FE simulation of joint volume effect on fracture behavior of BGA structure Cu/Sn3.0Ag0.5Cu/Cu interconnects under lap-shear loading

Non-linear finite element simulation by an elastic-viscoplastic constitutive model and the experimental characterization were carried out to investigate the volume effect of BGA structure solder joints under shear stress. A solder mask defined flat type copper pad of a circular opening 480 μm diameter and Sn3.0Ag0.5Cu (SAC) lead-free solder balls of 300-760 μm in diameter, were used to fabricate BGA structure Cu/SAC/Cu joints. The shear fracture behavior of BGA joints of different volumes were characterized using a dynamic mechanical analyzer (DMA). Experimental results show that the crack may initiate and propagate at a relatively low shear strain corresponding to the elastic deformation state. Simulation results show that the crack in both viscoplastic and perfect elastic solders may grow by opening mode rather than by shear mode, despite the BGA joints are subjected to shear stress. With increasing the standoff height, the critical nominal shear strain decreases. For BGA solder joints with a certain standoff height, the IMC layer thickness shows only a slight influence on the fracture behavior of the joints. For the predefined crack with a certain location in BGA joints, fracture parameters of the joints with different IMC thicknesses are very close, while for a certain interfacial IMC thickness, the kink angle decreases with increasing the distance of the predefined crack relative to the IMC/solder interface.