The Mechanism of Dense Interfacial Voids and Its Impact on Solder Joint Reliability

SAC 305 solder joints with ENIG and NiPdAu surface finishes are studied. In general, nano voids in Ni
₂
SnP can be only seen in SAC 305/ENIG but not in SAC 305/NiPdAu. However, when trace amount of impurities are present in NiPdAu, very dense nano voids are observed in Ni
₂
SnP. The voids formation mechanism related to interaction of interfacial impurities and vacancy flux towards the interface has been discussed to explain the observations. BGA ball shear test indicates the dense interfacial voids can degrade the solder joint strength dramatically.