Assessment of reliability prior distribution

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World Abstracts on Microelectronics and Reliabilit

Contractor experience using RADC ORACLE. CHARLES W. PLOTKIN. Proc. a. Reliab. Maintainab. Syrup. 222 (1984). Use of a D o D developed and owned computer implementation of MIL-HDBK-217 (Reliability Prediction of Electronic Equipment) is being required on some DoD contracts. This paper describes the experience of one contractor in the initial use of this program (ORACLE--Optimized Reliability And Component Life Estimator). The elements of experience described are the basic contractual requirement, advance preparation by the contractor, initial startup problems and actual use experience after the initial startup. Conclusions, as to benefits afforded by this requirement, include an assessment of the potential for increased productivity within the Reliability Engineering functions. A Bayes procedure combining black box estimates and laboratory tests. GARY G. BRUSH, JOHN D. HEALY and BURTON, S. LIEBESMAN. Proc. a. Reliab. Maintairab. Syrup. 242 (1984). Suppliers involved in competitive procurement situations are frequently required to submit reliability predictions based upon some specified black box component/device failure rates. Often the supplier has evidence that specific new components/devices he is using will perform better than these specified failure rates. The purchaser then needs some rationale for evaluating the claims of the supplier and determining how supplier evidence, such as lab tests, should be combined with black box estimates. This paper describes a Bayes procedure which combines laboratory data from the infant mortality period with the black box rate. The resulting estimate is a weighted average of the black box rate and the rate estimated in the lab test. The weights are proportional to equivalent total hours of operation. Illustrative examples are given to demonstrate the application of the theory. On criterion of comparison of reliabilities. JULIUS GOODMAN. Proc. a. Reliab. Maintainab. Symp. 231 (1984). The criterion for comparing two distributions is formulated. Based on this criterion, a method of comparison of two probabilities with uncertainties is developed. Specifically, the case when the difference between two distributions is not significant is considered. For the lognormal distribution frequently used for the failure rate of components, the allowable ratio of medians constituting the insignificant difference between two distributions vs. squared error factor is found. This ratio depends on confidence and significance levels. Classifying combined hardware/software R models. JORGE L. ROMBU and KIERON A. DEY. Proc. a. Reliab. Maintainab. Syrup. 282 (1984). The need for a combined hardware/software reliability model is increasing day by day; the need is due, among other factors, to increasing software-induced hardware failures which endanger system missions. On the other hand, already-developed models have not completely fulfilled this need. In this paper, the relevant literature is reviewed and a classification scheme for reliability models based upon model requirements, users' objectives and other related criteria is given. Some existing models are classified according to this scheme. Finally, from a macro point of view, the statement of the combined system reliability problem is approached, several areas of conflict are identified and some general conclusions are presented which may help to provide a better understanding of the problem and its eventual solution. Optimization of spares in a maintenance scenario. ROBERTJ. COUGHLIN. Proc. a. Reliab. Maintainab. Syrup. 371 (1984). This paper deals with a method for optimizing the allocation of spare parts used in the maintenance of a hardware system. Spares allocation can be optimized in either of two ways: (1) maximization of system operational availability for a certain maximum spares cost; and (2) minimization of spares cost for a certain minimum system operational availability.

The mathematical theory behind lhi~ meth,,d +~ dJ~c.s>,~ and computer outputs of sample runs are shown, Storage reliability with periodic test. 1~t <;v:>,t: ( M ~ t i ' ~ t z Proc. a. Reliab. Maintainab+ Syrup. 18l (1984). Electronic equipment can and does fail upon turn-on or e~en prior I~, turn-on. This implies that failure mechanism~ are at ~ , r k even when an electronic equipment is not energized : thal i~,+ when it is in a storage or dormant condition. This paper addresses the storage/dormancy reliability problem and explores methods for predicting the reliability of electronic items that must be in storage or dormancy for long periods of time prior to usage. One such method is to test the item periodically, repair any failures found, and in effect restore the item to near its inherent reliability. The mathematical model for such a system is developed and demonstrated by example. Computer programs were developed to make the calculations and trade-off analyses. Spacecraft anomalies and lifetimes. CHARLES E. Bt,OOMQUtSl. Proc. a. Reliab. Maintainab. Syrup. 186 (1984). One of NASA's primary concerns is the blprovement of spacecraft performance over time. As a first step in defining generic approaches for improving spacecraft reliability and longevity, comprehensive data on spacecraft anomalies, failures, and performance degradation as a function of time were collected, analyzed and documented. Analytical techniques included categorization of anomalous incidents, engineering analyses of particular classes of anomalies and mission effectiveness assessments versus time. Renresentative results: five classes of anomalies account for 50"~, of all in-flight problems; half of all spacecraft continue to report significant RFI/EMI problems; and missions are generally much more than 50 o~; effective far in excess of their design lives. Power-system reliability in perspective. R. B1LLINf(/N and R. N. ALLAN. Electronics Power 231 (March 1984). This article discusses several philosophical aspects concerning power-system reliability. It puts the reliability aspects in perspective, describes a hierarchical framework of analysis and discusses how the economics of reliability should be compared. Low energy electron microscopy utilized in dynamic circuit analysis and failure detection on LSI-VLSI internal circuits. LOUIS KOTORMAN. IEEE Trans. Components Hybrids Ml.q Technol. CHMT-6 (4), 527 (December 1983). Nonloading and nondestructive signal probing of state-of-the-art semiconductor arrays has been achieved with the electron beam (E-beam) probe, utilizing scanning electron microscopes (SEM's). To apply the electron beam circuit prober successfully, a low energy setup was developed in order to prevent damage which can be caused by any high energy electrons interacting with the sample in the typical SEM. Using a converted SEM (AMR 1000) with primary beam energies below 770eV, the accumulation of trapped charges in the quartz or polymide surface insulators was prevented. The probable electron penetration depth with these low energy electrons corresponds to 10nm or less on conventional silicon based microcircuits. The greatest concerns connected to the usage of very low energy beams were the lack of adequate spatial resolution and the available sample beam current (illumination) especially when using tungsten cathodes. These two concerns are eliminated, as our results have demonstrated better than 10OHm spatial resolution when using 750eV primary beam energy, and adequate brightness even with a 360eV beam when it is applied in the stroboscopic mode with less than 1 o~,duty cycle. Assessment of reliability prior distribution. A. ZONNENSHAIt~ and M. HAIM. Proc. a. Reliab. Maintainab. Syrup. 44 (1984). A method for assessing a prior distribution function of reli-

World Abstracts on Microelectronics and Reliability ability of a system during its development is described. The method combines and makes use of quantitative and qualitative information available when the reliability demonstration stage is reached. The method has been successfully applied in designing reliability demonstration programs for systems developed in RAFAEL, Armament Development Authority in Israel. A management guide to reliability predictions. FRANK A. STOVALL. Proc. a. Reliab. Maintainab. Syrup. 114 (1984). Reasonably accurate reliability predictions can be made using the procedure contained in MIL-HDBK-217 if enough is known about such variables as the operational environment, equipment design, vendor manufacturing capability, and delivery schedule. There are times, however, when management or others need a more rapid, less costly procedure to assess either vendor-claimed reliability levels or estimate the probable reliability level of a piece of equipment. For more than a decade the author has compared operational performance of aircraft electronic equipment with equipment part count, and the results have been consolidated into a simplified prediction chart. This chart, though perhaps not as accurate as MIL-HDBK-217, can be very useful early in a program to assist in deciding whether additional efforts - s u c h as part screening, failure-free burnin, thermal imaging, reliability growth tests, or other reliability enhancement techniques--are necessary to achieve desired reliability levels. The chart is also useful in assessing the credibility of a prospective vendor's claim for unusually high reliability in equipment not yet proven in the operational environment. Generalized acceleration factor in reliability. DER-YANG GUAN. Proc. a. Reliab. Maintainab. Syrup. 54 (1984). The calculation of the acceleration factor between an accelerated test and a single field condition is simple and straightforward. But a single-condition case seldom exists in the field, which normally sees a distribution of conditions. This paper shows that a new and single term called generalized acceleration factor can be developed analytically from such a distribution. The new factor has all the characteristics required by an acceleration factor and is unique to each distribution. With this new parameter in place, it not only simplifies the reliability assessment for a complicated field, but also broadens the conceptual contents of the acceleration factor.

Failure to safety in process-control systems. DONALD SMITH. Electronics Power, 227 (March 1984). There are those who wish failsafe systems on us everywhere. This is not always in the real interests of safety, and stultifies development in that field. In fact, such ideas may in practice be logically, ethically and legally wrong. Common errors in application of MIL-STD-781. TERRANCE W. ELLIOTT. Proc. a. Reliab. Maintainab. Syrup. 139 (1984). This paper discusses some common errors in application of MIL-STD-781 that lead to inflated estimates of true reliaability. These errors have occurred because of the availability and acceptability of this standard for electronic equipment. As electronic equipment has become more complex and flexible, testing schemes have deviated from Poisson requirements and functional test equipment often will not detect all the possible failure modes. This paper will discuss the impact of these errors along with recent work in mathematical deviation of equations for correct test design, DoD/industry--R & M case study analysis. PAUL F. GOREE and THOMASA. MUSSON. Proc. a. Reliab. Maintainab. Symp. 91 (1984). The Institute for Defense Analyses (IDA) was chartered by the Office of the Secretary of Defense to conduct a study to "identify and provide support for high payoff actions which the D o D can take to improve the military system design, development and support process so as to provide quantum improvement in R & M and readiness MR 24: ~-I

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through innovative uses of advancing technology and program structure." The task was given the short title: R & M Study. The Case Study portion of the overall IDA study, which focused on the program structure portion of the objective, is addressed in this paper. Also discussed is the process used to conduct the case study activity and the preliminary findings and conclusions. The analysis is still in progress at the time of writing this paper.

The operational readiness: the reliability and maintainability connection. MARTIN M. METH and KURT GREENE. Proc. a. Reliab. Maintainab. Symp. 83 (1984). A DoD-Industry study on reliability and maintainability was formed to identify actions to achieve high operational readiness. The focus was on two areas: identifying implementable solutions and the associated costs to improve system reliability and maintainability; and identifying new technologies which could provide high leverage to improve reliability and maintainability. Predicted vs test M T B F ' s . . . why the disparity? JEFFREY B. LYNCH and LAWRENCE J. PHALLER. Proc. a. Reliab. Maintainab. Syrup. 117 (1984). Over the years there has been much concern and skepticism over the accuracy and usefulness of reliability predictions. This concern stems from the large variations often experienced between predicted and test observed Mean-Time-Between-Failure (MTBF's). At the Westinghouse Defense and Electronic Center a case study on an Electric Countermeasures (ECM) radar system was performed to evaluate the reasons for this difference. The problems experienced in test were analyzed in light of the prediction models of MIL-HDBK-217, and it was concluded that certain assumptions inherent in these prediction models were largely responsible for this difference. These assumptions are related, but not limited to such factors as poor design and/or construction techniques, and poor quality control in the fabrication of the devices. As a result of this study a program has been instituted at the Westinghouse Defense and Electronic Center to identify and control these factors and it is identified in this paper. ITAD--A CAD system for environmental reliability design. ARNOLD H. MAYER. Proc. a. Reliab. Maintainab. Syrup. 23 (1984). The paper describes the ITAD (Integrated Thermal Avionic Design) Computer Aided Design for Reliability System from the points of view of development objectives, design features, development experiences, development status, future possibilities and illustrates a currently operational design scenario for the optimal reliability, minimum life cycle cost placement of electronic parts on a circuit card. A maintenance philosophy for mainframe computers. HAROLD L. PLATZER. Proc. a. Reliab, Maintainab. Syrup. 359 (1984). This paper tells how computers should be built so as to: • minimize the life cycle cost of their maintenance. • maximize their "nonstop" performance while meeting a specified performance. R/M design for long term dormant storage. GEORGE KASOUF and DAVID A. McGoYE. Proc. a. Reliab. Maintainab. Syrup. 168 (1984). The design of a missile system to sustain long periods of dormancy (operational ready in a "power-off" state) is addressed. This includes all the "ready storage" and deployed "captive carry" phases of the defined life cycle. Given the reliability and maintainability requirements, a reliability allocation is performed using the "wooden round" maintenance approach. The results show that the reliability risk presented by the dormant phases of the example mission profile constitutes 88 ~o of the overall reliability risk for a successful mission. A second reliability allocation is performed using a maintenance concept that allows Go/No-Go type confidence testing prior to deployment. A 43 % improvement in mission reliability is achieved using the G o / N o - G o maintenance concept in lieu of the "wooden round.'" A study