• Proceedings of the Korean Information Science Society Conference
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• 2001.04b
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• pp.568-570
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• 2001

fiducial mark는 PCB 정밀조립/검사 장비에서 위치보정을 위해 필수적으로 사용되는데, 실제 생산현장에서의 fiducial mark의 품질은 완전하지 않고, 손상된 상태인 경우가 많이 발생한다. 기존에 주로 사용되는 blob centroid 방법에 의한 mark의 위치추출은 mark의 상태가 손상되었을 경우, 큰 오차를 수반하게 된다. 본 논문에서는 Generalized Hough Transform을 이용한 fiducial mark의 중심위치 기법을 개발하여, 적용한 결과 손상된 mark에 대해서도 매우 강건한 결과를 보여주었다.

• Korean Journal of Remote Sensing
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• v.19 no.1
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• pp.61-70
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• 2003

This paper proposes an autonomous approach to localize the center of fiducial marks included in aerial photographs without precise geometric information and human interactions. For this localization, we present a conceptual model based on two assumptions representing symmetric characteristics of fiducial area and fiducial mark. The model makes it possible to locate exact center of a fiducial mark by checking the symmetric characteristics of pixel value distribution around the mark. The proposed approach is composed of three steps: (a) determining the symmetric center of fiducial area, (b) finding the center of a fiducial mark with unit pixel accuracy, and finally (c) localizing the exact center up to sub-pixel accuracy. The symmetric center of the mark is calculated tv successively applying three geometric filters: simplified ${\nabla}^2$G (Laplacian of Gaussian) filter, symmetry enhancement filter, and high pass filter. By introducing a self-diagnosis function based on the self-similarity measurement, a way of rejecting unreliable cases of center calculation is proposed, as well. The experiments were done with respect to 284 samples of fiducial marks composed of RMK- and RC-style ones extracted from 51 scanned aerial photographs. It was evaluated in the visual inspection that the proposed approach had resulted the erroneous identification with respect to only one mark. Although the proposed approach is based on weak constraints, being free from the exact geometric model of the fiducial marks, experimental results showed that the proposed approach is sufficiently robust and reliable.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.536-541
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• 2002

This paper proposes an approach of automatically calculating the center location of fiducial marks up to sub-pixel accuracy with model-free condition. The conceptual model, composed of two assumptions, about general geometric property of fiducial area and fiducial mark is established. The proposed approach is primarily based on the strategy of calculating the center of symmetry and is composed of three steps of processing: (a) determining horizontal center of fiducial area, (b) locating center of a fiducial mark, and, (c) finally calculating the exact center up to sub-pixel accuracy. Evaluation with respect to RMK style marks and RC style ones shows that the proposed approach can be evaluated as robust one. However there are several images which can't be analyzed by the proposed approach.

• Journal of Korean Society for Geospatial Information Science
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• v.10 no.3 s.21
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• pp.79-87
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• 2002

This paper proposes an approach of automatically identifying the center of fiducial marks using radiometric and geometric characteristics of those marks existing on aerial photographs. Candidate region surrounding a mark, based on radiometric strategy, is determined by producing a bi-level image and by applying morphological operations. Based on geometric strategy, the central location of a mark is determined by applying ${\bigtriangledown}^G$ filtering and symmetry-enhancement filtering, and by finding peak location of symmetry. Evaluation with respect to 66 cases of sub-images containing a fiducial mark showed that the central location of the mark is determined up to around one pixel difference whit it is compared to a manual inspection.

• Journal of the Korean Institute of Intelligent Systems
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• v.25 no.3
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• pp.260-265
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• 2015

This paper proposes a alignment system using edge feature. An alignment system obtains the position and orientation of printed circuit board(PCB) or liquid crystal display(LCD) panel through the fiducial marks. Thus, it is the indicator of the system performance how accurate we detect the positions of the fiducial marks in the target image. Edges have the geometrical characteristics such as positions, lengths, and shapes. These features are suitable for finding the marks and have the advantages of lighting variations, model occlusion, as well as variations in scale and angle. The performance of the proposed system is validated through the alignment experiment using an display panel alignment system included X, Y axis, and rotatable stage.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.6
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• pp.96-104
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• 2003

This paper presents the measurement and correction method of PCB alignment errors for PCB screen printer. Electronic equipment is getting smaller and yet must satisfy high performance standard. Therefore, there is a great demand for PCB with high density. However conventional PCB screen printer doesn't have enough accuracy to accommodate the demand for high-resolution circuit pattern and high-density mounting capacity of electronic chips. It is because the alignment errors of PCB occur when it is loaded to the screen printer. Therefore, this study focuses on the development of the system which is able to measure and correct alignment errors with high-accuracy. An automatic optical inspection part measures the PCB alignment errors using machine vision, and the high-accuracy 3-axis stage makes correction for these errors. This system used two CCD cameras to get images of two fiducial marks of PCB. The centers of fiducial marks are obtained by using moment, gradient method. The first method is calculating the centroid by using first moment of blob, and the latter method is calculating the center of the circle whose equation is obtained by curve-fitting the boundaries of fiducial mark. The operating system used to implement the whole set-up is carried in Window 98 (or NT) environment. Finally we implemented this system to PCB screen printer.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.11
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• pp.77-84
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• 2009

Alignment error of the BGA lithography equipment is mainly caused by the dimensional change of the BGA panel which is generated during the manufacturing processes. To minimize the alignment error, 'mark alignment' algorithm in place of 'center alignment' algorithm was proposed and the optimal solution for the algorithm was derived by simple analytic form. The developed algorithm distributes evenly the alignment error over the whole panel which was evaluated by the numerical simulation. Finally, the developed algorithm was implemented to the controller of the lithography equipment and the alignment error was measured at the fiducial mark location. From the measurement, it is also concluded that the developed alignment algorithm be effective to reduce the maximum value of alignment error.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.434-437
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• 2003

Evaluation or the patterning accuracy of e-beam lithography machines requires a high precision inspection system that is capable of measuring the true xy-locations of fiducial marks generated by the e-beam machine under test. Fiducial marks are fabricated on a single photo mask over the entire working area in the form of equally spaced two-dimensional grids. In performing the evaluation, the principles of self-calibration enable to determine the deviations of fiducial marks from their nominal xy-locations precisely, not being affected by the motion errors of the inspection system itself. It is. however, the fact that only repeatable motion errors can be eliminated, while random motion errors encountered in probing the locations of fiducial marks are not removed. Even worse, a random error occurring from the measurement of a single mark propagates and affects in determining locations of other marks, which phenomenon in fact limits the ultimate calibration accuracy of e-beam machines. In this paper, we describe an uncertainty analysis that has been made to investigate how random errors affect the final result of self-calibration of e-beam machines when one uses an optical inspection system equipped with high-resolution microscope objectives and a precision xy-stages. The guide of uncertainty analysis recommended by the International Organization for Standardization is faithfully followed along with necessary sensitivity analysis. The uncertainty analysis reveals that among the dominant components of the patterning accuracy of e-beam lithography, the rotationally symmetrical component is most significantly affected by random errors, whose propagation becomes more severe in a cascading manner as the number of fiducial marks increases

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.17 no.4
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• pp.321-330
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• 1999

Automation of observation and positioning of fiducial marks is made possible with the application of image matching technique, developed through the cooperative research effort of computer vision and digital photogrammetry. The major problem in such automation effort is to minimize the computing time and to increase the positional accuracy. Except for scanning and ground control surveying, the interior orientation process was automated in this study, through the development of an algorithm which applies the image matching and image processing techniques. The developed system was applied to close-range photogrammetry and the analysis of the results showed 54% improvement in processing time. For fiducial mark observation during interior orientation, the Laplacian of Gaussian transformation and the Hough transformation were applied to determine the accurate position of the center point, and the correlation matching and the least squares matching method were then applied to improve the accuracy of automated observation of fiducial marks. Image pyramid concept was applied to reduce the computing time of automated positioning of fiducial mark.

• Proceedings of the Korean Information Science Society Conference
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• 2010.06c
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• pp.442-446
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• 2010

본 논문에서는 거리변환 기반의 정밀한 fiducial 마크 정렬 알고리즘을 제안한다. 거리변환은 물체의 중심에 가중치를 가지는 특성이 있는데 이는 AOI 공정에서 에칭, 이동과 같은 다양한 요소들로부터 획득되는 타겟영상에 대하여 강인하게 물체의 중심으로 매칭할 수 있도록 한다. 제안한 방법은 우선 입력 타겟영상에 대하여 이진화를 진행하고, 다음 모델과 타겟영상에 대하여 거리변환을 이용하여 거리특징을 추출하고, 추출된 모델과 타겟영상에 대한 거리특징을 NCC(Normalized Cross Correlation)를 이용하여 매칭한 후, 매칭 스코어에 대하여 Sub-pixel 분석을 진행하여 sub-pixel 레벨의 정확도를 가지도록 한다. 실험결과로부터 제안한 거리특징을 이용한 매칭 알고리즘이 기존의 픽셀 밝기 값을 이용한 매칭보다 강인하고 정확하게 매칭됨을 확인할 수 있었다.