Abstract: The Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu solder joints were fabricated by the ultrasionc wave (USW) and the electric field (E) assisted soldering technique. The microstructure and mechanical properties of solder joints were analyzed by the scanning electron microscope (SEM), the energy dispersive spectrometer (EDS) and the X-ray diffraction (XRD). The Results showed that the USW or the USW-E have great influence on the microstructure of the solder joints. The USW or the USW-E assisted soldering technique not only can refine microstructure of the Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu solder joints and promote the proportion of eutectic structure, but also can reduce the average thickness, the roughness and the grain size of interfacial IMC. The shear strength of the Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu soldering joints under the USW-E assisted soldering is closely related to the roughness of interfacial IMC layer. The USW played an important role in the decrease of the roughness of the interfacial IMC during the USW-E assited soldering. Compared with shear strength of the traditional soldering joints, a 24.1% increase of shear strength of the soldering joints was achieved with the USW-E assisted soldering. With applying the USW or the USW-E, the fracture path of the Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu soldering joints was transferred from the interfacial transitional region composed of soldering seam and interfacial IMC layer to the side of soldering seam. The fracture mechanism of the soldering joints obtained by the USW or the USW-E assisted soldering was brittle-ductile mixed fracture with the cleavage of interfacial (Cu, Ni)6Sn5 IMC and the cleavage-dimple of soldering seam, which increased the proportion of ductile fracture zone and the shear strength of soldering joints.