This study proposes the design of a roll-to-roll system for flexible electronics that enables accurate and precise tension control. It analyzes the factors for change in the tension of a roll-to-roll system and develops a tension model for each section to successfully predict the tension that is applied to such a system, the sagging of film according to tension, and deformation due to residual stress. This series of modeling processes allow engineers to design a roll-to-roll system for flexible electronics. Both a velocity control method for the tension between in-feeder and out-feeder—where there is no change of roller radius—and torque control method for the tension in modules like the rewinder, where the roll radius changes, are proposed. A roll-to-roll system according to the proposed design procedure and tension control methods was manufactured and experimented on under various test conditions. The accuracy and precision of velocity control between the in-feeder and the out-feeder were 100.01% and 1.15%, respectively, whereas those of torque control between the out-feeder and the rewinder were 99.9% and 1.35%, respectively, both at one sigma. The experiments confirmed that the two proposed types of tension control methods were accurate and precise. The experimental result with a monitoring sensor showed that the modeling was valid and that an accurate roll-to-roll system minimizing tension reduction was built. This study successfully demonstrated roll-to-roll system design and control techniques that are applicable to various pieces of roll-to-roll process equipment.
With the development of technology, wireless and IoT devices are increasingly used from daily life to industry, placing demands on rapid and efficient manufacturing processes. This study demonstrates the fabrication of an IoT device using a roll-to-roll printing process, which could shorten the device fabrication time and reduce the cost of mass production. Here, the fabricated IoT device is designed to acquire data through the sensor, process the data, and communicate with end-user devices via Bluetooth communication. For fabrication, a four-layer circuit platform consisting of two conductive layers, an insulating layer including through holes, and a solder resist layer is directly printed using a roll-to-roll screen printing method. After the printing of the circuit platform, an additional layer of solder paste is printed to assemble the electrical components into the device, inspiring the fully roll-to-roll process for device fabrication. Successful IoT device deployment opens the chance to broaden the roll-to-roll fabrication process to other flexible and multilayer electronic applications.
One of the key challenges for adapting the roll-to-roll (R2R) process to flexible electronics production is to fulfill the tight registration requirements between layers. This study proposed a precise registration control for an R2R screen printing system based on a combination of registration error analysis, passive compensation, and active compensation. The registration error factors, such as film tension error, sintering error, reference alignment mark accuracy, screen printing error, and screen mask error, were evaluated. Meanwhile, with a refined correlation factor through the experiments, evaluation-based passive compensation was applied to the design layout for making a screen mask. Active compensation is based on combined control, which consists of the tension control and stage alignment control, reduces the registration error's varying term. As a result of passive and active compensation for polyethylene terephthalate film, achieving a machine direction registration error of 0 ± 9 µm (σ) and cross direction of 10 ± 4 µm (σ) was possible. The proposed R2R system with registration control was capable of accurate and precise registration over several hundred prints and was suitable for manufacturing flexible electronic devices.
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