Module-Level TIM Degradation in HALT

In this study, TIM degradation is driven through HALT using temperature cycling and random vibration for two commercially available materials providing thermal conductivities of 6.5 and 8.0 W/m-K. HALT specimen were prepared by applying TIM through a 4-mil stencil over AlSiC baseplates in the shape of those used in Wolfspeed CAS325M12HM2 power electronics modules. Baseplates were mounted onto aluminum carrier blocks with embedded thermocouples to characterize the thermal resistance across the baseplate and TIM layer. Thermal dissipation into the top of the baseplates was provided by a custom heating block, which mimics the size and placement of the die junctions in CAS325 modules, applying power loads of 200, 300, and 400W. After initial characterization, samples were transferred to the HALT chamber with one set of samples exposed to temperature cycling only (TCO) and the other temperature cycling and vibration (TCV). Both sample sets were cycled between temperature extremes of −40 and 180 °C with random vibrations applied at a peak acceleration of 3.21 Grms. After hundreds of cycles, samples were reevaluated to assess changes in thermal resistance to provide an accelerated measure of TIM degradation. This will allow for reliability calculations of useful lifetime, provide a basis for developing accelerated testing method to related temperature cycling to faster methods of degradation, and additionally provide a means by which to develop a maintenance schedule for servicing the power modules which will enhance cooling and lifetime operation.