Mechanical properties of Sn-In and Pb-In solders at low temperature

The growing number of applications using high temperature superconductors (HTS) has created new requirement for increasing the range of temperatures in which electronic assemblies can operate. Typically, eutectic lead-tin solders lose ductility below -150°C. In this paper, new solder formulations were evaluated for cryogenic applications. The mechanical properties of PbIn and Sn-In solders were determined over the temperature range -200°C to 100°C using the uniaxial tensile test, with the following results. The strength of two types of solder increases almost linearly with decreasing temperature. However, it was evident that the Sn-In alloying solders possess higher strength than the Pb-In (50 Pb/50 In) solder at low temperatures. For both types of solder, the total elongation decreases with decreasing temperature, and all of the solders displayed superplasticity at temperatures greater than 50°C. There was also doubling of the uniform elongation below -50°C for all of the tested solders. The deformation and fracture processes of the solders were investigated, and their fracture mechanism is proposed