Effect of surface treatment on the high-speed drop reliability of Pb-free solder interconnect

This study utilized a solder ball shear test to evaluate the mechanical behavior of Sn-3.0Ag-0.5Cu/Cu and Sn-3.0Ag-0.5Cu/electroless Ni-immersion Au solder joints under high speed loading and hence the drop reliability. The combination of the force-displacement graphs captured from the shear tests and the fracture morphology analysis discloses three fracture modes active in our samples, which include a ductile fracture occurring through the solder (Mode I), a brittle fracture along the interface with intermetallic compound (IMC) layer after some plastic deformation in the solder (Mode II), and a brittle fracture through the IMC layer with almost no plastic deformation (Mode III). Identifying a fracture mode dominant in the samples for different solder joints and shear speeds leads us to conclude that the drop reliability of solder joints is highly related to the morphology of the IMC formed at the interface and the strain rate applied to the joints. These results underscore the utility of the experimental methodology adopted in this study to evaluate the drop reliability of solder joints.