bluuebunny/crossref_metadata_2025_split huggingface dataset:
Integrated Optical Probing of the Thermal Dynamics of Wide Bandgap Power Electronics
Authors: Lundh James Spencer , Song Yiwen , Chatterjee Bikram , Baca Albert G. , Kaplar Robert J. , Armstrong Andrew M. , Allerman Andrew A. , Kim Hyungtak , Choi Sukwon 
Published: December 2019

Abstract
Researchers have been extensively studying wide-bandgap (WBG) semiconductor materials such as gallium nitride (GaN) with an aim to accomplish an improvement in size, weight, and power (SWaP) of power electronics beyond current devices based on silicon (Si). However, the increased operating power densities and reduced areal footprints of WBG device technologies result in significant levels of self-heating that can ultimately restrict device operation through performance degradation, reliability issues, and failure. Typically, self-heating in WBG devices is studied using a single measurement technique while operating the device under steady-state direct current (DC) measurement conditions. However, for switching applications, this steady-state thermal characterization may lose significance since high power dissipation occurs during fast transient switching events. Therefore, it can be useful to probe the WBG devices under transient measurement conditions in order to better understand the thermal dynamics of these systems in practical applications. In this work, the transient thermal dynamics of an AlGaN/GaN high electron mobility transistor (HEMT) were studied using thermoreflectance thermal imaging and Raman thermometry. Also, the proper use of iterative pulsed measurement schemes such as thermoreflectance thermal imaging to determine the steady-state operating temperature of devices is discussed. These studies are followed with subsequent transient thermal characterization to accurately probe the self-heating from steady-state down to sub-microsecond pulse conditions using both thermoreflectance thermal imaging and Raman thermometry with temporal resolutions down to 15 ns.
An Experimental Investigation on the Fluid Distribution in a Two-Phase Cooled Rack Under Steady and Transient IT Load
Authors: Khalili Sadegh , Rangarajan Srikanth , Sammakia Bahgat , Gektin Vadim 
Published: December 2019

Abstract
Increasing power densities in data centers due to the rise of Artificial Intelligence (AI), high-performance computing (HPC) and machine learning compel engineers to develop new cooling strategies and designs for high-density data centers. Two-phase cooling is one of the promising technologies which exploits the latent heat of the fluid. This technology is much more effective in removing high heat fluxes than when using the sensible heat of fluid and requires lower coolant flow rates. The latent heat also implies more uniformity in the temperature of a heated surface. Despite the benefits of two-phase cooling, the phase change adds complexities to a system when multiple evaporators (exposed to different heat fluxes potentially) are connected to one coolant distribution unit (CDU). In this paper, a commercial pumped two-phase cooling system is investigated in a rack level. Seventeen 2-rack unit (RU) servers from two distinct models are retrofitted and deployed in the rack. The flow rate and pressure distribution across the rack are studied in various filling ratios. Also, investigated is the transient behavior of the cooling system due to a step change in the information technology (IT) load.
Fatigue Life of Sn3.0Ag0.5Cu Solder Alloys Under Combined Shear and Compressive Loads
Authors: Dale Travis , Singh Yuvraj , Bernander Ian , Subbarayan Ganesh , Handwerker Carol , Su Peng , Glasauer Bernard 
Published: December 2019

Abstract
Solder joints in electronic assemblies experience damage due to cyclic thermomechanical loading that eventually leads to fatigue fracture and electrical failure. While solder joints in smaller, die-sized area-array packages largely experience shear fatigue due to thermal expansion mismatch between the component and the substrate, larger area-array packages experience a combination of cyclic shear and axial tensile/compressive loads due to flexure of the substrate. Additionally, on larger processor packages, the attachment of heatsinks further exacerbates the imposed axial loads, as does package warpage. With the increase in size of packages due to 2.5D Heterogeneous integration, the above additional axial loads can be significant. Thus, there exists a critical need to understand the impact on fatigue life of solder joints with superposed compressive/tensile loads on the cyclic shear loads. In this paper, we describe a carefully constructed microscale mechanical tester as well as fatigue test results on Sn3.0Ag0.5Cu (SAC305) solder joints subjected to controlled cyclic shear and constant compressive loads. The tester design allows one to apply cyclic shear loads up to 200 N while maintaining a constant axial load of up to 38 N in tension or compression. The tester is capable of maintaining the compressive load to within a tolerance of +/− 0.5 N during the entirety of fatigue experiment. Carefully constructed samples of Sn3.0Ag0.5Cu solder joints were isothermally fatigued under systematically increased compressive load imposed on the sample subject to repeated loading (R = 0) under lap-shear. In general, the imposition of the superposed compressive load increases the fatigue life of the solder joint compared to application of pure cyclic shear load. At larger compressive loads, friction between fractured surfaces is responsible for significant energy dissipation during the cyclic load-unload cycles.
Modeling of Underfilled PBGA Assemblies Using Both Viscoelastic and Elastic Material Properties
Authors: Chowdhury Promod R. , Suhling Jeffrey C. , Lall Pradeep 
Published: December 2019

Abstract
In microelectronics packaging industry, polymer based materials are used extensively. These polymer materials show viscoelastic behavior when subject to time dependent loads or deformations. The viscoelastic behavior highly depends on both temperature and time. In many cases, these viscoelastic properties are often neglected due to saving computational cost or unavailability of full characterization of the viscoelastic properties. To make accurate predictions of packaging mechanical behavior and reliability, it is important to accurately characterize the viscoelastic behavior of mold compounds, underfill encapsulants, adhesives and other polymers used in electronic assemblies. After characterization, these parameters can be used as input material property data for finite element analysis (FEA) simulations.
In this study, both frequency dependent dynamic mechanical analysis (DMA) measurements, and strain and temperature dependent stress relaxation experiments were performed on a typical underfill material in order to characterize its linear viscoelastic behavior. In both cases, a master curve was determined using the assumption of time-temperature equivalence, and Prony series expansions were utilized to model the underfill material relaxation behavior. After that, these viscoelastic underfill material parameters were used in finite element models of underfilled ball grid array packages (Ultra CSP) subjected to thermal cycling from −40 to 125 °C. Separate simulations were also performed using temperature dependent elastic properties for the underfill material. In both cases, the solder joint fatigue life was estimated, and the effects of using viscoelastic properties for the underfill in solder joint fatigue life simulation were investigated.
Process Capability of Aerosol-Jet Additive Processes for Long-Runs up to 10-Hours
Authors: Lall Pradeep , Abrol Amrit , Kothari Nakul , Leever Ben , Miller Scott 
Published: December 2019

Abstract
Traditionally, the printed circuit assemblies have been fabricated through a combination of imaging and plating based subtractive processes involving use of photo-exposure followed by baths for plating and etching to form the needed circuitry on rigid and flexible laminates. Additive electronics is finding applications for fabrication of IoT sensors. The emergence of a number of additive technologies poses an opportunity for the development of processes for manufacture of flexible substrates using mainstream additive processes, which are now commercially available. Aerosol-Jet printing has shown the capability for printing lines and spaces below 10 μm in width. The Aerosol-Jet system supports a wide variety of materials, including nanoparticle inks and screen-printing pastes, conductive polymers, insulators, adhesives, and even biological matter. The adoption of additive manufacturing for high-volume commercial fabrication requires an understanding of the print consistency, electrical and mechanical properties. Little literature exists that addresses the effect of varying sintering time and temperature on the shear strength and resistivity of the printed lines. In this study, the effect of process parameters on the resultant line-consistency, mechanical and electrical properties has been studied. Print process parameters studied include the sheath rate, mass flow rate, nozzle size, substrate temperature and chiller temperature. Properties include resistance and shear load to failure of the printed electrical line as a function of varying sintering time and varying sintering temperature. Aerosol-Jet machine has been used to print interconnects. Printed samples have been exposed to different sintering times and temperatures. The resistance and shear load to failure of the printed lines has been measured. The underlying physics of the resultant trend was then investigated using elemental analysis and SEM. The effect of line-consistency driftover prolonged runtimes has been measured for up to 10-hours of runtime. Printing process efficiency has been gauged a function of process capability index (Cpk) and process capability ratio (Cp). Printed samples were studied offline using optical Profilometry to analyze the consistency within the line width, line height, line resistance and shear load to study the variance in the electrical and mechanical properties over time.
Health Monitoring of PCB’s Under Mechanical Shock Loads
Authors: Lall Pradeep , Thomas Tony , Suhling Jeff , Blecker Ken 
Published: December 2019

Abstract
Feature vectors for health monitoring of electronic assemblies under repetitive mechanical shock have been developed for assemblies subject to 3,000g acceleration levels. The resistance and strain measurements of the PCB are acquired during each drop to analyze the changes in the values during the experiment. Analysis on the progression of failure was carried out using frequency-based techniques on the strain signals from different locations of the board and failure of the package was identified from the increase in the resistance values of the package during the drop. Feature vectors selected were based on the time-frequency data as well as the logarithmic decrement of the strain signals during the different drops. Different statistical approaches on identifying the changes in the damping characteristics of the package during drop were also carried out. Statistical analysis on the changes in the resistance values were quantified in accordance with the changes in the strain and correlation of the both were attempted. The dependence on position of the strain gauge on the PCB were also studied by comparing the variation of the feature vectors of the corresponding strain signals. The before and after failure strain signals were compared on the frequency components and as well as the changes in the damping characteristics of the strain signals.
Folding-Reliability of Flexible Electronics in Wearable Applications
Authors: Lall Pradeep , Jang Hyesoo , Leever Ben , Miller Scott 
Published: December 2019

Abstract
There is a growing need for flexible hybrid electronics solutions for wearable applications, in which the user may often wear electronics on body, on fabric or on skin. Electronics in wearable application may be subjected to stresses of daily motion including bending, twisting and stretching. Thus, there is need for technologies capable of flexibility, robustness and small size while being lightweight. Existing standards for focus on rigid electronics and there is scarcity of guidance for test-levels needed to assure reliability of flexible electronics. There is need for studies focused on the development of accelerated test conditions representative of field applications and the identification of failure mechanisms for test levels. In this study, experimental analysis on fatigue life of the PCB in cyclical folding load is conducted. A folding test-stand capable of replicating the stresses of daily motion in a lab-environment has been developed for the test. For the better understanding of the failure mechanism, analysis of failure modes is carried out. Consequently, it is found that fatigue life of the PCB is related to the several conditions: folding direction, moving distance, folding diameter and strain rate.
Development of a Technique to Measure Deliquescent Relative Humidity of Particulate Contaminants and Determination of the Operating Relative Humidity of a Data Center
Authors: Shah Jimil M. , Anand Roshan , Saini Satyam , Cyriac Rawhan , Agonafer Dereje , Singh Prabjit , Kaler Mike 
Published: December 2019

Abstract
A remarkable amount of data center energy is consumed in eliminating the heat generated by the IT equipment to maintain and ensure safe operating conditions and optimum performance. The installation of Airside Economizers, while very energy efficient, bears the risk of particulate contamination in data centers, hence, deteriorating the reliability of IT equipment. When RH in data centers exceeds the deliquescent relative humidity (DRH) of salts or accumulated particulate matter, it absorbs moisture, becomes wet and subsequently leads to electrical short circuiting because of degraded surface insulation resistance between the closely spaced features on printed circuit boards. Another concern with this type of failure is the absence of evidence that hinders the process of evaluation and rectification. Therefore, it is imperative to develop a practical test method to determine the DRH value of the accumulated particulate matter found on PCBs (Printed Circuit Boards). This research is a first attempt to develop an experimental technique to measure the DRH of dust particles by logging the leakage current versus RH% (Relative Humidity percentage) for the particulate matter dispensed on an interdigitated comb coupon. To validate this methodology, the DRH of pure salts like MgCl2, NH4NO3 and NaCl is determined and their results are then compared with their published values. This methodology was therefore implemented to help lay a modus operandi of establishing the limiting value or an effective relative humidity envelope to be maintained at a real-world data center facility situated in Dallas industrial area for its continuous and reliable operation.
Direct Ink Printing of Cavities in DPC Ceramic Substrates With Kaolin Pastes for Hermetic Packaging
Authors: Sun Qinglei , Peng Yang , Cheng Hao , Mou Yun , Chen Mingxiang 
Published: December 2019

Abstract
Fabrication of three-dimensional cavities containing kaolin pastes to be used as direct plated copper (3DPC) substrates ceramics is a very important advancement for electronic packaging of hermetic and ultraviolet light emitting diodes. This work demonstrates usage of pastes consisting of 32–40 wt% of kaolin clay and polyacrylic acid for direct ink printing (DIP) of 3DPC. Rheological and zeta potential tests were performed to determine printability and stability, respectively, of these kaolin pastes. Kaolin content variation had minimum effect on absolute values of the zeta potentials. All pastes had enough stability with the absolute values larger than 30 mV. 40 wt% kaolin solids mass paste was the optimal for DIP due to its excellent shear thinning and viscoelastic properties. Cured 40 wt% kaolin solids mass paste had superior compressive, flexural and bonding strengths. DIP using pastes containing 40 wt% of kaolin is promising for electronic chip integrated hermetic packaging.
Altered Vertical Ground Reaction Force Components While Walking in Individuals With Chronic Ankle Instability
Authors: Wikstrom Erik A. , Song Kyeongtak , Migel Kimmery , Hass Chris J. 
Published: December 2019

Aberrant loading is a mechanism by which individuals with chronic ankle instability (CAI) may negatively impact cartilage health and therefore long-term health outcomes. We aimed to quantify walking vertical ground reaction force (vGRF) component differences between those with and without CAI. Participants (n = 36) walked barefoot overground at a self-selected comfortable pace. Normalized peak vGRF, time to peak vGRF, and normalized loading rate were calculated. Higher normalized loading rates (CAI: 5.69 ± 0.62 N/BW/s; controls: 5.30 ± 0.44 N/BW/s, p = .034) and less time to peak vGRF (CAI: 1.48 ± 0.18 s; controls: 1.62 ± 0.16 s, p = .018) were observed in those with CAI. In conclusion, those with CAI demonstrate a higher normalized loading rate and less time to peak vGRF compared to controls.
Foundered lithospheric segments dropped into the mantle transition zone beneath southern California, USA
Authors: Yu Youqiang , Gao Stephen S. , Liu Kelly H. , Zhao Dapeng 
Published: December 2019

AbstractThe diverse range of active tectonics occurring in southern California, USA, offers an opportunity to explore processes of continental deformation and modification in response to the instability of the Pacific and Farallon plates. Here, we present a high-resolution receiver-function image of the mantle transition zone (MTZ). Our result reveals significant lateral heterogeneities in the deep mantle beneath southern California. Both seismic tomography and MTZ discontinuity deflections reveal foundered lithospheric segments that have dropped into the MTZ beneath the western Transverse Ranges, the Peninsular Ranges, and part of the southern Sierra Nevada. Water dehydrated from these foundered materials may contribute to the observed MTZ thickening. Our observations, combined with previous tomography and geochemical results, indicate that lithospheric foundering of fossil arc roots provides a way for geochemical heterogeneities to be recycled into the underlying mantle, and suggest that the foundered materials can play a significant role in inducing lateral variations of MTZ structure.
Magma accumulation beneath Santorini volcano, Greece, from P-wave tomography
Authors: McVey B.G. , Hooft E.E.E. , Heath B.A. , Toomey D.R. , Paulatto M. , Morgan J.V. , Nomikou P. , Papazachos C.B. 
Published: December 2019

AbstractDespite multidisciplinary evidence for crustal magma accumulation below Santorini volcano, Greece, the structure and melt content of the shallow magmatic system remain poorly constrained. We use three-dimensional (3-D) velocity models from tomographic inversions of active-source seismic P-wave travel times to identify a pronounced low-velocity anomaly (–21%) from 2.8 km to 5 km depth localized below the northern caldera basin. This anomaly is consistent with depth estimates of pre-eruptive storage and a recent inflation episode, supporting the interpretation of a shallow magma body that causes seismic attenuation and ray bending. A suite of synthetic tests shows that the geometry is well recovered while a range of melt contents (4%–13% to fully molten) are allowable. A thin mush region (2%–7% to 3%–10% melt) extends from the main magma body toward the northeast, observed as low velocities confined by tectono-magmatic lineaments. This anomaly terminates northwest of Kolumbo; little to no melt underlies the seamount from 3 to 5 km depth. These structural constraints suggest that crustal extension and edifice loads control the geometry of magma accumulation and emphasize that the shallow crust remains conducive to melt storage shortly after a caldera-forming eruption.
Outcome of patients with large vessel occlusion stroke after first admission in telestroke spoke versus comprehensive stroke center
Authors: Kaminsky Anne-Laure , Mione Gioia , Omorou Yacoubou , Humbertjean Lisa , Bonnerot Mathieu , Lacour Jean Christophe , Riou-Comte Nolwenn , Anadani Mohammad , Gory Benjamin , Richard Sébastien 
Published: December 2019

IntroductionWhile telestroke allows early intravenous thrombolysis (IVT) for ischemic strokes in spoke centers, mechanical thrombectomy (MT) for large vessel occlusion (LVO) is mainly performed at comprehensive stroke centers (CSCs). We aimed to compare 3 month outcome in patients with LVO after admission to a spoke center using telestroke compared with first CSC admission in our large regional stroke network, irrespective of final treatment decision.MethodsAll consecutive LVO patients who were admitted to one of six spoke centers or to the regional CSC within 6 hours of symptom onset were prospectively included from September 1, 2015 to August 31, 2017. All patients admitted to spoke centers were assessed on site with cerebral and vessel imaging. Primary outcome was 3 month favorable outcome (modified Rankin Scale score of 0–2).ResultsDistances between spoke centers and CSC ranged from 36 to 77 miles. Among 207 included patients, 132 (63.8%) were first admitted to CSCs and 75 (36.2%) to spoke centers. IVT was administered more in spoke centers (81.3% vs 53.8%, p<0.0001) while MT was performed less (26.7% vs 49.2%, p=0.001) and with a longer time from onset (303 vs 200 min, p<0.0001). No difference was found in 3 month favorable outcome between spoke centers compared with CSCs (32.0% and 35.1%, respectively; OR=0.68; 95% CI 0.42 to 1.10; p=0.12).ConclusionsDespite different distribution of reperfusion therapies for LVO patients managed by telemedicine, we could not demonstrate a difference in functional outcome according to admission location in a large area with long distances between centers.
Region-specific agreement in ASPECTS estimation between neuroradiologists and e-ASPECTS software
Authors: Neuhaus Ain , Seyedsaadat Seyed Mohammad , Mihal David , Benson John C , Mark Ian , Kallmes David F , Brinjikji Waleed 
Published: December 2019

Background and purposeThe Alberta Stroke Program Early CT Score (ASPECTS) is a widely used measure of ischemic change on non-contrast CT. Although predictive of long-term outcome, ASPECTS is limited by its modest interobserver agreement. One potential solution to this is the use of machine learning strategies, such as e-ASPECTS, to detect ischemia. Here, we compared e-ASPECTS with manual scoring by experienced neuroradiologists for all 10 individual ASPECTS regions.Materials and methodsWe retrospectively reviewed 178 baseline non-contrast CT scans from patients with acute ischemic stroke undergoing endovascular thrombectomy. All scans were reviewed by two independent neuroradiologists with a third reader arbitrating disagreements for a consensus read. Each ASPECTS region was scored individually. All scans were then evaluated using a machine learning-based software package (e-ASPECTS, Brainomix). Interobserver agreement between readers and the software for each region was calculated with a kappa statistic.ResultsThe median ASPECTS was 9 for manual scoring and 8.5 for e-ASPECTS, with an overall agreement of κ=0.248. Regional agreement varied from κ=0.094 (M1) to κ=0.555 (lentiform), with better performance in subcortical regions. When corrected for the low number of infarcts in any given region, prevalence-adjusted bias-adjusted kappa ranged from 0.483 (insula) to 0.888 (M3), with greater agreement for cortical areas. Intraclass correlation coefficients were between 0.09 (M1) and 0.556 (lentiform).ConclusionManual scoring and e-ASPECTS had fair agreement in our dataset on a per-region basis. This warrants further investigation using follow-up scans or MRI as the gold standard measure of true ASPECTS.