Effect of fullerene-C60&C70 on the microstructure and properties of 96.5Sn-3Ag-0.5Cu solder

In this study, fullerene nanoparticles (FNSs, a mixture of approximately 80%C60, 20%C70), by varying their weight fractions (0.05, 0.1 and 0.2wt. %) were successfully added into the SAC305 lead free solder to fabricate composite solders through the powder metallurgy processing route. As well as the retained ratios of fullerene reinforcements in the solder joints were firstly tested, the composite solders were also characterized in terms of their microstructure, melting points, electrical conductivity, wettability and mechanical properties. The retained ratio of FNSs reinforcements in the solder joints shows a considerable decrease with the increase of reflow cycles. After FNSs addition to the solder alloy, the Sn rich phase and IMC phases (Cu₆Sn₅ and Ag₃Sn) with a finer microstructure were observed in the solder matrix. With the increasing addition of fullerene, the composite solders showed an improvement in their wetting property but an insignificant change in their melting points and conductivity. The mechanical results indicated that the addition of 0.2wt. % fullerene can lead to 12.1% and 28.2% improvement in micro-hardness and shear strength respectively, when compared with that of the unreinforced solders. Furthermore, the FNSs doped composites exhibited better mechanical performance throughout the 360h aging period. These results obtained from this study proved that the addition of fullerene can improve not only the mechanical properties of the solder alloy, but also the wettability without any notable effect on the melting point and conductivity. Thus, these fullerene doped composite solders can be further developed as a potential material for microelectronics assembly and packaging industry.