• 한국정밀공학회지
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• 제15권10호
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• pp.103-112
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• 1998

The evolution of semiconductor manufacturing technology has accelerated the reduction of device dimensions and the increase of integrated circuit density. In order to improve yield within a short turn around time and maintain it at high level, a system that can rapidly determine problematic processing steps is needed. The statistical process control detects abnormal process variation of key parameters. Expert systems in SPC can serve as a valuable tool to automate the analysis and interpretation of control charts. A set of IF-THEN rules was used to formalize knowledge base of special causes. This research proposes a strategy to apply expert system to SPC in semiconductor manufacturing. In analysis, the expert system accomplishes the instability detection of process parameter, In diagnosis, an engineer is supported by process analyzer program. An example has been used to demonstrate the expert system and the process analyzer.

• 품질경영학회지
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• 제39권2호
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• pp.234-243
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• 2011

Multivariate control charts are widely used to monitor the performance of a multivariate process over time to maintain control of the process. Although existing multivariate control charts provide control limits to monitor the process and detect any extraordinary events, it is a challenge to identify the causes of an out-of-control alarm when the number of process variables is large. Several fault identification methods have been developed to address this issue. However, these methods require a normality assumption of the process data. In the present study, we propose a bootstrapped-based $T^2$ decomposition technique that does not require any distributional assumption. A simulation study was conducted to examine the properties of the proposed fault identification method under various scenarios and compare it with the existing parametric $T^2$ decomposition method. The simulation results showed that the proposed method produced better results than the existing one, especially in nonnormal situations.

• 산업경영시스템학회지
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• 제41권4호
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• pp.203-212
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• 2018

Quality requirements of manufactured products or parts are given in the form of specification limits on the quality characteristics of individual units. If a product is to meet the customer's fitness for use criteria, it should be produced by a process which is stable or repeatable. In other words, it must be capable of operating with little variability around the target value or nominal value of the product's quality characteristic. In order to maintain and improve product quality, we need to apply statistical process control techniques such as histogram, check sheet, Pareto chart, cause and effect diagram, or control charts. Among those techniques, the most important one is control charting. The cumulative sum (CUSUM) control charts have been used in statistical process control (SPC) in industries for monitoring process shifts and supporting online measurement. The objective of this research is to apply Taguchi's quality loss function concept to cost based CUSUM control chart design. In this study, a modified quality loss function was developed to reflect quality loss situation where general quadratic loss curve is not appropriate. This research also provided a methodology for the design of CUSUM charts using Taguchi quality loss function concept based on the minimum cost per hour criterion. The new model differs from previous models in that the model assumes that quality loss is incurred even in the incontrol period. This model was compared with other cost based CUSUM models by Wu and Goel, According to numerical sensitivity analysis, the proposed model results in longer average run length in in-control period compared to the other two models.

• Clinical and Experimental Pediatrics
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• 제51권1호
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• pp.1-25
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• 2008

목 적 : 1967년 이후로 1998년까지 대한소아과학회와 정부는 매 10년마다 한국 소아청소년 신체발육표준치를 제정하여 왔다. 지난 40년간의 한국 성장도표는 체계적이고 통계학적인 표준화를 거치지 않은 기술적인 도표였다. 전 세계적인 비만의 유행에 대하여 WHO나 CDC와 같은 국제적인 기관들은 이에 대처하기 위하여 성장도표의 제정 원리들을 변경하여 왔다. 본 논문은 고찰과 함께 새로운 2007년 성장도표 개발과정을 요약하였다. 방 법 : 질병관리본부 만성병조사과의 주도로 2005년에 새로운 성장도표 제정을 위한 신체계측 조사를 시행하였고, 그 결과 소아 비만의 급증과 청소년 최종 성장의 세대별 증가 현상이 정체된 것을 확인하였다. 이에 연구진은 혁신적인 방법론을 도입하였으며, 이를 통하여 새로운 성장도표를 제정하였다. 확보 가능한 원자료인 1997년 및 2005년 측정 자료를 표준화고 통합하였으며, LMS 방법을 도입하여 통계적 모델링을 시행하였다. 결 과 : 표준화된 자료로서 연령별 신장, 연령별 체중, 연령별 체질량지수, 연령별 두위, 신장별 체중 도표가 제공되며, 2005년 조사의 표준화되지 않은 자료로 제공되는 연령별 허리둘레, 연령별 가슴둘레, 연령별 상완둘레, 연령별 피부 두겹집기가 제공된다. 임상 지침도 함께 제공된다. 결 론 : 새로운 한국 성장도표의 개발 과정과 결과는 국제적인 기준인 WHO 표준성장도표 및 미국 CDC 성장도표의 방법론을 적용한 것으로서, 비만과 성 발육이 가속화된 현 상황에 적절하다. 이는 특히 한국 국민과 한민족에게 유용하다. 향후 보다 과학적인 표준을 제시하기 위하여 지속적인 연구가 요청된다.

• 통합자연과학논문집
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• 제5권3호
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• pp.151-156
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• 2012

Because of the equivalence between control chart procedures and hypothesis testing, we propose to use likelihood ratio test (LRT) statistic $Z_i^2$ as the multivariate control statistic for simultaneous monitoring means of the multivariate normal process. Properties and comparisons of the proposed control charts are explored and conducted for matched fixed sampling interval (FSI) and variable sampling interval (VSI) with two sampling interval charts. The result of numerical comparisons shows that EWMA chart with two sampling interval procedure is more efficient than the corresponding FSI chart for small or moderate changes. When large shift of the process has occurred, we also found that Shewhart chart is more efficient than EWMA chart.

• 대한산업공학회지
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• 제40권1호
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• pp.43-51
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• 2014

Statistical process control (SPC) is an important technique for monitoring and managing the manufacturing process. In spite of its easiness and effectiveness, some problematic sides of application exist such that the SPC techniques are hardly reflect the changes of the process conditions. Especially, update of control limits at the right time plays an important role in acquiring a reasonable performance of control charts. Therefore, we propose the control chart performance evaluation index (CPEI) based on count data model to monitor and manage the performance of control charts. The CPEI could indicate the degree of control chart performance and be helpful to detect the proper update cycle of control limits in real time. Experiments using real manufacturing data show that the proper update intervals are made by proposed method.

• 한국터널지하공간학회 논문집
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• 제12권6호
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• pp.463-473
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• 2010

통계 관리도 기법을 활용한 터널 굴착면 전방 단층대 예측 기법을 제시하고 적용성을 검토하였다. 5개의 RMR 변수와 기초 RMR에 대한 $x-R_s$ 관리도를 작성하여 단층대로 접근함에 따른 각 변수의 변화 분석을 통해 이상 구간을 통계적인 기준에 의해 판정하였으며, 이러한 이상 구간을 단층대 구간으로 간주하였다. 관리도 평가 기법을 터널 시공현장에 적용한 결과, 선진수평시추 및 막장 관찰을 통해 확인된 3 개소의 단층대 구간은 관리도 판정에 의해 단층대가 출현하는 시점보다 각각 1~3 굴착면 이전에 인지되었으며, 거리로 환산하면 2.2 m, 5.0 m, 6.0 m 이전에 해당된다.

• 한국데이터정보과학회:학술대회논문집
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• 한국데이터정보과학회 2003년도 춘계학술대회
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• pp.89-95
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• 2003

Cumulative sum(CUSUM) control charts for monitoring dispersion matrix under multivariate normal process are proposed. Performances of the proposed CUSUM charts are measured in terms of average run length(ARL) by simulation. Numerical results show that small reference values of the proposed CUSUM chart is more efficient for small shifts in the production process.

• 한국통계학회:학술대회논문집
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• 한국통계학회 2005년도 춘계 학술발표회 논문집
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• pp.191-196
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• 2005

Knowing the time of the process change could lead to quicker identification of the responsible special cause and less process down time, and it could help to reduce the probability of incorrectly identifying the special cause. In this paper, we propose a MLE of the process change point when control charts with the fixed sampling rate (FSR) scheme or the variable sampling rate (VSR) scheme monitor a process to detect changes in the process mean and/or variance of a normal quality variable.

• 품질경영학회지
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• 제37권1호
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• pp.29-39
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• 2009

This article investigates economic-statistical design of VSSI(variable sampling size and interval) cause-selecting charts considering two assignable causes. We consider a process which is composed of two dependent sub-processes. In each sub-process, two kinds of assignable cause may exist. We propose a procedure for designing VSSI cause-selecting charts, based on Lorenzen and Vance model. Computational experiments show that the VSSI cause-selecting chart is superior to the FSSI cause-selecting chart in the economic-statistical characteristics, even under two assignable causes.