Why is an acidic copper plating solution only partially suitable for iron?

Copper can deposit onto iron without current due to the electrochemical potential, as copper is more noble than iron. During this electroless deposition, iron oxidizes in the acidic solution, reducing copper ions and depositing copper onto the iron surface.

However, this electroless deposition results in poor copper adhesion because coarse copper crystals form, weakening the bond between copper and iron.

To mitigate these issues, the workpiece can be introduced into the solution under an electric current, leading to electrolytic copper deposition. The applied current enables controlled deposition, thus improving copper adhesion. This way, the problems of electroless deposition can be largely avoided.

To prevent this issue, a thin layer of alkaline copper electrolyte can be applied.