Highly reliable anisotropic interconnection system fabricated using Cu/Sn-Soldered microdumbbell arrays and polyimide films for application to flexible electronics

To fabricate high-performance flexible electronics, high-density electronic components should be safely integrated into limited areas, even under device deformation. However, simultaneously achieving device flexibility and strong bonds is challenging. Therefore, we fabricated Cu–Sn microdumbbell arrays on perforated polyimide (PI) substrates to develop a flexible interconnection system simultaneously exhibiting strong bonds and device flexibility by combining flexible PI films and metal–metal soldering. Cu microdumbbell arrays were formed by electroplating Cu on ∼5-μm-diameter microholes that were randomly distributed on flexible PI film surfaces and subsequently covering the dumbbell head surface with Sn by electroless plating. The Sn-covered dumbbell heads acted as metallic solder, enabling strong bonds with electronic components through hot pressing by forming nanolayered Cu/Sn intermetallic compounds. Electronic chips bonded by the Cu–Sn microdumbbell arrays exhibited excellent shear bonding strength, even after 10,000 bending cycles. Finite element simulations revealed that crack propagation was hindered by the space between the microdumbbells, thus enhancing the adhesion strength of the flexible interconnection system.