Application of the Nonlinear Fracture Mechanics Parameter ΔT* to Wire-liftoff Lifetime Estimation of Power Modules at Elevated Temperatures

Power modules are utilized for electric power control and play a key role in efficient energy conversion. One of the reliability problems in power modules is the wire-liftoff, in which an aluminum wire delaminates from a silicon chip. The wire-liftoff phenomenon is a thermal fatigue failure caused by repeated temperature cycles during the operation of power modules. According to an experimental study, the wire-liftoff lifetime decreases with increase in the maximum junction temperature of a temperature cycle, Tmax, then levels off above 200°C of Tmax. Such a saturation phenomenon of the wire-liftoff lifetime is main concern of the present study. We select the nonlinear fracture mechanics parameter T*-integral range, as a physical quantity describing the wire-liftoff lifetime. The T*-integral range, ΔT*, is only one fracture mechanics parameter that can be applied to thermal fatigue under a cyclic thermo-elastic-plastic creep condition. We perform nonlinear finite element analyses of a power module to calculate the ΔT* based on the mathematical expression of ΔT* for various temperature cycles. As a result, the ΔT* obtained from the exact method based on the mathematical expression of ΔT* is expected to be utilized for quantitative estimation of wire-liftoff lifetime in a wide temperature range of low to high temperatures.