Development and demonstration of a laser micro soldering process for cell interconnection
Process throughput of >2000 wafers/h by scanner-based quasi-simultaneous and simultaneous non-contact laser soldering
Experimental studies for identification of relevant thermal and mechanical influence during laser soldering
Development of laser soldering strategies with minimal stress and heat input
Production and evaluation of solar modules using laser-soldered strings
Main Project Achievements The laser soldering process was developed on the basis of two strategies: quasi-simultaneous soldering using galvo scanners for fast beam displacement, and simultaneous soldering using beam shaping optics to achieve a beam focus with the size of a busbar. The first approach led to soldering times of around 10 seconds, due to the comparatively low power of the diode laser used here (500 W). In contrast, the simultaneous soldering process utilized a 3kW laser and achieved one second process time per cell. This is realized by irradiating the copper ribbon on the busbar for 0.5 seconds, which is sufficient to melt the solder alloy and achieve high quality interconnections. With this process a throughput of 3,600 cells/h could be achieved, but this is limited by the capabilities of commercial stringer machine.
Production of 50 strings was conducted using the quasi-simultaneous approach, since module production had to start early in the third project year. Eight modules were prepared and evaluated by standard test procedures at Schott Solar. These modules performed very well and passed the IEC test criteria.