Cadmium connector plating is metallic coating which is robust. When cadmium is plated on different metals like cast iron, steel, copper, malleable iron, and powdered metal, it acts like a sacrificial coating and corrodes before the substrate metal. To increase protection to cadmium plating conversion coatings of chromate are used over the plated metal. Cadmium plating offers a very good bonding surface for adhesives which are mostly used in aircraft manufacturing. It is also considered the best coating for salt water environments. The other advantage of cadmium is its low resistance to electricity, superior solderability and conductivity that is outstanding. Cadmium is used in a lot of applications:· In Marine Environment cadmium is used in components and fasteners that are exposed to fresh and salt water· In formed products it is used in pre-plated or shaped parts· Aerospace – for protection against corrosion on flight critical components and galvanic coupler for mating stainless steel parts aluminum airframes· Consumer products – It is used in home construction products and window hardware· Electronics- In electronics it is used in connectors, chassis and relays· Transportation – In transportation it is used in radiator hose fittings, disc brake components and door latches
Nickel plated connectors
With environmental regulations tightening the use of Cadmium, black zinc nickel plating is used as a substitute for cadmium plating. Black zinc nickel plating has good environmental performance and also electrical performance and provides the same level of corrosion resistance as cadmium. Since black zinc nickel and cadmium have same electrical potential, parts with different plating can be mated with very little risk of galvanic corrosion.
Parts with zinc nickel plating can be easily switched in place of cadmium plated connectors and the result is nonreflective and nonmagnetic. Nickel plated connectors are used in communication equipment and metering and power generation equipment. It is also used in aerospace and electric drive vehicles. It may be used in harsh equipment vehicles of next generation.
Reasons for prohibiting Cadmium plating in electronic systems in aeronautics
Cadmium is a toxic material that should not be used in spaceflights that are manned. It is said that Cadmium sublimates in an environment of hard vacuum at temperatures of 75*C. The products of sublimation are conductive and can deposit back again causing short circuits. The sublimation products can also come in the way of sensitive optics.
Cadmium also spontaneously develops whiskers. Its propensity of developing whiskers is lower than that of zinc and tin. These whiskers can give rise to electrical failures which can range from sustained plasma arcing to parametric deviations that can cause short circuits that are catastrophic. Cadmium plating is mostly used on connectors like fasteners. The risks associated with using cadmium plating outweigh the benefits.
To prevent risks using cadmium plating connectors in space flights nickel plated connectors are used which do not have the risks associated with cadmium plated connectors.