Microstructural characteristics and properties of Cu@Ag NPs interconnect joints fabricated via ultrasound-assisted sintering

Silver-coated copper nanoparticles (Cu@Ag NPs), a two-phase core-shell structured material, were incorporated into solder paste, and ultrasound-assisted sintering technology was employed for the sintering process. Three sets of parameter experiments were designed to investigate the effects of sintering temperature, ultrasound time, and ultrasound power on the microstructure and mechanical properties of interconnect joints. The results demonstrate that in the sintered structure, silver and copper phases primarily existed as a replacement solid solution. With the introduction of ultrasound and an increase in sintering temperature, the density of the sintered structure increased significantly, ultimately achieving superior metallurgical bonding at temperatures ranging from 150 to 200 ℃ , enabling low-temperature connections. As ultrasound time increased from 2 s to 8 s and ultrasound power increased from 50 W to 350 W, the resulting sintered structure gradually became denser and more uniform. However, excessive ultrasound energy led to noticeable plastic deformation and cracks within the sintered layer. When sintering temperature of 150 ℃ was applied along with an ultrasound time of 6 s and an ultrasound power of 250 W, a uniformly dense sintered structure with shear strength reaching up to 149.5 MPa was obtained.