Abstract: A process used during manufacture of printed circuit boards comprises protecting metal pads and/or through-holes to provide a tarnish-resistant and solderable coating. In the method, the pads and/or through-holes are bright-etched, metal plated, preferably by an immersion process, and treated with a tarnish inhibitor. The tarnish inhibitor may be incorporated into the immersion plating bath. The metal plating is usually with silver or bismuth and the pads and/or through-holes comprise copper.

Abstract: An improved process for dissolution of metals by etching, and particularly the etching of copper in printed circuit board processing or the like, using an aqueous H.sub.2 O.sub.2 --H.sub.2 SO.sub.4 etching solution, in which the concentration of H.sub.2 SO.sub.4 in the etching solution is allowed to decrease during use of the etching solution from an initial, relatively high level at the time the etching solution is put into use, to a final, relatively low level. When a predetermined concentration of dissolved etched metal exists in the etching solution, the etching solution is removed from use, H.sub.2 SO.sub.4 is added to increase the concentration of H.sub.2 SO.sub.4 in the etching solution to approximately the initial, relatively high level, and the metal is precipitated out of the etching solution.