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Abstract
Thermosonic ball bonding is widely used in interconnections to integrated circuits. This work used a thermosonic bonding machine and a shear tester to study the effects of preload, preheat temperature, ultrasonic power, welding time, and wire diameters on shear force. The results reveal that shear force of thermosonic wire bonding can be elucidated from the viewpoint of interfacial microcontact phenomena such as energy intensity, interfacial temperature, and real contact area. As the energy intensity is increased, the shear force increases, reaches a maximum, and then decreases. The energy intensity at which the shear force reaches maximum is called the saturated energy intensity. After saturation (that is, the establishment of maximum atomic bonds), any additional energy input will damage the bonding, decreasing the shear force. The saturated energy phenomenon can be further confirmed by using wires with different diameters. It is also observed that the saturation phenomena, and thereby the optimal shear force, occurs under a certain range of interfacial temperature.