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

Copper can be deposited on iron without the need for a current due to the electrochemical potential, since copper is more noble than iron. During electroless deposition, the iron oxidises in the acidic solution, causing copper ions to be reduced and deposited on the iron surface.

However, this electroless deposition results in poor adhesion of the copper, since coarse-grained copper crystals form, weakening the connection between copper and iron.

To alleviate these problems, the workpiece can be introduced into the solution under tension, causing the copper to be deposited electrolytically. The applied voltage controls the deposition and significantly improves the adhesion of the copper. In this way, the problems of electroless deposition can be largely avoided.