Modeling noncoplanarity effects on thermal performance of computer chips

A project was undertaken to investigate the effects of noncoplanarity (the absence of perfect surface flatness) on heat transfer in computer chip packages. The goal of the project was to determine the level of model complexity required to accurately determine thermal contact resistance in the presence of non-coplanarity and to determine a method to accurately model these effects using conventional finiteelement and CFD packages. Various types of air gaps were modeled and results tabulated. It was found that heat transfer within gaps on the order of tens of microns could be analyzed by “scaling-up” the model so that minimum cell size of the meshing software was no longer an issue. The scaled and unscaled results agreed to within 97%. Published data and the CFD model results agreed to within 96%. While noncoplanarity was shown to have a significant effect on the thermal contact resistance, it was shown that a complex model of the thermal interface material is not needed for an accurate simulation.