A heat spreading resistance model for anisotropic thermal conductivity materials in electronic packaging

The electronic package structure often comprises of materials that occur in thin layers. In many instances, these materials are lumped. Together as a simplified compact model to represent their thermal performance enabling parametric studies of the package structure. This new compact structure will have a new set of thermal properties that differs from its constituent components. Their combined material properties often display anisotropic thermal conductivity because layers of conductive and less conductive materials results in an orthogonal heat transfer behavior. This paper addresses the analytical and numerical studies of heat spreading in an anisotropic conductivity material with particular reference to the printed circuit boards (PCB). The PCB is considered to be a single material with highly anisotropic thermal conductivity, depending on the distribution of copper planes and thermal vias. The motivation for this study is to determine an appropriate anisotropic spreading resistance formulation that can be used in compact models of electronic packages.