Effect of Different S AC Based Nanoparticles Types on the Reflow Soldering Process of Miniaturized Component using Discrete Phase Model Simulation

The wetting formation and nanoparticles dispersion on adding nanoparticles to the lead free solder Sn-3.0Ag-0.5Cu (SAC305) is methodically investigated using Discrete Phase Model (DPM) simulation and applied on a 01005 capacitor component. Different types of nanoparticles, namely titanium dioxide (TiO2), nickle oxide (NiO) and Iron (III) oxide (Fe2O3) with varying weight percentages, 0.01wt%, 0.05wt% and 0.15wt% that is doped in SAC305 are used. The study of two-way interactions between multiphase volume of fluid (VOF) and discrete phase model (DPM) shows excellent capability in tracking the dispersed nanoparticles immersed in the wetted molten solder. In this study, real reflow profile temperature setup will be used to mimic the conventional reflow process. Based on the findings, the fillet height managed to achieve the minimum required height set by IPC standards. As the concentration of the nanoparticles doped in the molten solder increases, higher time is required for the wetting process. In general, the doped NiO nanoparticles at 0.05wt% has the lowest wetting time compared to other cases. The study of the instantaneous nanoparticles trajectory tracking was also conducted on a 3D model and 2D cross sectional view to identify the exact movement of the particles. Additionally, it was also observed that the velocity and pressure distribution increases as the weight percentage of the nanoparticles increases

Modelling Fluid-Structure Interaction Problems with Coupled DEM-LBM

When studying the properties and behaviour of particulate systems, a multi-scale approach is an efficient way to describe interactions at different levels or dimensions; this means that phenomena taking place at one scale will inherently impact the properties and behaviour of the same system in a different scale. Numerical representation and simulation of fluid-structure interaction (FSI) systems is of particular interest in the present work. Conventional computational fluid dynamics (CFD) methods involve a top-down approach based on the discretisation of the macroscopic continuum Navier-Stokes equations; cells are typically much larger than individual particles and the hydrodynamic force is calculated for all the solid particles contained in singular a cell. Unlike traditional CFD solvers, the lattice Boltzmann method (LBM) is an alternative approach to simulate fluid flows in complex geometries in a mesoscale level. In LBM the fluid is deemed as a collection of cells, each one containing a particle that represents a density distribution function with a velocity field. The distinct element method (DEM) is in charge of handling the motion of particles and calculating the interparticle contact forces. The two methodologies LBM and DEM were selected among the available approaches to be combined in a single computational code to represent FSI systems. The key task to undertake was the implementation of a coupling code to exchange information between the two solvers LBM and DEM in a correct and efficient manner. The calculation of hydrodynamic forces exerted by the fluid on the particles is the major challenge in coupled FSI simulations. This was addressed by including the momentum exchange method, based on the link bounce-back technique, together with the immersed boundary method to deal with moving particles immersed in a fluid. In addition, in order to better understand the dynamics of FSI systems in a mesoscale level, the present work paid special attention to the accurate representation of individual particles displaying irregular geometries instead of the preferred spherical particles. This goal was achieved by means of X-ray microtomography digitisation of particles, allowing the capture of complex micro-structural features such as particle shape, texture and porosity. In this way a more realistic particle representation was achieved, extending its use to the implementation into computational simulations. The DEM-LBM coupling implementation carried out was tested quantitatively and qualitatively based on theoretical models and experimental data. Different cases were selected to simulate the dynamic process of packing particles, particle fluidisation and segregation, particles sedimentation, fluid permeability calculations and fluid flow through porous media. Results and predictions from simulations for a number of configurations showed good agreement when compared with analytical and experimental data. For instance, the relative error in terminal velocity of a non-spherical particle settling down in a column of water was 4.2%, showing an asymptotic convergence to the reference value. In different tests like the drag on two interacting particles and the flow past a circular cylinder at Re = 100, the corresponding deviations from the references published were 20% and 8.23% respectively. The extended Re range for the latter case followed closely the reference curve for the case of a rough cylinder, indicating the effects of the inherent staircase-like boundary in digital particles. Three dimensional simulations of applications such as fluidisation and sedimentation showed the expected behaviour, not only for spherical particles but also considering complex geometries such as sand grains. A symmetric array of spheres and randomly mixed particles were simulated successfully. Segregation was observed in a case configured with particles with different size and density. Hindered settling was also observed causing the slow settling of the small particles. Incipient fluidisation of spherical and irregular geometries was observed in relatively large computational domains. However, the minimum fluidisation velocity configured at the inlet was commonly 10 times larger than the calculated from the Ergun equation

Modelling Fluid-Structure Interaction Problems with Coupled DEM-LBM

When studying the properties and behaviour of particulate systems, a multi-scale approach is an efficient way to describe interactions at different levels or dimensions; this means that phenomena taking place at one scale will inherently impact the properties and behaviour of the same system in a different scale. Numerical representation and simulation of fluid-structure interaction (FSI) systems is of particular interest in the present work. Conventional computational fluid dynamics (CFD) methods involve a top-down approach based on the discretisation of the macroscopic continuum Navier-Stokes equations; cells are typically much larger than individual particles and the hydrodynamic force is calculated for all the solid particles contained in singular a cell. Unlike traditional CFD solvers, the lattice Boltzmann method (LBM) is an alternative approach to simulate fluid flows in complex geometries in a mesoscale level. In LBM the fluid is deemed as a collection of cells, each one containing a particle that represents a density distribution function with a velocity field. The distinct element method (DEM) is in charge of handling the motion of particles and calculating the interparticle contact forces. The two methodologies LBM and DEM were selected among the available approaches to be combined in a single computational code to represent FSI systems. The key task to undertake was the implementation of a coupling code to exchange information between the two solvers LBM and DEM in a correct and efficient manner. The calculation of hydrodynamic forces exerted by the fluid on the particles is the major challenge in coupled FSI simulations. This was addressed by including the momentum exchange method, based on the link bounce-back technique, together with the immersed boundary method to deal with moving particles immersed in a fluid. In addition, in order to better understand the dynamics of FSI systems in a mesoscale level, the present work paid special attention to the accurate representation of individual particles displaying irregular geometries instead of the preferred spherical particles. This goal was achieved by means of X-ray microtomography digitisation of particles, allowing the capture of complex micro-structural features such as particle shape, texture and porosity. In this way a more realistic particle representation was achieved, extending its use to the implementation into computational simulations. The DEM-LBM coupling implementation carried out was tested quantitatively and qualitatively based on theoretical models and experimental data. Different cases were selected to simulate the dynamic process of packing particles, particle fluidisation and segregation, particles sedimentation, fluid permeability calculations and fluid flow through porous media. Results and predictions from simulations for a number of configurations showed good agreement when compared with analytical and experimental data. For instance, the relative error in terminal velocity of a non-spherical particle settling down in a column of water was 4.2%, showing an asymptotic convergence to the reference value. In different tests like the drag on two interacting particles and the flow past a circular cylinder at Re = 100, the corresponding deviations from the references published were 20% and 8.23% respectively. The extended Re range for the latter case followed closely the reference curve for the case of a rough cylinder, indicating the effects of the inherent staircase-like boundary in digital particles. Three dimensional simulations of applications such as fluidisation and sedimentation showed the expected behaviour, not only for spherical particles but also considering complex geometries such as sand grains. A symmetric array of spheres and randomly mixed particles were simulated successfully. Segregation was observed in a case configured with particles with different size and density. Hindered settling was also observed causing the slow settling of the small particles. Incipient fluidisation of spherical and irregular geometries was observed in relatively large computational domains. However, the minimum fluidisation velocity configured at the inlet was commonly 10 times larger than the calculated from the Ergun equation

AlGaN/GaN sensors for direct monitoring of fluids and bioreactions

AlGaN/GaN based pH-sensors have been characterized and further developed for the in situ monitoring of cell reactions. Generally, good proliferation of different cell lines was observed on AlGaN and GaN surfaces without using any kind of thin films of organic material for improving of the cellular adhesion and biocompatibility. NG108-15 nerve cells were chosen for the investigation of the sensor response on cell activity. In an open setup with contact to normal atmosphere, the monitoring of the spontaneous cell activity (“breathing”) was recorded. By titration in complex electrolytes, it was demonstrated that these sensors are able to monitor complex cell reactions on different neuroinhibitors. Numerical simulations as well as simplified analytical calculations of ion fluxes give strong evidence that the signal in the cell-transistor coupling experiments is primarily generated by the Na+ flux. In conclusion, the AlGaN/GaN-ISFETs show stable operation under physiological conditions, exhibit a very good signal resolution and are suitable for long-time monitoring of cell reactions on different stimuli.In dieser Arbeit wurden AlGaN/GaN-Heterostrukturen, die ein hohes Potenzial für pH-Sensoren aufweisen, charakterisiert und weiterentwickelt für die elektronische Erfassung von Zellreaktionen. Dazu wurden NG108-15 Nervenzellen auf den Sensoroberflächen kultiviert und deren Antwort auf Stimulierung mit verschiedenen Neuroinhibitoren aufgezeichnet. Zunächst wurde ein Messaufbau für das Erfassen extrazellularer Potenzialänderungen entworfen und das bestehende Chipdesign sowie die Herstellungstechnologie weiterentwickelt. Für die Auswahl optimaler Sensoren für die Transistor-Zell-Kopplung wurden sowohl mittels PIMBE und MOCVD gewachsene Heterostrukturen charakterisiert bezüglich ihrer elektronischen Transporteigenschaften und ihres Verhaltens als pH-Sensor. Auf AlGaN- und GaN-Oberflächen konnte eine sehr gute Kultivierung verschiedener Zelllinien erzielt werden ohne die sie sonst übliche Verwendung organischer Zwischenschichten zur Erhöhung von Adhäsion (z.B. Fibroplasten). Der Einfluss verschiedener Technologie- und sensorrelevanter Behandlungsschritte auf die Oberflächeneigenschaften der AlGaN/GaN-Sensoren wurde untersucht und die Medienstabilität bzw. Wechselwirkungen wurden analysiert. In einem offenen Setup mit Gasaustausch zur Umgebung wurde eine spontane Zellaktivität erfasst ("Zellatmung"), die in einem abgeschlossenen Setup aufgrund des reduzierten Gasaustausches nicht auftrat. Weiterhin wurde die Empfindlichkeit des Sensors auf Potenzialänderungen durch Na+ and K+ Ionen und deren Reaktionen mit Neurotoxinen bestätigt. Durch Titration in komplexe Elektrolyte und durch Kultivierung von NG108-15 Nervenzellen auf der Sensoroberfläche wurde demonstriert, dass die Sensoren in der Lage sind, komplexe Zellreaktionen zu erfassen. Berechnungen mit Hilfe von Simulationen und vereinfachten analytischen Beschreibungen für die Ionenflüsse belegten, dass bei der Zell-Transistor-Kopplung das Sensorsignal im Wesentlichen durch die Na+ Flüsse erzeugt wird. Die experimentellen Beobachtungen und die theoretischen Modellierung zeigte dafür eine gute Übereinstimmung. Zusammenfassend wurde in dieser Arbeit gezeigt, dass AlGaN/GaN-ISFETs stabil unter physiologischen Bedingungen arbeiten, sehr gute Signalauflösung ermöglichen und für Langzeitmessungen mit lebenden Zellen geeignet sind

Mechanics study and application of micro-engineered smart surface

Naturally existing functional surfaces with micro-structure arose competing interests due to their potential application in engineering filed such as wetting control, optical control, micro-fluidic, tissue scaffolds, marine engineering, oil field, etc al. A patterned surface with stimuli responsive properties attracts considerable interest for its importance in advanced engineering, partly due to its reversibility, easy design and control, good compatibility and responsive behaviour to external stimuli. In this work, we have investigated various surface instabilities that enable a convenient strategy of micro-engineered structure impart reversible patterned feature to an elastic surface. We focus on the classic bi-layer system contains a stiff layer on a soft substrate that produces parallel harmonic wrinkles at uniaxial compression and ultimately develop into deep creases and fold. By introducing the microscale planar Bravais lattice holes, we guided these instabilities into various patterns to achieve an anisotropic manipulation of single liquid droplet by initialize localized surface morphologies. The Finite Element Analysis provided the fundamental theory on the surface instabilities evolution and development. The finding demonstrates considerable control over the threshold of a surface elastic instability and bi-axial switching of droplet shape that relevant to many novel applications including wearable electronic devices, bio-medical systems, micro-fluidics and optical devices

Development and Packaging of Microsystems Using Foundry Services

Micro-electro-mechanical systems (MEMS) are a new and rapidly growing field of research. Several advances to the MEMS state of the art were achieved through design and characterization of novel devices. Empirical and theoretical model of polysilicon thermal actuators were developed to understand their behavior. The most extensive investigation of the Multi-User MEMS Processes (MUMPs) polysilicon resistivity was also performed. The first published value for the thermal coefficient of resistivity (TCR) of the MUMPs Poly 1 layer was determined as 1.25 x 10(exp -3)/K. The sheet resistance of the MUMPs polysilicon layers was found to be dependent on linewidth due to presence or absence of lateral phosphorus diffusion. The functional integration of MEMS with CMOS was demonstrated through the design of automated positioning and assembly systems, and a new power averaging scheme was devised. Packaging of MEMS using foundry multichip modules (MCMs) was shown to be a feasible approach to physical integration of MEMS with microelectronics. MEMS test die were packaged using Micro Module Systems MCM-D and General Electric High Density Intercounect and Chip-on-Flex MCM foundries. Xenon difluoride (XeF2) was found to be an excellent post-packaging etchant for bulk micromachined MEMS. For surface micromachining, hydrofluoric acid (HF) can be used

Effects of high pressure on the electronic spectra and crystal structure of molecular materials

The fluorescence of solid-state molecular materials is a field of growing research interest, stimulated by technological applications, such as organic light-emitting diodes and optical sensing. Investigation of the relationship between pressure-induced changes in the structure and electronic spectra of such materials offers opportunities for understanding the influence of intermolecular interactions and conformational changes on optical properties. However, there have been few studies that directly correlate the results of high-pressure X-ray crystallography and high-pressure optical spectroscopy. An apparatus for the in situ measurement of UV-visible absorption and fluorescence emission spectra of crystals in a diamond anvil cell (DAC) has been developed. The effects of pressure (up to several GPa) on the structure and spectra of metal-organic frameworks (MOFs), molecular rotors, conjugated aromatic molecules and thermally activated delayed-fluorescence (TADF) materials have been studied. A Luminescent MOF material, Hf-peb, was studied. Hf-peb MOF is a MOF with two-fold interpenetrated linker, 1,4-phenylene-bis(4-ethynylbenzoate) (peb2-). X-ray crystallography reported in this thesis showed that the linker exists in two conformational states at ambient pressure (and room temperature), one in which the central phenyl ring is coplanar with the two terminal phenyl rings, and the second is the newly reported twisted conformer, where the central phenyl ring is perpendicular to the terminal phenyls. The fractional population of the twisted conformer increased with increasing pressure, from 28% at ambient pressure to 100% at 2.1 GPa. Both the absorption spectrum and the emission spectrum shifted to longer wavelength with increasing pressure. It was also found that the observed emission spectra, across the pressure range, can be well-fitted by linear combinations of the 2.1 GPa spectrum, assigned to the twisted conformer, and the ambient pressure spectrum. The fractional population of the twisted conformer at each pressure estimated in this manner was in good agreement with the values determined from the X-ray diffraction data. The close correlation indicates that the contribution of each conformer to the observed emission spectrum is determined by its ground-state population, and hence the two conformers must have very similar fluorescence brightness. A combined high-pressure UV-vis absorption spectroscopy and computational study on Zr-abdc MOF, a MOF containing an azobenzene dicarboxylate (abdc2-) linker has been carried out. It is revealed the effect of pressure on the absorption spectra in penetrating (methanol) and non-penetrating (FC-70) pressure media. Penetration of methanol into the porous MOF framework resulted in a hypsochromic shift that can be attributed to solvent-induced stabilisation of the more polar the ground state. In the non-penetrating FC-70 medium, pressure-induced compression of the unit cell volume caused a decrease in length of the abdc2- linker. DFT calculations predicted a consequent bending of the linker structure with increasing pressure. TDDFT calculations then predicted a decrease in the energy of the transition to the nπ* state, with increased bending. The TDDFT-predicted trend was in good agreement with the experimentally observed spectral shift. The effects of pressure on the fluorescence properties of two related molecular rotors, sym-pentaphenylcyclopentadiene (Ph5C5H) and sym-heptaphenylcycloheptatriene (Ph7C7H), have also been studied. The redshift in UV-vis absorption and emission spectra with increasing pressure on Ph5C5H could be attributed to stronger interphenyl interactions, which are already present at ambient pressure. On the other hand, X-ray crystallography on Ph7C7H demonstrated the influence of specific interphenyl interactions, both intramolecular and intermolecular, on the optical spectra. For Ph7C7H at high pressures, interphenyl interactions that closely resemble effective displaced-stacked benzene dimers can be identified. The observed fluorescence spectra could be interpreted in terms of relaxed excimer emission from these dimer-like species which occur only at high pressure. These observations elucidate the interactions that lead to aggregation-induced emission in molecular rotors of this type. The 1,4-bis(4-carbomethoxyphenylethynyl)benzene (BCPEB) is an example of a linear π-conjugated system, and also a molecular rotor, with three phenyl rings connected by acetylene linkers. The latter chromophore, commonly known as bis(phenylethynyl)benzene (BPEB), is considered to be a model system for one-dimensional molecular wires that have numerous applications in optoelectronics. The photophysical properties of BPEB are known to be strongly influenced by torsional isomerism. The solution phase and low-temperature fluorescence measurements showed very similar photophysical properties of both BPEB and BCPEB. The structure of BCPEB was investigated as a function of pressure, by single-crystal X-ray diffraction in a DAC, using synchrotron radiation. The pressure-induced hypsochromic shift and spectral profile evolution with decreasing pressure in the UV-vis absorption and emission spectrum can be related to decrease in intermolecular stacking interaction and increase in torsional movement, due to less restricted molecular movement in the crystal. Pressure-dependent properties were also studied for the well-known TADF material of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) and its derivative, 4CzIPN-tBu8. Single-crystal X-ray diffraction of 4CzIPN, obtained up to 4.16 GPa, showed a decrease in the intermolecular inter-carbazole distance with increasing pressure. In addition to steady-state UV-vis and fluorescence spectroscopy, time-resolved measurements of delayed fluorescence were conducted as a function of pressure. Both 4CzIPN and 4CzIPN-tBu8 show different response to pressure on the steady-state electronic spectra and its emission kinetics, in which the 4CzIPN-tBu8 experienced change in singlet-triplet energy gap at pressures higher than ~0.8 GPa. The observed pressure-dependence of the delayed fluorescence lifetime can be interpreted in terms of the effect of intermolecular interaction between the carbazole groups on the TADF process in the two systems. In summary, this thesis reports the relation between the crystal structure and the electronic spectra of photo-active materials, using a custom made high-pressure optical spectroscopy measurement system to elucidate various photophysical processes under high-pressure conditions

Fast algorithm for real-time rings reconstruction

The GAP project is dedicated to study the application of GPU in several contexts in which real-time response is important to take decisions. The definition of real-time depends on the application under study, ranging from answer time of μs up to several hours in case of very computing intensive task. During this conference we presented our work in low level triggers [1] [2] and high level triggers [3] in high energy physics experiments, and specific application for nuclear magnetic resonance (NMR) [4] [5] and cone-beam CT [6]. Apart from the study of dedicated solution to decrease the latency due to data transport and preparation, the computing algorithms play an essential role in any GPU application. In this contribution, we show an original algorithm developed for triggers application, to accelerate the ring reconstruction in RICH detector when it is not possible to have seeds for reconstruction from external trackers