Geometrical Effects of Cu@Ag Core–Shell Nanoparticles Treated Flux on the Growth Behaviour of Intermetallics in Sn/Cu Solder Joints

Solder ball of initial diameter 1.4 mm, was reflow soldered with Cu substrate at 523.15 K using flux doped with Cu@Ag core–shell nanoparticles (NPs) in the proportion 0–2 wt%. The solders were then air cooled to room temperature. The use of NPs, by reducing the base height (H) of the solder and enhanced the diameter (W) of the solder, caused an overall increase in the spread ratio of the solder. The altered magnitudes of heat and mass transfer in these geometrically different but constant volume specimens were analyzed using finite element method. The occurrence of differential concentration gradient, radial thermal gradient and velocity magnitudes, in solders with differing geometry were numerically elaborated. The $$\hbox {Cu}_{6}\hbox {Sn}_{5}$$ intermetallic compound (IMC) formed at the Cu/Sn interface, was obtained to be the thickest for the specimen using undoped flux, whereas it was found to be smallest for the sample processed with flux containing 0.5% NPs. From the growth kinetics study, it has been inferred that IMC thickness is linearly proportional to the geometrical parameter H and $$\hbox {W}^b$$ , with b < 1.