An integrated systems approach to process control and maintenance

Whenever defect data is encountered in industrial quality control applications, the Poisson distribution is generally assumed to be the underlying distribution. It has been widely reported that the defect distributions in integrated circuit fabrication exhibit clustering behavior, a condition which invalidates the Poisson distribution assumption. In this paper we employ an alternative model for defect data that exhibits clustering. To demonstrate the impact of the proposed model, we use it to design acceptance sampling plans and show a dramatic difference between these plans and those determined under the Poisson distribution assumption. Although advances in quality control and techniques such as design for manufacture have eliminated the need for acceptance sampling in many areas, integrated circuit fabrication still involves processes with high variability even using state of the art equipment. Thus acceptance sampling is widely used at various stages of manufacture to insure specified quality levels when 100 percent inspection is infeasible.

The Impact of Clustered Defect Distributions in IC Fabrication

An integrated model based on statistical process control and maintenance

This paper considers the problem of selecting the most economical production run for a continuous process having multi-tool machines. Each tool may have different but similar wear characteristics. The process produces a certain type of product having two measurable quality control characteristics which jointly determine the effectiveness of the product. Simultaneous gradual changes in process means and process variances are experienced as the time passes due to tools wearing out. The process is also subject to the occurrence of an assignable cause which could shift the process means. This assignable cause, however, will not affect the process variances. Thus, at any point in time, a total change in the product quality may result from drift or shift or both. The process is in control at the beginning of the production run and stopped at the end when all the tools are changed or reset. An expected total cost per unit is developed which consists of the cost of resetting the tools, the cost of defective items...

Optimal production run for a process having multilevel tool wear

As reliability requirements become increasingly demanding for many engineering systems, conventional system reliability demonstration testing (SRDT) based on the number of failures depends on a large sample of system units. However, for many safety critical systems, such as missiles, it is prohibitive to perform such testing with large samples. To reduce the sample size, existing SRDT methods utilize test data from either system level or component level. In this paper, an aggregation-based SRDT methodology is proposed for hierarchical systems by utilizing multilevel reliability information of components, subsystems, and the overall system. Analytical conditions are identified for the proposed method to achieve lower consumer risk. The performances of different SRDT design strategies are evaluated and compared according to their consumer risks. A numerical case study is presented to illustrate the proposed methodology and demonstrate its validity and effectiveness.

Design and Risk Evaluation of Reliability Demonstration Test for Hierarchical Systems With Multilevel Information Aggregation

Acceptance sampling plans indexed by Limiting Quality Levels (LQLs) are derived. These plans are compatible with the structure of MIL-STD-105D. The draft table of LQL indexed plans under discussion by the International Organization for Standardization (..

Reviews of Standards and Specifications: LQL Indexed Plans that are Compatible with the Structure of MIL-STD-105D

Acceptance sampling plans indexed by Limiting Quality Levels (LQLs) are derived. These plans are compatible with the structure of MIL-STD-105D. The draft table of LQL indexed plans under discussion...

LQL Indexed Plans that are Compatible with the Structure of MIL-STD-105D

There are many conditions that affect the choice of an acceptance sampling plan. The International Organization for Standardization (ISO) Technical Committee 69 on Applications of Statistics has formed a working group to prepare a guide to help in choos..

August B. Mundel

Papers

Reviews of Standards and Specifications: LQL Indexed Plans that are Compatible with the Structure of MIL-STD-105D

LQL Indexed Plans that are Compatible with the Structure of MIL-STD-105D

Reviews of Standards and Specifications: Guide for Selection of an Acceptance Sampling Plan

Quality through Statistical Thinking — Improving Process Control and Capability

Quantitative Methods for Quality and Productivity Improvement