The Cu/Cu-cored+SAC305/Cu and Cu/SAC305/Cu micro-solder joints were subjected to thermal aging tests with different length. The effects of thermal aging time on the interfacial microstructure and tensile properties of these two solder joints were analyzed by scanning electron microscope（SEM） and dynamic mechanical analyzer（DMA）. The results show that the grains in interfacial microstructures of solder joints gradually coarsen,the IMC layers become thicker and the tensile strength of solder joints reduce with increasing aging time. Compared with Cu/SAC305/Cu solder joints,under the same thermal aging time,adding Cu-cored can slow down the growth rate of IMC at solder joint interface and improve the tensile strength of solder joint,but has no significant effect on the microstructure morphologies of solder joints. Fracture analysis shows that the two kinds of solder joints are brittle fracture. However,there are a small number of dimples on the fracture surface of Cu/Cu-cored +SAC305/Cu solder joints,showing certain toughness.