A Method to Detect Defective Solder Joints by RS-Electroluminescence Imaging

Abstract

The tabbing step is a critical process step in module manufacturing. Defective solder joints lead to an increased series resistance, a lower fill factor and to mechanical stability problems. Out of several image-based methods, such as PL, PL-j0, EL, ReBEL, RS-EL, LBIC, DLIT and ILIT (all discussed in [1]) we investigate the potential of RS-electroluminescence as a non-destructive method to detect defective solder joints. This series resistance imaging method is based on the work of Haunschild [2]. The idea is to map the local series resistance of an interconnected solar cell with the help of a high and a low voltage EL-image. The potential of the method is demonstrated on a standard solar cell and on a MWT solar cell. For that matter we produce defined soldered interconnections on solar cells where we vary the parameters soldering force, soldering time and tabbing cell temperature during the tabbing step. The RS-EL method on these samples shows that defective solder joints can be detected and localised so that a spatially resolved quality control of the interconnection process becomes possible.