Growth kinetics of the intermetallic compounds during the interfacial reactions between Sn3.5Ag0.9Cu-nanoTiO2 alloys and Cu substrate

To develop a lead-free composite solder for advance electrical components, lead-free SAC solder was produced by mechanically mixing 0.5wt.% TiO₂ nanopowders with Sn3.5Ag0.9Cu solder. This paper investigated the formation of intermetallic compounds (IMCs) between Sn3.5Ag0.9Cu composite solder and Cu substrates during reflow soldering at temperatures ranging from 250 to 325°C. Scanning Electron Microscopy (SEM) and Energy Dispersive spectroscopy (EDS) were used to study the cross-sectional microstructure and stoichiometric information. The thickness of interfacial intermetallic layers was quantitatively evaluated from SEM micrographs using imaging software. Experimental results show that a discontinuous layer of scallop-shaped Cu-Sn intermetallic compounds formed during the soldering. Kinetics analysis shows that the growth of such interfacial Cu-Sn intermetallic compounds is diffusion controlled, with an activation energy of 27.23KJ/mol. During soldering reaction, doping TiO₂ nanopowders were found to refine the Ag₃Sn phase and β-Sn, which results in the formation of a large number of dot-shaped submicro Ag₃Sn precipitates in the SAC matrix after solidification.