Comprehensive properties of a novel quaternary Sn-Bi-Sb-Ag solder: Wettability, interfacial structure and mechanical properties

Abstract

Sn-58Bi eutectic solder is the most recommended low temperature Pb-free solder but is also limited from the interfacial embrittlement of Bi segregation. Since the quaternary Sn-38Bi-1.5Sb-0.7Ag solder provides a similar melting point as Sn-58Bi eutectic, this paper systematically investigated the properties of this solder from wettability, bulk tensile properties, interfacial microstructure in solder joints with a Cu substrate, interfacial evolution in joints during isothermal aging and the shear strength on ball solder joints with effect of aging conditions. The results were also compared with Sn-58Bi solder. The wettability of solder alloys was evaluated with wetting balance testing, and the quaternary Sn-38Bi-1.5Sb-0.7Ag solder had a better wettability than Sn-58Bi solder on the wetting time. Tensile tests on bulk solder alloys indicated that the quaternary Sn-38Bi-1.5Sb-0.7Ag solder had a higher tensile strength and similar elongation compared with Sn-58Bi solder due to the finely distributed SnSb and Ag3Sn intermetallics in the solder matrix. The tensile strength of solder decreased with a decrease in the strain rate and with an increase in temperature, while the elongation of solder was independent of the temperature and strain rate. When soldering with a Cu substrate, a thin Cu6Sn5 intermetallic compound (IMC) is produced at the interface in the solder joint. Measurement on IMC thickness showed that the quaternary Sn-38Bi-1.5Sb-0.7Ag had a lower IMC growth rate during the following isothermal aging. Ball shear test on solder joints illustrated that the quaternary Sn-38Bi-1.5Sb-0.7Ag solder joints had higher shear strength than Sn-58Bi solder joints. Compared with the serious deterioration on shear strength of Sn-58Bi joints from isothermal aging, the quaternary Sn-38Bi-1.5Sb-0.7Ag solder joints presented a superior high temperature stability. Therefore, the quaternary Sn-38Bi-1.5Sb-0.7Ag solder provides better performances and the possibility to replace Sn-58Bi solder to realize low temperature soldering.