Etude de la fiabilité de modules à base de LEDs blanches pour applications automobile

With rapid development of Lighting Emitting Diode (LED) market, LED performancesare now suitable for automotive high beam / low beam lighting applications. Due to the need of UltraHigh Brightness (UHB-LEDs), LEDs are packaged on high thermal conductivity materials to obtainmultichip module (4 chips in series), which deliver up to 1000 lumens at 1A. Currently, several LEDtechnologies are commercially offered for the same performances, and different packaging strategieshave been implemented in terms of chip configuration, bonding, down conversion phosphor layerand mechanical protection to optimize performances. This study addresses a dedicated methodologyfor reliability analysis, applied on two LED chip packaging technologies: On the one hand, a VerticalThin Film (VTF) technology; on the other hand a Thin Film Flip Chip (TFFC). Our methodology is basedon 3 main items: Packaging technology structure, materials analysis and electro-optical and thermal multichipmodels for both technologies to understand and extract the key parameters to monitor duringageing tests. Robustness assessment tests to define operating margins, adjust accelerated life-testingconditions, and identify failures signatures. Reliability study through a 6 000 hours High Temperature Operating Life (HTOL) acceleratedtests, to predict the Mean Time To Failure (MTTF) of these new light source technologiesregarding the automotive mission profile. Linked to failure analysis, convincing failuremechanisms are proposed.Based on these results, parametric variations are compared to failure analysis results topropose failure mechanisms. The HTOL tests reveal that both LED technologies have their specificreliability behavior and failure modes: catastrophic failure and gradual failure. Predictive lifetimeestimations (L70B50) of these multichip modules give a factor 6 between both technologies.Beyond these reliability results, the multichip architecture brings new issues for Solid StateLighting (SSL) sources in automotive, as well as partial failure or unbalanced behavior after stress.These new issues are discussed through the behavior modeling of a 10 LED modules batch for bothfailure modes. Modeling results demonstrate that the predictive lifetime of a LED multichiparchitecture is directly related with the LED technology failure mode.Les composants dédiés et actuellement disponibles pour le marché automobileprésentent une grande diversité technologique tant au niveau puce que stratégie de packaging ouencore architecture module (mono-puce ou multi-puce) pour des performances équivalentes. Cetteétude s’est attachée à développer une méthodologie d’évaluation de la fiabilité de deux filièrestechnologiques particulières de modules de LEDs multi-puce : l’une intègre une technologie verticale(VTF pour Vertical Thin Film) tandis que la seconde est focalisée sur une structure par puce montéeretournée(TFFC pour Thin Film Flip Chip). La méthodologie s’articule autour de trois principaux axes:· La connaissance des structures et le développement de modèles électro-optiques et thermiquesmulti-puce permettant d’extraire les paramètres clés à suivre au travers d’un panel varié detechniques d’analyse physique et non-destructives incluant les aspects électriques, optiques,thermiques….· Une analyse comportementale de robustesse par paliers afin de dégager les margesopérationnelles de fonctionnement ainsi que les modes et les signatures caractéristiques dedéfaillance.· Une étude de fiabilité conduite à partir de différents régimes de contraintes accélérées pourestimer les durées de vie moyennes de ces nouveaux composants en environnement automobileet l’impact au niveau système.Les résultats mettent en évidence une durée de vie très dépendante de la filière technologique(facteur 6 entre les deux filières étudiées). Les analyses de défaillance ont permis d’identifierprécisément les comportements de ces nouvelles sources d’éclairage pour dégager des indicateursprécoces de défaillance. Enfin, des préconisations ont été extraites afin de fiabiliser les futursprojecteurs à sources LEDs de puissance pour les applications en automobile

Curved CMOS sensor: characterization of the first fully functional prototype

Many are the optical designs that generate curved focal planes for which field flattener must be implemented. This generally implies the use of more optical elements and a consequent loss of throughput and performances. With the recent development of curved sensor this can be avoided. This new technology has been gathering more and more attention from a very broad community, as the potential applications are multiple: from low-cost commercial to high impact scientific systems, to mass-market and on board cameras, defense and security, and astronomical community. We describe here the first concave curved CMOS detector developed within a collaboration between CNRS-LAM and CEA-LETI. This fully-functional detector 20Mpix (CMOSIS CMV20000) has been curved down to a radius of R_c =150mm over a size of 24x32mm^2. We present here the methodology adopted for its characterization and describe in detail all the results obtained. We also discuss the main components of noise, such as the readout noise, the fixed pattern noise and the dark current. Finally we provide a comparison with the at version of the same sensor in order to establish the impact of the curving process on the main characteristics of the sensor

Effect of the cooling rate on encapsulant's crystallinity and optical properties, and photovoltaic modules' lifetime

Since the renewable energy thrive, performances and lifetime of photovoltaic (PV) modules have been one of the big international concern. The mechanical bonding between the different components and the materials' choice can significantly improve both performances and lifetime of PV modules. The manufacturing process plays also a significant part in the modules lifetime [G. Oreski, B. Ottersböck, A. Omazic, Degradation Processes and Mechanisms of Encapsulants, in Durability and Reliability of Polymers and Other Materials in Photovoltaic Modules (Elsevier, 2019), pp. 135–152]. This work deals with the controlled cooling part of the manufacturing process. The aim is to characterize its influence on an encapsulant properties, and its influences on modules degradation. This work is a part of improving both performances and lifetime of PV modules. First, the work focuses on describing the real temperature seen by a thermoplastic polyolefin encapsulant during the lamination process. A multi-chamber R&D laminator is used and studied in order to better know the industrial equipment. Results show that the cooling process reduces the time to cool down by a factor of ∼5 compared to natural air convection. Secondly, the material's micro-structure is analysed by Differential Scanning Calorimetry (DSC). The impact of the process is quantified. It does have an influence on the encapsulant crystallites' size distribution without modifying the total crystallinity. Thirdly, the impact of the cooling process on optical properties is investigated. Using spectrophotometry and haze-metry optical characterization, coupled with a known light spectrum, the light intensity coming out from the material is analysed. Results show that the cooling process does not have any influence on transmittance nor reflectance. However, a 34% reduction in the haze factor is recorded when using the industrial laminator cooling process. Fourthly, mechanical bond strength between glass and encapsulant is characterized over ageing. Normalized 10 mm width strips are used to estimate the bond strength. It demonstrates that applying pressure during cooling does not influence the bond strength between glass and encapsulant after 1000 h of damp heat ageing. Finally, impact of the cooling process over ageing on PV modules is discussed. Two accelerating ageing methods, 300 Thermal Cycles and 1000 h damp heat, are used to speed up ageing processes. The electrical components of the PV modules are analysed and used to assess the modules' degradation. Modules manufactured with the cooling process are more sensitive to damp heat after 500 h than modules cooled by natural convection. No significant differences were found in thermal cycling ageing

Curved sensors: experimental performance of CMOS prototypes and wide field related imagers

The emergence of curved sensors technologies opens a new way to design compact high-performance optical systems. Recent progress on the French activity on curved sensors are presented in terms of optical performance and experimental results. The existing prototypes are demonstrated at TRL4, for VIS and SWIR domains. We present the roadmap jointly developed by CEA and CNRS to reach a higher TRL either on the performance of the devices or on the mass production processes. We present the results obtained on two demonstrators

Curved CMOS sensor: characterization of the first fully functional prototype

Many are the optical designs that generate curved focal planes for which field flattener must be implemented. This generally implies the use of more optical elements and a consequent loss of throughput and performances. With the recent development of curved sensor this can be avoided. This new technology has been gathering more and more attention from a very broad community, as the potential applications are multiple: from low-cost commercial to high impact scientific systems, to mass-market and on board cameras, defense and security, and astronomical community. We describe here the first concave curved CMOS detector developed within a collaboration between CNRS-LAM and CEA-LETI. This fully-functional detector 20Mpix (CMOSIS CMV20000) has been curved down to a radius of R_c =150mm over a size of 24x32mm^2. We present here the methodology adopted for its characterization and describe in detail all the results obtained. We also discuss the main components of noise, such as the readout noise, the fixed pattern noise and the dark current. Finally we provide a comparison with the at version of the same sensor in order to establish the impact of the curving process on the main characteristics of the sensor

Reliability investigation of high power white LEDs multichip modules for automotive applications

Les composants dédiés et actuellement disponibles pour le marché automobileprésentent une grande diversité technologique tant au niveau puce que stratégie de packaging ouencore architecture module (mono-puce ou multi-puce) pour des performances équivalentes. Cetteétude s’est attachée à développer une méthodologie d’évaluation de la fiabilité de deux filièrestechnologiques particulières de modules de LEDs multi-puce : l’une intègre une technologie verticale(VTF pour Vertical Thin Film) tandis que la seconde est focalisée sur une structure par puce montéeretournée(TFFC pour Thin Film Flip Chip). La méthodologie s’articule autour de trois principaux axes:· La connaissance des structures et le développement de modèles électro-optiques et thermiquesmulti-puce permettant d’extraire les paramètres clés à suivre au travers d’un panel varié detechniques d’analyse physique et non-destructives incluant les aspects électriques, optiques,thermiques….· Une analyse comportementale de robustesse par paliers afin de dégager les margesopérationnelles de fonctionnement ainsi que les modes et les signatures caractéristiques dedéfaillance.· Une étude de fiabilité conduite à partir de différents régimes de contraintes accélérées pourestimer les durées de vie moyennes de ces nouveaux composants en environnement automobileet l’impact au niveau système.Les résultats mettent en évidence une durée de vie très dépendante de la filière technologique(facteur 6 entre les deux filières étudiées). Les analyses de défaillance ont permis d’identifierprécisément les comportements de ces nouvelles sources d’éclairage pour dégager des indicateursprécoces de défaillance. Enfin, des préconisations ont été extraites afin de fiabiliser les futursprojecteurs à sources LEDs de puissance pour les applications en automobile.With rapid development of Lighting Emitting Diode (LED) market, LED performancesare now suitable for automotive high beam / low beam lighting applications. Due to the need of UltraHigh Brightness (UHB-LEDs), LEDs are packaged on high thermal conductivity materials to obtainmultichip module (4 chips in series), which deliver up to 1000 lumens at 1A. Currently, several LEDtechnologies are commercially offered for the same performances, and different packaging strategieshave been implemented in terms of chip configuration, bonding, down conversion phosphor layerand mechanical protection to optimize performances. This study addresses a dedicated methodologyfor reliability analysis, applied on two LED chip packaging technologies: On the one hand, a VerticalThin Film (VTF) technology; on the other hand a Thin Film Flip Chip (TFFC). Our methodology is basedon 3 main items: Packaging technology structure, materials analysis and electro-optical and thermal multichipmodels for both technologies to understand and extract the key parameters to monitor duringageing tests. Robustness assessment tests to define operating margins, adjust accelerated life-testingconditions, and identify failures signatures. Reliability study through a 6 000 hours High Temperature Operating Life (HTOL) acceleratedtests, to predict the Mean Time To Failure (MTTF) of these new light source technologiesregarding the automotive mission profile. Linked to failure analysis, convincing failuremechanisms are proposed.Based on these results, parametric variations are compared to failure analysis results topropose failure mechanisms. The HTOL tests reveal that both LED technologies have their specificreliability behavior and failure modes: catastrophic failure and gradual failure. Predictive lifetimeestimations (L70B50) of these multichip modules give a factor 6 between both technologies.Beyond these reliability results, the multichip architecture brings new issues for Solid StateLighting (SSL) sources in automotive, as well as partial failure or unbalanced behavior after stress.These new issues are discussed through the behavior modeling of a 10 LED modules batch for bothfailure modes. Modeling results demonstrate that the predictive lifetime of a LED multichiparchitecture is directly related with the LED technology failure mode

Reliability investigation of high power white LEDs multichip modules for automotive applications

Les composants dédiés et actuellement disponibles pour le marché automobileprésentent une grande diversité technologique tant au niveau puce que stratégie de packaging ouencore architecture module (mono-puce ou multi-puce) pour des performances équivalentes. Cetteétude s’est attachée à développer une méthodologie d’évaluation de la fiabilité de deux filièrestechnologiques particulières de modules de LEDs multi-puce : l’une intègre une technologie verticale(VTF pour Vertical Thin Film) tandis que la seconde est focalisée sur une structure par puce montéeretournée(TFFC pour Thin Film Flip Chip). La méthodologie s’articule autour de trois principaux axes:· La connaissance des structures et le développement de modèles électro-optiques et thermiquesmulti-puce permettant d’extraire les paramètres clés à suivre au travers d’un panel varié detechniques d’analyse physique et non-destructives incluant les aspects électriques, optiques,thermiques….· Une analyse comportementale de robustesse par paliers afin de dégager les margesopérationnelles de fonctionnement ainsi que les modes et les signatures caractéristiques dedéfaillance.· Une étude de fiabilité conduite à partir de différents régimes de contraintes accélérées pourestimer les durées de vie moyennes de ces nouveaux composants en environnement automobileet l’impact au niveau système.Les résultats mettent en évidence une durée de vie très dépendante de la filière technologique(facteur 6 entre les deux filières étudiées). Les analyses de défaillance ont permis d’identifierprécisément les comportements de ces nouvelles sources d’éclairage pour dégager des indicateursprécoces de défaillance. Enfin, des préconisations ont été extraites afin de fiabiliser les futursprojecteurs à sources LEDs de puissance pour les applications en automobile.With rapid development of Lighting Emitting Diode (LED) market, LED performancesare now suitable for automotive high beam / low beam lighting applications. Due to the need of UltraHigh Brightness (UHB-LEDs), LEDs are packaged on high thermal conductivity materials to obtainmultichip module (4 chips in series), which deliver up to 1000 lumens at 1A. Currently, several LEDtechnologies are commercially offered for the same performances, and different packaging strategieshave been implemented in terms of chip configuration, bonding, down conversion phosphor layerand mechanical protection to optimize performances. This study addresses a dedicated methodologyfor reliability analysis, applied on two LED chip packaging technologies: On the one hand, a VerticalThin Film (VTF) technology; on the other hand a Thin Film Flip Chip (TFFC). Our methodology is basedon 3 main items: Packaging technology structure, materials analysis and electro-optical and thermal multichipmodels for both technologies to understand and extract the key parameters to monitor duringageing tests. Robustness assessment tests to define operating margins, adjust accelerated life-testingconditions, and identify failures signatures. Reliability study through a 6 000 hours High Temperature Operating Life (HTOL) acceleratedtests, to predict the Mean Time To Failure (MTTF) of these new light source technologiesregarding the automotive mission profile. Linked to failure analysis, convincing failuremechanisms are proposed.Based on these results, parametric variations are compared to failure analysis results topropose failure mechanisms. The HTOL tests reveal that both LED technologies have their specificreliability behavior and failure modes: catastrophic failure and gradual failure. Predictive lifetimeestimations (L70B50) of these multichip modules give a factor 6 between both technologies.Beyond these reliability results, the multichip architecture brings new issues for Solid StateLighting (SSL) sources in automotive, as well as partial failure or unbalanced behavior after stress.These new issues are discussed through the behavior modeling of a 10 LED modules batch for bothfailure modes. Modeling results demonstrate that the predictive lifetime of a LED multichiparchitecture is directly related with the LED technology failure mode

Integrated photovoltaics potential for passenger car : a focus on the sensitivity to electrical architecture losses

International audienceTo reduce greenhouse emissions and improve primary energy saving, vehicle integrated pho-tovoltaics have an ongoing interest. Therefore, we developed a simulation tool of the mileage covered by VIPV. This tool considers various use profiles, different characteristics of the vehicles and of the PV system and all the losses that may decrease energy yield. Focusing on passenger car, simulations show that many parameters influence the outputs of the model, mainly: geo-graphic location, shading losses, thresholds due to extra-consumption to charge the vehicle bat-tery from PV and frequency of recharge with the grid. With projections of the technology in 2030, with 30 % shading losses, VIPV cover up to 1444 km annual mileage. This represents up to 12 % of the total distance. For the best month, it can get up to 14 km/day. For average Europe and worst-case conditions, the VIPV cover only 293 km annual mileage. Life Cycle Assessment (LCA) of solarized passenger car shows negative balance for low-carbon electricity mix. The carbon footprint is up to 489 kg CO2-equivalent avoided emissions on 13 years lifespan in fa-vorable conditions. Beyond km and LCA focus, VIPV could provide useful functions in non-interconnected zones and for resilience in case of climatic catastrophes

Numerical simulation and experimental characterization of c-Si cells mechanical limits in spherical curvature shape

International audienceTo ensure the mechanical strength of the cells in shaped photovoltaic modules, it is important to know their double bending radius limit, as well as their mechanical breaking limits.This study focuses on the mechanical characterization of Si cells under double curvature load. It aims at determining the mechanical limits of silicon under double curvature, as well as the minimum radii of curvature reachable without breaking the cell.A numerical model representing the curvature of a cell in a double-curvature wedge has been implemented. It aims at predicting, for a given cell thickness, the acceptable double radius limit. This numerical model is validated with experimental tests to quantify the mechanical limits of silicon under double curvature. Experimental tests were performed on different types of cells -wafers, cells with or without interconnections- to evaluate the impact of each process step on the mechanical strength of cells under this double curvature load