Nonlinear thermal analysis of a rectangular diamond IIa heat spreader used for microwave power devices

We present a nonlinear thermal analysis for a rectangular diamond IIa heat spreader used for microwave power devices. The Kirchhoff transformation is used to take account of temperature dependent thermal conductivity. We point out what we believe to be errors in an analytical approach applied to the same problem published by Batchelor and Postoyalko (Proc. Roy. Soc. London, vol. A445, p.375, 1995). A comparison study with the case of circular spreaders indicates that for the same spreader thickness and cross-sectional area, a 2D circular model can be used to obtain the upper limit of the thermal behaviour for square spreaders within 3% errors.