Extended Reliability of substrate solder joints in power modules

The life time of the solder joint between base plate and ceramic substrate is usually tested by passively heating and cooling the power module (thermal cycling). This provokes delamination in the solder layer. But, the silicon dies in the power module are actively heated in the application. The accelerated life time test simulating this load is power cycling. The modules commonly fail at the end of their life due to bond wire fatigue or cracks in the solder layer between the dies and the substrate. The paper studies the behavior of the substrate solder layer under power cycling conditions with respect to its passive thermal cycling capability. The high number of power cycles is utilized to evaluate the solder life time at low temperature swings. The method proposed is applied to modules with copper base plate and substrate solder containing lead. A comparison with simulation results confirms the applicability of the method. Improved manufacturing technology allows for an increased thermal cycling capability of modules with lead free substrate solder and copper base plates. Experimental results on the thermal cycling capability of modules with AlSiC base plates and lead free substrate solder are presented.