Interfacial Reactions in Ni-doped SAC105 and SAC405 Solders on Ni-Au Finish during Multiple Reflows

Solder-joint performances for SAC405, SAC105 with 200ppm Ni and SAC105 with 500ppm Ni were reviewed for electrolytic Ni-Au BGA pad finish. For each alloy system, ball shear tests, cross-sectional analysis and 3-D etching were performed to study the interfacial reactions after repeated reflows. Also, the effect of solder-mask pad design on solder joint integrity was investigated. In this study, all three systems gave rise to only (Cu,Ni)6Sn5 IMC layer at the soldering interface after multiple reflows at 245degC. The (Cu,Ni)6Sn5 IMC had a needle-shaped structure after 1 time of reflow and the morphology remained the same after multiple reflows. SACN0.05 appeared to be inappropriate for a BGA pad finish. It exhibited a drastic increase in the IMC layer thickness after 11 times of reflow and this corresponded to a significant increase in IMC fracture mode percentage. NSMD pad design led to ball pad lifting because the bonding between the pad and substrate was weaker than the bulk solder strength and the IMC-pad interface bonding.