Browsing by Author "Tai, Y. T."

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A note on production yield measure for multiple lines
(2016)
Pearn, W. L.
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Tai, Y. T.
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Wu, C. H.
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工業工程與管理學系
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Department of Industrial Engineering and Management
In today\'s globally competitive environment, processes involving multiple manufacturing lines are quite common due to economies of scale considerations. Production yield measure indices C-pk and C-pu are the most popular yield-based indices and have been widely used in manufacturing industries for two-sided and one-sided specification limits, respectively. In this paper, two production yield indices for multiple lines C-pk(M) and C-pu(M) are considered and the approximate distributions of two natural estimators C-pk(M) and C-pu(M) are derived. For the convenience of industry applications, the lower confidence bounds and critical values are provided.
An analytical closed-form solution for multiple line supplier selection problem
(2019-07-04)
Pearn, W. L.
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Tai, Y. T.
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Tseng, S. C.
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工業工程與管理學系
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Department of Industrial Engineering and Management
Supplier selection is an essential issue, particularly, for semiconductor manufacturing. Nowadays, since high demands in the globally competitive semiconductor manufacturing environment, multiple-line processes are quite commonly applied. In the paper, we consider a two-stage method composing of quality verification and selection decision for multiple-line supplier selection problems. Since quality performance is an important criterion in supplier selection, we test whether the new supplier has a significantly better capability than the existing supplier based on the multiple-line yield index in the stage of quality verification. In selection decision, when the magnitude of capability outperformance is significant, switching contracts to a new entrant supplier is suggested. In addition, analytical closed-form solutions for asymptotical critical values and required sample sizes are derived and tabulated for the investigated multiple-line supplier selection problem. We demonstrate the applicability of the proposed supplier selection method by presenting a real-world example taken from a semiconductor packaging shop floor located in the Science-based Industrial Park in Hsinchu, Taiwan.
An Effective Powerful Test for Supplier Selection Evaluation with Multiple Characteristics
(2012-07-01)
Pearn, W. L.
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Tai, Y. T.
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Wang, C. Y.
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工業工程與管理學系
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Department of Industrial Engineering and Management
"Supplier selection in high-tech manufacturing industries has become more essential and has received considerable attention. In this paper, we consider a supplier selection problem with multiple characteristics in which we compare two-sided processes with multiple characteristics and select the better one with the higher capability. We first review an approach referred to as the division method. We then develop a new approach called the subtraction method. We compare the two methods in terms of their selection power. The results show that the proposed subtraction method is indeed more powerful than the division method. Two supplier-selection procedures are developed for practical applications. For practitioners' convenience in applying our procedures, the various sample sizes required for designated selection powers are tabulated and discussed. For illustration purposes, a case is considered and solved for supplier selection evaluation."
An Effective Scheduling Approach for Maximizing Polyimide Printing Weighted Throughput in Cell Assembly Factories
(2009-07-01)
Chung, S. H.
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Tai, Y. T.
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Pearn, W. L.
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工業工程與管理學系
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Department of Industrial Engineering and Management
Polyimide printing (PI) is an important process operation but also often the cause of bottlenecks in capital-intensive cell assembly factories. Therefore, the development of an effective scheduling method to maximize throughput in this PI process is essential and difficult. In the polyimide printing scheduling problem (PISP), jobs are given weights and clustered by their product types, which must be processed on identical parallel PI machines. The setup times for two consecutive jobs between different product types in the PI machines are sequence-dependent. In this paper, the PISP is formulated as a mixed integer linear programming model. The PISP is also transformed into a multiple tour maximum collection problem (MTMCP), a well-known network problem which has been investigated extensively. Based on this transformation, one can therefore solve the PISP near-optimally using the efficient algorithm.
An Effective Test for Supplier Selection Evaluation with Multiple Characteristics
(2011-11-01)
Tai, Y. T.
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Pearn, W. L.
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You, S. K.
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工業工程與管理學系
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Department of Industrial Engineering and Management
Recently, the extensive applications of thin-film transistor liquid crystal display (TFT-LCD) products have been increasing rapidly (for example, smart phones, monitors, and liquid crystal display televisions). Supplier selection in TFT-LCD manufacturing industries has become more essential and has received considerable attention. It is a problem of comparing two suppliers and selecting the one that has a significantly higher process capability. In this paper, we consider an effective test to determine supplier selection for glass substrate processes with multiple characteristics using the yield index S(pk)(T), which can provide an exact measure of the process yield. In order to determine the selection decisions, critical values of the hypothesis testing for two procedures are calculated. For the practitioners' convenience in applying our procedures, various sample sizes required for designated selection powers are tabulated and discussed. For illustration purposes, a real-world problem in TFT-LCD factories is considered and solved for supplier selection evaluation.
An Improved Manufacturing Yield Measure for Gold Bumping Processes With Very Low Nonconformities
(2019-05-01)
Wu, C. H.
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Pearn, W. L.
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Tai, Y. T.
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工業工程與管理學系
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Department of Industrial Engineering and Management
Nowadays, thinner and slimmer smartphones have been widely applied in daily life. In most portable devices, liquid-crystal display driver integrated circuit (IC) or new touch display driver IC are critical components, in which the gold bumping process is used as an essential interconnection technology and usually outsources to out-sourced assembly and testing factories. In semiconductor packaging manufacturing, due to popular high-definition requirements of display devices, gold bumping processes require very low fraction of nonconformities. For this reason, accurately evaluating the manufacturing yield is very important to guarantee the quality requirements being met. To evaluate the yield of gold bumping processes, the most popular yield index C-pk is widely employed in outsourcing contract arrangements. However, the typical existing nature estimator is a biased estimator and more conservative. In this paper, we provide an unbiased estimator to evaluate the gold bumping manufacturing yield more accurately. Based on the new estimator, we further propose a weighted parametric bootstrap method to obtain a reliable lower confidence bound that is closer to the true manufacturing yield. The new yield assessment can avoid underestimating the gold bumping manufacturing yield and can make more reliable decisions.
Approximately Unbiased Estimator for Non-Normal Process Capability Index C-Npk
(2014-11-01)
Pearn, W. L.
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Tai, Y. T.
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Hsiao, I. F.
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Ao, Y. P.
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工業工程與管理學系
Process capability indices (PCIs) have been extensively used to evaluate and measure whether the process meets the specifications and they provide quality assurance and guide a principal for quality improvement. The index C-pk is the most popular index and is widely used in the manufacturing industry for manufacturing yield evaluation. However, typical evaluations of C-pk depend heavily on the assumption of normal variability. When the underlying distributions are non-normal, the capability evaluations are highly unreliable. In the paper, we apply four various bootstrap methods to construct lower confidence bounds of C-Npk for non-normal processes. We also propose an approximately unbiased estimator of C-Npk for the non-normal processes. Comparisons among the four bootstrap methods with different estimators are provided.
Capability Assessment for Processes with Multiple Characteristics: A Generalization of the Popular Index C(pk)
(2011-12-01)
Pearn, W. L.
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Shiau, J. -J. H.
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Tai, Y. T.
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Li, M. Y.
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統計學研究所
Process capability index C(pk) is the most popular capability index widely used in the manufacturing industry. Existing research on the yield-based measure index C(pk) to date is restricted to processes with single characteristics. However, many manufacturing processes are commonly described with multiple characteristics, for example, the gold bumping process in the TFT-LCD (thin film transistor-liquid crystal display) manufacturing industry. In the gold bumping process, gold bumps have multiple characteristics all having effects on the process yield. Obtaining accurate gold bumping manufacturing yield is very important for quality assurance and in providing guidance toward process improvement. To obtain accurate yield assessment for processes with multiple characteristics, we propose a new overall yield-measure index C(pk)(T), which is a generalization of the index C(pk), and a natural estimator (C) over cap (T)(pk) of C(pk)(T). For the purpose of making inferences on the process capability, we derive a quite accurate approximation of the distribution of (C) over cap (T)(pk) since the distribution is analytically intractable. With this distribution, we tabulate the lower confidence bounds of the new index under various sample sizes for in-plant applications. In addition, we construct a statistical test on the new yield-measure index in order to examine whether the yield meets the customers' requirements. For illustration purpose, a real case in a gold bumping factory located in the Science-based Industrial Park at Hsinchu, Taiwan is presented. Copyright (C) 2011 John Wiley & Sons, Ltd.
Capability Assessment for Processes with Multiple Characteristics: A Generalization of the Popular Index C-pk
(2011-12-01)
Pearn, W. L.
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Shiau, J. -J. H.
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Tai, Y. T.
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Li, M. Y.
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統計學研究所
Process capability index C-pk is the most popular capability index widely used in the manufacturing industry. Existing research on the yield-based measure index C-pk to date is restricted to processes with single characteristics. However, many manufacturing processes are commonly described with multiple characteristics, for example, the gold bumping process in the TFT-LCD (thin film transistor-liquid crystal display) manufacturing industry. In the gold bumping process, gold bumps have multiple characteristics all having effects on the process yield. Obtaining accurate gold bumping manufacturing yield is very important for quality assurance and in providing guidance toward process improvement. To obtain accurate yield assessment for processes with multiple characteristics, we propose a new overall yield-measure index C-pk(T), which is a generalization of the index C-pk, and a natural estimator (C) over cap (T)(pk) of C-pk(T). For the purpose of making inferences on the process capability, we derive a quite accurate approximation of the distribution of (C) over cap (T)(pk) since the distribution is analytically intractable. With this distribution, we tabulate the lower confidence bounds of the new index under various sample sizes for in-plant applications. In addition, we construct a statistical test on the new yield-measure index in order to examine whether the yield meets the customers' requirements. For illustration purpose, a real case in a gold bumping factory located in the Science-based Industrial Park at Hsinchu, Taiwan is presented. Copyright (C) 2011 John Wiley & Sons, Ltd.
Convenient Ratio Approach for Industrial Implementation in Estimating and Testing Process Yield
(2015-07-01)
Pearn, W. L.
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Tai, Y. T.
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Kao, C. M.
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統計學研究所
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工業工程與管理學系
In recent years, since portable devices with thin and light designs are essential, the applications of the thin-film transistor liquid crystal display (TFT-LCD) have been applied extensively. Process yield is the most common criterion used in the TFT-LCD manufacturing industry for measuring process performance. The measurement index Spk establishes the relationship between the manufacturing specifications and the actual process performance, which provides an exact measure on process yield. In this paper, we provide two convenient ratio approaches to calculate the lower confidence bounds and critical values extensively for various values of alpha-risk, capability requirements, and sample sizes. Practitioners can use the proposed ratio approaches and procedures to determine whether their process meets the preset capability requirement and make reliable decisions. The convenient ratio approaches can bridge the gap between the theoretical development and factory applications for evaluation of process yields.
Cycle time estimation for semiconductor final testing processes with Weibull-distributed waiting time
(2012)
Tai, Y. T.
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Pearn, W. L.
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Lee, J. H.
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工業工程與管理學系
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Department of Industrial Engineering and Management
Accurate cycle time is an essential planning basis required for many production applications, especially on due date commitments, performance metrics analysing, capacity planning, and scheduling. The re-entrant final testing process is the final stage of the complicated semiconductor manufacturing process. To enhance the ability of quick responses and to achieve better on-time delivery in final testing factories, it is essential to develop an accurate cycle time estimation method. In this paper, we provide a statistical approach to calculate the cycle time for multi-layer semiconductor final testing involving the sum of multiple Weibull-distributed waiting times. In addition, percentiles of the cycle time are obtained which are useful to industrial practitioners for due date commitments satisfying the targeted on-time delivery rate. To demonstrate the applicability of the proposed cycle time estimation model, a real example in a semiconductor final testing factory which is located on the Science-based Industrial Park in Hsinchu, Taiwan, is presented.
Estimation of a Modified Capability Index for Non-Normal Distributions
(2016-09)
Pearn, W. L.
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Tai, Y. T.
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Wang, H. T.
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工業工程與管理學系
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Department of Industrial Engineering and Management
Process capability indices (PCIs), which are very important in quality control have been one of a numerical measure index in manufacturing processes. Index C-pk is the most popular one used in the manufacturing industry. It is applied under the assumption that the processes are normally distributed. In real-world applications, non-normal processes may occur in industries, and the index C-Npk has been proposed for non-normal processes in which its exact sampling distribution is mathematically intractable. Quality practitioners commonly use the existing NCPPM (non-conformities in parts per million) table of C-pk to obtain process yields. However, the table could not be applied directly via the value of index CNpk. For the consistency of NCPPM mapping, we propose procedures to obtain the modified index C-Npk* and its approximately unbiased estimator C-Npk* for three non-normal distributions, involving Log-normal, Gamma, and Weibull distributions. The values of modified index C-Npk* could be used to inquire the existing popular NCPPM table of C-pk. In addition, four bootstrap methods were used to construct the lower confidence bounds of the index C-Npk*, which are useful to the practitioners for making reliable decisions regarding process performance based on process yield.
Fast and effective algorithms for the liquid crystal display module (LCM) scheduling problem with sequence-dependent setup time
(2009-07-01)
Chung, S. H.
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Pearn, W. L.
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Tai, Y. T.
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工業工程與管理學系
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Department of Industrial Engineering and Management
The liquid crystal display module scheduling problem (LCMSP) is a variation of the classical parallel machines scheduling problem, which has many real-world applications, particular, in the thin film transistor liquid crystal display (TFT-LCD) manufacturing industry. In this paper, we present a case study on the LCMSP, which is taken from a final liquid crystal display module (LCM) shop floor in a TFT-LCD industry. For the case we investigated, the jobs are clustered by their product types and the machine setup time is sequentially dependent on the product types of the jobs processed on the machine. In LCMSP, the objective is to maximize the total profit subject to fulfilling contracted quantities without violating the due date and machine capacity restrictions. The LCMSP can be modelled as a multi-level optimization problem. The sub-problem of LCMSP can be transformed into the vehicle routing problem with time window (VRPTW). One can therefore solve the LCMSP efficiently using existing VRPTW algorithms. We present two new algorithms based on the savings algorithms with some modifications to accommodate the LCMSP. Based on the characteristics of the LCM process, a set of test problems is generated covering most of the real-world applications for test purposes. Computational results and performance comparisons show that the proposed algorithms solved the LCMSP efficiently and near-optimally. Journal of the Operational Research Society (2009) 60, 921-933. doi:10.1057/palgrave.jors.2602604
Group Supplier Selection for Multiple-Line Gold Bumping Processes
(2016-10)
Pearn, W. L.
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Tai, Y. T.
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工業工程與管理學系
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Department of Industrial Engineering and Management
Portable devices have been popularly used nowadays. Liquid crystal display driver integrated circuit is an essential component in portable devices in which gold bumping process is a critical interconnection technology. To enhance bargaining power and to reduce cost, group suppliers are commonly selected from multiple suppliers. For high-definition display devices, a very low fraction of defectives is the basic quality requirement in gold bumping processes. Unfortunately, conventional yield measurement methods for supplier selection no longer work since any sample of reasonable size probably contains no defective gold bump product items. In this paper, we propose a group supplier selection procedure for multiple suppliers with multiple-line processes that are quite common due to high demands in semiconductor industry. For various significance levels, the number of suppliers, the number of manufacturing lines, predetermined capability requirements, and sample sizes, different selected suppliers are suggested based on the multipleline yield index C-pk(M). In addition, the power comparisons between different methods are also discussed. For the illustration purpose, real-world applications in a gold bumping factory that is located in the Science-Based Industrial Park in Hsinchu, Taiwan, are included.
Measuring Manufacturing Yield for Gold Bumping Processes Under Dynamic Variance Change
(2010-04-01)
Pearn, W. L.
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Tai, Y. T.
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Chiang, W. L.
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工業工程與管理學系
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Department of Industrial Engineering and Management
Recently, the technology of gold bumping has become more popular due to high demand for LCD driver ICs. The requirement of higher resolution application, however, will increase the difficulties for manufacturing the gold bumps due to their high pin counts. For gold bumping processes, bump height is one of the key parameters to control process yield. In reality, some inevitable process variations and shifts regarding the bump height may occur under dynamic manufacturing environment. Conventionally, manufacturing yield for gold bumping processes is calculated under the assumption that the processes are stable. In practice, however, the processes are dynamic, particularly, in the operation of Au-plating in gold bumping factories. To obtain accurate measure of the manufacturing yield, we present a capability index method for manufacturing yield calculation with dynamic variance change considerations. Using this method, the magnitude of the undetected variance change, which is function of the detection power of the chart, is incorporated into the adjusted calculation of manufacturing yield. The detection powers of the chart under various subgroup sizes are tabulated. For illustration purposes, a real application in a gold bumping factory which is located in the Science-based Industrial Park in Hsinchu, Taiwan, is presented.
Measuring the Manufacturing Yield for Processes With Multiple Manufacturing Lines
(2012-05-01)
Tai, Y. T.
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Pearn, W. L.
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Kao, Chun-Min
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統計學研究所
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工業工程與管理學系
Process yield is the most common criterion used in the semiconductor manufacturing industry for measuring process performance. In the globally competitive manufacturing environment, photolithography processes involving multiple manufacturing lines are quite common in the Science-Based Industrial Park in Hsinchu, Taiwan, due to economic scale considerations. In this paper, we develop an effective method for measuring the manufacturing yield for photolithography processes with multiple manufacturing lines. Exact distribution of the estimated measure is analytically intractable. We obtain a rather accurate approximation to the distribution. In addition, we tabulate the lower conference bounds based on the obtained approximated distributions for the convenience of industry applications. We also develop a decision-making method for process precision testing to determine whether a process meets the process yield requirement preset in the factory. For illustration purposes, an application example is included.
Measuring the Manufacturing Yield for Skewed Wire Bonding Processes
(2015-08-01)
Tai, Y. T.
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Pearn, W. L.
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工業工程與管理學系
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Department of Industrial Engineering and Management
In semiconductor manufacturing, the technologies of stacked semiconductor packaging are important miniaturization strategies in which excellent quality is essential for a good reputation. Yield-based index C-pk has been the most popular tool for successful quality improvement activities and quality program implementation in multichip package processes. For in-plant applications, quality practitioners commonly use the nonconformities in parts per million (NCPPM) table of C-pk to obtain manufacturing yields. However, wire bonding processes are often skewed in multichip package factories. In such situations, the NCPPM table of C-pk is inappropriate to be applied directly. In order to reasonably access manufacturing yield for skewed wire bonding processes, we propose a new yield index C-sk. We are the first to modify the index C-sk for various skewed distributions for the consistency of NCPPM mapping between indices C-pk and C-sk. In addition, bootstrap methods are applied to construct lower confidence bounds which are useful to practitioners for making reliable decisions. An approximated unbiased estimator is also provided. For the purpose of illustration, practical applications are presented.
Minimising makespan on parallel batch processing machines with non-identical ready time and arbitrary job sizes
(2009)
Chung, S. H.
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Tai, Y. T.
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Pearn, W. L.
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工業工程與管理學系
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Department of Industrial Engineering and Management
This paper considers the parallel batch processing machine scheduling problem which involves the constraints of unequal ready times, non-identical job sizes, and batch dependent processing times in order to sequence batches on identical parallel batch processing machines with capacity restrictions. This scheduling problem is a practical generalisation of the classical parallel batch processing machine scheduling problem, which has many real-world applications, particularly, in the aging test operation of the module assembly stage in the manufacture of thin film transistor liquid crystal displays (TFT-LCD). The objective of this paper is to seek a schedule with a minimum total completion time for the parallel batch processing machine scheduling problem. A mixed integer linear programming (MILP) model is proposed to optimise the scheduling problem. In addition, to solve the MILP model more efficiently, an effective compound algorithm is proposed to determine the number of batches and to apply this number as one parameter in the MILP model in order to reduce the complexity of the problem. Finally, three efficient heuristic algorithms for solving the large-scale parallel batch processing machine scheduling problem are also provided.
Power analysis for group supplier selection with multiple production lines
(2018-12-01)
Pearn, W. L.
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Tai, Y. T.
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Wu, Yu-Wen
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Wang, Yuan-An
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工業工程與管理學系
Group supplier selection problem is a critical problem because outsourcing is an important issue for supply chain management. For the advanced production processes with extremely low fraction of defectives, typical supplier selection methods no longer work because any sample of reasonable size probably contains no defective items. Thus, process capability indices have been extensively used for advanced production processes to evaluate and measure whether the process meets the specifications and they also provide quality assurance. In the globally competitive production environment, processes involving multiple production lines are quite common due to economies of scale considerations. In this paper, we consider a group supplier selection problem for multi-supplier and multi-line, in which a supplier group containing the best suppliers is selected based on a multi-line yield index CpkM. To avoid the inflation of multiple comparisons, we apply the Bonferroni method and subtraction test statistic to tackle the group supplier selection problem. Critical values for testing procedure and required sample sizes for designated selection powers are obtained and tabulated. In addition, we apply multiple comparisons with the best method and compare the selection powers with the Bonferroni method for various power settings to provide more accurate group supplier decisions for real-world applications.
Process Capability Evaluation for Square Bumps with Mean Shift
(2011-09-01)
Pearn, W. L.
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Hung, H. N.
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Tai, Y. T.
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Hou, H. H.
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統計學研究所
Process capability indices have been widely used in manufacturing industries to provide numerical measures of process potential and performance. In in-plant applications, some inevitable process mean shift may be undetected when the statistical process control charts are applied, particularly, in the bumping process for square bumps. Bothe in 2002 provided a statistical reason for considering such a shift in the process mean to accommodate the undetected mean shifts for normally distributed processes when evaluating process capability. In this paper, we consider a bumping process for square bumps in which the data can be formulated as a non-central chi-square distribution, a class of non-normal distributions. To evaluate the popular yield-based process capability C(pk) more accurately, we accommodate the magnitudes of undetected mean shifts using the modified capability evaluation formula and tabulate the detection powers under various subgroup sizes and non-central chi-square parameters. Based on the modified process capability evaluation, we can provide a more reliable process capability evaluation of capability index C(pk) for square bumps and make more correct decisions. For illustration purpose, a real application in a bumping factory which is located on the Science-based Industrial Park in Hsinchu, Taiwan, is presented.