A review on the mechanisms of ultrasonic wedge-wedge bonding

By surveying existing work in the field, several gaps in current knowledge of the bonding mechanisms can be identified: 1) the relative motion behaviors between wire, substrate and bonding tool are uncertain; 2) the exact local temperature increments at the wire/substrate interface and the role of these temperature increments are not known; 3) the oxides removal mechanism is not well understood, mainly due to the nano-size of oxides and the very short duration of the self-cleaning process; 4) the understanding of the softening mechanism is incomplete and the influence of the softening on the substrate has not been examined; 5) the microwelds formation and breakage rates have been analyzed, neither experimentally nor numerically. Filling these gaps has the potential to further enhance the US wire bonding process.