The life cycle cost impacts of unsafe designs

546

World Abstracts on Microelectronics and Reliability

RA system using process failure analysis for ICs. A. TAKAIDE and N. MANAGE. Proc. IEEE Reliab. Maintainab. Syrup., Philadelphia (Jan. 18-20, 1977) p. 1. This paper presents a discussion on the reliability assurance system of integrated circuits, which at present mainly comprises sampling stress testing and screening. These procedures, especially sampling stress testing, are shown to be ineffective in assuring highly reliable devices. Upon careful examination, we have found out that the failure mechanisms observed in actual use correlate well with failure mechanisms experienced in manufacturing process, And we will show in this paper that these correlations are used effectively to establish a new reliability assurance system. The repair or modification of pads, tracks and plated-thru holes on PCB's. Electron. Prod. p. 19 (April 1977). Modern double-sided printed circuit boards feature extremely dense, highly complex, tightly interwoven networks of slender circuit tracks and component mounting pads. As a result, a critical problem facing the Electronics Industry today is how to repair or modify an ultra-complex, exceptionally high cost circuit board without further damaging it, or even worse ... ruining it entirely.

Reducing solder shorts in wave soldering. R. H. RUHL, DANIEL NETZ and R. HECKMAN. Electron. Prod. p. 8 (April 1977). In an effort to further reduce the level of shorting, a study was undertaken to do the following: (1) review the mechanism causing solder shorts, (2) investigate the suitability of applying process control techniques to the wave soldering process, (3) explore the effect of board design changes.

Travelling-wave tube reliability estimates, life tests and space flight experience. VINCENT R. LALLI and CARLTON E. SPECK. Proc. IEEE Reliab. Maintainab. Symp., Philadelphia (Jan. 18-20, 1977) p. 12. An assessment of the probable failure modes of high-power traveling wave tubes (TWT's) intended for use in space is presented. The infant mortality, useful life, and wearout phase of the tubes life are considered. The performance of existing developmental tubes. flight experience, and sequential hardware testing are evaluated. The reliability history of TWT's in space applications is documented by considering (I) the generic parts of the tube in light of the manner in which their design and operation affect the ultimate reliability of the device, (2) the flight experience of medium-power tubes, and (3) the available life test data for existing space-qualified TWT's in addition to those of high-power devices, Based on generic failure rate data from existing literature, an analytical estimate of the MTBF of a specific highpower TWT used for the Communications Technology Satellite (CTS) is calculated. The same procedure is also applied to a tube characteristic of existing space-qualified devices in order that the validity of the analytical predictions may be compared with demonstrated MTBF. A failure effects analysis with criticality ranking is then presented for the CTS tube in order to uncover those components which most strongly affect its reliability, the critical design weaknesses of the tube, and its wearout modes. A sequential test is then described which determined early within the development program whether the tube could demonstrate with reasonable confidence a given MTBF range.

Dormancy effects on nonelectronics. DONALD F. COTTRELL. Proc. IEEE Reliab. Maintainab. Syrup., Philadelphia (Jan. I 8-20, 1977) p. 7. The results of a 12-month study program conducted by Martin .Marietta Corporation to collect and analyze reliability data for nonelectronic components in the dormant mode form the basis of this report. Data were collected from such sources as private contractors, government facilities, research institutions, and

educational institutions. The collected data wcrc ti~en grouped, analyzed, and statistically tested. Approximatcly 170 billion part-hours of dormant data covering 90 major part classes and subclasses were collected.

Optimum test samples for reliability improvement. EL~Lr BOYLE and LELAND STEWART. Proc. IEEE Reliah. ~/lai,tainab. Syrup., Philadelphia (Jan. 18 21), [977~ p. 24Y F o p mulas are derived and discussed which provide optimum sample sizes for discovering failure mechanisms. T~t o cases are considered: (A) The sample size for a single hardwmc componcm is determined to obtain an optimal bala~ce between expected improvement in reliability and test cosL (B) The sample sizes are determined for all hardware components which comprise a system such that the expected improvement in reliability of the s~stem is maximized for a Nven fixed total test budget Reliability evaluation of integrated circuits, t'roc. 5ym?. 1 EE tferiot-Watt University, Edinburgh (March 31, 1977) p. (~r Every manufacturer has a slightly different method of generating his reliability data. It is therefore difficult lor a user inexperienced in reliability calculations to make a valid comparison. Towards this end the concepts introduced earlier will be of great value. The following list should be verified before any conclusions ~q" vendor superiority are drawn. 1. Confidence limit. 2. Reject criteria ldegradation, data si~ect, t'ul~clional, catastrophic, specific mechanismsl. 3. Temperature of test. 4. Activation energy. 5. Distortion of failure rate due to ~ lo~ number oi device hours. 6. Biasing configurations. 7. Test monitoring (system failures can produce imprcssire results due to less stringent stress being applied to the device). Only if all these factors are considered can a u'uly ol!icctix c comparison be made.

Contamination in solder baths. DONALD A, I!L.t,ID]I. Electron. Prod. p. 16 (April 19771. tt is necessary to maintain a control of the level of contamination in :t solder bath within specific limits in order to avoid problems. Grainy or gritty solder joints can result in the development of cracks within the joint, if not immediately detectable, then after the product has been put into service. Contamination in the solder can result in changing the mobility or fluidity of the solder. If solder becomes sluggish, the drainage characteristics as the printed circuit board exits from the solder wave might result in icicles and bridges which will require additional touch-up, an expensive operation which can be minimized using high-purity solder when initially filling the machine and by maintaining the alloy within limits by undertaking the minor expense of a solder analysis on a routine, periodic, quality control basis.

The life cycle cost impacts of unsafe designs. RicnaaD [, W~:BER. Proc, I EEE Reliab. Maintainak Syrup.. Phihutelphia (Jan. 18-20, 1977)p. 120. Accident costs represent a significant part of the cost of ownership. If life cycle costs are to be controlled, weapon system designs must consider the impact that unsafe designs have on the cost of ownership. Accident costs cannot be brought under control by concentrating on reducing only the accident rate; the average cost of each accident must also be reduced. Each of the cost elements that go to make up the cost incurred by an accident must be explicitly used to make those design tradeoffs necessary to reduce life cycle cost. The Air Force's Directorate of Aerospace Safety has been active in developing an awareness among program and system managers of the life cycle accident cost concept and in developing

World Abstracts on Microelectronics and Reliability the necessary methodology and procedures. An analytical model has been developed, cost elements and data sources are being defined, and directives are being changed.

Reliability, availability, maintainability/logistics (RAM/ LOG). L. L. BISHOP,T. A. CRONOGUE,R. HOFFMAN,D. RESIDE, G. DONALD and R. FLYNN. Proc. IEEE ReliabT. Maintainab. Syrup., Philadelphia (Jan. 18-20, 1977) p. 49. The need for accurate and timely data has always been recognized in order to properly manage a weapon system. This need has been heightened by the reintroduction of competitive fly-off into the weapon acquisition. If we want to have RAM logistics and operating and support costs be a discriminator in the selecting of a weapon system, we have to take action to obtain timely, accurate and applicable data. The RAM/LOG data collection system was designed to satisfy this requirement. The design of this methodology is based on years of experience in attempting to utilize existing data systems. The RAM/LOG data collection system is based on the following concepts: 1. Integrated Data Base. The 'data base has to be composed of many different sources. The RAM/LOG system was designed to be compatible with the contractor data items generated during an engineering development program in addition to controlled data collection during test.

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2. Data Elements and Flow Processes. One of the many elements of RAM/LOG is the emphasis toward the quality of the data. The data is well-controlled and receives numerous quality audits on-site as well as in the central facility. The controlled data collection is an in-depth and detailed event recording processes that are evaluated on an event basis for determining contractor performance. 3. Utilization of Feedback and Output Designs. The data system has taken into consideration the fact that it will have to be used with various models and by those involved in various technical disciplines with different objectives. The data system has been structured to provide practically any required information to exercise most RAM logistics and cost analysis models. The RAM/LOG data collection system has been implemented on the UH-1, UTTAS, 214, AAH, and AN-1 series aircraft, and is being considered for implementation on future R & D efforts. Feasibility of RAM/LOG for operational aircraft has been demonstrated and proven. The methodology, applicability and results of RAM/LOG efforts will be presented. A note on a four-state system. BALBIR S. DHILLON. Microelectron. Reliab. 15, 491 (1976). This short paper presents the newly developed state probabilities equations of an extended four-state system model.

3. CIRCUIT AND SYSTEMS RELIABILITY, MAINTENANCE AND REDUNDANCY Common mode failureanalysisof reliabilitynetworks. BALBIR SINGH DHILLON and C. L. PROCTOR. Proc. IEEE Reliab. Maintainab. Symp., Philadelphia (Jan. 18-20, 1977) p. 404. The reliability networks considered in this study are composed of two state devices. A device is said to have two states if it either operates or fails. This paper presents a simple extension to the classical reliability theory. New reliability hazard rate and M.T.T.F. formulas are developed for the parallel, k-out-of-n, parallel-series and bridge networks subject to common mode of failures (i.e. for identical components only.) The reliability plots are shown for the above configurations. The plots clearly show the effect of common mode of failure on redundant networks. There is a significant increase in the probability of redundant system failure (i.e. at least for the small value of 20 when common mode of failures are considered. In every example, the reliability of independent and common failure modes networks is compared to the reliability obtained from the conventional independent failure mode networks.

Incr~sed reliability of communication networks by distributing connections to transmission paths independent on one another. Csc, TRSTENSKY. Nachrichtentechnik Elektronik 27. 115 (1977). (In German only). Some possibilities are analysed with a view to increasing the reliability in communication networks by distributing connections to paths independent on one another. For this purpose reliability criteria are used, which are obtained by means of the theory of graphs and the calculus of probability. A cost effective approach to weapon acceptance. JAMESM. PERKINS and EDWARD E. LEACH. Proc. IEEE Reliab. Maintainab. Syrup., Philadelphia (Jan. 18-20, 1977) p. 252. The Pacific Missile Test Center has been conducting production acceptance test and evaluation on Navy guided weapon systems since 1959. Traditionally, acceptance testing of weapons has been based on some form of systems demonstration or proof firing of a sample from each production lot to indicate compliance with contractual specifications. This form of systems test has been particularly relevant for air launched guided missile systems due to t h e complexity of the weapons/aircraft/target interfaces and

the difficulty in developing adequate ground tests to demonstrate system performance and reliability. The purpose of this paper is to trace the development of production acceptance testing of weapon systems from 1959 to the present time. From the initial SIDEWINDER to the current PHOENIX air-to-air missile, we have seen a major evolution in weapon complexity. The attendant increase in unit cost, compounded by escalation of test and evaluation costs have created strong pressure to • reduce program costs through reduction of sample sizes and elimination of weapon expenditures. These economic constraints tended to destroy the statistical significance and effectiveness of the overall acceptance process. A concerted effort was undertaken to develop non-destructive test techniques to assess weapon reliability. A flight test simulation facility was completed that provides a capability to measure weapon reliability under environmental conditions that simulate the fleet operating environment. The results are integrated with results obtained from flight and ground tests to provide a balanced program that has proven to be effective in assessing production quality. The incorporation of this test process has: (1) provided an increase in the confidence of the acceptance process, and (2) reduced the cost of conducting acceptance testing relative to the cost of the hardware procurement. Prediction of software failures. M. Lmow and T. A. T~L~YER. Proc. IEEE Reliab. Maintainab. Syrup., Philadelphia (Jan. 18-20, 1977) p. 489, The number of errors discovered during the course of software development has a significant impact upon project costs in terms of m a n power and computer resources needed to correct the errors. Failures attributable to software which occur during system operations by the user, result in a maintenance cost, but even more importantly a loss of system availability and performance. In either phase it is desirable to be able to predict at the earliest possible moment the resources needed to correct the causes of software failures, and to determine where within the software to devote the most resources. Size of computer programs (in terms of number of source code statements in a higher level language such as FORTRAN or JOVIAL, or number of words in core