Reliable packaging technologies for power electronics: Diffusion soldering and heavy copper wire bonding

Production of a reliable power module capable of achieving higher switching frequencies and higher junction temperatures is limited by the present assembly and packaging methods, mostly in the areas of the die-attach and the top level interconnections. The present study aims to display the advances in packaging technologies of diffusion soldering and heavy copper wire bonding in the view of material characterization, process optimization and quality improvement. In diffusion soldering, the growth of intermetallic phases through thin-layer paste deposition and solder profile optimization with vapor phase soldering were investigated. Solder paste inspections were performed to evaluate the errors during deposition process for thin layers and influences on soldering process and related post-failure modes. In heavy wire copper bonding, the impact of substrates with a mechanically polished surface of reduced roughness was investigated. Furthermore the influence of applying the bond force in a ramp style was examined and inspected with the pull and shear forces. The bond width was also monitored in order to receive a non-destructive quality feature for the process monitoring. All test series were accompanied by a close control of the tool wear-out and its influence on process stability.