A Wafer-Level Sn-Rich Au–Sn Bonding Technique and Its Application in Surface Plasmon Resonance Sensors

Sn-rich Au–Sn solder bonding is systematically investigated. High shear strength (64 MPa) and good hermeticity (a leak rate lower than 1×10^?7 torr?l/s) are obtained for Au–Sn solder with 54 wt% Sn bonded at 310°C. The AuSn₂ phase with the highest Vickers-hardness among the four stable intermetallic compounds of the Au–Sn system makes a major contribution to the high bonding strength. This bonding technique has been successfully used to package the Surface Plasmon Resonance (SPR) sensors. The Sn-rich Au–Sn solder bonding provides a reliable, low-cost, low-temperature and wafer-level hermetic packaging solution for the micro-electromechanical system devices and has potential applications in high-end biomedical sensors.