This paper summarizes a phenomenological preliminary study of nano-particle reinforced composite solder pastes' spreading over Cu substrates. The nano reinforcements included Cu and non-Cu particles. Solder matrix were lead and lead-free systems (including binder and flux). This report focuses in particular on Cu reinforced Sn-Pb materials and indicates some differences vs. lead-free systems. Wettability of the composite over Cu substrates was investigated using a realtime in-situ visualization of the triple line movement as well as the equilibrium contact angle measurements. It was established that the addition of Cu nanoparticles hampers spreading of the eutectic Sn-Pb solder paste and lowers the melting temperature of a nano- composite, but does not significantly change the spreading time, the final spread domain and the equilibrium contact angle, if the content of nano particles is less than 2.5 %. Further increase of nano - particles' content up to 5% indicates a decrease in the final spreading domain and increase in the equilibrium contact angle.