Knowledge Based Qualification for Thermal Interface Material Reliability

For thermo-mechanical reliability, the difference between the actual use stress and accelerated qualification stress is most apparent in temperature cycling stress due to isothermal large temperature delta applied during temperature cycling vs. non-uniform low amplitude thermal changes in use condition. Power cycling is alternatively utilized to characterize these differences with common industry practice for power cycling is to stress functional devices since it requires to power on and off the components. To overcome the limited failure information that can be learned through functional device stressing, a novel power cycling tool is designed to stress test vehicles with dedicated electrical/thermal structures enabling targeted uniform or non-uniform power to be applied during stress and resulting temperature delta can be accurately measured through dedicated temperature sensors in the chip and package. Data collected with this tool is then compared with calculated acceleration through temperature cycling stress. Comparison shows temperature cycling based life estimations are conservative for thermal interface material degradation estimations. This work also encompassed use condition data collection and finite element modeling to derive the final knowledge-based requirements.