Investigations on the mechanisms of ultrasonic wire bonding

As a longterm and widely applied interconnection technique, the mechanisms of ultrasonic wire bonding are still not clear. In this dissertation, the relative motion at the two interfaces was first captured by a highspeed observation system and quantified. It was found that the relative motion is caused by both continuous plastic deformation and vibration. As the process goes, the vibration induced relative motion at the wire/substrate interface becomes more constrained due to the formation of microwelds while the relative displacement at the wire/tool interface increases. The oxide removal process was then analyzed via metalglass bonding with coated and noncoated wires. A complete removal process consists of four steps – cracks, detachment, milling and transport. Transport is driven by four mechanisms including penetration, oxide flow, pushing and metal splash. The energy flows during wire bonding processes were finally quantified. The results show that most energy flows to the vibration induced friction at the two interfaces and the vibration induced microwelds formation, deformation and breakage.