Liquid-state interfacial reactions between Sn-Ag-Cu-Fe composite solders and Cu substrate

Growth kinetics and interfacial morphologies of the intermetallic compound (IMCs) between Sn-3Ag-0.5Cu-xFe(0, 0.5wt.%, 1wt.%) composite solders and Cu substrates were investigated by reflowing for different durations at 250degC. Fe particles were deposited quickly in the vicinity of IMCs of the as-reflow samples due to the higher density of Fe than that of Sn-Ag-Cu. They formed a region about 30mum wide where the volume percentage of Fe particles could reach 19%. The isothermal equation of chemical reaction and phase diagrams is used to explain the effect of Fe on the growth kinetics of IMCs under liquid-state conditions. It is found that Fe can effectively retard the growth of Cu₆Sn₅ and Cu₃Sn during liquid-state aging and reduce the size of Cu₆Sn₅ particles. Some local small cracks were observed in the Cu₆Sn₅ particles near interfaces of SAC solder alloys after reflowing for about five minutes. Such cracks were found in the other composite solders only thirty minutes reflow.