Copper plating surface color shifts from light to dark orange to black in less than 12 hours

Question

We have been doing barrel-type copper plating on small parts, and all of a sudden there is an increase of copper plating discoloration after copper plating. The color shifts from bright orange (good) to reddish purple and brown, and finally to black in less than 12 hours. I know that oxides of copper are causing this change, but I don't know yet the cause of abrupt discoloration of the surface. Copper oxides naturally, but not this rapid. What parameters should I check? I already checked the process parameters (plating current, current density, loading ratio) and all are the same as before the discoloration had happened. In terms of plating solution, we are using copper pyrophosphate.

Answer 1

You are correct that the copper is oxidizing. Electrolyte left over on the surface would promote that reaction just as it is well known to do with iron rusting, so check your rinsing and drying.