Abstract: In order to improve the creep deformation resistance of Sn58Bi solder joints during service, Sn58Bi-xCf (x = 0, 0.02, 0.04, and 0.06 wt%) composite solders are prepared by incorporating different mass fractions of carbon fiber (Cf) powders into Sn58Bi via mechanical stirring in this paper. Sn58Bi-xCf/Cu solder joints were prepared on T2 copper sheet as substrate by using a temperature-controlled heating platform. The microstructure, elastic work, elastic modulus, and creep behavior of Sn58Bi-xCf/Cu solder joints are characterized using optical microscopy (OM) and nanoindentation. Based on the experimental data, the influence of Cf addition on the microstructure and properties of Sn58Bi/Cu solder joints is systematically evaluated. The results reveal that the incorporation of Cf significantly refines the microstructure of Sn58Bi/Cu joints and enhances their resistance to elastic and creep deformation. It is also found that the relationship between Cf content and joint performance is not strictly linear within the investigated range, and excessive Cf addition slightly deteriorates the joint properties. Among the tested compositions, the addition of 0.04 wt% Cf yields the finest microstructural refinement, as well as the optimal resistance to elastic and creep deformation.