An Estimation of Thermal Stress of Thermoelectric Devices in the Temperature Cycling Test

The life of TE device is defined as the number of temperature cycles when its electrical resistance increases by a certain percent over the initial value. The cause which decides this life is the thermal stress that affects the joints between the substrates and the dice. Usually Ni barrier peels off most frequently from the surface of a corner die. It is obvious that the thermal stress is determined by temperature difference, coefficients of thermal expansion, die height, die cross section, substrate size and so on. However, there were not explicit relations among these parameters. Assuming that the clamping force is large enough to prevent the bending of TE device under test, and the rigidity of the substrate is much larger than that of dice, the thermal stress of the corner die where the stress is most severe is estimated approximately. Although the obtained relation is no more than the first order approximation, it seems it can be a guide for the reliability design judging from the result of verification tests.