Thermal stresses and fatigue in silicon power rectifiers

Simple relations are derived for the approximate calculation of thermal stresses and strains. With these relations some considerations on the cracking of silicon are given and the mechanical fatigue endurance of hard and soft soldered devices is assessed. Results of the calculations agree reasonably well with observed fatigue properties. Measurements show only slight changes of electric characteristics by mechanical stresses. An increase of solder thickness at the base might improve the fatigue performance of soft soldered devices. A fatigue test for solders is proposed.