Interface evolution and mechanical properties of Sn–36Pb–2Ag solder joints under different aging conditions

Electronic packaging products are often subjected to reliability evaluation, Sn–Pb solder is widely used in high-reliability military products due to its excellent soldering performance. Sn–36Pb–2Ag eutectic solder joints were subjected to aging experiments at 75 °C, 100 °C, 125 °C, and 150 °C for 100 h, 250 h, 500 h, and 1000 h, respectively. Continuous Cu3Sn and (Au, Cu)6Sn5 compounds were formed on the printed circuit board (PCB) substrate side after aging experiments, and continuous (Au, Ni)Sn4 and (Au, Ni)3Sn4 compounds were formed on the electronic component side. In addition, the Pb–rich phase on the IMC layer side increased with the increase in aging time and aging temperature. Thus, the mechanical properties of the solder joints seriously reduced, and the push force of the fractured solder joint measured in the push–pull force experiment was reduced from approximately 85 N (125 °C–500 h) to approximately 42 N (150 °C–1000 h). The fracture mode of solder joint under 150 °C–1000 h aging conditions was brittle. Furthermore, the diffusion coefficient and activation energy of the Cu3Sn phase and (Au, Cu)6Sn5 phase on the PCB substrate side were calculated.