Low cost, rigid to flex interposer using a spray coated intrinsically conductive polymer in a roll to-roll process

We report on a complete roll-to-roll (R2R) processed rigid-to-flex interposer using poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT:PSS) doped with ethylene glycol (EG), spray coated onto a plastic polyethylene naphtalate (PEN) substrate with another single-sided adhesive PEN foil acting as a contact stencil mask for the interposer structures. A 355 nm solidstate R2R integrated laser, with a beam width of 20 μm in focus, is used to cut the pattern of the interposer layer onto the adhesive foil, this foil is then laminated onto the primary substrate foil at 150°C to enable a contact stencil. Multiple layers of the doped PEDOT:PSS is sprayed over the whole surface, then the substrate is processed in an EG bath to improve the conductivity. The PEN masking-layer is then delaminated from the substrate at 65°C, leaving behind only the interposer structures having a sheet resistance of ~15 Ω at room temperature with a 250/150 μm line/space finger geometry. The resulting structures are robust to flexing, have good current carrying capability (50 mA constant, 100 mA short-duration) and are air stable. The structures also exhibit a positive temperature coefficient of resistance, fair heat dissipation, transparencies of ~85% and can be bonded to an IC easily with silver conductive paste or an anisotropic conductive polymer.