IMC morphology, interfacial reaction and joint reliability of Pb-free Sn–Ag–Cu solder on electrolytic Ni BGA substrate

Abstract

The interfacial reaction, morphology of intermetallic compound (IMC) and shear strength between the Sn–3.5Ag–0.7Cu (in wt.%) solder and Ni ball grid array (BGA) substrates during reflow at 255 °C for up to 20 min were investigated. The reaction between the molten solder and Ni layer resulted in the formation of two IMCs such as (Cu, Ni) 6Sn 5 and (Ni, Cu) 3Sn 4 at the interface. The (Ni, Cu) 3Sn 4 IMCs were needle-like type, while the (Cu, Ni) 6Sn 5 IMCs were cylinders with a hexagonal cross-section and pointed tips. Compared to the quenched sample, the (Cu, Ni) 6Sn 5 IMCs nucleated heterogeneously on the (Ni, Cu) 3Sn 4 layer during the solidification of the solder. In the ball shear test, the shear strength value did not change much as a function of reflow time. In all samples, the fracture occurred in the bulk solder. The results of interfacial reaction and shear test in this study show that the Sn–Ag–Cu/Ni BGA solder joint has a desirable joint reliability.