Nickel plating of steel components of composite contacts is universal and a standard thickness of .0001/.0002 gives good protection. If salt spray tests are to be employed, heavier deposits will be required. These test conditions should be specified and plating thickness adjusted accordingly.

Silver plating, normally over copper or brass, is seldom a replacement for a silver base contact, but can be employed in non-arcing, low mechanical force applications. Normally, silver plating is used on permanent connectors, semi-permanent connectors, or most commonly, to increase the nobility of copper and brass backings of composite contacts. In these instances, thicknesses of .000050 to .000100 will satisfy most applications.

Gold plating is a far more complex system that can be described more thoroughly by investigation of some of the problems encountered. The degree of protection obtained from gold is normally measured by its shelf life and operational life. To some degree, the plating thickness is a measure that can be used. But other factors (such as the purity of the gold, its porosity, subsequent handling and environment) play a large role.

Two problems, with gold over silver, are porosity and diffusion at elevated temperatures. The result is that silver sulfide forms at the pore sites and spreads over the gold surface ultimately covering the entire contact surface. Silver sulfide over gold has much higher resistance than silver sulfide over silver. In low current, low contact force applications, this could be disastrous.

In the higher amperage, higher force areas, gold is a benefit and the amount of protection is now more dependent on plating thickness. This can be subdivided into three levels: low, medium and high.

Gold Flash

Low or minimal protection can be achieved by employing a gold flash. The normal thickness of a gold flash is .000010/.000020.

Gold Treatment

Frequently there is a requirement for protection between that afforded by a gold flash and that obtained by the heavy, more expensive gold plates. To offer the contact user protection in this medium area, Deringer has developed a unique process termed Gold Treatment. This is a multistage application of gold that produces a protection level unattainable by regular electroplating of the same thickness. In today's contaminated atmospheres, this level of protection is frequently required.

Gold Plate

In the higher protection area, there are the gold plates which begin at thicknesses of .000050 and higher. At .000100 thickness, one can expect a virtually pore-free condition and less probability of diffusion dependent on temperature.

In gold plating of contacts, there are two types of gold normally employed. The 24 Kt. gold is the most pure and being more ductile, is normally employed. In audio circuits, it will produce less noise and, unless otherwise specified, this is the material supplied. The 23+ Kt. Gold is harder because it contains nickel or cobalt co-deposited with the gold. Being a harder material, it is employed on sliding contact applications and on semipermanent connections, to withstand the mechanical wear.