Abstract
Printable electronics is a promising manufacturing technology for the potential production of low-cost flexible electronic devices, ranging from displays to active wear. It is known that rapid printing of conductive ink on a flexible substrate is vulnerable to several sources of variation during the manufacturing process. However, this process is still not being subjected to a quality control method that is both non-invasive and in situ. To address this issue, we propose controlling the printing accuracy by monitoring the spatial distribution of the deposited ink using terahertz (THz) waves. The parameters studied are the printing speed of an industrial roll-to-roll press with flexography printing units and the pre-calibration compression, or expansion factor, for a pattern printed on a flexible plastic substrate. The pattern, which is carefully selected, has Babinet’s electromagnetic transmission properties in the THz frequency range. To validate our choice, we quantified the geometric variations of the printed pattern by visible microscopy and compared its accuracy using one-dimensional THz spectroscopy. Our study shows a remarkable agreement between visible microscopic observation of the printing performance and the signature of the THz transmission. Notably, under specific conditions, one-dimensional (1D) THz information from a resonant pattern can be more accurate than two-dimensional (2D) microscopy information. This result paves the way for a simple strategy for non-invasive and contactless in situ monitoring of printable electronics production.
Highlights
Printed electronics (PE) has become a promising technology for the production of a wide range of flexible electronic components, ranging from photovoltaic devices, displays, sensors, and portable items to smart packaging[1,2,3,4,5,6,7,8,9,10]
Enlargement or shrinkage are monitored with optical microscopy (OM) under specific conditions, such as an appropriate illumination or along a particular direction, which might be problematic in an industrial environment[15,20]
1234567890():,; Fig. 1 2D optical microscopy characterization. a Designed samples, where black pixels correspond to ink and white is the substrate: (i) i-metallic checkerboard (MCB) pattern with ink stretching of Δd = +14 μm; (ii) is the target MCB pattern for perfect transmission property; (iii) capacitive MCB (c-MCB) pattern with ink compression of Δd = −14 μm
Summary
Printed electronics (PE) has become a promising technology for the production of a wide range of flexible electronic components, ranging from photovoltaic devices, displays, sensors, and portable items to smart packaging[1,2,3,4,5,6,7,8,9,10]. To increase the electrical functionality of printed devices, it is critical to monitor the dimensional distortions[19], which have been tested extensively[8,9,10]. Current approaches include defect detection realized by counting overlapping pixels or subtracting the expected image from the printed one[8,9]. These methods operate by using the on-site machine vision system to capture images of the final product, and comparing them with the desired reference[8,9,10]. A major challenge still remains in the mass production of PE devices for obtaining in-line feedback on print quality to ensure consistent production quality[4,5]
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