Pressure-Assisted Low-Temperature Sintering of Nanosilver Paste for 5$\,\times\,$5-${\rm mm}^{2}$ Chip Attachment

Abstract

For decades, soldering has been the technology of choice in die bonding for power electronics applications. However, conventional solders cannot meet the requirement for high-temperature applications. Recently, a low-temperature sintering technique involving a nanosilver paste was developed for attaching semiconductor chips to substrates. Sintered nanosilver joints showed high reliability in high-temperature applications. It was found that sintered nanosilver could generate a strong, highly electrical, and thermally conductive bond. In this paper, we use a nanosilver paste to attach large chips by introducing a low pressure of up to 5 MPa during the densification stage. Shear tests show that even a temperature of 225°C and a pressure as low as 5 MPa can be sufficient to generate bonds comparable to solders. The characterization of the microstructures of the fracture surface of sintered nanosilver joints indicates that the densification of nanosilver is almost complete when the sintering is carried out at 225°C for 10 min under a pressure of 5 MPa. We conclude that it is not worthwhile to increase the sintering time, the sintering temperature, and the applied pressure as a result of the drop of densification rate.