Three-dimensional finite element analysis of mechanical and fracture behavior of micro-scale BGA structure solder joints containing cracks in the intermetallic compound layer

In this study, a parametric study of the stress intensity factors (SIFs, KI and KII) at the crack tips of predefined cracks in the IMC layers of ball grid array (BGA) structure joints was performed using linear elastic fracture mechanics (LEFM) method through finite element (FE) simulation. It has been shown that the crack driving force KI is much larger than KII regardless of the crack length, contact angle of BGA solder joints, loading rate and the position of the crack. A long crack leads to an obviously value of both KI and KII under both shear and tensile loading modes. Moreover, a crack located much closer to the SAC/IMC interface would be more easily to propagate owing to higher KI and KII values at the crack tip. The change of the loading rate has an obvious influence on both KI and KII, a faster loading rate induces higher SIFs at the crack tip; while the change of the contact angle only has slight influence on both KI and KII. In addition, the effect of symmetric displacement cycling on the reliability of BGA solder joints was also analyzed. Calculation results show that the SIFs in the crack tip show almost no difference with the increase of cycle numbers. However, the plastic strain in the solder near the SAC/IMC interface will increase continuously under symmetric displacement cycling loading.