Effect of remelting heat treatment on the microstructure and mechanical properties of SnBi solder under high-speed self-propagation reaction

The heat source based on the self-propagation reaction of Al/Ni thin foil has the characteristics of concentrated heat, fast temperature rise/fall rate and small heat-affected zone; it can complete the melting and solidification crystallization of solder within milliseconds to realize solder interconnection, which can solve the problems of damage to heat-sensitive materials and components caused by monolithic heating of package structure. However, due to the highly non-stationary interconnection process, the resulting microstructure morphology may affect the service performance of the interconnected joints. In view of this, to investigate the post-solder microstructure of solder based on the self-propagation reaction, this paper analyzes the effect of the initial microstructure on the post-solder microstructure by heating 300-μm-thick SnBi solder with a 40-μm Al/Ni thin foil. The results indicated that the short melting time could resulted in the incomplete melting of heterogeneous phases and the non-uniform distribution of elements during the melting process, which had a significant effect on the morphology and composition distribution of the solidified microstructure, as well as the hardness distribution of the melted zone. The above conclusions have the potential to improve the interconnection process based on the self-propagation reaction, which is critical for both theoretical guidance and engineering application.