Chromic acid free etching of polymers for electroless plating

In the etching and wetting steps in the process of electrolytically plating a previously electroless plated polymer substrate containing units derived from at least one member of the group consisting of acrylonitrile, butadiene and styrene, in an environment free of chromium ions and carboxylic acids, the improvement comprising the initial steps of:

• (a) roughening and activating the surface of the polymer by contacting the same with a first solution, expressed in terms of total solution comprising:
• (i) about 0 to about 85% w/w of concentrated sulfuric acid of about 97% acid strength, about 0 to about 55% w/w of concentrated nitric acid of about 71% acid strength and about 0 to 80% w/w of concentrated phosphoric acid of about 85% acid strength, wherein said acids are present in about 10% w/w or above,
• (ii) about 0 to about 5% w/w of noble metal ion, excluding palladium,
• (iii) about 0 to about 30% by weight of an oxidant selected from the group consisting of nitric acid, hydrogen peroxide and persulfates provided that where nitric acid is present in (a)(i) in an amount of at least 10% w/w no additional amount of oxidant is required and
• (iv) about 90 to about 0% w/w of solvent capable of dissolving the above components, to 100%, provided that where the concentrated acid of (a)(i) is sulfuric acid alone, its concentration shall be at least 30% w/w, and where said acid is nitric acid or phosphoric acid alone, the presence of sulfuric acid in an amount of at least 10% w/w is required in (c)(i), followed by
• (b) washing with water, then
• (c) treating the surface of the polymer by contacting the same with a second solution, expressed in terms of total solution comprising:
• (i) about 0 to about 85% w/w of concentrated sulfuric acid, about 0 to about 55% w/w of concentrated nitric acid and about 0 to about 80% w/w of concentrated phosphoric acid, wherein said concentrated acids are defined above and are present in about 10% w/w or above,
• (ii) about 0 to about 5% w/w of noble metal ion, excluding palladium,
• (iii) about 0 to about 30% by weight of an oxidant selected from the group consisting of nitric acid, hydrogen peroxide and persulfates provided that where nitric acid is present in (c) (i) in an amount of at least 10% w/w no additional amount of oxidant is required and
• (iv) about 90 to about 0% w/w of solvent capable of dissolving the above components, to 100%, provided that where the acid of (c)(i) is concentrated nitric acid or concentrated phosphoric acid alone, the presence of sulfuric acid of at least 10% w.w concentration is required and further provided that at least 0.001% w/w of noble metal, excluding palladium shall be used in at least one of step (a) or step (c) and at least 0.1% w/w of oxidant shall be used in at least one of step (a) or step (c), followed by the subsequent steps comprising
• (d) washing with water, following step (c) to substantially remove noble metal ions from the polymer substrate;
• and
• (e) immersing the substrate in an aqueous suspension of Pd.sup.o containing at least 0.001 to 5.0% w/w thereof.