Effect of HCl and Cl2on Pd Inlay Coupons and Pd Connector Contacts

Field exposure studies indicate that a resistive palladium chloride film may grow on Pd coupons when the ambient contains both high relative humidity (RH) and chlorine. This behavior raises a concern about the use of palladium in separable connectors. Most connectors are shielded systems, and the contacts are subject to wipe on mating. Therefore contact resistance probe measurements on coupon surfaces may not be representative of the behavior of connector contacts. A study on a moderately shielded connector system was initiated to compare the effects of chlorine and HCl vapors in high relative humidities on connectors with the effects on coupon surfaces. A number of material combinations including Pd against Pd, Pd against gold, and 60Pd40Ag against gold were tested in the study. It is shown that the high contact resistance values measured on the coupons are not representative of the contact resistance changes detected on connector contacts subjected to an accelerated aging treatment in the mated condition. The changes in contact resistance are much lower on connector contacts than on coupons. Palladium and 60Pd40Ag against gold are much superior in performance to Pd against Pd when exposed to Cl2environments. Exposure of mated connector contacts to HCl at high relative humidity results in little degradation of contact resistance compared to chlorine exposure.