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

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.