CORROSION OF PRECIOUS METAL PLATED COPPER-ALLOYS DUE TO MIXED FLOWING GAS EXPOSURE

Corrosion of precious metal plated copper alloys after exposure to mixed flowing gas environment was studied. Six copper alloys used in electronic connectors were selected for study. All alloys were plated with a nickel underplate followed by a precious metal surface plating of gold or gold-flashed palladium. The coupons were then exposed to a mixed flowing gas environment containing chlorine, hydrogen sulfide, and nitrogen oxide. The base metal corrosion products arising from these exposures migrate to the surface through originating plating defects creating films and corrosion mounds on the surface and large etch pits in the copper alloy substrate. The surface corrosion products were analyzed by an electron microprobe and found to be very complex. All constituents of the copper alloys, as well as nickel from the underplate, were found in the corrosion products. The metals were found to be in combination with oxygen, chlorine, and sulphur in varying amounts and distributions. The attack of the environment on the base metal was also complex. Grain boundary corrosion and alloy separation were noted. Examples of the corrosion products and processes are discussed.