Effect of processing on the microstructure and fracture of solder microbumps in 3D packages

Solder microbumps are receiving increasing interest due to their application in 3D-packages which facilitate the miniaturization of electronic devices. The reliability of microbumps during a drop event is of great concern because of their large proportion of intermetallic compounds (IMCs) which are of brittle nature. In this paper, the growth kinetics of IMCs in solder joints were analyzed. Compact mixed mode (CMM) samples with an adhesive solder joint between Cu substrates were used to simulate microbumps for evaluation of the fracture properties. The effect of IMC proportion, strain rate, and mode mixity on fracture toughness were investigated. It was found that with increasing aging, the IMC proportion increased, leading to lower fracture toughness and more brittle fracture. In addition, the fracture toughness decreased with increasing strain rate and mode mixity.