Electrical Conductivity Control of Stretchable Printed Wires for In-mold Electronics Applications

Variations in electrical resistivity of stretchable wires printed with a silver-containing conductive paste consisting of a polyurethane binder on a glycol-modified polyethylene terephthalate (PETG) substrate were measured in situ during a vacuum-forming process to obtain a three-dimensional (3D) wire shape. When conductive paste containing silver flakes was used for the wire, the electrical resistivity was significantly reduced due to the stretching deformation during the forming process. It was also found that modifying the binder with a cross-linking agent effectively suppressed the electrical resistivity fluctuations of the 3D-shaped wires. The results of this study suggest that the conductivity of wires can be improved by controlling the material design and molding conditions. In addition, the wires bonded with chip LEDs using an electrically conductive adhesive were successfully integrally formed in a 3D shape by this process.