Damage behavior and life prediction for lead-free solder joints in a CSP assembly under thermal cycling

Finite element modeling (FEM) was applied to investigate the reliability of solder joints in a chip scale package (CSP) device mounted to a printed circuit board (PCB). The stress/strain field distribution on solder joint interface zone as well as the failure mode of solder joints subjected to thermal cycling was analyzed. A unified viscoplastic constitutive model was used to describe the deformation behavior of SnAgCu solder joint, and the solder joint life was predicted based on solder joint reliability analysis. For finite element analysis, submodel method was adopted, and the life model parameters were obtained by element volume-averaged technology during general postprocessing. The results showed that, the accumulated plastic work density for solder joint increased with the increase of the number of thermal cycles. The failure mode exhibited as that failure site was close to solder/intermetallic compound (IMC) interface, and the thicker the IMC layer, the more accumulated plastic work damage per cycle in the solder joint. These results demonstrate that EVIC impacts solder joint life, and the bond at interfacial IMC/solder interface is most vulnerable to thermofatigue damage.