Effects of Co Nanoparticles Embedded in Carbon Skeleton Nanosheet Addition to Sn-0.7Cu Solder on the Interfacial Reaction

The application of Sn-0.7Cu solder in electronic packaging is limited by its high melting point, low wettability, and poor solderability. Herein, we obtain Co nanoparticles embedded in carbon skeleton nanosheets (Co&C) via a metal-organic-framework (MOF)-derived method. The composite solder is successfully prepared by adding Co&C into Sn-0.7Cu. The results show that the addition of minor amounts of Co&C has little influence on the melting point of the composite solder. In addition, the wettability of the composite solder is effectively enhanced by the adsorption effect of Co&C. The minimum wetting angle of the composite solder is 27.9° when the content of Co&C is 0.08 wt %. With the addition of Co&C, the microstructure of the solder is refined, and the best refinement effect is achieved when the content of Co&C is 0.08 wt %. Furthermore, adding Co&C can reduce the thickness of the intermetallic compounds (IMCs) and transform the scalloped IMCs into a planar shape. Reflowed for 2100 s, the IMCs at the Sn-0.7Cu-0.08Co&C/Cu interface maintain a planar shape, and their thickness is reduced by 21.10% compared with that of the Sn-0.7Cu/Cu interface. The synergistic effect between Co and carbon in Co&C jointly controls the interface reaction and the growth of IMCs.