bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Diamond Microfluidics-Based Intra-Chip Cooling Technology for GaN
Authors: Altman David H. , Gupta Anurag , Tyhach Matthew
Published: November 2015

GaN on Diamond has been demonstrated to enable notable increases in RF power density without impacting High Electron Mobility Transistor (HEMT) peak junction temperature. However, Monolithic Microwave Integrated Circuits (MMICs) fabricated using GaN on Diamond substrates are subject to the same packaging thermal limitations as their GaN on SiC counterparts. Therefore, efforts to exploit GaN on Diamond to achieve substantial increases in MMIC power are stymied by external packaging thermal resistances that characterize the current “remote cooling” paradigm. This paper explores an intra-chip cooling alternative to the “remote cooling” paradigm, eliminating various heat spreader, heat sink and thermal interface layers in favor of integral microfluidic cooling in close proximity to the device junction. We describe an intra-chip cooling structure comprised of GaN on Diamond with integral micro-channels fed using a Si fluid distribution manifold. This structure exploits GaN on Diamond substrate technology to support increased HEMT areal power density while employing diamond microfluidics to affect scalable, low thermal resistance die-level heat removal. Thermal-electrical-mechanical co-design of integrated circuit (IC) features is performed to optimize conjugate heat transfer performance and manage the electrical and mechanical impacts associated with the presence of fluidic cooling near the electrically active region of the device. Through this, MMICs with significantly greater RF output than typical of the current state-of-the-art (SoA), dissipating die and HEMT heat fluxes in excess of 1 kW/cm2 and 30 kW/cm2, respectively, can be operated with junction temperatures that support reliable operation. The modeling, simulation and micro-fabrication results presented here demonstrate the potential of diamond microfluidics-based intra-chip cooling as a means to alleviate thermal impediments to exploitation of the full electromagnetic potential of GaN.
3-D Antenna Structures Using Novel Direct-Write Additive Manufacturing Method
Authors: Rahman Md Taibur , Panat Rahul , Heo Deuk
Published: November 2015

Sub-mm wavelength 3-D antennas are emerging as critical elements for ultrafast data transfer for various applications. The inherent 2-D nature of lithographic processes severely limits the available manufacturing routes to fabricate such antennas. In this work, we demonstrate a novel additive manufacturing method to fabricate 3-D metal-dielectric antenna structures at sub-mm length scale. A UV curable dielectric is dispensed from an Aerosol Jet system and instantaneously cured to form complex 3-D shapes. A metal nano particle ink is then dispensed over the 3-D dielectric, also by the Aerosol Jet technique, followed by thermal sintering. This novel method opens up the possibility of fabricating an entirely new class of 3-D antenna structures at sub-mm length scales.
Orientation Effects on Thermal Performance of Radial Heat Sinks Subject to Natural Convection
Authors: Li Bin , Byon Chan
Published: November 2015

Numerical study is carried out on natural convection heat transfer from three radial heat sinks subject to the influence of orientation. A finite volume method (FVM) numerical model was used to analyze the thermal performance of the radial heat sinks under upward, sideward and downward orientations. The effects of orientation with respect to gravity, fin number (15–30), the thickness of concentric ring (0.15–0.60) and Elenbaas number (15–55) on Nusselt number are investigated. Numerical results indicate that radiation is non-negligible in this study due to its high influence on thermal performance. The Nusselt number is relatively insensitive to the smaller ring thickness. The sideward facing orientation yields the worst thermal performance despite fin number changing. It is found that the thermal performance of heat sinks in upward and downward orientations depend on the number of fins significantly.
Hybrid Mini/Micro-Channel Heat Sink Using Liquid Metal and Water as Coolants
Authors: Mei Sheng-Fu , Deng Zhong-Shan , Liu Jing
Published: November 2015

The recent years have witnessed the tremendous development in electronics with high power density, such as highly integrated chips and high power LEDs. As a result, the continuous increase in power consumption of electronics is gradually leading to an urgent need for high performance cooling strategies. Among the existed cooling methods, liquid cooling has been proved to be a kind of effective cooling technology for the removal of a large amount of heat from high power devices. Traditional liquid cooling technique commonly refers to utilizing water as the coolant, which is low cost and owns a relatively higher specific heat capacity, however, lower convective coefficient. On the contrary, liquid metal owns much higher convective coefficient, however, lower specific heat capacity. In addition, the higher cost of liquid metal also limits its utilization with large quantity in electronic cooling areas. In this study, a hybrid mini/micro-channel heat sink, based on both of liquid metal and water, was demonstrated. The new system combines the advantages of the two coolants. Experimental studies were conducted to evaluate the capability of the cooling performances of the hybrid system under different operation conditions, including different flow rates, flow directions, pump failure and thermal shock. The experimental results indicate that the hybrid mini/micro channel heat sink owns better cooling performance than water-based heat sink.
Design Space Exploration of 3D CPUs and Micro-Fluidic Heatsinks With Thermo-Electrical-Physical Co-Optimization
Authors: Serafy Caleb , Srivastava Ankur , Bar-Cohen Avram , Yeung Donald
Published: November 2015

Three-dimensional integration (3D IC) is a new technology that shows great potential for high performance and energy efficiency. However past work has shown that 3D ICs suffer from serious thermal issues, and advanced cooling solutions such as micro-fluidic cooling are necessary to realize the true potential of these systems. The interactions between thermal, electrical and physical aspects of a 3D design with micro-fluidic cooling are substantial, and a comprehensive co-design approach to address them simultaneously is a must. Such co-design techniques are required throughout the design process, including during architectural design space exploration (DSE) in order to ensure that optimal design choices are not overlooked. In this paper we propose a DSE framework for 3D CPUs with micro-fluidic cooling that applies electro-thermal optimization techniques to the circuit layout and the heatsink design. By considering such physical optimization techniques we provide a more accurate view of a 3D architecture’s thermal and timing feasibility, as well as its performance and energy efficiency. Using our proposed thermo-electrical-physical co-design DSE framework we are able to improve performance by 1.54x and energy efficiency by 1.26x.
Embedded Two-Phase Cooling of Large 3D Compatible Chips With Radial Channels
Authors: Schultz Mark , Yang Fanghao , Colgan Evan , Polastre Robert , Dang Bing , Tsang Cornelia , Gaynes Michael , Parida Pritish , Knickerbocker John , Chainer Timothy
Published: November 2015

Thermal performance for embedded two phase cooling using dielectric coolant (R1234ze) is evaluated on a ∼20 mm × 20 mm large die. The test vehicles incorporate radial expanding channels with embedded pin fields suitable for through-silicon-via (TSV) interconnects of multi-die stacks. Power generating features mimicking those anticipated in future generations of processor chips with 8 cores are included. Initial results show that for the types of power maps anticipated, critical heat fluxes in “core” areas of at least 350 W/cm2 with at least 20 W/cm2 “background” heating in rest of the chip area can be achieved with less than 30 °C temperature rise over the inlet coolant temperature. These heat fluxes are significantly higher than those seen for relatively long parallel channel devices of similar base channel dimensions. Experimental results of flow rate, pressure drop, “device,” and coolant temperature are also provided for these test vehicles along with details of the test facility developed to properly characterize the test vehicles.
Thermal-Mechanical Impact of Thermal Solutions in Handheld Devices
Authors: Harirchian Tannaz , Liang Zuyang Frank , Yazzie Kyle , Schroeder Michael A. , Gupta Ashish , Mcallister Alan C.
Published: November 2015

Use of Thermal Interface Materials (TIM) is a common thermal solution approach in handheld devices to reduce junction temperature and control device skin temperature. This work summarizes the thermal benefits of using a TIM for enhancing the user experience and increasing System on Chip (SoC) performance. On the other hand, TIM induces a load on the package which in turn can impose stress on the package solder joints. This paper explains the impact of a variety of parameters such as TIM material and thickness and system boundary conditions on thermal performance of the SoC/system and the load distribution on solder joints. The complexity of mechanical load distribution is discussed through extensive data collection and simulation in phone and tablet form factors. Design guidelines for selection of appropriate TIM are proposed to improve the thermal performance without compromising the reliability of the SoC package.
Electrical-Thermal-Reliability Co-Design for TSV-Based 3D-ICs
Authors: Lu Tiantao , Srivastava Ankur
Published: November 2015

This paper presents an electrical-thermal-reliability co-design technique for TSV-based 3D-ICs. Although TSV-based 3D-IC shows significant electrical performance improvement compared to traditional 2D circuit, researchers have reported strong electromigration (EM) in TSVs, which is induced by the thermal mechanical stress and the local temperature hotspot. We argue that rather than addressing 3D-IC’s EM issue after the IC designing phase, the designer should be aware of the circuit’s thermal and EM properties during the IC designing phase. For example, one should be aware that the TSVs establish vertical heat conduction path thus changing the chip’s thermal profile and also produce significant thermal mechanical stress to the nearby TSVs, which deteriorates other TSV’s EM reliability. Therefore, the number and location of TSVs play a crucial role in deciding 3D-IC’s electrical performance, changing its thermal profile, and affecting its EM-reliability. We investigate the TSV placement problem, in order to improve 3D-IC’s electrical performance and enhance its thermal-mechanical reliability. We derive and validate simple but accurate thermal and EM models for 3D-IC, which replace the current employed time-consuming finite-element-method (FEM) based simulation. Based on these models, we propose a systematic optimization flow to solve this TSV placement problem. Results show that compared to conventional performance-centered technique, our design methodology achieves 3.24x longer EM-lifetime, with only 1% performance degradation.
Micro-Feature Heat Exchanger Using Variable-Density Arrays for Near-Isothermal Cold Plate Operation
Authors: Gallandat Noris , Hesse Danielle , Mayor J. Rhett
Published: November 2015

The purpose of this paper is to demonstrate the possibility to selectively tune the convective heat transfer coefficient in different sections of a heat sink by varying the density of micro-features in order to minimize temperature gradients between discrete heat sources positioned along the flow path. Lifetime of power electronics is strongly correlated to the thermal management of the junction. Therefore, it is of interest to have constant junction temperatures across all devices in the array. Implementation of micro-feature enhancement on the convective side improves heat transfer due to an increase in surface area. Specific shapes such as micro hydrofoils offer a reduced pressure drop allowing for combined improvement of heat transfer and flow performance. This study presents experimental results from an array of three discrete heat source (20 × 15 mm) generating 100 W/cm2 and positioned in line along the flow path with a spacing of 10 mm between each of the sources. The heat sink was machined out of aluminum 6061 and micro-hydrofoils with a characteristic length of 500 μm were embedded in the cold plate. The cooling medium used is water at a flow rate of 3.6–13.4 g/s corresponding to a Reynolds number of 420–1575. It is demonstrated that the baseplate temperature can be maintained below 90°C and the difference between the maximum temperatures of each heat source is less than 6.7 °C at a heat flux of 100 W/cm2 and a water flow rate of 4.8 g/s.
Harvesting CPU Waste Heat Through Pyroelectric Materials
Authors: Lee Soochan , Singh Nishant , Phelan Patrick E. , Wu Carole-Jean
Published: November 2015

Modern CPUs generate considerable wasted heat due to increased power dissipation from high-performance computation. Lots of research effort has extensively focused on using thermoelectric generators (TEGs) to harvest CPU waste heat to increase overall system energy efficiency. To harvest waste heat using TEGs requires a significant temperature differential between the processor as a heat source and the heat spreader/heat sink, as well as a high heat flow. However, the heat-to-electricity conversion efficiency is typically limited to 15 to 20 percent, due to large heat conductivity, low Seebeck coefficient, and low figure of merit of TEGs. In addition, TEGs on a CPU could significantly increase CPU junction temperature compared to the baseline CPU temperature due to its high thermal resistance. Contrary to using TEGs to harvest waste heat from a fixed, spatial temperature differential, this paper presents an approach to harvest CPU waste heat using pyroelectric (PE) materials from the time-varying, temporal temperature differential that is common in current processors. PE materials can generate electricity when subjected to a temporal temperature gradient. The operation of PE materials is distinctly different from TEGs and they have the following advantages. First, the theoretical efficiency is up to 50% using thin films. Second, the overall optimization of PE material is easier than thermoelectric material, since the conversion ratio, the ratio of net harvested energy divided by the heat taken from the hot reservoir, of PE material is independent of the material properties, whereas that of TEG is highly dependent on material properties. Although PE material is also a long-researched energy harvesting material, it is less explored by researchers compared to TEG in the application domain of processor waste heat management. In this paper, we review current PE materials in terms of pyroelectric coefficient and thermal conductivity, and also investigate the harvested power generation from CPU waste heat in a modern computing system.
Advanced Cooling Designs for GaN-on-Diamond MMICs
Authors: Campbell Geoffrey , Eppich Henry , Lang Keith , Creamer Carlton , Yurovchak Thomas , Chu Kanin , Kassinos Adonis , Ohadi Michael , Shooshtari Amir , Dessiatoun Serguei
Published: November 2015

Under the DARPA-sponsored ICECool Applications program, a microchannel cooling system using a 50-50 ethylene glycol-water mixture was optimized for cooling a high-power GaN-on-Diamond Monolithic Microwave Integrated Circuit (MMIC). Automated multi-objective optimization of the microchannel passages yielded an optimized design with a predicted thermal resistance of 22.4 K·cm2/kW at a pressure drop of only 121.4 kPa for an inlet temperature of 40°C. These values were corroborated by a coupled thermofluid analysis that included a detailed treatment of both the gate region and microchannel cooling geometry. Several versions of prototype coolers were fabricated, with one set consisting of pairs of coolers joined at their heated faces. These cooler pairs were used in heat exchange tests to characterize the average thermal resistance and the flow performance of the coolers. The performance testing results were consistent with the analytic predictions. Based on the analytical and experimental results, the system may be operated at inlet temperatures as high as 65°C without exceeding the transistor junction temperatures of 240 °C required for 106 hour mean-time-to -failure. The higher inlet temperature ameliorates system penalties associated with rejection of waste heat to ambient heat sinks.
Creating a Calibrated CFD Model of a Midsize Data Center
Authors: Pardey Zachary M. , VanGilder James W. , Healey Christopher M. , Plamondon David W.
Published: November 2015

Calibrating a CFD model against measured data is the first step to successfully utilizing this technology for change-management and the optimization of an existing data center. To date, there has been very little published on this calibration process; more focus has been placed on the use of CFD at the design stage and the development of modeling techniques and solvers. Further, few studies which feature comprehensive comparisons of CFD-predicted and measured data have been published for real data centers, and many that have, demonstrated only modest agreement at best. This study provides another such comparison — for a 7,400 ft2 (687 m2), 138-rack, raised-floor facility. The goals of the study are to benchmark the level of agreement that can be practically obtained and also to investigate the level of modeling detail required. Additionally, specific practical advice covering both CFD modeling and experimental measurements is provided. A plenum-only CFD model is compared to measured tile airflow rates and a room-model, which uses measured tile flow rates as boundary conditions, is compared to temperatures measured at each rack inlet. The level of agreement is among the best published to date and demonstrates that a CFD model can be adequately calibrated against measured data and is of value for ongoing data center operation.
A Model to Guide Template-Based Nanoparticle Printing Development
Authors: Rolfe David A. , Dorsey Kristen L. , Cheng Jim C. , Pisano Albert P.
Published: November 2015

Advective molding in vapor-permeable templates is an evaporation-driven process for submicron molding of nanoparticles with high fidelity. In this process, nanoparticle ink is drawn through channels in a vapor permeable template. The ink solvent is sorbed into the channel walls and evaporated through the template. As the complexity (e.g., width variation and turns in a channel) of the desired features increases, so does the likelihood of incompletely patterned nanoparticles. Patterning difficulties arise from dry-out, a condition where the nanoparticle ink dries before reaching the end of the channel and blocks the flow of more ink. Predicting dry-out during the template development stage is a critical step in patterning complex features. In this work, we present a method for predicting dry-out by incorporating two layers of finite element analysis. First, models for ink fluid flow and solvent diffusion through the template are used to determine wall sorption rate correlations. Fluid flow through complex templates is then modeled in a fluid-only model, with the flux rate into the template walls determined by the sorption rate correlations. The fluid velocities and wall sorption rates are then used to determine the likelihood of dry-out. The linked simulations successfully predict points of improper nanoparticle patterning in real templates.
Thermodynamic Characterization of a Direct Water Cooled Server Rack Running Synthetic and Real High Performance Computing Work Loads
Authors: Parnell Lynn , Vaughan Garrison , Thompson John , Duffy Daniel , Capps Louis , Steinke Mark E. , Kamath Vinod
Published: November 2015

High performance computing server racks are being engineered to contain significantly more processing capability within the same computer room footprint year after year. The processor density within a single rack is becoming high enough that traditional, inefficient air-cooling of servers is inadequate to sustain HPC workloads. Experiments that characterize the performance of a direct water-cooled server rack in an operating HPC facility are described in this paper. Performance of the rack is reported for a range of cooling water inlet temperatures, flow rates and workloads that include actual and worst-case synthetic benchmarks. Power and temperature measurements of all processors and memory components in the rack were made while extended benchmark tests were conducted throughout the range of cooling variables allowed within an operational HPC facility. Synthetic benchmark results were compared with those obtained on a single server of the same design that had been characterized thermodynamically. Neither actual nor synthetic benchmark performances were affected during the course of the experiments, varying less than 0.13 percent. Power consumption change in the rack was minimal for the entire excursion of coolant temperatures and flow rates. Establishing the characteristics of such a highly energy efficient server rack in situ is critical to determine how the technology might be integrated into an existing heterogeneous, hybrid cooled computing facility — i.e., a facility that includes some servers that are air cooled as well as some that are direct water cooled.
Embedded Two-Phase Cooling of High Flux Electronics via Micro-Enabled Surfaces and Fluid Delivery Systems (FEEDS)
Authors: Mandel Raphael , Dessiatoun Serguei , McCluskey Patrick , Ohadi Michael
Published: November 2015

This work presents the experimental design and testing of a two-phase, embedded manifold-microchannel cooler for cooling of high flux electronics. The ultimate goal of this work is to achieve 0.025 cm2-K/W thermal resistance at 1 kW/cm2 heat flux and evaporator exit vapor qualities at or exceeding 90% at less than 10% absolute pressure drop. While the ultimate goal is to obtain a working two-phase embedded cooler, the system was first tested in single-phase mode to validate system performance via comparison of experimentally measured heat transfer coefficient and pressure drop to the values predicted by CFD simulations. Upon validation, the system was tested in two phase mode using R245fa at 30°C saturation temperature and achieved in excess of 1 kW/cm2 heat flux at 45% vapor quality. Future work will focus on increasing the exit vapor quality as well as use of SiC for the heat transfer surface upon completion of current experiments with Si.
Thermal Modeling of Remote Radio Head Units
Authors: Sahini Manasa , Gebrehiwot Betsegaw , Agonafer Dereje , Colapietro Rocky
Published: November 2015

Thermal modeling of concealed Remote Radio Head (RRH) units which are placed on a cell tower is the main interest of this paper. RRH units which dissipate fixed amount of heat are modeled in higher ambient temperature. The effect of creating an enclosure on the open air assembly of RRH units is studied. The aim of this study is to analyze if concealment of the RRH units is possible under natural convection for cooling under boundary conditions with inlet temperature 55°C, solar loading and wind. Also, the study has been made to investigate if stacking of one, two, or three concealed sections is possible under natural convection cooling process.

Various configurations were modeled and analyzed using a computational fluid dynamics (CFD) tool. Different temperature profiles are reported. An enclosure has been created and the operating temperatures of the enclosed model and an open model are compared. After studying the air flow pattern in the model, specific design modifications, like placing baffles on top of each RRH unit, are suggested for proper air flow management thereby facilitating efficient thermal management inside the enclosure. Also, addition of baffles helped in removing the hot spots in the model.

Stacking concealed sections poses a challenge since hot exhaust air from a lower section may enter the air inlets of top sections. Thereby, higher surface temperatures on RRH units in the upper sections are observed. Orientation of the upper section has been changed to address this issue. Results show that with proper airflow management and arrangement of sections, it is possible to have three sections one on top of the other.
Thermal Behaviors of Passively-Cooled Hybrid Fin Heat Sinks for Lightweight and High Performance Thermal Management
Authors: Effendi Nico Setiawan , Kim Kyoung Joon
Published: November 2015

A computational study is conducted to explore thermal performances of natural convection hybrid fin heat sinks (HF HSs). The proposed HF HSs are a hollow hybrid fin heat sink (HHF HS) and a solid hybrid fin heat sink (SHF HS). Parametric effects such as a fin spacing, an internal channel diameter, a heat dissipation on the performance of HF HSs are investigated by CFD analysis. Study results show that the thermal resistance of the HS increases while the mass-multiplied thermal resistance of the HS decreases associated with the increase of the channel diameter. The results also shows the thermal resistance of the SHF HS is 13% smaller, and the mass-multiplied thermal resistance of the HHF HS is 32% smaller compared with the pin fin heat sink (PF HS). These interesting results are mainly due to integrated effects of the mass-reduction, the surface area enhancement, and the heat pumping via the internal channel. Such better performances of HF HSs show the feasibility of alternatives to the conventional PF HS especially for passive cooling of LED lighting modules.
Review of Most Recent Progress on Development of Polymer Heat Exchangers for Thermal Management Applications
Authors: Deisenroth David C. , Arie Martinus Adrian , Dessiatoun Serguei , Shooshtari Amir , Ohadi Michael , Bar-Cohen Avram
Published: November 2015

Polymeric materials have several favorable properties for heat transfer systems, including low weight, low manufacturing cost, antifouling, and anticorrosion. Additionally, polymers are typically electrical insulators, making them favorable for applications in which electrical conductivity is a concern. Examples of utilizing these favorable properties are discussed. The drawbacks to raw polymer materials include low thermal conductivity, low structural strength, and poor stability at elevated temperatures. Methods of mitigating these unfavorable properties, including loading the polymer with other materials and developing new polymers, are discussed. Enhanced geometric designs enabled by additive manufacturing can also improve thermal performance of polymer heat exchangers. Results of a research study utilizing additive manufacturing toward developing high-performance and cost-effective polymer heat exchangers for an air-to-liquid application are reviewed and discussed. Finally, needs for further research on enhancing polymer thermal performance are discussed.
Novel Flexible Interconnects and Packaging for Minimally Invasive Medical Electronics
Authors: Nagarkar Kaustubh , Galligan Craig , Klitzke Michael , Rose James , Shah Binoy , Sherman Donna
Published: November 2015

A novel interconnect approach was developed to enable packaging of miniature (<0.5 mm) MEMS pressure sensors for minimally invasive sensing applications. The interconnect approach is a variant of traditional flexible laminate circuits but does not require expensive patterning steps. It provides tight tolerance and assembly automation at relatively lower costs. In this paper, details of the novel interconnect and cabling approaches are disclosed. Examples of applications that benefit from this approach are also discussed. Experimental results on new ultra-miniature sensors utilizing the developed interconnect approach are presented.
Durability of Large Electronic Components Undergoing Multi-Axial Vibratory Excitation
Authors: Dasgupta Abhijit , Habtour Ed , Sridharan Raman , Lin Elaine
Published: November 2015

Shaker table vibration testing is nothing new for electronic components. Such environmental tests are most often conducted in a sequential uniaxial setup, where the test article is sequentially rotated and excited along three different orthogonal orientations. While sequential axis testing does excite modes in all three directions sequentially, it does not quantify or qualify how modes along different axes interact with one another when excited simultaneously.

Traditional linear dynamics does not predict any cross-axis interactions between different spectral modes in vibrating structures, but this has long been suspected to be an oversimplification for many cases. The authors demonstrated this in a previous experiment, in which printed wiring assemblies (PWAs) of the same design were subjected to sequential uniaxial and simultaneous biaxial excitations. Boards undergoing bi-axial excitation suffered fatigue damage accumulation rates much higher than the superposition of damage rates from sequential uniaxial tests. Even as far back as 2010, the military added multi degree of freedom (MDoF) vibration tests to their 810G standard — so MDoF testing is rapidly gaining traction in the accelerated stress testing community. The cost of performing MDoF vibration durability testing can be significant, so an important technical issue turns into identifying when MDoF testing is necessary, and when single degree of freedom (SDoF) testing is sufficient.

This study addresses this issue using a combination of mathematical models and FEA simulations. It is intuitively obvious that larger and more massive circuit components are more susceptible to these nonlinear cross-axis interactions, especially as the excitation levels become significant; however our long term goal is to quantify the effects of such parameters on the nonlinear interactions. The focus of the study is a simple beam with a tip mass — representing a circuit component with leads for mounting to the printed wiring board (PWB). The study also considers the effect of the PWB dynamics on the mechanical response of the circuit element, as it undergoes worst case excitation. The effects of several parameters are investigated, including component properties (e.g. mass, and height) as well as bi-axial excitation conditions (eg. frequency, relative phase and amplitude).
Effect of Temperature Cycling and High Temperature Aging on the Elastic Properties and Failure Modes of Thermal Interface Materials
Authors: Davis Taryn J. , Sinha Tuhin , Marston Ken , Iruvanti Sushumna
Published: November 2015

Highly filled thermally conductive silicone gels are routinely used as first level thermal interface materials (TIMs) between the die and lid, in flip-chip organic packages. The main challenge for these TIMs is overcoming the Coefficient of Thermal Expansion (CTE) mismatch between the die and lid materials. The TIMs must maintain excellent adhesion to both the die and lid surfaces in order to achieve and maintain optimal thermal performance. The CTE mismatch leads to increased mechanical stress and degradation of the TIM, which in turn degrades the thermal performance. In this work, the effective modulus of several TIMs was calculated by finite element modeling (FEM) in concert with mechanical testing of thin bond-line aluminum-TIM sandwiches subjected to varied stress conditions. These results are correlated to the corresponding stress die shear testing and the impact on package performance is analyzed.
The Efficiency of Heat Transfer Through the Interface of Sintered Silver Nanoparticles
Authors: Fałat Tomasz , Matkowski Przemysław , Stojek Krzysztof , Felba Jan , Płatek Bartosz , Mościcki Andrzej
Published: November 2015

Within the paper the efficiency of heat transfer through the thermal interface made of three different sintered nanosilver based materials was considered. The efficiency of heat conduction was analyzed by using the IR camera to monitor the changes of junction temperature in the chip of power transistor attached by different TIMs to copper lead-frame. Because in each case the transistor was powered in the same way so the lower difference between junction temperature and substrate temperature meant the better heat transfer efficiency. Moreover by using the X-ray inspection the structural analysis of interface was done.
Formation Characteristics of Bio-Coke Produced From Waste Agricultural Biomass
Authors: Mizuno Satoru , Ida Tamio , Fuchihata Manabu , Sanchez Edmundo , Yoshikuni Koji
Published: November 2015

We aimed to effectively use unutilized rice straw by producing Bio-coke, which is a new briquette (in the rest of this document referred to as the BIC) with high density and hardness, from rice straw with various conditions based on initial water content and processing temperature and evaluated characteristics of rice straw BIC. First of all, the apparent density of BIC was calculated from its weight and volume, and the cold compressive strength for each BIC was measured. From the results, it showed that the relationship between apparent density and maximum compressive strength derived from the compression test had a positive correlation. Furthermore, the hot compressive strength of the BIC produced with 5% initial water content and 453K processing temperature was measured. The rice straw BIC had a maximum compressive strength of 4.8MPa at a high temperature of 973K. This hot maximum compressive strength is equal to about one third of the hot maximum compressive strength of coal coke, which is 12MPa. Also, it was determined that the maximum compressive strength of rice straw BIC is highest on both cold and hot compression tests, and BIC produced from agricultural biomass like rice straw and rice husk had higher maximum compressive strength at room and high temperatures than BIC produced from other materials. Thus, it seemed that fiber and silica contained in agricultural biomass helps maintain of structure of BIC.
A Parametric Study of the Impact of Energy Relaxation Time on Thermal Behavior of Power Si MOSFET in Electro-Thermal Analysis
Authors: Kibushi Risako , Hatakeyama Tomoyuki , Nakagawa Shinji , Ishizuka Masaru
Published: November 2015

This paper describes the effect of variation of energy relaxation time on temperature distribution of power Si MOSFET in electro-thermal analysis. In previous our studies, thermal properties of power Si MOSFET are evaluated using electro-thermal analysis. However, in our previous calculation, energy relaxation time has been assumed to be constant at 0.3 ps, which is widely used value in electro-thermal analysis. This is because energy relaxation time cannot be calculated by classical physics, and it is difficult to detect exact energy relaxation time. However, energy relaxation time is important for evaluating heat generation in electro-thermal analysis. One method to obtain energy relaxation time is Monte Carlo simulation. In this research, we performed Monte-Carlo simulation, and electrical field and lattice temperature dependencies of energy relaxation time were evaluated. Then, we performed electro-thermal analysis of power Si MOSFET with various energy relaxation times, and the effect of change of energy relaxation time on temperature distribution of power Si MOSFET in electro-thermal analysis was discussed. Energy relaxation time in the range of 0.1–1000 kV/cm of electrical field was evaluated in Monte Carlo simulation. The results of Monte-Carlo simulation showed that maximum energy relaxation time becomes about 0.6 ps, and minimum energy relaxation time is about 0.30 ps. Following the results, to investigate the effect of variation of energy relaxation time on temperature distribution of power Si MOSFET, we changed energy relaxation time in electro-thermal analysis, and thermal properties of power Si MOSFET was calculated. The results of electro-thermal analysis showed that energy relaxation time has an effect on temperature distribution of power Si MOSFET. Therefore, accurate energy relaxation time should be considered in electro-thermal analysis for appropriate temperature distribution of power Si MOSFET.
Chip Package Interaction Study to Analyze the Mechanical Integrity of a 3-D TSV Package
Authors: Rajmane Pavan , Mirza Fahad , Khan Hassaan , Agonafer Dereje
Published: November 2015

The convergence and miniaturization of computing and communications dictates building up rather than out. As planar device miniaturization continues to its ultimate limits, the complexity of circuit interconnections for 2-D devices becomes a limitation for performance and drives up power dissipation [1]. As the consumers demand more functions on their hand-held electronic devices, the need for more devices such as memory, CPU and GPU in hand-held type footprints is increasing. Chip-stacking (3-D) is emerging as a powerful tool that satiates such IC package requirements. A 3-D FPGA would overcome the interconnect limitations, resulting in greater silicon efficiency per function (number of used gates/total number of gates), faster signal/data throughput, and faster switching of the gate-level configuration. 3-D through-silicon-via (TSV) technology is being termed as the “next big thing” in the semiconductor arena and has the potential of revolutionizing the packaging industry but it has some inherent issues that need to be addressed before it could be implemented in the mainstream electronics industry. TSV fabrication process, thermal management of 3-D TSV packages, TSV joule heating, and chip package interaction (CPI), are some of the key issues in this technology [2, 3, 4, 5, 6].

In this paper, the thermo-mechanical chip-package-interaction (CPI) analysis is carried out and a full field compact 3D modeling methodology has been leveraged to assess the mechanical integrity of a 2 die 3D TSV package during attachment to substrate. This modeling methodology would provide damage predictions caused due to global and local CTE mismatch between the different package components. Mechanical interaction at the Si/TSV regions, back-end Cu/low-k stack, and the inter die μ-bumps during chip attachment is demonstrated in this paper.
Crack Non-Circularity and Finite Erosion Effects on the 3D SIFs of a Bauschinger Modified Pressurized Thick-Walled Cylinder
Authors: Ma Qin , Levy Cesar , Perl Mordechai
Published: November 2015

Our previous studies have demonstrated that the 3D SIFs of a pressurized cylinder can be greatly affected by many factors. While an autofrettage process may introduce favorable residual stresses at the bore of the cylinder, other factors such as erosions and cracks, once introduced, may greatly reduce the effectiveness of the autofrettage results. In this study, we focus on how the non-circularity of cracks affects the 3D SIFs for a cylinder that contains finite erosions while keeping other conditions and material properties unchanged. Numerical analysis was performed using ANSYS, a standard commercially available finite element package. The residual stress due to any autofrettage process was simulated using the equivalent thermal loading. A closer look was given to problems with different crack configurations and how non-circularity of cracks affects the overall fatigue life of the cylinder when combined with other factors in comparison with circular crack only configurations.
Quantitative Comparison of Environmental Fatigue Methods
Authors: de Haan - de Wilde F. H. E. , Blom F. J. , Hannink M. H. C.
Published: November 2015

For many nuclear power plants worldwide the operation period will be extended from 40 to 60 years in the coming years. As the operation period increases the importance of knowledge of ageing mechanisms like fatigue increases. Knowledge of the influence of the environment is crucial, since environmental fatigue is a relatively new development which is a modification to the existing assessment method and has to be projected to 60 years as well.

This paper is a follow up of the ASME PVP2013-97695 paper: overview of international implementation of environmental fatigue. A quantitative comparison of the resulting cumulative usage factors including environmental fatigue is made for the most commonly used and well defined methods.

The comparison of the environmental fatigue codes is made on a spray nozzle of the pressurizer. This is a known fatigue relevant location with high stresses due to thermal loading. The high thermal loading is due to the spraying of relative cold water into the warm pressurizer.

The comparison is made for 11 methods, sets of fatigue curves and environmental fatigue correction factors (Fen factor), and 4 types of material. The 4 materials are: low alloy, carbon, nickel alloy and austenitic stainless steel. The fatigue curves of ASME 2007, ASME 2010, KTA 1996, KTA 2013, NUREG/CR-6909 and Code Case N-792 are compared. The Fen factors are compared for the following methods: NUREG/CR-6583, NUREG/CR-5704, NUREG/CR-6909, Code Case N-792, JNES SS-0503, JNES SS-1005 and NUREG/CR-6909 rev1. Code Case N-761 is included for the final comparison of the cumulative usage factors including environmental fatigue.

The differences in percentages are considerable between the different methods. For this specific case, the difference in cumulative usage factor including environmental fatigue for austenitic steels is 70 %. For nickel alloy materials the difference is 115%. For low alloy materials the difference is the highest: 267%. For carbon steels the difference in cumulative usage factor is 146%.

The most conservative cumulative usage factors including environmental fatigue are ASME 2007 or KTA 1996 fatigue curves combined with the NUREG/CR-5704 (austenitic steel and nickel alloy) or NUREG/CR-6583 (low alloy and carbon steel). The next highest results are found by the Japanese methods (JNES-SS-0503 and JNES-SS-1005). The common factor for these methods, is the fatigue curve for austenitic steels as used before 2010. The lowest cumulative usage factors are obtained by implementing NUREG/CR-6909. Using the latest revision of NUREG/CR-6909 the cumulative usage factors increase slightly (about 7%). The paper shows the considerable differences of usage factors when different codes are applied to the same problem.
Comparative Studies of Stress Intensity Factors for Nozzle Corner Cracks and Flat Plate Cracks
Authors: Smith S. M. , Holliday J. E.
Published: November 2015

Using the finite element software Abaqus, the present study utilized explicit flaw modeling techniques to compute nozzle corner crack stress intensity factors for a range of semi-elliptical and sawcut cracks in a nozzle and semi-elliptical cracks in a flat plate. Additionally, a weight function method (WFM) for a semi-elliptical crack in a flat plate was evaluated. Stress intensity factors were computed for a number of loading conditions. A transient thermal stress analysis was performed for the nozzle explicit flaw models and discussed. Results of this study indicate that stress intensity factors at the bisecting position of the elliptical crack front from the flat plate model agree well with the analogous nozzle crack bisector position results and WFM solution.
Effect of Heat Cycling and Joining Method on the Mechanical Performance of Multi-Material Single Lap Joints
Authors: Sakai Kaori , Nassar Sayed A.
Published: November 2015

In this experimental study, both environmental effects and various joining methods are investigated for their impact on the static and dynamic performance of multi-material lightweight single lap joints (SLJ). Adherends are conveniently divided into either composite-based or steel-based lightweight materials that include glass fiber reinforced polymer (GFRP), steel (St), aluminum (Al), or magnesium (Mg). A commercially available adhesive is selected for bonded-only and hybrid bonded-and-bolted joints. Changes in joint static load transfer capacity (LTC) and durability life are investigated for bonded-only, bolted-only, and hybrid bonded-and-bolted joints. Cyclic temperature profile fluctuates between 20° C and 80° C at a constant relative humidity (RH) level of either 20 % or 85 %. Effect on durability life is also studied under a cyclic load that fluctuates between 67.5 % and 75 % of the static load transfer capacity at ambient condition. Detailed discussion of the results, observations, and conclusions are presented in this paper.
Development of a Simplified Methodology for Evaluation of Piping Vibration due to Multi-Phase Flow
Authors: Santos Humberto R. , Pfeil Michèle S. , Tinoco Ediberto B. , Battista Ronaldo C.
Published: November 2015

Excessive piping vibration is a major cause of idleness, leaks, failures, fires and explosions in the petrochemical industry. One of the causes of vibration in piping is the occurrence of multiphase flow regimes, specially the one called slug flow. The main purpose of this work is the verification and improvement of a methodology for evaluation of excessive piping vibration caused by multiphase flow. This methodology is capable of generating, from the measured acceleration signals, forces equivalent to those induced by the two-phase flow. In other words, this methodology enables simplified models to represent adequately the dynamic structural behavior of the piping system when new boundary conditions are imposed, allowing to estimate the risk of failure in operation of piping system or to propose technically feasible solution to mitigate the vibration problem. A physical model made of acrylic pipes and PVC bends was assembled and used to measure, simultaneously, the accelerations at four points of this loop when subjected to multiphase flow and with two different boundary conditions. The methodology could therefore be applied, refined, and validated with the data obtained from the experiment and with the aid of numerical simulation.
A Renaissance in the Use of the Small Punch Testing Technique
Authors: Hurst Roger C. , Matocha Karel
Published: November 2015

The underlying purpose of this paper is to evaluate whether the CEN CWA 15627 “Small Punch Test Method for Metallic Materials” first published in 2006 has indeed succeeded in providing a stimulus for a wider implementation of the small punch test technique in industrial applications throughout Europe and indeed worldwide. A wealth of research progress has been apparent, as strongly evidenced in three dedicated SSTT (Small Specimen Testing Techniques) conferences held in Europe over the last five years, but also in the wider literature. In particular it is important to mention the recent publication of a Japanese standard and the announcement of parallel progress in China. The present paper concentrates on progress within Europe from the launch of the Code to the present day. In particular attention is focused on the need for industrial acceptance of the test methodology and methods for evaluating the results. Some scepticism still seems to prevail within sectors of the conventional power generation industry, an industry which can potentially benefit most from successful remanent lifetime extension tools of which small punch testing can be considered as a prime candidate. In spite of this, it is demonstrated that a major proportion of the Small Punch testing research of the last decade has been carried out on power plant steels. Meanwhile it is shown that there is evidence that the original remit of the methodology in assessing the integrity of irradiated nuclear plant remains active, new interest is developing for aerospace and next generation nuclear applications enhancing further the credibility of the Code.