With the recent development of printed electronics on flexible substrate, urge for low temperature sintering process has emerged. In the frame of temperature sensitive substrates like plastics (PET, ABS, PC, etc.) conventional convective oven cannot be suitably used to achieve near‐bulk electrical resistivity. Consequently, several alternative sintering technologies have been reported and tested. In this present work, the prospective advantage of variable frequency sintering is studied for selective and fast sintering of metal inks. This variable frequency mode (VFM) improves the distribution of the electromagnetic field within the cavity and impedes arcing phenomena that could happen on metal surface. Inkjet-printed devices were processed using a VFM mode with a central frequency of 6.425 GHz with a bandwidth of 1.15 GHz and a sweep rate of 0.1 second has been used. A solid calibration step is required for temperature measurements and control during the process. The procedure includes a camera-based observation coupled with a pyrometer and an optic fiber. A reliable determination of the substrate and ink emissivity is compulsory to tailor the temperature feedback so as to not overcome the substrate's glass transition. The direct impact of microwave has been analyzed comparatively to conventional sintering assisted sintering where a thermally conductive susceptor or matrix is exploited. A huge shrink in electrical resistivity is particularly observable for samples prepared with conventional rapid thermal annealing (RTA), while those prepared in VFM quickly exhibit resistivities below 8 μΩ.cm, about 6 time the silver bulk resistivity. The electrical resistivity shrinkage is mainly originating from the contribution of the grain size. Through a strong coupling between microwave and silver nanoparticle, selective sintering of metallic parts is achieved on low temperature substrates enabling very low electrical resistivity without damaging the plastic substrate. These promising results open ways to successful implementation of microwave sintering in industrial process for flexible electronic application.