Synthesis of Ag3Sn Submicrometer Particles via an Adapted Polyol Process in View of Their Use As Die-Attach Material in Power Modules

Intermetallic Ag3Sn was synthesized in the form of submicrometer particles through an adapted two-step polyol process. The precursor salts were tin (II) chloride (SnCl2) and silver nitrate (AgNO3), while the polyol used was ethylene glycol (EG). Sodium hydroxide (NaOH) and sodium borohydride (NaBH4) were selected as alkaline and reducing agents, respectively, and polyvinylpyrrolidone (PVP) was used to prevent the particles from coalescing. In the first step, Ag nanoparticles were obtained when silver nitrate and PVP, dissolved in polyol, were heated at 160 degrees C. The as-obtained Ag nanoparticles served as seeds for the nucleation and growth of the Sn species obtained in the second step. In this second step, the SnCl2 salt, combined with NaOH and NaBH4 as a strong reducing agent, was added to the polyol solution. Stannous ions, which were likely adsorbed at the Ag nanoparticle surface, were reduced to tin metal using the strong reducing power of NaBH4. Then, the Sn atoms diffused inside the Ag nanoparticles producing Ag3Sn submicrometer particles with diameter in the range of 100-200nm. The submicrometer size of the Ag3Sn particles, as well as its high melting point at approximately 485 degrees C makes this compound a good candidate for a lead-free die-attach material in power module devices.