Thermo-mechanical properties and creep deformation of lead-containing and lead-free solders

For a long time, both high Pb-Sn and eutectic 63Sn-37Pb have been the suitable materials for the interconnection of electronic components because of their low cost and appropriate physical properties. Due to environmental awareness and health hazards caused by lead in the solders, large efforts have been made to develop a lead-free soldering technology. Among the large variety of lead-free solders, the Sn-Ag alloys are expected to be the best candidates. Furthermore, from a reliability point of view, there has been interest in the improved thermal fatigue resistance of solder interconnects. Therefore, in this study two lead-free solder alloys (Sn96.5Ag3.5, Sn95.5Ag3.8Cu0.7) and one lead-containing solder alloy (Sn59Pb40Ag1) were investigated and compared with each other in order to give an estimation of the creep resistance of the lead-free solders. These investigations were focused on mechanical and physical properties (coefficient of thermal expansion, Young's modulus) as well as on the microstructural appearance of the solder. The mechanical and thermomechanical behavior of the solders was examined by TMA, DMA, and creep tests.