Reliability improvement of multiterminal networks

900

World Abstracts on Microeleetronics and Reliability

that are used over the metallization pattern are outlined, and the adverse effects of localized defects in passivation layers are indicated. The implications of moisture and of contaminants on the reliability of devices both in hermetic and in plastic packages are reviewed. An extensive list of references to pertinent techniques for characterizing thinfilm materials and for studying thin-film corrosion effects is included. Transient damage resulting in faihwe of a component exposed to ionizing radiation environment. R. P. S. YADAV and KRISHAN LAL. Microelectron. Reliab., 19, 223 (1979). Transient effects are manifested in the interaction of radiation with material of the component with an associated

3. C I R C U I T

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SYSTEMS

RELIABILITY,

Model for failure rate curves. G. BOSCH. Microelectron. Reliab., 19, 371 (1979). The failure rate of electronic components is determined by the initial distribution of the critical parameters and by the nature of the degradation mechanism. Assuming the mechanism to be determined by a first order differential equation with respect to time it turns out that a simple relation exists between the life histories of components with different initial conditions. With only one failure mechanism and a (truncated) normal distribution function, with average # and standard deviation ~r, it is shown that the shape of the faihire rate curve is determined by a dimensionless characteristic parameter b = n(cr/#)2, in which n is typical for the underlying failure mechanism. For b < ¼a "bath tub" like failure rate curve will occur in general; for b > ¼ the failure rate decreases continuously as a function of time. By considering the complete failure rate curve, including the rejects during testing, a relation between yield and failure rate can be indicated. A prediction about the temperature-dependence of the failure rate curve is given. The effect of stress testing at elevated temperature can be made quantitative by a simple scaling rule. Fault-tolerant system optimization. JOHN ROSE. Proc. Annual Reliability and Maintainability Symposium, San Francisco, p. 95 (22-24 January 1980). Fault-tolerant systems have the potential for providing the high levels of reliability necessary for advanced commercial airplane flight control systems. The paper describes the decisions to be made in the design of fault-tolerant systems and provides some details of a comprehensive model which is being developed to cost optimize such .systems. Contrary to expectation, MonteCarlo simulation is proving to be an economical and effective method for analysis of reliability, as well as maintainability and operation. Work on the development of a Cost Benefit Design Optimization Model was supported by NASA-Langley Research Center under Contract NAS115506. A guidebook for software reliabifity assessment. ALAN SUKERT and AMI~JT L. GOEL. Proc. Annual Reliability and Maintainability Symposium, San Francisco, p. 186 (22-24 January 1980). Currently within DoD there exists the need for specifying software reliability requirements in RFPs and for performing reliability assessments of developed software to insure these requirements are being met. To help satisfy these needs, Rome Air De)/elopment Center (RADC) has initiated a long term effort to develop a handbook for software reliability assessment, similar to MIL-HDBK-217, that can be used by appropriate Air Force personnel in specifying and assessing software reliability requirements. This paper will outline the status of this effort, with emphasis on the initial version of this proposed handbook

excitation (including ionization) and de-excitation of electrons. The ionizing radiations modify the physicochemical structure of matter by distributing packets of energy that remain localized within a volume of molecular dimensions and are sufficient to disrupt chemical bonds. By taking the perturbations and recombination reactions to be similar to those of optical excitation of electrons an attempt has been made here to estimate the overall transient damage to the component due to ionizing radiation. As a particular case, an excess current due to this damage is assumed to be following normal distribution and the failure probability of the component has been estimated by taking a critical value I'~ for the excess current which when exceeded, brings the component in a failed state.

MAINTENANCE

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REDUNDANCY

that will serve as an interim guide to software reliability assessment and on the nonhomogeneous Poisson process software reliability predictioh model that forms the basis of this initial guidebook. Field maintenance organization analysis models. RONALD Proc. Annual Reliability and Maintainability Symposium, San Francisco, p. 24 (22-24 January 1980). This paper discusses analytical and simulation models which have been developed to aid in the analysis of proposed changes in the field maintenance organization of the National Airspace System. The major outputs of these models are performance measures such as technician productivity and facility restoration time. The analytical mode1 was applied to evaluate varying increases in the level of maintenance organization centralization which may be possible when the existing ground based equipment mix is modernized. The simulation model was verified by a field test and applied to assessing the operational feasibility of alternative maintenance organizations that are based upon a partial equipment modernization program. BI~.

Effect of switch failure on 2, redundant systec~s, jAx S1NGH. IEEE Trans. Reliab. R-29 (1) 82 (April 1980). The effect of imperfect switch on 2 redundant systems has been studied. Model I is a standby redundant complex system with preemptive-repeat repair policy. Model II has 2 dissimilar units and an imperfect switch. Limiting behaviour and the case of perfect switch are discussed. Age replacement policies for Welbnll failure limes. PANDU R. TADIKAMALLA.IEEE Trans. Reliab. R-29 (1) 88 (April 1980). Barlow's age replacement policy with WcibuU failure times is considered. The optimal replacement interval and the minimum cost of operation are tabulated for a wide range of the Weibull parameters. Asymptotic distribution of downtime for a cold-standby system. OLE PLATZ. IEEE Trans. Reliab. !i-29 (1) 79 (April 1980). The asymptotic distribution of the total time spent in the down state in an interval is derived for a 2-unit coldstandby system with a single repair facility. The time to failure of the working unit is exponentially distributed and the distribution of the repair time is arbitrary. Reliability improvement of multitermlnai networks. J. M. KONTOLEON. IEEE Trans. Reliab. R-29 (1) 75 (April 1980). An algorithm obtains the best improvement of multiterminal network reliability when an additional directed link having a specified reliability is connected to the network. The links of the network are directed or undirected. The network success criterion is that there should be at least one path from the input node to each of the network terminal

World Abstracts on Mieroelectronics and Reliability nodes. For 1-terminal networks the Con,nection of the additional link between the input and the terminal node results in the maximum reliability improvement. For multiterminal networks the maximum reliability is obtained when the additional link goes from the input node to a node terminal obtained using a computer algorithm. Performance/availability model of shared resource multiwoeessars. "1~.C. K. CHOU and J. A. ABRAHAM.IEEE Trans. Retiab. 11-29 (1) 70 (April 1980). Shared-resource systems are particularly vulnerable to faults which contaminate the shared-resource, and result eventually in system failure. In shared-memory computer Systems, resource guardians can provide some protection. A model is developed which incorporates both a performance and availability measure of a general gracefully-degradable shared-resOurce multiprocessor. Various system parameters are studied and their effects are compared on the basis of a performance/cost ratio. As the number of processors increases or a s the reliability of a processor or memory module decreases, some resource protection becomes necessary. There is a class of systems for which adding resource protection provides no measurable benefit. Maximum likelihood estimation of linear failure rate. ANTHONY A. SALVIA.IEEE Trans. Reliab. R-29 (1) 49 (April 1980). This paper presents a method for determining the maximum likelihood estimators for a distribution with linear failure rate. Estimates of the variance-covariance matrix are also obtained, and a numerical example given. Optimi~tton system reliability via redundancy and/or design considerations. L. C. Fg~dR, P. M. GHAtE and K. L. FRAIR. IEEE Trans. Reliab. R-29 (1) 33 (April 1980). The two traditional methods used in improving the reliability of a multi-stage system are examined. The first method is the creation of redundancy in system components, whereas the second method consists of overdesigning the system components. An Integrated Reliability Optimization ~Model that includes both of these two methods for improving the reliability of a system is presented. It is shown that under certain assumptions the integrated model reduces to a Redundancy Optimization Model and under certain other assumptions reduces to a Design Optimization Model. Several methods that have been previously suggested for obtaining solutions to the Integrated Optimization Model are reviewed and a generalized sohitior~ procedure for such a model is presented. This solution procedure involves the successive solution of two subproblems a number of times. The first subproblem is a design optimization problem that is solved by the David-Fletcher-Powell optimization algorithm. The second subproblem is a reliability redundancy optimization problem that is solved with the heuristic approach of Aggarwal et aL Reliability evaluation of a flow network. S. H. LEE. IEEE Trans. Reliab. R-29 (1) 24 (April 1980). This paper presents a method for evaluating reliability of a flow network using the concept of lexicographic ordering. Associated with each branch of the network are the flow capacity and the probability that the branch functions properly. The network is successful if a specified unit of flow can be transmitted through the network. A labelling scheme is used to route the flow through the network and a computer program for implementing the algorithm is given in the Supplement. Proba~lity plots for life test data based on optimum spacing method. MASAArd TSUJZTANI, Hmosm OHTA and SmGEO KASE. IEEE Trans. Reliab. R-29 (1) 66 (April 1980). The research of graphical method reported in this article is originally motivated with the intention of analyzing life data more effectively than the conventional techniques. Tables

901

are provided, for selecting optimum graphical plotting positions so as to assess the validity of fitting a theoretical distribution to large data set and to obtain graphical estimates of unknown parameters. Estimation of the guarantee time in an exlmmmtial failure model. DANNY DYER and JegOME KEATING. IEEE Trans. Reliab. R-29 (1) 63 (April 1980). The location parameter/~ in a 2-parameter exponential failure model is often termed the guarantee time since no failure can occur until life exceeds ~. Several point estimators of # are compared by examining each estimator's risk corresponding to a loss function which features a greater penalty for overestimating than for underestimating/~. The estimators considered in this fashion are: maximum likelihood, minimum variance unbiased, best invariant, and median unbiased. A new estimator of/L is derived which has smaller risk under our assumptions than any of the aforementioned estimators. A 2-fold pairwise comparison technique is then used which examines (a) the odds in favour of the new estimator's being closer to # than is a competitor, and (b) each estimator's risk not only when it is closer to/~ than is the other but also when it is not. General failure model applied to preventive nmiateunee policies. FRANK BEICHELTand KLAUS FISCHER. IEEE Trans. Reliab. R-29 (1) 39 (April 1980). The reliability behaviour of systems is investigated if two types of failures can happen. Type 1 is removed by minimal repair, Type 2 by replacement. Reliability expressions are derived. The results are used for calculating the s-expected long-run cost rate for a generalized age-replacement policy and repair limits. Sequential destruction method for Monte Carlo evaluation of system reliability. MALCOLM C. EASTON and C. K . Wot¢o. IEEE Trans. Reliab. R-29 (1) 27 (April 1980). Circumstances favouring the use of Monte Carlo methods for evaluating the reliability of large systems are discussed. A new method, that of Sequential Destruction (SD) is introduced. The SD method requires no preparatory topological analysis of the system, and remains viable when element failure probabilities are small. It applies to a variety of reliability measures and does not require element failures to be sindependent. The method can be used to improve the performance of selective sampling techniques. Substantial variance reductions, as well as computational savings, are demonstrated using a sample system with more than 100 elements. Confidence intervals for comparing two life distributions. ELISA T. LEE and DAVID R. THOMAS. IEEE Trans. Reliab. R-29 (1) 51 (April 1980). The performance of several sconfidence interval procedures for comparing two life distributions is studied by Monte Carlo methods. Three life models are considered: exponentials, nonparametric proportional hazard functions (Lehmann alternatives), and nonparametric scale alternatives. The s-confidence procedures are based on (a) for exponential distributions: The F-statistic, a likelihood radio statistic (LR), and maximum likelihood estimator (MLE), (b) for nonparametric proportional hazard functions, a LR and MLE based on Cox's conditional likelihood function, (c) for nonparametric scale alternatives, the generalized Wilcexon and the CoxMantel statistics. The procedures are compared with respect to coverage probabilities, robustness, and power. The simulations include seyeral cases of censored and uncensored samples from the WeibuU distribution. When samples are from exponential distributions, with or without censoring, all the procedures are valid. The three parametric procedures have higher power than the nonparametric procedures when there is no censoring and have similar power when there is censoring. When samples are from the Weibull distributions, the three parametric procedures are not robust. If the two shape parameters are