The effect of poly (N-vinylpyrrolidone) (PVP) molecular weight (MW) on the flash light sintering of copper nanopaste was investigated. The copper nanopaste was coated on polyimide substrates using doctor blade method. PVP was used as reducing agent to functionalize the copper nanoparticles during flash light sintering process. To find the optimum sintering conditions of copper nanoparticles, the various MWs of PVP (10 000, 40 000 and 55 000) were used and the flash light irradiation energy was varied from 7.5 J/cm(2) to 17.5 J/cm(2). Meanwhile, other flash light irradiation conditions (pulse numbers, on-time and off-time durations) and amounts of PVP were fixed to clarify the effect of the PVP MW. As the results, it was found that flash light sintered copper nanofilms have the resistivity of 54 mu Omega cm without any damages to the polymer substrate. To characterize the microstructures and transformation crystal phase of the sintered copper nanofilms, scanning electron microscopy and X-ray diffraction were conducted. In order to understand the interaction between oxidized copper and PVP, X-ray photoelectron spectroscopy was analyzed. To observe the electrical conductivity of flash light sintered copper nanofilms, the sheet resistance of the sintered copper nanofilms was measured using a four-point probe method and the sheet resistance changes during the flash light irradiation process were monitored using in-situ monitoring system. (C) 2014 Elsevier B.V. All rights reserved.