bluuebunny/crossref_metadata_2025 huggingface dataset:
A Method for Failure Analysis for Devices With Simultaneous Imaging of Electron Emission and Near IR Thermoreflectance
Authors: Yazawa Kazuaki , Kendig Dustin , Christofferson James , Shakouri Ali
Published: January 2014

Thermal characterization is useful for identifying the cause of circuit failures. Unusually high local temperatures can occur due to unexpected and localized power dissipation in a particular device, which was not anticipated nor designed in the device. Unintended high temperatures may be the source of circuit damage or it might be caused by the failure itself, such as a tiny short-circuit. However, it is often difficult to obtain enough information about the physical structure and characteristics of the circuit to clearly identify the cause of the failure. The method we present here is an imaging technique with both thermal distribution and emission intensity superimposed on a single image.

Thermoreflectance thermal imaging takes advantage of the differences in light reflectivity of the surface with a changing temperature. This relationship is quite linear in a typical temperature range of interest. Using 1300 nm wave length for the illuminating source, the metal circuitry of interest is directly observed through the almost transparent silicon substrate of a flip chip mounted device. With the same photo detecting imaging sensor, i.e. InGaAs junction array, the emission from the target device through the silicon substrate is also detected. If there are some local electron collisions, e.g. due to a current concentration at a defect or a tiny whisker, a localized excess energy by electron-electron collision yields the photon generation and emits an electromagnetic wave. The photons having a sufficient energy level at wavelength transparent to silicon, reach the photo detecting imaging sensor. With software processing and precise synchronization of the driving circuit, illumination, and imaging, we can separate the thermal signal from the emission and observe transient behavior on a nanosecond time scale. The time response is helpful in some cases to separate cause and effect. As an example, an unintended small short-circuit resulting from the fabrication process may be reproduced for a small number of samples. The emission would be observed first, followed by the thermal signal which propagates in time. Another example is for a circuit with low design margin, in this case only a single sample exhibits a difference between emission and/or thermal image while numbers of good samples are identical with respect to the emission and thermal image. This difference clearly indicates the location of a potential failure.
Effect of Meniscus Recession on the Effective Pore Radius and Capillary Pumping of Copper Metal Foams
Authors: Shirazy Mahmood R. S. , Fréchette Luc G.
Published: January 2014

An experimental study is performed to characterize the effect of meniscus recession on the effective pore radius and capillary pumping of copper metal foams which are to be used as wicks in heat pipes for electronic cooling. Knowledge of the effective pore radius is critical in defining the capillary pumping of a wicking material, but is rarely measured under operating conditions. It is known that the meniscus of a liquid recedes when evaporating from a porous media, which could impact the effective pore radius and therefore the capillary pumping capabilities of the foam. To elucidate this impact, the evaporation rate is measured from foam strips wicking ethanol from a reservoir while applying heat fluxes to the foam. Using thermocouple and IR camera measurements, the measured evaporation rates are corrected to account for different thermal losses, including natural convection, direct thermal conduction to the liquid, and evaporation from the container. An analytical model is then developed to relate the evaporated mass to the maximum capillary pressure (minimum effective pore radius) provided by the foam. It is shown for the first time, that just before the onset of dryout, the recessed meniscus will lead to 15%, 28% and 52% decrease in effective pore radius for samples with 68%, 75% and 82% porosities respectively. The capillary pumping therefore increases during evaporation. This can have significant impact on the prediction of the capillary limits in two phase capillary driven devices.
Improving the Thermal Performance of a Forced Convection Air Cooled Solution: Part 2 — Effect on System-Level Performance
Authors: Fernandes John Edward , Ghalambor Saeed , Eiland Richard , Agonafer Dereje , Mulay Veerendra
Published: January 2014

The heat sink assembly of an air cooled CPU is modified to improve thermal performance of the module-level solution. This modification is employed in a dual-socket server that relies on system fans to move air for forced convection cooling of all heat generating components on the motherboard. Currently, in the data center industry, the focus is on reducing power consumption through application of energy-efficient cooling solutions. Fans installed in the server operate as a function of CPU die temperatures and represent a parasitic load that must be minimized. Improvement in system-level performance can be quantified in terms of reduced fan and server power consumption. The server is subjected to varying CPU utilizations and corresponding average fan speeds and power consumption are reported. Similarly, reduction in CPU junction temperature and server power at a given utilization can be computed by operating the fans at a constant speed. Difference in thermal performance and power consumption between the baseline and modified heat sink configurations was found to negligible when a TIM is applied. However, in the absence of a TIM, the modified assembly delivered as much as 24.4% reduction in CPU die temperature and 6.2% reduction in server power consumption. In addition, there is indiscernible variation in server power consumption between the baseline (with employment of TIM) and modified (with and without TIM application) heat sink assemblies. Thus, the modified configuration has possible applications in systems where a TIM may be undesirable or difficult to apply.
Improving the Thermal Performance of a Forced Convection Air Cooled Solution: Part 1 — Modification of Heat Sink Assembly
Authors: Ghalambor Saeed , Fernandes John Edward , Agonafer Dereje , Mulay Veerendra
Published: January 2014

Forced convection air cooling using heat sinks is one of the most prevalent methods in thermal management of microelectronic devices. Improving the performance of such a solution may involve minimizing the external thermal resistance (Rext) of the package. For a given heat sink design, this can be achieved by reducing the thermal interface material (TIM) thickness through promotion of a uniform interfacial pressure distribution between the device and heat sink. In this study, a dual-CPU rackmount server is considered and modifications to the heat sink assembly such as backplate thickness and bolting configuration are investigated to achieve the aforementioned improvements. A full-scale, simplified model of the motherboard is deployed in ANSYS Mechanical, with emphasis on non-linear contact analysis and torque analysis of spring screws, to determine the optimal design of the heat sink assembly. It is observed that improved interfacial contact and pressure distribution is achieved by increasing the number of screws (loading points) and positioning them as close to the contact area as possible. The numerical model is validated by comparison with experimental measurements within reasonable accuracy. Based on the results of numerical analysis, the heat sink assembly is modified and improvement over the base configuration is experimentally quantified through interfacial pressure measurement. The effect of improved interfacial contact on thermal performance of the solution is discussed.
Analysis of 3D-Strain Singular Field Near the Corner of Si Chip Using Digital Image Correlation Method
Authors: Koguchi Hideo , Tsukada Yasuyuki , Kurahashi Takahiko
Published: January 2014

Portable electronics 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 study, a strain singular field near inter-face edge in three-dimensional joints is investigated using digital image correlation method. A specimen which silicon chip was embedded in resin is used in experiment and tensile load is applied to the specimen. Photograph of specimen surface is taken before and after loadings by laser microscope. Displacement on the surface was evaluated by the digital image correlation method (DICM) using data of surface pattern on the specimen, which the cross correlation coefficients for surface pattern are maximized. Strain on surface of specimen is calculated by using the moving least square method. On the other hand, 3D element free Galerkin method is applied to compute the displacement and strain distribution in a three-dimensional model of the specimen. In the element free Galerkin method, the physical values, i.e., displacement, strain and stress, can be obtained by using the displacement data at node. In this research, strain distribution near the edge of interface is computed based on the element free Galerkin method. Finally, the strain distribution obtained by the digital image correlation method and the moving least square method is compared with that obtained by the element free Galerkin method. The intensity of strain singularity is determined numerically and experimentally.
A Transient Model for Parallel Flow and Counter Flow Heat Exchangers
Authors: Abbasi K. , Del Valle M. , Wemhoff A. P. , Ortega A.
Published: January 2014

The transient and steady-state response of single pass constant-flow (concentric parallel flow, concentric counter flow) heat exchangers was investigated using a finite volume method. Heat exchanger transients initiated by both step-change and sinusoidally varying hot stream inlet temperatures were investigated. The wall separating the fluid streams was modeled by conduction with thermal mass; hence the heat exchanger transient behavior is dependent on the thermal mass of the fluid streams as well as the internal wall. The outer wall is approximated as fully insulating. The time dependent temperature profiles were investigated as a function of heat exchanger dimensionless length and dimensionless time for both fluids. It was found that the transient response of the heat exchanger is controlled by a combination of the residence time and thermal capacitance of the fluid streams, the overall heat transfer coefficient between the fluid streams, and the thermal capacitance of the internal wall.
Early Power Delivery Analysis of Bump Depopulation
Authors: Gan Houle , Bharath Krishna
Published: January 2014

In this paper, a modeling flow has been developed for the analysis of large-area die-package power delivery networks. The analysis is implemented in an early pathfinding phase of a product development cycle so that technology options such as bump pitch and pattern can be defined before the real physical design is completed. The flow utilizes a popular commercially available on-die power delivery simulator, combined with a suite of custom software developed internally, and delivers worst-case static and dynamic voltage drops across a sufficiently representative portion of the die (larger than 1mm2 and with full silicon metal stack). Scenarios of different bump depopulation are then compared and any potential power delivery risk is identified. The flow has been employed to analyze the power delivery problem of a realistic on-die region containing logics from graphics block, where the impact of increasing levels of bump depopulation due to encroachment from adjacent I/O circuits was studied. Results have shown the effectiveness and efficiency of the proposed flow.
Integration of a Multiple-Condenser Loop Heat Pipe in a Compact Air-Cooled Heat Sink
Authors: Kariya H. Arthur , Hanks Daniel F. , Staats Wayne L. , Roche Nicholas A. , Cleary Martin , Peters Teresa B. , Brisson John G. , Wang Evelyn N.
Published: January 2014

We present the characterization of a compact, high performance air-cooled heat sink with an integrated loop heat pipe. In this configuration, heat enters the heat sink at the evaporator base and is transferred within the heat pipe by the latent heat of vaporization of a working fluid. From the condensers, the heat is transferred to the ambient air by an integrated fan. Multiple condensers are used to increase the surface area available for air-cooling, and to ensure the equal and optimal operation of the individual condensers, an additional wick is incorporated into the condensers. We demonstrated with this design (10.2 cm × 10.2 cm × 9 cm), a total thermal resistance of less than 0.1 °C/W while dissipating a heat load of 500 W from a source at 75 °C. Furthermore, constant thermal resistance was observed in the upright as well as sideways orientations. This prototype is a proof-of-concept demonstration of a high performance and efficient air-cooled heat sink design that can be readily integrated for various electronics packaging and data center applications.
Heat Transfer Performance of an Air-Assisted Impinging Water Jet Under a Fixed Pumping Power Constraint
Authors: Trainer Daniel , Kim Sung Jin
Published: January 2014

Air injection into a liquid impinging jet has been shown to be a method of improving non-phase change heat transfer rates by up to twice the normal amount. Previous work has shown that there exists an optimal operating point in terms of the volumetric fraction of air injection when the pumping power is held constant because of an optimal two-phase flow pattern. However, previous work focused on heat transfer from the impingement point only, and neglected performance at other points. The present work studies the local heat transfer performance of an air-assisted water jet, at the impingement point and at positions moving radially outward, under constant pumping power conditions. The area-averaged heat transfer is also considered. Heat transfer at the stagnation point is shown to be optimized between β = 0.1∼0.2, where a bubbly flow pattern exists. Nuavg(r/D ≤ 1) is optimized when the flow pattern was plug-flow and off-center peaks in Nur exist. Nuavg(r/D > 1) is optimized when the water is accelerated by the injected air, but splattering is avoided. Flow patterns have no direct effect outside the impingement region.
Reliability Evaluation of a 3D SIC Package by the Combination of the SEM-DIC and the FEM
Authors: Ikeda Toru , Oka Masatoshi , Miyazaki Noriyuki
Published: January 2014

Numerical methods such as the finite element method (FEM) have been used to evaluate the reliability of electronic packages. The accuracy of the analyses should be verified by some experimental measurements. In this study, we evaluated the thermal strain of a test chip for three-dimensional stacked integrated circuits (3D SIC) with both measurement and an analysis. First, the distribution of thermal strain on the cross-section of a test chip was measured using scanning electron microscope (SEM) and the digital image correlation. Then, the distribution of strain of the test chip was also analyzed by the FEM considering the viscoelastic material properties of underfill (UF) resin measured with the stress relaxation test and the elastic-plastic material properties of components measured with the nano-indentation tests. The accuracy of the nonlinear finite element analysis was verified using the strain measurements with the SEM-DICM.

A test specimen for the 3D SIC packages was built and cut out a part of the test specimen and polished its cross-section. We took digital images using a SEM (FEI Quanta 200) to measure the strain distributions on the cross-section of a specimen by the DICM. The specimen was subjected to thermal loading in a heat chamber. The temperature in the chamber was raised from 30° C to 130°C.

The FE analyses were carried out using MSC.Marc™. We assumed the initial temperature of the analysis to be 150°C, which was the curing temperature of the UF resin, and decreased the temperature to 30°C during 100 seconds. Then, the temperature was raised up to 130°C, which is the same with the experiment. We compared the numerical result with the measurement and modified the model of the FE analyses.
Effect of Fin Interruptions on Natural Convection Heat Transfer From a Rectangular Interrupted Single-Wall
Authors: Mostafavi Golnoosh , Ahmadi Mehran , Bahrami Majid
Published: January 2014

Steady-state external natural convective heat transfer from a single-wall vertically-mounted rectangular interrupted fin arrays is investigated. A systematic numerical, experimental, and analytical study is conducted on the effect of adding interruptions to a single vertical plate, on natural convective heat transfer. COMSOL Multiphysics software is used in order to develop a two-dimensional numerical model for investigation of fin interruption effects. To perform an experimental study and to verify the analytical and numerical results, a custom-designed testbed was developed. Results show that adding interruptions to a vertical single fin enhances the thermal performance of it and reduces the weight of the heatsink, which in turn, can lead to lower manufacturing costs. A compact relationship for the Nusselt number based on geometrical parameters for interrupted fins is presented using a blending technique for two asymptotes of interruption length.
Effect of Aging on Impression Creep Behavior of Pb-Free Solders
Authors: Talebanpour B. , Sahaym U. , Dutta I. , Kumar P.
Published: January 2014

During service and/or storage, Sn-Ag-Cu (SAC) solder alloys are subjected to temperatures ranging from 0.4 to 0.8 Tm (where Tm is the melting temperature of SAC alloys), making them highly prone to significant microstructural coarsening. The microstructures of these low melting point alloys continuously evolve during service. This results in evolution of creep properties of the joint over time, thereby influencing the long-term reliability of microelectronic packages. Here, we study microstructure evolution and creep behavior of two Sn-Ag-Cu (SAC) alloys, namely Sn-3.0Ag-0.5Cu and Sn-1.0Cu-0.5Cu, isothermally aged at 150°C for various lengths of time. Creep behavior of the two SAC solders after different aging durations was systematically studied using impression creep technique. The key microstructural features that evolve during aging are Ag3Sn particle size and inter-particle spacing. Creep results indicate that the creep rate increases considerably with increasing inter-particle spacing although the creep stress exponent and creep activation energy are independent of the aging history.
Experimental Study of the Convective Heat Transfer From a Geometrically Scaled Up 2D Impinging Synthetic Jet
Authors: Silva Luis , Ortega Alfonso , Rose Isaac
Published: January 2014

Synthetic jets are created by periodically ejecting and injecting fluid from an orifice or channel. Despite delivering no net mass flow per cycle, a synthetic jet delivers flow with net positive momentum. Small, compact synthetic jet actuators can be fabricated to operate in the subaudible acoustic range and can be packaged in orientations that allow them to deliver cooling air flow to electronic devices. The most promising orientation is one that delivers the jet flow in a direction normal to the heated surface such that it impinges on the surface as a periodic jet. In previous studies, numerical simulations have been performed by the authors, utilizing a canonical geometry, with the purpose of eliminating actuator artifacts from the fundamental physics that drive the problem. The present paper reports on laboratory experiments that have been performed in order to nearly replicate the idealized synthetic jet geometry and thus allow comparison to the previous numerical investigations. The periodic volume change in an upstream plenum required to produce the synthetic jet is accomplished with an acoustic speaker operated at low frequencies. The amplitude and the frequency at which the jet is actuated determine the Reynolds and Strouhal numbers, which are the dominant non-dimensional groups that control the behavior of the impinging synthetic jet. By maintaining the Re and the St in the laboratory experiments to match those of the small scale actuators, the laboratory experiments have been geometrically scaled up to allow highly resolved measurements of the unsteady velocity field and the local time-dependent Nusselt number on the target heated surface. Experiments were performed at variable jet Re, frequencies, and height from the target surface. The dependence of the surface averaged Nu to jet parameters generally agrees with the computational results. However, discrepancies found between numerical and empirical local data are under revision.
Effect of the Lattice Mismatch Between Copper Thin-Film Interconnection and Base Material on the Crystallinity of the Interconnection
Authors: Fan Chuanhong , Furuya Ryosuke , Asai Osamu , Suzuki Ken , Miura Hideo
Published: January 2014

In the present study, a new material, ruthenium whose lattice mismatch against copper is about 6%, was used as the seed layer of electroplated copper thin-film interconnections for semiconductor devices. The crystallinity of the copper thin-film interconnections was evaluated through an EBSD (Electron Back-scattered Diffraction) method and it is found that the crystallinity of them is improved drastically compared with those electroplated on the copper seed. The resistance and electro migration (EM) tolerance of the copper interconnections are also improved a lot compared with the interconnections electroplated on copper seed. Based on these results, a new guideline to design highly reliable electroplated copper thin-film interconnection has been established.
Evaluation of the Crystallographic Quality of Electroplated Copper Thin-Film Interconnection Embedded in a Si Substrate
Authors: Furuya Ryosuke , Asai Osamu , Fan Chuanhong , Suzuki Ken , Miura Hideo
Published: January 2014

Electroplated copper thin films have started to be applied to the interconnection material in TSV structures because of its low electric resistivity and high thermal conductivity. However, the electrical resistivity of the electroplated copper thin films surrounded by SiO2 was found to vary drastically comparing with those of the conventional bulk material. This was because that the electroplated copper thin films consisted of grains with low crystallinity and grain boundaries with high defect density. Thus, in this study, both the crystallinity and electrical properties of the electroplated copper thin films embedded in the TSV structure was evaluated quantitatively by changing the electroplating conditions and thermal history after the electroplating. It was observed that many voids and hillocks appeared in the TSV structures after the high temperature annealing which was introduced for improving the crystallinity of the electroplated films. Therefore, it is very important to evaluate the crystallographic quality of the electroplated copper thin films after electroplating to assure both the mechanical and electrical properties of the films.
Microtexture and Electrical and Mechanical Properties of the Cold-Sprayed Copper Deposit
Authors: Watanabe Yusuke , Ichikawa Yuji , Ogawa Kazuhiro , Miura Hideo
Published: January 2014

Cold-spray (CS) technique is a new coating technology that is based on the high-velocity impinging of small solid particles on a substrate. The CS technique can make a thick deposit with less heat influence. Recently, this CS technique has been applied to the formation of an electrically conductive copper layer on dielectric materials such as polymers or ceramics. Previous researches show that the deposits made by the CS technique have high strength and residual stress comparing with bulk copper. However, since the deposits show brittle fracture and cracks propagate along the interfaces of the deposited particles, the deposits can not be applied to the products for which high reliability is indispensable. Therefore, it is very important to clarify the dominant factors which change the crystallinity of the deposits comparing with that of bulk copper in order to improve the quality of the deposits. One of the important factors should be the integrity of the interfaces between the deposited fine particles. This study is to evaluate the micro-texture and physical properties of the cold-sprayed copper deposit. Electron back-scatter diffraction method was applied to the evaluation of the crystallinity of the deposits. In addition, the relationship between the crystallinity with both mechanical and electrical properties of the deposits was clarified quantitatively.
Experimental Measurement of Server Thermal Effectiveness for Compact Transient Data Center Models
Authors: VanGilder James W. , Pardey Zachary M. , Zhang Xuanhang (Simon) , Healey Christopher
Published: January 2014

Server thermal mass can significantly affect the rate at which a data center heats up following a loss of cooling and moderate transient temperature fluctuations due to changing CPU utilization. Recently, a compact server model has been introduced which captures the effects of thermal mass while avoiding the impractical level of detail that would be required by an explicit representation of all relevant server components. Inputs to that model include server mass, overall effective specific heat, and a parameter called the “server thermal effectiveness”. The latter characterizes the server’s ability to transfer heat to/from the airstream passing through it and can take values between zero (no heat exchange) and one (maximum possible heat exchange). Server thermal mass is a physical property of a server and is not influenced by external factors.

In order to use the compact model for practical applications, we must experimentally measure the thermal effectiveness of actual servers. The present study reviews the compact model and describes the development of an experimental technique for measuring thermal effectiveness. The technique is validated using simple plate fin heat sinks in place of an actual server. This “server proxy” is sufficiently simple so that it can be modeled accurately in detail in CFD, providing well-controlled benchmark data. CFD and experimental measurements both yield a value of server thermal effectiveness of approximately 0.6, providing confidence in the model and measurement technique for the future characterization of actual servers.
Large-Scale Damage Path Simulation for Solder Joints in a BGA Package
Authors: Omori Takahiro , Hirohata Kenji , Monda Tomoko , Mukai Minoru
Published: January 2014

There is high demand for fatigue life prediction of solder joints in electronic packages such as ball grid arrays (BGAs). A key component of fatigue life prediction technology is a canary device, which warns of the impending risk of failure through loss of function before other important parts become severely impaired. In a BGA package, thermal fatigue of solder joints normally starts from the solder joints at the outermost part of the package. This can be taken advantage of by using the outermost solder joints as canary devices for detecting the degree of cumulative mechanical fatigue damage. To accurately estimate the lifetimes of other functional solder joints, it is essential to understand the relationship between the fatigue lives of canary joints and other functional joints. Damage path simulation is therefore proposed for predicting the crack propagation in solder joints on electronic packages through numerical simulation. During the process of designing the layout of canary joints and other joints, it is very useful to know not only the relationship between the fatigue lives of the canary and other joints, but also the path of crack propagation through all joints. This paper presents a method for estimating the relationship between the fatigue lives of canary joints and other joints by using damage path simulation. Some BGA packages mounted on a printed circuit board are modeled to demonstrate the process of estimating the lifetime of each joint under thermal cycle loading. A large-scale finite element model is used to accurately represent the geometrical properties of the printed circuit board and package. Both crack initiation and crack propagation processes can be simultaneously evaluated by modeling all of the solder joints on each package. The results show that damage path simulation and large-scale modeling are useful for determining the layout of canary joints in electronic packages.
A Field Investigation Into the Limits of High-Density Air-Cooling
Authors: Patterson Michael K. , Martin Randall , von Oehsen J. Barr , Pepin Jim , Joshi Yogendra , Arghode Vaibhav K. , Steinbrecher Robin , King Jeff
Published: January 2014

In this paper we report on a field investigation into airflow management challenges in high density data centers. This field investigation has also served to validate laboratory investigations into high density air cooling issues. In data centers with significant power consumption, and consequently high cooling loads per rack, high volumes of room airflow are required to meet server cooling airflow requirements. These volumes of air can be difficult to deliver in raised floor hot aisle / cold aisle layouts. The velocity of the airflow is such that it creates a negative pressure near the bottom of the rack. This negative pressure entrains air from under and behind the rack, causing recirculation and warmer air being provided to the servers at the base of the rack. This can cause operational problems and server performance impacts. This phenomenon has been demonstrated in previous papers reporting on test data using particle imaging velocimetry (PIV) techniques. The current work validates those studies by looking at airflow, infrared thermography, and actual IT performance while the under rack recirculation flows are occurring. Additionally, we demonstrate significant improvement by employing rigorous airflow management practices. We also discuss the limitations of current CFD modeling, the majority of which does not have sufficient grid-wise resolution to capture the problem. Further we discuss typical operational conditions that have suppressed the problem (or perhaps the awareness of) to date. Finally, the paper recommends best practices to mitigate the problem in high density data centers.
Effect of Isothermal Aging on Microstructure and Creep Properties of SAC305 Solder: A Micromechanics Approach
Authors: Chauhan Preeti , Mukherjee Subhasis , Osterman Michael , Dasgupta Abhijit , Pecht Michael
Published: January 2014

SnAgCu (SAC) solders undergo continuous micro structural coarsening during both storage and service. In this study, we use cross-sectioning and image processing techniques to periodically quantify the effect of isothermal aging quantitatively on phase coarsening and evolution, in SAC305 (Sn3.0Ag0.5Cu) solder. SAC305 alloy is aged for (24–1000) hours at 100°C (∼ 0.7–0.8Tmelt). The characteristic parameters monitored during isothermal aging include size, volume fraction, and inter-particle spacing of both nanoscale Ag3Sn intermetallic compounds (IMCs) and micronscale Cu6Sn5 IMCs, as well as the volume fraction of pure tin dendrites in SAC305 solder.

Effects of above microstructural evolution on secondary creep constitutive response of SAC305 interconnects were modeled using a mechanistic multiscale creep model. The mechanistic phenomena modeled include: (1) dispersion strengthening by coarsened nanoscale Ag3Sn IMCs and reinforcement strengthening by micronscale Cu6Sn5 IMCs, respectively; and (2) load sharing between pure Sn dendrites and the surrounding eutectic Sn-Ag phase.

The coarse-grained polycrystalline Sn micro structure in SAC305 solder was not captured in the above model because isothermal aging did not appear to cause any significant change in the initial grain morphology of SAC305 solder joints. The above model is shown to predict the drop in creep resistance due to the influence of isothermal aging on SAC305 solder joints.
Experimental Measurement of the Thermal Performance of a Two-Die 3D Integrated Circuit (3D IC)
Authors: Choobineh Leila , Vo Nick , Uehling Trent , Jain Ankur
Published: January 2014

Accurate measurement of the thermal performance of vertically-stacked three-dimensional integrated circuits (3D ICs) is critical for optimal design and performance. Experimental measurements also help validate thermal models for predicting the temperature field in a 3D IC. This paper presents results from thermal measurements on a two-die 3D IC. The experimental setup and procedure is described. Transient and steady-state measurements are made while heating the top die or the bottom die. Results indicate that passage of electrical current through the heaters in top/bottom die induces a measureable temperature rise. There appears to be a unique asymmetry in thermal performance between the top die and the bottom die. The top die is found to heat up faster and more than the bottom die. Results presented in this paper are expected to play a key role in validation of simulation-based and analytical thermal models for 3D ICs, and lead to a better fundamental understanding of heat transport in stacked systems. This is expected to lead to effective thermal design and characterization tools for 3D ICs.
Interfacial Reaction Between Molten Sn and Plasma Nitrided Stainless Steel
Authors: Hattori Shingo , Matsubara Naoya , Shohji Ikuo , Kuwahara Hideyuki
Published: January 2014

Erosion behavior of plasma nitrided stainless steel by molten Sn was examined. To investigate the erosion behavior, the interfacial reaction was investigated at the temperature ranging from 350 to 450°C using plasma nitrided SUS304 and SUS316 stainless steel which sandwich pure Sn foil. As the results, it was found that the surface area of the nitrided layer is peeled and subsequently FeSn2 phases form in the reaction interface. FeSn2 phases grow toward molten Sn and Sn diffuses into the nitrided layer. Moreover, Ni3Sn4 phases form and grow in molten Sn. Apparent activation energies of the Sn diffusion into the nitrided layer were estimated to be 153 kJ/mol and 133 kJ/mol for plasma nitrided SUS304 and SUS316, respectively.
Multiphysics Simulation of RF-MEMS With Quantified Uncertainties
Authors: Sun Lin , Kim Hojin , Strachan Alejandro , Mathur Sanjay R. , Murthy Jayathi Y.
Published: January 2014

RF-MEMS devices area complex systems governed by the interaction of a variety of forces, including electrostatics, solid deformation, fluid damping and contact. The performance and reliability of these devices is strongly dependent on device geometry and composition, and also on material microstructure and related properties. In this paper, we consider multiscale simulation of RF MEMS switched. At the device level, we introduce a comprehensive integrated numerical framework to simulate the major governing physics and their interactions. At the micron scale, we develop a mesoscale contact model to describe the history-dependent force-displacement relationships in terms of the surface roughness, the long-range attractive interaction between the two surfaces, and the repulsive interaction between contacting asperities (including elastic and plastic deformation). The inputs to this model are obtained from atomic level simulations and nanoscale surface topography characterization. The mesoscale contact model is integrated in the device-level simulation to predict the pull-in and pull-out behavior of these switches. The uncertainties associated with the simulation are quantified and propagated using a non-intrusive collocation method based on generalized Polynomial Chaos (gPC) expansions. With such a framework, we are able to predict the PDFs of pull-in and pull-out voltage, identify the critical factors that have the most influence on the quantities of interest, and therefore guide resource allocation and risk-informed decision-making.
A Minimal Order Model From Zero to High Frequencies for Finite-Element Based Analysis of General 3-D Electromagnetic Problems
Authors: Sheng Feng , Jiao Dan
Published: January 2014

Modern integrated circuits (IC) and package design has scaled into the deep submicron regime and the nanometer regime. Fast and broadband frequency-domain electromagnetic analysis has become increasingly important. The large problem size encountered in the analysis of ICs and packages is a major challenge especially for a finite element method (FEM) based electromagnetic analysis.

To reduce the computational cost for large-scale electromagnetic analysis, model order reduction (MOR) methods have been developed to preprocess the huge linear system into reduced order models. However, in order to meet the modeling and simulation challenges arising from the IC and package design, existing MOR methods still have to overcome the following shortcomings. First, many existing MOR methods lack a closed-form error bound. Given an accuracy requirement, the model generated from existing methods may not be compact enough. Second, most of the existing reduced order models depend on frequency and right hand side. They lose efficiency when analyzing frequency-dependent problems with a large number of right hand sides. Last but not least, many existing MOR methods suffer from low frequency breakdown problem. Additional models have to be built if low frequency solutions, including DC solution, are required.

This paper proposes a minimal order model for any prescribed accuracy for the finite element based solution of general 3-D problems having arbitrary lossless/lossy structures and inhomogeneous materials. This model entails no theoretical approximations. It is frequency and right hand side independent, and hence can be employed for both fast frequency and right hand side sweep. Moreover, the model does not suffer from low-frequency breakdown and is accurate from zero to high frequencies. To facilitate the application of such a minimal order model, we have also developed an efficient algorithm to generate this model. Numerical experiments have demonstrated the accuracy and efficiency of the proposed method. In addition to frequency-domain analysis, the proposed model can also be used for fast time-domain analysis.
Simulations of Deformation and Stress During Copper Wirebond on ULK Chips
Authors: Lin Hung-Yun , Upreti Kritika , Tippmann Allen , Subbarayan Ganesh , Jung Dae Young , Sammakia Bahgat
Published: January 2014

In this paper, we develop a multi-level modeling procedure for copper wirebonding that provides insights into (a) deformation and stress in wire, pad, and die (b) an assessment of the risk of ULK fracture during impact stage and ultrasonic vibration steps. First, we construct a nonlinear, dynamic finite element model (global) to study the mechanical responses of wire, pad, and the underlying ULK stacks during the impact stage and the last cycle of ultrasonic vibration in copper wirebonding. Specifically, these process steps are modeled through prescribing touch down and in-plane oscillatory motions on capillary, which result in dissimilar critical states of stress locally in the ULK stacks. Next, we develop a isogeometric model (local) for a generic configuration of ULK stacks with eight levels of metallization by composing the geometric primitives representing ILD layers, copper lines/vias, as well as the material interfaces following the Hierarchical Partition of Unity Field Composition technique. The description for material moduli in the entire ULK stacks is further enriched with a bi-linear damage law. The critical states of stress obtained in the global wirebond model are then converted into boundary conditions for the local ILD model under plane strain condition to simulate the crack initiation in the ULK stacks. We observe, from the simulation results, potential crack initiation sites along vertical /horizontal interfaces in the ULK stacks due to local compressive/tensile loading during impact/vibration step, respectively.
Dynamically Controlled Long Duration Operation of a Highly Energy Efficient Chiller-Less Data Center Test Facility
Authors: David Milnes P. , Parida Pritish R. , Schultz Mark D. , Simons Robert E. , Gaynes Michael , Schmidt Roger , Chainer Timothy J.
Published: January 2014

Data center energy consumption makes up a significant and rapidly growing portion of the national energy use. A large fraction of this energy consumption, in the range of 25%–40%, is used by the data center cooling infrastructure, particularly by the computer room air handlers (CRAH) and by the chiller plant. A joint US Department of Energy and IBM effort investigated the use of warm water server cooling and water side economization to help improve energy efficiency in a volume server by minimizing the use of CRAH and chiller hours with the goal of reducing the ratio of cooling energy to IT energy from the conventional value of approximately 50% to less than 10%. Previous work focusing on system characterization and one day runs found significant energy savings as compared to a traditional chiller based data center. In the work reported in this paper we discuss the development and implementation of a dynamic control approach followed by details and results from a 60+ day run of the data center test facility starting May 11th, 2012. Results from this long term study found the average cooling energy consumption to be 3.5% of the IT energy, which is consistent with previous short one day runs. The implemented control scheme was also able to reliably control the water temperature to within 0.5°C of the set-point under most conditions and could react and stabilize to a new set-point in 30 minutes. The work presented demonstrates the high energy efficiency of a warm water cooled, water-side economized, chiller-less data center over a long sustained period of time and highlights the benefits of energy aware control to help limit cooling energy.
Impact of Material Properties on Cooling COP of Integrated Thermoelectric Microcoolers
Authors: Koh Yee Rui , Yazawa Kazuaki , Shakouri Ali
Published: January 2014

Thermoelectric (TE) microcooling is promising for removing hotspots in integrated circuit chips. The cooling coefficient-of-performance (COP) of the on-chip thin film or superlattice micro-cooler (SLC) is a metric for assessing the energy efficiency of the hot spot removal. The COP is key for lowering total power consumption and minimizing heat sinking requirements. Due to the moderate performance compared to vapor compression cycles, researchers have devoted considerable effort to improving the figure-of-merit (ZT) of the material over the past decade. However, the impact of each of the individual thermoelectric properties has not been studied separately. We report our study based on an analytical model and analysis results that show the intrinsic impact of electrical conductivity, the Seebeck coefficient, and thermal conductivity, while the device thickness and the drive current are optimized for maximizing cooling COP. The results show that the power factor of the TE materials is a more important parameter than thermal conductivity reduction for improving the cooling performance of the on chip SLC.
A Flow Visualization Study on the Temperature Oscillations Inside a Loop Heat Pipe With Flat Evaporator
Authors: Mo Dongchuan , Zou Guansheng , Lu Shushen , Zhang L. Winston
Published: January 2014

This paper presents a flow visualization study on the temperature oscillations inside a loop heat pipe in order to gain a better understanding of its heat transfer characteristics. A flat loop heat pipe (FLHP) with a flat evaporator instead of a typical cylindrical evaporator was built using copper as the shell and water as the working fluid. An experimental setup was designed by using the transparent material instead of copper in some parts of the FLHP. The experiment results showed that there were at least three different flow patterns in the vapor line as the heating power increased. The temperatures in different locations of the loop oscillated even when the heating power was kept constant. The largest amplitude of the temperature oscillation in the loop was located at the condenser outlet. It was found that the temperature oscillation at the condenser outlet could be divided into two types, one with smaller amplitudes and the other with larger amplitudes. The smaller amplitude temperature oscillations were always there when the heating power was increased step by step, while the larger amplitude temperature oscillations would disappear initially and show up later. Finally, the location of the vapor/liquid interface inside the condenser varied with the temperature oscillations, resulting in liquid/vapor interface motion in the compensation chamber.
Analytic Optimization of Porous Medium Heat Sinks for Energy Efficiency and Minimum Mass
Authors: Trifale Ninad , Nauman Eric , Yazawa Kazuaki
Published: January 2014

Use of microchannel heat sinks for high heat flux applications is substantial for thermal management and it is also critical for scalable power generation. For both applications, the energy efficiency consideration of the pump power is crucial. A number of models have been created that predict the performance as a function of the geometrical parameters, taking into account, the pressure loss over the length and volume constraints. Most of the approaches either involve sophisticated calculations incorporating fluid dynamics in channels, or have an analogy with the pin-fin model, which gives simpler calculations but considers only a single laminar flow regime for optimization. Even with the simplified models available, the geometrical impact on mass and pumping power is nonlinear and not apparent for optimization. We propose an optimization of porous medium heat sinks with respect to the heat transfer rate, mass, and pumping power. These are functions of the simplest geometric parameters, i.e. porosity, pore density, and length of the porous medium.

Considering large production, mass (cost of raw material) is nearly proportional to the cost of the heat sink, we consider minimizing the mass for indirectly minimizing the overall cost. The other factor for saving energy considered here is the pumping power. This connects to both the heat transfer rate and the power consumption to drive the fluid through the porous medium.

The optimization is performed for a specific value of porosity and length of the heat sink. The model considers the effect of flow through the porous medium and the effective thermal conduction as a function of combined conductivity of the solid ligaments and the fluid in pores.

An optimum coefficient of performance (COP) is found at over 90% of porosity for minimum mass, pumping work and maximum heat transfer. This mathematical expression of the model will give a quantifiable figure-of-merit to take into account the impact of the mass and the pumping power on the performance to cost ratio.
A Study on Impact Stresses in Ceramic Capacitors
Authors: Kawakami Takashi , Horikawa Noriyo , Kinoshita Takahiro , Inagaki Tomohiro
Published: January 2014

Multilayer ceramic capacitors (MLCCs) are used very widely as electric devices on printed circuit boards (PCBs). Impact loads are applied on MLCCs during PCB manufacturing processes with fast mounting machines or floor dropping of mobile appliances and MLCCs may crack sometime due to the mechanical design. In this paper, impact stresses, which were induced in MLCCs by split Hopkinson bar impact tests, were analyzed with large scale parallel computing method.