Ultrasonic bonding of In/Au and Al/Al for hermetic sealing of MEMS packaging

In this paper the feasibility of ultrasonic bonding for hermetic MEMS packaging has been demonstrated for the first time adopting two different sets of materials; indium-to-gold and aluminum-to-aluminum. The process utilizes purely mechanical vibration energy and enables low temperature bonding between similar or dissimilar materials without precleaning of the bonding surfaces. As such, ultrasonic bonding can be broadly applied not only for electrical interconnection, but also for hermetic MEMS sealing and packaging especially where temperature limitation is a critical issue. This paper describes the ultrasonic bonding and hermetic sealing processes as well as the bonding tool characterization and equipment setups.