Formation and growth of interfacial intermetallics in Sn-0.3Ag-0.7Cu-xCeO2/Cu solder joints during the reflow process

Abstract The effects of adding CeO2 nanoparticles on the formation and growth of interfacial intermetallic compounds (IMCs) between Sn-0.3Ag-0.7Cu-xCeO2 (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3 wt%) (SAC0307-xCeO2) solders and Cu substrates during reflow soldering were investigated. Scanning electron microscopy (SEM) was used to observe the microstructural evolution of the solder joints and measure the thickness and grain size of the intermetallic layers. The results show that the thicknesses and grain sizes of the IMCs decrease with CeO2 nanoparticle addition to the SAC0307 solder and that these parameters decrease significantly at a particle concentration of approximately 0.15 wt%. At higher concentrations, the thicknesses and grain sizes of the IMCs increase slightly. The growth exponents for the IMC layers and grains are determined by curve fitting to study the growth kinetics of the IMCs during reflow soldering. The results reveal that the growth exponents of the IMC layers range from 0.335 to 0.374 and those of the IMC grains range from 0.302 to 0.318, thus suggesting that the growth of the IMCs is controlled by the combined kinetic processes of atomic interdiffusion, interfacial reactions, and grain ripening. These data also show that among the tested solders, the SAC0307–0.15CeO2 solder joint has the smallest growth rate and exhibits the most significant effects in IMC growth suppression and grain size refinement. Based on the theories of heterogeneous nucleation and adsorption, a mechanism for reducing the IMC growth rate by the addition of CeO2 nanoparticles to the SAC0307 solder is proposed.