Mechanical and microstructural enhancements of Ag microparticle-sintered joint by ultrasonic vibration

Silver (Ag) microparticle sintering bonding is a promising die-attach method for power device packaging. In this study, an ultrasonic-assisted bonding method that bonds chestnut-burr-like Ag microparticles rapidly at low temperatures is reported. Robust joints with an average shear strength of 36.2 MPa were achieved under ~ 240 °C (actual) 7 MPa in 300 s. Based on characterization of sintered microstructures obtained with different ultrasonic time and power, effects of the ultrasonic vibration were studied. Two unique microstructures, microbridges and dense layers, were generated with the ultrasonic vibration. The former achieved microparticle sintering, and the latter changed fracture mode of the joints from brittle interfacial debonding to ductile fracture. The results indicate the microbridges and dense layers enhanced the joints within a certain range and are generated due to crystallization driven by localized plastic deformation and localized high temperatures.