Flexible electronics are becoming the next generation of devices due to their advantages, such as mechanical flexibility, eco-friendliness, large-area applicability, and scalability for mass production. However, solution-based manufacturing processes are prone to defects like discontinuities and local smudging, which can significantly degrade both device quality and yield. To tackle these challenges, rapid and accurate defect classification is crucial for real-time diagnosis during manufacturing. This study investigates the impact of data scale and key training hyperparameters on the performance of deep learning–based defect diagnosis models, using a dataset of conductive pattern defects in flexible electronics. We specifically examine how the number of training images affects model accuracy and generalization, and we analyze how adjustments to hyperparameters—such as L2 regularization and dropout—influence model performance in data-limited scenarios. Our findings offer insights into optimal training strategies tailored to different data scales and learning constraints, providing practical guidelines for designing and developing AI-based defect diagnosis models for flexible electronic devices.

We present an extrusion-based dispensing system designed for the planar patterning of tungsten ink through direct ink writing. This system achieves uniform ink deposition by precisely controlling the dispensing pressure and the motion of the substrate along predefined writing paths. To assess the impact of pressure on pattern geometry, we fabricated line patterns under various pressure conditions and analyzed their widths and thicknesses. To gain further control over pattern width, we employed an adjacent line overlapping strategy, where several lines, each approximately 200 μm wide, were written with partial overlap. We quantitatively verified the relationship between the number of adjacent lines and the resulting pattern width. This method was also adapted to create planar patterns with complex geometries, including variable widths, curved paths, and discontinuous features. The resulting patterns demonstrated uniform quality and precision. These findings confirm that our proposed system provides a versatile solution for fabricating planar conductive patterns with intricate geometries, suitable for applications in printed electronics and interconnects.

In-Mold Electronics (IME) is a manufacturing method that integrates printed decorations and electronic circuitry with thermoforming and injection molding processes. The method enables the production of ergonomic, lightweight and durable parts through cost-effective processes that require less assembly. Herein, the effect of circuit shape on line-width change by thermoforming was investigated through experiments and analysis based on the K-BKZ nonlinear viscoelastic model. Two circuit shapes, a horseshoe and a coil, were proposed and their line widths after thermoforming were measured and compared to that of a straight line shape. In the horseshoe-shaped circuit, the line width decreased as the radius increased due to the influence of vertical stretching caused by thermoforming. However, the effect of the angle on the line width was insignificant. In the coil-shaped circuit, the width of the line decreased as the pitch increased. However, as the amplitude increased, the line width also increased, but the effect was not significant. For the circuit shapes of the straight line, horseshoe and coil shapes, the rate of change in line width was 4.4, 0.4, and 0.2%, respectively. After conducting research, it was found that the coil-shaped circuit is more effective in minimizing line-width change caused by film thermoforming.

Printed electronics is a manufacturing technology that fabricates electronic devices using printing techniques. Due to its characteristics of low cost and simple process, a roll-to-roll printing technique has been used to achieve the large area and mass production of flexible electronic devices such as a thin film transistor. In the roll-to-roll printing process, a fidelity of the engraved pattern position is one of the most important techniques to fabricate high resolution multi-layer electronic devices. In this study, an engraved register mark position measurement system was developed to numerically evaluate the position accuracy of engraved mark in printing roll. The proposed system is based on a high-precision encoder based position control system and a high-resolution machine vision system. The measurement error of the developed system is within the camera resolution ±2.1 μm, verifying the superiority of the system. Using the developed system, we measured the position errors of the engraved register marks for six industrial scale printing rolls. This study suggests that the position error of the engraved mark should be considered to achieve a high precision register control below ±10 μm and necessity of the developed system.

In the printed circuit board (PCB) manufacturing industry, the yield is an important management factor as it significantly affects the product cost and quality. However, in real situations, it is difficult to ensure a high yield in a manufacturing process, because the products are manufactured through numerous nanoscale manufacturing operations. Thus, for improving the yield, it is necessary to analyze the key process parameters and equipment parameters that result in a low yield. In this study, critical equipment parameters that affect the yield were extracted through a mutual analysis of the equipment parameters (x) and process parameters (y) in the plastic ball grid array (PBGA) manufacturing process. To this end, the study uses the correlation coefficient to apply the heuristic algorithm that extracts critical parameters that keep the redundancy among the equipment parameters to a minimum and exert maximum impact on the critical process parameters. Additionally, by using the general regression neural network technique, the effects of the critical equipment parameters on the process parameters were confirmed. The test results were applied to the PBGA production line and an improvement in the yield was confirmed.

In this study, a free-fall drop tester was studied to test the impact reliability of small electronic components. The electronic component was fixed to the drop table and the table was fallen along guide rods. The impact energy was adjusted by the initial drop height, and the impact duration time was adjusted by inserted soft layers under the drop table. Table acceleration was achieved in the form of a half-sine that conforms to international standards. The developed tester was evaluated by a small printed circuit board. It was observed that the developed tester was fully utilized for the impact reliability assessment of electronic components.

By patterning finely with a laser with a thickness of 100 μm or less such as ABS and forming an electronic circuit through plating, a high-density flexible PCB applicable to wearable and mobile devices can be realized. ABS films with a thickness of 60, 90, and 120 μm were prepared, and a crater measuring 100 μm or less was formed by irradiating a fiber laser with a wavelength of 1064 nm with a single pulse. The size of the craters is affected by the intensity of laser irradiation and the thickness of the film, and the heat dissipation layer reduces the change in size caused by the difference in the thickness of the film. For films with a thickness of 60 μm, it has been found that small craters of more than 10% can be obtained due to the heat dissipation layer. Thermal analysis showed in the ABS film without the heat dissipation layer, the maximum temperature increased to 373oC, but decreased to 261℃ in the ABS film with the heat dissipation layer. With a decrease in the thickness of the film, the heat dissipation layer further reduces the pattern by laser irradiation.

Among the various next-generation solar cells, a perovskite solar cell can solve the economic problem because it can perform the low temperature solution process and the material is inexpensive. Photovoltaic conversion efficiency is comparable to silicon solar cells and thin-film solar cells. However, to commercialize the perovskite solar cells, there are many problems to be resolved, such as stability, upscaling, and efficiency. Thus, in this study, perovskite crystallization experiments were conducted according to the coating conditions such as the coating speed of the meniscus solution sheared coating process, and large-area perovskite solar cells with p-i-n structures were fabricated. Perovskite crystallization is one of the crucial factors that determine the efficiency of solar cells, and it is an integral process condition for manufacturing large-area perovskite solar cells.

Printed electronics is a technology which is used for manufacturing flexible electronic devices dubbed as next-generation electronics such as wearable applications. To commercialize them, it is important to guarantee their electrical performance under various environmental conditions such as temperature and humidity. Moreover, flexible electronic devices usually undergo mechanical deformations such as bending and twisting, hence, it is necessary to observe the electrical performance of flexible devices under mechanical deformation considering both temperature and humidity. The effects of temperature and humidity on flexible printed electrodes, as an example of the simplest flexible electronics, under static deformation of bending and twisting are studied. Electrodes that do not deform are also strongly affected by temperature and humidity, and the increase in resistances of the electrodes with deformation is highest when twisting. The magnitude of static deformation does not affect the conductivity. The effect of line width is important for the twisting deformation. To commercialize printed electronics devices, the effects of temperature and humidity should be considered, with further consideration of the effects of mechanical deformation on the design of the devices.