A novel approach to extract effective thermal properties of substrate in IC packages

Substrate is a critical component in an IC package. The thermal properties of a substrate must be accurately evaluated when developing IC packages. The very heterogeneous nature of substrate, consisting of highly conductive metal layers, thermally poor dielectric, layer-by-layer stack up, and vias between metal layers, poses many challenges to such thermal evaluations. This paper reports a novel approach to accurately compute effective thermal properties of a substrate. The approach starts with a component-level 1-D heat conduction model in each direction of a substrate with detailed design. The effective thermal conductivities of the substrate are extracted by applying Fourier's law and principle of thermal resistance network to the 1-D heat conduction problem. The extracted effective thermal conductivities are then verified at package-level simulations. A same package, first with the detailed substrate and then with the compact substrate (built with the extracted effective thermal conductivities), is simulated in turn for their respective junction-to-board thermal resistances. The agreement of the two thermal resistances immediately indicates the accuracy of the effective thermal conductivities. The approach has been validated and shows good accuracy. The proposed approach can be confidently adopted to predict thermal performance of laminate packages.