Mechanical Failure of Cu-Sn Solder Joints

The effects of the microstructure on the fracture mechanisms of Cu-Sn intermetallic compounds (IMC) in solder joints under tensile load are studied with numerical simulations. When solder joints are exposed to elevated temperature environments Cu6Sn5 and Cu3Sn nucleate and grow due to the reaction of Cu and Sn, and the fracture strength is degraded. During early stages of the thermal treatment, the Cu3Sn layer of the IMC is thin and composed of a single stack of grains, and the simulations indicate that failure occurs at the Cu6Sn5/Cu-3 Sn interface. After hundreds of hours at temperatures over 150. the Cu3Sn layer thickness grows and is composed of a stack of several grains. Then, failure switches to intergranular fracture inside the Cu3Sn layer. Therefore, the reduction of the fracture strength is a consequence of a transition in the Cu3Sn layer from a single stack of grains to a multi-stacked structure. This structural transition occurs by the reduction of grain size and the growth of the Cu3Sn layer thickness.

Automated summary

The fracture mechanisms of Cu-Sn intermetallic compounds in solder joints are influenced by microstructure. With prolonged thermal treatment, the Cu3Sn layer transitions from a single stack of grains to a multi-stacked structure, leading to a shift in fracture mechanism from interface failure to intergranular fracture.