Formation mechanism analysis and experimental investigation of single-step printing customized circuits by liquid-metal direct writing

Liquid-metal direct writing is a cost-effective and green technology, which is very promising for the customized fabrication of flexible circuits and functional devices. However, owing to the high surface tension of metal ink, the printed circuits are prone to intermittent outflow, large forming size error, and unstable forming. The smooth flowing and conveying of liquid-metal ink are still huge challenges that need significant attention. Herein, the force mechanism of liquid-metal ink transported by ball rotation and translation of the printing head was analysed, and the wetting characteristics of liquid metal on the surface of different substrates and its influence on forming morphology were investigated. The stable output printing of gallium indium alloy (GaIn24.5) liquid metal was realized. The changing characteristics of the shape and size of the liquid-metal circuits formed under different printing speeds and writing pressures were experimentally studied. The effective process window for obtaining the best circuit quality was established. Based on this, a flexible printed circuit board and functional electronic pattern were successfully printed under the writing pressure W=1 N and printing speed F800 mm min−1. The printed lines of GaIn24.5 exhibited a smooth surface, uniform width, small size error, and ability to connect electronic components and conduct electricity. This research proposes a new technical approach for customized printing of personalized electronic circuits and has important application prospects in the future.