Metallurgical Behavior of Au/Al Bond Interface during High Temperature Storage of Ultrasonic Wedge Bonding

Ultrasonic wedge bonding, which can be done at room temperature, is widely used in microelectronic package. It is primarily used to bond either Al wire or Au wire. After bonding and aging, the joint cross-section of 25mum Au wire bonded on Al metallization pad was analyzed by SEM with EDX. It is found that, there was evident diffusion of Au and Al, and Au₅Al₂ intermetallic compound (IMC) formed first after aging for 10 days at 200 degC in atmosphere, and there was also some Au₂Al formed at the edge of the interface. After aging for 20 days, the IMC developed slightly, and also Kirkendall voids generated at the interface. After aging for 30 days, the IMC began to transform to other Au-Al IMCs, and it became Au₂ Al IMC finally after aging for 40 days