bluuebunny/crossref_metadata_2025 huggingface dataset:
Server Rack Rear Door Heat Exchanger and the New ASHRAE Recommended Environmental Guidelines
Authors: Schmidt Roger , Iyengar Madhusudan
Published: January 2011

The patented [1] rear door heat exchanger mounted to the rear of IT equipment racks was announced in April, 2005 by IBM and has shown improvements in data center energy efficiency and reducing hot spots. It also allows data center operators to more easily implement some of the features of the newly approved ASHRAE data center recommended data center environmental guidelines [2]. This paper will describe several case studies of implementing the rear door heat exchanger in various data center layouts. The implementation of the water cooled rear door in these data centers will show the effects of various failure modes and how the new ASHRAE environmental temperature guidelines are still being met with the failure modes examined.
Application of a Thermal Network Method to Thermal Analysis of Electronic Devices Using Phase Change Materials
Authors: Takakuwa Sadakazu , Ishizuka Masaru , Nakagawa Shinji , Takagi Kanji
Published: January 2011

This paper describes transient cooling technology for electronic equipment using Phase Change Materials (PCMs) and a heat sink with pin fins. We designed an electronic module including paraffin as the PCM and measured its transient temperature rise. The effects of the diameter of pin fins and heat dissipation values were investigated as design parameters. The results show that the temperature rise values were controlled by the thermal absorption effect due to the latent heat of the PCM. It is also confirmed that the proposed thermal network method with an equivalent specific heat model has strong potential for use in the analysis of electronic modules using PCMs.
Observation of UV Nanoimprint Lithography Process by Micro-Digitalholographic-PTV
Authors: Taniguchi Jun , Satake Shin-ichi , Unno Noriyuki , Kanai Takahiro
Published: January 2011

UV nanoimprint lithography (UV-NIL) is powerful tool of nano-fabrication. This process is simple and quickly pattern transfer method because of room temperature process. Now, in this process sometimes generates the errors about shortage of filling or volume shrinking by photo-curable process. Therefore, observation of UV photo-curable resin behaviors at curing process is important. To observe this phenomenon, micro digital-holographic particle-tracking velocimetry (micro-DHPTV) method was used. This measurement method has sub-micron three dimensional spatial resolutions and high time-resolution at Newton fluid. The UV photo-curable resin is low viscosity liquid and observation was carried out. In conclusion, curing process of UV photo-curable resin was observed by micro-DHPTV.
Splicing of Polarization Maintained (PANDA) Optical Fibers in an Electronics Manufacturing Environment
Authors: Kulkarni Rohan , Srihari Krishnaswami
Published: January 2011

Optoelectronics technology has been undergoing continuous improvement in order to accommodate customer demand for smaller, faster and cheaper products [1]. The demand is satisfied by using novel material fibers, design techniques and processes. This results in challenges for the handling and usage of fibers during the assembly process. The focus of this research endeavor is restricted to the splicing processes of Polarization Maintaining (PM) fibers during optoelectronic assembly. Until recently, the technology of transmitting higher rate of data was limited to laboratories. However, the manufacturing technology was not standard. It took a longer period of time for the commercialization of these products. Due to the market driven demand and shorter product launch times, Original Equipment Manufacturers (OEMs) decided to outsource the manufacturing of fiber optics products to the Electronics Manufacturing Service (EMS) providers. This paper focuses on the splicing of Panda fibers in an EMS provider’s manufacturing environment. The objective of the study was to develop the splicing process for Panda fibers and outline the splicing parameters that have a significant impact on obtaining low loss splices. A ‘design of experiments’ approach has been used to perform the splices along with a real time splice loss measurement using a power meter and source. Prefuse power, prefuse time, arc power and arc time were the factors selected for experimentation. Experiments have been conducted using the aforementioned parameters and the ‘best’ combination was used to perform a verification run. An effort has been made to obtain (near) optimal values for the significant parameters that can be used for production in an EMS provider’s environment.
Optical Methodology for Testing of Microsystems
Authors: Pryputniewicz Ryszard J. , Marinis Ryan T. , Hefti Peter
Published: January 2011

Advancing the emerging technologies of MEMS, especially relating to the applications, constitutes one of the most challenging tasks in today’s micromechanics. In addition to design, analysis, and fabrication capabilities, this task also requires advanced test methodologies for determination of functional characteristics of devices produced to enable verification of their operation as well as refinement and optimization of specific designs. The tools used can be categorized as analytical, computational, and experimental. Solutions using the tools from any one category alone do not usually provide all of the necessary information on MEMS and extensive merging, or hybridization, of the tools from different categories is used. One of the approaches employed in the development of micro-structures of contemporary interest, is based on a combined use of the analytical, computational, and experimental solutions (ACES) methodology. In this paper, applicability of the ACES methodology is illustrated by use of selected MEMS samples. The representative results presented in this paper indicate that the optical methodology is a viable tool for micro-scale measurements and, as such, it is particularly useful for development of MEMS, especially while considering MEMS reliability assessment. In fact, this methodology is being used in various manufacturing stages of MEMS for high-performance applications.
Energy-Efficient Air Cooling of Data Centers at 2000 W/ft2
Authors: Herrlin Magnus K. , Patterson Michael K.
Published: January 2011

Increased Information and Communications Technology (ICT) capability and improved energy-efficiency of today’s server platforms have created opportunities for the data center operator. However, these platforms also test the ability of many data center cooling systems. New design considerations are necessary to effectively cool high-density data centers. Challenges exist in both capital costs and operational costs in the thermal management of ICT equipment. This paper details how air cooling can be used to address both challenges to provide a low Total Cost of Ownership (TCO) and a highly energy-efficient design at high heat densities. We consider trends in heat generation from servers and how the resulting densities can be effectively cooled. A number of key factors are reviewed and appropriate design considerations developed to air cool 2000 W/ft2 (21,500 W/m2). Although there are requirements for greater engineering, such data centers can be built with current technology, hardware, and best practices. The density limitations are shown primarily from an airflow management and cooling system controls perspective. Computational Fluid Dynamics (CFD) modeling is discussed as a key part of the analysis allowing high-density designs to be successfully implemented. Well-engineered airflow management systems and control systems designed to minimize airflow by preventing mixing of cold and hot airflows allow high heat densities. Energy efficiency is gained by treating the whole equipment room as part of the airflow management strategy, making use of the extended environmental ranges now recommended and implementing air-side air economizers.
Numerical Simulation of Threshold Current Density of Electromigration Damage in Cu Interconnect Tree
Authors: Sasagawa Kazuhiko , Kirita Akihiko , Abo Takehiro , Hassan Abdul Hafiz Nor
Published: January 2011

As silicon integrated circuits (ICs) continue to scale down, several reliability issues have emerged. Electromigration — the transportation of metallic atoms by the electron wind — has been recognized as one of the key damage mechanisms in metallic interconnects. It is known that there is the threshold current density of electromigration damage in via-connected line. The evaluation of the threshold current density is one of the great interests from the viewpoint of IC reliability. Recently, the threshold current density in interconnect tree was evaluated. However, it might not be so accurate because of evaluation of two-dimensional structure by combining one-dimensional analysis. In this study, the evaluation method of the threshold current density based on the numerical simulation is applied to several kinds of interconnect tree.
Transition Temperature Stratified Thermal Energy Storage Systems Applied to On-Demand Cooling of High Power-Density Hand-Held Electronics
Authors: Yaquinto Matt , Wirtz Richard
Published: January 2011

A thin-slab thermal storage volume that is sandwiched between a hand-held unit’s skin and a heat spreader that is in thermal contact with the electronics is analyzed. The storage volume is assumed to be filled with a conductivity enhanced, “dry” phase change material. Three storage volume configurations are considered. Configuration I is a single phase change material transitioning at one temperature. Configuration II is a two-layer system with phase change material-1 in thermal contact with the heat spreader and phase change material-2 in thermal contact with the unit’s skin. Configuration III consists of several layers, such that the phase transition temperature varies across the volume. A finite element model is built and numerical simulations provide temperature responses for each configuration. Results show that by employing a stratification of transition temperatures, relative to a non-stratified storage volume, up to a 20% decrease in recovery time is realized. Furthermore, utilization of two or more transition temperatures results in improved temperature control.
Evaluation of Secondary Wire Bond Integrity on Ag Plated and Ni/Pd Based Lead Frame Plating Finishes
Authors: Srinivasan G. , Murcko R. , Srihari K.
Published: January 2011

As the legislatures demand the use of lead (Pb) free plating finishes in lead frame manufacturing, different plating finishes are being offered by the lead frame makers. Lead frames are most often designed with two different Pb free plating finishes, primarily tin and nickel/palladium (Ni/Pd) based. The tin post mold plated lead frames use silver selective plating on the lead fingers for secondary wire bonding whereas the pre-plated Ni/Pd based lead frames use the same Ni/Pd based finish throughout. Enhanced versions of Ni/Pd based plating finishes such as nickel/palladium/gold (Ni/Pd/Au), nickel/palladium/gold-palladium (Ni/Pd/Au-Pd) and nickel/palladium/gold-silver (Ni/Pd/Au – Ag) are now available to further improve the wirebondability, solderability and reliability of the package. The development of a new lead frame finish involves a wide variety of concerns which must be addressed and thus mandates further evaluation of these new structures. Using the common Pb free lead frame plating finish of selectively plated silver (Ag) as the basis, a comparative approach was used to evaluate the secondary wire bond integrity of a 25 micron (1 mil) thick gold wire on Ni/Pd based lead frame plating finishes. The integrity of the secondary wire bonds for different plating finishes was investigated at various assembly thermal exposure stages using the wire pull strength test as the arbiter. Reliability tests, such as High Temperature Storage (HTS) and Unbiased Highly Accelerated Stress Test (UBHAST), were also conducted. Finally, failure analysis was conducted with the help of metallographic cross sectioning, SEM/EDX (Scanning Electron Microscope/Energy Dispersive X-ray) analysis and statistical analysis of the wire pull strength test results. Before wire bonding the lead frames, the plating surface was investigated for its surface integrity with the help of plating quality tests, such as: (i) adhesive tape test, (ii) bend test, (iii) heating test and the (iv) scribing test. Also, since wire pull is a destructive test, a statistical method called a nested gauge R&R study was used to estimate the repeatability and reproducibility of the measurement system. Failure analysis showed that there were silver and copper migrations over the Ag plated lead frame when exposed to a high temperature storage test at 175°C for 1000 hrs, but this did not affect the bond integrity. However, the Ni/Pd based lead frames did not show any metal migration since nickel acts as a barrier against the base metal diffusion.
Evaluation of Resistance Change as a Predictor of Thermal Actuator Displacement
Authors: Constable J. H. , Stevenson Michael , Hung Ming Hung , Infantolino Bill
Published: January 2011

The required voltage and current to produce a desired displacement with a MEMS electrothermal actuator can vary considerably between devices due to manufacturing process variation. This article presents a case for using resistance change divided by the ambient temperature resistance (ΔR/R0) as the quantity sensed in a feedback system to control the displacement, and avoid either melting the actuator with over drive, or not producing the desired actuation with under drive. The electrical resistance of a MEMS thermal actuator was calculated using a resistivity model that includes both the extrinsic and intrinsic conduction mechanisms in silicon. The model also accounts for the change in resistivity due to the strain in the silicon resulting from the confinement of the actuator by the two mounting posts. Using the model, it was shown that ΔR/R0 is a unique function of the effective temperature over the operating temperature range. The displacement of the actuator was calculated from a simple model, and was used to generate plots of the resistance change versus displacement. These plots were compared with the nearly universal plot of ΔR/R0 versus displacement found experimentally for thermal actuators with a range of dimensions. The calculated and measured curves were in reasonable agreement.
Energy Efficiency Analyses and Comparison of Air and Water Cooled High Performance Servers
Authors: Ellsworth Michael J. , Iyengar Madhusudan K.
Published: January 2011

This paper presents a study that illustrates the energy efficiency benefits of using water cooling for server thermal management versus utilizing air-cooling for high performance server applications. In 2008 IBM introduced the water cooled Power 575 Supercomputing Node, which is packaged in a super-dense 2U (88.9 mm) form factor. A fully configured system can dissipate as much as 72 kW with 80% of the heat load going to water. A fully air cooled version of this system, developed by Hitachi, operates 3.5 GHz and dissipates 61 kW at the frame level. In this paper, numerical analyses is first carried to help provide a context for the data center air-conditioning energy consumption, necessary to cool comparable performance clusters for both the air and water cooled racks, respectively. The room level CFD calculations are then extended to the facility level, by including the energy consumption of the refrigeration chiller, the building and condenser water pumps, and the cooling towers. Recent innovations that enable the use of water side economizers as well as 100% water cooling of racks are also discussed. The results show that there can be as much as a 45% reduction in the facilities power to cool the water cooled system compared to the energy required for the air cooled equivalent. When 100% of the server heat load is transferred directly to the chilled water supplied to the racks, there can be a 50% energy savings compared to traditional air-cooling. Lastly, use of 100% water cooling in conjunction with water side economizers can yield more than 90% cooling energy savings compared to the air-cooled configurations.
Optimization of the Tip of Microwave AFM Probe
Authors: Ju Yang , Hamada Motohiro , Hosoi Atsushi , Fujimoto Akifumi
Published: January 2011

In order to develop a new structure microwave probe, the fabrication of the atomic force microscope (AFM) probe on a GaAs wafer was studied. The fabricated probe had a tip of 8 μm high and curvature radius approximately 30 nm. The dimensions of the cantilever are 250 × 30 × 15 μm. A waveguide was introduced by evaporating Au film on the top and bottom surfaces of the GaAs AFM probe. The open structure of the waveguide at the tip of the probe was introduced by using focused ion beam (FIB) fabrication. To improve the resolution of AFM measurement, only the metal film was removed at the end of the probe tip. AFM topography of a grating sample was measured by the fabricated probe. As a result, it was found that the resolution of AFM measurement and the ratio of signal to noise were enhanced.
Site-Specific and On-Demand High Heat-Flux Cooling Using Superlattice Based Thin-Film Thermoelectrics
Authors: Chowdhury Ihtesham , Prasher Ravi , Lofgreen Kelly , Narasimhan Sridhar , Mahajan Ravi , Koester David , Venkatasubramanian Rama
Published: January 2011

We have recently reported the first ever demonstration of active cooling of hot-spots of >1 kW/cm2 in a packaged electronic chip using thin-film superlattice thermoelectric cooler (TEC) cooling technology [1]. In this paper, we provide a detailed account of both experimental and theoretical aspects of this technological demonstration and progress. We have achieved cooling of as much as 15°C at a location on the chip where the heat-flux is as high as ∼1300 W/cm2, with the help of a thin-film TEC integrated into the package. To our knowledge, this is the first demonstration of high heat-flux cooling with a thin-film thermoelectric device made from superlattices when it is fully integrated into a usable electronic package. Our results, which validate the concept of site-specific micro-scale cooling of electronics in general, will have significant potential for thermal management of future generations of microprocessors. Similar active thermal management could also be relevant for high-performance solid-state lasers and power electronic chips.
Application of Excel to Thermal Analysis of Electronic Equipment: Program-Less Analysis and Visualization of Its Process by Using Spreadsheet of Excel
Authors: Tomimura Toshio , Koito Yasushi , Torii Shuichi , Ishizuka Masaru
Published: January 2011

Some practical examples solved by using the spreadsheet software like Excel have been reported recently. In the numerical analysis using Excel, each cell can be regarded as a nodal point, and calculations are performed by using equations written in those cells without making any program. Iterative calculations are carried out automatically. Moreover, the calculated results shown in the computational domain are immediately visualized using the Chart Wizard. Two typical examples of thermal analysis on a printed circuit board with power devices by the thermal network method, and a straight rectangular fin by the finite difference method are shown in the present study.
Strain-Rate Effects on Constitutive Behavior of Sn3.8-Ag0.7-Cu Lead-Free Solder
Authors: Tan Kok Ee , Pang John H. L.
Published: January 2011

In this paper, the strain-rate dependent mechanical properties and stress-strain curve behavior of Sn3.8Ag0.7Cu (SAC387) solder is presented for a range of strain-rates at room temperature. The apparent elastic modulus, yield stress properties and stress-strain curve equation of the solder material is needed to facilitate finite element modeling work. Tensile tests on dog-bone shaped bulk solder specimens were conducted using a non-contact video extensometer system. Constant strain-rate uni-axial tensile tests were conducted over the strain-rates of 0.001, 0.01, 0.1 and 1 (s−1) at 25°C. The effects of strain-rate on the stress-strain behavior for lead-free Sn3.8Ag0.7Cu solder are presented. The tensile yield stress results were compared to equivalent yield stress values derived from nano-indentation hardness test results. Constitutive models based on the Ramberg-Osgood model and the Cowper-Symond model were fitted for the tensile test results to describe the elastic-plastic behavior of solder deformation behavior.
Mathematical Approaches for Thermal Design of a Vapor Chamber
Authors: Koito Yasushi , Shiki Yuta , Mochizuki Masataka , Torii Shuichi , Tomimura Toshio
Published: January 2011

This paper presents three mathematical models (Model 1, Model 2-a, Model 2-b) for the thermal design of the vapor chamber. Model 1 is a detailed model, where the equations of continuity, momentum and energy are solved numerically to obtain the velocity, pressure and temperature distributions inside the vapor chamber. Model 2-a and Model 2-b are simplified conduction-based models for the purpose of obtaining the temperature distribution inside the vapor chamber in a shorter time and a lower cost by Microsoft Excel. Model 2-a is a disk-shaped two-dimensional model and the numerical calculation is conducted using one worksheet of Excel. Model 2-b, on the other hand, is constructed in a three-dimensional rectangular coordinate system and Excel VBA Macro is used to obtain the numerical results. The numerical results of Model 2-a and Model 2-b are compared with those of Model 1 and the authors’ previous experimental results, confirming the validity of the present Excel simulation. The mathematical approach with Excel is visual, handy and cost-effective for the thermal design of the vapor chamber.
The IP Landscape for MEMS Packaging
Authors: Bauer Charles E. , Fillion Raymond A. , Neuhaus Herbert J. , Papageorge Marc
Published: January 2011

Early MEMS devices employed packages developed for conventional semiconductor microelectronics. Today, MEMS packages reflect the unique environment, mechanical, chemical and thermal requirements of MEMS devices themselves. A casual search of on-line databases reveals nearly 40,000 patents worldwide containing the words “MEMS” and “package.” While not all relevant, the number of IP documents easily overwhelms researchers, investors and IP practitioners. The authors systematically analyze the relevant IP and organize it by generic technology categories. A unique mapping methodology provides greater understanding of the landscape of IP in the MEMS packaging arena across a wide range of considerations including geography, IP development and ownership trends, infrastructure implications and application concepts. The authors also present a rudimentary valuation of IP within the MEMS packaging field based on citation analysis. Finally, the authors demonstrate a method to develop a strategic framework based on the IP landscape useful for investment, market development and strategic alliance planning.
Leading-Indicators Based on Impedance Spectroscopy for Prognostication of Electronics Under Shock and Vibration Loads
Authors: Lall Pradeep , Lowe Ryan , Suhling Jeff , Goebel Kai
Published: January 2011

Leading indicators of failure have been developed based on high-frequency characteristics, and system-transfer function derived from resistance spectroscopy measurements during shock and vibration. The technique is intended for condition monitoring in high reliability applications where the knowledge of impending failure is critical and the risks in terms of loss-of-functionality are too high to bear. Previously, resistance spectroscopy measurements [Constable 1992, Lizzul 1994, Prassana 1995] have been used during thermal cycling tests to monitor damage progression due to thermo-mechanical stresses. The development of resistance spectroscopy based damage pre-cursors for prognostication under shock and vibration is new. In this paper, the high-frequency characteristics, and system transfer function based on resistance spectroscopy measurements have been correlated with the damage progression in electronics during shock and vibration. Packages being examined include ceramic area-array packages. Second level interconnect technologies examined include copper-reinforced solder column, SAC305 solder ball, and 90Pb10Sn high-lead solder ball. Assemblies have been subjected to 1500g, 0.5 ms pulse [JESD-B2111]. Continuity has been monitored in-situ during the shock test for identification of part-failure. Resistance spectroscopy based damage pre-cursors have been correlated with the optically measured transient strain based feature vectors. High speed cameras have been used to capture the transient strain histories during shock-impact. Statistical pattern recognition techniques have been used to identify damage initiation and progression and determine the statistical significance in variance between healthy and damaged assemblies. Models for healthy and damaged packages have been developed based on package characteristics. Data presented shows that high-frequency characteristics and system-transfer characteristics based on resistance spectroscopy measurements can be used for condition-monitoring, damage initiation and progression in electronic systems. A positive prognostic distance has been demonstrated for each of the interconnect technologies tested.
Effect of Dicing Technique on the Fracture Strength of Si Dies With Emphasis on Multi-Modal Failure Distribution
Authors: Chae Seung-Hyun , Zhao Jie-Hua , Edwards Darvin R. , Ho Paul S.
Published: January 2011

The ball-on-ring (BOR) and 3-point bending (3PB) tests were used in this study to characterize the effect of dicing process on the fracture strength of Si dies. Dies prepared by a blade dicing process and a laser dicing process were studied. The edge-initiated fracture was distinguished from the surface-initiated fracture by the fractographic analysis. The fracture strength distributions related to surface flaws in the 3PB test as well as the BOR test were consistent regardless of dicing process. For the edge defect-induced failure mode, on the other hand, blade-sawn dies showed wider spread distribution than laser-sawn dies. It was due to the scattered nature in size and location of edge flaws induced by blade dicing. The laser-sawn dies showed a tighter distribution of the die strength although the average die strength was slightly lower than that of the blade-sawn dies. This work successfully demonstrated that the die failure caused by the edge defects can be deconvoluted from the 3PB test data by using the fractographic observation.
Solder Fatigue Impacts of Conformal Coating for Tin Whisker Mitigation on Chip-Scale Thin Small Outline Packages
Authors: Geisler Karl J. L.
Published: January 2011

This study explores the impact of polyurethane conformal coating on the solder fatigue life of 0.5 mm pitch, thin small outline package (TSOP) components. Test samples were subjected to temperature cycling from −40°C to + 100°C. Uncoated samples were tested in addition to sets with 10, 13, and 20 μm thick coatings. Solder joint failure data fit to 3-parameter Weibull distributions demonstrate characteristic fatigue life reductions of 30% with increasing coating thickness but relatively subtle changes to the failure distribution shape.
Mapping Growth of an Emerging Technology: A Case Study of Flexible Electronics
Authors: Poranki Srikanth , Nagarur Nagen , Srihari Krishnaswami
Published: January 2011

Technological innovation is viewed as one of the main economic multipliers. In high-technology sectors, with intense competition and short product life cycles, failure to detect an emerging technology could be devastating to both incumbent technology pursuers and innovators. Firms typically employ methods such as a Delphi method, Technology growth curves or technology road-mapping methods to identify and forecast growth. Some of these methods are based on a life cycle approach where a technology is expected to follow an S-curve and then become obsolete in due time, which is analogous to market diffusion of products. In the case of emerging technologies, forecasting methods are not always reliable due to lack of historical data. Hence, both qualitative and quantitative methods are employed to forecast; however, there are risks associated with both of these methods. A general consensus in technology forecasting community is to apply multiple methods for forecasting. In the last few decades there has been explosion of new technologies, especially in the high-technology sector of electronics. Several new applications such as Large Area Displays (several square feet in area), low cost electronics (e.g. RFID tags being manufactured for pennies or cents per unit) and body conformable electronic applications are a few of a long and growing list. The aforementioned applications could broadly be categorized to form a new and emerging field of electronics called flexible electronics. These applications utilize the rugged lightweight plastics to potentially offer attractive characteristics such as low-cost processing, mechanical flexibility, large area coverage, etc. these characteristics are not easily implemented with established silicon technologies. This research analyzes flexible electronics technology by first identifying a few key innovations. Patent and publications data are collected and technology growth curves based on the indicators would be generated, and compared with those of incumbent technology innovations, to assess technology growth potential. Based on the study, technology adoption strategies would also be recommended by which business leaders could anticipate and plan for the effects of these innovations.
Microgap Cooling Technique Based on Evaporation of Thin Liquid Films
Authors: Zaitsev D. V. , Kabov O. A.
Published: January 2011

Thin and very thin (less than 10 μm) liquid films driven by a forced gas/vapor flow (stratified or annular flows), i.e. shear-driven liquid films in a narrow channel is a promising candidate for the thermal management of advanced semiconductor devices in earth and space applications. Development of such technology requires significant advances in fundamental research, since the stability of joint flow of locally heated liquid film and gas is a rather complex problem. The paper focuses on the recent progress that has been achieved by the authors through conducting experiments. Experiments with water in flat channels with height of H = 1.2–2.0 mm show that a liquid film driven by the action of a gas flow is stable in a wide range of liquid/gas flow rates. Map of isothermal flow regime was plotted and the length of smooth region was measured. Even for sufficiently high gas flow rates an important thermocapillary effect on film dynamics occurs. Scenario of film rupture differs widely for different flow regimes. It is found that the critical heat flux for a shear driven film can be 10 times higher than that for a falling liquid film, and exceeds 400 W/cm2 in experiments with water for moderate liquid flow rates. This fact makes use of shear-driven liquid films promising in high heat flux chip cooling applications.
Experimental Investigation of Flow Boiling in a Single, Surface-Augmented Silicon Microchannel
Authors: Thiagarajan Naveenan , Pate Daniel T. , Bhavnani Sushil H. , Jones Rory J.
Published: January 2011

Advances in electronics such as chip level integration and die stacking have led to a bottleneck in further development since dissipation of the resulting high heat fluxes continues to be a challenge. Ongoing research in the field of flow boiling to meet the rising demands has resulted in the evolution of potential cooling technologies such as microchannel heat sinks. In an effort to understand the flow boiling in these micro-structures, experiments were previously conducted by the authors using 19 parallel, surface enhanced microchannels with a hydraulic diameter of 253μm. Flow instabilities which can be attributed to channel-to-channel interaction and the effect of compressible volumes at channel exit and inlet were observed under certain subcooled boiling conditions although these were mitigated in saturated conditions by the presence of re-entrant cavities. To completely eliminate the instabilities, it is important to identify the underlying mechanisms by isolating these causes. To achieve this, a study of flow boiling of dielectric fluid FC72 (C6F14) in a single microchannel test section of height 347 microns and width ranging from 100–400 microns was conducted. The base of the microchannel was augmented with reentrant cavities. The study was performed at mass fluxes ranging from 500–2000 kg/m2-s and inlet subcooling up to 20°C. The results include the parametric effects of inlet subcooling, mass flux, heat flux and number of cavities on the pressure drop. It was observed that the pressure drop oscillations in the subcooled boiling regime observed earlier in the multichannel configuration, were not observed in the subcooled regime in the single channel test device of width 100 microns. Further, adiabatic experiments were conducted to study the effect of channel size on the friction factor. These studies will help provide fundamental design input to enable the development of microchannel heat sinks.
Analysis of Nanofluids in Liquid Electronic Cooling Systems
Authors: Roberts N. A. , Walker D. G.
Published: January 2011

Nanofluids are solutions of a small fraction of suspended nanoparticles in a bulk fluid. Nanofluids have shown great promise as heat transfer fluids over typically used bulk fluids and fluids with micron sized particles. The nanoparticles do not settle in the fluid and do not cause clogging or damage to surfaces as with micron sized particles. In the current work we compare the performance of different volume loadings of water-based alumina nanofluids in a commercially available electronics cooling system to that of pure DI-water. The commercially available system is a water block used for liquid cooling of a computational processing unit. The size of the nanoparticles in the study is varied from 20 nm to 30 nm. Results show an enhancement in convective heat transfer, but not in the temperature increase through a heated tube or commercial cooling system in nanofluids with volume loadings of nanoparticles up to 2% by volume. The current nanofluids showed significant settling within an hour of preparation.
Novel Application-Specific LED Packages Integrated With Compact Freeform Lens
Authors: Wang Kai , Chen Fei , Liu Zongyuan , Luo Xiaobing , Liu Sheng
Published: January 2011

It has been widely accepted that solid state lighting, in terms of white light emitting diodes (LEDs), will be the fourth illumination sources due to their superior performance. In this study, an effective compact freeform lens design method for LED packaging was introduced. A compact silicone LED packaging lens with the refract index of 1.54 was designed for street lighting based on this method. Integrated with this small lens, a novel application-specific LED package, whose manufacturing process can be easily integrated into current LED packaging processes, was suggested. Two application-specific LED array modules, with the type of chip on board (CoB) package, were also designed by integrating 3×3 freeform silicone and polycarbonate (PC) lens arrays. Numerical simulation results demonstrated that the optical performances of these application-specific LED modules could directly meet the requirements of street lighting. By comparing with the traditional LED illumination module consisting of an LED and secondary optics, the novel application-specific LED packages have the advantages of low profile, small volume, high light output efficiency (LOE), low cost and convenience for customers to use, and they will probably become the trend of LED packages, providing more cost-effective solution to general lighting.
Multi-Objective Optimization of Graphite Heat Spreader for Portable Systems Applications
Authors: Lakhkar Nikhil , Banerjee Arijit , Refai-Ahmed Gamal , Agonafer Dereje
Published: January 2011

The advancement made in portable electronic systems has primarily been due to miniaturization of electronic devices. This results in an increase in power density that leads to higher temperatures and formation of hot spots. There is a temperature specification of system surfaces for human comfort (such as the surface close to a keyboard on laptops). The challenge of cooling portable devices is that there is not enough room to accommodate heat sinks. It is therefore important to have heat spreaders that can transfer the heat from critical devices to regions where cooling is available. Traditionally, copper has been the best heat spreader due to its high thermal conductivity. However, copper has a relatively high density and correspondingly high weight. Graphite is a suitable alternative. Recent advances in graphite technology have resulted in fairly high conductivity in the planar directions. In spite of these advances, the cost of graphite is an issue. In this paper, a multi-objective optimization is utilized that considers weight of the graphite heat spreader as objective functions. The data is then compared to published data that utilizes graphite in a laptop.
Wetting Hysteresis, Metastability, and Droplet Impact on Superhydrophobic Surfaces
Authors: Varanasi Kripa K. , Deng Tao , Hsu Ming F. , Bhate Nitin
Published: January 2011

We study the wetting energetics and wetting hysteresis of sessile and impacting water droplets on superhydrophobic surfaces as a function of surface texture and surface energy. For sessile drops, we find three wetting regimes on these surfaces: equilibrium Cassie at small feature spacing, equilibrium Wenzel at large feature spacing, and an intermediate state at medium feature spacing. We observe minimum wetting hysteresis not on surfaces that exhibit Cassie wetting but rather on surfaces in the intermediate regime. We argue that droplets on these surfaces are metastable Cassie droplets whose internal Laplace pressure is insufficient to overcome the energy barrier required to homogeneously wet the surface. These metastable Cassie droplets show superior roll-off properties because the effective length of the contact line that is pinned to the surface is reduced. We develop a model that can predict the transition between the metastable Cassie and Wenzel regimes by comparing the Laplace pressure of the drop to the capillary pressure associated with the wetting-energy barrier of the textured surface. In the case of impacting droplets the water hammer and Bernoulli pressures must be compared with the capillary pressure. Experiments with impacting droplets show very good agreement with this simple pressure-balance model.
Effective Thermal Management of Data Centers Using Efficient Cabinet Designs
Authors: Mulay Veerendra , Agonafer Dereje , Irwin Gary , Patell Darshan
Published: January 2011

Rising heat load trends in data center facilities have raised concerns over energy usage. The environmental protection agency has reported that the energy used in 2006 by data center industry was 1.5% of the total energy usage by entire nation. The experts agree that by year 2010, this usage will approach 2% of the annual energy use nationwide. Although many new concepts such as airside economizers and cogeneration are gaining traction, many data center facilities spend considerable energy in cooling. In this study, various cabinet designs are discussed. Isolating the supplied cold air from hot exhaust air is always a challenge in thermal management of data center facilities. A cabinet design that employs chimney to aid the isolation of hot and cold air is discussed. A computational model of representative data center is created to study the effectiveness of design under various supply air fractions.
Energy-Efficiency Through the Integration of Information and Communications Technology Management and Facilities Controls
Authors: Patterson Michael K. , Meakins Michael , Nasont Dennis , Pusuluri Prasad , Tschudi William , Bell Geoffrey C. , Schmidt Roger , Schneebeli Ken , Brey Tom , McGraw Monty , Vinson Wade , Gloeckner Jason
Published: January 2011

Increasing energy-efficient performance built into today’s servers has created significant opportunities for expanded Information and Communications Technology (ICT) capabilities. Unfortunately the power densities of these systems now challenge the data center cooling systems and have outpaced the ability of many data centers to support them. One of the persistent problems yet to be overcome in the data center space has been the separate worlds of the ICT and Facilities design and operations. This paper covers the implementation of a demonstration project where the integration of these two management systems can be used to gain significant energy savings while improving the operations staff’s visibility to the full data center; both ICT and facilities. The majority of servers have a host of platform information available to the ICT management network. This demonstration project takes the front panel temperature sensor data from the servers and provides that information over to the facilities management system to control the cooling system in the data center. The majority of data centers still use the cooling system return air temperature as the primary control variable to adjust supply air temperature, significantly limiting energy efficiency. Current best practices use a cold aisle temperature sensor to drive the cooling system. But even in this case the sensor is still only a proxy for what really matters; the inlet temperature to the servers. The paper presents a novel control scheme in which the control of the cooling system is split into two control loops to maximize efficiency. The first control loop is the cooling fluid which is driven by the temperature from the physically lower server to ensure the correct supply air temperature. The second control loop is the airflow in the cooling system. A variable speed drive is controlled by a differential temperature from the lower server to the server at the top of the rack. Controlling to this differential temperature will minimize the amount of air moved (and energy to do so) while ensuring no recirculation from the hot aisle. Controlling both of these facilities parameters by the server’s data will allow optimization of the energy used in the cooling system. Challenges with the integration of the ICT management data with the facilities control system are discussed. It is expected that this will be the most fruitful area in improving data center efficiency over the next several years.
Development of a Metal Micro-Textured Thermal Interface Material
Authors: Kempers R. , Frizzell R. , Lyons A. , Robinson A. J.
Published: January 2011

Typical thermal interface materials (TIMs) consist of high thermal conductivity solid particles dispersed in a continuous, low thermal conductivity organic compound. Despite using filler materials of very high thermal conductivity, the effective thermal conductivity of these TIMs is often two orders of magnitude lower than the pure filler materials. In addition, dispensing and flow of the particle-matrix composite results in voids being trapped within the bond. To address these issues, a novel metal micro-textured thermal interface material (MMT-TIM) has been developed. This material consists of a thin metal foil with raised micro-scale features that plastically deform under an applied pressure thereby creating a continuous, thermally conductive, path between the mating surfaces. Numerical tools have been developed that couple the mechanical and thermal properties and behaviour of MMT-TIMs as they undergo large-plastic deformation during assembly. This study presents the modelling approach and predictions of MMT-TIM performance based on these numerical techniques. The predictions show good agreement with experimental results, which were obtained using prototype MMT-TIMs and an advanced TIM characterization facility. Finally, a future outlook for this technology is presented based on these promising initial results.
Heat Switch to Control the Local Thermal Resistance Using Liquid Pillar Control
Authors: Jeong Su-Heon , Nakayama Wataru , Lee Sun-Kyu
Published: January 2011

This paper presents the heat switch for electronic package to be operated at room temperature. The heat switch controls the thermal resistance between two objective plates using liquid pillar. By forming the liquid pillar, the temperature of the specific area can be controlled locally. In order to realize the desired switch operation, the heat switch should be provided with reservoir, switching channel and breathing channel. The channels are carefully designed to control the liquid pillar precisely. The liquid pillar formation depends on the liquid contact angle. The designed channel geometry can generate hydrophobic surface by using suddenly diverging shape like as capillary stop valve. Thus, the liquid pillar can be created at desired point with high stability. To verify the switch operation, the switch panel was designed and experiments were performed on a designed switch for the liquid pillar control and the heat flow regulation. The experiments show that the heat switch is able to work properly. Also, the temperature distribution and thermal resistance was changed in accordance with channel state as desired. As a result, the heat switch can be a good candidate of thermal management in the commercial electronics packages.
Temperature Effects on the Performance and Reliability of MEMS Gyroscope Sensors
Authors: Patel Chandradip , Jones Allen , Davis Joshua , McCluskey Patrick , Lemus David
Published: January 2011

Elevated temperatures can significantly affect the performance and reliability of MEMS gyroscope sensors. A MEMS vibrating resonant gyroscope measures angular velocity via a displacement measurement which can be on the order on nanometers. High sensitivity to small changes in displacement causes the MEMS Gyroscope sensor to be strongly affected by changes in temperature which can affect the displacement of the sensor due to thermal expansion and thermomechanical stresses. Analyzing the effect of temperature on MEMS gyroscope sensor measurements is essential in mission critical high temperature applications, such as inertial tracking of the movement of a fire fighter in a smoke filled indoor environment where GPS tracking is not possible. In this paper, we will discuss the development of a test protocol which was used to assess temperature effects. Both stationary and rotary tests were performed at room and at elevated temperatures on 10 individual single axis MEMS gyroscope sensors.