Superplasticity Deformation of Sn-Bi-Based Solder Alloys

Low-temperature solder alloys have drawn a large amount of attention. Because using low-temperature soldering also reduces the energy cost of fabrication processes. It allows the fabrication of inexpensive assembly materials, such as printed circuit boards, without high-assembly temperature resistance and temperature-sensitive components, such as LEDs, by avoiding thermal damage. The superplasticity mechanism of Sn-based alloys has not yet been clearly established. Therefore, this study investigated the effects of third-element addition on the microstructure and superplastic behavior of Sn-Bi-based alloys. Low-melting-point Pb-free Sn-BiSb and Sn-Bi-Zn solder alloys were used in this study. Tensile tests were carried out on the alloys under various cooling rates, temperatures (25, 40, 60, and 80 degrees C), and strain rates (10(-3)-10(-1)/s). The Sb- and Zn-added Sn-Bi-based alloys demonstrated superplastic deformation at 80 degrees C. The strain-rate sensitivity index of the Sn-Bi-based alloys at 80 degrees C exceeded 3, which is the threshold considered for superplastic deformation behavior. These results suggest that the superplastic deformation of Sn-Bi-based alloys is independent of the grain size of the primary Sn phase.