Copper Foil for a Printed Circuit and a Method for the Production Thereof

The present invention will be illustrated by the following Examples, which should not be construed as limitative of the present invention.

With use of a solution containing 240 g of nickel sulfate (hexahydrate), 45 g of nickel chloride (hexahydrate) and 30 g of boric acid per liter of the solution and having a pH of 2.9, at 43.degree. C., as the electrolyte, electroplating was applied to the matte side (i.e. the bonding surface) of electrodeposited copper foil having a thickness of 35 microns, at a current density of 2.2 A/dm.sup.2 for 30 seconds. The amount of electrodeposition of nickel per apparent surface area of the matte surface corresponded to a thickness of about 0.2 micron and the surface presented a nickel color having no lustre. The foil was washed with water, and then with use of a solution adjusted to pH 13 by adding 3 g of chromic acid anhydride and 3.4 g of sodium hydroxide per liter of the solution at room temperature as the electrolytic bath, electrolysis was carried out at a current density of 3 A/dm.sup.2 for 5 seconds with the above nickel surface as the cathode. There was observed no change in appearance after said treatment. The treated foil was washed with water, dried and thereafter laminated on a glass-epoxy substrate to form a copper-clad laminated board. The results of measurement of various properties of this board are shown in Table 1 together with those of Comparative example 1 in which a foil not subjected to the chromic acid treatment was used.

The same treatment as described in Example 1, except for using a solution of pH 4.2 containing 300 g of nickel sulfamate and 15 g of ammonium sulfate per liter of the solution at 40.degree. C. as the electrolyte, was applied on the matte side of electrodeposited copper foil.

Then, following the procedures similar to Example 1, the properties of the resultant product were measured to obtain the results as shown in Table 1 together with those of Comparative Example 2 without treatment with chromic acid.

With use of a solution containing 250 g of nickel chloride (hexahydrate) and 53 g of hydrochloric acid per liter of the solution at 22.degree. C. as the electrolyte, electroplating was effected on the matte surface of electrodeposited copper foil with a thickness of 35 microns at a current density of 2 A/dm.sup.2 for 57 seconds. After washing the electroplated foil with water, electrolytic treatment was applied on the above nickel surface as the cathode at a current density of 3 A/dm.sup.2 for 5 seconds, using a solution adjusted to pH 9 by addition of 1 g of chromic acid anhydride and 2.5 g of sodium hydroxide per liter of the solution at room temperature as the electrolytic bath. Then, following the procedures similar to Example 1, the properties of the product were measured to obtain the results as shown in Table 1 together with those for Comparative example 3 in which no treatment with chromic acid was conducted.

The same treatment as described in Example 3 was applied on the matte surface of electrodeposited copper foil, except that there was employed a solution containing 1 g of chromic acid anhydride as the chromic acid solution at 50.degree. C. as the electrolytic bath and the electrolytic treatment was conducted under the conditions of a current density of 3 A/dm.sup.2 for 5 seconds.

The properties of the product were determined similarly as in Example 1 to obtain the results as shown in Table 1.

The treatment was conducted in the same manner as in Example 1, except that there was employed a solution containing 5 g/l of sodium chromate as the chromic acid treatment solution and the cathodic chromic acid treatment was conducted at a current density of 3 A/dm.sup.2 for 5 seconds. There was no change in appearance after said treatment.

After washing with water drying, the thus treated foil was laminated on a glass-epoxy substrate to provide a copper-clad laminated board, of which properties were measured to give the results as shown in Table 1.

The same treatment as in Example 1 was conducted except that the cathodic chromic acid treatment was effected at a current density of 3 A/dm.sup.2 for 5 seconds at room temperature, using a solution containing 4.5 g/liter of potassium dichromate as the chromic acid treatment solution. There was observed no change in appearance as the result of said treatment.

The thus treated foil was washed with water and dried, and then laminated on a glass-epoxy substrate to provide a copper-clad laminated board. The properties of the board were measured to give the results as shown in Table 1.

The treatment was conducted in the same manner as in Example 3 except that the cathodic chromic acid treatment was effected at a current density of 3 A/dm.sup.2 for 5 seconds at room temperature, using a solution containing 5 g/liter of sodium chromate as the chromic acid treatment solution. There was no change in appearance by the treatment.

The treated foil, after washing with water and drying, was laminated on a glass-epoxy substrate to provide a copper-clad laminated board. The properties of this board were measured to obtain the results as shown in Table 1.

Example 3 was repeated except that the cathodic chromic acid treatment was effected at a current density of 3 A/dm.sup.2 for 5 seconds at room temperature, using a solution containing 4.5 g/liter of sodium dichromate as the chromic acid treatment solution. There was no change in appearance by the treatment.

After washing with water and drying, the treated foil was laminated on a glass-epoxy substrate to provide a copper-clad laminated board. The properties of the board were measured to give the results as shown in Table 1.