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Board-Level thermal management systems with application in electronics and power electronics

In this study, heat removal and thermal management solutions for electronic devices were investigated at board-level. The generated heat at an electronic chip, installed on a printed circuit board (PCB), can be dissipated either through a heat sink, that is attached directly to the chip, or can be transferred through the PCB to the other side and then be dissipated to the ambient. In any case, thermal interface materials (TIMs) should be used to reduce the thermal contact resistance (TCR) at the solid-solid interface, and also to electrically insulate the live electrical component from the heat sink which is normally exposed to the ambient. Graphite, due to its low cost, lightweight, low thermal expansion coefficient, high temperature tolerance, and high corrosion resistance properties is shown to be a promising candidate to be used as a TIM. In this study, a new analytical model was developed to predict the thermal conductivity of graphite-based TIMs as a function of pressure applied during the production, and flake mechanical properties. The model was verified with the experimental results obtained from testing multiple graphite-based TIM samples. Transferring the heat to the back of the PCB could potentially provide more surface area for the heat transfer, as normally the backside of PCBs is less populated compared to the front side. However, this comes with its own challenges, due to the low thermal conductivity of the FR4, the main material used in the PCB composition. Thermal vias, which are copper-plated through holes, are proposed as a solution, since they can provide a thermal bridge for heat. A new analytical model was developed for predicting the enhanced thermal conductivity of PCBs equipped with thermal vias. The results were validated by the experimental data obtained from testing nine PCB samples. Effects of vias diameter and their arrangement on the thermal performance were investigated. The results indicated that by using staggered arrangement of thermal vias with larger diameters, the effective thermal conductivity of the PCB can be improved.