ABSTRACT
The selective deposition of precious metals for electronic connector contacts typically leaves adjacent areas of base metal exposed. In aggressive environments such as those containing H2S-NO2-Cl2 species, the common connector materials i.e., nickel and copper (alloys) could be attacked. Under extreme conditions, copper sulfide films may creep across the surface of the combined metals. The contact finish and the reactivity of the metal substrate can have a major influence on the creep process. Because pure gold does not form oxides or readily tarnish, it shows little resistance to the creep of the sulfide corrosion products. Other precious metals, such as palladium, have shown better resistance as have certain base metals which are characterized by stable surface oxide films.
This work will report upon an evaluation of two precious metal inlays, WE#1 (69Au25AgPt) and diffused gold-palladium-silver, in combination with several base metals (C72500, C52100, C65400, C17200) which were exposed to a range of severe environments. The materials were exposed as a) bare coupons and b) assembled connectors. The environmental exposures were carried out in a laboratory chamber using Battelle Class II and III atmospheres, respectively. The chamber test periods simulated outdoor life exposures of two to twenty years for Battelle Class II and on to ten years for Battelle Class III. Sample coupons and connectors were characterized by measurements of contact and low-level circuit resistance, respectively.
The beneficial effects of a protective layer over copper alloys to prevent creep of corrosion products were demonstrated. Two methods were used to retard corrosive attack and creep. They were a) the use of a commercial lubricant and b) the shielding of a connector housing.
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