Copper/solder cleaning

Hi All: First of all, GREAT SITE! To the matter at hand: I have a questions regarding cleaning of a copper heat sink with 60/40 tin lead soldered copper fins. The current process involves alkaline soak, reverse clean with a brief reverse at the end, room temp 10% sulfuric acid. The solder becomes discolored, and adhesion of e/n is poor. Is there a better cleaning method? To solve the problem, a copper strike is applied. Thanks in advance! Chris

Chris, I think what is happening is the sulfuric acid is reacting with the lead in the solder and forming an insoluble lead sulfide. Try using a dilute hydrochloric acid (10-30%) instead. You could also consider using one of several comercially available alkaline E-nickel strikes prior to your build-up plate. This would help minimize contamination of your plating solution.