The morphology and kinetic evolution of intermetallic compounds at Sn–Ag–Cu solder/Cu and Sn–Ag–Cu-0.5Al₂O₃ composite solder/Cu interface during soldering reaction

In this work, Sn3.0Ag0.7Cu (SAC) composite solders were produced by mechanically intermixing 0.5 wt% Al₂O₃ nanoparticles into Sn3.0Ag0.7Cu solder. The formation and growth kinetics of the intermetallic compounds (IMC) formed during the liquid–solid reactions between SAC-0.5Al₂O₃ composite solder and Cu substrates at various temperatures ranging from 250 to 325 °C were investigated, and the results were compared to the SAC/Cu system. Scanning electron microscopy (SEM) was used to quantify the interfacial microstructure for each processing condition. The thickness of interfacial intermetallic layers was quantitatively evaluated from SEM micrographs using imaging software. Experimental results showed that IMC could be dramatically affected by a small amount of intermixing 0.5 wt% Al₂O₃ nanoparticles into Sn3.0Ag0.7Cu solder. A continuous elongated scallop-shaped overall IMC layer was found at SAC/Cu interfaces. However, after the addition of Al₂O₃ nanoparticles, a discontinuous rounded scallop-shaped overall IMC layer appeared at SAC-0.5Al₂O₃/Cu interfaces. Kinetics analyses showed that growth of the overall IMC layer in SAC/Cu and SAC-0.5Al₂O₃/Cu soldering was diffusion controlled. The activation energies calculated for the overall IMC layer were 44.2 kJ/mol of SAC/Cu and 59.3 kJ/mol for SAC-0.5Al₂O₃/Cu soldering, respectively. This indicates that the presence of a small amount of Al₂O₃ nanoparticles is effective in suppressing the growth of the overall IMC layer.