bluuebunny/crossref_metadata_2025 huggingface dataset:
Lid-Integral Cold Plate Topology Integration, Performance, and Reliability
Authors: Schlottig Gerd , de Fazio Marco , Escher Werner , Granatieri Paola , Khanna Vijayeshwar D. , Brunschwiler Thomas
Published: November 2015

We demonstrate the Lid-Integral Silicon Coldplate topology as a way to bring liquid cooling closer to the heat source IC. It allows to eliminate one thermal interface material (TIM2), to establish and improve TIM1 during packaging, to use wafer-level processes, and to ease integration in 1st level packaging. We describe the integration, and analyze reliability aspects of this package using modeling and test vehicle builts. To compare the impact of geometry, materials and mechanical coupling on warpage, strains and stresses, we simulate finite element models of five different topologies on an organic LGA carrier. We measure the thermal performance in terms of thermal resistance from coldplate base to inlet liquid and obtain 15mm2K/W at 30 kPa pressure drop across the package. We build two different topologies using silicon coldplates and injection molded lids. Gasket-attached coldplates pass an 800 kPa pressure test, direct-attached coldplates fracture in the coldplate. The results advise to use a compliant layer between coldplate and the manifold lid and promise a uniformly thick TIM1 layer in the Si-Si matched topology. The work shows the feasibility of composite lids with integrated silicon coldplates in high heat flux applications.
Thermodynamic Analysis of Full Liquid-Cooled Data Centers
Authors: Bhalerao A. , Wemhoff A. P.
Published: November 2015

One way to model the thermodynamic efficiency of a data center is to perform a second-law analysis using exergy calculations of the individual components. The in-house data center modeling tool Villanova Thermodynamic Analysis of Systems (VTAS) was applied to determine the effect of direct liquid cooling with cold plates on data center efficiency. The effectiveness of the cold plate as a function of the heat output of the servers was also examined. VTAS was used to study a configuration of two rows with eight racks each. Each rack was assumed to have twelve servers, each producing 200 W of heat. In addition to the cold plates and servers, this configuration also included a computer room air handling (CRAH) unit, a chiller, and a cooling tower. Preliminary results show that data center second-law efficiency increases as the cold plate removes more heat than the CRAH unit. Specifically, when using cold plates to remove all of the heat from the servers, the overall data center exergy destruction was reduced by over 30% compared to a configuration with only a CRAH unit and between 12–18% compared to a configuration with hybrid liquid-air technologies, thus showing that configurations with direct liquid cooling are thermodynamically more favorable. Furthermore, the effectiveness of the cold plate increases as the heat output of each server increases, suggesting that cold plates are most effective when removing a greater amount of heat.
Centrifugally Pumped Thermosiphons for Motor Rotor Cooling
Authors: McElhinney S. A. , Jahns T. M. , Shedd T. A.
Published: November 2015

This paper presents a detailed approach to provide improved cooling and heat spreading in electric machine rotors using centrifugally-pumped revolving thermosiphons. Design concepts are discussed that offer the following advantages: (1) high thermal performance across a wide range of operating points; (2) low-impedance heat paths; (3) excellent opportunities for integration with electric machine design for improved electromagnetic performance and structural design, as well as practical, cost-effective manufacturing. It takes advantage of centrifugal force to provide effective inertial pumping over a wide range of operating conditions. In addition, the new thermosiphon design is compatible with existing standard electric machine manufacturing techniques and cooling needs. A condenser section fin and ramp structure provides consistently high condensation performance. Surface texture design to promote effective nucleate boiling at high speeds is discussed, and fluid fill factor is analyzed. Applications include induction and PM synchronous machines. Benefits of these thermosiphons include increased steady-state power and torque density, increased and more consistent efficiency, and reduced permanent magnet volume and cost in PM synchronous machines. Other applications may include centrifugal gas compression, chemical processes, and machine tools.
Modeling of Flow and Heat Transfer in a Molten Glass Mini-Film for High Temperature Heat Collection in a Falling-Film Solar Central Receiver
Authors: Reed Ruth H. , Raade Justin , Elkin Benjamin , Carey Van P.
Published: November 2015

In concentrating solar power plants, there is a strong incentive to increase the collection temperature and the overall exergy efficiency of the system. Some molten glass mixtures are attractive working fluids for high temperature solar thermal heat collection because optimized glass mixtures can be more stable, less-toxic, and less-corrosive at high temperatures (≥1000 °C). A specific phosphate glass mixture is considered in this study to explore its performance in a molten glass falling film central receiver design for collection of heat at conditions resulting in a mini-film with a thickness equal or less than 3mm. In our falling molten glass thin film, the phosphate glass flow is treated as a laminar, Newtonian and gravity-driven flow over a slightly inclined flat plate using an explicit finite difference scheme to evaluate its heat transfer performance for a direct absorption receiver concept. One of the main challenges of modeling transport in molten glass is the strong dependence of its viscosity on temperature. To incorporate this effect in our numerical analysis, a temperature-dependent viscosity model is used in the momentum equation to model the fluid behavior as it flows down the surface and is progressively heated. Using viscosity versus temperature data provided by Halotechnics, Inc. for the phosphate glass considered here, an exponential function is used to model the viscosity as it changes with temperature. Also, a variable film thickness model is implemented that adjusts to the viscosity variation with temperature. In order to avoid stability issues, the finite difference scheme is organized in terms of non-dimensional parameters that includes all important properties that govern the system. The results of our model indicate that thinning of the film as it flows over the heated surface enhances the heat transfer performance on the lower portion of the receiver system. The heat transfer coefficient increases instead of remaining constant (as normally expected for fully developed laminar flows) on the lower portion of the heated surface. Our analytical results further indicate that using a thin mini-film of molten glass for solar thermal heat collection provides high heat transfer performance.
Performance and Integration Implications of Addressing Localized Hotspots Through Two Approaches: Clustering of Micro Pin-Fins and Dedicated Microgap Coolers
Authors: Green Craig E. , Kottke Peter A. , Sarvey Thomas E. , Fedorov Andrei G. , Joshi Yogendra , Bakir Muhannad S.
Published: November 2015

An evaluation of two approaches to localized hotspot cooling is conducted through both numerical modeling and experimental demonstration, with the advantages and limitations of each approach highlighted. The first approach, locally increasing the density of pins in a micro pin fin heat sink, was shown through numerical modeling to deliver a factor of two enhancement in effective heat transfer coefficient by doubling the pin density near the hotspot. This simpler approach to maintaining temperature uniformity eliminates the need for hotspot specific fluid routing and delivery, and also has minimal impact on the larger flow field. Dedicated hotspot coolers, on the other hand, have the ability to dissipate significantly larger heat fluxes while maintaining manageable pressure drops, because the flow rate to the dedicated cooler can be closely matched to the demands of the hotspot. Dissipation of hotspot heat fluxes in excess of 2 kW/cm2 is demonstrated experimentally using a two phase dedicated hotspot cooler. However, dedicated coolers require additional fluidic routing and manifolding to efficiently deliver the coolant to the hotspot. These integration concerns are considered in concert with the performance of the hotspot cooler itself to enable better informed thermal design for both system level and device level cooling.
Physics of Interfacial Heat Transfer Events in Flow Boiling of FC-72 Liquid in Microchannels
Authors: Bigham Sajjad , Moghaddam Saeed
Published: November 2015

This work examines the microscale physics of heat transfer processes in flow boiling of FC-72 in a single microchannel. Experimental results discussed in this paper provide new physical insight on the nature of heat transfer events. The study is enabled through development of a device with a composite substrate that consists of a high thermal conductivity material coated by a thin layer of a low thermal conductivity material with embedded temperature sensors. This novel arrangement enables measurement of local heat flux with a spatial resolution of 40–65 μm and a temporal resolution of 50 μs. The device generates isolated bubbles from a 300 nm in diameter artificial cavity fabricated at the center of a pulsed function micro-heater. Analysis of the temperature and heat flux data along with synchronized images of bubbles show that four mechanisms of heat transfer are active as a bubble grows and flows through the channel. These mechanisms of heat transfer are 1) microlayer evaporation, 2) interline evaporation, 3) transient conduction, and 4) micro-convection. The magnitude and time period of activation of these mechanisms of heat transfer are determined and their characteristics are discussed in details.
Design of the Next Generation Antenna Mounts
Authors: Savio Ruben Gregory Puthota Dominic , Gebrehiwot Betsegaw , Agonafer Dereje , Skrepcinski Al , Palmer Tom
Published: November 2015

Design of new antenna mount with low effective projected area (EPA) and high load carrying capacity for telecommunication towers is discussed in this paper. The main aim is to reduce the EPA of the mount against the wind pressure direction at the desired elevation from ground by reducing the mount frame structure parts compared to the previous mount designs used in the market. The model in itself has to withstand its dead weight, operator’s weight along with five antenna-radio units. The new model has been designed with a single horizontal frame and four supporting structure for EPA reduction and also the EPA is calculated through Image Processing using MATLAB tool which has not been done previously for mounting structures in the telecommunication field. The preliminary stress and deformation results calculated using ANSYS 15.0 tool and future work that has to be carried out for the design are also discussed in this paper.
Characterization of Doped SAC Solder Materials and Determination of Anand Parameters
Authors: Ahmed Sudan , Basit Munshi , Suhling Jeffrey C. , Lall Pradeep
Published: November 2015

In the electronic packaging industry, it is important to be able to make accurate predictions of board level solder joint reliability during thermal cycling exposures. The Anand viscoelastic constitutive model is often used to represent the material behavior of the solder in finite element simulations. This model is defined using nine material parameters, and the reliability prediction results are often highly sensitive to the Anand parameters.

In present work, three new doped lead free solder materials recommended for high reliability applications have been chemically analyzed and then mechanically tested in order to determine the nine Anand parameters. The alloys are referred to as Ecolloy (SAC_R), CYCLOMAX (SAC_Q), and Innolot by their vendors. The first two doped alloys (SAC_R and SAC_Q) were found to be composed of Sn, Ag, Cu, and a single X-element dopant. Such solders are commonly referred to as SAC-X in the literature. For the third material (Innolot), three different dopants are present along with Sn, Ag and Cu. The EDX method was used to determine the approximate chemical composition of the materials, and Bismuth (Bi) was found to be the X-additive for both SAC_R and SAC_Q. In addition, the SAC_R material was found to have no silver (Ag), which is the reason it is marketed as a low cost (economy) material.

The nine Anand parameters were determined for each unique solder alloy from a set of uniaxial tensile tests performed at several strain rates and temperatures. Testing conditions included strain rates of 0.001, 0.0001, and 0.00001 (sec−1), and temperatures of 25, 50, 75, 100, and 125 C. The Anand parameters were calculated from each set of stress-strain data using an established procedure that is described in detail in the paper. The mechanical properties and the values of Anand parameters for these new doped alloys were compared with those for standard SAC105 and SAC405 lead free alloys.

Although the SAC_R material does not have any silver, it was shown to have better mechanical behavior than SAC105 due to the presence of Bismuth (Bi) along with a little higher percentage of Copper (Cu). The SAC_Q and Innolot materials were shown to have significantly higher strength than SAC405. After deriving the Anand parameters for each alloy, the stress-strain curves have been calculated for various conditions, and excellent agreement was found between the predicted results and experimental stress-strain curves.
Non-Intrusive Case Temperature Measurement Method of Direct-Water-Cooled Power Module
Authors: Horiuchi Keisuke , Konishi Yuichiro , Nishihara Atsuo
Published: November 2015

In this paper, we present a non-intrusive case temperature measurement method of the direct-water-cooled power module. It uses the structure function, which in this case comprises the cumulative thermal capacitance and the cumulative thermal resistance. Since the effective heat transfer rate of the pinfin heatsink varies with the water flow rate, in this study we assumed the inflection point of the structure function corresponding to the change in the flow rate was junction-case thermal resistance. We compared numerical simulation results with experimental results and present our findings. Finally, we show that the design area in which the heat spreading angle of 45 degrees, the well-known rule of thumb, is suitable.
Boiling/Evaporation Characteristics of a Droplet on a Nano-Particles-Accumlated Bi-Porous Layer
Authors: Yuki Kazuhisa , Fukushima Katsuki , Suzuki Koichi
Published: November 2015

Boiling/evaporation characteristics of a water droplet on nanoparticles-accumulated bi-porous layers produced by boiling adhesion method are evaluated. In the boiling adhesion method, the bi-porous layer is coated by dropping or spraying nanoparticles-contained solution on a heated metal substrate. By this method, it is possible to produce nanoscale of pore layer formed by accumulating the nanoparticles that have high wettability and microscale of pores formed by boiling bubbles blowing through the layer that work as vapor discharging. Visualization experiments with a high speed camera clarify that the boiling/evaporation performance is improved on the nanoparticles bi-porous layer and also a wetting limit temperature drastically increases. Furthermore, there are many cases where the life time of the droplet shortens even in a low superheated temperature regime. These results suggest that the nanoparticles bi-porous layer would contribute not only to boiling heat transfer enhancement but also to the increase in the critical heat flux.
An Inverse Procedure for Estimating the Anand Viscoplastic Constitutive Model Parameters for Copper Free-Air Ball
Authors: Paranjothy Sai Sudharsanan , Subbarayan Ganesh , Jung Dae Young , Sammakia Bahgat G.
Published: November 2015

Due to its superior mechanical and electrical properties, as well as low cost, Cu is gradually replacing Au as wire bonding material. However, since copper is a stiffer material, it requires greater bonding force, which in turn increases risk of bond pad cratering and inter-layer dielectric (ILD) fracture. A critical challenge to numerically modeling the pad cratering or ILD fracture is the availability of appropriate constitutive models for the Cu free-air balls (FAB). In this work we first present rate and temperature dependent force-displacement response of micron-sized Cu FAB characterized using a custom-built high-precision microtester. From the experimental force-displacement data, Anand viscoplastic constitutive model parameters are obtained using an inverse finite element analysis procedure, where the material parameters are iterated through an automated procedure until the finite element and experimental force-displacement responses match. The constitutive model parameters to describe the FAB behavior at low and intermediate strain rates and at high temperatures are obtained and reported in this paper.
DiffCode: A System for the Simulation of Diffusion Driven Phase Evolution in Solids
Authors: Sadasiva Subramanya , Subbarayan Ganesh
Published: November 2015

Diffusion is an important mechanism for failure inducing phenomena in many applications. The common Pb-free solder alloys used in the current generation of electronics packages are complex multiphase multicomponent materials. As the scale of the solder joint decreases, it becomes increasingly important to account for the effect of surface phenomena such as grain boundary evolution, surface diffusion and interfacial reactions in the mechanics of the solder joints. The dynamics of these diffusion driven interfacial phenomena are affected by the state of stress and the electric current in the solid. The primary challenges to modeling the dynamics of evolution are the tracking of the interface while satisfying the boundary conditions for the bulk problem.

In previous work, the authors utilized the phase field method in conjunction with a commercial finite element code to study the effect of stress and electrical fields on the diffusion driven evolution of voids in solder interconnects. The utilization of commercial tools for the simulation of the stress, electrical and thermal fields allowed for the use of pre-existing meshes and allowed the study of electromigration failure in assemblies of solder joints. However, the use of commercial tools can be expensive and the options for parallel simulation are limited, restricting the size and complexity of the simulations.

In this work, the authors describe DiffCode, a parallel adaptive finite element code for three-Dimensional simulation of electromigration and stress migration driven failure due to void evolution and growth in solder as well as line interconnects using the phase field method. Several illustrative two-dimensional and three-dimensional electromigration driven void evolution simulations are demonstrated using the code.
Heat Transfer Characteristics of Self-Rewetting Fluid and its Application in Heat Pipe
Authors: Wang S. F. , Hu Y. X. , Zhou Y. , Zhang W.
Published: November 2015

Self-rewetting fluids (SRWFs) are non-azeotropic solutions enjoy a particular surface tension behavior — an increase in the surface tension with increasing temperature. Due to the unique property, the SRWF can spontaneously wet hotter region and enhance heat transfer. The interesting behavior makes the SRWF become the research hotspot in phase change heat transfer research field. To clarify the heat transfer characteristics of SRWF, a series of boiling experiments have been carried out by employing dilute heptanol aqueous solution as SRWF. It is found out that, the bubble size of the SRWF is much smaller than that of pure water, and the critical heat flux of SRWF is much higher than that of water, which is beneficial for application in heat pipes. To find out the heat transfer performance of SRWF in heat pipes, experimental studies are performed on oscillating heat pipe (OHP) consisting of 4 meandering turns, with heat transfer length (L) of 150 mm and inner diameter (Di) of 1.3 mm. Compared with the water, the SRWF exhibits much better thermal performance, which indicates that SRWF is a promising and useful working liquid for the application in high efficient cooling devices with micro structure.
Computational Modeling of Extreme Heat Flux Microcooler for GaN-Based HEMT
Authors: Lee Hyoungsoon , Won Yoonjin , Houshmand Farzad , Gorle Catherine , Asheghi Mehdi , Goodson Kenneth E.
Published: November 2015

This study explores an extreme heat flux limit of microcooler for GaN-based HEMTs (high electron mobile transistors) which have local power densities exceeding 30 kW/cm2 using both solid conduction simulation and single-phase/two-phase conjugate simulations. Solid conduction simulation models are developed for full geometry of the microcooler to account for the overall thermal resistances from GaN HEMT to working fluid. This allows investigating the temperature distribution of the suggested microcooler. Parametric studies are also performed to investigate the impact of geometries and heat transfer coefficients on the junction temperature. The solid conduction simulation results using COMSOL Multiphysics agree well with single-cell ANSYS Fluent simulation results.

Separately, fluid-solid conjugate CFD (Computational Fluid Dynamics) simulation models provide the detailed flow information in the microchannel using a single-channel geometry with symmetry boundary conditions. Single-phase CFD simulations obtain the lower bound of total pressure drop and heat transfer coefficient at the microchannel walls for a mass velocity range of G = 6000–24000 kg/m2-s. The local temperatures and velocity distributions are reported that can help with identifying the locations of the maximum velocity and recirculation regions that are susceptible to dryouts. Two additional alternative tapered inlet designs are proposed to alleviate the significant pressure loss at the entrance of the SiC channel. The impact of the tapered inlet designs on pressure drops and heat transfer coefficients is also investigated.

Two-phase simulations in microchannel are conducted using Volume-of-Fluid (VOF) method embedded in ANSYS Fluent to investigate two-phase flow patterns, flow boiling, and temperature distributions within the GaN HEMT device and SiC etched mircochannels. A user-defined function (UDF) accounts for the phase change process due to boiling at the microchannel walls. The results show that the time relaxation factor, ri has a strongly influence on both numerical convergence and flow solutions.
A Composite Cu/HOPG Heat Spreader for Immersion Cooling of High Power Chips
Authors: Suszko Arthur , El-Genk Mohamed S.
Published: November 2015

Presented are the results of a 3-D numerical analysis of a composite heat spreader for immersion cooling of a 20 × 20 mm microprocessor. The spreader is comprised of two 0.5 mm thick Copper (Cu) laments separated by a layer of highly ordered pyrolytic graphite (HOPG), 0.25–1.0 mm thick. The exposed surface of the top Cu lament has an average roughness, Ra = 1.79 μm and is cooled by saturation nucleate pool boiling of PF-5060 dielectric liquid. Investigate is the impact of δHOPG on the total power removed, the maximum temperature of the underlying chip, Tmax, and mitigating the chip hot spots. Increasing δHOPG increases the total power removed, but also increases Tmax. The spreader with a 1.0 mm-thick δHOPG is capable of removing 318 W, without exceeding 90% of the critical heat flux (CHF), at Tmax = 120°C. This power removal is significantly higher than that with an all Cu spreader of the same thickness of 90 W, but at much lower Tmax of 67°C. Composite spreaders with δHOPG = 0.25, 0.5, and 0.75 mm are capable of removing up to 160 W at Tmax = 85°C, 228 W at 100°C, and 292W at 115°C, respectively. The HOPG suppresses the transmission of hot spots to the spreader surface and increasing δHOPG does not mitigate the hot spots.
Numerical Investigation of Thermal Resistance in a Rectangular Flux Channel With Non-Uniform Heat Convection in the Sink Plane
Authors: Razavi Masood , Dehghani-Sanij Alireza , Muzychka Yuri S.
Published: November 2015

Thermal analysis of electronic devices is essential for designing thermal management systems and for assuring a perfect working condition. In order to have a precise thermal analysis, thermal spreading resistance should be calculated. In this paper, a numerical study is conducted on the thermal resistance of a 2D flux channel with a non-uniform convection coefficient in the heat sink plane. For this purpose, the Finite Volume Method (FVM) is used. As a case study, a 2D flux channel with a discrete specified heat flux and convection edges is assumed. Also, the heat transfer coefficient in the sink boundary condition is determined symmetrically using a hyperellipse function. This function can model a wide variety of different distributions of a heat transfer coefficient from a uniform cooling to the most intense cooling in the central region. All results are compared and validated with the COMSOL commercial software package. The proposed method is useful for thermal engineers for modeling different flux channels with different properties and boundary conditions such as the variable heat transfer coefficient.
Mechanical Constitutive Properties of Two High-Temperature Lead-Rich Solders
Authors: Jiang Qian , Mukherjee Subhasis , Vogt Bastian , Dasgupta Abhijit , Shaddock David , Yin Liang
Published: November 2015

This study focuses on the mechanical properties of two kinds of solders for high temperature interconnections (melting temperature above 280 °C after reflow). They are both lead-rich solders in wire form: 93.5Pb/5Sn/1.5Ag and 92.5Pb/5Sn/2.5Ag. The mechanical constitutive tests conducted in this study include: (i) monotonic elastic-plastic stress-strain response at constant strain rates and constant temperatures; and (ii) isothermal, viscoplastic creep strain response at several constant stress levels and different temperatures. The sensitivities of the material viscoplastic constitutive response to temperature, loading rate and stress level were systematically studied, so that the mechanical performance of these two solders could be compared with those of other solders, at similar test conditions. Both the Pb-rich solders studied had statistically similar behavior at the tested stress levels and temperatures in creep tests. The Ramberg-Osgood model and the Garofalo model were used to represent the elastic-plastic and creep behavior, respectively, of each solder and the corresponding model constants are presented in the paper.
Design Considerations of Packaging a High Voltage Current Switch
Authors: De Ankan , Morgan Adam , Bhattacharya Subhashish , Hopkins Douglas C.
Published: November 2015

In this paper an attempt has been made to demonstrate various package design considerations to accommodate series connection of high voltage Si-IGBT (6500V/25A die) and SiC-Diode (6500V/25A die). The effects of connecting the cathode of the series diode to the collector of the IGBT versus connecting the emitter of the IGBT to the anode of the series diode has been analyzed in regards to gate terminal operation and the parasitic line inductance of the structure. ANSYS Q3D/MAXWELL software have been used to analyze and extract parasitic inductance and capacitances in the package along with electromagnetic fields, electric potentials, and current density distributions throughout the package for variable parameters. SIMPLIS-SIMETRIX is used to simulate typical switch behavior for different parasitic parameters under hard switched conditions. Various simulation results have then been used to redesign and justify the optimized package structure for the final current switch design. The thermal behavior of such a package is also conducted in COMSOL in order to ensure that the thermal ratings of the power devices is not exceeded, and to understand where potentially harmful hotspots could arise and estimate the maximum attainable frequency of operation. The main motivation of this work is to enumerate detailed design considerations for packing a high voltage current switch package.
Morphological Impact on Thermal Interface Resistance of Self Catalyzing Fecralloy MWNT TIMs
Authors: Longson Timothy J. , Maddocks James , Kashani Ali
Published: November 2015

Self catalyzing Fecralloy substrates are investigated as a growth substrate for Multi-walled Carbon Nanotubes (MWNT) Thermal Interface Materials (TIMs). Fecralloy is used without any additional catalyst and with minimal surface preparation to grow double-sided MWNT TIM assemblies. The growth behavior is studied by way of the array morphologies, i.e. array height, density, crystallinity, and diameter distribution. The effects of growth temperature and time are used to observe the growth kinetics, showing a bimodal growth rate with temperature and an optimal growth rate at 725°C with a noticeable onset of amorphous carbon at higher temperatures. The contact resistance of dozens of such samples are evaluated using a DC, 1D reference bar, thermal conductivity measurement system. Temperature and pressure dependent measurements offer insight into the interfacial phonon conduction physics and elastic deformation mechanics of the CNTs tips respectively. Due to the challenges associated with deliberately controlling a single array morphology, a multivariate, statistical approach is used to observe the trends of contact resistance. The contact resistance shows the strongest correlation with array height, following a R ∼= L−0.5, which contradicts Fourier’s law. However, this is likely a result of the mechanical compliance rather than a ballistic conduction mechanism. Finally, several attempts were made at modeling the relationship between the measured array morphologies and the contact resistance. However, the modeling is relatively unsuccessful, forcing one to rely on the empirical relations found in the exploratory data analysis.
Pre-Applied Inter Chip Fill for 3D-IC Chip Joining
Authors: Kawase Yasuhiro , Ikemoto Makoto , Sugiyama Masaya , Yamamoto Hidehiro , Kiritani Hideki
Published: November 2015

Three dimensional integrated circuits (3D-IC) have been proposed for the purpose of low power and high performance in recent years. Pre-applied inter chip fill is required for fine pitch interconnections, large chips, and also thin chips. In addition to them, pre-applied joining process with high thermal conductive inter chip fill (HT-ICF) is strongly required for the cooling of 3D-IC. Some kinds of matrix resins and thermal conductive fillers were simulated and evaluated for pre-applied ICF. As a result, matrix and cure agent appeared to be important to both pre-applied ICF process compatibility and thermal conductivity, so that we’d selected epoxy type matrix based on controlling super molecular structure due to its mesogen unit. And not only matrix but also filler appeared to be the key to improve thermal conductivity for pre-applied ICF at the same time. The thermal conductivity of conventional silica filler was only 1W/mK, so that, taking into account of thermal conductivity, density and its stability, we’d selected aluminum oxide and boron nitride as thermal conductive filler and optimized HT-ICF for pre-applied process. After composite was mixed and cured, some physical properties were measured and thermal conductivity was 1.8W/mK, CTE was below 21ppm/K and Tg was 120°C. Furthermore, new high thermal conductive filler was also studied. We’d synthesized completely new spherical BN (diameter <5um) and applied it to HT-ICF and the thermal conductivity was almost two times higher than conventional BN. In this study, we confirmed ICF physical characteristics and its pre-applied joining for 3D-IC and void-less joining was also discussed.
A Numerical Study on the Thermal Conductivity of Hybrid-Filler-Nanoparticle Composite Materials
Authors: Ngo Ich-Long , Byon Chan
Published: November 2015

Augmenting the thermal conductivity of polymer materials is actively being attempted by adding one or more fillers with higher thermal conductivity into matrix materials. In this study, the effective thermal conductivity of composite materials was investigated numerically under the effects of the thermal conductivity ratio between two particle fillers and the matrix material, and the particle volume fractions. The results indicate that the effective thermal conductivity of composites containing hybrid filler is higher than that of single filler. The effective thermal conductivity increases with the increase of thermal conductivity ratio between two fillers in general when this ratio is less than unity, and the maximum effective thermal conductivity approaches when this ratio is less than and close to unity. However, this trend is changed when this ratio is greater than unity. Based on the results, a generalized correlation is proposed as a function of four non-dimensional parameters. The results obtained in this study can be widely utilized for predicting the thermal conductivity of hybrid-filler-nanoparticle composite materials.
Numerical Analysis of Allowable Current Density for Electromigration of Interconnect Tree Structure With Reservoir
Authors: Fujisaki Kazuhiro , Narita Hikaru , Sasagawa Kazuhiko
Published: November 2015

The high current density induces electromigration (EM) in metal lines used for electric wirings in integrated circuits. The growth of voids formed by EM in the line material leads to the line failure. Recently, multilevel interconnections are widely used in the circuit in electronics devices and MEMS. Metal lines aligned on upper and lower layer are connecting through the vias in the multilevel interconnections. The reservoir structure is often constructed in the line structure to prevent the EM damages. There is a threshold current density relating to the EM damage of the lines in the interconnection with vias. It is important to evaluate the threshold value for determination of an allowable electric current of the line. In this study, a numerical simulation technique for analyzing the atomic density distributions in the line material under high current density was used to evaluate the EM risks of metal lines in the several cases of interconnect tree structure with reservoir. The thresholds of current density leading to EM damage were calculated in the simulations considering the reservoir locations and pattern of electric current flow in the tree.
Reliable Integration of Microchannel Coolers for Power Electronics
Authors: Squiller David , Khanna Sumeer , Dessiatoun Serguei , Mandel Raphael , Ohadi Michael , McCluskey Patrick
Published: November 2015

Power electronic modules are exhibiting ever increasing power density as a result of compound semiconductor devices being placed in packages of decreasing size. This has led, in turn, to higher volumetric heat generation, which is driving the development of advanced thermal management approaches, including integration of single and two-phase microchannel coolers into the power electronics package. Reliable integration and operation of these coolers is essential for maintaining the performance and reliability of the power electronic system as a whole. This paper will present models for the critical failure mechanisms in microchannel coolers, including erosion/corrosion and cooler fracture.
Correlated OLED Thermal Modeling Methods and Thermal Design Recommendations
Authors: Ruiz Carin Lundquist
Published: November 2015

Cutting edge tablet and phone designs are increasingly utilizing OLED (Organic Light Emitting Diode) displays. Although these displays are very thin and have excellent picture quality, they come at the cost of higher power than traditional displays which presents new thermal challenges. For thermal purposes, there are essentially 2 basic types of OLED displays based on their power distribution. In this presentation, I show thermal modeling methods I developed for both types of OLED displays and show the successful correlation of these models to experimental results. In addition, this presentation discusses some of the unique structural design requirements with OLED displays and ways to integrate both the thermal and structural solutions into an elegant combined solution. A thermal engineer can use the simulation methods and design recommendations described in this presentation to enable integration of this technology into products at an early stage of the design process.
Reliability of Interconnections Made of Sintered Silver Nano Particles
Authors: Matkowski Przemyslaw K. , Falat Tomasz , Moscicki Andrzej
Published: November 2015

This study investigates the effect of silver paste composition on reliability of sintered silver interconnections. The interconnections are formed between SMD 1206 chip jumpers and electroless nickel immersion gold (ENIG) coating of FR4 printed circuit board (PCB) solder pads. They are made of pastes that vary in their composition (various proportions of micro and nano particles). The sintering process was conducted in convective oven. After the process the interconnections were subjected to X-Ray inspection in order to characterize the structure of interconnections (presence of voids, total surface of interconnection etc.). During accelerated reliability tests the PCBs were subjected to combined temperature cycling and vibration loading. During the tests daisy chains of interconnections were connected to dedicated programmable multichannel event detector developed in LIPEC lab. The event detector is able to detect and store information about object condition based on the real-time resistance measurements and applied novel algorithm of event detection. Failure modes were confirmed by using X-Ray computed tomography. The paper presents results of comparative Weibull analysis.
Analysis of Intermetallic Formation During Ultrasonic Ball Bonding
Authors: Sepehrband Panthea , Gholamirad Maryam
Published: November 2015

During ultrasonic ball bonding of copper wire to aluminum pad, the two alloys are joined over an immensely short period of time (<100ms), at a relatively low temperature (< 200°C). Bond formation in such condition is related to accelerated diffusional processes and formation of intermetallic compounds (IMC). Despite the industrial importance of the phenomenon, the micro-mechanism of IMC formation is not clearly understood, nor deeply studied. One of the main barriers toward understanding the phenomena is the limited capability of experimental analysis for analyzing processes occurring over short period of time. In this research, a combination of theoretical analysis and finite element simulation is used to investigate the mechanisms that lead to diffusion enhancement and, as a result, IMCs formation.
A Hybrid Absorption Cycle for Water Heating, Dehumidification, and Evaporative Cooling
Authors: Chugh Devesh , Nasr Isfahani Rasool , Gluesenkamp Kyle , Abdelaziz Omar , Moghaddam Saeed
Published: November 2015

In this study, development of a novel system for combined water heating, dehumidification, and space cooling is discussed. The system absorbs water vapor from an air stream into an absorbent. The latent heat of absorption, released into the absorbent, is transferred into the process water that cools the absorbent. The solution is regenerated in the desorber, where it is heated by a heating fluid. The water vapor generated in the desorber is condensed and its heat of phase change is also transferred to the process water. The condensed water is then used in an evaporative cooling process to cool the dehumidified air exiting the absorber. Essentially, this open-absorption cycle collects space sensible heat and transfers it to hot water. Another novel feature of the cycle is recovery of the heat energy from the solution exiting the desorber by heat exchange with process water rather than with the solution exiting the absorber. This approach has enabled heating the process water from an inlet temperature of 15°C to 57°C (conforming to the required DOE building hot water standard) and compact fabrication of the absorber, solution heat exchanger, and desorber in plate and frame configuration. The system under development currently has a water heating capacity of 1.5 kW and a thermal coefficient of performance (COP) of 1.45.
Investigations on Crack-Like Leaks in Piping
Authors: Bläsius Christoph , Heckmann Klaus , Sievers Jürgen
Published: November 2015

Methods to demonstrate break preclusion for pressure retaining components in nuclear power plants are summarized in the newly developed German safety standard KTA 3206, especially the requirements for the leak-before-break assessment of crack-like leaks. In this context numerical and simplified calculation methods for both the leak opening area and fluid flow rates of crack-like leaks were examined and validated on selected experiments.

Second topic of the paper is an accident analysis for a postulated leak in form of a through-wall crack in the pressurizer surge line (SL) of a German PWR Konvoi type. The initial size of the leak as well as the changing size depending on system pressure and temperature during the postulated leak accident was calculated with a FEM analysis model of a cooling loop. The reduction of the leak area amounts in the examined transient to ca. 25 % after 1 h and leads also to an approximately 23 % smaller leak rate. These results depend on the assumed position of the leak and on the initial leak size. Therefore, the results of accident analyses due to postulated leaks can be influenced by the change of the leak size during the course of the accident.
A Rational Methodology for Determination of Service Life for a Delayed Coker Drum
Authors: Aumuller John J. , Chen Jie , Carucci Vincent A.
Published: November 2015

Delayed unit coker drums operate in a severe service environment that precludes long term reliability due to excessive shell bulging and cracking of shell joint and shell to skirt welds. Thermal fatigue is recognized as the leading damage mechanism and past work has provided an idealized description of the thermo-mechanical mechanism via local hot and cold spot formation to quantify a lower bound life estimate for shell weld failure.

The present work extends this idealized thermo-mechanical damage model by evaluating actual field data to determine a potential upper bound life estimate. This assessment also provides insight into practical techniques for equipment operators to identify design and operational opportunities to extend the service life of coke drums for their specific service environments.

A modern trend of specifying higher chromium and molybdenum alloy content for drum shell material in order to improve low cycle fatigue strength is seen to be problematic; rather, the use of lower alloy materials that are generally described as fatigue tough materials are better suited for the high strain-low cycle fatigue service environment of coke drums. Materials such as SA 204 C (C – ½ Mo) and SA 302 B (C – Mn – ½ Mo) or SA 302 C (C – Mn – ½ Mo – ½ Ni) are shown to be better candidates for construction in lieu of low chromium alloy steel materials such as SA 387 grades P11 (1¼ Cr – ½ Mo), P12 (1 Cr – ½ Mo), P22 (2¼ Cr – 1 Mo) and P21 (3 Cr – 1 Mo).
Flutter Analysis and Experiments of a Rectangular Sheet Supported by a Wire
Authors: Hiroaki Keiichi , Watanabe Masahiro , Morita Ryosuke
Published: November 2015

This paper deals with a flutter analysis of a rectangular sheet supported by a wire in axial flow. In the flutter analysis, Doublet-point method based on the unsteady lifting surface theory is used to calculate the unsteady fluid force acting on the sheet surface. The equation of motion of the sheet supported the wire with tension is derived by using the finite element method. The flutter velocity and mode of the sheet are examined through the root locus of the flutter determinant of the system with changing the flow velocity. In this study, experiments are conducted and compared with the analytical results. The flutter velocity, its mode, and the local work by the fluid force acting on the sheet surface with changing tension of wire are determined. Moreover, the effects of boundary condition on flutter characteristic are determined. As the tension of the wire becomes higher, the flutter velocity and its frequency increase. Traveling-wave mode flutter occurs to the sheet when the flow velocity becomes higher. In the case of lower tension of the wire, the amplitude of the flutter mode at the upstream end is large. The local work done by the fluid force around the center of the sheet is positive, and that near the downstream end of the sheet is negative. Moreover, local work on the sheet surface and flutter mode for different boundary condition depend on dominant mode contribute to flutter mode.
Joining Tube to Tube Sheet for Coil Wound Heat Exchangers by Hybrid Friction Diffusion Bonding
Authors: Roos Arne , Alba Diego R. , Hanke Stefanie , Wimmer Georg , dos Santos Jorge F.
Published: November 2015

Coil-wound heat exchangers (CWHE) for low temperature applications such as the liquefaction of natural gas (LNG) are often made of aluminium alloys. The fabrication of these aluminium coil-wound heat exchangers holds several challenges, one of which is joining the tubes to the tube sheet. For this specific task, conventional joining technologies such as laser beam welding (LBW) or tungsten inert gas (TIG) welding cannot be easily performed in fully-mechanised mode or are not cost-effective. A joint project between the Helmholtz-Zentrum Geesthacht (HZG) and LINDE Engineering aims at the development of a new solid state joining process, Hybrid Friction Diffusion Bonding (HFDB), to fabricate tube-to-tube-sheet connections for aluminium coil-wound heat exchangers. In the present study, the HFDB process has been developed to industrial maturity and the quality of the joints has been demonstrated by gas leak tightness tests and tensile pull-out tests. The joints meet the requirements for industrial application. Furthermore, the thermal field development in the weld area and the applied process forces have been monitored and correlated to process parameters. The microstructure of the joint has been investigated, and dynamic recrystallization is assumed to be the primary grain refinement mechanism in the thermomechanically affected zone.
Probabilistic Fracture Mechanics Evaluations That Consider Nozzles in the Extended Beltline Region of Reactor Pressure Vessels
Authors: Stevens Gary L. , Kirk Mark T. , Dickson Terry
Published: November 2015

For many years, ASME Section XI committees have discussed the assessment of nozzle penetrations in various flaw evaluations for reactor pressure vessels (RPVs). As summarized in Reference [1], linear elastic fracture mechanics (LEFM) solutions for nozzle penetrations have been in use since the 1970s. In 2013, one of these solutions was adopted into ASME Code, Section XI, Nonmandatory Appendix G (ASME App. G) [2] for use in developing RPV pressure-temperature (P-T) operating limits. That change to ASME App. G was based on compilation of past work [3] and additional evaluations of fracture driving force [4][5].

To establish the P-T limits on RPV operation, consideration should be given to both the RPV shell material with the highest reference temperature as well as regions of the RPV (e.g., nozzles, flange) that contain structural discontinuities. In October 2014, the U.S. Nuclear Regulatory Commission (NRC) highlighted these requirements in Regulatory Issue Summary (RIS) 2014-11 [6].

Probabilistic fracture mechanics (PFM) analyses performed to support pressurized thermal shock (PTS) evaluations using the Fracture Analysis Vessels Oak Ridge (FAVOR) computer code [7] currently evaluate only the RPV beltline shell regions. These evaluations are based on the assumption that the PFM results are controlled by the higher embrittlement characteristic of the shell region rather than the stress concentration characteristic of the nozzle, which does not experience nearly the embrittlement of the shell due to its greater distance from the core. To evaluate this assumption, the NRC and the Oak Ridge National Laboratory (ORNL) performed PFM analyses to quantify the effect of these stress concentrations on the results of the RPV PFM analyses. This paper summarizes the methods and evaluates the results of these analyses.