A new void free soldering process in large-area, high power IGBT modules

A new void free process for the solder joint between a chip mounted AlN substrate and a metal substrate in large-area, high power IGBT modules has been investigated. The following new process consists of two steps. First, Ar/sup +/ ions were used to clean the surface of Ni plated films on the metal and AlN substrates by followed by coating with a thin Ag film, and secondly, 50 wt.% Pb-Sn solder sandwiched between the two substrates was heated in vacuum at 503 K for 5 min. and then cooled in a N/sub 2/ atmosphere. Using this process, the area percentage of voids in a soldering area up to 130/spl times/190 mm/sup 2/ can be reduced to less than 0.2%. The fatigue life time of solder joints made with this new method are found to be about 3 times longer than those by the soldering methods in H/sub 2/ (abbreviated as H/sub 2/ process hereafter).