Optimizing construction of scheduled data flow graph for on-line testability

The objective of this work is to develop a new methodology for behavioural synthesis using a flow of synthesis, better suited to the scheduling of independent calculations and non-concurrent online testing. The traditional behavioural synthesis process can be defined as the compilation of an algorithmic specification into an architecture composed of a data path and a controller. This stream of synthesis generally involves scheduling, resource allocation, generation of the data path and controller synthesis. Experiments showed that optimization started at the high level synthesis improves the performance of the result, yet the current tools do not offer synthesis optimizations that from the RTL level. This justifies the development of an optimization methodology which takes effect from the behavioural specification and accompanying the synthesis process in its various stages. In this paper we propose the use of algebraic properties (commutativity, associativity and distributivity) to transform readable mathematical formulas of algorithmic specifications into mathematical formulas evaluated efficiently. This will effectively reduce the execution time of scheduling calculations and increase the possibilities of testability

Automatic programming methodologies for electronic hardware fault monitoring

This paper presents three variants of Genetic Programming (GP) approaches for intelligent online performance monitoring of electronic circuits and systems. Reliability modeling of electronic circuits can be best performed by the Stressor - susceptibility interaction model. A circuit or a system is considered to be failed once the stressor has exceeded the susceptibility limits. For on-line prediction, validated stressor vectors may be obtained by direct measurements or sensors, which after pre-processing and standardization are fed into the GP models. Empirical results are compared with artificial neural networks trained using backpropagation algorithm and classification and regression trees. The performance of the proposed method is evaluated by comparing the experiment results with the actual failure model values. The developed model reveals that GP could play an important role for future fault monitoring systems.This research was supported by the International Joint Research Grant of the IITA (Institute of Information Technology Assessment) foreign professor invitation program of the MIC (Ministry of Information and Communication), Korea

Designing Fault-Injection Experiments for the Reliability of Embedded Systems

This paper considers the long-standing problem of conducting fault-injections experiments to establish the ultra-reliability of embedded systems. There have been extensive efforts in fault injection, and this paper offers a partial summary of the efforts, but these previous efforts have focused on realism and efficiency. Fault injections have been used to examine diagnostics and to test algorithms, but the literature does not contain any framework that says how to conduct fault-injection experiments to establish ultra-reliability. A solution to this problem integrates field-data, arguments-from-design, and fault-injection into a seamless whole. The solution in this paper is to derive a model reduction theorem for a class of semi-Markov models suitable for describing ultra-reliable embedded systems. The derivation shows that a tight upper bound on the probability of system failure can be obtained using only the means of system-recovery times, thus reducing the experimental effort to estimating a reasonable number of easily-observed parameters. The paper includes an example of a system subject to both permanent and transient faults. There is a discussion of integrating fault-injection with field-data and arguments-from-design

HARMONIC AND RANDOM VIBRATION DURABILITY INVESTIGATION FOR SAC305 (Sn3.0Ag0.5Cu) SOLDER JOINT

ABSTRACT Title of Dissertation: HARMONIC AND RANDOM VIBRATION DURABILITY INVESTIGATION FOR SAC305 (Sn3.0Ag0.5Cu) SOLDER INTERCONNECTS Yuxun Zhou, Doctor of Philosophy, 2008 Dissertation directed by: Professor Abhijit Dasgupta Department of Mechanical Engineering Vibration loading is commonly encountered during the service life of electronic products. However, compared to thermal cycling durability, vibration durability is more complex and has been less investigated. In surface mount technology, solder joints are the primary mechanical, thermal and electrical interconnects between the component and the PWB. So the reliability of solder joints is very crucial for most electronic assemblies. The vibration durability of Pb-free solder joints is the focus of this dissertation. The characteristics of the stress from vibration loading are low amplitude and high frequency, while those from cyclic thermal loading are high amplitude and low frequency. In this study, several exploratory vibration tests were conducted, using both narrow band and broad-band, step-stress excitation at several different isothermal and thermal cycling conditions. The effect of thermal pre-aging on solder joint vibration failures was also investigated. Some of the vibration durability results were analyzed in detail, to obtain quantitative insights into the vibration fatigue behavior of the SAC305 solder material. A time-domain approach was adopted to investigate the durability of solder interconnects under different kinds of vibration and quasi-static mechanical loading. First, the solder interconnects were subjected to narrow-band (harmonic) vibration loading. The test were conducted at the first natural frequency of the test board using constant-amplitude excitation and solder fatigue properties were extracted with the help of a time-domain analysis that is based on quasi-static finite element simulation. Compared to broad-band step-stress vibration durability tests, the advantage of the harmonic constant-amplitude test is less complexity in the model extraction process, hence, less uncertainty in the desired fatigue constants. Generalized strain-based S-N curves have been obtained for both SAC305 and Sn37Pb solder materials. The strain-life model constants show that SAC305 solder material has superior fatigue properties compared to Sn37Pb solder material under low-cycle fatigue loading, while the reverse is true for high-cycle fatigue loading. These results are consistent with test results from other researchers. In actual application, SAC305 assemblies almost always fail before Sn37Pb assemblies under comparable vibration excitation because of (i) higher solder strain at a given excitation level; and (ii) multiple failure modes such as copper trace cracking. Next, durability was investigated under step-stress, broad-band (random) excitation. These test results show that SAC305 interconnects are less durable than Sn37Pb interconnects under the random excitation used in this study, which agrees with the harmonic durability results. The random and harmonic durability results were quantitatively compared with each other in this study. Finite element simulation was used to investigate the stress-strain response in the interconnects. The output of this simulation is the strain transfer function due to the first flexural mode of the PWB. This transfer function is used to obtain the solder strain from the measured board strain. This fatigue assessment method demonstrated that the model constants obtained from the harmonic test overestimate the fatigue life under random excitation by an order of magnitude. The causes for this discrepancy were systematically explored in this study. The effects of cyclic loading and mean stress on the vibration durability were addressed and found to be minimal in this study. The stress-strain curves assumed for the solder material were found to have a very large effect on the durability constants, thus affecting the agreement between harmonic and random durability results. The transient response of the components on the test board under both harmonic and random excitation was also included in the strain transfer function with the help of dynamic implicit simulation, and found to have a much stronger effect on the vibration durability at the high frequencies used in broad-band excitation compared to the low frequency used in narrow-band test. Furthermore, the higher PWB vibration modes may play a strong role and may need to be included in the strain transfer-function. This study clearly reveals that the solder strain analysis for broad-band random excitation cannot be limited to the quasi-static strain transfer-function based on the first PWB flexural mode, that has been used in some earlier studies in the literature. The time-domain approach used in this study provided fundamental and comprehensive insights into the key factors that affect vibration durability under different types of excitation, thus leading to a generalized S-N modeling approach that works for both harmonic and random vibration loading

Thermal management of solid state power switches

The transient temperature of solid state power switches is investigated using thermal resistance network modelling and experimental testing. The ability of a heat sink mounted to the top of the device to reduce the transient temperature is assessed. Transient temperatures for heat pulses of up to 100ms are of most interest. The transient temperature distribution inside a typical stack-up of a solid state power switch is characterised. The thermal effects of adding a heat sink to the top of the device are then assessed. A variety of heat sink thicknesses and materials are evaluated. Components of the device stack-up are varied in order to assess their affect on the effectiveness of the heat sink in reducing the device temperature. Thermal networks are successfully applied to model the transient heat conduction inside the stack-ups. This modelling technique allowed a good understanding of the thermal behaviour inside the stack-up and heat sink during the transient period. The concept of using a heat sink to suppress the transient temperature was validated experimentally on two types of solid state power switch

Thermal management of solid state power switches

The transient temperature of solid state power switches is investigated using thermal resistance network modelling and experimental testing. The ability of a heat sink mounted to the top of the device to reduce the transient temperature is assessed. Transient temperatures for heat pulses of up to 100ms are of most interest. The transient temperature distribution inside a typical stack-up of a solid state power switch is characterised. The thermal effects of adding a heat sink to the top of the device are then assessed. A variety of heat sink thicknesses and materials are evaluated. Components of the device stack-up are varied in order to assess their affect on the effectiveness of the heat sink in reducing the device temperature. Thermal networks are successfully applied to model the transient heat conduction inside the stack-ups. This modelling technique allowed a good understanding of the thermal behaviour inside the stack-up and heat sink during the transient period. The concept of using a heat sink to suppress the transient temperature was validated experimentally on two types of solid state power switch

Analyse de défaillance de nouvelles technologies microélectroniques (nouvelles approches dans la méthodologie de préparation d'échantillon)

Dans le développement des technologies microélectroniques, l analyse de défaillance permet par l étude des mécanismes de défaillance potentiels de définir des solutions correctives. La mise en œuvre des techniques de localisation et d observation des défauts requiert une méthodologie, dont l étape clé est la préparation d échantillons. Celle-ci doit continuellement évoluer pour s adapter aux innovations technologiques qui introduisent de nouveaux matériaux, et augmentent la complexité des composants assemblés. Cette thèse s est intéressée à la méthodologie de préparation d échantillons pour l analyse de défaillance de deux familles de produits : les produits discrets et IPAD, et les micro-batteries. Pour les produits discrets et IPAD, une optimisation de la méthodologie existante a été réalisée en intégrant de nouvelles approches, développées pour résoudre des cas jusqu alors en échec. Pour les micro-batteries, les matériaux utilisés et leur architecture ont nécessité une remise en question complète de la méthodologie de préparation d échantillon.In the development of microelectronic technologies, the failure analysis makes it possible to define corrective actions thanks to the understanding of the failure mechanism. In order to define the most adequate localization and observation techniques to use, a failure analysis flow is required. The sample preparation is a key step of this flow. This flow must continuously evolve to take into account the technological innovations that introduce new materials, and increase the complexity of assembled components. This work concerned the sample preparation flow for the failure analysis of two product families : the discrete products and IPAD, and the micro-batteries. Concerning the discrete products and the IPAD, an optimization of the current flow was performed with the integration of new approaches developed to solve failed cases. For the micro-batteries, the used materials and their architecture required an entire reappraisal of the sample preparation flow.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Diagnostic de défaillances de systèmes optoélectroniques émissifs pour applications de télécommunication : caractérisations électro-optiques et simulations thermomécaniques

Ce mémoire présente les travaux de conception et de réalisation d'un banc de mesures de paramètres électriques et optiques dédié au diagnostic de défaillances de systèmes optoélectroniques émissifs infrarouge (880 - 1550 nm). Les performances du banc comprenant des mesures courant-tension, puissance optique et spectre optique en température ont permis la discrimination de dégradations relatives au composant ou à l'alignement optique de diodes électroluminescentes ou têtes optiques. Les niveaux de contraintes apportées par des vieillissements, appliquées à des têtes optiques émissives 1310 nm à cavité Fabry-Pérot ont induit une chute de puissance optique de plus de 10% après un nombre réduit de cycles. L'origine de cette diminution de puissance optique peut être initiée par une défaillance au sein de la puce ou une instabilité du couplage avec la fibre optique. Les dérives du courant de seuil et du spectre optique ont confirmé des dégradations de la zone active. En revanche, les analyses électro-optiques ne permettent pas de déterminer l'origine de la défaillance dans le cas d'une dérive du couplage optique. Les tolérances submicroniques des éléments passifs d'alignement optique étant fréquemment à l'origine des défaillances, des simulations physiques non-linéaires par éléments finis ont été également effectuées afin de déterminer la susceptibilité thermomécanique d'un module optoélectronique émissif complet DFB 1550 nm. Cette étude a démontré l'accumulation de contraintes résiduelles après les tirs YAG, utilisés pour souder les sous parties entre elles, susceptibles de provoquer une déviation de l'axe optique théorique de 0,03° responsables d'une chute de 15 % de la puissance optique. Un macromodèle, tenant compte des différentes étapes de fabrication et des caractéristiques expérimentales des matériaux en présence, a été développé, en accord avec le fabricant, pour optimiser les règles de conception de nouvelles générations de têtes optiques robustes.This thesis presents work of design and realization of test bench for measurements of electrical and optical parameters dedicated to the diagnosis of failures of infrared emissive optoelectronic systems (880 - 1550 nm). The performances of this test bench including current-voltage, optical power and optical spectrum measurements versus temperature allowing the discrimination of degradations related to the component or the optical alignment of light emitting diodes or laser modules. Ageing tests applied to emissive laser modules 1310 nm with Fabry-Pérot cavity induced an optical power decrease of more than 10% after a short number of cycles. The origin of this drop can be initiated by a failure within the chip or an instability of the optical coupling. The drift of the threshold current and the optical spectrum has confirmed degradations located in the active zone. On the other hand, the electrooptical analyses do not allow to determine the origin of the failure in the case of an optical coupling drift. The submicronic tolerances of passive elements for optical alignment are generally related to the failures. So, non-linear finite elements physical simulations were also carried out in order to determine the thermomechanical susceptibility of an emissive 1550 nm DFB optoelectronic module. This study has showed the accumulation of residual stresses after laser Nd : YAG, used to weld the different parts between them, responsible of theoretical optical axis deviation near 0,03° leading to a 15 % optical power decrease. A parametric model, taking into account of the various stages of manufacturing process and experimental characteristics of materials, was developed, in agreement with the manufacturer, to optimize design rules for improvement of robust laser modules

Contribution à l'amélioration de la fiabilité des modules IGBT utilisés en environnement aéronautique

L’augmentation de la puissance électrique consommée à bord des avions a récemment conduit à introduire des convertisseurs électroniques de puissance à base d'interrupteurs à IGBT dans de nombreuses applications aéronautiques. L'utilisation de ces interrupteurs diffère de leurs emplois traditionnels dans les domaines du ferroviaire ou de l'automobile. En effet, les sollicitations environnementales ainsi que les cycles de commandes électriques sont différents de ceux rencontrés jusqu’alors, ce qui amène à remettre en cause les résultats actuels au sujet de la durée de vie et de la fiabilité de ces interrupteurs. Face à ces interrogations, les sociétés THALES et Hispano-Suiza se sont associées au sein du programme de l’avion plus électrique MODERNE (MODular ElectRical NEtwork) initié par Airbus, en vue de développer des solutions à haut niveau de fiabilité pour des applications aéronautiques sévères. C’est dans ce contexte que prennent place les présents travaux, dont les objectifs sont dans un premier temps de proposer de nouvelles architectures de modules susceptibles de présenter de meilleures performances d’intégration, et dans un second temps d’en étudier la fiabilité. Pour répondre à ces questions, un état de l'art des technologies utilisables a été mené. La confrontation de ses technologies aux contraintes et recommandations aéronautiques a conduit au choix de deux approches d'assemblage, proposées avec un jeu de matériaux sélectionnés pour leurs propriétés physiques et en conformité avec les réglementations sur l’utilisation de matériaux polluants. À l'issue d'une analyse de défaillances, différents développements ont été conduits afin de modéliser et caractériser le comportement thermique, mécanique puis à défaillance des modules. Des modèles Éléments Finis de structures représentatives des solutions proposées ont alors été mis au point et exploités pour l'élaboration de règles de conception, sur la base de plans d'expériences couplés à de la simulation numériques. Les informations générées ont servi à la conception de trois prototypes destinés à des applications différentes. Les performances de ces prototypes ont été évaluées, notamment leurs fiabilités obtenues par des calculs mécano-fiabilistes ayant permis l'optimisation de la conception des différents modules. ABSTRACT : Within the framework of the electric plane programs, the aircraft industry is facing higher demands of electric power, fact which involves an increasing use of IGBT modules in aeronautical power converters. Although such modules have been well studied and known in railway and the automotive domains, they will be subjected to stresses and operational cycles specific to the aeronautical environment. Consequently, this requires manufacturers to answer some questions about their lifetime and reliability issues. Faced with these questions, THALES and Hispano-Suiza have associated in the more electric aircraft project launched by Airbus (MODERNE - MODular ElectRical NEtwork), with the aim of developing high reliability solutions for harsh aeronautic applications. This work takes place in this context, with the objectives of proposing power modules architectures likely to exhibit better performances and integration level, and then study the reliability of different prototypes. To answer these questions, technological studies of the possible packaging and connecting solutions, faced with aeronautical stresses and requirements led to the choice of two basic assembling approaches. A set of materials selected for their physical properties and their compliance with polluting materials regulations was also proposed. The potential failure modes of these solutions were pointed out and taken into account within experimental and numerical developments, to model and characterize the thermal, mechanical and failure behaviour of the modules. Then, different Finite Element models representative of the proposed technologies structures were developed and investigated for defining design rules on the basis of Designs of Experiments. The whole knowledge generated by the simulations was used to design three prototypes of IGBT module for different applications. The performance of these prototypes have been evaluated and compared to the requirements, including their reliability obtained by mechanical calculations coupled with probabilistic methods which led to their optimization