Ag–Sb合金めっきの加熱処理後の表面構造と接触信頼性

抄録

Silver–antimony electroplating, or Ag–Sb plating, has been widely used in various automotive terminals for its electrical conductivity, contact reliability, and wear resistance. These terminals are not only used at ambient temperatures but also at elevated temperatures. We have investigated the effects of Sb concentration and heat treatment in air at 200°C on the microstructure, chemical state, and contact resistance of Ag–Sb plating. In the range of 2.2–3.4 wt.% Sb, only the α phase is observed both before and after heat treatment, indicating that the Sb atoms are dissolved in the silver matrix. After heat treatment in air, Sb on the outermost surface is found to be entirely oxidized and increases in concentration. It is likely that Sb atoms diffuse through the recrystallized grain boundaries to the surface and then are oxidized during heat treatment. The contact resistance of the Ag–Sb plating after 500 hours of heat treatment increases significantly with higher Sb concentrations and lower vertical loads, which can be ascribed to the antimony oxides on the surface as per the aforementioned mechanism.