Scalable Forming and Flash Light Sintering of Polymer-Supported Interconnects for Surface-Conformal Electronics

Abstract

Conformally integrating conductive circuits with rigid 3D surfaces is a key need for smart materials and structures. This paper investigates sequential thermoforming and flash light sintering (FLS) of conductive silver (Ag) nanowire (NW) interconnects printed on planar polymer sheets. The resulting interconnect–polymer assemblies are thus preshaped to the desired 3D geometry and can be robustly attached to the surface. This conformal circuit integration approach avoids interconnect delamination in manual conformation of planar flexible electronics, eliminates heating of the 3D object in direct conformal printing, and enables easy circuit replacement. The interconnect resistance increases after thermoforming, but critically, is reduced significantly by subsequent FLS. The resistance depends nonlinearly on the forming strain, interconnect thickness, and FLS fluence. The underlying physics behind these observations are uncovered by understanding interconnect morphology and temperature evolution during the process. With the optimal parameters found here, this process achieves interconnect resistance of <10 Ω/cm within 90.8 s at 100% maximum strain over a 1 square inch forming area. The application of this process for complex surfaces is demonstrated via a simple conformal LED-lighting circuit. The potential of this approach to enable surface size and material insensitivity, robust integration, and easy replaceability for conformal circuit fabrication is discussed.