Silver sintering for power electronics integration

Silver sintering is an attractive alternative to soldering in power electronics, as it offers higher electrical and thermal performance. Furthermore, sintered attaches can operate at a higher temperature. In this paper, we investigate the use of silver sintering for the bonding of passive components, and for the manufacturing of so-called 3D-modules. It is shown that this technique is well suited, as it makes it possible to operate at very high temperature (up to 310 °C demonstrated), and as it simplifies the assembly process (several identical sintering steps can be performed successively without problem

Électronique haute température -- Contraintes sur la puce et le packaging

Doctora

Le Packaging en électronique de puissance

Le packaging, qui regroupe toutes les fonctions d’isolation, de connexion, de gestion thermique et de protection physique des puces à semiconducteur, a des effets majeurs sur leurs performances. Les éléments constitutifs d’un boîtier sont présentés dans le premier chapitre de ce mémoire, qui constitue un état de l’art du packaging de puissance. Les limites des solutions existantes sont exposées, que ce soit au niveau de leurs performances électriques, de leur fiabilité, ou de leur température maximale de fonctionnement.Dans le second chapitre, nous nous intéressons à des structures innovantes, destinées à dépasser les limites des solutions actuelles. En particulier, les solutions permettant de refroidir les puces de façon plus efficace (refroi-dissement « double face ») sont présentées en détails, en s’appuyant sur des prototypes réalisés au laboratoire.Le troisième chapitre présente les développements autour du packaging pour la haute température (température ambiante supérieure à 200 °C), qui a constitué le pricipal axe de mes travaux au laboratoire Ampère. Il débutepar une étude du comportement électro-thermique de composants en carbure de silicium, qui se révèlent adaptés au fonctionnement en haute température, mais nécessitent néanmoins une gestion thermique performante. La suite du chapitre est consacrée à l’étude de méthodes d’attache de puce alternatives aux brasures et permettant le fonctionnement à haute température. Deux méthodes sont identifiées (soudure en phase liquide transitoireet frittage d’argent), mais seule la seconde se révèle applicable aux puces actuelles.En plus des applications en haute température, la partie prospective du mémoire présente des possibilités de développement vers l’intégration en électronique de puissance, et vers le packaging pour la haute tension

Management strategies can buffer the effect of mass mortality in early life stages of fish

Mass mortality (MM) events affecting early life stages of fish can have strong and long-term consequences for population abundance and demography as well as the economic activity supported by exploited stocks. Adaptive fishery management may help mitigate economic impacts and ensure sustainable resource use following a MM event. Using a state-space life cycle model, we simulated ‘what-if’ scenarios of MM on Northeast Arctic cod (Gadus morhua) eggs and larvae. We compared the expected catches, total stock biomass (TSB), and interannual variability in catches over a period of 10 years after the simulated disturbance. We further evaluated a range of management mitigation strategies, namely reductions in fishing mortality of varying duration (1–10 years) and intensity (no fishing reduction to full ban). A large range of reductions in fishing led to an increase in expected catches over 10 years compared to no reductions, especially when applied immediately after the perturbation and when the cod population was characterized by a high mean age and high TSB. Severe fishing reductions can increase catches substantially but are associated with high interannual variability. Fishing reductions of moderate intensity applied between 1 and 4 years would allow to increase catches with only a slight increase in interannual variability. Our findings demonstrate the potential benefits of an adaptive approach to fisheries management and highlight that mitigation actions may ensure the sustainable exploitation of fish stocks in the wake of unexpected disturbances. Synthesis and application. Mass mortality events during early life stages of fish can potentially have substantial and long-term effects on the population. Mitigation is more efficient when the affected population has a diverse age structure and when the mitigation strategy is applied immediately after the perturbation. Severe reduction in fishing mortality is an efficient measure to increase the expected average catch but is associated with high interannual variability. Fishing reduction of moderate intensity applied during 1–4 years after the event also increases the expected average catch with only slightly higher interannual variability in catches.publishedVersio

Etude de l'interaction choc/turbulence/combustion en écoulement cisaillé réactif : analyse des jets réactifs fortement sous-détendus.

This dissertation is devoted to the study of sheared supersonic reactive flows and more specifically the dynamics of highly underexpanded jets. Such complex compressible turbulent flow conditions are of praclical interest for scramjets as well as rocket engines applications. Similar condit ions may also be found during the accidentai releases of flammable substances into the atmosphere during high pressure vessel rupture or venting. This work is conducted with a high fidelity computational solver: CREAMS (Compressible Multi-reactive species Solver). It uses high precision numerical schemes third-order Runge Kutta scheme for time integration, plus a combination of seventh and eighth-order centered and WENO schemes for spatial integration. The molecular transport terms and chemical sources terms are handled with the most accurate descriptions, i. e., including detailed transport and chemistry. Inert flow simulations allow to characterize the importance of shock/turbulence interactions with a special emphasis placed on the small-scale scalar mixing. Highly under-expanded reactive hydrogen jet simulations underline the specific difficulties associated to ignition and combustion stabilization even in the presence of an external deposit of energy. Finally, the analysis of the rocket engine igniter jet reveals some specific features of self-ignition phenomena in such non-premixed conditions.Cette Thèse de Doctorat est consacrée à l'étude des écoulements cisaillés réactifs supersoniques et plus particulièrement à la dynamique des jets compressibles fortement sous détendus. Ce type d'écoulement est rencontré dans un certain nombre d'applications relatives, par exemple, à l'injection d'hydrogène dans les superstatoréacteurs ou bien à l'allumage de moteurs fusées. Il est aussi représentatif du percement de réservoirs à haute pression. Ce travail s'appuie sur l'emploi d'un outil de simulation numérique haute fidélité: CREAMS (Compressible REActive Multi-species Solver). Ce code de calcul met en oeuvre des schémas numériques d'ordre élevé: schéma d' intégration d'ordre 3 en temps et d'ordre 7 et 8 en espace. Il s'appuie sur une description des termes de transport moléculaire et des termes sources chimiques la plus précise possible (transport détaillé et chimie complexe). Les simulations réalisées dans des conditions inertes permettent de caractériser l'importance des interactions choc/turbulence avec une attention particulière accordée au mélange turbulent à petite échelle. Les simulations réactives de jets fortement sous détendus d' hydrogène montrent les difficultés d'allumage et de stabilisation de la combustion pour ce type de conditions, même en présence d'un apport externe d' énergie. Enfin, l'analyse d'un jet représentatif d'un allumeur de moteur fusée révèle certaines spécificités de l'auto-allumage dans ces conditions non-prémélangées rapides

Highly integrated power electronic converters using active devices embedded in printed-circuit board

International audienceIn this paper, we present a short overview of the power dies interconnects based on PCB technology, then we focus on embedding of power dies in the PCB material. In the second part of the article, we present in details the technology we developed to embed dies in PCB. Results show that the electrical performance of the die remains satisfying after embedding, but that dies with a copper topside metal layer are required for this process

Nutrient limitation can explain a rapid transition to synchrony in an upwelling-driven diatom community

Identifying the mechanisms controlling the temporal dynamics of ecological communities is key to understand their vulnerability to natural and anthropogenic impacts and to identify early warnings of critical transitions. At community level, inter-specific synchrony is an important indicator of ecosystem stability and variation in function. Using wavelet analysis on time-series of abundance of 12 dominant diatom species, sampled monthly (1994-2009) in a coastal upwelling embayment at the northern limit of the Canary Current Upwelling System, we find a sudden onset of synchrony between 1998 and 2002, concomitant with an increase in the amplitude of the upwelling index at different temporal scales. To better understand the underlying mechanism that could generate this sudden onset of synchrony among competitors, we analyzed a general model of competition between two species for two essential nutrients (e.g., nitrogen and silicate). We incorporate environmental variation by varying the concentration of one of the essential nutrients entering the system. Increase in the amplitude of environmental variation always leads to greater synchrony among competitors. This occurs because the system shifts from a state in which species are limited by different nutrients to one where species are often limited by the same nutrient. We show that the transition from asynchronous to synchronous dynamics can occur suddenly as the amplitude of environmental variation increases. While it is not possible to rule out alternative mechanisms, our model demonstrates that sudden changes in the extent of synchronization should be a common feature when species compete for essential nutrients in variable environments.En prensa3,38

Demographic responses to protection from harvesting in a long-lived marine species

Marine protected areas (MPAs) are usually considered to have positive effects on the recovery of over-exploited populations. However, resolving the extent to which MPAs function according to their conservation goals re- quires that essential demographic information such as individual survival and population size are quantified. To this end, we analyzed a 16-year replicated mark-recapture study on European lobster (Homarus gammarus, n = 8793) conducted at several protected and unprotected sites in southern Norway, quantifying the impact of MPAs on local population dynamics by means of a “before-after control-impact” study approach (BACI). Lobster sur- vival and abundance were estimated by applying multi-state and robust design models to the mark-recapture data. These models revealed underlying positive responses to protection. Annual survival rates and population abundances reached higher values in the MPAs, compared to the unprotected sites (abundance range: MPAs = 96–1172, control areas = 92–747). In general, female survival was higher than male survival (range of survival: male = 0.13–0.75, female = 0.37–0.85), while larger males benefited more from protection compared to smaller males (range of increase in survival after protection: big = 100–125%, small = 55–101%). We also detected regional differences in demographic responses to protection, as not all MPAs showed the same changes in abundance over time. Our results show that MPAs can reach conservation goals by increasing the local survival and abundance of lobster, but they also highlight demographic differences between sexes and geographic areas that are worth considering for the management and design of both current and future MPAs.publishedVersio

Thermal Considerations of a Power Converter with Components Embedded in Printed Circuit Boards

International audiencePrinted-Circuit-Board (PCB) technology is attractive for power electronic systems as it offers a low manufacturing cost for mass production. Integration technologies such as device embedding have been developed to take advantage of the inter-layer space in multi-layer PCBs and to increase the performances (Electrical, Thermal). However, the PCB technology offers limited power dissipation due to the low thermal conductivity (≈0.3 W/(m·K)) of its composite substrate. In this paper, we consider PCB embedding for a 3.3 kW AC/DC bidirectional converter. We describe the integration of not only the power dies, but also the gate drive circuits and the power inductor, with a special focus on the thermal management. The manufacturing processes of the boards are presented. Two thermal models based on finite elements (FE) of this converter stage are introduced. The accuracy of these models is validated against experiments. The results show that a simplified FE model offers satisfying accuracy and fast simulation, even considering the relatively complex structure and layout of the PCBs