Calculation of thermal stresses during the soldering of solar cell strings

The soldering of solar cell strings is a critical step in the production of photovoltaic modules. Mechanical load and temperature induced stresses can cause cracking in the cells. Five different soldering techniques were investigated by numerical simulation to find a suitable technique and to optimize the process control. For different methods of mechanically coupling the heat source it was found that highest stresses were induced by a beam bit soldering technique using a fixed process time. Using a radiative heat source with a uniform preheating stage, as in an automized continous process, stresses were reduced by more than 50% and the process time by 60%. Comparing this radiative heating technique to a moving point heat source process there is a 35% reduction in stresses and a 93% reduction in process time. The used simulation model is readily applicable to different soldering techniques. It can both identify the specific weak point of different techniques and optimize the process control