Printing Stable Patterns on Curvilinear Surfaces for Omnidirectional Antenna

Introduction With the advantages of low cost, light weight, and design freedom, conformal circuits have attracted widespread attention in the research for structural electronics recently. Those circuits are composed of complex conductive patterns on curvilinear surfaces and can be fabricated by water transfer, screen-pad printing, dispenser printing, and lithography. Among these fabricating methods, omnidirectional printing with dispenser has shown its advantage in simple pattern formation with low-cost instrument. Printing quality of conformal circuits is important to device effectiveness. It has been reported that conductive traces with minor edge raggedness can induce negative impact for electronic devices and then cause deficient performance. To print patterns with well-defined boundaries, it is crucial to control the contact line stability of the printed liquid trace. For printed liquid lines, defects such as broken lines, bulges, and ragged edges, are commonly observed due to contact line motion. To resolve these issues, previous studies have proposed proper fluid control methods, such as increasing ink viscosity or advancing angles, to enhance the boundary stability on flat surfaces. However, similar analyses have not been applied on curvilinear surfaces. Recently, it has been reported that liquid traces may be susceptible on curved surface due to high internal hydrostatic pressure. Thus, printing quality control can be much more complicated than those on flat surface can and it is necessary to investigate the fundamental mechanism of edge stability. In this study, we explored the stability criteria for pattern fidelity on curved surface. Edge distortion, raggedness, or bulge formation associated with printing process will be carefully examined. Method or approaches to remove these printing issues will be proposed to attain great fidelity for printed liquid trace.