Au-Sn SLID bonding for high temperature applications

Abstract

Au-Sn solid-liquid-interdiffusion (SLID) bonding is a novel and promising interconnect technology for high temperature (HT) applications. In combination with Silicon Carbide (SiC) devices, Au-Sn SLID has the potential of being a key technology for the next generation of innovative, cost effective and environmentally friendly drilling and well intervention systems for the oil industry. However, limited knowledge about Au-Sn SLID bonding for combined HT and high power applications is a major restriction to fully realize the high temperature potential of SiC devices. This paper presents a comprehensive study of fluxless Au-Sn SLID bonding. Two different processing techniques – electroplating of Au / Sn layers and sandwiching of eutectic Au-Sn preform between electroplated Au layers – have been studied in a simplified metallization system. The latter process was further investigated in two different Cu / Si3N4 / Cu / NiP / Au-Sn / Ni / Ni2Si / SiC systems (different Au-layer thickness). Die shear tests and cross-sections have been performed on “as bonded”, thermally cycled and thermally aged samples to characterize the bonding properties associated with the different processing techniques, metallization schemes and environmental stress tests. A uniform Au-rich bond interface is produced (the ζ phase with a melting point of 522 °C). The importance of excess Au on both substrate and chip side in the final bond is demonstrated. It is shown that Au-Sn SLID can absorb thermo-mechanical stresses induced by large CTE mismatches (up to 12 ppm/K) in a packaging system during HT thermal cycling. The bonding strength of Au-Sn SLID is shown to be superb, exceeding 78 MPa. Importantly, Au-Sn SLID is shown to be an excellent interconnect technology for HT packaging.