bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of Droplet Motion Under Electrowetting Actuation
Authors: Annapragada S. Ravi , Dash Susmita , Garimella Suresh V. , Murthy Jayathi Y.
Published: February 2012

The static shape of droplets under electrowetting actuation is well-understood. The steady-state shape of the droplet is obtained based on the balance of surface tension and electrowetting forces, and the change in apparent contact angle is well-characterized by the Young-Lippmann equation. However, the transient droplet shape behavior when a voltage is suddenly applied across a droplet has received less attention. Additional dynamic frictional forces are at play during this transient process. We present a model to predict this transient behavior of the droplet shape under electrowetting actuation. The droplet shape is modeled using the volume of fluid method. The electrowetting and dynamic frictional forces are included as an effective dynamic contact angle through a force balance at the contact line. The model is used to predict the transient behavior of water droplets on smooth hydrophobic surfaces under electrowetting actuation. The predictions of transient behavior of droplet shape and contact radius are in excellent agreement our experimental measurements. The internal fluid motion is explained and the droplet motion is shown to initiate from the contact line. An approximate mathematical model is also developed to understand the physics of the droplet motion and to describe the overall droplet motion and the contact line velocities.
Two-Dimensional Strain-Distribution Sensor Using Carbon Nanotube-Dispersed Resin
Authors: Suzuki Yusuke , Ohashi Yusuke , Ohnishi Masato , Suzuki Ken , Miura Hideo
Published: February 2012

A new highly sensitive strain measurement method has been developed by applying the change of the electronic conductivity of CNTs. It is reported that most multi-walled carbon nanotubes (MWCNTs) show metallic conductivity and they are rather cheap comparing with single-walled carbon nanotubes (SWCNTs). The effect of the longitudinal axial strain on the band structures of electrons in CNTs was analyzed by applying the abinitio calculation based on the density functional theory. The change of the band structure of a MWCNT under uni-axial strain was analyzed. It was found that the electric conductivity of (MWCNTs) changes drastically because of the large change of their band gap. Therefore, the authors have focused on the possibility of the application of MWCNTs to a highly sensitive strain sensor. Multi-walled CNTs were dispersed in various kinds of resins such as epoxy, polycarbonate, and polyisoprene to form a thin film which can be easily attached to rounded surfaces. The length and diameter of the CNTs were about 5 μm and 50 nm, respectively. 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. 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 400%/%strain and that under the compressive strain was about 150%/%strain. The CNTs were also dispersed in polyisoprene by about 5%. Uni-axial tesile strain was also applied to the CNT-dispersed rubber. The maximum strain was 240%. It was found that the resistance of the rubber increased monotonically with the increase of the amplitude of the applied strain. The increase rate also increased with the amplitude of the applied strain, and the maximum rate reached about 25%/%strain. Two-dimensional strain fields were evaluated by using finely area-arrayed CNT-dispersed resin made by MEMS technology with spatial resolution of 50 μm.
Evaluation of Joining Strength of Silicon-Resin Interface at a Vertex in 3D Joint Structure
Authors: Koguchi Hideo , Hoshi Kazuhisa
Published: February 2012

Portable electric devices such as mobile phone and portable music player become compact and improve their performance. High-density packaging technology such as CSP (Chip Size Package) and Stacked-CSP is used for improving the performance of devices. CSP has a bonded structure composed of materials with different properties. A mismatch of material properties may cause stress singularity, which lead to the failure of bonding part in structures. In the present paper, stress analysis using boundary element method and an eigenvalue analysis using finite element method are used for evaluating the intensity of singularity at a vertex in three-dimensional joints. Three-dimensional boundary element program based on the fundamental solution for two-phase isotropic materials is used for calculating the stress distribution in a three-dimensional joint. Angular function in the singular stress field at the vertex in the three-dimensional joint is calculated using eigen vector determined from the eigenvalue analysis. The joining strength of interface in several kinds of sillicon-resin specimen with different triangular bonding areas is investigated analytically and experimentally. Experiment for debonding the interface in the joints is firstly carried out. Stress singularity analysis for the three-dimensional joints subjected to an external force for debonding the joints is secondly conducted. Combining results of the experiment and the analysis yields a final stress distribution for evaluating the strength of interface. Finally, a relationship of force for delamination in joints with different bonding areas is derived, and a critical value of the 3D intensity of singularity is determined.
Stress Intensity Factor Analysis of an Interfacial Corner Between Piezoelectric Bimaterials in a Two Dimensional Structure Using the H-Integral Method
Authors: Ikeda Toru , Hirai Hiroshi , Abe Mitsutoshi , Chiba Masatsugu , Miyazaki Noriyuki
Published: February 2012

A corner of bonded dissimilar materials is one of the main causes of the failure of electronic packages or MEMS structures. These materials are sometimes anisotropic materials and piezoelectric materials. To evaluate the integrity of a corner of bonded piezoelectric materials is useful for the reliability of electronic packages and MEMS. Asymptotic solutions around the interfacial corner between piezoelectric bimaterials can be obtained by the combination of the Stroh formalism and the Williams eigenfunction expansion method. Based on an extension of the Stroh formalism and the H-integral derived from Betti’s reciprocal principle for piezoelectric problems, we analyzed the stress intensity factors (SIFs) and asymptotic solutions of piezoelectric bimaterials. The eigenvalues and eigenvectors of an interfacial corner between dissimilar piezoelectric anisotropic materials are determined using the key matrix. The H-integral for piezoelectric problems is introduced to obtain the scalar coefficients, which are related to the SIFs. We propose a new definition of the SIFs of an interfacial corner for piezoelectric materials, and we demonstrated the accuracy of the SIFs by comparing the asymptotic solutions with the results obtained by the finite element method (FEM) with very fine meshes. Proposed method can analyze the stress intensity factors of a corner and a crack between dissimilar isotropic materials, anisotropic materials and anisotropic piezoelectric materials.
Two-Phase Minichannel Cold Plate for Army Vehicle Power Electronics
Authors: Sharar Darin J. , Morgan Brian , Jankowski Nicholas R. , Bar-Cohen Avram
Published: February 2012

Army programs have focused on increasing the use of power-dense electronic components to improve system weight, fuel usage, design flexibility, and overall functionality, thus, stressing the thermal management requirements. Recent cooling designs focused on flowing 80–100 °C engine coolant through single-phase microchannel cold plates but concern over pumping power, heat dissipation, cold plate temperature inconsistency, and contaminate clogging have prompted interest in two-phase flow in a minichannel cold plate. In the course of this study, both single- and two-phase experiments were conducted with a 6.8 × 2.7 × 0.9 cm offset fin minichannel cold plate using 25 °C, 80 °C, and 99 °C de-mineralized water, respectively, with flowrates ranging from 0.33 cm3/s to 45 cm3/s. Heat dissipation using solder attached chip resistors was incrementally increased from 0 W to more than 1000 W while simultaneously measuring cold plate pressure drop, chip surface temperature, inlet and outlet fluid temperature, and flowrate. Preliminary results indicate that utilizing a minichannel cold plate with two-phase heat transfer offers the ability to significantly reduce clogging potential, flowrate, and associated pumping power, while improving thermal resistivity by more than a factor of 4 and temperature consistency by greater than a factor of 10. Single- and two-phase correlations were used to compare performance with theoretical values.
Topology Optimization on Targeting Frequency and Mode of Ultrasonic Bonding Tool for Microchip Packaging
Authors: Ha Chang Yong , Lee Soo Il
Published: February 2012

Ultrasonic flip chip bonding is one of the widely used methods in semiconductor chip or microsystem packaging and ultrasonic (US) bonding tool is important part for the bonding machine. To perform the proper operation of US bonding, the adequate vibration frequency and mode of US tool is required and the vibration design of the tool is very important. Until recent days, however, the most of practical aspect of the tool design follows the trial-and-error approach. In this study, we introduce the method of topology optimization for US bonding tools. The solid isotropic material with penalization (SIMP) method is used to formulate topology optimization and optimal criteria (OC) method is introduced for the update scheme. The objective resonance frequency and longitudinal mode is tracked using Modal Assurance Criterion (MAC). We compare between 2D and 3D finite element models, and realize two types of US tools which are based on 3D optimization results. To ensure the validity of topology optimization applied to the high frequency and tough devices such as US bonding tools, the vibration displacements at anti-nodal points of the optimized US tools are measured by laser vibrometer.
The Effect of the Surface Roughness of Al Layer of DBA Substrate on Fatigue Life of Solder Joint in Power-Devices
Authors: Zhao Shiqiang , Yu Qiang , Akaeda Hiroki
Published: February 2012

On the reliability evaluation, the phenomenon of surface roughness on the Al surface of DBA (Direct Brazed Aluminum) on power device is confirmed. This surface roughness is generated by cyclic thermal stress under thermal cycle test. In this study, the surface roughness characteristic after thermal cycle test is executed to DBA substrate and the generating mechanism was investigated. Furthermore, the effect on the fatigue life of solder joint on DBA substrate is also investigated.
Effect of Chip Size and Thermal Amplitude on Fatigue Life of Pb-Free Solder Bump
Authors: Ishikawa Shoho , Tohmyoh Hironori , Saka Masumi , Watanabe Satoshi , Kuroha Motohisa , Nakano Yoshikatsu
Published: February 2012

Due to environmental concerns, Pb-free solders are widely used in electronic industry for assembling electronic components on the substrate. Under the various operation conditions, solder bumps are subjected to cyclic stress and failed by fatigue. To ensure the reliability of electronic products, it is becoming important to predict the fatigue failure of the Pb-free solder bumps. In this study, effects of chip size and thermal amplitude on fatigue life of the Pb-free solder bumps were investigated by experiments and elastic-plastic finite element analysis. A parameter, which is valuable to compare the fatigue damage of electronic packages with different chip size, is introduced.
Prediction of Transient Thermal Behavior of Planar Interconnect Architecture Using Proper Orthogonal Decomposition Method
Authors: Barabadi Banafsheh , Joshi Yogendra K. , Kumar Satish
Published: February 2012

A major challenge in maintaining quality and reliability in today’s microelectronics devices comes from the ever increasing level of integration in the device fabrication as well as the high level of current densities that are carried through the microchip during operation. Cyclic thermal events during operation, stemming from Joule heating of the metal lines, can lead to fatigue failure due to the varying thermal expansion coefficients of the different materials that compose the microchip package. To aid in the avoidance of such device failures, it is imperative to develop a predictive capability for the thermal response of micro-electronic circuits. This work studied the problem of transient Joule heating in interconnects in a two-dimensional (2D) inhomogeneous system using a reduced order modeling approach of the Proper Orthogonal Decomposition (POD) method and Galerkin Projection Technique. This study considers an interconnect structure embedded in the bulk of a microelectronic device. The effect of different types of current pulses, pulse duration, and pulse amplitude were investigated. By using a representative step function as the heat source, the model predicted the exact transient thermal behavior of the system for all other cases without generating any new observations, using just a few POD modes. To validate this unique capability, the result of the POD model was compared with a finite element (FE) model developed in LS-DYNA®. The behaviors of the POD models were in good agreements with the corresponding FE models. This close correlation provides the capability of predicting other cases based on a smaller sample set which can significantly decrease the computational cost.
Influence of Experimental Uncertainty on Prediction of Holistic Multi-Scale Data Center Energy Efficiency
Authors: Breen Thomas J. , Walsh Ed J. , Punch Jeff , Shah Amip J. , Kumari Niru , Bash Cullen E. , Heath Scot , Rubenstein Brandon
Published: February 2012

As the energy footprint of data centers continues to increase, models that allow for “what-if” simulations of different data center design and management paradigms will be important. Prior work by the authors has described a multi-scale energy efficiency model that allows for evaluating the coefficient of performance of the data center ensemble (COPGrand), and demonstrated the utility of such a model for purposes of choosing operational set-points and evaluating design trade-offs. However, experimental validation of these models poses a challenge because of the complexity involved with tailoring such a model for implementation to legacy data centers, with shared infrastructure and limited control over IT workload. Further, test facilities with dummy heat loads or artificial racks in lieu of IT equipment generally have limited utility in validating end-to-end models owing to the inability of such loads to mimic phenomena such as fan scalability, etc. In this work, we describe the experimental analysis conducted in a special test chamber and data center facility. The chamber, focusing on system level effects, is loaded with an actual IT rack, and a compressor delivers chilled air to the chamber at a preset temperature. By varying the load in the IT rack as well as the air delivery parameters — such as flow rate, supply temperature, etc. — a setup which simulates the system level of a data center is created. Experimental tests within a live data center facility are also conducted where the operating conditions of the cooling infrastructure are monitored — such as fluid temperatures, flow rates, etc. — and can be analyzed to determine effects such as air flow recirculation, heat exchanger performance, etc. Using the experimental data a multi-scale model configuration emulating the data center can be defined. We compare the results from such experimental analysis to a multi-scale energy efficiency model of the data center, and discuss the accuracies as well as inaccuracies within such a model. Difficulties encountered in the experimental work are discussed. The paper concludes by discussing areas for improvement in such modeling and experimental evaluation. Further validation of the complete multi-scale data center energy model is planned.
Numerical Study on the Reduction of Recirculation Using Sealed Cold Aisles and its Effect on the Efficiency of the Cooling Infrastructure
Authors: Ibrahim Mahmoud , Sammakia Bahgat , Bhopte Siddharth , Murray Bruce , Iyengar Madhusudan , Schmidt Roger
Published: February 2012

The increase in computing performance of electronic equipment is causing higher power consumption and in turn higher heat dissipation. On the larger scale, data centers that house hundreds of these individual electronic equipment are foreseeing an inevitable increase in heat dissipation on a facility level. The cooling cost of these rooms is becoming a major challenge, where a specified inlet temperature must not be exceeded in order to insure the safe and reliable operation of the electronic equipment. Most of the data centers in use today adopt the hot aisle-cold aisle configuration, where air is supplied through a plenum. The major problem with this configuration is the mixing of cold supply air from the tiles with hot exhaust air from the servers. This affects the efficiency of the cooling infrastructure and in turn affects the cost of operation. This study concentrates on the idea of sealing the cold aisle. Completely sealing the cold aisle is not practical due to pressure and noise problems, and therefore a perforated ceiling is proposed. A parametric study is generated to look at the effects of perforated ceiling resistance and different CRAC (Computer Room Air Conditioning) airflow supply percentage on the inlet temperature of the racks. A metric is proposed to quantify the variation of inlet temperature across the height of a rack and for a given cold aisle.
Thermal Resistance Measurement and Thermal Network Analysis of Printed Circuit Board With Thermal Vias
Authors: Hatakeyama Tomoyuki , Ishizuka Masaru , Nakagawa Shinji , Takakuwa Sadakazu
Published: February 2012

Thermal vias are widely used to reduce thermal resistance of a printed circuit board (PCB). However, fine via structure becomes an obstacle to computational fluid dynamics (CFD) simulation because fine structure requires a huge number of meshes. Therefore, an efficient modeling method of thermal via structure is needed to reduce computational time. In this paper, an effect of thermal vias on reduction of thermal resistance was experimentally and numerically investigated to gather fundamental data for thermal management of electronics. We used printed circuit board models with some kind of arrangements of thermal vias. Board materials and copper dissipating pad patterns were explored as experimental parameters. Copper pipes (unfilled vias) or rods (filled vias), the diameter of which was 1.5, 3.0 and 5.0 mm, were used as thermal via. Three materials (Glass epoxy, Stainless, and Polycarbonate), thermal conductivity of which were different, were used as board materials. The experimental results showed that area of heat dissipating copper pad patterns and board materials have strong effect on the temperature rise of the heat source. On the other hand, the number of thermal vias and via shapes have no effect on the heat source temperature. Then we performed thermal network analysis to evaluate the experimental results. From the results of the thermal network analysis, it was confirmed that an effect of thermal via is saturated at certain ratio of via area.
Constitutive Behavior of SAC Leadfree Alloys at High Strain Rates
Authors: Lall Pradeep , Shantaram Sandeep , Kulkarni Mandar , Limaye Geeta , Suhling Jeff
Published: February 2012

Electronic products are subjected to high G-levels during mechanical shock and vibration. Failure-modes include solder-joint failures, pad cratering, chip-cracking, copper trace fracture, and underfill fillet failures. The second-level interconnects may be experience high-strain rates and accrue damage during repetitive exposure to mechanical shock. Industry migration to leadfree solders has resulted in proliferation of a wide variety of solder alloy compositions. Few of the popular tin-silver-copper alloys include Sn1Ag0.5Cu and Sn3Ag0.5Cu. The high strain rate properties of leadfree solder alloys are scarce. Typical material tests systems are not well suited for measurement of high strain rates typical of mechanical shock. Previously, high strain rates techniques such as the Split Hopkinson Pressure Bar (SHPB) can be used for strain rates of 1000 per sec. However, measurement of materials at strain rates of 1–100 per sec which are typical of mechanical shock is difficult to address. In this paper, a new test-technique developed by the authors has been presented for measurement of material constitutive behavior. The instrument enables attaining strain rates in the neighborhood of 1 to 100 per sec. High speed cameras operating at 300,000 fps have been used in conjunction with digital image correlation for the measurement of full-field strain during the test. Constancy of cross-head velocity has been demonstrated during the test from the unloaded state to the specimen failure. Solder alloy constitutive behavior has been measured for SAC105, and SAC305 solders. Constitutive model has been fit to the material data. Samples have been tested at various time under thermal aging at 25°C and 125°C. The constitutive model has been embedded into an explicit finite element framework for the purpose of life-prediction of leadfree interconnects. Test assemblies has been fabricated and tested under JEDEC JESD22-B111 specified condition for mechanical shock. Model predictions have been correlated with experimental data.
Determination and Verification of Silicon Die Strength Using Ball-Breaker Test
Authors: Chen Pei-Chi , Yang Shin-Yueh , Chiang Kuo-Ning
Published: February 2012

3D or stacked-die packages are becoming increasingly popular in the electronic packaging industry because of the current market demand for cheaper and smaller products with high performance characteristics. As a result, the IC silicon wafers have to be grinded through wafer-thinning processes to achieve greater packaging density. However, it is possible to induce crack of the chips during stacking process or in the use of the device. Therefore, this study aims to determine the die strength of (1 0 0) silicon which can provide to designers for reliability of the die. Several methods have already been adopted to determine the strength of silicon die. These methods include three-point bending test (3PB), four-point bending test (4PB) and ball-breaker test. However, 3PB and 4PB have difficulty for application not only in experiment set ups and silicon die sample preparation aspects but also in actual use because of their sensitivity to both edge and surface defects. Therefore, the ball-breaker test is then proposed in this study to measure the maximum allowable force of silicon die. Meanwhile, comparing with experiment data, the finite element method (FEM) analysis using commercial software ANSYS/LSDYNA3D® are introduced to determine the silicon die strength. Moreover, the 3D model of the ball-breaker test is verified through the Hertzian contact theory. The effect of the thickness on silicon die strength and the failure modes are also discussed in this study. As the applied force increases, the crack appears on the edge of the contact area on the top surface and flare out within the die. However, the radial crack occurs on the bottom surface while the bending effect on the bottom side of the test die has become significant as the die thickness decreases. The early failure may occur at the position and then crack through the top surface causing the die breakage. In other words, the determined strength in this experiment decreases as the thickness of test die becomes increasingly thin. Furthermore, the simulation results show that the allowable force of silicon dies increases as the softer foundation material is applied while the bending behavior is not significant. However, the breakage of the thinner test die placed on the softer material is much easier to happen because the tensile stress on the bottom surface resulting from the bending behavior increases rapidly and significantly influences the die breakage.
Effects of TSV Interposer on the Reliability of 3D IC Integration SiP
Authors: Lau John H. , Zhang Xiaowu
Published: February 2012

The effect of Cu-filled through-silicon vias (TSVs) interposers on the reliability of 3D IC integration system-in-package (SiP) is investigated in this study. Emphasis is placed on the determination of the stresses at the Cu-low-k pads on a Moore’s law chip and the creep strain energy density per cycle at the corner solder joints between the Moore’s law chip and an interposer. Also, thermal cycling tests and failure analysis results of a test vehicle is presented and discussed.
Energy Efficient Data Centers Using Evaporative Cooling and Air Side Economizers
Authors: Iyengar Madhusudan , Schmidt Roger
Published: February 2012

Information Technology (IT) data centers consume a large amount of electricity in the US and world-wide. Cooling has been found to contribute about one third of this energy use. The two primary contributors to the data center cooling energy use are the refrigeration chiller (about 50% of cooling) and the Computer Room Air Conditioning units (about 33% of cooling). This paper focuses on a data center configuration that eliminates the use of the chiller plant thereby yielding substantial energy savings. One method of eliminating the chiller plant is to directly pump outdoor air into a data center with some amount of conditioning (particulate filtration). This configuration is can be called Direct Air Side Economizer (ASE). Since computer equipment is usually designed with the assumption that the rack air inlet temperatures are in the 15–32 °C range, the use of ASE is constrained to use only in those geographies where the outdoor air conditions allow such direct air use. One method to reduce the sensible air temperature of the outdoor air that is being ducted into a data center room is water evaporation directly into the air stream. Such a method can be called Evaporative Air Side Economizer (EASE). This paper discusses the benefits of EASE data center configurations in the context of the climate in the USA and realizable energy savings compared with traditional chiller plant based cooling loops. Hour by hour outdoor air temperature data for a typical year and psychometric charts are utilized in conjunction with simple transfer functions to model cooling via evaporative media. Phoenix, a US city in a hot climate is used to illustrate the use of the relatively new method of data center cooling. A comparison to the traditional chiller plant based approach resulted in about 30% of energy savings at the data center level.
High Performance Thermal Conductive Sheets Made of Carbon Fibers
Authors: Aramaki Keisuke , Ryoson Hiroyuki , Ishida Yuichi
Published: February 2012

Today, the quality of LCD (Liquid Crystal Display) TVs has improved along with the quality of the installed LSI (Large Scale Integration) Thus, the cooling system needs to have high performance. However, LCD TV requires a large area but thin cooling system, so the TIM in which used in LCD TV requires highly softness. Thus we have developed high-quality yet soft thermal conductive sheets in which carbon fibers are directed in the thickness direction. The thermal conductivity of the 2-mm-thick sheets is more than 23 W/mK, and the compressibility is more than 10%. In this case the thermal conductivity was measured in accordance with ASTM D5470. The compressibility means the ratio of the difference between the initial thickness and the thickness when the sheets were loaded. The carbon fibers are more than 100 μm long and about 10 μm in diameter. This sheet contains alumina and aluminum nitride particles. The manufacturing process for the sheet is as follows. Step 1: The mixing process. Step 2: The resin including the carbon fibers and the particles is pressed into a long rectangular cast. Step 3: The resin is heated to harden it. Step 4: The resin is sliced into sheets. In step 1, because the carbon fibers are long, the fibers are likely affected by shear stress. Thus, the fibers are aligned in a lengthwise direction. In Step 4, we used a supersonic wave cutter to achieve ideal slicing, thereby reducing the thermal contact resistance. These processes produced high-quality yet soft thermal conductive sheets. In these processes, the carbon fibers aligned in the thickness direction, which was determined in an SEM observation. Moreover, we found that, by slicing in the orientation direction at inclining angles, only the softness improved, without any deterioration in the thermal conductivity.
Effect of Interfacial Layers on the Performance of Cu-In Liquid Phase Sintered Composites as Thermal Interface and Interconnect Materials
Authors: Liu J. , Kumar P. , Dutta I. , Nagaraj C. M. , Raj R. , Renavikar M. , Mahajan R.
Published: February 2012

In this study, a novel architecture composed of uniformly distributed high melting phase (HMP, e.g. Cu) in a low melting phase (LMP, e.g. In) matrix, which can be produced via liquid phase sintering (LPS), is proposed to produce next generation thermal interface materials (TIMs) and interconnect (IC) materials. The LMP determines the shear compliance of these composites whereas the HMP determines its thermal and electrical conductivities. The volume fraction of In was optimized to produce a Cu-In solder with suitable mechanical, electrical and thermal properties for TIM and IC applications. Since, Cu and In react to form several Cu-In intermetallic compounds (IMCs), which may deteriorate the long-term performance of these solders, interfacial-layers of Au and Al2O3 were applied on Cu to further improve the performance of the Cu-In solders. The effect of interfacial-layers on the reaction between Cu and In, during sintering at 160°C and during aging at 125°C, was studied and its impact on the mechanical, thermal and electrical properties was evaluated. Au interfacial layer (50∼200nm) quickly reacted with In to form AuIn2 IMC, which acted as a tenacious diffusion-barrier and slowed down the reactions between Cu and In. 8-monolayer thick Al2O3 did not react with either Cu or In and inhibited reactions between Cu and In. During short-time sintering, the effect of interfacial layer on the thicknesses of IMCs was insignificant to affect the yield strength of the as-sintered composites. However, IMC layer thickened rapidly in the Cu-In composites without an interfacial-layer, which led to a drastic decrease in the volume fraction of unreacted In leading to an increase in the yield strength of the solder. On the other hand, the interfacial-layers effectively suppressed the growth of IMCs during aging and hence the yield strength of such composites increased at slower rates. Since, the IMCs formed at the interface radically affect the contact resistance, significant differences in the thermal and electrical conductivities were recorded for the solders with different interfacial-layers.
Silicon Hot Spot Remediation With a Germanium Self Cooling Layer
Authors: Nochetto Horacio , Wang Peng , Bar-Cohen Avram
Published: February 2012

Driven by shrinking feature sizes, microprocessor hot spots have emerged as the primary driver for on-chip cooling of today’s IC technologies. Current thermal management technologies offer few choices for such on-chip hot spot remediation. A solid state germanium self-cooling layer, fabricated on top of the silicon chip, is proposed and demonstrated to have great promise for reducing the severity of on-chip hot spots. 3D thermo-electrical coupled simulations are used to investigate the effectiveness of a bi-layer device containing a germanium self-cooling layer above an electrically insulated silicon layer. The parametric variables of applied current, cooler size, silicon percentage, and total die thickness are sequentially optimized for the lowest hot spot temperature compared to a non-self-cooled silicon chip. Results suggest that the localized self-cooling of the germanium layer coupled with the higher thermal conductivity of the silicon chip can significantly reduce the temperature rise resulting from a micro-scaled hot spot.
IC-Package Thermal Co-Analysis in 3D IC Environment
Authors: Pan Stephen H. , Chang Norman , Zheng Ji
Published: February 2012

Power on chip is highly temperature dependent in deep sub-micron VLSI. With increasing power density in modern 3D-IC and SiP, thermal induced reliability and performance issues such as leakage power and electromigration must be taken into consideration in the system level design. This paper presents a new methodology and its applications to accurately and efficiently predict power and temperature distribution for 3D ICs.
Thermal Stress of Through Silicon Vias and Si Chips in 3D SiP
Authors: Kinoshita Takahiro , Kawakami Takashi , Hori Tatsuhiro , Matsumoto Keiji , Kohara Sayuri , Orii Yasumitsu , Yamada Fumiaki , Kada Morihiro
Published: February 2012

Thermal conduction and mechanical strength around TSV (Through Silicon Via) structures of 3D SiP (Three Dimensional System in Package) were discussed both cases of with and without void in TSV by using a large scale simulator based on FEM, ADVENTURECluster® for ensuring the reliability of 3D SiP. In the results, the thermal performance that was required in 3D SiP was estimated to ensure the reliability. Simulations for thermal stresses around TSV structure in 3D SiP under thermal cycle condition due to power ON/OFF were carried out. In case that void was not in TSV, stresses in TSV were close to hydrostatic pressure and the magnitude of the equivalent stress was lower than the yield stress of copper. However, the level of the stresses, especially in Si chips, should not be negligible in inducing damages to TSVs and Si single crystals. In case that void was in TSV, stress was concentrated around void in TSV and the magnitude of the equivalent stress was lower than the yield stress of copper. The level of stresses applied to Si chip was slightly reduced due to void in TSV. However, its level should not be negligible in inducing damages to TSVs and Si single crystals.
Spectral Detail of Phonon Conduction and Scattering in Graphene
Authors: Singh Dhruv , Murthy Jayathi Y. , Fisher Timothy S.
Published: February 2012

This paper examines the thermodynamic and thermal transport properties of the 2D graphene lattice. The interatomic interactions are modeled using the Tersoff interatomic potential and are used to evaluate phonon dispersion curves, density of states and thermodynamic properties of graphene as functions of temperature. Perturbation theory is applied to calculate the transition probabilities for three-phonon scattering. The matrix elements of the perturbing Hamiltonian are calculated using the anharmonic interatomic force constants obtained from the interatomic potential as well. An algorithm to accurately quantify the contours of energy balance for three-phonon scattering events is presented and applied to calculate the net transition probability from a given phonon mode. Under the linear approximation, the Boltzmann transport equation (BTE) is applied to compute the thermal conductivity of graphene, giving spectral and polarization-resolved information. Predictions of thermal conductivity for a wide range of parameters elucidate the behavior of diffusive phonon transport. The complete spectral detail of selection rules, important phonon scattering pathways, and phonon relaxation times in graphene are provided, contrasting graphene with other materials, along with implications for graphene electronics. We also highlight the specific scattering processes that are important in Raman spectroscopy based measurements of graphene thermal conductivity, and provide a plausible explanation for the observed dependence on laser spot size.
Frequency Resolved Phonon Transport in Si/Ge Nanocomposites
Authors: Singh Dhruv , Murthy Jayathi Y. , Fisher Timothy S.
Published: February 2012

In this paper, we analyze cross plane phonon transport and thermal conductivity in two-dimensional Si/Ge nanocomposites. A non-gray BTE model that includes full details of phonon dispersion, the spread in phonon mean free paths and the frequency dependent transmissivity is used to simulate thermal transport. The general conclusions inferred from gray BTE simulations that the thermal conductivity of the nanocomposite is much lower than its constituent materials and interfacial density as the parameter determining thermal conductivity remain the same. However, it is found that the gray BTE significantly overpredicts thermal conductivity in the length scales of interest and quantitatively reliable results are obtained only upon inclusion of the details of phonon dispersion. The transition of phonon transport from ballistic regime to near diffusive regime is observed by looking at a large range of length scales. Non-equilibrium energy exchange between optical and acoustic phonons and the granularity in phonon mean free paths are found to significantly affect thermal conductivity leading to departures from the frequently employed gray approximation. It is also found that the frequency content of thermal conductivity in the nanocomposite extends out to a much larger frequency range unlike bulk Si and Ge. Scattering against heterogeneous interfaces is very effective in suppressing thermal conductivity contribution from the low frequency acoustic phonons but less so for high frequency phonons, which have much smaller mean free paths.
Ionic Polymer Metal Composite (IPMC) for MEMS Actuator and Sensor
Authors: Yanamori Hiroki , Kobayashi Takuma , Omiya Masaki
Published: February 2012

An ionic polymer-metal composite (IPMC) consisting of a thin perfuorinated ionomer membrane, electrodes plated on both faces, undergoes large bending motion when a small electric field is applied across its thickness in a hydrated state. On the other hand, when small load is applied on IPMC, the electric field is induced in the polymer membrane depending on the magnitude of loading. The characteristics of IPMC are ease of miniaturization, low density and mechanical flexibility. Therefore, it is considered to have a wide range of applications from MEMS sensors to actuators. In this paper, we developed the fabrication process of IPMC actuator with palladium electrodes, which have lower stiffness than the conventional IPMC actuator with Au or Pt electrodes. The deformation of IPMC actuator is evaluated under various solvents, various temperatures, and various frequencies of input voltages. We developed the numerical model of IPMC actuator that can change the solution temperature and the ion species and compared the simulation results to the experimental results.
The Microelectronics Cooling Impact and Comparison of 2D and 3D Unsteady Effects of a Pair of Opposed Confined Angled Impinging Air Jets
Authors: Chiriac Victor Adrian , Rosales Jorge Luis
Published: February 2012

The unsteady laminar flow and heat transfer characteristics for a pair of angled confined impinging air jets centered in a channel were studied numerically. The time-averaged heat transfer coefficient for a pair of heat sources centered in the channel was determined, as well as the oscillating jet frequency for the unsteady cases. The present study is a continuation of the authors’ previous investigations, identifying the similarities and differences arising from the expansion to the third dimension. It examines the interaction between the angled jets and the associated impact on the cooling of the heat sources placed on the board at a jet Reynolds number of 100 and 600. Maintaining the inlet jet width, W, at 1 cm, as in the previous studied cases, the interaction between the 45° angled jets leads to the formation of unsteady symmetrical jets that impinge on the two heat sources placed on the board at a Reynolds number of 100. A second case investigates the hydrodynamic interaction between the 45° angled jets at a Reynolds number of 600. In this case the jets interact and form a region of unsteady shear causing the jets to sweep the target board and the heated components placed on it. The nature of this unsteadiness depends on the proximity of the jet inlets, the channel dimensions and the jet Reynolds number. The jet unsteadiness causes the stagnation point locations to sweep back and forth over the impingement region causing the jets to “wash” a larger surface area on the target wall. The relevant trends for the 2D and 3D jet hydrodynamic and thermal fields are further documented by comparing the field plots and the Nusselt numbers on the target walls for the cases under evaluation. Although similar in nature, the unsteady 3D opposite jets produce results that deviate from the 2D unsteady opposite jets. The complex vortex patterns resulting from the jet interaction at various jet inlet locations, as well as the velocity, vorticity and temperature fields for both 2D and 3D cases are thoroughly evaluated.
Thinner Thermal Solution Module by Combination of Thin Heat Pipe and Piezo Fan
Authors: Jalilvand Ahmad , Mochizuki Masataka , Saito Yuji , Kawahara Yoji , Wuttijumnong Vijit , Nguyen Thang
Published: February 2012

A high-density and slim-type packaging technology in a notebook PC or a handheld PC has been developed as the importance of portability is increased more and more recently. The heat generated in small-sized electronic units should be dissipated effectively for operational stability during system lifetime. Considering the technical trend for miniaturized packaging of components, which requires very limited space, installed in the system; it is inevitable to develop and apply a micro-cooling device. In the present study, a very thin cooling device which operates on the basis of piezoelectricity has been introduced. First, the operation principal of Piezo fan is explained and then this new type of Piezo fan is introduced. Performance test results on thin laptop thermal solution module combined with this new Piezo fan is investigated. The original thermal solution module was composed of thin heat spreader (1 mm thick) and thin heat pipe (less than 2 mm) with finned heat sink at the condenser cooled by mini cooling fan (brushless mini fan). The mini fan is replaced by this new type of much thinner Piezo fan and then performance is studied and the results are compared with thin cooling module when cooled by mini cooling fan. In addition, this work consists of various developments that have been conducted to improve the performance of this Piezo fan that includes enhancement of cooling performance and reduction of acoustic noise.
Use Condition Characterization of Package Components
Authors: Wojewoda Leigh , Athreya Dhanya , Hill Michael J.
Published: February 2012

Discrete components, such as capacitors and inductors, play an important role in the analysis and design of electronic packages and printed circuit boards. Although the electrical parameters of discrete components are described by manufacturers, the component performance at product operating conditions can vary drastically from the manufacturer’s specification. Accurate characterization of discrete package components at operating conditions is essential to understand product operation. This paper will introduce a method to characterize discrete capacitors and inductors while applying multiple operating conditions simultaneously. Several inductor options will be evaluated, including a newly introduced metal composite component.
A Quantum Mechanical Study of the Thermal Conduction Across a ZrB2-SiC Interface as a Function of Temperature and Strain
Authors: Samvedi Vikas , Tomar Vikas
Published: February 2012

Atomistic analyses of thermal conduction across ZrB2/SiC based nanocomposite interface are performed using first principles density functional theory (DFT) with plane-wave basis sets. The changes in the thermal properties of nanocomposites have been analyzed under the effect of straining and temperature and compared for their phononic and electronic dependence.
A Note on the Reliability of Cu/Au Wire Interconnects
Authors: Lau J. , Wu S. , Lau J. M.
Published: February 2012

The pull force and displacement of gold (Au) and copper (Cu) wires in microelectronics are investigated in this study. Emphasis is placed on (1) the development of a set of equations for determining the internal forces and deformations of wires when subjected to an external pull force, (2) the determination of the maximum pull force (when the wire breaks) based on some failure criteria of the wires; and (3) the experimental verification of the present equations.
Pressure-driven flow of rarefied gas through a slit at a various pressure ratios
Authors: Sazhin Oleg
Published: February 2012

This paper numerically studies a pressure-driven flow of rarefied gas through a slit using a direct simulation Monte Carlo method. A gas mass flow rate through a slit and a gas flow field were calculated. The calculations were carried out for various values of the pressure ratio over a wide range of gas rarefaction. The dependency of the mass flow rate and the flow field characteristics on the pressure ratio value and gas rarefaction degree was determined. In addition, the paper presents a discussion on the existence of the shock waves within a flow field in a hydrodynamic regime of the gas flow.
Temporal and spectral masking release in low- and mid-frequency regions for normal-hearing and hearing-impaired listeners
Authors: Léger Agnès C. , Moore Brian C. J. , Lorenzi Christian
Published: February 2012

“Masking release” (MR), the improvement of speech intelligibility in modulated compared with unmodulated maskers, is typically smaller than normal for hearing-impaired listeners. The extent to which this is due to reduced audibility or to suprathreshold processing deficits is unclear. Here, the effects of audibility were controlled by using stimuli restricted to the low- (≤1.5 kHz) or mid-frequency (1–3 kHz) region for normal-hearing listeners and hearing-impaired listeners with near-normal hearing in the tested region. Previous work suggests that the latter may have suprathreshold deficits. Both spectral and temporal MR were measured. Consonant identification was measured in quiet and in the presence of unmodulated, amplitude-modulated, and spectrally modulated noise at three signal-to-noise ratios (the same ratios for the two groups). For both frequency regions, consonant identification was poorer for the hearing-impaired than for the normal-hearing listeners in all conditions. The results suggest the presence of suprathreshold deficits for the hearing-impaired listeners, despite near-normal audiometric thresholds over the tested frequency regions. However, spectral MR and temporal MR were similar for the two groups. Thus, the suprathreshold deficits for the hearing-impaired group did not lead to reduced MR.