Formation and growth of intermetallics around metallic particles in eutectic Sn-Ag solder

Incorporation of metallic particulate reinforcements in eutectic Sn-Ag solder results in the formation of intermetallic compounds (IMCs) along particulate/solder interfaces with different morphologies. For instance, “sunflower” and “blocky faceted” IMC shapes have been observed around Ni particle reinforcements incorporated in the eutectic Sn-Ag solder matrix. The time and temperature above solder liquidus during the heating stage of the reflow process has been found to play a significant role in determining the IMC morphology in these Ni particulate-reinforced solders. Similar studies were carried out with Cu and Ag particulate reinforcements using the same solder matrix. The amount of heat input caused no significant change in morphology of the IMCs formed around Cu and Ag particulate reinforcements. Also, the IMC morphology around Ni particles was sensitive to the Cu content in the solder, whether the Cu came from the substrate during reflow or it was already present within the solder.