Processing and aging characteristics of eutectic Sn-3.5Ag solder reinforced with mechanically incorporated Ni particles

Composite solders offer improved properties compared to non-composite solders. Ni reinforced composite solder was prepared by mechanically dispersing 15 vol.% of Ni particles into eutectic Sn-3.5Ag solder paste. The average size of the Ni particle reinforcements was approximately 5 microns. The morphology, size and distribution of the reinforcing phase were characterized metallographically. Solid-state isothermal aging study was performed on small realistic size solder joints to study the formation and growth of the intermetallic (IM) layers at Ni reinforcement/solder and Cu substrate/solder interfaces. Effects of reflow on microstructure and solderability, were studied using Cu substrates. Regarding solderability, the wetting angle of multiple reflowed Ni reinforced composite solder was compared to the solder matrix alloy, eutectic Sn-3.5Ag. General findings of this study revealed that Ni particle reinforced composite solder has comparable wetting characteristics to eutectic Sn-3.5Ag solder. Significant IM layers growth was observed in the Ni composite solder joint under isothermal aging at 150 C. Microstructural evolution was insignificant when aging temperature was lower than 100 C. Multiple reflow did not significantly change the microstructure in Ni composite solder joint.