Effect of Trace Ge on Wettability and High-Temperature Oxidation Resistance of Sn-0.7Cu Lead-Free Solder

Abstract

Sn-0.7Cu and Sn-0.7Cu-xGe solder alloys were prepared to investigate the influence of trace Ge on liquid Sn-0.7Cu lead-free solder at high temperature. The spreadability and the wetting force of solders were tested, and the oxidation-resistance was also evaluated by eye observation and skimming at 250℃～370℃. The results have shown that trace Ge can improve the spreading rate of Sn-0.7Cu, but have a few effect on the wettability. The oxide slag quantity of Sn-0.7Cu was three times more than the Sn-0.7Cu-0.012Ge at the same temperature and period, the optimal content of Ge to improve the oxidation resistance of Sn-0.7Cu was 0.012 mass%. The growth factor of oxide film on the surface of liquid Sn-0.7Cu solder (k_250℃ = 1.59 × 10⁻⁶, k_370℃ = 3.03 × 10⁻⁶) were both twice higher than the Sn-0.7Cu-0.012Ge (k_250℃ = 0.56 × 10⁻⁶, k_370℃ = 1.04 × 10⁻⁶) at 250℃ and 370℃ respectively.