Self-Propagating Exothermic Reactive Bonding With Cu–Sn Nanocomposite Interlayer for Electronic Interconnects

Stacking multiple components is a crucial technique for integrating power electronics, achieved through reliable bonding techniques. Self-propagating exothermic reactive (SPER) bonding has become attractive for microelectronic interconnections, due to its minimal heat excursion and interventions to components. However, the associated issues of high porosity and solder bleeding undermine its further exploitation. In this article, a unique Cu-Sn nanocomposite interlayer (Cu-Sn NI) consisting of an Sn matrix embraced with Cu nanowire array, was prepared to act as an intermediary for Cu-Cu SPER bonding through initiation and combustion of Al/Ni nanofoils. For comparison, a Sn interlayer of the same thickness was also electroplated for SPER bonding under the same conditions. Both bonded structures were examined in terms of their microstructures and mechanical integrity. The interconnects formed with Cu-Sn NI exhibited significantly lower porosity, less solder bleeding, and higher shear strength than those with Sn interlayer under the same conditions, although both cases demonstrated that the bonding quality of the interconnects could be improved by increasing preheat temperature and pressure. It was evident that the Cu nanowire array embedded in the Sn matrix remained the solid state, serving as a “scaffold” and confined the flow of molten Sn during SPER bonding, hence leading to the more evenly distributed microvoids with much reduced porosity as well as the least solder bleeding.