Influence of TiO2 nanoparticles on IMC growth in Sn–3.0Ag–0.5Cu–xTiO2 solder joints in reflow process

Abstract

The influence of TiO2 nanoparticles on the growth kinetics of intermetallic compound (IMC) between Sn–3.0wt.% Ag–0.5wt.% Cu–xwt.%TiO2 (x=0, 0.02, 0.05, 0.1, 0.3, and 0.6) solder and copper substrate during reflow process has been investigated in this study. Scanning electron microscope (SEM) was applied to observe the microstructural evolution of the solder joints, to measure the thickness of the IMC layer, and to estimate the grain size of the IMC layer. The IMC phases were identified by energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD). Results show that both the thickness and grain size of IMC decrease when TiO2 nanoparticles are added into the Sn–3.0Ag–0.5Cu solder system, and have a significant drop when the weight percentage of TiO2 nanoparticles is about 0.1wt.%. Beyond this amount, the thickness and grain size of IMC increase slightly. The growth exponents for both the IMC layers and grains are determined by curve-fitting to study the growth kinetics of IMC in the soldering reaction process. Results reveal that the growth exponents of the IMC layer range from 0.354 to 0.358, and those of the IMC grains range from 0.332 to 0.346, which suggests that the growth of the IMC layer is controlled by the combined kinetics process of atomic interdiffusion, interfacial reaction, and grain ripening. These data also show that Sn–3.0Ag–0.5Cu with about 0.1wt.% TiO2 nanoparticles solder system exhibits the smallest growth rate and gives the most prominent effect in suppressing IMC growth and refining IMC grain size. Based on the theory of adsorption, heterogeneous nucleation, and Ostwald ripening, a mechanism for retarding the IMC growth rate due to TiO2 nanoparticles addition is proposed.