Abstract: The microstructure and shear property of Cu/InSn-45Ni/Cu composite solder joints aged at 300℃ for different time were studied. The results show that with the increase of aging time, the thickness of the intermetallic compound(IMC) at the interface increases, and the interface morphology changes from scallop shape to planar shape. As the aging time increases, the solder reacts with the Cu atoms of the Cu substrate, and a large amount of brittle phase Cu3(In,Sn) is formed at the interface. The volume shrinkage of the brazing seam structure occurs caused by phase transformation and holes form, which increases continuously during aging process, and finally aggregates to form microcracks. Furthermore, the shear strength of the solder joints decreases as the aging time increases. The shear strength decreases from 15.89 MPa without aging treatment to 6.93 MPa after aging for 216 h. The fracture mode of the solder joints changes from intergranular fracture to transgranular fracture after aging.