Mechanical Reliability of Sn-Ag BGA Solder Joints With Various Electroless Ni-P and Ni-B Plating Layers

Abstract

The mechanical reliability of Sn-3.5 wt.%Ag solder joints with four different electroless Ni plating layers [Ni-1B, Ni-3B, Ni-7P, and Ni-10P (in wt.%)] was investigated as a function of aging time up to 60 days at 150° C. The ultimate shear stresses for fracture were higher in the ball shear tests when using Ni-B samples than those with Ni-P metallization if the aging treatment at 150° C was shorter than 15 days, and vice versa when the aging time was higher than 45 days. In all the joints, Ni3Sn4 intermetallic compounds (IMCs) were formed at the interfaces. The thickness of the IMC layer increased with decreasing B or P content, i.e., increasing Ni content. The reaction rate between the Sn-Ag solder and Ni-P was slower than that between the Sn-Ag solder and Ni-B. In the shear test, the failure mode switched from a bulk-related failure (ductile fracture) to an interface-related failure (brittle fracture), depending on the aging time. After prolonged aging treatment, weak solder/Ni3Sn4 interfaces led to a failure mode of brittle fracture for all the solder joints, due to the formation of thick Ni3Sn4 IMCs. The failure for the Sn-Ag/Ni-B joints was more abrupt and brittle due to the formation of the thick, interfacial Ni3Sn4 IMC. The results demonstrated that the Sn-Ag/Ni-P joint was more reliable than the Sn-Ag/Ni-B joint from the viewpoints of interfacial IMC thickness and long-term mechanical reliability.