Ultra-low temperature sintering of Cu@Ag core-shell nanoparticle paste by ultrasonic in air for high-temperature power device packaging

•Cu@Ag nanoparticles were successfully sintered at low temperature by ultrasonic.•Ag shells dewetting, dense and crystallized Cu cells were formed in the joints.•Abrupt high temperature generated by ultrasonic attributed to the deep sintering.•Void-free and dense sintered microstructure contributes the joint with good property.