Component size and effective thermal conductivity of printed circuit boards

Numerical solutions of the three-dimensional heat conduction equation were used to study variation of the effective thermal conductivity of printed circuit boards (PCBs) with component size. Solutions were obtained for two PCB thicknesses, three numbers of internal copper layers, and different size components. Cases with and without a copper layer on the component side were investigated. It was shown that the effective thermal conductivity of a PCB with/without a copper layer on the component side would be larger/smaller than the values given by the one-dimensional effective thermal conductivity model if the components mounted on the PCB were smaller than the PCB itself. The difference was more pronounced for smaller components. Correlations were obtained for the effective thermal conductivity of PCBs.