Effect of Si3N4 nanoparticles on IMC as well as mechanical properties of Sn58Bi/Cu solder joints during thermal aging

This paper investigated the changes in microstructure, intermetallic compounds (IMC), and mechanical properties of Sn58Bi/Cu and Sn58Bi-0.6 Si3N4 /Cu solder joints in the thermal aging process at 125°C. With the increase of the thermal aging time, the Bi-phase was gradually coarsened, but the coarsening of the Bi-phase was suppressed after adding Si3N4 NPs. The thickness of the IMC increased continuously, and some areas even detached into the solder matrix, accompanied by gradual grain growth. For the samples with Si3N4 NPs, the IMC thickness significantly decreased, and the grain size was finer. Fractures mainly occur in the Bi-rich phase of the solder matrix following a brief period of thermal aging. However, as the aging time increases, the fracture location gradually shifts from the solder matrix to the IMC, resulting in intergranular and transgranular fractures. However, the shear strength of solder joints with added Si3N4 NPs was higher during the same aging period.