Influence of tool edge angle on the bondability of aluminum in ultrasonic bonding

A transitional stage in the relative motion was confirmed through in-situ observation using a high-speed camera and digital image correlation. In the earlier bonding time within the first 20 ms, relative motion predominantly occurred between the bonding materials, resulting in the formation of an initial bond at the bonding interface. The initial bond developed toward the vibration direction with increasing bonding time. The formation of a larger bonded region was observed at larger edge angles, resulting in greater joint strength. In the latter stage of bonding time beyond 50 ms, the relative motion between the tool edge and the bonding material became predominant because of bond formation at the bonding interface. The relative motion between the bonding tool and the bonding material caused macroscopic plastic flow in the bonding part when larger edge angles were used, leading to the observed increase in joint strength. The enhancement of bond creation at larger edge angles is discussed on the basis of finite element analysis focusing on the change in stress distribution at the bonding interface with the penetration of the tool edge.