Microstructure investigation of Sn‐0.5Cu‐3.5Ag and Sn‐3.5Ag‐0.5Cu‐0.5B lead‐free solders

Identifies the intermetallics formed in Sn‐0.5Cu‐3.5Ag and Sn‐3.5Ag‐0.5Cu‐0.5B (wt%) lead‐free solders, and the influence of boron on these precipitates. SEM, TEM and SIMS were employed to reveal the difference of microstructure in both solder alloys. It was found that the intermetallics formed were Ag₃Sn and Cu₆Sn₅. Both solders were found to have a dispersion structure of Ag₃Sn particles with network‐shaped subgrains. The microstructure of Ag₃Sn was also found to become finer and more uniform in Sn‐3.5Ag‐0.5Cu‐0.5B solder, due to the addition of boron, while there was little effect from the boron on the Cu₆Sn₅ phase.