Journal of the Korean Society for Precision Engineering

Electrochemical Impedance Analyses of ePTFE-reinforced Polymer Electrolyte Membrane-based PEMFC with Varying Thickness and Relative Humidity: Gyutae Park, Subin Jeong, Youngjae Cho, Junseo Youn, Jiwon Baek, Jooyoung Lim, Dongjin Kim, Taehyun Park; J. Korean Soc. Precis. Eng. 2025;42(11):901-907.
Published online November 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.052

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The polymer electrolyte membrane fuel cell (PEMFC) generates electrical energy through electrochemical reactions and is a key technology for sustainable energy. The electrolyte membrane significantly affects performance under varying conditions. This study examines the impact of membrane thickness and relative humidity (RH) on PEMFC performance using j-V curves and electrochemical impedance spectroscopy (EIS). Experiments were conducted with membrane thicknesses of 30, 15, and 5 μm under RH conditions of 100%-100% and 100%-0%. Under RH 100%-100%, performance improved as the membrane thickness decreased, with values of 954, 1050, and 1235 mW/cm² for the 30, 15, and 5 μm membranes, respectively. The 5 μm membrane demonstrated a 23% performance improvement over the 30 μm membrane. Under RH 100%-0%, performances were 422, 642, and 852 mW/cm², with degradation rates of 55.8%, 39.0%, and 32.1%. The 5 μm membrane exhibited the lowest degradation rate, indicating superior performance under low humidity. These results suggest that thinner membranes generally enhance performance and maintain efficiency even in dry conditions.

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Fabrication of LSC Cathode for High-performance Solid Oxide Fuel Cell with Suppressed LSC/YSZ Interface Side Reactions: Jisung Yoon, Miju Ku, Hyojun Ahn, Hunhun Jung, Young-Beom Kim; J. Korean Soc. Precis. Eng. 2025;42(5):361-366.
Published online May 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.008

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In this study, we introduce a novel flash light sintering (FLS) method to address the issue of secondary phase formation in conventional high-temperature thermal sintering processes. The microstructure and cross section of the Lanthanum strontium cobalt (LSC) air electrode were analyzed using field emission scanning electron microscopy (FE-SEM). The presence of secondary phases was evaluated using X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) in SEM. Electrochemical performance was assessed using NiO-YSZ anode-supported LSC cathode cells at 750oC. The maximum power density of the thermally sintered LSC cathode at 900oC was 272.4 mW/cm², while the flash light sintered LSC cathode by 18.5 J/cm² achieved 2,222 mW/cm². These results demonstrate that the flash light sintering process can effectively prevent secondary phase formation and successfully sinter the electrode, thereby enhancing the performance and reliability of SOFCs.

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Evaluation of Electrochemical Performance of PEMFCs with Decontamination Devices at Marine Environments: Ye rim Kwon, Ho Jun Yoo, Byung Gyu Kang, Ki Won Hong, Sun Ki Kwon, Sanghoon Lee, Gu Young Cho; J. Korean Soc. Precis. Eng. 2025;42(1):57-63.
Published online January 1, 2025; DOI: https://doi.org/10.7736/JKSPE.024.109

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In this study, we developed and evaluated a simple device for removing ionic impurities that affect the performance of a polymer electrolyte membrane fuel cell (PEMFC) in a marine environment. In such environments, PEMFCs may experience performance degradation due to the presence of Na+ and Cl- in the air. To address this issue, the decontamination device was designed with both heating and cooling components. This device was positioned between a humidifier containing NaCl solution and a humidifier containing deionized water, both connected on the cathode side. The decontamination device effectively removed impurities (Na+ and Cl-) during experiments. As a result, the electrochemical performance of the fuel cell with the decontamination device improved compared to that of the fuel cell without it. Notably, the activation resistance and electrochemical surface area were significantly enhanced, and the ohmic resistance also improved when compared to the fuel cell without the decontamination device.

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Effects of NaCl Solution on Proton Exchange Membrane Fuel Cell with Serpentine Flow Channel of Different Depths
Dong Kun Song, Ho Jun Yoo, Jung Soo Kim, Ki Won Hong, Do Young Jung, George Ilhwan Park, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2025; 42(5): 399. CrossRef

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Cutting of Chemically Strengthened Glass Using the Combination of Electrochemical Discharge and Grinding Processes: Jonghwan Kim, Jihong Hwang; J. Korean Soc. Precis. Eng. 2024;41(12):957-964.
Published online December 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.096

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Chemically strengthened glass has recently gained attention for use in mobile device display covers due to its enhanced mechanical properties. However, cutting chemically strengthened glass poses challenges because of its high surface compressive stress, derived from the ion exchange between Na+ and K+ during the strengthening process. To address this, we propose an efficient method for cutting chemically strengthened glass by integrating electrochemical discharge (ECD) and grinding processes. The ECD process helps alleviate surface compressive stress through reverse ion exchange, while the grinding process helps mitigate compressive stress on the bottom surface without flipping the glass. Chemical composition analysis of the cross-section of glass cut along the line treated by the ECD process revealed that this method can induce reverse ion exchange on both the upper and bottom surfaces of chemically strengthened glass. Furthermore, nano-indentation hardness tests conducted on the cross-section demonstrated that the subsurface hardness could be reduced by the ECD process, indicating a relaxation of the surface compressive layers. It has also been proven that chemically strengthened glass can be successfully cut using this method, suggesting it offers a viable solution for efficient glass cutting.

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2-step CMP Strategy for Dishing Control of TGV Interposers: Seunghun Jeong, Yeongil Shin, Jongmin Jeong, Seonho Jeong, Haedo Jeong; J. Korean Soc. Precis. Eng. 2024;41(6):467-472.
Published online June 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.027

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Chemical mechanical planarization (CMP) is an essential polishing process in semiconductor manufacturing. Advances in memory technology, including increased capacity and performance, have increased the importance of electronic packaging. In heterogeneous integration, the interposer acts as an important intermediary between the logic die and the substrate, solving numerous I/O bump problems in high-bandwidth memory (HBM) and logic chips. Traditionally, board-to-memory connections were made through wire bonding, which required additional space for wire connections and introduced latency due to extended signal transmission paths. A through-type approach has emerged as a solution that can significantly reduce waiting time and installation space by improving space efficiency and enabling vertical connections without extending wiring. Due to these new approaches, the importance of CMP is reemerging. Implementation of this important process requires precise control of the CMP dishing/protrusion of bonding surfaces. Improper selection of Cu pad dishing/protrusion can cause problems such as increased RC delay time and signal short circuit in the wiring. In this paper, we proposed a strategy to control dishing using CMP, especially for Through-glass-via (TGV).

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Structural Analysis and Optimization of Electrochemical Hydrogen Compressor End Plate Using Taguchi Method and Gray Relational Analysis: Sang Duk Seo, Won Tae Kwon; J. Korean Soc. Precis. Eng. 2023;40(12):955-964.
Published online December 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.083

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The Electrochemical Hydrogen Compressor is an optimal device for compressing low-pressure hydrogen to high-pressure hydrogen. It has a similar structure to the Proton Exchange Membrane Fuel Cell but operates at extremely high pressures, requiring multiple cells sealed with End Plates. The End Plate design must provide initial cell activation support, withstand maximum operating pressure within the stack, and prevent internal gas leakage. This study applies a multi-objective optimization method and grey relation analysis to determine the optimal design parameters for the End Plate based on the activation area of Dummy Cells. Finite Element Method (FEM) analysis is conducted to verify the effectiveness of the optimized End Plate design, considering the uniform pressure distribution with stacked Dummy Cells (1, 3, 6, 12). The analysis reveals that the parameters affecting the uniform pressure distribution include the End Plate design, stack sealing pressure, individual Cell design parameters, and the number of Cell stack layers.

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Evaluate the Activation Effect according to the Voltage Range: Jung Soo Kim, Ho Jun Yoo, Ji Woong Jeon, Dong Kun Song, Ye Rim Kwon, Young Jo Lee, Seung Hyeok Hong, Su Min Lee, Da Hye Geum, Gu Young Cho; J. Korean Soc. Precis. Eng. 2023;40(10):847-852.
Published online October 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.056

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Polymer electrolyte membrane fuel cells (PEMFC) require activation to maximize their performance. Thus, an appropriate activation process is essential for the performance of the fuel cell. In this study, the performance of the fuel cell was investigated by changing the voltage range during the activation process. There were three voltage ranges: 0.3-0.9 V, 0.3-0.6 V, and 0.6-0.9 V. When the fuel cell was activated in the low voltage region, the highest performance was output. On the other hand, it showed the lowest performance at high voltage. The results suggest that it is advantageous to activate the fuel cell with a high current. On the other hand, if activation is performed while outputting at a low current, the generation of water and the electrochemical reaction are insufficient, resulting in a load on the fuel cell. Through this experiment, it was confirmed that the control method greatly affects fuel cell performance when activated.

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A Study on Electrochemical Resistance Change through the Pressurization Process of MEA for PEMFC: Ye Rim Kwon, Dong Kun Song, Ho Jun Yoo, Gye Eun Jang, Young Jo Lee, Jung Soo Kim, Ji Woong Jeon, Da hae Guem, Gu Young Cho; J. Korean Soc. Precis. Eng. 2023;40(7):539-544.
Published online July 1, 2023; DOI: https://doi.org/10.7736/JKSPE.022.150

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In this study, the electrochemical characteristics of fuel cell were evaluated after applying a compressive load to the activation area of membrane electrode assembly (MEA) in polymer electrolyte membrane fuel cells. The effects of the pressed area under the compressive load were systematically investigated using polarization curves and electrochemical impedance spectroscopies (EIS) of the fuel cell. Interestingly, the performance of the fuel cell was improved as the pressed area of the MEA was increased from 25.2% to 100% of the active area. In addition, the increased pressed area led to a decrease in the ohmic resistance and the activation resistance of fuel cells.

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Prediction of CMP Material Removal Rate based on Pad Surface Roughness Using Deep Neural Network: Jong Min Jeong, Seon Ho Jeong, Yeong Il Shin, Young Wook Park, Hae Do Jeong; J. Korean Soc. Precis. Eng. 2023;40(1):21-29.
Published online January 1, 2023; DOI: https://doi.org/10.7736/JKSPE.022.119

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As the digitization of the manufacturing process is accelerating, various data-driven approaches using machine learning are being developed in chemical mechanical polishing (CMP). For a more accurate prediction in contact-based CMP, it is necessary to consider the real-time changing pad surface roughness during polishing. Changes in pad surface roughness result in non-uniformity of the real contact pressure and friction applied to the wafer, which are the main causes of material removal rate variation. In this paper, we predicted the material removal rate based on pressure and surface roughness using a deep neural network (DNN). Reduced peak height (Rpk) and real contact area (RCA) were chosen as the key parameters indicative of the surface roughness of the pad, and 220 data were collected along with the process pressure. The collected data were normalized and separated in a 3 : 1 : 1 ratio to improve the predictive performance of the DNN model. The hyperparameters of the DNN model were optimized through random search techniques and 5 cross-validations. The optimized DNN model predicted the material removal rate with high accuracy in ex-situ CMP. This study is expected to be utilized in data-driven machine learning decision making for cyber-physical CMP systems in the future.

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Precision Engineering and Intelligent Technologies for Predictable CMP
Somin Shin, Hyun Jun Ryu, Sanha Kim, Haedo Jeong, Hyunseop Lee
International Journal of Precision Engineering and Manufacturing.2025; 26(9): 2121. CrossRef
Prediction of Normalized Material Removal Rate Profile Based on Deep Neural Network in Five-Zone Carrier Head CMP System
Yonsang Cho, Myeongjun Kim, Munyoung Hong, Joocheol Han, Hong Jin Kim, Hyunki Kim, Hyunseop Lee
International Journal of Precision Engineering and Manufacturing-Green Technology.2025; 12(3): 869. CrossRef

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Analysis of Electrochemical Behavior of PEMFC Humidified with NaCl Solution Mist Using an Ultrasonic Vibrator: Ho Jun Yoo, Gye Eun Jang, Young Jo Lee, Dong Kun Song, Heeyun Lee, Gu Young Cho; J. Korean Soc. Precis. Eng. 2022;39(12):939-946.
Published online December 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.096

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Durability evaluations were conducted using polymer electrolyte membrane fuel cells in a marine environment. Deionised water and 3.5 wt% of NaCl solution were supplied to the cathode using an ultrasonic vibrator. Performance and electrochemical impedance spectroscopy of fuel cells were measured to evaluate the electrochemical behaviors. Additionally, long-term stability evaluations of PEMFCs were carried out at 0.65 V for 20 h. Following the experiments, scanning electron microscope analysis was conducted to confirm the presence of NaCl on membrane electrode assembly and micro porous layer of fuel cells.

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Effects of NaCl Solution on Proton Exchange Membrane Fuel Cell with Serpentine Flow Channel of Different Depths
Dong Kun Song, Ho Jun Yoo, Jung Soo Kim, Ki Won Hong, Do Young Jung, George Ilhwan Park, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2025; 42(5): 399. CrossRef
Evaluation of Electrochemical Performance of PEMFCs with Decontamination Devices at Marine Environments
Ye rim Kwon, Ho Jun Yoo, Byung Gyu Kang, Ki Won Hong, Sun Ki Kwon, Sanghoon Lee, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2025; 42(1): 57. CrossRef
A Study of Effects of the Repetition of Assembly and the Addition of Activation on Electrochemical Characteristics of PEMFCs
Ji Woong Jeon, Gye Eun Jang, Young Jo Lee, Dong Kun Song, Ho Jun Yoo, Seung Hyeok Hong, Jung Soo Kim, Ye Rim Kwon, Da Hye Geum, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2023; 40(11): 867. CrossRef
A Study on Electrochemical Resistance Change through the Pressurization Process of MEA for PEMFC
Ye Rim Kwon, Dong Kun Song, Ho Jun Yoo, Gye Eun Jang, Young Jo Lee, Jung Soo Kim, Ji Woong Jeon, Da hae Guem, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2023; 40(7): 539. CrossRef

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Effect of Slurry Film Thickness Variation according to Spray Range Using Ultrasonic Spray Nozzle on Material Removal Rate: Seongnyeong Heo, Seonho Jeong, Minji Kim, Youngwook Park, Haedo Jeong; J. Korean Soc. Precis. Eng. 2022;39(9):675-682.
Published online September 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.036

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Most of the consumables used in the CMP (Chemical Mechanical Planarization) process are discarded because it is difficult to reuse them. Slurry accounts for most of the consumables, so research is being conducted to reduce the amount of slurry used. A previous study explains that when the same amount of slurry is injected, the material removal rate is improved when the slurry is injected wide and thin instead of the tube nozzle, which is the conventional slurry injection method. However, there was no change in the injection method due to the problems of the injection method suggested in previous studies and the lack of follow-up studies. Thus, in this paper, an injection method through an ultrasonic spray nozzle is proposed to improve the problems of the injection method proposed in previous studies. Additionally, it is intended to calculate the slurry film thickness according to the spraying range and to explain the effect of the film thickness on the material removal rate.

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Investigation of Planarization Using Real Contact Area Measurement in CMP Process: 김민지 , Seonho Jeong, 신영일 , Youngwook Park, Haedo Jeong; J. Korean Soc. Precis. Eng. 2022;39(8):547-555.
Published online August 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.028

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Chemical Mechanical Planarization (CMP) is an essential process for device integration and planarization in a semiconductor manufacturing process. The most critical function in the CMP process, is to predict and cover the geometrical characteristics of various sizes and densities, of patterned wafers for local and global planarization. To achieve the wafer-level and die-level planarization, it is necessary to understand the contact mechanism between the CMP pads and the macro-scale patterns. In the macro-scale pattern, pad deformation is divided into two layers: an asperity layer and a bulk pad layer. Through bulk pad deformation, asperity contact distribution within the pattern is predicted. In this paper, the distribution of asperity contact according to the pattern geometrical characteristics was analyzed, through large-area real contact area (RCA) measurement. Bulk pad deformation was predicted by analyzing RCA distribution according to pattern geometry such as pattern size and density, pattern shape and step height according to the polishing time, and applied pressure. Additionally, through the distribution of the contact area and the number of contact points, the rounding phenomenon and planarization characteristics in the pattern CMP were predicted.

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Effects of NaCl Solution Humidification on Electrochemical Characteristics of PEMFCs: Ho Jun Yoo, Hye Gang Noh, Gye Eun Jang, Young Jo Lee, Dong Kun Song, Gu Young Cho; J. Korean Soc. Precis. Eng. 2022;39(6):451-456.
Published online June 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.030

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In this study, polymer electrolyte membrane fuel cells (PEMFCs) were humidified with NaCl solutions. NaCl solutions were provided to the cathode side of fuel cells by bubbling. De-Ionized water, 3.5 wt% NaCl solution, and 20 wt% NaCl solution were used to evaluate the effects of NaCl. Current density-voltage curves and electrochemical impedance spectroscopies (EIS) of fuel cells were measured. Additionally, the constant-voltage mode long-term stability of PEMFCs humidified with NaCl solution were investigated. Constant-voltage measurements and EIS results imply that the degradation of fuel cells is clearly related with the concentration of NaCl solutions.

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Effects of NaCl Solution on Proton Exchange Membrane Fuel Cell with Serpentine Flow Channel of Different Depths
Dong Kun Song, Ho Jun Yoo, Jung Soo Kim, Ki Won Hong, Do Young Jung, George Ilhwan Park, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2025; 42(5): 399. CrossRef
Analysis of Electrochemical Behavior of PEMFC Humidified with NaCl Solution Mist Using an Ultrasonic Vibrator
Ho Jun Yoo, Gye Eun Jang, Young Jo Lee, Dong Kun Song, Heeyun Lee, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2022; 39(12): 939. CrossRef

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Effects of Current Collecting Methods for Polymer Bipolar Plate of Ultra-Light Polymer Electrolyte Membrane Fuel Cells: Gye Eun Jang, Young Jo Lee, Gu Young Cho; J. Korean Soc. Precis. Eng. 2022;39(2):109-114.
Published online February 1, 2022; DOI: https://doi.org/10.7736/JKSPE.021.118

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In this study, polymer bipolar plates for ultra-light polymer electrolyte membrane fuel cells (PEMFCs) were fabricated. Various methods for current collecting were applied to ensure electron conductivity of the polymer bipolar plates. Direct wire contact and Ag sputter process were applied. The Ag current collecting layer fabricated by the sputter process showed a well-covered and defectless surface. After preparations of bipolar plates, the effects of current collecting methods of bipolar plates on the electrochemical properties of PEMFCs were systematically investigated. The maximum power density of PEMFCs with the Ag current collecting of layered polymer bipolar plates decreased 37.39% because of increased ohmic resistance. However, the power/weight of PEMFCs with the Ag current collecting of layered polymer bipolar plates increased 27.23% because of the dramatically reduced weight (-50.63%) of bipolar plates compared to the graphite bipolar plates. We affirm that results in this report can provide meaningful insight for portable electrochemical energy devices.

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A Study on Electrochemical Resistance Change through the Pressurization Process of MEA for PEMFC
Ye Rim Kwon, Dong Kun Song, Ho Jun Yoo, Gye Eun Jang, Young Jo Lee, Jung Soo Kim, Ji Woong Jeon, Da hae Guem, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2023; 40(7): 539. CrossRef

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A Study on the Selection of Failure Factors for Transient State Lithium-Ion Batteries based on Electrochemical Impedance Spectroscopy: Miyoung Lee, Seungyun Han, Jinhyeong Park, Jonghoon Kim; J. Korean Soc. Precis. Eng. 2021;38(10):749-756.
Published online October 1, 2021; DOI: https://doi.org/10.7736/JKSPE.021.040

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Lithium-ion batteries are one of the main parts of electrical devices and are widely used in various applications. To safely use lithium-ion batteries, fault diagnosis and prognosis are significant. This paper analyzes resistance parameters from electrochemical impedance spectroscopy (EIS) to detect the fault of lithium-ion batteries. The internal fault mechanisms of batteries are so complex; it is difficult to detect abnormalities by direct current-based methods. However, by using alternating-current-based impedance by EIS, the internal degradation processes of the batteries can be detected. Impedance variation from EIS is verified under accelerated degradation test conditions and normal cycling test conditions. The results showed a significant relationship between fault and increase in resistance.

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Research into the Detection of Faulty Cells in Battery Systems Using BMS Cell Balancing Counts
Hyunjun Kim, Woongchul Choi
Transaction of the Korean Society of Automotive Engineers.2025; 33(8): 637. CrossRef
PEDOT:PSS‐Based Prolonged Long‐Term Decay Synaptic OECT with Proton‐Permeable Material, Nafion
Ye Ji Lee, Yong Hyun Kim, Eun Kwang Lee
Macromolecular Rapid Communications.2024;[Epub] CrossRef
Lithium-Ion Batteries (LIBs) Immersed in Fire Prevention Material for Fire Safety and Heat Management
Junho Bae, Yunseok Choi, Youngsik Kim
Energies.2024; 17(10): 2418. CrossRef