Electrical Characterization of β→α-Sn Transition in High Tin Content Solder Alloys with Different Inoculators

Abstract

The identification of allotropic transition of the metallic β-Sn to non-metallic α-Sn in Sn-rich solders joints is crucial for electronics working in sub-zero temperatures. This phenomenon was characterized by electrical resistance measurements in SnCu1 and Sn99Ag0.3Cu0.7 alloys inoculated with InSb, CdTe and α-Sn. Samples were stored at −18 • C for 10 weeks. The transition showed characteristic differences at the different alloys and inoculators, like different nucleation, growth and the saturation stages. Although the presence of α-Sn initiates the transition faster than the other inoculators, but the higher diffusion rate of the non-tin inoculators results in much more serious destruction of the samples. The results of the electrical resistance measurements were validated with metallurgical cross-sections.