Abstract: In this paper, Cu / Sn0.3Ag0.7Cu / Cu composite solder joints were prepared by transient liquid phase diffusion bonding ( TLP ) process. The effects of reflow time on the microstructure and growth kinetics of intermetallic compounds at the interface of Sn0.3Ag0.7Cu / Cu solder joints were studied by scanning electron microscopy and energy dispersive spectroscopy. The results show that the thickness of intermetallic compounds ( IMC ) at the interface of Sn0.3Ag0.7Cu / Cu solder joints is positively correlated with the reflux time when the reflux temperature is constant. With the increase of reflux time, the thickness of intermetallic compounds at the interface of Cu / Sn0.3Ag0.7Cu / Cu solder joints increases gradually, and the morphology of intermetallic compounds in solder joints changes from serrated to scalloped. When the reflux time is 12 h, the weld forms a full intermetallic compound. Due to the influence of temperature gradient, the growth rate of intermetallic compounds at the cold end is greater than that at the hot end. The diffusion coefficient and growth kinetic index of IMC at the cold end are 0.568μm²·h^-1 and 0.95, respectively. The diffusion coefficient and growth kinetic index of IMC at the hot end are 0.019μm²·h^-1 and 0.32, respectively. The growth of IMC at the cold end is in the reaction-controlled stage, the growth of IMC layer is affected by the expansion rate of Cu atoms, and the growth of IMC at the hot end is in the grain boundary expansion stage.