Sn-rich Au-Sn hermetic packaging at wafer level and its application in SPR sensor

Sn-rich Au-Sn solder bonding has been systematically investigated for low cost and low temperature wafer-level hermetic packaging of high-end MEMS devices. The AuSn₂ phase with the highest Vickers-hardness among the four stable intermetallic compounds of Au-Sn system makes major contribution to the high bonding strength. The maximum shear strength of 64 MPa and a leak rate lower than 1 × 10^-7 torr·l/s have been obtained for Au46Sn54 solder bonded at 310 °C. This bonding method has been successfully used to package the SPR sensors, and dramatically simplifies the sensor structure and fabrication process. The bonding results indicate that the Sn-rich Au-Sn solder bonding has provided a reliable, low-cost, low temperature, wafer-level hermetic packaging solution for MEMS device and has potential applications in high-end compact biomedical sensors.