An Experimental Method to Determine the Effective Thermal Conductivity of Printed Circuit Boards

Abstract

An experimental method to determine the effective thermal conductivity is proposed for flat plates such as Printed Circuit Boards (PCB), using an analytical model with constant boundary conditions. The centre temperature of a heated, horizontally placed (anisotropic) PCB is a function of the thermal conductivities of the various materials constituting the board. By fitting the thermal conductivity of the isotropic analytical model until the centre temperature is equal to the measured centre temperature ensures that this thermal conductivity can be interpreted as the effective thermal conductivity of the considered PCB. Because the analytical solution requires constant and uniform boundary conditions, special attention has been paid to construct the same set of boundary conditions in the experimental set-up. Packing the PCB with a material of which both the thermal conductivity λ and the thickness c are well known guarantees that the unknown and non-uniform heat transfer coefficient a is replaced by a known and uniform quotient λ/c. Packing once more the packed PCB between two aluminium plates, kept at a constant temperature, forces the reference temperature to a constant value. Both the heat dissipation and the temperature measurement were performed via contactless means. The calibration and validation of the device showed a good agreement with known data for PTFE and Glass G291 test samples. The results have been compared with literature data.