Improved Inkjet-Printed Pattern Fidelity: Suppressing Bulges by Segmented and Symmetric Drop Placement

Abstract

Inkjet printing is a promising technique for printed micro-electronics due to low cost, customizability and compatibility with large-area, flexible substrates. However, printed line shapes can suffer from bulges at the start of lines and at corner points in 2D line patterns. The printed pattern can be multiple times wider than the designed linewidth. This can severely impact manufacturing accuracy and achievable circuit density. Bulging can be difficult to prevent without changing the ink-substrate-system, the drying conditions or the circuit design, all of which can be undesirable. Here, we demonstrate a novel printing methodology that solves this issue by changing the order in which drops are placed on the substrate. The pattern is split up into segments of three drops where the central drop is printed last. This symmetric printing prevents the unwanted ink flow that causes bulging. Larger bulge-free patterns are created by successively connecting segments. Line formation in both traditional linear printing and our novel segmented and symmetric printing was analyzed to understand and optimize results. The printing of X-, T-, and L-shapes is considerably improved compared with the traditional linear printing methodology.

Machine learning based data driven inkjet printed electronics: jetting prediction for novel inks

“…All of these ink properties affect the jetting and the pattern formation on the substrate. Pattern formation on the substrate can be further manipulated by changing the properties of the substrate and the spacing and order in which drops are deposited [10][11][12][13][14][15][16][17]. Here, we will focus on the ejection of drops from the nozzle, which is the first step in the inkjet process.…”

Machine vision methodology for inkjet printing drop sequence generation and validation

“…Then, the next segment starts with the fourth drop placed at a distance of (DSp + 2CDSp) relative to the center of the first segment (the third drop), leaving 2CDSp of vacant space between two segments for a connecting drop to be filled in after all the segments have been printed. Previous work has experimentally shown that CDSp should be smaller than DSP, and the optimum CDSp varies between 0.6 and 0.95 times DSp for different substrate and ink combinations [20]. Here, the symmetric printing process is implemented for arbitrary patterns using a vision pipeline shown in figure 6(b).…”

“…Following the printing of the outer two drops of each segment, the central drop is printed and does not experience a pressure gradient due to the symmetry of the segment. Subsequently, the three-drop segments are joined with a connecting drop while maintaining pressure equilibrium on either side of the pattern [20]. Figure 6(a) compares the raster and symmetric drop ordering methodologies.…”

“…There has been significant work to understand the fluid mechanics of these nonidealities and avoid them for simple designs such as lines or squares by changing the location and order in which drops are printed. Inkjet pattern control has been thoroughly investigated for lines [12,[15][16][17][18][19][20][21] and 2D shapes [22][23][24] by characterizing ink and substrate properties and manipulating drop and lineto-line spacing [25,26], which can enhance printed morphologies. However, automated implementation of optimized drop and line-to-line spacing for arbitrary complex circuit patterns and industrial inkjetmanufacturing is still a challenge.…”

“…The morphology of micro-scale liquid tracks, especially bulging, has been investigated before using fluid dynamics methods [15,19]. Pattern segmentation and symmetric printing of segments can inhibit bulging in line patterns compared to traditional raster printing [20]. Preprinting the contour of any feature improves corner morphology through enhanced pinning and additional anchoring in front of each segment can significantly subdue the bulging effect [21,26].…”