L’intégration 3D est la suite de l’évolution de la microélectronique vers la miniaturisation à haute performance. Les pièces à pas fins permettent la conception de produits dits 3D (ou 2.5D) qui maximisent l’espace pour les données et accélèrent les transferts, tout en minimisant l’espace physique et l’énergie requise par le dispositif. Le procédé de fabrication le plus largement utilisé est celui de puces à protubérances inversées (ou flip-chip) et il implique l’alignement de la puce sur son substrat à l’aide d’une tête automatisée. Le procédé de puces inversées est particulier du fait que les puces comportent une matrice d’interconnexions couvrant la majorité de leur surface, en comparaison au procédé de fils soudés (wire bond) où les connexions sont en périphérie des puces. Elles doivent donc être renversées pour être placées pour la soudure. Le rôle primaire du flux est de s’assurer que les boules de soudure sont bien désoxydées avant l’étape de brasure afin de garantir la qualité et la conductivité de cette dernière. L’objectif de la recherche était de trouver un flux trempable qui satisfasse aux exigences des produits à pas fins soudés par thermocompression. Pour ce faire, les flux candidats ont été caractérisés tant sur le volet physico-chimique que sur le volet des phénomènes visco-inertiels en trempage. Cette caractérisation a permis de prédire le comportement des flux en trempage pour leur mouillabilité et la quantité de flux retirée, ainsi que la température où survenait un changement structurel important dans le flux, indiquant le moment où la réaction chimique de désoxydation culminait. La partie sous-jacente de l’objectif du projet devait aussi s’assurer de la compatibilité du nouveau flux avec les étapes d’encapsulation suivantes. Dans un tel procédé, cela signifiait la propreté après lavage, la compatibilité avec l’agent de remplissage époxy qui protège les pièces, l’ajout du capot métallique et les tests de fiabilité. Des trois candidats de flux testés, un seul a été choisi pour valider la méthode de trempage développée au travers des tests de fiabilités. Ces tests n’ont démontré aucune défaillance électrique et une fiche parfaite pour le test accéléré en humidité et température sous tension (HAST). Le test en cyclage thermique a fait apparaître des défauts mineurs sur 12% des pièces du flux choisi et d’un flux témoin.

Modification of land use/land cover in South Florida has posed a major challenge in the region’s eco-hydrology by shifting the surface-atmosphere water and energy balance. Although drainage and development in South Florida took place extensively between the mid- and late- 20th century, converting half of the original Everglades into agricultural and urban areas, urban expansion still accounts for a dominant mode of surface cover change in South Florida. Changes in surface cover directly affect the radiative, thermophysical and aerodynamic parameters which determine the absorption and partitioning of radiation into different components at the Earth surface. The alteration is responsible for changing the thermal structure of the surface and surface layer atmosphere, eventually modifying surface-induced convection. This dissertation is aimed at analyzing the extent and pattern of land cover change in South Florida and delineating the associated development of urban heat island (UHI), energy flux alteration, and convective rainfall modification using observed data, remotely sensed estimates, and modeled results. Urban land covers in South Florida are found to have increased by 10% from 1974 to 2011. Higher Landsat-derived land surface temperatures (LST) are observed in urban areas (LSTu-r =2.8°C) with satisfactory validation statistics for eastern stations (Nash-Sutcliffe coefficient =0.70 and R2 =0.79). Time series trends, significantly negative for diurnal temperature range (DTR= -1°C, p=0.005) and positive for lifting condensation level (LCL > 20m) reveal temporal and conspicuous urban-rural differences in nocturnal temperature (ΔTu-r = 4°C) shows spatial signatures of UHI. Spatially higher (urban: 3, forest: 0.14) and temporally increasing (urban: 1.67 to 3) Bowen’s ratios, and sensible heat fluxes exceeding net radiation in medium and high-intensity developed areas in 2010 reflect the effect of urbanization on surface energy balance. Radar reflectivity-derived surface-induced convective rainfall reveals significantly positive mean differences (thunderstorm cell density: 6/1000 km2and rain rate: 0.24 mm/hr/summer, p < 0.005) between urban and entire South Florida indicating convective enhancement by urban covers. The research fulfils its two-fold purposes: advancing the understanding of post-development hydrometeorology in South Florida and investigating the spatial and temporal impacts of land cover change on the microclimate of a subtropical city.

Methane is the second most important long-lived greenhouse gas. However, it is typically emitted to the atmosphere by spatially and temporally heterogeneous sources, meaning that local measurements cannot easily be extrapolated to represent global scales. As a consequence, its global sources and sinks are generally poorly quantified. This thesis focuses on the use of airborne observations to improve flux estimates of methane at regional scales. A commercially available cavity-enhanced absorption spectrometer has been modified here for airborne measurements of methane and carbon dioxide. An algorithm employing the system's simultaneous water vapour measurement has been derived, using laboratory experiments, to determine dry air mole fractions without the need for sample drying. The system was found to be relatively independent of the aircraft's motion and its measurements were found to be accurate to within 1.28 ppb (1 standard deviation repeatability at 1Hz of 2.48 ppb) for methane and 0.17 ppm (1 standard deviation repeatability at 1Hz of 0.66 ppm) for carbon dioxide. This new measurement capability has been deployed during three international field campaigns, data from which is used in this thesis. The composition of boreal biomass burning was measured in eastern Canada. Methane emission factors showed a high degree of variability (range 1.8 $\pm$\ 0.2 to 8.5 $\pm$\ 0.9 g (kg dry matter)$^{-1}$), accentuating the challenges with using a purely bottom-up approach to determine total methane emissions and that top-down constraints are needed. Two case studies have shown that an aircraft mass balance approach can be a valuable tool for deriving regional scale top-down flux estimates, when a suitable sampling strategy can be employed under appropriate atmospheric conditions. First, this technique was applied to the European Arctic wetlands; and second, its suitability to derive emissions from a megacity was investigated using London, UK as a test case. On both occasions, the derived fluxes were found to be in good agreement with coincident surface observations within the aircraft's sampling domain. In the case of the Arctic wetlands the excellent agreement with seasonally averaged surface observations allowed this information to be used for the evaluation of land surface models. Two commonly used models, the Joint UK Land Environment Simulator and Hybrid8 were found to underestimate the methane emission flux for this region by an order of magnitude, highlighting the large uncertainties present in future methane emission scenarios at regional scales under a changing climate.

Carbon dioxide (CO2) is the leading contributor to global warming and climate change. The increases in fossil fuel emissions, deforestation, and changes of land use have resulted in increased CO2 levels in the atmosphere from 280 ppm in 1765 to 390 ppm in 2010. Carbon mitigation policies for managing the biosphere to increase net CO2 uptake are dependent upon accurate knowledge of the biosphere fluxes. However, Northern Hemisphere bottom-up and top-down biosphere flux estimates show significant discrepancies, especially in North America. In this study, we design an analysis framework that integrates observations with models with the goal of reducing some of the key uncertainties in estimating CO2 fluxes and concentrations in the Midwest, USA. In this research, the biosphere model, WRF-VPRM model (Ahmadov et al., 2007) is used to simulate CO2 biosphere fluxes and atmospheric CO2 concentrations in the Midwest, USA at high spatial resolution. Reducing uncertainties in the predictions is accomplished by improving the model transport configurations (i.e. the WRF planetary boundary layer (PBL) scheme, the number of vertical layers and the horizontal resolution), utilizing a more detailed land cover map, optimizing VPRM photosynthesis and respiratory parameters for major crops (i.e. corn and soybean) against flux towers, and integrating CO2 tall tower observations and model through a top-down data assimilation method to improve the VPRM model parameters and in turn improving the flux and concentration estimates. The WRF-VPRM model configuration with the YonSei University PBL scheme produced the most accurate CO2 concentration predictions at the WBI tower at all three tower levels with the maximum error reduction of 17.1%. Increasing the number of vertical layers improved the CO2 estimates during nighttime and early morning, especially at 30 m, where the error was reduced by a maximum of ~ 20%. The differences in the monthly average net fluxes over the State of Iowa between the high resolution WRF-VPRM model and coarse resolution Carbon Tracker were significant, 71%, 18%, and 62% in June, July, and August, respectively. The fluxes calculated by the VPRM model are primarily dependent on 4 model parameters, half saturation value of photosynthesis (PAR0), light use efficiency (ë), and respiration parameters (á and â). These parameters are specific to vegetation types, regions, and time period. The default settings do not distinguish between corn and soybean, which are major crops in the Midwest and have significant different photosynthesis rates. When corn and soybean are explicitly included in the model, the flux estimate changed by 31.3% at 12 pm and 24.5% at 12 am. Two different methods were used to optimize for the VPRM model parameters which are optimization against Ameriflux NEE and using a top-down variational method. The simulation using optimized parameters from the variational method reduced the error during the daytime from 11.6 ppm to 7.8 ppm. The average fluxes optimized using the variational method changed by 17% and 38.6% at 12 pm and 12 am, respectively. The more accurate VPRM parameters lead to the more accurate biosphere fluxes, which will ease the evaluation of benefits of different carbon mitigation policies.

Water is undoubtedly a key life element. Its importance is very clear from a religious perspective: “We made from water every living thing. Will they not then believe?” Surah Al-Anbiya verse 30 Also as highlighted in the United Nations resolution 64/292 which recognizes water as a basic necessity for human survival. As the world water demand grows, so does the need to use renewable water sources most available in the form of saline ocean water. Desalination of this water for potable use relies mainly on thermal and membrane-based technologies, mainly multi-stage flash (MSF), multi-effect distillation (MED), and seawater reverse osmosis (SWRO). However, these mature technologies are recognized for their high energy and chemicals use. To cope with these challenges, development of novel desalination processes is required to assure more sustainable water supply for the future. Membrane distillation (MD) has emerged as a process which combines advantages of both membrane and thermal technologies. It has a potential of being cost effective by utilizing renewable or waste heat energies as a driving force. Air gap membrane distillation (AGMD) is one of the four main MD configurations. AGMD’s main feature is the presence of an air gap which is enclosed between the membrane behind which flows the hot feed and condensation surface behind which flows a coolant. While improving the heat transfer across the membrane, the air gap negatively affects mass transfer resistance thereby reducing vapor flux and increasing process footprint. This dissertation investigates the effect of condensation plate surface modifications on AGMD process efficiency. The modifications are made by utilizing three different approaches including alterations of the surface shape and surface coating (to modify its contact angle) and by varying module inclination angle. A numerical simulation is carried out to determine the key factors which facilitate AGMD vapor flux increase. The second part of this thesis focuses on developing a promising novel approach utilizing Peltier’s process as a heat source to operate the MD process with less energy requirement. The morphological modifications of a plate surface positively affected vapor flux because of the air gap reduction. The highest vapor fluxes were observed when condensation plate had hydrophilic coatings. Based on the observed results, a thin film-wise condensation was suggested as a primary condensation mechanism. The formed film reduced the air gap thickness and this effect was more prominent at 45° when condensation plate was positioned over the membrane surface. A 2-dimensional mathematical model was developed and the model results agreed with the experimental data. Finally, the thermocouple-based MD concept was introduced and experimentally validated.

Presented here are the results from the steady state flow boiling of R245FA in a laboratory scale horizontal stainless-steel test tube with an inner diameter of 8.5 mm and a length of 900 mm at a saturation temperature of 35 °C and 40 °C. Experiments were conducted at mass fluxes ranging between 200 and 300 kg/m²s at inlet vapour qualities from 0.2 to 0.7 under uniform, and non-uniform imposed heat flux cases that are expected to exist in horizontal parabolic trough solar collectors. Nine (9) different heat flux distributions were investigated. Local and average heat transfer coefficients (HTC’s) were determined based on wall temperature measurements taken along the length and around the circumference of the test section. Through the choice of the fluid being linked to the possible usage of DSG technology in organic Rankine cycles, the qualitative trends and observed performance variations can be used to predict the same for a working fluid such as water. It was found that the non-uniformity of the heat flux greatly alters the HTC’s of the fluid undergoing boiling but has no effect on the pressure drop characteristics of the fluid undergoing boiling. Heating only on the sides of the tube yielded HTC’s that were 46 % lower than achieved under uniform heating. Heating only from the top proved to be more effective in heat transmission to the fluid than heating only from the bottom (as is the case on PTC solar fields), by only a slight margin, and both these cases yielded HTC’s that were 30 % lower than the uniform heating case. Applying a bell curve heat flux distribution over the tube walls yielded overall HTC’s that differed from the uniform case by a maximum of 5 %, even as the peak heat flux position changes around the circumference of the tube. A further study may be done to quantify the degree to which the non-uniformity of the heat flux influences the local HTC’s, and to develop correlations that may aid in predicting these cases. An integration with flow pattern mapping may also be done to solidify the understanding of the phenomenon governing these observations. / Dissertation (MEng)--University of Pretoria, 2021. / Department for International Development (DFID) through Royal Society-DFID Africa Capacity Building Initiative. / The UK Engineering and Physical Sciences Research Council (EPSRC) [grant numbers EP/T03338X/I and EP/P004709/1]. / Russian Government "Megagrant" project 075-15-2019-1888. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

This thesis deals with possibilities of increasing the yield of BGA repair process. First there is mentioned basic problematics and its notions, problems and possibilities. Next it deals with technological aspects of repairing of devices in BGA covers. Also there is mentioned basic problematics of evaluating of yield. There is stated current state of solving the problem and also there is suggested new design of application which would be more optimal for evaluation of the yield of process. This thesis contains results of practical testing of methods of application of flux affecting final quality of solder joints as well as kind of flux which was used. At the end

Most heat transfer tubes are designed for either fully uniform wall temperature or fully uniform wall heat flux boundary conditions under forced convection. Several applications, including but not limited to the solar collectors of renewable energy systems, do however operate with non-uniform boundary conditions. Limited research has been conducted on non-uniform wall heat flux heat transfer coefficients in circular tubes, especially for mixed convection conditions. Such works are normally numerical in nature and little experimental work is available. In this experimental investigation the effects of the circumferential heat flux distribution and heat flux intensity on the single phase (liquid) internal heat transfer coefficient were considered for a horizontal circular tube. Focus was placed on the laminar flow regime of water within a stainless steel tube with an inner diameter of 27.8 mm and a length to diameter ratio of 72. Different outer wall heat flux conditions, including fully uniform and partially uniform heat fluxes were studied for Reynolds numbers ranging from 650 to 2 600 and a Prandtl number range of 4 to 7. The heat flux conditions included 360˚ (uniform) heating, lower 180˚ heating, upper 180˚ heating, 180˚ left and right hemispherical heating, lower 90˚ heating, upper 90˚ heating and slanted 180˚ heating. Depending on the angle span of the heating, local heat fluxes of 6 631 W/m2 , 4 421 W/m2 , 3 316 W/m2 , 2 210 W/m2 and 1 658 W/m2 were applied. Results indicate that the local and average steady state Nusselt numbers are greatly influenced by the applied heat flux position and intensity. Highest average heat transfer coefficients were achieved for case where the applied heat flux was positioned on the lower half (in terms of gravity) of the tubes circumference, while the lowest heat transfer coefficients were achieved when the heating was applied to the upper half of the tube. Variations in the heat transfer coefficient were found to be due to the secondary buoyancy induced flow effect. The relative thermal performance of the different heating scenarios where characterised and described by means of newly developed heat transfer coefficient correlations for fully uniform heating, lower 180° heating, and upper 180° heating. / Dissertation (MEng)--University of Pretoria, 2018. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Salinity is one of the fundamental ocean state variables. Variations of ocean salinity can be used to infer changes in the global water cycle and air-sea freshwater exchange. Many institutions have developed gridded Argo products of global coverage. However, the existing gridded salinity products have not yet been dedicatedly intercompare and assessed. In this study, the mean state, annual and interannual variabilities, and decadal changes of ocean salinity from five Argo-based gridded salinity products, available from UK Met Office, JAMSTEC, Scripps Institution of Oceanography, China Second Institute of Oceanography, and International Pacific Research Center, are examined and compared for their overlapping period of 2005-2015 within two depth intervals (0-700 m and 700-2000 m), as well as the sea surface. Though some global and regional features are relatively reproducible, obvious discrepancies are found particularly for the deeper layer. These discrepancies are not apparent on the 11-year climatological mean or the trend patterns, but are readily evident on temporal variations. For instance, the potentially undersampled current systems in the North Atlantic and Southern Ocean are one of the main reasons for the observed discrepancies. The gridded products from Scripps, JAMSTEC and Met Office show large deviation from the ensemble mean, particularly in regions like the Atlantic Ocean and the tropical Pacific. Large disagreements are found in the first and final years, which can lead to different estimates on decadal trends. This study can serve as a useful reference on how to utilize and improve the existing gridded salinity products.

Thesis advisor: Gail C. Kineke / An observational study was conducted from 2013 to 2016 to investigate suspended-sediment transport processes in the stratified Connecticut River estuary. Time-series measurements of velocity and suspended-sediment concentration from the upper estuary were analyzed to determine the relative importance of different processes driving sediment flux under highly-variable river discharge. Results indicate that under high discharge the salt intrusion is forced towards the mouth causing large seaward sediment fluxes throughout the water column. Seaward fluxes are dominated by mean advection, with some contribution due to tidal pumping. Under low discharge the salt intrusion extends to the upper estuary, advancing as a bottom salinity front during each flood tide. Stratification and strong velocity shear during the ebb tide cause the upper and lower water column to become dynamically decoupled. Sediment flux near the bed is landward throughout the tidal cycle despite the net seaward depth-integrated flux, and is almost fully attributed to the mean estuarine circulation. River discharge is the primary factor affecting the magnitude and direction of sediment flux because of its high variability and direct connection to the salt-wedge dynamics. A generalized three-phase conceptual model describes suspended-sediment transport in shallow, stratified estuaries with low trapping efficiencies. First, fine sediment bypasses the estuary during high river flows and exports to the coastal ocean where a portion of this sediment is temporarily deposited outside the mouth. Second, during low discharge offshore mud deposits are reworked by wave- and tidally-driven currents and some sediment is advected back into the estuary with the advancing salt intrusion that transports sediment landward. Third, spatial salinity gradients facilitate sediment transport from the main channel to channel margins, marshes and off-river coves where it is retained and deposited long-term, as demonstrated in prior studies. This re-introduction and trapping of recycled sediment under low-discharge conditions can have important implications for pollutant transport, shoaling of navigation channels and harbors, and salt marsh accretion in the face of rising sea levels. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.