Effect of the Second-Phase Particle Distribution on the Brittle Fracture Behavior of Sn-3Ag-0.5Cu Solder

The low-temperature impact test was used to examine the fracture morphology of Sn-3Ag-0.5Cu (SAC305) solder. The second-phase distribution of Ag 3 Sn and Cu 6 Sn 5 particles on the grain boundary of SAC305 solder was obtained using a nanometer-scale focused ion beam and observed using a transmission electron microscope. The results show that as the temperature drops, the fracture mode of SAC305 solder shifts from ductile to brittle, and that the fracture mode is primarily influenced by crystal morphology. On the grain boundaries of the crystal, a large number of Ag 3 Sn particles and fewer Cu 6 Sn 5 particles are discovered. The compositional analysis of the nanometer-scale fracture morphology reveals that the majority of the Cu elements are dispersed in the Sn matrix. The phase diagram and Sn activity help to understand this occurrence. The inhibitory effect of Ag on the creation of Cu compounds is further discussed, which not only promotes the connection between the soldering material and the Cu solder disc, but also reduces the fracture problem produced by the Cu 6 Sn 5 second-phase particles.