Extension of the process boundaries for the soldering of elongated interconnectors with a simultaneous energy deposition

Soldering processes are used to bond elongated interconnectors to metallized silicon wafers, e.g., for the production of solar cells. In order to obtain a cost-effective production cycle, a minimal process time is required. The minimal process time is expected to be limited due to the thermoshock induction in the substrate, the required time for the energy deposition, and the wetting process of the solder. The simultaneous energy deposition realized with a diode laser and a line generating optic lowers the process time for interconnectors with a joining length of 140 mm below 1 s. Furthermore, the selective energy deposition on the interconnector is expected to reduce the temperature-induced stress in the substrate. We evaluate the soldering process with a high-speed camera and compare them with the characteristic temperature profile measured with a pyrometer. Different process times and the effect of short-term overheating to reach process times below 0.5 s are investigated. The minimum process time is assessed regarding the development of the process stages and the effect on the solder quality.