Laser welding of copper terminals on ceramic substrates for power module packaging

Abstract:
Today there are a large number of technologies in series available for contacting ceramic circuit carriers. For this application the Laser welding technology has received relatively little attention up to now. Next to the difficulties in welding copper, DCB substrates are especially sensitive to welding depth variations and thermal shock. Within this report, the basic feasibility of this technology was examined and evaluated with the help of reliability tests. A comparison of different laser sources showed that for the here used application both a green laser sources (515 nm) and an IR fiber sources (1070 nm) with a small spot sizes can be used to establish reliable connections. The core criterion for evaluating the welded joint was the absence of cracks after the laser process and after the reliability test (PC, TCT). Here, the absence of cracks after 500 TCT could be demonstrated for both Al2O3-DCB substrates and Si3N4-AMB substrates. In the same time, it was possible to achieve tensile strength of the welded connections that exceeded the strength of the terminal itself. With the lasers used here, welding of DCB substrates is feasible. Crack-free, reliable and strong connections are possible.