Low temperature crack-less solder bonding technique using self-propagating exothermic nanolayers

In this article, a new low temperature solder bonding technique using Al/Ni exothermic reactive film is described. Al/Ni reactive film is able to generate heat enough to melt SnAg solder film. During the reaction, the volume is definitely shrunk by 12% because of the changes in crystallographic structure and lattice constant. The volume shrinkage yields cracking in reacted NiAl. In this study we focus on the control of crack position and its propagation direction for realizing crack-less solder bonding using Al/Ni exothermic film. A multiple ignitions system to simultaneously start the reaction from several parts was developed. It was demonstrated that major cracks were produced at the portion where two reactions ran into each other. By changing reaction start point, Al/Ni film´s thickness and the overlap width, crack-less solder bonding in 20mm-square silicon chips was achieved.