Cell to Module Loss Reduction and Module Reliability Enhancements by Solder Ribbon Optimization
André Felipe Schneider, Matthias Pander, T. Korvenkangas, Aulehla, S., Rudolf Harney, Horttana, T. · EU PVSEC · 2014
The key for increasing the production yield in state of the art crystalline module production lines is the optimization of the stringing and soldering process. Besides the cell to module (CTM) losses the choice of the appropriate solder ribbon defines the mechanical damage during and after the soldering process in the crystalline silicone solar cell. Soft ribbons with very low yield strength offer a possibility to limit the mechanical stress to a low level during the soldering process leading to less cracks, metallization damages and hot spot risk on cell level. Nevertheless the yield strength has to be addressed in alignment with ribbon thickness and width to achieve lowest possible damages. The aim of this work is to investigate the impact of the ribbons mechanical specification as yield strength and dimension on crystal damage, peel strength and metallization failure after soldering. In order to investigate the impact of additional stress and its effect on electrical performance thermo-cycling (TC) was performed. It was found that with larger yield strength the crystal damage strongly increases coming along with a strong reduction in peel strength and Pmpp. Furthermore the ribbon thickness and width could be identified as key parameters for reducing Pmpp losses during TC testing. Finite element simulations were performed to analyse the internal stresses evolution and gain further insight in mechanism leading to cell damage. These results are aligned with the experimental findings. With the results on hand the module maker can optimize the production process in terms of CTM loss and stress reduction.