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Birth-death and bug counting
176
World Abstracts on Microelectronics and Reliability
active devices, the characteristics displayed in a circuit are very sensitive to output current level, but much less sensitive to output supply voltages as long as they exceed a minimum value. As supply voltages are reduced, the power dissipated decreases proportionately, but operating characteristics need not be changed. A series of "paper" designs can quickly verify the independence of operating conditions with respect to the output supply voltage. The result is less waste power, less cooling requirement, and, because of the sensitivity of MTBF (mean time between failure) to device temperature, increased overall MTBF, allowing systems to approach their life expectancy more closely. The subject of electron tube circuit reliability is also included in the discussion, first because the same principles that apply to bipolar and field-effect transistors apply to electron tubes as well, and because high-power transmitters still must use electron tubes in their final stages. The same principles that apply to the selected electron tubes apply to the high-power transmitting devices as well, and similar benefits accrue. Modest changes in design procedure can lead to substantial reduction of input power requirements in electronic circuits using active devices. In addition, the improved design control that results can lead to circuits having generally improved operating characteristics. Extensive field results have verified the validity of the approach. The resulting possible systematization of reliability design procedures, including a series of "paper designs" based on computer analysis at successively lower output supply voltages, can help to find the best ratio of output signal power to source input power under operating conditions, and can lead to a quantum jump in this aspect of reliability improvement while at the same time improving operation, reducing required power and reducing cooling requirements.
Microelectronic system reliability prediction. IEEE Trans. Reliab. R-32 (1), 9 (1983). The paper reviews the US MILHDBK-217 (MH-217) method of part stress-analysis failurerate prediction for microelectronic systems and investigates the extent to which the MH-217 failure-rate formula is compatible with the physics of actual failure modes. A new formula is proposed which takes account separately of the reliability of the microelectronic devices in a system and of the system-level determinants of reliability. It is simpler than the current MH-217 formula, and more useful. It enables the system level aspects such as reliability program activities to be taken into account in the prediction, and allows better correlation to be made between part test and system test data. An example applies the new formula to a typical microelectronic system. By considering separately the failure physics of parts and the system level determinants, reliability prediction can be made a more useful tool both for part stress analysis and for reliability program management. The model would enable better correlations to be made between part and system test results. More work needs to be done to refine and validate the parameters. For high-reliability programs with closely controlled maintenance or with no maintenance, the use of a decreasing failure rate model for part failures should be considered. The failure rate formulae for other electronic parts used in microelectronic systems would also need to be reviewed, but apart from removal of the environmental factor and reduction in the failure rate values proportionate to that proposed for microelectronic parts, no changes should be necessary. The model is recommended as a basis for further work to improve the effectiveness and usefulness of reliability prediction for mieroelectronic systems.
Birth-death and bug counting. WILHELMKREMER.IEEE Trans. Implications of hoard testing at speed. BOB LAYTON.Electron.
Reliab. R-32 (1), 37 (1983). Many software reliability time-
Prodn, 14 (July 1983). Outlines the underlying problems encountered when need arises to test a pcb at its operational speed.
domain bug-counting models are, as fault counters, special cases of the stochastic process known as the death process. Generalization to a nonhomogeneous birth-death process achieves three ends: stochastic fault introduction, the synthesis of a time-dependent failure rate with imperfect debugging and fault introduction, and the mathematical unification of much bug-counting theory. Often, the price for generalization is mathematical intractabili{y. Yet useful and tractable reliability measures with strong intuitive appeal are derived. The paper opens with a brief general discussion of software reliability and a selective review of some bug-counting models. Thereafter, the fundamental concepts and equations of a birth-death process are presented and applied to software reliability modelling. Assumptions for this application are then dealt with at some length. Reliability measures --initial, present, and future -are developed. Finally, the practical application of the model in the reliability assessment of a software package is discussed.
Reliability is enhanced by TAAF testing. JOHN H. JONES. Proc. A. Reliab. Maintainab. Symp. 136 (1983). A technique for conducting a Test Analyse And Fix (TAAF) program on a complex memory subsystem is described in this paper. All aspects of this TAAF program are discussed. The Tracking, Growth and Prediction (TGP) Model, developed by Grumman Aerospace Corporation, was used to establish the reliability growth guidelines and is reviewed. The environmental profile used during the TAAF program included: temperature cycling, vibration sweeps and dwells, shock impulses, power-on-and-off cycling, and air flow and humidity variation. This profile was developed based on analysis measured data recorded during E2C aircraft operation. A closed loop failure reporting system provided the data necessary for visibility of failure identification, assignment of the appropriate engineering disciplines to develop the corrective action, and assessment of the corrective action in the operating environment. The effectiveness of the TAAF program was demonstrated by the results of the Reliability Demonstration Test (RDT). The RDT was performed with production equipment which included the corrective actions that were developed as a result of failures experienced during the TAAF test.
Sequential method for comparing two constant failure-rates. DOLUN {~)KSOY.IEEE Trans. Reliab. R-32 (1), 84 (1983). An exact sequential test is given for testing two similar types of equipment in terms of their constant failure rate difference. The results are useful for incentive plans and are fundamental in life testing of these equipments against one anot.her, during their constant failure-rate period. The theory and equations for the tables are developed and the related references are included. Six test plans are summarized.
Correspondence of types 1 & II censored-sample estimators. J. E. BILIKAM. IEEE Trans. Reliab. R-32 (1), 100 (1983). Maximum likelihood parameter estimation from censored samples can be done with one algorithm for both type l mission life analysis and type 11 sample censoring.
Optimum simple step-stress plans for accelerated life testing. ROBERT MILLER and WAYNE NELSON. IEEE Trans. Reliab. R-32 (1), 59 0983). This paper presents optimum plans for simple (two stresses) step-stress tests where all units are run to failure. Such plans minimize the asymptotic variance of the maximum likelihood estimator (MLE) of the mean life at a design stress. The life-test model consists of: (1) an exponential life distribution with (2) a mean that is a log-linear function of stress, and (3) a cumulative exposure model for the effect of changing stress. Two types of simple step-stress tests are considered: (1) a time-step test and (2) a
World Abstracts on Microelectronics and Reliability
active devices, the characteristics displayed in a circuit are very sensitive to output current level, but much less sensitive to output supply voltages as long as they exceed a minimum value. As supply voltages are reduced, the power dissipated decreases proportionately, but operating characteristics need not be changed. A series of "paper" designs can quickly verify the independence of operating conditions with respect to the output supply voltage. The result is less waste power, less cooling requirement, and, because of the sensitivity of MTBF (mean time between failure) to device temperature, increased overall MTBF, allowing systems to approach their life expectancy more closely. The subject of electron tube circuit reliability is also included in the discussion, first because the same principles that apply to bipolar and field-effect transistors apply to electron tubes as well, and because high-power transmitters still must use electron tubes in their final stages. The same principles that apply to the selected electron tubes apply to the high-power transmitting devices as well, and similar benefits accrue. Modest changes in design procedure can lead to substantial reduction of input power requirements in electronic circuits using active devices. In addition, the improved design control that results can lead to circuits having generally improved operating characteristics. Extensive field results have verified the validity of the approach. The resulting possible systematization of reliability design procedures, including a series of "paper designs" based on computer analysis at successively lower output supply voltages, can help to find the best ratio of output signal power to source input power under operating conditions, and can lead to a quantum jump in this aspect of reliability improvement while at the same time improving operation, reducing required power and reducing cooling requirements.
Microelectronic system reliability prediction. IEEE Trans. Reliab. R-32 (1), 9 (1983). The paper reviews the US MILHDBK-217 (MH-217) method of part stress-analysis failurerate prediction for microelectronic systems and investigates the extent to which the MH-217 failure-rate formula is compatible with the physics of actual failure modes. A new formula is proposed which takes account separately of the reliability of the microelectronic devices in a system and of the system-level determinants of reliability. It is simpler than the current MH-217 formula, and more useful. It enables the system level aspects such as reliability program activities to be taken into account in the prediction, and allows better correlation to be made between part test and system test data. An example applies the new formula to a typical microelectronic system. By considering separately the failure physics of parts and the system level determinants, reliability prediction can be made a more useful tool both for part stress analysis and for reliability program management. The model would enable better correlations to be made between part and system test results. More work needs to be done to refine and validate the parameters. For high-reliability programs with closely controlled maintenance or with no maintenance, the use of a decreasing failure rate model for part failures should be considered. The failure rate formulae for other electronic parts used in microelectronic systems would also need to be reviewed, but apart from removal of the environmental factor and reduction in the failure rate values proportionate to that proposed for microelectronic parts, no changes should be necessary. The model is recommended as a basis for further work to improve the effectiveness and usefulness of reliability prediction for mieroelectronic systems.
Birth-death and bug counting. WILHELMKREMER.IEEE Trans. Implications of hoard testing at speed. BOB LAYTON.Electron.
Reliab. R-32 (1), 37 (1983). Many software reliability time-
Prodn, 14 (July 1983). Outlines the underlying problems encountered when need arises to test a pcb at its operational speed.
domain bug-counting models are, as fault counters, special cases of the stochastic process known as the death process. Generalization to a nonhomogeneous birth-death process achieves three ends: stochastic fault introduction, the synthesis of a time-dependent failure rate with imperfect debugging and fault introduction, and the mathematical unification of much bug-counting theory. Often, the price for generalization is mathematical intractabili{y. Yet useful and tractable reliability measures with strong intuitive appeal are derived. The paper opens with a brief general discussion of software reliability and a selective review of some bug-counting models. Thereafter, the fundamental concepts and equations of a birth-death process are presented and applied to software reliability modelling. Assumptions for this application are then dealt with at some length. Reliability measures --initial, present, and future -are developed. Finally, the practical application of the model in the reliability assessment of a software package is discussed.
Reliability is enhanced by TAAF testing. JOHN H. JONES. Proc. A. Reliab. Maintainab. Symp. 136 (1983). A technique for conducting a Test Analyse And Fix (TAAF) program on a complex memory subsystem is described in this paper. All aspects of this TAAF program are discussed. The Tracking, Growth and Prediction (TGP) Model, developed by Grumman Aerospace Corporation, was used to establish the reliability growth guidelines and is reviewed. The environmental profile used during the TAAF program included: temperature cycling, vibration sweeps and dwells, shock impulses, power-on-and-off cycling, and air flow and humidity variation. This profile was developed based on analysis measured data recorded during E2C aircraft operation. A closed loop failure reporting system provided the data necessary for visibility of failure identification, assignment of the appropriate engineering disciplines to develop the corrective action, and assessment of the corrective action in the operating environment. The effectiveness of the TAAF program was demonstrated by the results of the Reliability Demonstration Test (RDT). The RDT was performed with production equipment which included the corrective actions that were developed as a result of failures experienced during the TAAF test.
Sequential method for comparing two constant failure-rates. DOLUN {~)KSOY.IEEE Trans. Reliab. R-32 (1), 84 (1983). An exact sequential test is given for testing two similar types of equipment in terms of their constant failure rate difference. The results are useful for incentive plans and are fundamental in life testing of these equipments against one anot.her, during their constant failure-rate period. The theory and equations for the tables are developed and the related references are included. Six test plans are summarized.
Correspondence of types 1 & II censored-sample estimators. J. E. BILIKAM. IEEE Trans. Reliab. R-32 (1), 100 (1983). Maximum likelihood parameter estimation from censored samples can be done with one algorithm for both type l mission life analysis and type 11 sample censoring.
Optimum simple step-stress plans for accelerated life testing. ROBERT MILLER and WAYNE NELSON. IEEE Trans. Reliab. R-32 (1), 59 0983). This paper presents optimum plans for simple (two stresses) step-stress tests where all units are run to failure. Such plans minimize the asymptotic variance of the maximum likelihood estimator (MLE) of the mean life at a design stress. The life-test model consists of: (1) an exponential life distribution with (2) a mean that is a log-linear function of stress, and (3) a cumulative exposure model for the effect of changing stress. Two types of simple step-stress tests are considered: (1) a time-step test and (2) a