/cm² is applied, and the deposition speed of the high-purity metal film 5 is set to 25 to 100 µm/min. Precipitation of nickel as the high-purity metal film 5 requires high-speed plating conditions such that the the cathode and the anode are spaced at a distance of 300 to 350 mm from each other, and an electrolytic solution of 40 to 48 °C is supplied between these electrodes for air stirring. Preferably, in this case, nickel sulfate or nickel sulfamate, for example, is used for the plating solution, a current of cathode-current density of 2.2 to 4.0 A/cm² is applied, and the deposition speed of the high-purity metal film 5 is set to 0.8 to 1.5 µm/min. Also, a nickel-phosphorus alloy may be used for the high-purity metal film 5. Preferably, in this case, electroless nickel plating is performed under the condition that a plating solution of 35 to 10 °C is oscillated so that the solution contact speed at the surface of the conductive substrate 2 ranges from 40 to 80 mm/sec. Preferably, in this case, an electroless nickel solution, containing hypophosphorous acid or boron-based reducing agent, or the like is used as the plating solution, and the deposition speed of the high-purity metal film 5 is set to 1 to 3 µm per 30 minutes. After high-speed plating, the high-purity metal film 5 is laminated electrolytically on the conductive substrate 2 which has the required surface roughness as aforesaid. Therefore, the high-purity metal film 5 is adhered to the conductive substrate 2 with a proper force. Further, its surface roughness is within a suitable range for obtaining a desired adhesion force between the copper foil 6 and the high-purity metal film 5 mentioned later, by high-speed plating under the aforementioned plating conditions. In other words, according to this embodiment, the surface roughness of the high-purity metal film 5 can be controlled suitably by combining the individual conditions including the surface roughness of the conductive substrate 2, the solution contact speed of the plating solution, and the electrolytic current density. Thus, according to this embodiment, the surface of the high-purity metal film 5, laminated by the high-speed plating, does not require any special surface treatment after the plating. Moreover, the conductive substrate 2 made of a stainless-steel or nickel plate is subject to electrochemical defects. These defects include intermetallic compounds, nonmetallic inclusions, segregations, pores, etc. These defects are produced during the manufacture of the stainless-steel plate by fusion, rolling, etc., and cannot be removed by only treating the surface of the conductive substrate 2. Such defects would cause pinholes in the copper foil 6. The surface of the high-purity metal film 5, which is formed on the surface of the conductive substrate 2, is electrochemically smooth, and the production of cracks, wrinkles, or pinholes in the copper foil 6, which is low in mechanical strength, can be prevented by forming the copper foil 6 on the high-purity metal film 5, as mentioned later. Subsequently, the copper foil 6 is formed (Step S13 of Fig. 2; Fig. 8) on the high-purity metal film 5 in the same manner as in the above described step of the present invention, and the surface of the copper foil 6 is roughened (Step S14 of Fig. 2). Thereafter, the conductive substrate 2, formed with the copper foil 6 with the interposition of the high-purity metal film 5, is put on the insulating substrate 10 for lamination, and is pressure-bonded thereto with heat (Step S15 of Fig. 2; Fig. 9) by means of a hot press. The aforementioned materials may be used for the insulating substrate 10. After the copper foil 6 and the insulating substrate 10 are firmly adhered to each other, only the conductive substrate 2 is removed by peeling (Step S16 of Fig. 2; Fig. 10). In this step, the force of adhesion between the conductive substrate 2 and the high-purity metal film 5 is smaller than those between the high-purity metal film 5 and the copper foil 6 and between the copper foil 6 and the insulating substrate 10. As shown in Fig. 10, therefore, the high-purity metal film 5 and the copper foil 6 are transferred in a body to the insulating substrate 10. In the transfer step described above, if the high-purity metal film 5 and the copper foil 6 are made of the same metal, i.e., copper, the high-purity metal film 5 need not be removed after the transfer, and it is necessary only that the total thickness of the two layers be adjusted to a desired thickness in advance. If the high-purity metal film 5 is made of nickel or some other metal different from the material of the copper foil 6, it must be removed (Step S17 of Fig. 2; Fig. 6) by etching using an acid, for example, after the transfer. Also after the end of these steps of production, the surface of the conductive substrate 2 is polished and activated. By doing this, the coductive substrate 2 can be repeatedly subjected to the steps. Among steps of production according to still another embodiment of the present invention, the steps including the pretreatment of the planar conductive substrate (Step S21 of Fig. 3), formation of the high-purity metal film (Step S22 of Fig. 3; Fig. 7), copper electroforming (Step S23 of Fig. 3; Fig. 8), copper foil surface roughening (Step S24 of Fig. 3), and transfer lamination (Step S25 of Fig. 3; Fig. 9) are the same as the aforementioned steps of production according to the second embodiment. In this third embodiment, however, the thickness of the high-purity metal film is set to 70 to 250 µm. In this embodiment, moreover, the high-purity metal film is peeled of together with the conductive substrate after the transfer lamination, as mentioned later. Therefore, the surface roughness of the high-purity metal film 5 must be set so that the force of adhesion between the high-purity metal film 5 and the copper foil 6 is smaller than those between the high-purity metal film 5 and the conductive substrate 2 and between the copper foil 6 and the insulating substrate 10. The surface treatment of the high-purity metal film 5 to attain this is not limited to any special method. For example, a chromate coating film may be formed on the surface of the high-purity metal film 5 by treating the surface of the metal film 5 with a chromate in the aforementioned manner. The chromate coating film serves as, so to speak, a peeling film, which facilitates separation between the high-purity metal film 5 and the copper foil 6. After the end of the step of transfer lamination shown in Fig. 9, the conductive substrate 2 and the high-purity metal film 5 are peeled together from the copper foil 6 and the insulating substrate 10, and only the copper foil 6 is left adhering to the insulating substrate 10. After the separation of the copper foil 6, the high-purity metal film 5 remains on the surface of the insulating substrate 10, and the surface of the high-purity metal film 5 is polished as required. Thereafter, the copper foil 6 is formed again on the metal film 5, and can be repeatedly subjected to the aforesaid steps. Alternatively, after the high-purity metal film 5 removed once, the surface of the insulating substrate 10 is polished, and the high-purity metal film 5 and the copper foil 6 are formed successively on the insulating substrate 10. Thus, the aforesaid steps can be repeated. Figs. 11 to 14 show an example of a horizontal plating apparatus for effecting high-speed plating in Step S2 of Fig. 1. The planar insoluble anode 14 is set horizontally in the center of the top portion of the frame 12 of the plating apparatus 11, and the cathode 1 is fixed facing the anode 14 so as to extend parallel thereto. As shown in Figs. 11 to 13, the insoluble anode 14 includes two copper plates 14a and 14b joined together in order to permit a large current flow. A lead coating 14c is deposited uniformly to a thickness within a range of 2 to 10 mm, preferably 3 to 7 mm, over the whole surfaces of the copper plates 14a and 14b, by means of an acetylene torch or the like. Usually, a lead alloy containing 93 % lead and 7 % tin is used for the lead coating 14c. If the interelectrode distance is subject to an irregularity of 100 µm, an electroformed copper film of 35-µm thickness is subject to a variation of several microns. When using the copper film with a high-current density (0.8 to 1.2 A/cm²) for a long period of time (1,000 hours or more), the variation of the film thickness increases due to partial electrolytic dissipation of the electrode. Therefore, the interelectrode distance must be maintained by reprocessing the electrode. Instead of using the electrode coated with lead, the insoluble anode 14 may be formed by applying a pasty mixture of thermopolymerizable resin and impalpable powder of platinum or palladium to the surface of a titanium plate with a roughened surface, and then baking the coated plate at 700 to 800 °C. With use of such a titanium-plate anode, electrolytic dissipation is reduced considerably, and the electrode need not be reprocessed even after prolonged use (for 1,000 hours or more). The cathode 1 is fixedly mounted so that the polished surface of the conductive substrate 2 faces the anode 14 in the step of forming the high-purity metal film, or Step S12 of Fig.2 or Step S22 of Fig. 3, and that the surface of the conductive substrate 2 formed with the high-purity metal film 5 faces the anode 14 in the step of electroforming the copper foil or Step S2 of Fig. 1. The distance between the cathode 1 and the insoluble anode 14 is adjusted to values best suited for the step of forming the high-purity metal film 5 and the step of electroforming the copper foil 6, individually. One end of a nozzle 15, which serves to feed the plating solution 23 at high speed, is connected to the inlet side of a cavity portion 13 between the cathode 1 and the insoluble anode 14. At the inlet portion of the cavity portion 13, the nozzle 15 opens so as to cover the substantially overall width of the insoluble anode 14, as shown in Fig. 12. The other end of the nozzle 15 is connected to a pump 17 by means of a duct 16. Further, the pump 17 is connected to a plating solution tank (not shown) by means of another duct (not shown). On the outlet side of the cavity portion 13 (on the opposite side of the insoluble anode 14 to the location of the nozzle 15), an exhaust port 18 opens so as to cover the substantially overall width of the insoluble anode 14. The exhaust port 18 is connected to the plating solution tank by means of a duct 19. The cross-sectional shapes of the nozzle 15 and the exhaust port 18, with respect to the direction of the solution flow, vary smoothly so that the plating solution 23 can flow with a uniform speed distribution, in the cavity portion 13. The plating solution 23 discharged from the pump 17 is returned to the plating solution tank successively through the duct 16, the nozzle 15, the cavity portion 13 between the cathode 1 and the insoluble anode 14, the exhaust port 18, and the duct 19. Thereafter, the plating solution 23 is circulated continuously through the aforesaid route by the pump 17 again. When the plating solution 23 is fed from the nozzle 15 to the interelectrode cavity portion 13 at the aforementioned suitable plating speed, the flow of the plating solution is disturbed in the vicinity of the surface of the cathode 1. Thus, the plating film can be developed at high speed by suppressing the growth of a polarized layer in order to prevent the metallic-ion concentration in the vicinity of the surface of the electrode from lowering extremely. In the plating step according to the present invention, the aforesaid required high current is fed between the cathode 1 and the insoluble anode 14 through the medium of a feeder plate 20 having high electrical conductivity and chemical resistance to copper, graphite, lead, etc., an anode power supply cable 21, and a cathode power supply cable 22. Thus, the copper film can be electrolytically precipitated, at a deposition speed of about 25 to 100 µm per minute, on that surface of the cathode 1 facing the insoluble anode 14. Fig. 15 shows a vertical plating apparatus for effecting the process of the present invention. Whereas the cathode 1 and the anode 14 in the plating apparatus 11 shown in Figs. 11 to 14 are arranged horizontally, the plating apparatus 25 shown in Fig. 15 differs from the apparatus 11 in that its cathode 1 and insoluble anode 14 are arranged vertically. In Fig. 18, like reference numerals are used to designate like portions having substantially the same functions as their counterparts in the plating apparatus 11 shown in Figs. 11 to 14. A detailed description of those portions is omitted herein (and the same will apply hereinafter). The plating apparatus 25 comprises a stand 27 fixed on a baseplate 26, posts 30 and 31 (only two posts are shown in Fig. 15) arranged at the four corners of a quadrilateral, a top plate 28 horizontally supported by telescopic rods 30a and 31a, and a highly conductive feeder plate 20 and the insoluble anode 14 fixed between the top surface of the stand 27 and the undersurface of the top plate 28 so as to face each other, extending vertically and parallel to each other. The rods 30a and 31a can be extended or contracted vertically, and the top plate 28 moves up or down as the rods 30a and 31a extend or contract. The feeder plate 20 and the anode 14 are spaced at a predetermined interelectrode distance. Like the anode shown in Figs. 9 to 11, the insoluble anode 14 is formed of a titanium plate coated with impalpable powder of platinum or the like, which permits a large current flow. The cathode 1 is fixedly mounted by means of a vacuum chuck (not shown) or the like so that the polished surface of the conductive substrate 2, polished in Step S11 of Fig. 2, faces the feeder plate 20 in the step of forming the high-purity metal film shown in Step S12 of Fig. 2, and that the surface of the conductive substrate 2 formed with the high-purity metal film 5 faces the feeder plate 20 in the step of electroforming the copper foil shown in Step S2 of Fig. 1. In mounting the cathode 1, the top plate 28 is moved up, and the cathode 1 is inserted along that surface of the feeder plate 20 on the side of the anode 14, and is fixed by means of the vacuum chuck or the like. Thereafter, the top plate 28 is lowered again to be adhered to the respective top walls of the anode 14 and the feeder plate 20. Thus, the mounting of the cathode 1 is completed. In Fig. 15, numeral 29 denotes an O-ring for sealing. The distance between the cathode 1 and the insoluble anode 14 is adjusted to values best suited for the step of forming the thin metal layer 5 and the step of electroforming the conductor circuits 6, individually. A ramp portion 38a, into which the plating solution 23 is flows at high speed, is formed on the inlet side of a cavity portion 38 between the cathode 1 and the insoluble anode 14. At the inlet portion of the cavity portion 38, the ramp portion 38a opens so as to cover the substantially overall width of the insoluble anode 14, in the same manner as shown in Fig. 14. The opposite side of the ramp portion 38a to the cavity portion 38 is connected to a pump 17 by means of a rectifying unit 35 and a duct 34. Further, the pump 17 is connected to a plating solution tank 33. On the outlet side of the cavity portion 38 (on that side of the cavity portion 38 at the upper portion thereof for the discharge of the plating solution 23), an exhaust port 38b opens so as to cover the substantially overall width of the insoluble anode 14. The exhaust port 18 is connected to the plating solution tank 33 by means of a duct 40. The internal space of the rectifying unit 35 is divided into by means of two rectifying plates 35a and 35b which, each having a number of perforations, are arranged in the flowing direction of the plating solution 23. The rectifying plates 35a and 35b serve to rectify the flow of the plating solution 23 flowing into the ramp portion 38a, thereby equalizing the speed distribution of the plating solution 23 flowing upward through the cavity portion 38. The plating solution 23 discharged from the pump 17 is returned to the plating solution tank 33 successively through the duct 34, the rectifying unit 35, the ramp portion 38a, the cavity portion 38 between the cathode 1 and the insoluble anode 14, the exhaust port 38b, and the duct 40. Thereafter, the plating solution 13 is circulated continuously through the aforesaid route by the pump 17 again. The plating apparatus 25 shown in Fig. 15 feeds the plating solution 23 further upward to the interelectrode cavity portion 13 through the rectifying unit 35. Therefore, the plating solution 23 in the cavity portion 13 has a turbulence speed distribution more uniform than that of the plating apparatus 11 shown in Fig. 11. Such a situation is well suited for the electroforming of copper foil of a uniform thickness. Also in the plating apparatus shown in Fig. 15, the aforesaid required high current is fed between the cathode 1 and the insoluble anode 14 through the medium of a feeder plate 20 having high electrical conductivity and chemical resistance to copper, graphite, lead, etc., an anode power supply cable 21, and a cathode power supply cable 22. Thus, the copper film can be electrolytically precipitated, at a deposition speed of about 25 to 100 µm per minute, on that surface of the cathode 1 facing the insoluble anode 14. Figs. 16 to 18 show a rotary high-speed plating apparatus 41 for effecting the process of the present invention. The plating apparatus 41 comprises a frame 42, a stand 43 disposed inside the frame 42 and bearing the insoluble anode 14 thereon, a housing 45 located above the anode 14, a rotating body 46 rotatably contained in the housing 45 and adapted to hold the cathodes 1, and a drive mechanism 47 for driving the rotating body 46. The apparatus 41 further comprises a drive mechanism 48 disposed at the upper portion of the frame 42 and serving to raise and lower the housing 45, a plating solution tank 33 storing the plating solution, and a pump 17 for feeding the plating solution in the plating solution tank 33 into a liquid-tight cavity portion 13 defined between the respective opposite end faces of the anode 14 and the rotating body 46. The frame 42 includes four posts 42b, 42b (only two of them are shown) set up on a baseplate 42a, and a top plate 42c fixed on the respective upper end faces of the posts 42b, 42b. The stand 43 is mounted on the baseplate 42a so as to be situated substantially in the center of the arrangement of the four posts 42b of the frame 42. The insoluble anode 14 is a square board fixed on the stand 43. A hole 14a is bored substantially through the center of the anode 14. The anode 14 is formed, for example, of a base material of titanium and an oxide of platinum or iridium deposited thereon to a thickness of 20 to 50 µ. Thus, the anode 14 is an insoluble anode which never causes the plating solution to change its composition, and can prevent penetration of impurities. A frame body 43a is fitted on the anode 14 in a liquid-tight manner with the aid of a seal member 43b. The height of the frame body 43a is substantially twice the thickness of the anode 14 Holes 43c and 43d are bored substantially through the respective centers of two facing side walls of the frame body 43a. The housing 45, which is square in shape as viewed from above (Fig. 17), is composed of a lower frame 50, an intermediate frame 51, an upper frame 52, a top lid 53, an inner gear 54 interposed between the lower and intermediate frames 50 and 51, and a slip ring 55 for current collection interposed between the intermediate and upper frames 51 and 52. All these members are firmly fixed together for integral formation. A large-diameter hole 50a, used to contain the rotating body, is bored through the center of the lower frame 50 of the housing 45. Supporting members 57, 57 are fixed individually to two opposite sides of the upper surface of the top lid 53, protruding sideways therefrom. The rotating body 46 is contained in the housing 45, and its basal portion 46a is rotatably housed in the hole 50a of the lower frame 50 of the housing 45 with a narrow gap left between the basal portion 46a and the lower frame 50. The upper end of a shaft 46b is rotatably supported by the top lid 53, projecting upward through a shaft hole 53a in the top lid 53. In this state, a lower end face 46c of the basal portion 46a of the rotating body 46 faces a top surface 14b of the anode 14 in parallel relation at a predetermined distance therefrom. As shown in Figs. 16 and 18, a plurality of holes 46d, e.g., four in number, are bored through the basal portion 46a of the rotating body 46, extending parallel to the axial direction and arranged at regular intervals in the circumferential direction. A second rotating body 60 is rotatably contained in each of these holes 46d. The rotating body 60 is rotatably supported in the hole 46d, with a narrow gap around it, by means of a bearing (not shown). The cathode 1 is grasped and fixed in a hole in the lower end face of each rotating body 60 by means of a chuck mechanism 110. The cathodes 1 are electrically connected to the slip ring 55 by means of their corresponding conductive members (not shown) and brushes 103. A gear 65 is fixed on the upper end face of each rotating body 60. The gears 65 are in mesh with the inner gear 54 attached to the housing 45. A motor 70 for driving the drive mechanism 47 (Fig. 16) is fixedly mounted on the top lid 53 of the housing 45. A gear 72, which is mounted on the rotating shaft of the motor 70, is in mesh with a gear 73 which is fixedly screwed on the upper end face of the shaft 46b of the rotating body 46. A motor 80 for driving the drive mechanism 48 is fixedly mounted on the top plate 42c of the frame 42 shown in Fig. 16. The motor 80 serves to drive a screw shaft 85 and also to drive a screw shaft 86, for use as a driven shaft, through the medium of a pulley 83, a belt 87, and a pulley 83. The respective free ends of the screw shafts 85 and 86 are screwed individually in threaded holes 57a, 57a of their corresponding supporting members 57, 57 of the housing 5. Power supply cables 21 and 22 are fixed to one side face of the anode 14 (Fig. 16) and a predetermined position of the upper surface of the slip ring 55, respectively. One end of a plating solution passage (duct) 140 is connected in a liquid-tight manner to the hole 14a of the anode 14 from below the anode. The other end of the passage 140 communicates with the plating solution tank 33 through the pump 17. Open ends of passages 141 and 142, on one side thereof, are connected in a liquid-tight manner to the holes 43c and 43d, respectively, of the frame body 43a of the anode 14. The respective other ends of the passages 141 and 142 are connected to the plating solution tank 33. The operation of the rotary high-speed plating apparatus 41 will now be described. First, the motor 80 for the drive mechanism 48 is driven to rotate the screw shafts 85 and 86, so that the housing 45 is raised to and stopped at an upper limit position indicated by two-dot chain line in Fig. 16. At this time, the lower end of the housing 45 is situated off and above the frame body 43a. Then, the second rotating bodies 60 of the rotating body 46 are fitted individually with the cathodes 1 which are each composed of the conductive substrate 2 to be plated. The motor 80 for the drive mechanism 48 is driven to rotate the screw shafts 85 and 86 reversely to the aforesaid case, so that the housing 45 is moved to and stopped at the position indicated by full line in Fig. 16. In this state, the lower end of the housing 45 is fitted in the frame body 43a in a liquid-tight manner, and the top surface 14b of the anode 14 and the individual cathodes face parallel to one another at a predetermined distance. The plating solution is fed from the plating solution tank 33 into the liquid-tight cavity portion 13, defined between the top surface 14b of the anode 14 and the lower end face 46c of the rotating body 46, via the pump 17 and the duct 140. Thus, the cavity portion 13 or the space between the anode 14 and the cathodes 1 is filled with the plating solution. The plating solution fed into the cavity portion 13 is returned to the plating solution tank 33 from either side through the passages 141 and 142. After the supply of the plating solution is started, the motor 70 for the drive mechanism 47 is driven to rotate the rotating body 46, for example, in the counterclockwise direction, as indicated by arrow CC in Fig. 18. As the rotating body 46 rotates in this manner, the second rotating bodies 60 are rotated in the clockwise direction, as indicated by arrows C in Fig. 18, through the medium of the inner gears 65 in mesh with the inner gear 54. These rotating bodies 60 rotate (or revolve on their own axes) at a rotating speed of, e.g., 10 m/sec to 30 m/sec. If the rotating bodies 60 or the cathodes 1 rotated at such a speed in the plating solution, the polarized layer of the metallic concentration of the plating solution in contact with the cathodes 1 becomes very fine, so that the Reynolds number Re of the plating solution flow exceeds 2,900 (Re > 2,900). For any portion of the plating solution in contact with the cathodes 1, moreover, the Reynolds number Re is not less than 2,300 (Re > 2,300). The aforementioned DC power source is turned on with the metallic-concentration polarized layer of the plating solution, in contact with the cathodes 1, kept very fine, thereby causing a required DC current to flow successively through the power supply cable 21, anode 14, plating solution, cathodes 1, carbon brushes 103, slip ring 55, and power supply cable 22. Thus, those end faces of the cathodes 1 opposed to the top surface 14b of the anode 14 are plated. After the passage of a predetermined time, the aforesaid current supply is interrupted to stop the operations of the pump 17 and the drive motor 70, thereby bringing the plating of the cathodes 1 to an end. The cathodes 1 are removed from the rotating bodies 60 by reversely following the aforementioned process of their mounting. In the rotary high-speed plating apparatus, the cathodes are rotated at high speed in the plating solution in order to make the metallic-concentration polarized layer of the plating solution very fine, so that the plating solution can be supplied to the liquid-tight cavity portion 13 at only a low flow rate. Accordingly, some advantages, such as miniaturization of the pump, economy of electric power, reduction in running cost, etc., can be obtained. Further, there is no need of an approach run of the plating solution for the very fine polarized layer of the metallic concentration of the plating solution, which has conventionally been required. Consequently, such a favorable effect as a reduction of the apparatus size can be enjoyed. Thus, according to the process of the present invention, high-speed plating is performed by means of the high-speed plating apparatus shown in Figs. 11 to 18, permitting electrolytic precipitation of copper film at an efficiency 10 to 200 times as high as that of the conventional plating technique, and ensuring a very efficiency of production. By setting the plating solution speed, current density, etc., according to the predetermined conditions, moreover, the surface roughness of electrolytically precipitated copper film and the size of deposited crystalline particles can be adjusted to desired values. The high-speed plating apparatus for effecting the process of the present invention is not limited to the apparatus described above, and must only be a plating apparatus which can provide a turbulence with the Reynolds number Re of about 2,300 or more. Examples according to the present invention will now be described. Table 1 shows the results of an evaluation test on copper-clad laminates with a high-purity metal film produced by the process according to embodiments of the present invention (example 2,3,4) and processes for comparison (control 1-5). In this evaluation test, the transferability, the peeling strength between the copper foil 6 and the insulating substrate 10, the elongation percentage of the copper foil 6, etc., were evaluated varying several conditions including the surface roughness of the conductive substrate 2, the electrolytic conditions for the high-purity metal film 5 and the copper foil 6, and the roughening conditions for the copper foil 6. The following are other testing conditions than those shown in Table 1, which are common to all the sample circuit boards. Conductive Substrate : Material: Single hardened stainless-steel plate (SUS630). Surface Treatment: Polishing to the roughness shown in Table 1 by using a rotary buffing apparatus with oscillator. High-Purity Metal Film : Material: Thin copper film (deposited to a thickness of 3 µm on the surface of the conductive substrate for Examples 2 and 4 and Controls 1 to 4, and to a thickness of 70 µm for Example 3). Electrolytic Conditions: Interelectrode distance of 11 mm; use of a copper sulfate plating solution containing 180 g/l sulfuric acid. Copper Foil Electroforming : Electrolytic Conditions: Interelectrode distance of 11 mm; use of a copper sulfate plating solution containing 180 g/l sulfuric acid; deposited film thickness of 35 µm (9 µm for Control 3). Roughening Process : (Nodular plating) Electrolytic Conditions: Use of a mixed solution containing 100 g/l copper sulfate, 50 g/l sulfuric acid, and 30 g/l potassium nitrate; deposited film thickness of 3 µm. Insulating Substrate : Material: Glassepoxy G10. In Table 1, the electrolytic conditions for the highpurity metal film 5 of Examples 2 to 4, are prepared by the process according to embodiments of the present invention. The time required for the deposition of the copper foil is very short, and the transferability, the peeling strength between the copper foil 6 and the insulating substrate 10, and the elongation percentage of the copper foil 6 are all satisfactory. The synthetic evaluations for Examples 1 to 4 are all "nondefective" (circles). If the current density exceeds its upper limit value provided by the process of present invention when the copper foil 6 is electrolyzed, nodular plating or the so-called "plating scald" is caused, and the elongation percentage of the formed copper foil 6 is as low as 8 %. Thus, the copper foil cannot be used for circuits for flexhble substrates (Control 1). If the solution contact speed of the electrolytic solution exceeds its upper limit value provided by the process of the present invention, the copper foil plating layer peels off too early (Control 2). If the current density at the time of electroplating, in the process of roughening the surface of the copper foil 6, is lower than its lower limit value provided by the process of the present invention, the plated surface is lustrous and cannot enjoy rough-surface plating (Control 3). If the surface of the copper foil 6 transferred to the insulating substrate 10 is roughened only insufficiently, the peeling value obtained between the copper foil 6 and the insulating substrate 10 is 0.7 kg/cm, which indicates lack of adhesion strength. In Control 5 in which the surface roughness of the conductive substrate (single plate) is low, on the other hand, the high-purity metal film 5 or the copper foil 6 is separated (peeled too early) from the conductive substrate 2 during its formation. In Control 4 in which the surface roughness exceeds its upper limit value, the adhesion strength between the conductive substrate 2 and the high-purity metal film 5 or the copper foil 6, during the transfer step, is so great that the high-purity metal film 5 or the copper foil 6 partially remains on the conductive substrate 2. If the surface roughness of the conductive substrate 2 is great, moreover, a number of pinholes are produced in the high-purity metal film 5 or the copper foil 6. When the insulating substrate 10 is stacked for lamination, the bonding agent of the insulating substrate 10 penetrates these pinholes. The bonding agent in the pinholes sticks to the surface of the conductive substrate 2, so that the insulating substrate 10 and the conductive substrate 2 adheres so strongly to each other that the transferability is lowered. When one or more pinholes with a diameter of 100 µm or less existed per 1 dm², the pinholes in all were regarded as many. Thus, Controls 1 to 5, in which some of the conditions including the surface roughness of the conductive substrate 2, the electrolytic conditions for the copper foil 6, and the roughening conditions for the copper foil 6 are not in compliance with the requirements provided by the present invention, are subject to the drawbacks as aforesaid. The synthetic evaluations for Controls 1 to 6 are all "defective" (crosses). Industrial Availability A process for producing a copper-clad laminate according to the present invention combines the so-called singleplate pressing method and high-speed plating method. According to this process, therefore, a copper film with a high elongation percentage fitted specially for use in flexible circuit boards can be formed in a short period of time, thus ensuring high productivity and simple steps of production. Accordingly, the necessary equipment for the manufacture of the copper-clad laminate and the installation space therefor can be reduced. If a high-purity metal film is interposed between a conductive substrate and a copper foil, the copper foil, which is formed by plating, cannot easily suffer pinholes or other defects, and the transferability is improved. Besides these and various other advantages, the process of the invention is advantageous in that the thickness of the copper foil is 10 µm or less, so that a very thin copper-clad laminate adapted for use in high-density conductor circuit boards can be obtained. Thus, the process of the invention is highly useful in the field of conductor circuit boards.

Claims: A process for producing a copper-clad laminate comprising the steps of: forming a copper foil (6) with a thickness of 10 µm or less on the surface of a planar, electrically conductive substrate (2), for use as a cathode (1), by spacing said cathode and a planar anode (14) at an interelectrode distance of 3 to 30 mm from each other, and supplying an electrolytic solution to said electrodes so that said electrolytic solution comes into contact with said electrodes at a solution contact speed of 2.6 to 20.0 m/sec, thereby electroplating said electrodes under a current density of 0.15 to 4.0 A/cm²; roughening the surface of said copper foil; laminating and bonding together an insulating substrate (10) and said conductive substrate, with the thus formed copper foil therebetween, with use of heat and pressure; and peeling said copper foil and said insulating substrate together from said conductive substrate. A process as claimed in claim 1, wherein said cathode and said anode are both fixed, and said electrolytic solution is supplied compulsorily between said electrodes. A process as claimed in claim 1, wherein said cathode is rotated so that said solution contact speed of said electrolytic solution is obtained. A process as claimed in any one of claims 1 to 3, wherein said surface-roughening step is a step of plating the surface of said copper foil for roughening so that a deposited film thickness of 2 to 5 µm is obtained with use of an acid electrolytic solution containing copper ions and nitrate ions, under the conditions of a current density of 0.25 to 0.85 A/cm², a solution contact speed of said acid electrolytic solution, with respect to said electrodes, ranging from 0.1 to 0.8 m/sec, and an interelectrode distance of 26 to 50 mm. A process as claimed in claim 4, wherein the surface of said copper foil is further subjected to a chromate treatment after said plating for roughening. A process as claimed in any one of the preceding claims, wherein said copper foil (6) with a thickness of 10 µm or less is formed on a high-purity metal film (5) with a thickness of 0.1 to 3 µm formed on the surface of a planar, electrically conductive substrate (2), for use as a cathode (1), spacing said cathode and a planar anode (14) at an interelectrode distance of 3 to 30 mm from each other, and compulsorily supplying an electrolytic solution to said electrodes so that said electrolytic solution comes into contact with said electrodes at a solution contact speed of 2.6 to 20.0 m/sec, thereby electroplating said electrodes under the condition of a current density of 0.15 to 4.0 A/cm², said copper foil adhering to said high-purity metal film (5) with a force of adhesion greater than that between said cathode and said high-purity metal film; roughening the surface of said copper foil; laminating and bonding together an insulating substrate (10) and said conductive substrate, with the thus formed copper foil therebetween, with use of heat and pressure; and peeling said high-purity metal film and said copper foil, together with said insulating substrate, from said conductive substrate. A process as claimed in claim 6, wherein said high-purity metal film is a thin copper film. A process as claimed in claim 6, wherein said high-purity metal film is a thin film of a metal other than copper, and is removed after being peeling from the conductive substrate. A process as claimed in any one of claims 1 to 5, wherein said copper foil (6) with a thickness of 10 µm or less is formed on a high-purity metal film (5) with a thickness of 70 to 250 µm formed on the surface of a planar, electrically conductive substrate (2) for use as a cathode (1), spacing said cathode and a planar anode (14) at an interelectrode distance of 3 to 30 mm from each other, and compulsorily supplying an electrolytic solution to said electrodes so that said electrolytic solution comes into contact with said electrodes at a solution contact speed of 2.6 to 20.0 m/sec, thereby electroplating said electrodes under the condition of a current density of 0.15 to 4.0 A/cm², said copper foil adhering to said high-purity metal film with a force of adhesion smaller than that between said cathode and said high-purity metal film; roughening the surface of said copper foil; laminating and bonding together an insulating substrate (10) and said conductive substrate, with the thus formed copper foil therebetween, with use of heat and pressure; and peeling only said copper foil and said insulating substrate together from said conductive substrate so that said high-purity metal film is allowed to remain on the surface of said conductive substrate. A process as claimed in claim 9, wherein said high-purity metal film is in the form of a foil or a plate having an electrochemically uniform surface such that pores or segregations in the metal of the metal film are reduced by degassing or rolling. A process as claimed in claim 9 or claim 10, wherein said high-purity metal film is formed by electroplating.

Inventors: TOUYAMA TASUKU - KITAWAKI, WADA TATSUO - TOWDATE BLDG, YAMAMOTO TERUAKI - OGURO -CHOM, YAMASHITA KEIZO - ISHIDA -CHOM, TOUYAMA, TASUKU 127-4, KITAWAKI, WADA, TATSUO 4-406, TOWDATE BLDG., YAMAMOTO, TERUAKI 11-5, OGURO 2-CHOME, YAMASHITA, KEIZO 12-23, ISHIDA 2-CHOME
Applicants: MEIKO ELECTRONICS CO LTD, MEIKO ELECTRONICS CO., LTD.
Application year: 1987
Main classification: H05K3
IPC codes: B32B43, H05K3, B32B38, B32B37, B32B15