Transient thermal contact resistance in a diode heat-sink assembly

An infrared thermal imaging system is used to record developing temperature distribution on a diode heat-sink assembly. The quality of contact of a mechanical joint formed by a diode baseplate and a heat sink is determined in terms of instantaneous contact conductance, hi. The results of instantaneous contact conductance are compared with the corresponding steady-state results obtained in an earlier investigation. The results are presented for three different conditions of the interface. These conditions are (i) the mating surfaces are bare, (ii) aluminum foil is inserted between the mating surfaces and (iii) a high thermal conductivity grease is applied to the mating surfaces. Two levels of contact pressure are used for the interface with the aluminum foil. The results indicate that the power input to the diode heat-sink assembly and the condition of the interface determine the duration of transient analysis needed to closely approximate the parameter of interest in the steady-state condition. In all the interface conditions studied and at high power input to the diode heat sink assembly, it took only 45 min from the cold start to obtain a variation of less than 10% between the instantaneous and corresponding steady-state values.