High-Viscosity Silver Nanoink: Direct-Write Processing and Low-Temperature Sintering for Flexible Electronics

This study developed a high-viscosity, conductive silver ink containing uniformly dispersed Ag micro- and nanoparticles (average size: 350 nm) to improve printing stability during direct-write fabrication. The ink’s solvent system enabled controlled evaporation kinetics, thereby preventing stratification and ensuring stable rheology. Orthogonal experiments were used to evaluate the effects of nozzle height, extrusion pressure, and writing speed on line-width variation. Thermal sintering at 300 °C for 30 min produced interconnected Ag conductive layers on PI substrates with an average sheet resistance of 5.4 mΩ sq⁻¹. LED interconnects fabricated at 200 °C produced functional circuits, although interfacial voids were observed at the joint fracture surfaces, suggesting that further improvement of joint robustness is needed. This work establishes a thermal processing window for direct-written Ag conductive patterns on PI-based flexible substrates and provides a basis for future low-thermal-budget sintering strategies.