Numerical Investigation of a Novel Lid Design for Automotive HPC Cooling

Thermal stresses caused by CTE mismatches arising from different materials used in electronic assemblies are one of the major causes of mechanical failure in electronics packaging. This problem becomes only more severe in autonomous driving, where high power densities combined with challenging environmental conditions are putting even more extreme thermal and mechanical loads on the package, where strict reliability standarts has to be adhered at all times. Most flip-chip packages that can be used in automotives either include a heat sink directly attached to the flip-chip back side, referred as bare-die packaging, or a lid is attached to the flip-chip to ensure a more reliable TIM interface and better mechanical performance. Here, a modular approach that falls in between is investigated, where the heat spreader is decoupled from the assembly and embedded within the cooler. Compared to lidded packaging, this approach can allow the heat spreader to expand within soft TIMs without limiting the flexibility of the package, offering better mechanical performance. At the same time, it can offer an expanded heat transfer area and heat spreading that can be enhanced with heat pipes. FEA results show the thermal performance and possible improvements of the concept, while initial thermo-mechanical simulations show that using this approach can reduce the shear stresses at the chip-underfill interface, highlighting a possible improvement on thermo-mechanical performance.