To perform a rational thermal design of a printed circuit board (PCB) with highly anisotropic heat transfer nature in its initial stage, effective thermal conductivities in thickness direction and in in-plane direction must be given depending on the electric circuit of the board. However, a simple evaluation method for the effective thermal conductivities of such PCB has not been developed yet. In this study, as the first step to propose a simple evaluation method, the heat transfer coefficient by natural convection around a horizontal disk, which is indispensable for measuring the effective thermal conductivity, has been evaluated. Furthermore, the thermal conductivity of the glass epoxy resin in in-plane direction has been evaluated by applying the evaluated heat transfer coefficient, and then, the validity of the proposed thermal conductivity measurements of the anisotropic PCB has been confirmed.

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