Inkjet Printing of conductive silver tracks in high resolution and the (alternative) sintering thereof

We present different methods to improve the resolution of inkjet printed lines. The first is a direct method without surface treatment. Small droplets of a single picoliter have been inkjet printed directly onto a polymeric foil that has a surface energy smaller than that of common polymer foils. On the other hand the surface energy was high enough to form continuous tracks, which is usually the case when printing, for example, onto Teflon foil. The second method uses a combination of inkjet printing and hot-embossing. The latter technique is used to create microchannels in a polymer foil by pressing a master into the substrate, which is held above its glass transition temperature, after which an inkjet printer is used to dispense single droplets of a silver nanoparticulate ink over these as-formed channels. Subsequently, the channels will fill by means of capillary forces and afterwards sintering resulted not only in narrow tracks smaller than 10 μm, but also gave higher conductivity values than the conventional inkjet printed lines. Typically, conductivities up to 20% were revealed, which can be explained by a higher packing due to the capillary forces used for filling the channels.Moreover, we present an alternative technique to sinter in a selective method inkjet printed silver tracks on common polymer foils, by microwave radiation. This alternative technique is capable of a low temperature decomposition of the organic binding material that is around each metal nanoparticle. This results in the formation of conductive tracks. After applying this selective sintering technique, the features have a conductivity similar to conventional convection-radiation sintering, which is the most commonly used sintering technique at the moment.