Geometrical effects on growth kinetics of interfacial intermetallic compounds in Sn/Cu joints reflowed with Cu nanoparticles doped flux

摘要

In this study, Cu nanoparticles prepared by chemical reduction method, were doped into flux (0-2 wt%) and disseminated to the pure Sn solder ball at 250. The enhanced spreading rate due to use of nanoparticles, increased the base diameter (W) and decreased the height (H) of the solder at constant volume. The finite element analysis for Cu concentration, temperature and velocity; in relation to the magnitudes of W and H show that larger W is responsible for enhancement of supersaturation and radial thermal gradient, whereas smaller H is responsible for reduction in flow velocity. The growth kinetics of interfacial Cu Sn-6( 5) film during isothermal reflow is proportional to W (2/3) during isothermal reflow whereas linearly dependent on H during air cooling. As the ripening at isothermal stage and precipitation at cooling stage contribute to the gross growth behavior of Cu Sn-6( 5) intermetallic compounds layer growth, the combined geometrical effect of base diameter and height of the solder specimen renders solder corresponding to flux with 2.0 wt% nanoparticles to have the overall thickest intermetallics.