When a high-power electronic component is mounted in the electronic equipment, temperature of the component needs to be estimated and properly controlled. When the heat is transferred to the housing of the electronic device by means of contact, it is necessary to estimate the thermal contact resistance at the contact surface between the component and the housing, because the thermal contact resistance determines the temperature of the component. Therefore, estimation method of thermal contact resistance is required. In general, theoretical equation proposed by Tachibana and Sanokawa is used for estimating thermal contact resistance of uniform contact surface. This equation was derived based on the shape and the thermal conductivity of real contact point at the contact surface and considers an additional thermal resistance caused by the constriction and the expansion of heat flow area when the diameter of real contact point is 60 μm. Given the above fact, the estimation error occurs if the condition of real contact diameter deviates from the value of 60 μm. In this study, we derived a prediction formula for the thermal contact resistance including the additional thermal resistance that varies with the diameter of the real contact point. The prediction results by means of the derived formula agreed well with a thermal analysis. Additionally, we discovered that a ratio of the thermal contact resistance and the thermal resistance of an air layer is exclusively determined by a dimensionless parameter composed of the shape of real contact point, thermal conductivity of material, etc. This finding was also demonstrated by the thermal analysis and the experiment.

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