Investigation of the melt dynamics during the laser impulse metal bonding process with keyhole measurement

The laser welding process requires a comparable aspect ratio between the material thicknesses of joining partners due to the penetration depth and the high energy absorption. The high energy absorption during the joining process is commonly not tolerated for the sensitive PCB-substrates below the joining partners. However, the Laser Impulse Metal Bonding (LIMBO) process enables a laser based weld joint between an interconnector and a metallization on sensitive substrate. The main approach is the spatial separation of both joining partner combined with the temporal beam modulation for the energetic separation between the melting and the joining phase. Consequently, a low penetration depth is achieved and the laser welding process is applicable for the interconnection and packaging of power electronic devices. In this paper the keyhole depth during the LIMBO process is investigated with an optical coherence tomography. Subsequently, a correlation between the keyhole depth and penetration depth during the LIMBO process is further investigated.