Copper plating is done more than any other type of plating except for nickel. It is an excellent undercoat for other types of plating because it is able to cover defects in the substrate, is easy to buff, and has good corrosion resistance. Copper is also inexpensive, has good coverage and throwing power, and is less environmentally hazardous than other plated metals. Copper is also highly conductive, second only to silver. The copper plating process can also be used as a mask in surface hardening procedures.
There are primarily three types of solutions used in copper plating; alkaline, acid and mildly alkaline.
Alkaline has the best throwing power but cannot be plated at as high a current density as acid copper and typically involves the use of cyanide. This bath is often used as a strike for acid copper which is better at increasing deposit thickness. There are non-cyanide processes available however they are not practical for all applications.
Acid copper is less expensive, easy to control, and can be plated at high current densities. However, it cannot be plated directly onto steel or zinc diecast and it does not have the throwing capability of alkaline copper.
Mildly alkaline copper plating is often used on printed circuit boards. It is less corrosive than acid baths and is essentially non-toxic. This bath has good throwing power but like acid copper it cannot be plated directly onto copper or steel without a cyanide copper strike.
Typical specifications for copper plating include Mil-C-14550 and ASTM B734.
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