Effect of 0.5 wt% nano-TiO2 addition into low-Ag Sn0.3Ag0.7Cu solder on the intermetallic growth with Cu substrate during isothermal aging

The interfacial evolution of nano-TiO2 reinforced low-Ag Sn0.3Ag0.7Cu composite solder on Cu substrate was investigated during 100 and 175 °C isothermal aging for up to 7 days. The thickness of interfacial intermetallic compound (IMC) layers was quantitatively evaluated from SEM micrographs using imaging software. It was found that the mean thickness of interfacial Cu–Sn IMC layers increased linearly with the square root of the aging time. This relationship indicates that the growth of the IMC layer is a diffusion-controlled process. Kinetics analysis shows that the apparent activation energies for the growth of Cu–Sn IMC layers were 40.25 kJ/mol for low-Ag Sn0.3Ag0.7Cu solder and 50.85 kJ/mol for low-Ag Sn0.3Ag0.7Cu composite solder. The reduced diffusion coefficient was proved for the low-Ag Sn0.3Ag0.7Cu composite solder/Cu joints.