Electrical connector reliability can be significantly improved by using a gold coating on an electrical contact. When gold is used as a contact interface it can provide a stable contact and offer low contact resistance over a connector functional life. Gold is also thought of as a way to reduce fretting corrosion risk. When temperatures are not extreme, gold will not react with environmental contaminants to form electrically insulating films. Because of the stability of gold, it is the material of choice for contact plating/coating in high performance electrical contact applications. But surely a gold coated contact surface would never require a connector grease? Not so.
A thin film of connector grease costs far less than a thick layer of gold, it’s a more cost effective way to seal the surface pores and protect against scratching and substrate oxidation.
Pure gold can have relatively poor sliding wear performance and since gold is soft, it can be scratched or scared easily. One option to make gold harder it so add a hardener such as nickel but the process can negatively effect the otherwise inertness of gold. The solution is to make sure the gold coating applied is of a sufficient thickness. What thickness? There are theories and white papers on the web giving advice on gold plating/coating thicknesses but when gold is applied on a contact surface, much depends on the variables involved such as contact design, contact forces, temperature, expected functional life (number of cycles) etc.
Generally we see problems with gold plated contact with gold thickness below 0.8 microns. This is not a definitive answer. Much depends on the number of cycles and contact forces the gold surface is expected to endure. Gold plated nickel contacts tends to be the most common combination. It can be the case that gold plating around or below 1.0 micron is enough for a connector operating in unchallenging conditions.
A crucial point when considering a very thin coating of gold is that the plating will be microscopically porous. The thin plating is easily compromised, maybe just on the initial/assembly of the connector. Over time oxides of the exposed substrate can ooze through the pores of an unlubricated gold plating and could cause open circuit resistance.
Increasing the thickness of a gold coating will decrease the porosity of the surface and so reduce the contact surface vulnerability. The reader may disagree but from our experience, when looking to reduce the gold surface vulnerability to oxide issues and mating damage, a gold coating thickness of 1.3 or 1.5 microns or more is required. However, a thin film of connector grease costs far less than a thicker layer of gold, so it’s a more cost effective way to seal the gold surface pores and protect against scratching and substrate oxidation.