CoSn₃ Intermetallic Nanoparticles for Electronic Packaging

At present, composite solder pastes are getting a lot of attention, especially composite Sn based solders reinforced by nanoparticles. Indeed, CoSn₃ is a strong nucleating agent of Sn crystal, which has potential application value in the field of electronic packaging. However, there is no reliable synthetic path for CoSn₃ nanoparticles at present. In this article, a chemical synthesis method for CoSn₃ nanoparticles is developed. Here, CoCl₂ and SnCl₂ are reduced by NaHB₄ in triethylene glycol (TEG), dispersed by ultrasonics, and heated to 350 °C in a tube furnace for growth. The CoSn₃ nanoparticles with a diameter of about 150 nm are obtained by heating at 350 °C for 10 min. The CoSn₃ nanoparticles undergo a step reaction in the process of synthesis and go through different stages of merging and annexation during their growth. The crystal growth behavior and the process of orientation change during the nucleation and growth of CoSn₃ nanoparticles are studied, especially the two growth mechanisms, namely OU (orientation unified) and OA (orientation attached). By mixing CoSn₃ nanoparticles with SAC305, we obtain a kind of strengthened composite soldering paste. There are obvious six-fold cyclic twins in the joints made by this soldering paste.