Engineering of uniform anisotropic interconnection system with polyimide films for flexible electronics

To address the drawbacks of conventional anisotropic conductive films in flexible electronics, this study explored a novel flexible interconnection system comprising a flexible polyimide (PI) film with uniformly distributed Cu-filled holes. Periodic holes were formed along the PI film thickness. The holes were filled with Cu via electroplating, and both sides of the Cu ends were electrolessly Sn-plated to form solder bumps. The resulting Sn-coated Cu vias exhibited low electrical resistance (22 mΩ) and high shear bonding strength (63.76 MPa). Nonconductive adhesive layers were applied on both sides of the films. Consequently, the interconnected chips exhibited a high shear bonding strength (85.55 MPa) and electrical conductivity (22 mΩ), maintaining 98.84 % and 100 % of the initial values respectively, even after 1,000 cycles of bending and ambient stability test at 85 ℃. Light-emitting diodes integrated with a flexible printed circuit board using the proposed system demonstrated uninterrupted brightness, even under bending.