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In this article, the shear properties of Sn–0.3Ag–0.7Cu-xCeO2 composite solder alloys were investigated at strain rates of 10−3s−1, 10−2s−1, and 10−1s−1 under three different temperatures of 25 °C, 75 °C, and 125 °C. Scanning electron microscope equipped with Energy-dispersive X-ray spectroscopy was used to observe the microstructural evolution and the fracture surface of the composite solder alloys. The results show that appropriate addition of CeO2 nanoparticles can improve the shear stress of the composite solder alloys. However, the excessive addition of CeO2 nanoparticles could degrade the mechanical properties. With an increase in strain rate or a decrease in test temperature, the shear stress of all solder alloys shows an increasing trend. A modified constitutive model was used to describe the effect of strain rate and temperature on shear stress. The optimum addition concentration of CeO2 nanoparticles in Sn–0.3Ag–0.7Cu-xCeO2 solder alloys is about 0.5 wt%, which possesses the highest shear stress.

The influence of the joint size on the growth of intermetallic compound (IMC) between Sn-3.0Ag-0.5Cu-0.1TiO 2 composite solder and Cu pad during isothermal aging at temperatures of 100 °C, 120 °C, and 150 °C has been investigated in this study. Scanning electron microscopy was used to observe the microstructural evolution of the solder joints and to measure the thickness of IMC layer. Results for micro-joints show that the size of the solder joints has a significant effect on the interfacial reaction. The IMC thickness and the growth rate increase, whereas the activation energy decreases with the increase in joint size for all aging temperatures. The size effect might be due to the difference in Cu concentration near the IMC interface. Finite-element model was applied to examine the thermo-mechanical stresses at the interface of the solder joint as thermo-mechanical stress can cause the formation of crystal defects in solder matrix and interfacial IMC layer. We assume that these crystal defects serve as fast diffusion paths for atomic diffusion and affect Cu distribution.

In this study, the effect of nano-TiO 2 particles additive on the growth of interfacial Cu 6 Sn 5 and Cu 3 Sn intermetallic compound (IMC) layers between Sn 3.0Ag 0.5Cu xTiO 2 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 Cu 6 Sn 5 transformed from scalloped to plate-like after solid-state aging, while that of the Cu 3 Sn phase remains the layer-type. Nano-TiO 2 particles have a strong influence on the growth of both the Cu 6 Sn 5 and Cu 3 Sn IMC layers. The thickness of Cu 3 Sn layer increases promptly with aging temperature and time, while that of Cu 6 Sn 5 layer increases slowly. This might be due to the Cu 3 Sn grows at the expense of Cu 6 Sn 5 layer. The growth exponent value of the Cu 6 Sn 5 layer ranges from 0.52 to 0.8, while that of the Cu 3 Sn ranges from 0.45 to 0.64. The addition of nano-TiO 2 significantly affected the Cu 6 Sn 5 layer growth, but very little influence on the growth of Cu 3 Sn layer, especially at the low aging temperature. The activation energies for the Cu 6 Sn 5 and Cu 3 Sn 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-TiO 2 to Sn 3.0Ag 0.5Cu 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 Cu 6 Sn 5 and Cu 3 Sn growth when nano-TiO 2 is added.

The influence of joint size on the interfacial reaction in Sn-3.0Ag-0.5Cu-0.1TiO 2 solder joints was investigated in this study. The thickness and grain size of the intermetallic layer were characterized by scanning electron microscope (SEM). Results show that both the thickness and grain size of the intermetallic compound (IMC) increases with the increase in joint size. The growth exponents for both IMC layers and grains are determined by curve-fitting to study the growth kinetics of IMC in wetting reaction. Results reveal that the growth exponents for IMC layer and grains increase with increase in joint size. The size effect might be due to the difference of Cu concentration distribution near the IMC interface in the molten solder. A two dimensional finite element method was adopted to investigate the kinetics of the Cu diffusion behavior in solder joint during the reflow process. Results reveal that the diffusion of Cu atoms might be influenced by the coarsening of the scallop like grains.