Finite element simulation of fracture behavior of BGA structure solder interconnects

The influences of the standoff height (H), contact angle (θ), pad size and loading rate on shear fracture behavior of BGA structure Cu/Sn-3.0Ag-0.5Cu/Cu joints were investigated by finite element (FE) method. The simulation results show that the maximum Von Mises stress zones locate on the edge of the solder near the intermetallic compound (IMC) layer in the BGA joint under shear stress, the cracks are more prone to initiate in the zones and this has been proved by the experimental observation. The standoff height and contact angle have slight influence on the value of the maximum Von Mises stress, while significantly affecting the size and location of the maximum Von Mises zones. Contrast with the standoff height and contact angle, the maximum Von Mises stress increases with the increase of the loading rate. Moreover, the simulation results show that cracks may more easily propagate along the IMC layer with decreasing h and θ, according to the criterion of maximum energy release rate. Furthermore, the crack tip stress intensity factors (SIFs) were calculated to estimate the fracture mode. It has been shown that SIFs are significantly influenced by the standoff height while being slightly affected by the contact angle and loading rate, and K_I is always higher than K_II regardless of the standoff height and contact angle of BGA solder joints. This may mean that for BGA joints subjected to shear stress the fracture or failure of BGA joints may dominantly occur by mode I (i.e., opening mode).