Influences of Ag and Au Additions on Structure and Tensile Strength of Sn-5Sb Lead Free Solder Alloy

It is important, for electronic application, to decrease the melting point of Sn-5Sb solder alloy because it is relatively high as compared with the most popular eutectic Pb-Sn solder alloy. Adding Au or Ag can decrease the onset melting temperature (233 degrees C) of this alloy to 203.5 degrees C and 216 degrees C, respectively. The results indicate that the Sn-5Sb-1.5Au alloy has very good ultimate tensile strength (UTS), ductility, and fusion heat, which are better than both those of the Sn-5Sb-3.5Ag and Sn-5Sb alloys. The formation of intermetallic compounds (IMCs) AuSn(4) and Ag(3)Sn enhanced the microstructure stability, while retained the formation of SbSn precipitates in the solidification microstructure, thus significantly improved the strength and ductility. For all alloys, both UTS and yield stress (sigma(y)) increase with increasing strain rate and decrease with increasing temperature in tensile tests, but changes of ductility are generally small with inconsistent trends.