Constitutive behaviour of lead-free solders vs. lead-containing solders-experiments on bulk specimens and flip-chip joints

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 the health hazards caused by the 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 two lead-containing solder alloys(Sn63Pb37 Sn59Pb40Agl) were investigated and compared with each other in order to give an estimation of the reliability enhancement of the new lead-free soldering technology. These investigations were focused on mechanical and physical properties (coefficient of thermal expansion, stress-strain curves at different strain-rates, ultimate strength) as well as on the microstructural appearance of the solders