Direct metal to metal bonding for microsystems interconnections and integration

In microsystems integration, microsystem devices with different functions are needed to be electrically connected. To meet higher component needs, more functions are configured within each device which leads to a significant potential in microsystems integration, industrial interests have grown exponentially in search of complementing integration and low temperature direct interconnection bonding technology to bridge this bottleneck. This area is especially profound in flip-chip thermocompression technology and chip design for high-density interconnection, since conventional soldering process may not be able to address the generic limitation of relatively high process temperature, solder bump geometry, under-bump-metallization (UBM) schemes and intermetallic effects. This underlying problem necessitates a low temperature direct metal bonding technique for joining multifunctional microsystems which offers more reliable and higher density interconnections than soldering and the wire bonding techniques. In this paper, Au-Au bonding was identified as potential technique to integrate microsystems. Bonding parameters and bond quality were deliberated in multifactorial experiments to determine optimum loading and temperature. Bonding mechanisms and reliability were established with tensile and shear test evaluation. The results show that Au-Au bonding can be achieved at temperatures only above a threshold value. Results for Au-Au bonding exhibit a critical temperature beyond which no bonding can take place. Above the critical temperature, tensile strength of the Au-Au joint reaches a maximum with increase in bonding pressure.