Abstract: Cu/Sn0.3Ag0.7Cu/Cu composite solder joints were prepared by transient liquid phase diffusion bonding 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 compound （IMC） at the interface of Sn0.3Ag0.7Cu/Cu solder joint is positively correlated with the reflux time when the reflux temperature is constant.With the increase of reflux time,the thickness of IMC layer in Cu/Sn0.3Ag0.7Cu/Cu solder joint increases gradually,and the morphology of intermetallic compound in solder joint changes from serrated to scalloped.When the reflow time is 12h,the IMC grow together at the hot and cold ends.The complete reaction of Sn element in the solder matrix leads to the transformation of Cu₆Sn₅ phase into Cu₃Sn phase,and the volume shrinkage caused by the phase transformation causes defects in the weld.The growth rate of IMC at the cold end is greater than that at the hot end.The diffusion coefficients of IMC at the cold and hot ends are 0.568μm~2/h and 0.019μm~2/h,respectively.The growth of the cold end IMC is in the reaction control stage,the growth of the IMC is affected by the diffusion rate of Cu atoms,and the growth of the hot end IMC is controlled by grain boundary diffusion.The growth of IMC is affected by the rate of Cu atoms passing through the grain boundary,and the growth is extremely slow.The shear strength of the welded joint was reduced from 34.54MPa to 20.99MPa,which was reduced by 39.2%.