The introduction of new packages as well as the ongoing miniaturization in SMT make the evaluation of the reliability of solder joints a permanent task. Passive thermal cycling is an important test to evaluate the lifetime of solder joints. However, tin-lead solder behaves viscoplastically. Therefore it is mandatory to take the metallurgical behaviour of the solder into account when accelerated tests are designed. Two different deformation mechanisms occur, depending on the temperatures of the test as well as the temperature gradient: Grain boundary sliding (GBS) and dislocation climb (DC). Therefore, one is not free in choosing the parameters of a testcycle because test parameters (temperature ramp, dwell time) have a major influence on the growth of cracks. Furthermore the stress under service conditions must be taken into account.