Comparative study on the wettability and thermal aging characteristics of SAC 305 nanocomposite solder fabricated by stir-casting and ultrasonic treatment

The present work introduces ultrasonic treatment as an effective tool to disperse ZnO nanoparticles in Sn3.0Ag0.5Cu (SAC 305) solder and compares it against the conventional stir-cast process. In stir-casting, the wettability improved until 0.1 wt% ZnO addition and thereafter declined. However, nanocomposite solder fabricated by ultrasonic treatment retains good wettability until 0.2 wt% ZnO addition. DSC analysis confirms 4.9°C and 9.9°C reduction in undercooling of SAC 305–0.1ZnO by stir-cast and ultrasonic treatment processes, while the melting temperature was the same. Ultrasonically dispersed SAC 305–0.1ZnO exhibited better β-Sn grain refinement in the as-cast condition. Besides, after aging at 175°C, ultrasonically dispersed SAC 305–0.1ZnO exhibited minimum grain coarsening. Ultrasonic cavitation accompanied by an acoustic streaming mechanism is responsible for ZnO dispersion. Well-distributed ZnO pins the β-Sn grain boundaries during thermal aging, reflected in their microstructure and mechanical properties. The tensile yield strength of SAC 305–0.1ZnO by ultrasonic treatment in the as-cast condition is 18.2% higher than that of the monolithic, while retaining the ductility. Also, ultrasonically dispersed SAC 305–0.1ZnO showed excellent thermal stability by exhibiting less grain coarsening after thermal aging. Effective deagglomeration and dispersion by ultrasonic treatment contributed to the improved wettability, microstructure, and stable mechanical properties.