Mechanical alloying synthesis and soldering microstructures of nanocrystalline Sn–3.5Ag–0.7Cu alloy powders

Nanocrystalline Sn–3.5Ag–0.7Cu alloy powders were successfully fabricated by mechanical alloying (MA). During MA, Sn, Ag and Cu powders were deformed, overlapped and cold-welded together to form lamellar composites. The lamellar composites were then transformed into equiaxial particles. The milled powders were composed of a supersaturated solid solution, named Sn(Ag, Cu), and intermetallic compounds (IMCs) of Ag3Sn and Cu6Sn5. The average particle size (D4,3) and the melting point of the 60 h milled Sn–3.5Ag–0.7Cu powders were 19.9 μm, and 219 °C, respectively. After melting the powders on a Cu substrate at 260 °C, a dense solder was formed, consisting of a hypereutectic structure of oval shaped primary β-Sn and eutectic products of β-Sn, Cu6Sn5, and Ag3Sn. Meanwhile, the Ag3Sn laths at the solder/Cu6Sn5 layer interface and the coarse Cu6Sn5 plates in the solder were also detected.