Combined laser beam soldering and welding process for electrical contacting

Due to the increasing power, contacting of high-power semiconductor components requires ever larger cross sections, which can no longer be handled by conventional joining processes such as ultrasonic wire and ribbon bonding. To generate larger cross sections than those that can be joined by an ultrasonic bonding process, an alternative joining method must be selected. Laser beam welding offers the possibility of contactless joining without additional external force. Due to the process, however, a minimum thickness of the lower joining partner is required, on the one hand to prevent a through-weld and on the other hand to reduce the thermal stress for sensitive layers below the lower joining partner. A joining process that can also be used for contacting thin metallizations is laser-based soldering. An advantage of this method is the lower thermal load on sensitive components. However, disadvantages are on the one hand a higher contact resistance at the joining point and on the other hand a poor solderability of some materials (e.g. stainless steel, aluminum) when using a soft soldering process. In the context of this work, first results from the development of a combined laser-based joining process of freely combinable welding and soldering technology are presented. The contacting on a substrate to be soldered is done by means of a tin-plated strip connector and the contacting on the metallized semiconductor is done as laser welding. In both cases, the contact material or the connector is designed as a tin-plated ribbon material. This provides the user with a process with which the connection can be carried out either as welding, as soldering or in a combination of welding and soldering.