• Journal of Sensor Science and Technology
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• v.24 no.3
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• pp.169-174
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• 2015

In this study, we developed a system to detect the various defects in the metallic objects using the phenomenon that the defects cause the changes of the natural resonant frequencies. Our system consists of a FFT Amp, an Auto Impact Hammer, a Hammer controller and a PC. Auto Impact Hammer creates vibrations in the metallic objects when tapped on the surface. These vibrational signals are converted to the voltage signals by an acceleration sensor attached to the metallic part surface. These analog voltage signals were fed into an ADC (analog-digital converter) and an FFT (fast fourier transform) conversion in the FFT Amp to obtain the digital data in the frequency domain. Labview graphical program was used to process the digital data from th FFT amp to display the spectrum. We compared those spectra with the standard spectrum to find the shifts in the resonant frequencies of the metal parts, and thus detecting the defects. We used PCB's acceleration sensor and TI's TMS320F28335 DSP (digital signal processor) to obtain the resolution of 2.93 Hz and to analyze the frequencies up to 44 kHz.

• Journal of Broadcast Engineering
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• v.26 no.4
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• pp.409-418
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• 2021

Conformal coating is a technology that protects PCB(Printed Circuit Board) and minimizes PCB failures. Since the defects in the coating are linked to failure of the PCB, the coating surface is examined for air bubbles to satisfy the successful conditions of the conformal coating. In this paper, we propose an algorithm for detecting problematic bubbles in high-risk groups by applying image signal processing. The algorithm consists of finding candidates for problematic bubbles and verifying candidates. Bubbles do not appear in visible light images, but can be visually distinguished from UV(Ultra Violet) light sources. In particular the center of the problematic bubble is dark in brightness and the border is high in brightness. In the paper, these brightness characteristics are called valley and mountain features, and the areas where both characteristics appear at the same time are candidates for problematic bubbles. However, it is necessary to verify candidates because there may be candidates who are not bubbles. In the candidate verification phase, we used convolutional neural network models, and ResNet performed best compared to other models. The algorithms presented in this paper showed the performance of precision 0.805, recall 0.763, and f1-score 0.767, and these results show sufficient potential for bubble test automation.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.2
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• pp.22-27
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• 2009

In this paper, an automatic functional inspection system EVT (Emulated Vision Tester) for LCD drive module PCB has been proposed and implemented. Typical automatic inspection system such as probing methods and vision-based systems are widely known and used, however, there exist undetectable defects due to critical timing factors which they may miss to catch from LCD equipments. Especially typical vision-based systems have inconsistency on acquisition of images so that distinction between gray scales can be difficult which results in low level of performance and reliability on the inspection results. The proposed EVT system is pure hardware solution. It directly compares pattern signals from a pattern generator to output signals from LCD drive module. It also inspects variety of analog signals such as voltage, resistance, wave forms and so forth. The EVT system not only shows high performance in terms of reliability and processing speed but reduces costs on inspection and maintenance. Also, full automation of entire production line can be realized when EVT is applied in in-line inspection processes.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.343-348
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• 1992

Using the real-time image processing technique, we have developed an automatic visual inspection system which detects the defects of the surface muonted components in PCB( missing components, mislocation, mismounts, and reverse polarity, etc ) and collects the quality control and production management data. An image processing system based on a commercial parallel processor, TRANSPUTER by which the image processing time can be largely reduced was designed. Analyzing the collected data, the proposed inspection system contributes to the productivity improvement throughthe reduction of defective rate.

• Transactions on Electrical and Electronic Materials
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• v.13 no.3
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• pp.129-135
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• 2012

A number of surface mount technology (SMT) process variables including land design are considered for minimizing tombstone defect in flexible printed circuit assembly in high volume manufacturing. As SMT chip components have been reduced over the past years with their weights in milligrams, the torque that once helped self-centering of chips, gears to tombstone defects. In this paper, we have investigated the correlation of the assembly process variables with respect to the tombstone defect by employing statistically designed experiment. After the statistical analysis is performed, we have setup hypotheses for the root causes of tombstone defect and derived main effects and interactions of the process parameters affecting the hypothesis. Based on the designed experiments, statistical analysis was performed to investigate significant process variable for the purpose of process control in flexible printed circuit manufacturing area. Finally, we provide beneficial suggestions for find-pitch PCB design, screen printing process, chip-mounting process, and reflow process to minimize the tombstone defects.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.10a
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• pp.570-573
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• 2022

This paper presents the identification of void diameters for a cast-resin transformer using an artificial neural network (ANN) model. A PD signal was measured by the Rogowski coil sensor which has the planar and thin structures fabricated on a printed circuit board (PCB), and the PD electrode system was fabricated to simulate a PD defect by a void. In addition, void samples with different diameters were fabricated by injecting air in a cylindrical aluminum frame using a syringe during the epoxy curing process. To identify the diameter of void defects, PD characteristics such as the discharge magnitude, pulse count, and phase angle were extracted and back propagation algorithm (BPA) was designed using virtual instrument (VI) based on the Labview program. From the experimental results, the BPA algorithm proposed in this paper has over 90% accurate rate to identify the diameter of void defects and is expected to use reference data of maintenance and replacement of insulation for cast-resin transformers in the on-site PD measurement.

• Korean Journal of Materials Research
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• v.24 no.4
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• pp.186-193
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• 2014

A thin Cu seed layer for electroplating has been employed for decades in the miniaturization and integration of printed circuit board (PCB), however many problems are still caused by the thin Cu seed layer, e.g., open circuit faults in PCB, dimple defects, low conductivity, and etc. Here, we studied the effect of heat treatment of the thin Cu seed layer on the deposition rate of electroplated Cu. We investigated the heat-treatment effect on the crystallite size, morphology, electrical properties, and electrodeposition thickness by X-ray diffraction (XRD), atomic force microscope (AFM), four point probe (FPP), and scanning electron microscope (SEM) measurements, respectively. The results showed that post heat treatment of the thin Cu seed layer could improve surface roughness as well as electrical conductivity. Moreover, the deposition rate of electroplated Cu was improved about 148% by heat treatment of the Cu seed layer, indicating that the enhanced electrical conductivity and surface roughness accelerated the formation of Cu nuclei during electroplating. We also confirmed that the electrodeposition rate in the via filling process was also accelerated by heat-treating the Cu seed layer.

• Journal of Welding and Joining
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• v.31 no.3
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• pp.84-88
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• 2013

These days embedded technology may be the most significant development in the electronics industry. The study focused on the development of active device embedding using flexible printed circuit in view of process and materials. The authors fabricated 30um thickness Si chip without any crack, chipping defects with a dicing before grinding process. In order to embed chips into flexible PCB, the chip pads on a chip are connected to bonding pad on flexible PCB using an ACF film. After packaging, all sample were tested by the O/S test and carried out the reliability test. All samples passed environmental reliability test. In the future, this technology will be applied to the wearable electronics and flexible display in the variety of electronics product.

• Journal of the Semiconductor & Display Technology
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• v.10 no.4
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• pp.125-130
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• 2011

The recent PCB (Printed Circuit Board) wet etcher has been needed to process pattern within $20{\mu}m$ width on a $20{\mu}m$ thick board. A previous PCB etcher can be used with multiple points of roller rolls or slips off a board. Also, the damage of the board by contacting the roller increases the friction defects. A vertical type boards transporting process is developed to solve the problems of boards friction and sagging in a horizontal etcher. In this research, CFD (Computational Fluid Dynamics) method is used to design an improved spray nozzle including the critical part of etcher, and establish the design method. Meanwhile, major spray characteristics are expected in diverse nozzle types and variables. Lastly, diverse simulation results are adapted to design an improved nozzle and spray system.

• Journal of Institute of Control, Robotics and Systems
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• v.3 no.3
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• pp.323-331
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• 1997

A new probing mechanism and an active compliance control algorithm have been developed for the in-circuit test of a PCB( printed circuit board ). Commercially available robotic probing devices are incapable of controlling contact force generated through rigid probe contacts with a solder joint, at high speed. The uncontrollable excessive contact force often brungs about some defects on the surface of the solder joint, which is plastically deformable over some limited contact force. This force also makes unstable contact motions resulting in unreliable test data. To overcome these problems, we propose that a serially connected macro and micro device with active compliance provide the best potential for a safe and reliable in-circuit test. This paper describes the design characteristics, modeling and control scheme of the newly proposed device. The experimental results clearly show the effectiveness of the proposed system.