• Journal of the Korean Society for Precision Engineering
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• v.15 no.10
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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.

• Journal of Korean Society for Quality Management
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• v.39 no.2
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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.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.41 no.4
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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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• v.51 no.1
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• pp.1-25
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• 2008

Purpose : Since 1967, The Korean Pediatric Society and Korean Government have developed Korean Growth Standards every 10 years. Last version was published in 1998. During past 40 years, Korean Growth Standards were mainly descriptive charts without any systematic nor statistical standardization. With the global epidemic of obesity, many authorities such as World Health Organization (WHO) and United States' Centers for Disease Control (CDC) have been changed their principles of growth charts to cope with the situations like ours. This article summarizes and reviews the whole developmental process of new 2007 Korean Growth Charts with discussion. Methods : With the initiative of Division of Chronic Disease Surveillance in Korea Centers for Disease Control and Prevention, we have performed new national survey for the development of new Standards in 2005 and identified marked increase of childhood obesity and plateau of secular increment of final height in late adolescents. We have developed new Growth Standards via adapting several innovative methods, including standardization of all available raw data, which were acquired in 1997 and 2005 national survey and full application of LMS method. Results : We could get new standardized charts; weight-for-age, length/height-for-age, weight-for-height, head circumference-for-age and BMI-for-age. Other non-standardized charts based on 2005 survey data were also published; waist circumference-for-age, mid-arm circumference-for-age, chest circumference-for-age and skinfold-for-age. Clinical guideline was also developed. Conclusion : Developmental process and results of new Korean Growth Charts are comparable with other internationally well-known Growth Standards, WHO 2006 Growth Standards and CDC Growth Charts. 2007 Korean Growth Charts are relevant especially in Korea and Korean ethnic groups.

• Journal of Integrative Natural Science
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• v.5 no.3
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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.

• Journal of Korean Institute of Industrial Engineers
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• v.40 no.1
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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.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.6
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• pp.463-473
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• 2010

A new approach for prediction of a fault zone ahead of tunnel face by using statistical control charts is suggested and applied to the construction site. $x-R_s$ control charts of RMR parameters were investigated as approaching and passing through fault zone. The abnormal signal from the control charts was observed and analyzed based on statistical criteria. Fault zones in the application area were predicted in advance using this method and it was verified by comparing with observation data like horizontal boring and face mapping.

• 한국데이터정보과학회:학술대회논문집
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• 2003.05a
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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.

• Proceedings of the Korean Statistical Society Conference
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• 2005.05a
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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.

• Journal of Korean Society for Quality Management
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• v.37 no.1
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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.