Failure study of Sn-Ag-Cu lead-free solder joint by digital image speckle analysis (DISA)

Failure analysis of lead-free solder joints for PBGA assemblies subjected to thermal cycling aging is reported. A micro-digital image speckle correlation system (Micro-DISC) was employed for micro-deformation and strain analysis. The Sn-3.8Ag-0.7Cu (SAC) soldered assembly was subject to a temperature ramp from room temperature of 25 /spl deg/C to 125 /spl deg/C. The growth of interfacial IMC compounds and the interfacial voids/crack formation between SAC ENIG surface finish were observed on all the solder joints and correlated with effect of stress. It is noted that IMC layer thickness at different locations are different after 3000 thermal cycling aging. The highest IMC layer thickness was observed at the outermost solder joint. The formation of void/crack and the failure site agrees with the strain field measured by DISA technique.