Effects of thermal aging on long-term reliability and failure modes of nano-silver sintered lap-shear joint

In this study, evolution of microstructure and shear strength for nano-silver sintered joint were studied after thermal aging at 125oC–350 °C for up to 500 h. The joints show stable microstructure and high shear strength after aging at 125 °C and 225 °C. Thermal aging at 275 °C and 350 °C increases the size of silver particles and pores significantly, thus weakening shear strength. Three types of failure modes including cohesive failure in sintered-silver layer, mixed failure between sintered-silver and plated-silver/copper surface, and adhesive failure on plated-silver/copper surface are described. Copper substrates oxidized after aging at 275 °C and 350 °C are obvious. The combination of microstructure change and copper oxidation leads to change of failure mode from cohesive failure in sintered-silver layer to adhesive failure on plated-silver/copper surface. In addition, the significant failure mechanism in the sintered-silver layer is found to be intergranular fracture.