A transient method for the accurate measurement of interface thermal resistances

Heat dissipation of active devices has become one of the limiting factors in further miniaturisation. Component manufacturers do succeed in a continuous decrease in the package´s overall thermal resistance, by optimal choice of materials, thinner packages, and the use of heat spreaders. Consequently, the influence of the resistance formed by the interface between device and board, heatsink or cold plate is increasing. Because the theoretical treatment of contact heat transfer is still very difficult, we have to rely heavily on experiments. Literature reveals that most methods that are currently in use are based on steady-state experiments. These are difficult to perform if a high accuracy is required, and they also take a rather long time, typically hours. The paper discusses a transient method which overcomes these problems. The emphasis is on numerical analysis of the proposed method. Various alternatives are investigated, and it is shown that a high resolution can be achieved in a very short time, typically minutes. Based on these results, a prototype has been built. Some preliminary experimental data subscribe to the conclusions originating from the numerical analysis