The silver NanoPaste® having silver nanoparticles with 5 nm in average diameter, coated either on a polyimide substrate or a copper one, is successfully sintered with CW lasers. A rapid metallization from the paste surface with the visible laser makes the evaporation of solvent and dispersant difficult, resulting in an insufficient sintering with large pores. In contrast, the near-infrared laser with a little absorption in the paste heats the substrate first, and then develops metallization up to the paste surface, so that an easy evaporation makes the structure denser. No peeling was observed at the interface of the laser-sintered Ag film and the substrates. Its adhesive strength is nearly equal to that of the furnace-sintered sample.