Wire bonding degradation induced by temperature gradients under active cyclic loading

It is well known that high temperature storage can degrade wire bonding contacts significantly due to interdiffusion of pad metal and bonding wire. Looking at harsh applications such as engine management we notice an additional failure mode caused by the temperature gradient during the pulsed active cycling period. Especially when we aim at components with high temperature capability and we substitute the power aluminium metallisation with power copper in order to avoid the formation of lifetime limiting intermetallics, the degradation of wire bonds (Au, Al, Cu) must be assessed with respect to the electrical pulse width, the dissipated power and the number of active cycles, which can exceed 500 millions in automotive applications. This paper presents experimental data with different temperature stress. The time dependent temperature distribution in the device is determined with an electrothermal simulator (TESI). The calculated temperature gradients will be used to enable a thermal-mechanical simulation (ANSYS). As a result a prediction, which kind of pulses can reduce the lifetime of the components under investigation, should be possible.