Experimental and finite element analysis of the shear speed effects on the Sn–Ag and Sn–Ag–Cu BGA solder joints

An experimental investigation was combined with a non-linear finite element analysis using an elastic–viscoplastic constitutive model to study the effect of ball shear speed on the shear forces of BGA solder joints. Two solder compositions were examined in this work: Sn–3.5Ag and Sn–3.5Ag–0.75Cu. The Cu substrates had been surface finished electrolytically with a 7 μm thick Ni diffusion barrier followed by an 0.5 μm thick Au layer to enhance solderability. Ag3Sn and a few AuSn4 intermetallic compound (IMC) particles were found inside the two solders. Only a continuous Ni3Sn4 layer was observed at the interface between the Au/Ni plated layer and the Sn–3.5Ag, while a continuous (Ni1−xCux)3Sn4 layer and a small amount of discontinuous (Cu1−yNiy)6Sn5 particles were formed at the interface between the substrate and the Sn–3.5Ag–0.75Cu. The IMC was identified using energy dispersive spectrometer (EDS) and electron probe micro analysis (EPMA). Shear tests were carried out over a shear speed range from 10 to 700 μm/s at a shear ram height of 50 μm. The shear force was observed to linearly increase with shear speed and reach a maximum value at the highest shear speed in both the experimental and the computational results. All test specimens fractured in a ductile mode. The failure mechanisms were discussed in terms of von Mises stresses and plastic strain energy density distributions.