8.1 Need for Plating

In printed circuit boards, copper is used for interconnecting the components on the substrate. Although it is a good conducting material on the PCB to form the conducting track pattern, it is liable to tarnish due to oxidation, if exposed to atmosphere over a long period of time. It undergoes corrosion and thus loses its solderability. Therefore, various techniques are used for the protection of the copper tracks, and via holes and printed through-holes (PTH). They are organic lacquer coating, oxide coating and plating.

Organic lacquer coating, though simple in application, is not suitable for long term usage due to variations in thickness, composition and curing cycles. It can also bring about unpredictable deviation in solderability. Oxide coating can be used to protect the circuit from corrosion, but it fails to preserve the solderability. Plating or the metal coating process is a standard practice to ensure solderability and protect the circuit from corrosion. So it plays an important role in the PCB manufacturing of single-sided, double-sided and multi-layer (PTH) boards. In particular, plating a solderable metal over the tracks has now become a standard practice to afford solderable protection to the copper tracks.

Edge connectors with spring contacts mating with suitably designed connector tabs on printed circuit boards, are used for the interconnection of various modules in electronic equipment. Such contacts should have a high degree of wear resistance and low contact resistance. This requirement has resulted in precious metal plating on these...