Wear of Gold Electrodeposits: Effect of Substrate and of Nickel Underplate

This investigation concerns the wear of gold electrodeposits such as are used on the contacts of electronic connectors. The wear of contact finishes is important to connector reliability because, if base metal is exposed, oxide or corrosion films form which may lead to unacceptably high contact resistance. Connector contact surfaces generally consist of gold platings hardened with from 0.1 to 0.5 weight percent of codeposited cobalt or nickel and having a thickness in the range of 0.5 to 5 /im. Underplatings of copper or ductile nickel are often used, chosen for their expected value in retarding substrate diffusion and for their effect in mitigating 323 the formation of corrosion and tarnish films which can develop in aggressive environments at pores in the gold deposit. Wrought pure gold and silver-gold alloy weldments or claddings are also employed, generally on only one member of a contact pair. Among the common substrates are copper and copper alloys, as in the edge contacts of printed circuit boards and the spring elements of connectors. Lubricants may also be used to lower insertion forces and to reduce wear. Prior research in the wear of gold has been summarized. 1 A role of underplate was found by Holden 2 and Solomon and Antler, 3 who recognized that contact finishes having low deformability are desirable and that the effective hardness of a multi-layer finish can be increased by the use of some underplatings, such as nickel. Studies with connectors have borne out their predictions, 4,5 but it is also common experience that nickel underplating may not change the wear of gold in some cases and, when associated with poor finishing practices which lead to nonadherent coatings or nodular surfaces, may even degrade wear behavior.