In-situ-X-Ray investigation on pressure release during conventional and diffusion soldering

The need for higher operating temperatures in power electronics is driving the research and development on alternative technologies to conventional soldering. One of them is diffusion soldering. Khaja et al. proposed a new approach by printing very thin layers of solder paste. This approach requires a special soldering process to reduce the void content to an acceptable value. Vacuum soldering and overpressure soldering were shown to be appropriate processes [2], [3]. This work investigates both process types with In-situ-X-Ray-analysis. We showed that overpressure reduces the outgassing of voids significantly whereas negative pressure accelerates it. This can be explained by Le Chatelier´s principle. Furthermore we showed that the solder joints should be cooled immediately after the pressure was reapplied in order to achieve a low void content. The analysis of single voids before and after the pressure change proves that they change their volume according to the ideal gas law. As result of our investigations we conclude that vacuum soldering processes are more suitable for diffusion soldering than overpressure processes.