Diffusion wave model and growth kinetics of interfacial intermetallic compounds in Sn–3.0Ag–0.5Cu–xTiO2 solder joints

The growth kinetics of the interfacial intermetallic compounds (IMCs) between Sn–3.0Ag–0.5Cu–xTiO2 composite solder and Cu substrate during reflow process has been investigated in this work. Scanning electron microscope was adopted to observe the microstructure evolution of solder joints and measure the thickness of the interfacial IMC layer. The IMC phases were identified by energy-dispersive X-ray spectroscopy and X-ray diffractometry. Results show that both the reflow time and nano-TiO2 addition affects the microstructural morphology of IMCs. The thickness of Cu6Sn5 IMC was observed to increase with an increase in the reflow time, decrease with nano-TiO2 addition, and has a significant drop with the nano-TiO2 proportion of about 0.1 wt%. The growth of IMC layer was found to deviate the classical Fick’s diffusion law at the early stages of the IMC growth and then to approach the parabolic law. To explore the interfacial IMC growth kinetics, a diffusion wave model was proposed for predicting the IMC growth. Results show that the theoretical model was well consistent with the experimental data, which shows the feasibility of the model to predict the interfacial IMC growth for Sn–3.0Ag–0.5Cu–xTiO2 solder joints in the reflow process.