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On Bayes estimation for mixtures of two exponential life distributions from right-censored samples
World Abstracts on Microelectronics and Reliability base consisting of approximately 1000 variables and 150,000 data points. The resulting discriminant model is shown to be stable under various conditions. It is demonstrated that large-scale systems can be rendered more manageable by a careful scrutiny of variables on a univariate basis. A useful table of the upward bias is provided for reliability analysts working with large data bases.
On Bayes estimation for mixtures of two exponential life distributions from right-censored samples. A. S. PAPADAPOULOSand W. J. PADJETT. IEEE Trans. Reliab. R35, 102 (1986). In life testing and reliability estimation, the underlying failure time distribution need not be homogeneous. It can be a mixture of two distinct lifetime distributions due to two different failure modes. A failure-time distribution is assumed which is the mixture of two exponential distributions. Estimation of the two scale parameters, the mixing parameter and the reliability is considered. MLEs, and Bayes estimators with respect to proper priors and to Jeffreys' vague priors, are given based on right-censored data. The right-censorship considered here includes types I & II and random right-censoring as special cases. Monte Carlo simulation indicates that the proper Bayes estimators are best with respect to root mean square error (RMSE) under the assumed priors and that the MLEs perform well overall and are quite satisfactory in practice. The Bayes estimators with respect to Jeffreys' vague priors for the scale parameters do not perform as well as the MLE in the sense of RMSE and tend to have a greater bias. VLSI impact on RAMS strategies in avionics design. L. R. WEBSTER, and J. M. MADER. Proc. a. Reliab. Maintainab. Syrup., 303 (1986). This paper discusses the impact of very large scale integrated circuits (VLSI) on the reliability, availability, maintainability and supportability (RAMS) characteristics of avionics systems to be deployed in the 1990 time frame. A reliability sensitivity analysis of a 4.5 million gate system is presented with data from more than 25 major system redundancy configurations analyzed. The impact of these various redundancy architectures on chip, module, equipment and system RAMS characteristics is detailed. Using this medium-sized digital equipment analysis as a model, then we oroceed to uncover the implications of dramatically increased use of custom VLSI in avionics (and other) systems. The purpose is to provide RAMS prac-
589
titioners with some insight into the design and use implications of the "super-chips" that will soon become commonplace. Some of the conclusions are: (1) non-monolithic interconnections essentially determine system reliability; (2) increased chip complexity provides high leverage RAMS opportunities; (3) RAMS personnel must cause communication to happen between systems definition and VLSI implementation personnel if the full potential of VLSI is to be realized; (4) there are tough design challenges in thermal, electrostatic discharge radiation protection and circuit/ system architecture which must be met in the design, production and support of systems using these devices.
Army reliability growth management policy. RAYMONDBELL. Proc. a. Reliab. Maintainab. Syrup., 210 (1986). In an effort to field modernized reliable equipment at a faster pace than has generally been achieved in the past, the Army has embarked on a new acquisition strategy that gets a system to a low rate initial production decision (Milestone III) in not more than four years after entering the Army's Demonstration and Validation Phase (Milestone I) of a development program. With this streamlined acquisition strategy, it is more important than ever that reliability be intensively managed. A major tool for this management effort concerns a new Army policy on reliability growth management. This policy involves establishing firm reliability growth requirements at three key events in a development program: (1) at the completion of the Demonstration and Validation Phase; (2) at the completion of the Full Scale Engineering Development Phase; (3) at IOC. A study has been performed to develop an overall framework for addressing the methods needed for the new reliability requirements and for successfully meeting these values. In this paper, a thorough discussion of these three new reliability requirements will be made. Methodology for establishing these requirements will be presented and a means for achieving these requirements will be addressed. In addition, a discussion of Army experience in reliability growth rates, growth management strategy and fix effectiveness factors and their relationship to these new requirements will be noted. Further, the setting of realistic requirements, the engineering effort needed to meet these requirements and the test effort involved will also be discussed.
4. M I C R O E L E C T R O N I C S - - G E N E R A L
X-ray lithography: can it be justified? ALAN D. WILSON. Solid St. Technol., 249 (May 1986). The question of whether or not x-ray lithography can be justified for future manufacturing of submicron devices is examined. Future chip lithography requirements are projected and potential resolution/depth of focus limits of optical lithography are reviewed. Throughput constraints of electron beam systems are discussed, and exposure costs of optical, e-beam and x-ray lithography are determined. The dawn of epitaxy's new era. PIETER BURGGRAAF. Semiconductor int., 68 (May 1986). The advent of "new generation" epitaxy reactors should reduce the cost and increase the application of this important process. Offshore assembly: a time of change. RON ISCOFF. Semiconductor int., 96 (June 1986). New companies, and new countries, have joined the list of Asian contract assemblers, as the members of this specialized sector begin to regroup from the semiconductor industry's worst recession. Growing interdependence within the microelectronics industry: an overview perspective. RAY D. RUST and DARYL ANN
DOANE. Solid St. Technol., 125 (June 1986). Within the microelectronics industry, the three "sister" industries--integrated circuit, printed circuit and hybrid circuit manufacturing-are becoming more interdependent. This move towards interdependency from a historical position of independence is being caused by the availability of new substrate materials for the printed circuit industry, by more stringent electrical requirements caused by large scale integration, and by everdecreasin 9 feature sizes within the integrated circuit industry. This article defines some of the primary "forces of change" within the microelectronics industry and describes their effects on each of the three sister industries. It concludes by relating the topics covered by the lithography articles in this issue of Solid State Technolooy to one another and to the forces of change.
Megaceiis simplify end to end design tasks. JOHN STOCKTON. Solid St. Technol., 127 (August 1986). Two major topics of interest in today's IC market are discussed, viz. simplifying test program development as a part of the normal design process and the use of Megacells for large building blocks in new designs. These topics are related by necessity because the time required to design circuits is steadily increasing while
On Bayes estimation for mixtures of two exponential life distributions from right-censored samples. A. S. PAPADAPOULOSand W. J. PADJETT. IEEE Trans. Reliab. R35, 102 (1986). In life testing and reliability estimation, the underlying failure time distribution need not be homogeneous. It can be a mixture of two distinct lifetime distributions due to two different failure modes. A failure-time distribution is assumed which is the mixture of two exponential distributions. Estimation of the two scale parameters, the mixing parameter and the reliability is considered. MLEs, and Bayes estimators with respect to proper priors and to Jeffreys' vague priors, are given based on right-censored data. The right-censorship considered here includes types I & II and random right-censoring as special cases. Monte Carlo simulation indicates that the proper Bayes estimators are best with respect to root mean square error (RMSE) under the assumed priors and that the MLEs perform well overall and are quite satisfactory in practice. The Bayes estimators with respect to Jeffreys' vague priors for the scale parameters do not perform as well as the MLE in the sense of RMSE and tend to have a greater bias. VLSI impact on RAMS strategies in avionics design. L. R. WEBSTER, and J. M. MADER. Proc. a. Reliab. Maintainab. Syrup., 303 (1986). This paper discusses the impact of very large scale integrated circuits (VLSI) on the reliability, availability, maintainability and supportability (RAMS) characteristics of avionics systems to be deployed in the 1990 time frame. A reliability sensitivity analysis of a 4.5 million gate system is presented with data from more than 25 major system redundancy configurations analyzed. The impact of these various redundancy architectures on chip, module, equipment and system RAMS characteristics is detailed. Using this medium-sized digital equipment analysis as a model, then we oroceed to uncover the implications of dramatically increased use of custom VLSI in avionics (and other) systems. The purpose is to provide RAMS prac-
589
titioners with some insight into the design and use implications of the "super-chips" that will soon become commonplace. Some of the conclusions are: (1) non-monolithic interconnections essentially determine system reliability; (2) increased chip complexity provides high leverage RAMS opportunities; (3) RAMS personnel must cause communication to happen between systems definition and VLSI implementation personnel if the full potential of VLSI is to be realized; (4) there are tough design challenges in thermal, electrostatic discharge radiation protection and circuit/ system architecture which must be met in the design, production and support of systems using these devices.
Army reliability growth management policy. RAYMONDBELL. Proc. a. Reliab. Maintainab. Syrup., 210 (1986). In an effort to field modernized reliable equipment at a faster pace than has generally been achieved in the past, the Army has embarked on a new acquisition strategy that gets a system to a low rate initial production decision (Milestone III) in not more than four years after entering the Army's Demonstration and Validation Phase (Milestone I) of a development program. With this streamlined acquisition strategy, it is more important than ever that reliability be intensively managed. A major tool for this management effort concerns a new Army policy on reliability growth management. This policy involves establishing firm reliability growth requirements at three key events in a development program: (1) at the completion of the Demonstration and Validation Phase; (2) at the completion of the Full Scale Engineering Development Phase; (3) at IOC. A study has been performed to develop an overall framework for addressing the methods needed for the new reliability requirements and for successfully meeting these values. In this paper, a thorough discussion of these three new reliability requirements will be made. Methodology for establishing these requirements will be presented and a means for achieving these requirements will be addressed. In addition, a discussion of Army experience in reliability growth rates, growth management strategy and fix effectiveness factors and their relationship to these new requirements will be noted. Further, the setting of realistic requirements, the engineering effort needed to meet these requirements and the test effort involved will also be discussed.
4. M I C R O E L E C T R O N I C S - - G E N E R A L
X-ray lithography: can it be justified? ALAN D. WILSON. Solid St. Technol., 249 (May 1986). The question of whether or not x-ray lithography can be justified for future manufacturing of submicron devices is examined. Future chip lithography requirements are projected and potential resolution/depth of focus limits of optical lithography are reviewed. Throughput constraints of electron beam systems are discussed, and exposure costs of optical, e-beam and x-ray lithography are determined. The dawn of epitaxy's new era. PIETER BURGGRAAF. Semiconductor int., 68 (May 1986). The advent of "new generation" epitaxy reactors should reduce the cost and increase the application of this important process. Offshore assembly: a time of change. RON ISCOFF. Semiconductor int., 96 (June 1986). New companies, and new countries, have joined the list of Asian contract assemblers, as the members of this specialized sector begin to regroup from the semiconductor industry's worst recession. Growing interdependence within the microelectronics industry: an overview perspective. RAY D. RUST and DARYL ANN
DOANE. Solid St. Technol., 125 (June 1986). Within the microelectronics industry, the three "sister" industries--integrated circuit, printed circuit and hybrid circuit manufacturing-are becoming more interdependent. This move towards interdependency from a historical position of independence is being caused by the availability of new substrate materials for the printed circuit industry, by more stringent electrical requirements caused by large scale integration, and by everdecreasin 9 feature sizes within the integrated circuit industry. This article defines some of the primary "forces of change" within the microelectronics industry and describes their effects on each of the three sister industries. It concludes by relating the topics covered by the lithography articles in this issue of Solid State Technolooy to one another and to the forces of change.
Megaceiis simplify end to end design tasks. JOHN STOCKTON. Solid St. Technol., 127 (August 1986). Two major topics of interest in today's IC market are discussed, viz. simplifying test program development as a part of the normal design process and the use of Megacells for large building blocks in new designs. These topics are related by necessity because the time required to design circuits is steadily increasing while