In today’s printed circuit boards, copper is used especially for interconnecting the components on the substrate. Traditionally, copper is used as a material to form an electrical connectivity track pattern; whenever copper is exposed without proper coating and exposed to air over a long period of time, copper will be easily tarnish because of oxidation. It will then get corroded and thus loses its solderability. Because of this issue, multiple techniques are used to protect the copper tracks, via holes and printed through-holes (PTH). One of the methods is coated with organic coating, oxide coating and the plating method that many manufacturers used long time ago. PCB Organic coating, though simple in application, is not recommended for long term usage due to capability of PCB pcb prototype assembly manufacturer process control in thickness, composition and also the curing cycles. It can also cause unpredictable deviation in solderability. However, with the enforcement of lead-free, it is widely use on consumer PCB now.
Oxide coating can protect the circuit from corrosion, however, it fails to preserve the PCB solderability. The most standard method since long time ago for PCB manufacturers is metal coating process which was standard practice to ensure solderability and protect the circuit from corrosion before the enforcement period of lead-free era. So it was a key factor and plays an important role in the PCB manufacturing of double-sided and multi-layer (PTH) boards in the past. In particular, plating a solderable metal over the tracks was a standard practice to afford solderable protection to the copper tracks. Also, the edge connectors added 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 electrical contacts expected to have a high degree of wear resistance and low contact resistance. This will ensure precious metal plating on these contacts and the most commonly used metal is gold. Other metals used for coating are tinning of the tracks, nickel plating and in some instances, copper plating to build up some of the track areas.