To perform a rational thermal design of a printed circuit board (PCB) with highly anisotropic heat transfer nature, effective thermal conductivities in the direction of the thickness and in the plane direction must be given depending on the electric circuit of the board. However, a simple evaluation method for the effective thermal conductivities of the anisotropic board has not been developed yet. In this study, the heat transfer coefficient by natural convection around a horizontal disk has been evaluated, which is indispensable for measuring the effective thermal conductivity.
