212 research outputs found

    Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

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    This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

    Evaluation and Modeling of Electrochemical Migration on Printed Circuit Boards

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    Electrochemical migration (ECM) is the growth of conductive metal filaments on a printed circuit board (PCB) through an electrolyte solution under a DC voltage bias. ECM can cause a reduction in surface insulation resistance (SIR) between adjacent conductors and lead to intermittent or catastrophic circuit failures. To evaluate the current leakage and electrochemical migration behavior on printed circuit boards, IPC B-24 comb structures were exposed to 65°C and 88% relative humidity conditions under direct-current (DC) bias for over 1000 hours to determine the effects of some key factors to ECM. The key factors include: solder alloy (eutectic tin-lead and lead-free), board finish (organic solderability preservative versus lead-free hot air solder leveling), spacing (25 mil versus 12.5 mil), and voltage (40 V versus 5 V bias), solder mask (using and not using), flux solids content. In-situ measurements of SIR, energy-dispersive spectroscopy after testing and optical inspection before and after test were used. The relationships between the electrical behavior and electrochemical behavior of solder alloys were established. The long term electrochemical behaviors of tin-lead and lead-free solders were obtained. The morphology and distribution of migrated species, including Sn, Pb, Cu and Ag were investigated. Compared with solder alloy, board finishes played a secondary role in affecting SIR due to their complexation with or dissolution into the solder. The competing effect between electric field and spacing was also investigated. Solder mask was found to stabilize SIR and reduce the chances for ECM to occur due to its "walling effect". Compared to low solids flux, medium solids flux increased the characteristic lives of PCBs due to their encapsulation effects. The prolonged SIR decline of Sn-3.0Ag-0.5Cu soldered boards was simulated by three-dimensional progressive and instantaneous nucleation models, whose predictions were compared with experimental data. The kinetics of the electrochemical migration process between copper traces in deionized water was investigated using electrochemical impedance spectroscopy and cyclic voltammetry. The rate limiting step was identified before and during dendritic growth. The time to generate an embryonic dendrite was measured experimentally on copper traces and modeled using Nernst Planck equations, which matched experimental results well

    Effects of Air Pollution, Temperature and Moisture Content on Copper and Silver Corrosions and the Reliability of Data Center Equipment

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    The effects of moisture content, temperature, and pollutant mixture on atmospheric corrosion of copper and silver were investigated by exposing test specimens to different environmental conditions, followed by surface characterization using the coulometric reduction, Scanning Electron Microscopy, and Energy Dispersive Spectrometry (SEM/EDS). Printed circuit board test cards (PCBs) with bare copper were also used to investigate the effects of voltage bias on the PCBs on the corrosion rate. The test specimens were exposed to mixed flowing gases (MFG) environment with eight different combinations of the following five pollutants at the fixed concentration levels: 60 ppb O3, 80 ppb NO2, 40 ppb SO2, 2 ppb Cl2, and 10 ppb H2S. Temperature and relative humidity (RH) were varied from a reference condition (21°C and 50% RH which is within the current ASHRAE-recommended thermal envelope) to a higher value (28°C, 70% RH, or 80% RH) to increase the moisture content of the test environment. Test results revealed the dominating effect of Cl2 on copper corrosion and that of H2S on silver corrosion. Increasing the moisture content at 21°C caused more severe corrosion of copper when Cl2 was present, but not for silver. When the temperature was increased from 21°C to 28°C at 50% RH, it reduced the corrosion of copper, but not for silver. Voltage-biased PCBs had less effect on corrosion than PCBs without the voltage bias. A mechanistic model based on the multi-ion transport and chemical reactions was also proposed to predict the corrosion of copper due to Cl2-containing pollutant mixtures. The model\u27s prediction of the effects of temperature and RH agreed well with the experimental results. These findings provided the basis for possible expansion of the ASHRAE-recommended thermal envelope for data centers when Cl2 and H2S are not present and limiting the thermal envelope when Cl2 or H2S is present. They also improved the understanding of the corrosion mechanisms for the copper when Cl2 is present in the data center environment

    Effects Of Air Pollution, Temperature And Moisture Content On Copper And Silver Corrosions And The Reliability Of Data Center Equipment

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    The effects of moisture content, temperature, and pollutant mixture on atmospheric corrosion of copper and silver were investigated by exposing test specimens to different environmental conditions, followed by surface characterization using the coulometric reduction, Scanning Electron Microscopy, and Energy Dispersive Spectrometry (SEM/EDS). Printed circuit board test cards (PCBs) with bare copper were also used to investigate the effects of voltage bias on the PCBs on the corrosion rate. The test specimens were exposed to mixed flowing gases (MFG) environment with eight different combinations of the following five pollutants at the fixed concentration levels: 60 ppb O3, 80 ppb NO2, 40 ppb SO2, 2 ppb Cl2, and 10 ppb H2S. Temperature and relative humidity (RH) were varied from a reference condition (21°C and 50% RH which is within the current ASHRAE-recommended thermal envelope) to a higher value (28°C, 70% RH, or 80% RH) to increase the moisture content of the test environment. Test results revealed the dominating effect of Cl2 on copper corrosion and that of H2S on silver corrosion. Increasing the moisture content at 21°C caused more severe corrosion of copper when Cl2 was present, but not for silver. When the temperature was increased from 21°C to 28°C at 50% RH, it reduced the corrosion of copper, but not for silver. Voltage-biased PCBs had less effect on corrosion than PCBs without the voltage bias. A mechanistic model based on the multi-ion transport and chemical reactions was also proposed to predict the corrosion of copper due to Cl2-containing pollutant mixtures. The model’s prediction of the effects of temperature and RH agreed well with the experimental results. These findings provided the basis for possible expansion of the ASHRAE-recommended thermal envelope for data centers when Cl2 and H2S are not present and limiting the thermal envelope when Cl2 or H2S is present. They also improved the understanding of the corrosion mechanisms for the copper when Cl2 is present in the data center environment

    Smoke Aerosol Characterization for Spacecraft Fire Detection Systems

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    Appropriate design of fire detection systems requires knowledge of both the expected fire signature and the background aerosol levels. Terrestrial fire detection systems have been developed based on extensive study of terrestrial fires. Unfortunately there is no corresponding data set for spacecraft fires and consequently the fire detectors in current spacecraft were developed based upon terrestrial designs. There are a number of factors that affect the smoke particle size distribution in spacecraft fires. In low gravity, buoyant flow is negligible which causes particles to concentrate at the smoke source, increasing their residence time, and increasing the transport time to smoke detectors. Microgravity fires have significantly different structure than those in 1-g which can change the formation history of the smoke particles. Finally the materials used in spacecraft are different from typical terrestrial environments where smoke properties have been evaluated. It is critically important to detect a fire in its early phase before a flame is established, given the fixed volume of air on any spacecraft. Consequently, the primary target for spacecraft fire detection is pyrolysis products rather than soot. This dissertation is a compilation of experimental investigations performed at three different NASA facilities which characterize smoke aerosols from overheating common spacecraft materials. The earliest effort consists of aerosol measurements in low gravity, called the Smoke Aerosol Measurement Experiment (SAME), and subsequent ground-based testing of SAME smoke in 55-gallon drums with an aerosol reference instrument. The feasibility of the moment method for characterizing smoke from limited data, including the lognormal assumption, is explored. Experiments in low gravity are very rare and expensive, so detailed studies to exploit every possible aspect of the data to increase the science outcome are warranted. Another set of experiments were performed at NASA’s Johnson Space Center White Sands Test Facility (WSTF), with additional fuels and an alternate smoke production method. Measurements of these smoke products include mass and number concentration, and a thermal precipitator was designed for this investigation to capture particles for microscopic analysis. Smoke particle morphology and chemical composition are analyzed for various fuels. The final data presented are from NASA’s Gases and Aerosols from Smoldering Polymers (GASP) Laboratory, with selected results focusing on realistic fuel preparations and heating profiles with regards to early detection of smoke. Additional research on ambient air quality in the International Space Station (ISS) is presented which sheds light on background aerosols that may interfere with smoke detection in spacecraft

    30th International Conference on Electrical Contacts, 7 – 11 Juni 2021, Online, Switzerland: Proceedings

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    Heat Transfer in Energy Conversion Systems

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    In recent years, the scientific community’s interest towards efficient energy conversion systems has significantly increased. One of the reasons is certainly related to the change in the temperature of the planet, which appears to have increased by 0.76 °C with respect to pre-industrial levels, according to the Intergovernmental Panel on Climate Change (IPCC), and this trend has not yet been stopped. The European Union considers it vital to prevent global warming from exceeding 2 °C with respect to pre-industrial levels, since this phenomenon has been proven to result in irreversible and potentially catastrophic changes. These climate changes are mainly caused by the emissions of greenhouse gasses related to human activities, and can be drastically reduced by employing energy systems, for both heating and cooling of buildings and for power production, characterized by high efficiency levels and/or based on renewable energy sources. This Special Issue, published in the journal Energies, includes 12 contributions from across the world, including a wide range of applications, such as HT-PEMFC, district heating systems, a thermoelectric generator for industrial waste, artificial ground freezing, nanofluids, and others

    Integration of optical interconnections and optoelectronic components in flexible substrates

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    Licht als informatiedrager voor datacommunicatie kende een ongezien succes in de laatste decennia. Wegens de lage verliezen en hoge datasnelheden hebben ze voor het overbruggen van lange afstanden hun elektrische tegenhangers reeds geruime tijd verdrongen. Deze trend zet zich ook voort voor korte afstand communicatie op printplaten. Naast zijn functie als informatiedrager, wordt licht ook gebruikt om een waaier aan fysische grootheden te meten. Ook hier heeft licht enkele significante voordelen t.o.v elektrische informatiedragers, waardoor optische sensoren wijdverspreid zijn. Een tweede duidelijke trend binnen de elektronica is het gebruik van flexibele printkaarten. Deze zijn veel dunner, lichter en betrouwbaarder dan de klassieke harde printkaarten, waardoor ze uiterst geschikt zijn voor draagbare toepassingen waar compactheid en een laag gewicht hoge vereisten zijn. De flexibiliteit van de printplaten laat ook toe hen te gebruiken op onvlakke oppervlakken en op bewegende onderdelen. Het doel van het gepresenteerde doctoraatswerk is de ontwikkeling van een nieuw technologieplatform dat bovengenoemde trends combineert. Alle bouwblokken van optische communicatie, gaande van actieve opto-elektronische componenten, aanstuurelektronica, golfgeleiderbaantjes en galvanische verbindingen tot optische koppelstructuren tussen de verschillende bouwblokken, worden zodanig gerealiseerd dat elke component flexibel is en geïntegreerd wordt in een dunne folie met een dikte van slechts 150µm. Op die manier bekomen we een flexibele folie met alle passieve en actieve onderdelen voor optische communicatie geïntegreerd met enkel een elektrische interface naar de buitenwereld, wat de aanvaarding en toepassing van deze technologie in de huidige elektronica aanzienlijk kan versnellen. Binnen het doctoraatswerk werden alle voorgestelde technologieën en processen gerealiseerd en geoptimaliseerd. Bovendien werden de optische verliezen, warmteaspecten, hoogfrequent gedrag, mechanisch gedrag en betrouwbaarheid van de technologie gekarakteriseerd en vergeleken met de huidige state-of-the-art
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