Bonding of Cu to Cu bulks through the low temperature sintering of Ag nanoparticle paste

In electronic industry, there has been a great demand for the high temperature electronics. To support these devices in packages, joints that can serve at high temperature are required. Ag nanoparticle paste has a potential to be a lead-free material which is suitable for high temperature service with low process temperature. In this study, Ag nanoparticle paste was prepared by chemical reduction reaction of AgNO3 using sodium citrate dehydrate as reducing agent. Each particle was covered with an about 1 nm thin organic shell of citrate groups, which average size was about 45.4 nm with a distribution ranging from 20 to 110 nm. The thermal gravimetric analysis showed that the temperature above 200°C was necessary for the decomposition of organic shell in air. The sintering-bonding with Ag nanoparticle paste of silver plated pure coppers instead of the semiconductor device and printing circuit board was performed. The effects of bonding temperature, pressure on the interface bonding and shear strength of joints were investigated. Higher bonding temperature and pressure were beneficial to joint formation. The results showed that strong joints with shear strength of 39.6 MPa were obtained at sintering temperature of 250°C for 30 min under 10 MPa. Copyright © 2010 MS&T'10®.