Fast Liquid-To-Liquid Thermal Shock: Experimental Assessment and Mechanical Model for Plastic Package

In this paper, a liquid-To-liquid thermal shock test is performed on TO-247 packages. By employing liquid with a high heat transfer coefficient as an energy transfer medium, it becomes possible to quickly couple thermomechanical stresses at the module interface. The temperature jump is achieved by maintaining the hot chamber at 150°C and the cold one at-65°C, by immerging the samples in each chamber for 8 minutes. Using ANSYS Mechanical, a numerical model was developed to evaluate the lifetime of the TO-247 under thermal shock test. In addition, this model was also used to compare the lifetime of these packages when a temperature cycle is considered. Experimental results showed differences between cold and hot ramp rate. In more detail, the average ramp rate of the 4 samples in hot environment is about 90°C/s while in the cold one it is about 65°C/s. Difference between heating and cooling rate could be addressed to the temperature effect on fluid viscosity. The numerical results show that the thermal shock test (with a soak time of 5 minutes) anticipates crack initiation compared to the temperature cycle (with the same soak time), suggesting that the difference in accumulation of inelastic work due to fatigue lies in the different ramp rates. A further comparison between two thermal shock was done, decreasing the soak time to 2 minutes, which confirmed the previous results.