Effect of strain rate on interfacial fracture behaviors of Sn-58Bi/Cu solder joints

The interfacial reactions and mechanical properties of Sn-58Bi/Cu solder joints reflowed at different temperatures ranging from 180 to 220 °C for constant time of 10 min were investigated with various strain rates. Only a continuous Cu6Sn5 intermetallic compound (IMC) layer was formed at the interface between the Sn-58Bi solder and the Cu substrate during reflow. The equivalent thickness of the Cu6Sn5 layer increased with increasing reflow temperature, and the relationship between Cu6Sn5 layer equivalent thickness (X) and reflow temperature (T) is obtained by using method of linear regression and presented as X=0.01×T+0.187\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ X = 0.01 \times T + 0.187 $$\end{document}. For the tensile property, the tensile strength of solder joint gradually decreased as the reflow temperature it increased, whereas it increased with increasing strain rate. Moreover, the fracture behavior of Sn-58Bi/Cu solder joint indicated the ductile fracture with low strain rate (5 × 10−4 and 1 × 10−3 s−1), while toward brittle fracture with high strain rate (2 × 10−3 and 1 × 10−2 s−1). The strain rate sensitivities of the solder joints fractured with various modes were also investigated, and it is found that the tensile strength of the solder is more sensitive to the strain rate than that of the IMC layer.