Connector Contact Materials: Effect of Environment on Clad Palladium, Palladium-Silver Alloys, and Gold Electrodeposits

Abstract

Electrodeposited pure gold, cobalt-hardened gold, and clad palladium, 60Pd40Ag and 40Pd60Ag were exposed for up to four years in air-conditioned telephone central offices and in a nonair-conditioned room at a central office location. The contact resistance of these materials was determined by probing, and surface films were evaluated by several analytical methods. None of the metals were significantly degraded at sites that were relatively free of gaseous air pollutants and where relative humidity was controlled to moderate levels. The gold-coated samples typically displayed lower and more stable contact resistances than the palladium materials. Palladium and the palladium-silver alloys acquired tarnish films which significantly increased contact resistance in the nonair-conditioned room where relative humidity was high some of the time and which contained traces of gaseous chlorine compounds. The 40Pd60Ag alloy was worse than palladium and 60Pd40Ag, in part because it reacted with sulfur-containing pollutants as well as with the chlorine compounds. Porous golds on copper and nickel underplate were not affected by any of the test environments. A finely divided particulate at one site degraded the contact behavior of the smooth claddings, but not the electrodeposited golds which had micronodular surface roughness.