This paper investigates sequential Thermoforming and Flash Light Sintering (FLS) of conductive silver nanowire interconnects printed on planar polymer sheets. The resulting interconnect-polymer assemblies are pre-shaped to a desired 3D geometry and can be robustly attached to the surface. This 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 effect of the forming strain and FLS fluence on the resistance of the interconnect are studied. The interconnect resistance increases after thermoforming but is reduced significantly by subsequent FLS. The resistance depends nonlinearly on the forming strain, interconnect thickness, and FLS fluence. With the optimal parameters found here this process achieves interconnect resistance of < 10 Ω/cm within 90.8 seconds 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.