Abstract: The heat diffusion process was applied to fabricate the brazing filler metals with tin coatings. The differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and X ray diffraction (XRD) were used to analyze the effect of heat diffusion process on the melting temperature, diffusion interface microstructure and phase of the brazing filler metals with tin coatings. The results show that the thickness of transition interface layer increase with the diffusion temperature under the condition of the working time is constant. The temperature of solid and liquid phase of brazing filler metals are decreased and the melting temperature range of brazing filler metals decrease with the diffusion temperature or working time increasing. The phase of diffusion interface are mainly compose of Ag3Sn and Cu3Sn. The optimum heat diffusion process are temperature of 220 ℃ and time of 24 h. Under the condition of the optimum heat diffusion process, the thickness of transition zone and the melting temperature range of brazing filler metal are 9.1 μm and 642.34 ℃~676.37 ℃. Then the tin content during the brazing filler metals is 7.2%, it's nearly 31% higher than that of traditional method.