Novel transient liquid phase bonding through capillary action for high-temperature power devices packaging

A novel transient liquid phase (TLP) bonding was achieved by using a hybrid solder preform containing porous Cu interlayer, which was prepared by compacting a thin layer of Cu powders with Sn foils. This method combines the advantages of the conventional TLP bonding and sintering, and it can accelerate the reaction rate, suppress the voids formation, and be performed with lower pressure. During bonding process, liquid Sn on the two interfaces flows rapidly into the gaps between neighbored Cu particles through a strong capillary action, resulting in the densification of the microstructure. The TLP process can be accomplished at a temperature of 250 °C within 20 min, sequentially producing a high heat-resistant joint, which is comprised primarily of Cu-Sn intermetallic compounds (IMCs) matrix and dispersive Cu particles. In this study, the microstructure evolution, mechanical property, thermal reliability, and the effects of Cu particle size and morphology on the bonding process were investigated systematically.