Corrosion mechanism and Electrical contact behavior of various plated surfaces in the polluted environment

摘要

It is found that electrical contact failure is mainly caused by serious contamination formed at the contacts. On gold plating surface, special corrosion pattern is observed which is shown as a central corrosion core surrounding with one or more corrosion rings. The rings are accumulated with numerous small corrosion products. Formation mechanism of the pattern is combination effect of pore corrosion and tidal pushing action on the corrosion products. The core and rings as well as area between the rings appear higher contact resistance than normal value. Therefore, they can be considered as failure area. Calculation of MTTF on thin gold plating is only about 1.6 months of exposure time. During micro motion over the above failure area, contact resistance is high and fluctuated. With 50 grams of contact force, it takes about 100 cycles and 10 cycles to wipe off the corrosion core and rings respectively and finally obtain normal contact resistance. On silver plating surface, corrosion products are formed as various rings but no corrosion core is seen. The formation of corrosion rings is probably the combination effect of galvanic corrosion due to different concentration of electrolyte on silver surface and high potential difference between silver and copper substrate. Sliding contact resistance is also higher than 10 mΩ after 200 sliding cycles with 80grams of normal force. Corrosive gases such as Cl_2 and SO_2 may destroy the oxide film covered on nickel plating surface and corrode the metal during long-term indoor air exposure. Micro motion may reduce the contact resistance but gradually increase to a very high and fluctuated value. Accumulation of debris on the contact interface may contribute to the failure.