This paper describes a measurement method for the in-plane thermal conductivity of Printed Circuit Boards (PCBs). We designed two types of PCBs with several wiring patterns on their surfaces. This means copper amount on the PCBs is different. We measured their effective thermal conductivity in thickness direction to investigate the effects of the wiring patterns on the in-plane thermal conductivity of the PCBs. One is normal PCBs and the other is about 18 times larger PCBs than the normal PCBs. The experimental results showed that the thermal conductivity of normal PCBs was not dependent on the wiring patterns. On the other hand, the thermal conductivity of larger PCBs increased with increasing amount of copper wire due to the heat diffusion in in-plane direction by copper wires. We concluded that the effect of the wiring patterns on the in-plane thermal conductivity can be observed with our measurement method. We also performed Computational Fluid Dynamics (CFD) analyses and clarified the correlation between amount of copper wire and in-plane thermal conductivity of the PCBs.
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