Active element Ti improves the Sn-based alloy filler/graphite soldering interface: A combined first-principles and experimental study

Abstract

Active element Ti plays a crucial role in the graphite soldering process. However, the atomic interaction mechanism between the active element Ti and graphite remains unclear. In this study, the enhancement effect of the active element Ti on the Sn-based alloy filler/graphite soldering interface was investigated by employing first-principles calculations combined with experimental methods. Based on the first-principles calculations, the adhesion work of the Sn/graphite interface models doped with two and four Ti atoms is 0.884 J/m2 and 1.896 J/m2, respectively, while that of the clean model is negative. Moreover, the segregation heat of the Sn/graphite interface model doped with more Ti atoms is more negative. All of these results indicate that Ti atoms doped at the Sn/graphite interface play a significant role in enhancing the interface. The electronic structures of the interface models with different numbers of titanium atoms were analyzed. The results revealed that the enhancement of the Sn/graphite interface was attributed to the transfer of electrons from the Ti-3d orbitals to the C-2p orbitals, leading to a strong interaction between the Ti and C atoms. The segregation of Ti was clearly observed at the Sn3·5Ag4Ti (Ce,Ga)/graphite soldering interface in the experiments, which was consistent with the results from the first-principles calculations. The shear strength of the Sn3·5Ag4Ti (Ce,Ga)/graphite soldered joint was tested, and an enriched region of titanium was found in the fracture surface on the graphite side. In addition, a tensile simulation was performed on the clean and Ti-doped Sn/graphite interfaces, and the results indicated that the Sn/graphite interface model enriched with Ti atoms had greater tensile simulation strength than that of the clean Sn/graphite interface model. These results further showed that Ti played a reinforcing role at the Sn/graphite interface. The results from our study provide a theoretical basis for exploring low-temperature active bonding methods in the packaging process of graphite connected to the heat dissipation surface of electronic devices.