Effect of Nano-TiO2 particles on growth of interfacial Cu6Sn5 and Cu3Sn layers in Sn3.0Ag0.5CuxTiO2 solder joints

In this study, the effect of nano-TiO2 particles additive on the growth of interfacial Cu6Sn5 and Cu3Sn intermetallic compound (IMC) layers between Sn3.0Ag0.5CuxTiO2 solder and Cu substrate was investigated under different isothermal aging temperatures of 120 °C, 150 °C, and 190 °C. Scanning electron microscopy (SEM) was adopted to observe the morphological evolution of interfacial IMC layers. The composition and phase of the IMCs were identified by energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), respectively. Results show that the morphology of the Cu6Sn5 transformed from scalloped to plate-like after solid-state aging, while that of the Cu3Sn phase remains the layer-type. Nano-TiO2 particles have a strong influence on the growth of both the Cu6Sn5 and Cu3Sn IMC layers. The thickness of Cu3Sn layer increases promptly with aging temperature and time, while that of Cu6Sn5 layer increases slowly. This might be due to the Cu3Sn grows at the expense of Cu6Sn5 layer. The growth exponent value of the Cu6Sn5 layer ranges from 0.52 to 0.8, while that of the Cu3Sn ranges from 0.45 to 0.64. The addition of nano-TiO2 significantly affected the Cu6Sn5 layer growth, but very little influence on the growth of Cu3Sn layer, especially at the low aging temperature. The activation energies for the Cu6Sn5 and Cu3Sn layers are the range of 14.91 kJ/mol to 20.95 kJ/mol and 85.51 kJ/mol to 86.23 kJ/mol, respectively. Adding 0.1 wt% nano-TiO2 to Sn3.0Ag0.5Cu solder exhibits the smallest growth rate for both the two IMC layers and gives the most prominent effect in suppressing IMC growth. Based on the theory of adsorption, grain boundary pinning is one of the most important mechanisms for regarding the Cu6Sn5 and Cu3Sn growth when nano-TiO2 is added.