Nanomaterials have been added to many materials in order to reinforce or alter the material properties, with much success. Similarly, metal nanoparticle additions to solder pastes have been shown to affect the resulting solder joints. However, little focus has been placed on lead-free nanosolder additions to lead-free solder pastes to form a more homogeneous composition. This study showed the effect of nanosolder particles on the intermetallic compound (IMC) formation and growth of solder pastes, and its relationship to the solder joint mechanical properties. Herein, Sn/Ag and Sn/Ag/Cu nanoparticles were synthesized using a chemical reduction method that resulted in spherical nanosolders between 20 – 30 nm. Pastes containing varying nanosolder additions (0.1 - 5 wt%) were prepared, printed and subjected to a reflow process to form the solder joints. The interface was observed for intermetallic compounds formed, before and after thermal aging, for relationships to the resulting solder joint reliability.