Microstructure and Joint Properties of Nano-Silver Paste by Ultrasonic-Assisted Pressureless Sintering

In recent years, sintering nano-silver paste has become a popular worldwide technology. This paper presents the effect of ultrasonic vibration on the microstructure and mechanical properties of pressureless sintered nano-silver joints. Ultrasonic waves have been introduced prior to sintering using a new type of nano-silver paste in order to improve bonding of large-area chips (≥10 × 10 mm2). The results show that ultrasonic vibration can not only reduce black pores, increase the size and the density of sintered silver, but also transfer the fracture mode of joints to cohesive failure. With increasing ultrasonic power or time, the shear strength of joints gradually increases linearly. The surface of the sintered silver, the fracture surface, and the cross section of joints were examined, and the microstructure has a transition zone at the edge of the joints that is insufficiently sintered. Ultrasonic vibration can reduce the transition zone and thus improve the reliability of joints.