In this paper, carbon nanotube (CNT) and Nicoating modified CNT (Ni-CNT) were compared as the reinforcing dopants in the Sn57.6Bi0.4Ag solder joints. The comparisons were made in three main aspects, including the dispersion of the dopants, the micromorphology evolution of the solder matrix and the reinforcement of reliability performance of the solder joints. The dispersion was evaluated via observing the agglomeration of dopants. Micromorphology changes in the ball grid array (BGA) solder joints were detected via optical and scanning electron microscopy. Ball shear testing was applied to assess the bonding strength of the doped solder joints. Thermal shock testing was used to estimate the reliability performance. According to the results,the dispersion process of the CNT is greatly optimized by applying Ni coating, eliminating the agglomeration of CNT in the solder joints. Furthermore, the mechanical performance of the solder joints containing Ni-CNT performed better. However, the reliability performance became worse as the amount of doping increased. This work contributes to a better understanding on the impact of the CNT dispersion and the effectiveness of nickel-coating modified CNTs in the solder joints.