A wafer-level Sn-rich Au–Sn intermediate bonding technique with high strength

Sn-rich Au–Sn solder bonding has been systematically investigated for low temperature wafer-level hermetic packaging of high-end micro-electro-mechanical systems (MEMS) devices. 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. A maximum shear strength of 64 MPa and a leak rate lower than 4.9 × 10⁻⁷ atm-cc s⁻¹ have been obtained for Au46Sn54 solder bonded at 310 °C. In addition, several routines have been used to effectively inhibit the solder overflow and preserve a good bonding strength and water resilience: producing dielectric SiO₂ structures which do not wet the melting solder to the surrounding bonding region, reducing the bonding pressure, and prolonging the bonding time. This wafer level bonding technique with good hermeticity can be applied to MEMS devices requiring a low temperature package. (paper)