The energy consumption for cooling electronic equipment in data centers using central systems is significant and will continue to rise. The motivation of the present study research is based on the need to determine optimization strategies to improve and optimize the thermal efficiency of data centers using a simulation-based approach. Here, simulation is used to model and optimize a proposed research data center for use as an environment to test equipment and investigate best practices and strategies such as containment and hybrid cooling. The optimization technique used in this study finds the optimal operating conditions and containment strategies of the data center while still meeting certain thermal conformance constraints. More specifically, optimum cooling units supply flow rate and supply temperature setpoint are sought under different containment configurations including both hot aisle and cold aisle containment strategies in both full and partial setups. The optimization process developed in the present study can serve as a generalized procedure for the optimization of any new air-cooled data center.

This study focused on the improved designs of airflow management in container data center having overhead air supply. The computational fluid dynamics (CFD) model is first validated with experimental results. Then, the impact of grille diameter, deflector angle and air supply layout on the data center thermal performance is investigated. Results show that the larger grille diameter may reduce the volumetric flowrate through the front grille S1, causing insufficient air supply and strong hot-air recirculation at the first rack A1. By decreasing the grille diameter from 335 mm to 235 mm, the average rack cooling index (RCI) and supply heat index (SHI) can be improved from 25.4% and 0.292 to 65% and 0.258, respectively. However, implementing small diameter grilles is not an economic way for data center performance improvement as far as the energy consumption is concerned due to the high pumping power. Afterwards, raising the deflector angle below 30° in grille S1 can provides moderate improvement on temperature of A1 rack. A further rise of the deflector to 40° may impose severe deterioration with pronounced hot-spot area. The data center performance can be improved by changing from center-cold-aisle arrangement to center-hot-aisle layout. The layout provides much higher return air temperature and the RCI and SHI can be improved by 32.7% and 34.5%, respectively.

This paper presents an experimental analysis for minimizing the thermal contact resistance (R) between an optical fiber and copper heat sink by using the low-melting temperature alloy (LMTA) as the thermal interface material (TIM) subject to high-flux operation (up to 250 W?m-1). For the cases without LMTA, the temperature rise (?T) can easily surpass 195 ? at a heating load of 25 W·m-1. By contrast, ?T is dramatically reduced to be less than 1 ? with LMTA as TIM with a much higher heating power of 150 W·m-1. The corresponding thermal resistance (R) can be reduced from 6.5-8.2 K·m·W-1 to 0.004-0.013 K·m·W-1. The improvement is far superior to existing studies. Besides, decreasing the surface roughness and increasing contact pressure also help to reduce R, especially for the cases when the LMTA is not melted. As the LMTA melts, a significant reduction of R by 56% is achieved as compared to the case without melting. The effect of surface roughness and contact pressure on the thermal contact resistance is also examined, and it is found that the influences are small once LMTA melts.

Studies on CNT, Au, and Ag solar enabled steam generation with potential application in water purification, distillation, and sterilization of medical equipment are ongoing. The key challenge with these nanoparticles is the cost of production hence limiting its full application for clean water production. This work for the first time, reports on activated carbon enabled steam generation hence addressing the cost limitations of metallic nanoparticles. Activated carbon has high solar absorptivity at various wavelengths of visible light under low concentration. Experiments were carried out using activated carbon and CNT nanofluids and polyurethane membrane with immobilized activated carbon and CNT. A simulated solar light of 1 KW ~1 Sun was used. The rate of evaporation, temporal, and spatial evolution of bulk temperature in the water were monitored automatically and recorded for further data reductions. Parametric studies of the effect of nanoparticle concentration, water quality, and salinity were performed. Experimental evidence showed that activated carbon has potential in water purification. We reported for the first time that optimal activated carbon concentration for maximum steam generation is 60 % vol. We also obtained a 160 % increase in steam production rate at 60 % concentration of activated carbon when compared with D.I water.

This paper presents a new analytical filling time model to predict the flow of non-Newtonian underfill fluid during flip-chip encapsulation process. The current model is formulated based on the regional segregation approach, instead of the conventional porous media approximation. In this approach, the flow times were computed separately at different filling stages, before being summed up till the required filling distance. The non-Newtonian property of underfill fluid is modelled using the conventional power-law constitutive equation. Additionally, the spatial aspects of the underfill flow were incorporated into the present analysis. For instance, the evolution of underfill menisci from convex to concave was analytically developed and the contact line jump criterion was improved using minimal flow assumption. Upon validated with three distinct past underfill experiments, the current analytical model is found to have the best performance as it predicted the filling times with the least discrepancy among other existing filling time models. Quantitatively, the discrepancies were averagely reduced by an absolute value of at least 8.68% and 4.90% for the validation studies based on two benchmark industrial experiments. Generally, this model is particularly useful in manufacturing lines to estimate the process time of flip-chip underfill, as well as for the optimizations of process and package design.

The objective of this study is to numerically investigate the effect of cryogenic intake air temperature on the in-cylinder temperature and formation of exhaust emissions in a CI engine. The experimental setup was consisted of a single-cylinder diesel engine. The intake air temperature was varied from 18 °C to 40 °C, which was controlled by cooler and heater. Submodels were applied for the simulations of physical/chemical phenomenon of spray and combustion behaviors. The intake air temperature in numerical condition was varied from −18 °C to 18 °C. The numerical results were validated with experimental results for the reliability of this work. The results of this work were compared in terms of cylinder pressure, rate of heat release (ROHR), indicated specific nitrogen oxide (ISNO), indicated specific carbon monoxide (ISCO), ignition delay, in-cylinder temperature distributions, equivalence ratio distributions, NO mass fraction, and CO mass fraction. When the intake air temperature was decreased in steps of 9 °C, the cylinder temperature and cylinder pressure were decreased in steps of about 14.5 °C and 0.05 MPa, respectively. In all cases, the area where the NO formed in the cylinder was identified with the area of the high equivalence ratio and temperature in the cylinder. The amount of CO generation shows the similar distributions in the cylinder according to the intake air temperature conditions. However, the oxidation rate of formed CO under the low intake air temperature was lower than those of the high intake air temperature.

A comprehensive stochastic model is proposed to predict Package-on-Package (PoP) stacking yield loss. The model takes into account all pad locations at the stacking interface while considering the statistical variations of the warpages and the solder ball heights of both top and bottom packages. The goal is achieved by employing three statistical methods: (1) an advanced approximate integration-based method called eigenvector dimension reduction (EDR) method to conduct uncertainty propagation (UP) analyses, (2) the stress-strength interference (SSI) model to determine the noncontact probability at a single pad, and (3) the union of events considering the statistical dependence to calculate the final yield loss. In this first part, theoretical development of the proposed stochastic model is presented. Implementation of the proposed model is presented in a companion paper.

The stochastic model for yield loss prediction proposed in Part I is implemented for a package-on-package (PoP) assembly. The assembly consists of a stacked die thin flat ball grid array (TFBGA) as the top package and a flip chip ball grid array (fcBGA) as the bottom package. The top and bottom packages are connected through 216 solder joints of 0.5 mm pitch in two peripheral rows. The warpage values of the top and bottom package are calculated by finite element analysis (FEA), and the corresponding probability of density functions (PDFs) are obtained by the eigenvector dimension reduction (EDR) method. The solder ball heights of the top and bottom package and the corner pad joint heights are determined by surface evolver, and their PDFs are determined by the EDR method, too. Only 137 modeling runs are conducted to obtain all 549 PDFs in spite of the large number of input variables considered in the study (27 input variables). Finally, the noncontact open-induced staking yield loss of the PoP assembly is predicted from the PDFs.

The high temperature gas cooled reactor (HTGR) has advantages for irradiation applications such as large space available for irradiation at reflector region and high thermal neutron spectrum with the graphite moderator. High temperature engineering test reactor (HTTR), a prismatic type of the HTGR, has been constructed to establish and upgrade the basic technologies for the HTGRs. Many irradiation regions are reserved in the HTTR to be served as a potential tool for an irradiation test reactor in order to promote innovative basic researches such as materials, fusion reactor technology, and radiation chemistry and so on. This study shows the overview of some possible irradiation applications at the HTTRs including neutron transmutation doping silicon (NTD-Si) and 125I productions. The HTTR has possibility to produce about 40 tons of doped Si-particles per year for fabrication of spherical silicon solar cell. Besides, the HTTR could also produce about 1.8×105GBq/year of 125I isotope, comparing to 3.0×103GBq of total 125I supplied in Japan in 2016.

High-concentration photovoltaic systems can provide power conversion efficiency that is nearly double that of conventional solar panels. Concentrating photovoltaics (CPV) cannot compete with fixed silicon panels for rooftop installations due to the complexity and cost of CPV two-axis pedestal tracking systems. Fixed optic designs have recently been proposed that have a transparent middle sheet with small, widely spaced, and highly efficient solar cells sandwiched between a fixed lenslet array on top and fixed reflector array on the bottom. Precision actuators position the middle sheet at the focal points of the lenslet/reflector array to microtrack the sun throughout the day. This paper discusses the kinematic design and control of Shape Memory Alloy (SMA) actuators used for the first time in this application. SMA actuators have the potential to be less expensive, easier to integrate, and lower power than electric motors. The kinematic design maintains upper and lower bounds on wire tension to prevent failure and ensure reversible actuation, respectively. The SMA actuators under quasi-linearized PID control can position the middle sheet with +/− 7 mm of range in the vertical and horizontal directions while ensuring less than 1.9 µm of steady state error in SMA actuator stroke. The middle sheet position and orientation errors, however, exceed 1 mm and 0.5°, respectively. These relatively large errors are due to flexibility in the suspension system, friction at wire supports, and large kinematic gains at extreme positions and indicate the need for middle sheet error measurement and feedback control.

Thermal stress-induced protrusions of copper through-silicon-vias (Cu-TSVs) during thermal processing pose substantial reliability concerns in three-dimensional system integration. In this study, a phase-field-crystal model is used to investigate the protrusions and microstructural evolutions of blind Cu-TSVs under different loading conditions. Protrusions are observed only when the TSVs are under $\varepsilon_x$, $\varepsilon_y$ and $\gamma_{xy}$, whereas no protrusions are observed when the TSVs are subjected to pure shear strains $\gamma_{yx}$. The simulation results suggest that the grains in the top layer of a TSV contribute more to both the protrusion profile and the protrusion height than the grains in the lower layers. Moreover, the protrusion is larger when the misorientation among the grains is larger and the grain size along the $y$-direction is smaller. In addition, a phenomenological model linking protrusion and microstructural factors and a visual guide from the viewpoint of plastic flow are provided to understand the origins of Cu-TSV protrusion.

This study presents a comprehensive assessment of the process-induced warpage of molded wafer for chip-first, face-down fan-out wafer-level packaging during the fan-out fabrication process. A process-dependent simulation methodology is introduced, which integrates nonlinear finite element analysis and element death-birth technique. The effects of the cure-dependent volumetric shrinkage, geometric nonlinearity and gravity loading on the process-induced warpage are examined. The study starts from experimental characterization of the temperature-dependent material properties of the applied liquid type epoxy molding compound (EMC) system through dynamic mechanical analysis and thermal mechanical analysis. Furthermore, its cure state (heat of reaction and degree of cure) during the compression molding process is measured by differential scanning calorimetry tests. Besides, the cure dependent-volume (chemical) shrinkages of the EMC system after the in-mold cure and post-mold cure are experimentally determined, by which the volumetric shrinkage at the gelation point is predicted through a linear extrapolation approach. To demonstrate the effectiveness of the proposed theoretical model, the prediction results are compared against the in-line warpage measurement data. One possible cause of the asymmetric/non-axisymmetric warpage is also addressed. Finally, the influences of some geometric dimensions on the warpage of the molded wafer are identified through parametric analysis.

Ultraviolet light-emitting diodes (UV-LEDs) have drawn considerable attentions in environment, life science, and industry fields, such as the applications of near UV-LEDs in resin curing, illumination, and identification, and deep UV-LEDs in disinfection, medical treatment, and biochemical inspection. However, due to the limitation of packaging technology, UV-LED devices exhibit low light efficiency and poor reliability compared with visible LEDs. The organic encapsulation materials are prone to UV aging, thermal degradation, and non-airtightness, which significantly reduce the performances of UV-LEDs. In order to solve this issue, UV-LED packaging technology have been proposed for UV-LED devices instead of conventional LED packaging. In this review, we detailedly investigated the overview and challenges of NUV-LED/DUV-LED packaging. For the packaging of UV-LEDs, all inorganic encapsulation materials, hermetic packaging structures with low-temperature bonding, reduced reflection losses, UV stable and transparent materials, and effective thermal management are key progresses to enhance the light efficiency and reliability of UV-LEDs. In addition, the summary and perspectives of NUV-LED/DUV-LED packaging were introduced and discussed.

Quantum dot (QD) attracts great attention in light-emitting diode (LED) packaging for high-quality light sources, while it leads to low light efficiency due to the significantly high reabsorption loss between QDs. Accordingly, we experimentally study the reabsorption properties of QD color convertors (QCCs) for LED packaging considering various thicknesses and concentrations under different injection current. The results indicate the QCC configuration with a small thickness and large concentration can have the same absorption ability for chip light as that with the opposite configuration, resulting in the same QD light proportion. However, the QCC configuration having smaller thickness is more useful to decrease the reabsorption loss, leading to higher radiant power (an increase of larger than 37.2 %). Moreover, it is essential to gain a high radiant power of QD light with small reabsorption loss, which can be realized by combining QCCs with a low QD content and a source with a large injection current. Based on this simple and effective approach, a conversion loss smaller than 20 %, close to their quantum yield, can be achieved, which is approximately 4 times smaller than that gained by QCCs with a high QD content. However, it introduces additional radiant power of chip light, suppressing further improvement in the QD light proportion. Much work is still required to make full use of the redundant chip light. This study provides a better understanding of the reabsorption properties of QCCs, and can significantly accelerate their applications in illumination and display applications.

This paper demonstrates the concept and fabrication process for a novel (copper, nickel)-tin, (Cu, Ni)-Sn, transient liquid phase (TLP) high-temperature bond that exploits the addition of a pure aluminum (Al) core layer for die attachment in a power electronics power card structure. The bond quality and composition of the bond layer are characterized using confocal scanning acoustic microscopy (CSAM), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). The experimental results indicate that the material composition and established fabrication process enable a crack-free bond that exhibits a void fraction of 2% or less. Compared to a traditional foil-based TLP bonding system, the proposed TLP/metal laminated structure displays a significant, e.g., ~60%, reduction in thermal stress built-in after fabrication, as verified through steady-state thermal stress simulations.

A molded wafer-level package simulation model was successfully developed for calculating solder ball fatigue life during a temperature cycle test, revealing that the most crucial factor affecting fatigue life, rather than being the maximal stress in solder balls, is the equivalent strain range in solder balls during the creep effect. Accordingly, in a temperature cycle test, the fatigue life of the solder balls, which are located from the outer edge to the center, is negatively correlated with the equivalent strain range; the earliest solder balls to rupture are those located at the outer edges, which have the highest equivalent strain range but not the highest stress. Regarding the fatigue life distribution, the simulation results differed from the experiment results by only 6.4%. Additionally, the effects of mold compound protection type and thickness on fatigue life were investigated. When the thickness was changed from 85 to 25 µm, the solder ball fatigue life increased to approximately 1230 cycles, which satisfies the production standard of 500 cycles and is 1.86 times longer than the fatigue life in the existing production line. Reduction of mold compound thickness reduced the amount of material required to 29% of that in the current production line. The model established in this study is expected to be applied in future integrated circuit package design for product reliability.

Successful utilization of the inherent capability of wide bandgap materials and architectures for radio frequency (RF) power amplifiers (PAs) necessitates the creation of an alternative thermal management paradigm. Recent “embedded cooling” efforts in the aerospace industry have focused on overcoming the near-junction thermal limitations of conventional electronic materials and enhancing removal of the dissipated power with on-chip cooling. These efforts, focusing on the use of diamond substrates and microfluidic jet impingement, are ushering in a new generation (Gen3) of thermal packaging technology. Following the introduction of a modified Johnson's figure-of-merit (JFOM-k), which includes thermal conductivity to reflect the near-junction thermal limitation, attention is turned to the options, challenges, and techniques associated with the development of embedded thermal management technology (TMT). Record GaN-on-Diamond transistor linear power of 11 W/mm, transistor power fluxes in excess of 50 kW/cm 2 , and heat fluxes, above 40 kW/cm 2 , achieved in Defense Advanced Research Projects Agency (DARPA)'s near-junction thermal transport (NJTT) program, are described. Raytheon's ICECool demonstration monolithic microwave integrated circuits (MMICs), which achieved 3.1× the CW RF power output and 4.8× the CW RF power density relative to a baseline design, are used to illustrate the efficacy of Gen3 embedded cooling.

As modern electronics become miniaturized with high power, thermal management for electronics devices has become significant. This motivates the implementation of new cooling solutions to dissipate high-heat levels from high-performance electronics. Evaporative cooling is one of the most promising approaches for meeting these future thermal demands. Thin-film evaporation promotes heat dissipation through the phase change process with minimal conduction resistance. In this process, it is important to design surface structures and corresponding surface properties that can minimize meniscus thickness, increase liquid-vapor interfacial area, and enhance evaporation performances. In this study, we investigate thin-film evaporation by employing nanotextured copper substrates for varying thermal conditions. The liquid spreading on the nanotextured surfaces is visualized using a high-speed imaging technique to quantify evaporative heat transfer for various surfaces. The permeability is calculated using an enhanced wicking model to estimate the evaporation effect combined with the mass measurements. Then, infrared thermography is employed to examine two-dimensional temporal temperature profiles of the samples during the evaporative wicking with a given heat flux. The combination of optical time-lapse images, evaporation rate measurements, and temperature profiles will provide a comprehensive understanding of evaporation performances using textured surfaces.

Light-emitting diodes (LEDs) have gained wide adoption in general illumination applications in the last decade. However, the efficiency droop of LEDs with increasing current density limits the luminous flux per wafer area. In contrast, laser diodes (LDs) can achieve higher efficiency at high current density. Likewise, the etendue of LDs is very low due to the small emitting area and divergent angle, facilitating the high luminance. Hence, LDs may outperform LEDs in future high-luminance solid-state lighting (SSL). However, the rapid development of high-luminance laser-based white lighting (WLD) is still facing some challenges. Firstly, the heat flux of LD chip is extremely high, leading to a higher junction temperature. Secondly, the laser beam exhibits an elliptical and astigmatic pattern with Gaussian intensity distribution, which may deteriorate the lighting performances. Thirdly, to achieve high-luminance lighting, the laser beam is usually focused onto the phosphor layer, which may easily increase the phosphor temperature to the thermal quenching region. A comprehensive understanding of these problems enables the advancements of packaging designs for WLDs. In this review, we summarized the recent progress in the packaging of WLDs. First, the advantages and applications of LDs were presented. Then, the state-of-the-art methods of generating white light using LDs were reviewed, in terms of packaging structures and performances. Finally, the challenges and corresponding progresses for the packaging of WLDs were overviewed. This review intends to contribute to the development of next-generation high-luminance laser-based white lighting.

A prototype non-invasive blood glucose level measurement optical device (NI-BGL-MOD) has been developed. The NI-BGL-MOD uses a discrete Fourier transform (DFT) method and a fast artificial neural network algorithm to optimize device performance. The appropriate light-emitting diode for the sensory module was selected based on near-infrared spectrophotometry of a blood glucose model and human blood. DFT is implemented in an analog-to-digital converter module. An in vitro trial using the blood glucose model along with a clinical trial involving 110 participants were conducted to evaluate the performance of the prototype. The root-mean-square error of the prototype was 10.8 mg/dl in the in vitro trial and 3.64 mg/dl in the clinical trial, which is lower than the ISO-15197:2016 mandated value of 10 mg/dl. In each trial, consensus error grid analysis indicated that the measurement error was within the safe range. The sensitivity and specificity of the prototype were 0.83 (0.36, 1.00) and 0.90 (0.55, 1.00) in the in vitro trial and 0.81 (0.75, 0.85) and 0.83 (0.78, 0.87) in the clinical trial, respectively. In general, the proposed NI-BGL-MOD demonstrated good performance than gold-standard measurement. Key words: Non-invasive blood glucose measurement, optical device, discrete Fourier transform, multi-formulatric regression, fast artificial neural network