Usability of Silver Plating and Silver Bismuth Alloy Plating on Electrical Contacts

Silver plating has many advantages, such as low resistivity, good solderability and low cost compared with gold plating, but it is easy for silver to form sulfide film in the environment containing sulfur, which restrains the application of silver plating on the electrical contacts, especially in signal connectors. However, driven by the cost pressure in recent years, silver is reconsidered to be a candidate of finish material on the electrical contacts under certain conditions, and silver alloy plating is also proposed to improve the performance of pure silver plating. In this paper, the pure silver plating and silver bismuth (AgBi) alloy plating on electrical contacts were assessed by corrosion simulation and contact resistance measurement. By using sulphurous acid vapour test, the porosity of both silver plating with various thicknesses and AgBi alloy plating was measured. Then by sulfur hydrogen gas test, the relationship between the characters of corroded products and the electrical performance of both silver plating and AgBi plating was studied. The crystal structure of both pure silver plating and AgBi plating was detected by X-ray diffractometer to explain the difference of corrosion resistance. The usability of pure silver plating and AgBi plating on the electrical contacts was discussed based on the corrosion tests and structure analysis.