We studied the cost effective direct laser patterning of copper (Cu) on thin polyimide substrates (PI thickness: 12.5–50 µm) using a 405 nm laser module attached to an inexpensive 3D printer. The focal length of the laser was intentionally controlled to reduce defects on patterned Cu and surface damage of PI under predetermined process conditions. The appropriate focal length was examined at various focal distances. Focal distances of − 2.4 mm and 3 mm were found for the shorter focal length (SFL) and longer focal length (LFL), respectively, compared to the actual focal length. This resulted in clean Cu line patterns without line defects. Interestingly, the SFL case had a different Cu growth pattern to that of LFL, indicating that the small difference in the laser incident angle could affect Cu precursor sintering. Cu square patterns had a lower resistivity of 70 μΩ·cm for an LFL after three or four laser scans, while the SFL showed a resistivity below 48 μΩ·cm for a one-time laser scan. The residues of the Cu precursor on PI were easily removed with flowing water and normal surfactants. However, the resistivity of the patterns decreased after cleaning. Among the scan gaps, the Cu square pattern formed at a 70 μm scan gap had the lowest sheet resistance and the least change in resistance from around 4 to 4.4 Ω/ϒ after cleaning. This result implies that the adhesion of the patterned Cu could be improved if the coated Cu precursor was well sintered under the proper process conditions. For the application of this method to bioelectronics, including biosensors, LEDs were connected to the Cu patterns on PI attached to the arm skin and worked well, even when the substrate PI was bent during power connecting.

No abstract

This study aims to explore the optimal process conditions for patterning indium‐tin‐oxide electrodes with polyethylene terephthalate films using a low‐cost laser‐marking machine equipped with an F‐theta lens. The feasibility of applying this equipment in roll‐to‐roll (R2R) processes and flexible sensors is also investigated. Moreover, the study involves analyzing the laser characteristics, precision, and focal length of the equipment, as well as adjusting the laser power and focal length to achieve the desired line width without damaging the substrate. The proposed equipment and an R2R patterning method are applied to a pressure‐leak sensor that employs a surfactant as the sensing material. The findings show that the low‐cost laser‐marking machine can be used for flexible sensor research and can support a fast, cost‐effective patterning method, making it possible to develop new sensors quickly.