Thermal Excursion Can Cause Bond Problems

The purpose of this paper is to illustrate the failure mode caused by thermal deformation and how thermal deformation affects bond integrity. Wedge bonding in small-signal transistors, microcircuits and LSI circuits is the subject of this work. Repeated switching of the devices between high and low power at a rate that allows thermal expansion and contraction in the interconnecting wire causes the wire to flex at the point of reduced cross-sectional area until finally the wire breaks due to metal fatigue. It was observed that the thermal deformation was related to many factors such as device power dissipation, current density in the wire, wire dress and length, thermal time constant and frequency of operation.