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How we put reliability tools into the hands of designers
590
World Abstracts on Microeleetronics and Reliability
assumptions such as processor/computer architecture; language; sizing and timing; design/development history (of the design team); and software and hardware failure history. In this paper, these concepts are organized into a rigorous methodology leading to a reliability prediction for each system concept analyzed. The predictions can then be compared for trade-off analyses. A cost benefit analysis methodology is also presented to permit the predictions technique to analyze for optimum hardware and software configurations and to enhance the return on investment. Lower bound on reliability for Weibull distribution when shape parameter is not estimated accurately. ZHAOFENG HUANG and ALBERT A. PORTER. Proc. A. Reliab. Maintainab. Syrup., 183 (1991). This paper investigates the mathematical relationships between the shape parameter/~ and estimates of reliability and a life limit lower bound for the two-parameter Weibull distribution. It shows that under rather general conditions, both the reliability lower bound and the allowable life limit lower bound (often called a tolerance limit) have unique global minima over a range of ~. Hence, lower bound solutions can be obtained without assuming or estimating ~. The existence and uniqueness of these lower bounds are proven in the Appendix. Some real data examples are given to show how these lower bounds can be easily established and to demonstrate their practicality. The method developed in the paper has proven to be extremely useful when using the Weibull distribution in analysis of no-failure or few-failures data. Furthermore, the results are widely applicable, not only in the aerospace industry, but anywhere that system reliabilities are high. The mixed exponential failure process. FRANK McNOLTY, WILLIAM SHERWOOD and JEAN MIRRA. Proc. A. Reliab. Maintainab. Symp., 226 (1991). The paper characterizes the mixed exponential failure process by a time-dependent distribution from which the random hazard rate is obtained directly as an expected value rather than as the ratio of a failure distribution and the corresponding reliability. The properties of the time-dependent distribution are studied-in particular, its mean, variance, and characteristic function (c.f.). It is shown that the random hazard rate is also expressible in terms of a singularity of the c.f. in the complex z plane. The location of this singularity as a function of time is related to the random hazard rate. Further insight into the mixed process is obtained by constructing an electrical filtering analog involving bandpass and low-pass filters. The paper also defines a non-homogeneous second-order differential equation for which the mixing distribution is a particular solution. The non-homogeneous component has the unusual invariance property that an integral of this quantity from zero to infinity yields a simple function of a single intrinsic parameter. Interdisciplinary applications of the mixing procedure are discussed in terms of photoresponRive detectors which yield generalized Laquerre-polynomial discrete distributions for the photoelectron count. Analysis of contaminated field failure data for repairable systems. CHRISTIAN KORNERUP nANSEN and POUL THYI~GOD. Proc. A. Reliab. Maintainab. Symp., 604 (1991). In this paper we present a simple model for electronic systems with repair, and a method for analyzing recorded field failure data for such systems. The work performed has resulted in analytical results that may be used for assessing the product reliability. The method was originally developed for use under quite ideal circumstances, but in this paper the method is adapted for use also with "contaminated" data, i.e., data where the failure times are observed imbedded by noise. We propose a simple model for the noise that enables an analytical solution for the mean cumulative number of failures. The expression is compared with the expression for non-contaminated data, for the purpose of assessing the
effect of the contamination, and for the purpose of correcting estimates in the parametric model. The method is illustrated by a reel world example of industrial failure data recorded on a field basis, and the effect caused by contamination in these data is investigated under a "worst case" assumption. The example indicates that the model is quite robust to contamination. Only one of the three key parameters is affected significantly by assuming the data to be contaminated. Burn-in effectiveness---theory and measurement. HANCE H. HUSTON, MICHAEL H. WOOD and VINCENT M. DEPALMA. IEEE/IRPS, 271 (1991). Semiconductor chip reliability is commonly improved through burn-in. In this work bum-in effectiveness is modeled as a function of time, temperature, electrical stress, stress coverage and failure mechanism. Actual field data for a variety of products are used to validate or deduce the relevant burn-in parameters. How we put reliability tools into the hands of designers. TYRONE JACKSON. Proc. A. Reliab. Maintainab. Symp., 168 (1991). This paper describes the managerial issues encountered during the development of FRATOOLS, a new computerized methodology for performing failure rate analysis. FRATOOLS was developed in-house because a tool was needed for performing failure rate analysis in a concurrent engineering environment. No suitable commerical software or shareware could be found which adequately supports concurrent engineering. A number of commercial failure rate analysis programs were evaluated, but each was found to require the skills of an experienced reliability engineer for effective utilization. FRATOOLS consists of several stand-alone programs integrated together to work as a single software package. These tools were successfully used by designers to analyze the F18 radar upgrade (RUG) system. The FRATOOLS methodology fully complies with the methods contained in Mil-Hdbk-217E. Some of the novel elements of FRATOOLS include the use of "smart" software for automating the decision-making process, capability to compute the failure rates for advanced technology devices which are not covered in Mil-Hdbk-217E, and integrating the methodology with the design process in a manner which fully supports concurrency in the design of radar systems. Predicting the reliability of new products at IBM. JOHN S. USHER, SURAJ M. ALEXANDER and JOHN D. THOMPSON. Proc. A. Reliab. Maintainab. Syrup., 208 (1991). This paper provides an overview of the development and implementation of a computerized reliability prediction model at the IBM facility located in Research Triangle Park, North Carolina. The model utilizes historical system life data to analyze the life distribution of various types of components. The resulting component life distribution estimates are then used to predict the reliability of new system configurations. This approach is based upon the well-known theory of competing risks, but is unique in that it allows for the analysis of a pooled set of life data, i.e., life data from different types of systems, to obtain component estimates. The advantage of the approach lies in the fact that it yields component reliabilities based upon their performance in actual operating systems. We present the model, discuss various issues that were found to be critical to its successful implementation at IBM, and present an example to illustrate its use. Modelling and monitoring the decay of equipment reli~illty. PAUL RITCHIE. Proc. A. Reliab. Maintainab. Syrup., 312 (1991). This paper presents the results of an investigation into the reliability degradation of airborne equipment. The aim of the investigation is to automate the reliability monitoring function as much as possible. Results have
World Abstracts on Microeleetronics and Reliability
assumptions such as processor/computer architecture; language; sizing and timing; design/development history (of the design team); and software and hardware failure history. In this paper, these concepts are organized into a rigorous methodology leading to a reliability prediction for each system concept analyzed. The predictions can then be compared for trade-off analyses. A cost benefit analysis methodology is also presented to permit the predictions technique to analyze for optimum hardware and software configurations and to enhance the return on investment. Lower bound on reliability for Weibull distribution when shape parameter is not estimated accurately. ZHAOFENG HUANG and ALBERT A. PORTER. Proc. A. Reliab. Maintainab. Syrup., 183 (1991). This paper investigates the mathematical relationships between the shape parameter/~ and estimates of reliability and a life limit lower bound for the two-parameter Weibull distribution. It shows that under rather general conditions, both the reliability lower bound and the allowable life limit lower bound (often called a tolerance limit) have unique global minima over a range of ~. Hence, lower bound solutions can be obtained without assuming or estimating ~. The existence and uniqueness of these lower bounds are proven in the Appendix. Some real data examples are given to show how these lower bounds can be easily established and to demonstrate their practicality. The method developed in the paper has proven to be extremely useful when using the Weibull distribution in analysis of no-failure or few-failures data. Furthermore, the results are widely applicable, not only in the aerospace industry, but anywhere that system reliabilities are high. The mixed exponential failure process. FRANK McNOLTY, WILLIAM SHERWOOD and JEAN MIRRA. Proc. A. Reliab. Maintainab. Symp., 226 (1991). The paper characterizes the mixed exponential failure process by a time-dependent distribution from which the random hazard rate is obtained directly as an expected value rather than as the ratio of a failure distribution and the corresponding reliability. The properties of the time-dependent distribution are studied-in particular, its mean, variance, and characteristic function (c.f.). It is shown that the random hazard rate is also expressible in terms of a singularity of the c.f. in the complex z plane. The location of this singularity as a function of time is related to the random hazard rate. Further insight into the mixed process is obtained by constructing an electrical filtering analog involving bandpass and low-pass filters. The paper also defines a non-homogeneous second-order differential equation for which the mixing distribution is a particular solution. The non-homogeneous component has the unusual invariance property that an integral of this quantity from zero to infinity yields a simple function of a single intrinsic parameter. Interdisciplinary applications of the mixing procedure are discussed in terms of photoresponRive detectors which yield generalized Laquerre-polynomial discrete distributions for the photoelectron count. Analysis of contaminated field failure data for repairable systems. CHRISTIAN KORNERUP nANSEN and POUL THYI~GOD. Proc. A. Reliab. Maintainab. Symp., 604 (1991). In this paper we present a simple model for electronic systems with repair, and a method for analyzing recorded field failure data for such systems. The work performed has resulted in analytical results that may be used for assessing the product reliability. The method was originally developed for use under quite ideal circumstances, but in this paper the method is adapted for use also with "contaminated" data, i.e., data where the failure times are observed imbedded by noise. We propose a simple model for the noise that enables an analytical solution for the mean cumulative number of failures. The expression is compared with the expression for non-contaminated data, for the purpose of assessing the
effect of the contamination, and for the purpose of correcting estimates in the parametric model. The method is illustrated by a reel world example of industrial failure data recorded on a field basis, and the effect caused by contamination in these data is investigated under a "worst case" assumption. The example indicates that the model is quite robust to contamination. Only one of the three key parameters is affected significantly by assuming the data to be contaminated. Burn-in effectiveness---theory and measurement. HANCE H. HUSTON, MICHAEL H. WOOD and VINCENT M. DEPALMA. IEEE/IRPS, 271 (1991). Semiconductor chip reliability is commonly improved through burn-in. In this work bum-in effectiveness is modeled as a function of time, temperature, electrical stress, stress coverage and failure mechanism. Actual field data for a variety of products are used to validate or deduce the relevant burn-in parameters. How we put reliability tools into the hands of designers. TYRONE JACKSON. Proc. A. Reliab. Maintainab. Symp., 168 (1991). This paper describes the managerial issues encountered during the development of FRATOOLS, a new computerized methodology for performing failure rate analysis. FRATOOLS was developed in-house because a tool was needed for performing failure rate analysis in a concurrent engineering environment. No suitable commerical software or shareware could be found which adequately supports concurrent engineering. A number of commercial failure rate analysis programs were evaluated, but each was found to require the skills of an experienced reliability engineer for effective utilization. FRATOOLS consists of several stand-alone programs integrated together to work as a single software package. These tools were successfully used by designers to analyze the F18 radar upgrade (RUG) system. The FRATOOLS methodology fully complies with the methods contained in Mil-Hdbk-217E. Some of the novel elements of FRATOOLS include the use of "smart" software for automating the decision-making process, capability to compute the failure rates for advanced technology devices which are not covered in Mil-Hdbk-217E, and integrating the methodology with the design process in a manner which fully supports concurrency in the design of radar systems. Predicting the reliability of new products at IBM. JOHN S. USHER, SURAJ M. ALEXANDER and JOHN D. THOMPSON. Proc. A. Reliab. Maintainab. Syrup., 208 (1991). This paper provides an overview of the development and implementation of a computerized reliability prediction model at the IBM facility located in Research Triangle Park, North Carolina. The model utilizes historical system life data to analyze the life distribution of various types of components. The resulting component life distribution estimates are then used to predict the reliability of new system configurations. This approach is based upon the well-known theory of competing risks, but is unique in that it allows for the analysis of a pooled set of life data, i.e., life data from different types of systems, to obtain component estimates. The advantage of the approach lies in the fact that it yields component reliabilities based upon their performance in actual operating systems. We present the model, discuss various issues that were found to be critical to its successful implementation at IBM, and present an example to illustrate its use. Modelling and monitoring the decay of equipment reli~illty. PAUL RITCHIE. Proc. A. Reliab. Maintainab. Syrup., 312 (1991). This paper presents the results of an investigation into the reliability degradation of airborne equipment. The aim of the investigation is to automate the reliability monitoring function as much as possible. Results have