Copper plating, exclusive of continuous strip plating and nickel, is the most common metal plated. It is a soft, red, ductile and solderable surface. It is not often used as a final plate , however, because it tarnishes easily.
Copper may be plated from a variety of baths depending on the final finish desired. Probably the most commonly used is still the copper bath, which is used for both a finish coat and as an underplate or "strike," followed by another finish coating of copper of some other metal.
The following are several good reasons for copper plating's popularity:
1. Copper is an excellent choice for an underplate, since it often covers minor imperfections in the base metal. It is easy to buff or polish copper, giving it a high gloss.
2. Copper plate is relatively inert in most plating baths of other common metals.
3. Copper have very high plating efficiency, resulting in excellent coverage, even on otherwise difficult parts.
4. Copper is highly conductive, making it an excellent coating for printing on circuit boards or as a coating on steel wire used to conduct electricity.
Among the most common copper plating specifications are Mil-C-14550 and GM 4252 M (copper and tin plating), now superseded by ASTM B 734 and B 545. Typically, copper will be applied to 0.0001 to 0.0002 in. (2.5 to 5.0 um) and finish coatings for "commercial" copper plate will run 0.0002 to 0.0004 in (5.0 to 10 um). The upper limit of 0.0004 in (10um) applies generally to externally threaded parts, but it common to most applications as well. Some automotive applications require 0.0005 in. (12.5 um) minimum.