bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Low-Noise and High-Performance Cooling Structure for Full-HD Plasma Display TV Sets
Authors: Isoshima Nobuyuki , Watanabe Masatoshi , Ri Mika , Yamada Yutaka , Sugimoto Koichi
Published: January 2011

A low-noise and high-performance “inclined fan-blowing-upward structure” for full high definition plasma display panel television sets was developed by using computational fluid dynamics with heat transfer based on a Cartesian grid system. In the conventional structure, the plasma panel and boards are cooled by fans and upward flow induced by natural convection. However, simulation results indicated that low-temperature flows between the bottom and rear inlets and fans are formed along the back cover, and the flows are not sufficiently supplied to the plasma panel and address-driver modules. Our solution is to mount the cooling fans inclined to the plasma panel so that the flows produced by the fans impinge on the panel to supply the low-temperature air to the panel and address-driver modules directly. In the new structure, larger fans can be used because fans are mounted inclined. With the larger fans, the rotation speed of the fans can be reduced, and the flow rate is increased. The experimental results show that the temperature of the panel and address-driver modules decreases respectively 3C and 8C at the same noise output level.
Evaluation of the Electrical Behavior of Polydisperse and Monodisperse Carbon Nanotube Networks
Authors: Jackson Roderick , Graham Samuel
Published: January 2011

In order to fully realize the potential of single wall carbon nanotube (SWNT) networks in organic electronic devices, it may be necessary to utilize monodisperse networks that leverage the homogeneity of the film to achieve optimal device performance. Therefore, the optoelectronic characteristics of SWNTs in homogeneous and heterogeneous electronic type compositions are evaluated in this report. In particular, sources of film to film conductivity variation and the effect of moderate and heavy charge carrier doping are elucidated. The electrical conductivity analysis is supported by corroborative optical absorption spectra and SWNT electronic band structure theory.
An Investigation Into the Penetration of Phase Change Material in Carbon Foam for Transient Thermal Management
Authors: Sanusi Omar , Weinstein Randy D. , Fleischer Amy S.
Published: January 2011

Phase Change Materials (PCMs) are used for thermal management and are ideal for cyclic operations due to their high capacity to store heat. Most PCMs do not exhibit sufficient conductivity to be effective at larger sizes. Enhancing conductivity can be done in a number of ways including carbon foam. It is not widely known how well PCMs penetrate inside the carbon foam structure. Initial research suggests that the carbon foam-PCM matrix acts more as a conductor than a thermal storage device. Through the use microscopy, we will examine how the well the PCM penetrates into the carbon foam. We will also use experimental data comparing carbon foam enhanced modules to pure PCM modules. A volume displacement test will also be used to determine the quantity of PCM that enters into the carbon foam structure. This knowledge will allow better design of enhanced PCM modules and will determine if carbon foam is indeed a viable conduction enhancer for PCM thermal management.
Multiscale Modeling of Hot Spots in GaN High Electron Mobility Transistors
Authors: Christensen Adam , Graham Samuel
Published: January 2011

A coupled Lattice Boltzmann (LB)-Finite Difference (FD) method is used to solve for the heat transport in a 6 finger GaN high electron mobility transistor. The LB method is used to capture relevant phonon physics near a microscopic heat generation region by solving the Boltzmann Transport Equation, while an FD model is used to capture the thermal transport at the macroscopic level. The coupling region between the LB and FD domains, which enables multiscale modeling, is discussed. The results of the multiscale models were compared to results generated from other numerical methods. An increasing departure from diffusion theory is observed with increasing dissipated power under the gray phonon model. This difference is attributed to a combination of boundary scattering effects as well as phonon confinement within the small dimensions of the hot spot.
Thermoelectric Cooling Analysis Using Modified Graphical Method
Authors: Phan Huy N. , Agonafer Dereje
Published: January 2011

Comprehensive analysis of thermoelectric cooling systems involves many parametric equations, which require solving complex mathematical or computation-fluid-dynamic (CFD) models. In this study, a Modified-Graphical Method (MGM) based on previous study by Lineykin and Ben-Yaakov is proposed to analyze an active cooling system using thermoelectric module. The MGM provides quicker visualization of the cooling requirement using only common parameters from TEC manufacturers to obtain pertinent design information such as the optimum operating currents, temperature of the hot side and coefficient of performance (COP).
Predicting Thermal Characteristics of Particle Laden Thermal Interface Materials
Authors: Khiabani Reza H. , Joshi Yogendra , Aidun Cyrus
Published: January 2011

Particle laden Thermal Interface Materials (TIMs) are used extensively in thermal packaging of electronic components to enhance the heat transfer between heat dissipating components and the thermal management layers. In this paper, the thermal performance of particle laden TIMs is studied numerically, using the Lattice Boltzmann method. The effect of particle volume fraction, particle size and the thermal conductivity ratio on the thermal performance of particle laden TIMs are examined. The results for the effective thermal conductivity of particle laden greases are in agreement with the existing analytical and experimental results reported in the literature.
Micro Texture Dependence of Mechanical Properties of Electroplated Copper Thin Films Used for Thin Film Interconnection
Authors: Murata Naokazu , Tamakawa Kinji , Suzuki Ken , Miura Hideo
Published: January 2011

Electroplated copper thin films have been used for interconnection of semiconductor devices. Both the mechanical and electrical properties of the films were found to be quite different from those of bulk material, and thus, the reliability of the devices is not so high as to be expected. The main reason for the difference was found to be their micro texture. When the films consist of fine columnar grains with weak grain boundaries, their mechanical properties show strong anisotropy and complicated fracture mode. Thus, the fatigue strength of the electroplated copper thin films was measured under uniaxial stress. The mechanical properties such as the yield stress, fracture elongation and Young’s modulus of each film were quite different from those of bulk copper due to their unique micro structure. The micro texture of each film was observed by using SEM (Scanning Electro Microscope) and SIM (Scanning Ion Microscope). The low-cycle fatigue strength varied drastically depending on their micro texture, while the high-cycle fatigue strength was almost same. The fracture surfaces were observed by SEM after the fatigue test. It was found that there were two fracture modes under the fatigue test. One was a typical ductile fracture, and the other was brittle one even under the fatigue load higher than its yield stress. The crack seemed to propagate in the grains when the ductile fracture occurred since typical striations and dimples were observed clearly on the fractured surfaces. On the other hand, the crack seemed to propagate along grain boundaries of columnar grains when the brittle fracture occurred. No striations or dimples remained on the fractured surfaces. One of the reasons for this brittle fracture can be explained by cooperative grain boundary sliding of the films which consist of fine columnar grains with weak grain boundaries. These results clearly indicated that the fatigue strength of the electroplated copper thin films varies depending on their micro structure. Since the initial micro texture was found to change significantly even after the annealing at temperatures lower than 300°C, the effect of the thermal history of them after electroplating on both their micro texture and fatigue strength was investigated quantitatively. Not only the average grain size, but also the crystallographic structure of the films changed significantly depending on their thermal history, and thus, the fatigue strength of the films varied drastically. It is important, therefore, to control the micro texture of the films for assuring their reliability.
Development of Advanced High Heat Flux Cooling System for Power Electronics
Authors: Shinmoto Yasuhisa , Miura Shinichi , Suzuki Koichi , Abe Yoshiyuki , Ohta Haruhiko
Published: January 2011

Recent development in electronic devices with increased heat dissipation requires severe cooling conditions and an efficient method for heat removal is needed for the cooling under high heat flux conditions. Most researches are concentrated on small semiconductors with high heat flux density, while almost no existing researches concerning the cooling of a large semiconductor, i.e. power electronics, with high heat generation density from a large cooling area. A narrow channel between parallel plates is one of ideal structures for the application of boiling phenomena which uses the cooling for such large semiconductors. To develop high-performance cooling systems for power electronics, experiments on increase in critical heat flux (CHF) for flow boiling in narrow channels by improved liquid supply was conducted. To realize the cooling of large areas at extremely high heat flux under the conditions for a minimum gap size and a minimum flow rate of liquid supplied, the structure with auxiliary liquid supply was devised to prevent the extension of dry-patches underneath flattened bubbles generated in a narrow channel. The heating surface was experimented in two channels with different dimensions. The heating surfaces have the width of 30mm and the lengths of 50mm and 150mm in the flow direction. A large width of actual power electronics is realizable by the parallel installation of the same channel structure in the transverse direction. The cooling liquid is additionally supplied via sintered metal plates from the auxiliary unheated channels located at sides or behind the main heated channel. To supply the liquid to the entire heating surface, fine grooves are machined on the heating surface for enhance the spontaneous liquid supply by the aid of capillary force. The gap size of narrow channels are varied as 0.7mm, 2mm and 5mm. Distribution of liquid flow rate to the main heated channel and the auxiliary unheated channels were varied to investigate its effect on the critical heat flux. Test liquids employed are R113, FC72 and water. The systematic experiments by using water as a test liquid were conducted. Critical heat flux values larger than 2×106W/m2 were obtained at both gap sizes of 2mm and 5mm for a heated length of 150mm. A very high heat transfer coefficient as much as 1×105W/m2K was obtained at very high heat flux near CHF for the gap size of 2mm. This paper is a summary of experimental results obtained in the past by the present authors.
Thermal Characterization of High-Density Interconnects in the Form of Equivalent Thermal Conductivity
Authors: Nakayama Wataru , Koizumi Katsuhiro , Fukue Takashi , Ishizuka Masaru , Nakajima Tatsuya , Koike Hiroko , Matsuki Ryuichi
Published: January 2011

The issue addressed in the present study is how to model wiring substrates to perform heat conduction analysis on moderate computational resource. Equivalent thermal conductivity is a convenient measure in thermal modeling. However, its notion needs re-examination where higher accuracy of heat conduction analysis is pursued. Proposed is a scheme where the indexed volumetric metal contents are used to estimate the equivalent conductivity of representative volume element (RVE). The index is designed to reflect the effect of metal pattern on heat flow through RVE. In order to illustrate the core concept we report the analysis performed on template models of high-density interconnect (HDI) substrates. The element of HDI contains copper in several forms; through-via, continuous plane, and cross wires. Five heat flow directions are assumed; two are linear and three are right-angled turn. From combinations of the metal pattern and the heat flow direction twenty five templates are created, then, they are subjected to detailed numerical analysis. The values of equivalent thermal conductivity derived from the numerical solutions reveal that the gross volumetric metal content is totally inadequate as a parameter of thermal characterization. The paper also outlines the overall organization of our analysis system which is being developed in an industry-academia cooperative effort under the auspices of JSME.
Plastic Strain Distribution as a Precursor for Transition From Ductile to Brittle Failure in Lead-Free Solder Joints
Authors: Gao Feng , Jing Jianping , Liang Frank Z. , Williams Richard L. , Qu Jianmin
Published: January 2011

One of the major failure modes in lead-free solder joints is the brittle fracture at the solder/Cu pad interface under dynamic loading conditions. Such brittle fracture often leads to catastrophic premature failure of portable electronic devices. Therefore, it is desirable to design the package and the solder joints in such a way that brittle interfacial fracture can be avoided during drop test. To develop such design guidelines, we studied in this paper the dynamic failure of a single solder joint (SSJ). The SSJs with different geometry and substrate surface finish were prepared by laser-cutting from a BGA package assembled on a printed circuit board (PCB). The SSJs were tested under various shear loading rates, ranging from 5 mm/s to 500 mm/s. In conjunction with the experimental tests, finite element analyses (FEA) of these SSJ samples subjected to various loading rates were also conducted. Results from both experimental testing and numerical simulations show that the distribution of plastic strain near the solder/IMC interface is a key indictor of the failure mode. For a given sample geometry and loading rate, if the maximum solder plastic strain lies near the solder/IMC interface, the failure will be more likely to be ductile failure within the solder alloy. On the other hand, if the maximum plastic strain is mainly located at the edge of the interface between solder and the IMC layer with very little plasticity within the solder near the interface, brittle fracture of the IMC/Cu interface will be more likely to occur. Since numerically computing the plastic strain distribution in a solder joint is much easier than predicting joint failure, results of this study provide us with an effective means to predict the type of failure mode of a solder joint under dynamic loading.
Electronic Structure and Contact Resistance at the Interface Between Carbon Nanotubes and Copper Pad
Authors: Gao Feng , Qu Jianmin , Yao Matthew
Published: January 2011

Due to their unique and superior mechanical and electrical properties, carbon nanotubes (CNTs) are a promising candidate as electrical interconnects in nanoscale electronics. A key element in using CNT as electrical interconnects is the full understanding of the mechanical and electrical behavior of the interface between the CNT and copper (Cu) pad. The objective of this paper is to study the electronic structure and the electrical contact resistance at the interface between the open end of a single wall CNT and a Cu pad. To accomplish this, simulation cell consisting of an open-end single wall CNT with each end connected to a Cu electrode was created. The Cu/CNT/Cu system is fully relaxed first before a potential bias is prescribed between the Cu electrodes. The first-principle quantum mechanical density functional and non-equilibrium Green’s function (NEGF) approaches are adopted to compute the transport coefficient, while the current-voltage (I-V) relation is then extracted by invoking the Landauer-Buttiker formalism. The average density of state (DOS) and local density of states (LDOS) are also calculated to obtain the electron energy distribution around Fermi level point. Our simulation results show that electrons are conducted through the Cu/CNT/Cu system. In the low voltage bias regime (0.0∼0.1 V), I-V relationship is found to be linear. At higher voltage (> 2.0 V), the I-V relationship is nonlinear. Our results also show that the electrical contact resistance at the CNT/Cu interface is ∼3.6 kΩ at 0.1 V, and ∼4.8 kΩ at 2.0 V. These results indicate that for open-end CNTs, the contact resistance at the CNT/Cu interface is at least comparable to that of solder/Cu interface.
Estimation of the Optimum Dimensions of a Vertical Channel Model for Natural Air Cooling in Electronic Equipment
Authors: Nishino Yasushi , Ishizuka Masaru , Nakagawa Shinji
Published: January 2011

The cooling capability in compact electronic equipment in natural convective flow fields has been investigated. The relationship between air passage width in the channel and natural cooling capability was obtained. Temperature and velocity measurements were carried out using a channel model of electronic equipment comprising a vertical duct of rectangular section. The channel model had two copper walls and two transparent acrylic walls. The clearance between the copper walls was used as a parameter for the channel model. Velocity profiles of natural cooling flow in the channel were quantitatively measured using particle image velocimetry (PIV). The temperature and velocity results demonstrated that changes in the velocity profiles closely depend on the wall clearances. It is clarified that the clearance from 8 mm to 10 mm is the best size for natural cooling in the channel.
Life Prediction of SAC305 Interconnects Under Temperature Cycling Conditions Using an Arbitrary Loading Fatigue Model
Authors: Herkommer Dominik , Punch Jeff , Reid Michael
Published: January 2011

This paper presents the application of a new semi-empirical model for lifetime predictions. The model has been acquired by isothermal mechanical cycling testing using joint-scale solder samples on a novel testing apparatus. The calibrated model is here employed with an FEA model to predict the failure of a BGA device under thermal cycling. The modelling results show state-of-the-art agreement with the test data and superiority over Morrow model constants from literature that have been applied to this data set.
Thermotunneling Systems for Advanced Efficient Cooling
Authors: Arik Mehmet , Weaver Stanton , Bray James W.
Published: January 2011

Refrigeration for electronics components has been studied to keep the junction temperature below allowable limits. Thermoelectrics have been investigated heavily for their dual use over the last six decades These devices can be used for both cooling and power generation. Thermotunneling devices, on the other hand, have been known only for the last two decades, and nobody has been able to manufacture or show the performance of those devices. In this study, we will discuss the thermodynamic efficiency of these systems and design bottlenecks to reach high efficiencies, such as thermal back path and electrical losses. Concepts for possible device designs will be discussed. Then attention will be turned to near field radiation heat transfer that becomes critical in nano scale device designs.
Advanced Cooling With Embedded Heat Pipes for High Power Microelectronics
Authors: Chiriac Victor Adrian
Published: January 2011

The transient thermal behavior of a complex testing system including multiple fans, a mixing enclosure, Cu inserts and a leaded package dissipating large amounts of power over short time durations is evaluated via numerical simulations. The system performance is optimized with heat sink/fan structure for device efficient operation under constant powering. The study provides meaningful understanding and prediction of a transient powering scenario at high powering levels, evaluating the impact of alternative cooling fan/heat pipe configurations on the thermal performance of the system. One design is chosen due to its effective thermal performance and assembly simplicity, with the package embedded in heat sink base with multiple (5) heat pipes. The peak temperature reached by the modified design with 4 cooling fans is ∼95°C, with the corresponding Rja thermal resistance ∼0.58°C/W. For the transient study (with embedded heat pipes and 4 fans), after one cycle, both peak temperature (at 45 s) and the end temperature (at 49 s) decrease as compared to the previous no heat pipe/single fan case (especially the end temperature reduces by ∼16%). The temperature drop between peak and end for each cycle is ∼80.2°C, while the average power per transient cycle is ∼31.27W. With this power, the design with 5 perpendicular heat pipes, 4 fans and insert reaches a steady state peak temperature of ∼98°C. Applying the superposition principle, the maximum transient temperature after a large number of operating cycles will not exceed ∼138.1°C, satisfying the thermal budget under the current operating conditions. The benefit of the study is related to the possibility to extract the maximum/minimum temperatures for a real test involving a large number of heating-cooling cycles, yet maintaining the initial and peak temperatures within a certain range for the optimal operation of the device. The flow and heat transfer fields are thoroughly investigated: using a combination of numerical and analytical study, the thermal performance of the device undergoing large number of periodic thermal cycles is predicted. Further comparison between measurement and simulation results reveals good agreement.
Numerical Calculation for Phonon Properties of a Nano-Porous Si
Authors: Miyazaki Koji , Nagai Daisuke , Kido Yohei , Tsukamoto Hiroshi
Published: January 2011

We carried out molecular dynamics simulations (MD) of heat conduction in Si with a nano-hole to represent the nano-structure, in order to investigate the mechanism of the thermal conductivity reduction of nano-structured materials. The Stillinger-Weber potential is used in this study. The temperature is kept constant at 300K by velocity scaling. Periodic boundary conditions are applied in the x, y and z directions. Phonon dispersion curves are calculated by using the time-space 2D Fourier transform. The phonon group velocity is calculated from the slope of the dispersion curve. The velocity is reduced by nano-holes, even if those are random. Phonon mean free path can be evaluated from the width of dispersion curve, and the long waves are clearly scattered by nano-holes. Phonon density of states (DOS) is also calculated by the Fourier transform of a velocity correlation. The DOS of Si with periodic nano-holes are slightly smaller than that of a single crystal Si. In other words, the specific heat is reduced by periodic nano-holes due to the reduced phonon modes. We discuss the mechanism of the reduction of the thermal conductivity of nano-porous material on the atomic scale.
Heat Balance of Micro Hot-Film Sensor Elements Under the Different Gas Operation
Authors: Nagayo Hidetomo , Honami Shinji , Kamiunten Shoji , Motosuke Masahiro
Published: January 2011

The precise measurement of a mass flow rate of the gas is strongly required from the viewpoints of energy saving and the environmental problem in the manufacturing process. It is necessary to develop an accurate sensor for the mass flow rate with high sensitivity. The present micro hot-film sensor fabricated by utilizing MEMS technology is a thermal type gas flow sensor which is used for the measurement of the mass flow rate. The sensor which consists of the two heaters in a 1 μm-thick silicon-nitride membrane with cavity structure can detect the near-wall flow velocity proportional to the two heater electric power consumption. The static characteristics of the sensor have been poorly understood under the different gas operation instead of air. The purpose of the present paper is to clarify the heat balance of the sensor element corresponding to the heater as well as the static characteristics of the sensors by the experiment and the simulation, when the sensor is applied to the measurements for the different species of the gas. The air and helium are used as the working fluid. It is found that a unique correlation on the heater electric power is obtained regardless of the gas species used and the arrangement of the heater element. And, the simulation by SPICE provides with a similar tendency to the experiment about the arrangement of the heater element.
Manipulation of Thin Metallic Wires by Joule Heat Joining
Authors: Tohmyoh Hironori , Takeda Hironao , Akanda M. A. Salam , Saka Masumi
Published: January 2011

Various kinds of metallic thin wires are expected to be key elements in future NEMS or MEMS due to their excellent physical properties and geometrical merits. However, it is not so easy task to manipulate thin wires for many kinds of application nowadays. We report manipulation techniques based on weld-joining on a substrate by Joule heating. The Pt thin wires with the diameter of about 625 nm were welded onto In wires as substrates. The Pt wires on the In substrate were taken for the three-point bending test and potential drop test for determining their mechanical and electrical properties. Moreover, based on the manipulation technique, by twisting the Pt thin wire around a core wire, simply-supported micro-coils on electrode chips were successfully fabricated, and their utility as electromagnetic actuators was realized.
Electroless Nickel Plating Process Optimization for Aluminum Terminals
Authors: Westby Philip , Mattson Kevin , Haring Fred , Baer Jacob , Steele Matt , Ahmad Syed Sajid , Reinholz Aaron
Published: January 2011

An Electroless Ni plating process for aluminum was evaluated and optimized, leading to smooth and uniform nickel growth approaching 28.2 μm/hr. The effects of temperature, and process time were investigated. Nickel bumping die for solder adhesion was performed and the quality of the adhesion between the nickel and aluminum layers was evaluated.
An Experimental Investigation of Flow Boiling Characteristics in a Single Transparent Heated Microtube
Authors: Kawanami Osamu , Huang Shih-Che , Kawakami Kazunari , Honda Itsuro , Kawashima Yousuke , Ohta Haruhiko
Published: January 2011

In the present study, flow boiling in a transparent heated microtube having a diameter of 1 mm was investigated in detail. The transparent heated tube was manufactured by the electroless gold plating method. The enclosed gas-liquid interface could be clearly recognized through the tube wall, and the inner wall temperature measurement and direct heating of the film were simultaneously conducted by using the tube. Deaerated and deionized water that was subcooled temperature of 15 K was used as a test fluid, and constant and stable mass velocities of 50, 100, and 200 kg/m2s were provided by using a twin plunger pump. Among our experimental results, a vapor bubble grew up in a direction opposite the flow at a low heat flux and low mass velocities; however, this flow pattern was not observed at a high mass velocity of 200 kg/m2s. Under the conditions of G = 50 kg/m2s and high heat flux, the liquid film surrounding an elongated bubble near the heated tube wall occasionally thickened partially. The inner wall temperature exhibited large random oscillations in this regime; however, the visual observation revealed that dry-patches did not occur. The mass velocity had a negligible effect on the boiling heat transfer except in the counter-growth bubble flow regime.
Novel Miniature DMFC With Monolithic Si Electrodes
Authors: Hayase Masanori , Saito Yosuke
Published: January 2011

A through-chip porous Ru-Pt catalyst layer was fabricated on a Si wafer and a novel miniature DMFC (Direct Methanol Fuel Cell) was realized. Recently, we found that porous noble metal layer can be synthesized on Si substrate by immersion plating on a porous Si. In order to realize a DMFC with our novel structure, a porous Ru layer was synthesized on the Si substrate using the immersion plating on the porous Si, then Pt was deposited by galvanic replacement reaction on the porous Ru. The porous Ru-Pt structure showed catalytic activity on methanol oxidization. A through-chip porous Ru-Pt layer was fabricated on a Si wafer by plasma etching and monolithic electrodes with catalyst layers and fuel channels were realized. A preliminary DMFC prototype successfully demonstrated power generation of 2mW/cm2.
Application of Micro-Channel Fin for Cold Plate of Liquid Cooling System and Vapor Chamber
Authors: Mashiko Koichi , Mochizuki Masataka , Saito Yuji , Horiuchi Yasuhiro , Nguyen Thang , Ping Xiao , Nguyen Tien , Wuttijumnong Vijit
Published: January 2011

Recently energy saving is most important concept for all electric products and production. Especially, in Data-Center cooling system, power consumption of current air cooling system is increasing. For not only improving thermal performance but also reducing electric power consumption of this system, liquid cooling system has been developed. This paper reports the development of cold plate technology and vapor chamber application by using micro-channel fin. In case of cold plate application, micro-channel fin technology is good for compact space design, high thermal performance, and easy for design and simulation. Another application is the evaporating surface for vapor chamber. The well-known devices for effective heat transfer or heat spreading with the lowest thermal resistance are heat pipes and vapor chamber, which are two-phase heat transfer devices with excellent heat spreading and heat transfer characteristics. Normally, vapor chamber is composed of sintered power wick. Vapor chamber container is mechanically supported by stamped pedestal or wick column or solid column, but the mechanical strength is not enough strong. So far, the application is limited in the area of low strength assembly. Sometime the mechanical supporting frame is design for preventing deformation. In this paper, the testing result of sample is described that thermal resistance between the heat source and the ambient can be improved approximately 0.1°C/W by using the micro-channel vapor chamber. Additionally, authors presented case designs using vapor chamber for cooling computer processors, and proposed ideas of using micro-channel vapor chamber for heat spreading to replace the traditional metal plate heat spreader.
Remote Strain Measurement by Multi-Walled Carbon Nanotube-Dispersed Resin
Authors: Osaki Katsuya , Fuji Hideki , Onishi Masato , Suzuki Ken , Miura Hideo
Published: January 2011

A new remote strain measurement method has been developed by applying the highly sensitive change of electronic conductivity of CNTs. Multi-walled CNTs were dispersed in various kinds of resins to form a thin film which can be attached rounded surfaces. The length of the CNTs was about a few μm. One of the base materials of resin employed was polycarbonate and the volumetric concentration of CNT dispersed was about 11.5%. The thickness of the film was about 500 μm. An uni-axial strain was applied to the CNT-dispersed resin by applying a 4 point bending method, and the change of the electric resistance was measured. The range of the applied strain was from −0.025% to 0.025%. The electric resistance changed almost linearly with the applied strain. The ratio of the resistance change under the tensile strain was about 40%/1000-μstrain and that under the compressive strain was about 15%/1000-μstrain. The micro wave of 99.5 GHz was irradiated to the CNT-dispersed polycarbonate film through the metallic prove 1 mm in diameter. The change of the intensity of the beam reflected from the film was measured by changing the amplitude of the uni-axial in-plane strain applied to the film. The intensity of the reflected beam increased almost linearly with the increase of the applied tensile strain and the change rate of the intensity was about 0.5%/1000-μstrain. This result clearly indicated that the surface dynamic strain can be detected by micro wave nondestructively and remotely.
Visco-Elastic Effect of Underfill Material in Reliability Analysis of Flip-Chip Package
Authors: Kanda Yoshihiko , Zama Kunihiro , Kariya Yoshiharu , Mikami Takao , Kobayashi Takaya , Sato Toshiyuki , Enomoto Toshiaki , Hirata Koichi
Published: January 2011

The effect of viscoelasticity of underfill on the reliability analysis of flip-chip package by using FEA has been investigated in this study. The analytical result on thermal warpage of a package is different depending on whether the underfill is assumed to be elastic or viscoelastic. The difference is prominent in materials with low Tg, specifically during the cooling process. The viscoelastic effect of the underfill on the fatigue life of the solder bumps is also appears in materials with low Tg, and the predicted fatigue life of a package is about twice as short if the underfill is assumed to be elastic instead of viscoelastic. Thus, the differences in the assumption regarding the viscoelastic properties of the underfill affect the reliability analysis of the packages under thermal cycling condition using FEA.
Surface Roughness Effects on Flow Boiling in Microchannels
Authors: Jones Benjamin J. , Garimella Suresh V.
Published: January 2011

The influence of surface roughness on flow boiling heat transfer and pressure drop in microchannels is experimentally explored. The microchannel heat sink employed in the study consists of 10 parallel, 25.4 mm long channels with nominal dimensions of 500 μm × 500 μm. The channels were produced by saw-cutting. Two of the test piece surfaces were roughened to varying degrees with electrical discharge machining (EDM). The roughness average, Ra, varied from 1.4 μm for the as-fabricated, saw-cut surface to 3.9 and 6.7 μm for the two roughened EDM surfaces. Deionized water was used as the working fluid. Experiments indicate that the surface roughness has little influence on boiling incipience and only a minor impact on saturated boiling heat transfer coefficients at lower heat fluxes. For wall heat fluxes above 1500 kW/m2, the two EDM surfaces (3.9 and 6.7 μm) have similar heat transfer coefficients that were 20 to 35% higher than those measured for the saw cut surface (1.4 μm). Analysis of the pressure drop measurements indicates that only the roughest surface (6.7 μm) has an adverse effect on the two-phase pressure drop.
Effect of Viscoelasticity on Thermalmechanical Stress in Polymers
Authors: Pang Yaoyu , Zhao Jie-Hua , Edwards Darvin
Published: January 2011

Polymers are being widely used in microelectronic packages and viscoelasticity is one of the important characteristics of polymers. In practice, most package stress studies arbitrarily neglect the polymer viscoelasticity and use elastic models although viscoelastic constitutive relation is different from commonly used elastic-plastic behavior due to the fact that the characterization of viscoelasticity is complex and time-consuming. With this in mind, special response of thermal-mismatch stress induced by temperature excursion within polymers are expected to be very different than the linear elastic response, and better knowledge for thermomechanical stress behavior in polymers needs to be developed. In this paper, a bi-material plate consisting of a polymer film on an elastic substrate was used to demonstrate the significance of polymer viscoelasticity. The constitutive relation for a linear viscoelastic thermorheologically simple material (TSM) was adopted for the polymer layer. The effect of polymer viscoelasticity on stress evolution under different temperature profiles has been investigated.
Novel Fluorescent Visualization Method to Characterize Transport Properties in Micro/Nano Heat Pipe Wick Structures
Authors: Chamarthy Pramod , de Bock H. Peter J. , Russ Boris , Chauhan Shakti , Rush Brian , Weaver Stanton E. , Deng Tao , Varanasi Kripa
Published: January 2011

Heat pipes have been gaining a lot of popularity in electronics cooling applications due to their ease of operation, reliability, and high effective thermal conductivity. An important component of a heat pipe is the wick structure, which transports the condensate from condenser to evaporator. The design of wick structures is complicated by competing requirements to create high capillary driving forces and maintain high permeability. While generating large pore sizes will help achieve high permeability, it will significantly reduce the wick’s capillary performance. This study presents a novel experimental method to simultaneously measure capillary and permeability characteristics of the wick structures using fluorescent visualization. This technique will be used to study the effects of pore size and gravitational force on the flow-related properties of the wick structures. Initial results are presented on wick samples visually characterized from zero to nine g acceleration on a centrifuge. These results will provide a tool to understand the physics involved in transport through porous structures and help in the design of high performance heat pipes.
Reliable Power Electronics for Wind Turbines
Authors: McCluskey Patrick , Hansen Peter , DeVoto Douglas
Published: January 2011

Power electronics are used to minimize losses in converting the energy produced by the generator in a wind turbine, and to drive motors that control the pitch and yaw of the wind turbine to ensure maximum power extraction. The power electronic system is based on a series of three-phase pulse width modulated (PWM) power modules consisting of IGBT power switches and associated diodes that are soldered to a ceramic substrate and interconnected with wirebonds. The design of the packaging and cooling of the power electronics is crucial to enhancing the energy efficiency and the reliability of the electronics, which generate heat loads in the hundreds of watts/cm2, and are often placed in harsh and inaccessible offshore environments. Without adequate heat removal, the increase in device temperature will reduce the efficiency of power electronic devices leading to thermal runaway and eventual failure of the entire power electronic system. Furthermore, the increased temperatures can lead to failure of the packaging elements as well. This paper will provide an overview of the fundamental packaging level mechanisms that can cause failures in the power electronic system. These include wirebond and lead fatigue, die attach fatigue, substrate cracking, and lead bonding fatigue.
Pb-Free Thin Small Outline Package (TSOP) Board Level Reliability Study
Authors: Xie Weidong , Liu Kuo-Chuan , Brillhart Mark
Published: January 2011

Thin Small Outline Package (TSOP) are one of the most commonly used surface mount components due to its low overall cost. Traditionally leadframe packages such as TSOP or Quad Flat Package (QFP) are less of a concern (if assembled with SnPb eutectic solder paste) about their long term reliability and often exempted from board level qualification testing as the mechanical compliance of metal leads mitigate the stresses due to the Coefficient of Thermal Expansion (CTE) mismatch between the package and Print Circuit Board (PCB). Therefore more attention has been put on the solder joint reliability of Pb-free Ball Grid Array (BGA) packages over leadframe packages while the industry is moving away from SnPb eutectic solder materials to meet RoHS regulatory requirements. The authors have observed that TSOPs if assembled with Pb-free solder materials could fail at very early stages during qualification testing (in some case as early as 300 cycles under standard 0°C to 100°C thermal cycling). Since most Pb-free solder materials such as SnAgCu are mechanically more rigid than SnPb eutectic solder material, higher stresses are expected be induced in solder joints during temperature excursions. Pb-free solder materials’ wicking behavior may also contribute to the early failures. In this study, long term reliability of a flash memory TSOP has been investigated. These tested TSOPs, assembled on 93mil-thick PCBs with SAC305 paste, are of two configurations: one with single die and the other with stacked quadruple dies. Some test vehicles have been thermally aged under four different thermal aging conditions to study the aging effect on Pb-free solder joint life. Finite element analysis (FEA) modeling has also been employed to further investigate the impact of other parameters such as die size, package size, and the number of dies that being stacked inside one package.
Virtual Qualification Using Field Life Temperature Data
Authors: McCluskey Patrick , Hansen Peter , Lenakakis Christian , Wondrak Wolfgang
Published: January 2011

A method is presented that converts field life temperature data collected underhood during actual driving conditions into a segmented temperature cycling life cycle profile using rainflow counting techniques. This profile can then be used as the true field condition in performing Physics of Failure based virtual qualification or accelerated testing of an automotive engine control unit operating in an elevated temperature environment. The specific elements of this method and its validation on an engine control unit will be presented.
Reduced Order Thermal Modeling of Data Centers via Distributed Sensor Data
Authors: Samadiani Emad , Joshi Yogendra , Hamann Hendrik , Iyengar Madhusudan K. , Kamalsy Steven , Lacey James
Published: January 2011

In this paper, an effective and computationally efficient Proper Orthogonal Decomposition (POD) based reduced order modeling approach is presented, which utilizes selected sets of observed thermal sensor data inside the data centers to help predict the data center temperature field as a function of the air flow rates of Computer Room Air Conditioning (CRAC) units. The approach is demonstrated through application to an operational data center of 102.2 m2 (1,100 square feet) with a hot and cold aisle arrangement of racks cooled by one CRAC unit. While the thermal data throughout the facility can be collected in about 30 minutes using a 3D temperature mapping tool, the POD method is able to generate temperature field throughout the data center in less than 2 seconds on a high end desktop PC. Comparing the obtained POD temperature fields with the experimentally measured data for two different values of CRAC flow rates shows that the method can predict the temperature field with the average error of 0.68 °C or 3.2%.
Optimization of Location of a Power Cell for Energy Efficient Operation of Air Cool Drives
Authors: Karajgikar Saket , Mulay Veerendra , Menon Abhilash , Agonafer Dereje , Zhang Jiahui
Published: January 2011

In this paper, Siemen’s air cooled drive systems is analyzed for its energy efficient operation. It consists of various individual power cells, which further houses different electrical/electronic components of the system. The cells are stacked in an array of 3×3. An blower is used to pull the ambient air through the individual cells in order to operate them at low temperatures. However, distribution of air through all the cells may not be uniform. Thus, in order to operate electronics within permissible limits, sometimes it may be desirable to have flow rates higher than required. In this paper, first a simple representative cell (mimic cell) was fabricated whose system resistance was similar to that of original power cell. The simpler mimic cell was further used to perform numerical optimization wherein location of all the mimic cell is varied in order to reduce the mal distribution. The analysis showed that location of all the power cells is extremely critical. Also, the location of fan had a noticeable effect on the flow distribution. The optimized case resulted in mal-distribution of 16 cfm compared to 29.5 cfm for the baseline scenario.
Analysing Transient Thermoreflectance Data Using Network Identification by Deconvolution
Authors: Ezzahri Y. , Shakouri A.
Published: January 2011

Network Identification by Deconvolution (NID) method is applied to the analysis of the thermal transient pulsed laser heating. This is the excitation used in many optical experiments such as the Pump-Probe Transient Thermoreflectance experiment. NID method is based on linear RC network theory using Fourier’s law of heat conduction. This approach is used to extract the thermal time constant spectrum of the sample after excitation by either a step or pulsed heat source at one surface. Furthermore, using network theory mathematical transformations, the details of the heat flux path through the sample can be analyzed. This is done by introducing the cumulative and differential structure functions. We show that the conventional NID method can be modified to analyze transient laser heating experiments. The advantage is that the thermal resistance of the top material layers and the major interface thermal resistances can be extracted without the need of assuming a specific multilayer structure. Some of the limitations due to the finite thermal penetration depth of the transient heat pulse will be discussed.
Role of Process and Microstructural Parameters on Mixed Mode Fracture of Sn-Ag-Cu Solder Joints Under Dynamic Loading Conditions
Authors: Kumar P. , Huang Z. , Dutta I. , Mahajan R. , Renavikar M. , Sidhu R.
Published: January 2011

Electronic packages in mobile devices are often subjected to drops, leading to impact loading. Since solder joints, which serve as mechanical and electrical interconnects in a package, are particularly prone to failure during a drop, the fracture behavior of solders at high strain rates is a critical design parameter for building robust packages. Here we report on a methodology for measuring mixed-mode fracture toughness of Sn3.5Ag0.7Ag (SAC387) solder joints under dynamic loading conditions (at strain rates up to 100s−1), and use this method to investigate the role of solder microstructure and interfacial intermetallic compound (IMC) layer thickness on the joint fracture toughness at different mode-mixities and strain rates. Modified compact mixed mode (CMM) samples with adhesive solder joints between Cu plates and a thin film interfacial starter crack were used for the measurements. The interfacial IMC layer thickness was adjusted by controlling the dwell time during reflow, while the solder microstructure was controlled via the post-reflow cooling rate and subsequent thermal aging. The critical strain energy release rate (Gc) was measured as a function of these microstructural and loading variables, and these data were correlated with the associated crack path, details of which were elicited through fractography as well as crack-profile observations. The crack profile studies were based on samples with double interfacial starter cracks, one of which propagated only partially. Associated with the alteration of the joint microstructure, transitions in the fracture behavior were noted. In all cases, the cracks remained confined to the interfacial region, although the details of the crack propagation path and its interaction with interfacial IMCs, the adjacent solder and the pad surface finish varied significantly. Fracture toughness decreased with an increase in the strain rate and decreased with increasing mode-mixity. A thicker/coarser interfacial IMC layer (due to high dwell times) decreased toughness, while coarser solder microstructures (due to slow cooling during reflow or post-reflow aging) increased toughness. Correlations between joint microstructure and the observed deformation and fracture mechanisms will be highlighted, and a qualitative model based explanation for the inter-play between solder and IMC, and the associated interfaces will be presented.