bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Stresses of Contacts in Wire Saw Slicing of Polycrystalline and Crystalline Ingots: Application to Silicon Wafer Production
Authors: Li J. , Kao I. , Prasad V.
Published: February 2008

Wire saw slicing is a cost effective technology with high surface quality for slicing large diameter silicon wafers. Though wire saws have been deployed to cut polycrystalline and single crystal silicon ingot since the early 1990s, very little is known about the fundamental cutting process. We investigate this manufacturing process and propose a contact stress model of wire saw slicing that illustrates the interactions among the wire, ingot, and abrasives (e.g., SiC) carried by the slurry. Stresses created by wire saw slicing silicon wafers are analyzed in this paper. During the cutting process, the wire moves at high speed (5–15 m/s) with respect to the silicon ingot. The abrasives in the slurry are lose third-body particles caught between the wire and ingot at the contact surface. The forces applied by the wire carry the abrasive particles and cause them to roll on the surface and at the same time to be constrained to indent the surface. Such rolling-indenting interactions result in the formation of isolated chips and surface cracks. The cracks and discontinuity on the surface also cause high stress concentration. As a result, the material is cut and removed. The stress fields of a single circular cone of the abrasive particle indenting on silicon crystal with normal and tangential forces can be calculated and analyzed from the modeling equations and boundary conditions. The stresses are expressed with dimensionless stress measures, as functions of normalized geometric parameters. The results show that the maximum normal stress occurs at the indentation point, while the maximum shear stress (σzx) occurs below the surface of contact, as expected. Such subsurface shear facilitates the peeling effects of the silicon cracks. Both the normal and tangential forces applied at the contacts are incorporated in the model. The model is very effective in explaining and predicting the behaviors and distributions of stresses during the cutting process, and can be used to determine the optimal geometry of the abrasive particles in the rolling-indenting process.
An Effective Approach for Three-Dimensional Finite Element Analysis of Ball Grid Array Typed Packages
Authors: Cheng H. C. , Chiang K. N. , Lee M. H.
Published: February 2008

In the literature, the local-global finite element analysis technique plays a very important role in the area array packaging. In this study, the underlying goal is to propose an improved equivalent model for the use in the local/global analysis, and most importantly, provide a systematic procedure in approaching this equivalent model. In addition, the choice of the equivalent beam model will also be extensively investigated. Since the configuration of the solder joint is far from being close to a “beam-like” structure, defining the corresponding equivalent beam involves great levels of difficulties. In order to remove the possible difficulties, an effective way is proposed: incorporating analytical derivations and optimization. To this end, one practical application is presented to substantiate the proposed methodology.
Constitutive Modeling of Polymer Films From Viscoelasticity to Viscoplasticity
Authors: Qian Z. , Lu M. , Liu S.
Published: February 2008

A unified constitutive model for polymer films is proposed with viscoelastic characterization at small deformation and viscoplastic characterization at large deformation based on molecular chain deformation mechanisms. The evolution equations and the temperature dependence of drag stress and back stress are established from molecular network theories in this paper. The material constants are then determined by master curves and a consistent procedure. A good agreement between the experimental data of polycarbonate film tests and model predictions is achieved.
A Review of Changes and Trends Affecting Military Electronics Manufacturing
Authors: Rafanelli A. J.
Published: February 2008

Dramatic business changes in the aerospace and military defense industries have caused contractors to drastically alter their design and manufacturing processes. These changes appear to have been influenced by recent events or movements: the U.S. Department of Defense initiative (Perry, 1994; U.S. Department of Defense, 1994) discourage dependence on military specifications/standards (the “Perry Initiative”) which resulted in trends within the electronics industry to use commercial materials in typical military environments (alternative component initiatives). Consequently, changes are underway regarding some of the traditional technologies used in defense electronics. Specifically, this paper will present an overview of the changing nature of some of these technologies, e.g., interconnections, coatings, and plastic encapsulated microcircuits (PEMs), and the standards/practices related to these from a manufacturing aspect. The information provided is by no means all-inclusive, but it does identify a focus for increased discussion and study.
Measurement of Wafer Surface Using Shadow Moire´ Technique With Talbot Effect
Authors: Wei S. , Wu S. , Kao I. , Chiang F. P.
Published: February 2008

In this paper, a modified shadow moire´ technique is applied to measure surface topology of wafers. When a wafer is sliced, either by an inner-diameter (ID) saw or wiresaw, the surface needs to be measured to ensure the consistency of quality. Two important characteristics of the wafer surface measurements are the warpage and total thickness variation (TTV). Currently, the most commonly used method of wafer measurement employs a pair of capacitive measuring probes which sample points on the surface of a rotating wafer to obtain the contours of surface. Many sampling points on the surface are needed for more accurate measurements; however, this will require more time for the inspection of wafers during production. An innovative alternative for full-field, whole-wafer measurement is developed using a laser light source and the modified shadow moire´ technique. This methodology enables one to examine the whole wafer surface quickly and simultaneously. In this study, a 40 lines/mm (1000 lines/inch) reference grating is employed as the standard to create a shadow moire´ pattern. In addition, the Talbot effect is utilized to adjust the gap, or the so-called Talbot distance, between the grating and the wafer surface such that a fringe pattern of good quality can be obtained. By using the phase shifting technique, the resolution (or sensitivity) can be enhanced by two order of magnitude. The results show that not only the full view of the whole wafer surface can be obtained, but enhanced surface resolution and accuracy can also be realized. In addition, warpage due to excessive residual stresses can be observed distinctly with fringe patterns because of the global and interconnected moire´ fringes. This process is faster, especially when dealing with wafers with diameter larger than 200 mm (8”). Experimental results of both 200 mm single crystalline and 100 × 90 mm polycrystalline wafers are presented. The system can also be fully automated to become an on-line inspection tool.
Electronic Packaging Reflow Shape Prediction for the Solder Mask Defined Ball Grid Array
Authors: Chiang K.-N. , Chen W.-L.
Published: February 2008

The increasing need to create high density and fine pitch electronic interconnections presents a number of challenges. The fatigue-induced solder joint failure of surface mounted electronic devices has become one of the most critical reliability issues in electronic packaging industry. Prediction of the shape of solder joint has drawn special attention in the development of electronic packaging for its practical engineering application. Many solder joint models have been developed based on energy minimization principle (Patra et al., 1995) or analytical method (Heinrich et al., 1993; Liedtke 1993). These methods are extensively utilized to the shape design of solder joint. However, it is important to find a suitable method in real application. In this study, an efficient numerical method used to predict the shapes of solder joint is investigated, and the results are compared with Surface Evolver program (Brakke, 1994). The changes of geometric shape with respect to different parameters of solder joint are also discussed in this paper. The influences of the geometric parameters, such as volumes of solder joint, package weight, contact angles, pads sizes, solder surface tension, and gravity forces to the shape of solder joint, are investigated. Results presented in this study can be used to determined the optimally balanced stand-off height of single ball module (SBM) or multiple ball module (MBM) solder joint models.
Creep Behavior of a Flip-Chip Package by Both FEM Modeling and Real Time Moire´ Interferometry
Authors: Wang J. , Qian Z. , Zou D. , Liu S.
Published: February 2008

In this paper, the creep behavior of a flip-chip package under a thermal load was investigated by using nonlinear finite element technique coupled with high density laser moire´ interferometry. The real-time moire´ interferometry technique was used to monitor and measure the time-dependent deformation of flip-chip packages during the test, while the finite element method was adapted to analyze the variation of stresses at edges and corners of interfaces with time by considering the viscoelastic properties of the underfill and the viscoplastic behavior of the solder balls. The results show that the creep behavior of the underfill and the solder balls does not have significant effect on the warpage of the flip-chip under the considered thermal load due to their constrained small volume. The variation of the time-dependent deformation in the flip-chip package caused by the creep behavior of the underfill and the solder balls is in the submicro scale. The maximum steady-state U-displacement is only reduced by up to 6.7 percent compared with the maximum initial state U-displacement. Likewise, the maximum steady-state V-displacement is merely reduced by up to 10 percent compared with the maximum initial state V-displacement. The creep behavior slightly weakens the warpage situation of the flip-chip package. However, the modeling results show that the localized stresses at corners and edges of interfaces greatly decrease due to the consideration of viscoelastic properties of the underfill and the viscoplastic properties of the solder balls, and, thereby, effectively preventing interfaces from cracking. In addition, the predicted deformation values of the flip-chip package obtained from the finite element analysis were compared with the test data obtained from the laser moire´ interferometry technique. It is shown that the deformation values of the flip-chip package predicted from the finite element analysis are in a fair agreement with those obtained from the test.
Fatigue Life Estimation of Solder Joints in SMT-PGA Packages
Authors: Mukai M. , Kawakami T. , Hiruta Y. , Takahashi K. , Kishimoto K. , Shibuya T.
Published: February 2008

The fatigue life estimation of solder joints is one of the most critical requirements in the development of reliable electronic components. In this study, we first examined a constitutive model for Sn63-Pb37 solder based on the results of material tests. It was confirmed that the behavior of the solder material can be expressed by the elastic-creep constitutive equations when the strain rate was low. Secondly, elastic-creep stress analysis was carried out for the solder joints of a SMT-PGA (surface mount technology pin grid array) package. The location of the failure predicted by the analytical results agreed well with those of the thermal cycle tests (TCT). It was shown that the fatigue life estimation of solder joints based on the present method is satisfactory for engineering purposes.
Thermal Enhancement Coatings for Microelectronic Systems
Authors: Fletcher L. S. , Lambert M. A. , Marotta E. E.
Published: February 2008

The power densities and heat generation in microelectronic systems have increased dramatically as individual electronic components have been miniaturized. As a result of the growing number of thermally-induced failures in these systems, their thermal performance has become the focus of increasing concern. The use of thermally conducting interstitial coatings within and between electronic components has proven to be one technique suitable for thermal enhancement. This review will address both metallic and nonmetallic coatings suitable for thermal enhancement and discuss some of the major areas of application.
Package-to-Board Attach Reliability — Methodology and Case Study on OMPAC Package
Authors: Nagaraj B. , Mahalingam M.
Published: February 2008

Over molded pad array carrier (OMPAC), also called plastic Ball Grid Array (pBGA) package family offers increased I/O density at the board level; further, package size and thickness are reduced in comparison to other competing package types leading to many product applications. The OMPAC package is investigated for solder pad interconnect reliability. Elastic and inelastic finite element method (FEM) simulations are employed with experimental temperature cycling data. Linear elastic analyses are performed for various package parameters that influence the stress distribution in the solder pad interconnect for temperature loading. The package parameters considered are (a) ratio of thickness of die to substrate (tdie/tsub.), (b) ratio of width of die to substrate (wdie/wsub.), and (c) ratio of height to diameter of the solder pad interconnect ((h/d)pad). The results are evaluated based on the maximum Tresca (maximum shear stress) failure criterion. The key parameter is (h/d)pad ratio. As this ratio increases, the maximum Tresca failure criterion decreases. The performance of the solder pads are evaluated based on the maximum total permanent strain (plastic + creep) range per temperature cycle. FEM simulation was performed up to eight consecutive temperature cycles. The permanent strain (plastic + creep) range were calculated for each temperature cycle and observed that after a few temperature cycles the strain ranges stabilize. The maximum stabilized total permanent strain range is in the inner solder pad and is equal to 0.005. This maximum total strain range in the solder pad per temperature cycle loading can be used to estimate the life time of the solder pads. The FEM simulation results are correlated with the experimental data. Both the simulation and the experimental results are indicate that the outer pads are not as critical as the inner or the middle pads. The experimental results indicate that there is slightly larger probability for the middle pads to fail before the inner pads. However, the simulation data indicate that the inner pads are more critical than the middle pads. We believe that this small discrepancy in simulation result is due to the actual temperature variation on the package not being included in the present analysis.
Reliability of Underfill-Encapsulated Flip-Chips With Heat Spreaders
Authors: Doi H. , Kawano K. , Yasukawa A. , Sato T.
Published: February 2008

The effect of a heat spreader on the life of the solder joints for underfill-encapsulated, flip-chip packages is investigated through stress analyses and thermal cycling tests. An underfill with suitable mechanical properties is found to be able to prolong the fatigue life of the solder joints even in a package with a heat spreader and an alumina substrate. The delamination of the underfill from the chip is revealed as another critical failure mode for which the shape of the underfill fillet has a large effect.
The Effect of Underfill and Underfill Delamination on the Thermal Stress in Flip-Chip Solder Joints
Authors: Rzepka S. , Korhonen M. A. , Meusel E. , Li C.-Y.
Published: February 2008

The stresses occurring in the solder joints during thermal loads have been studied by finite element analysis. Besides the cases of no underfill and perfect adhesion, underfill delaminations at the interfaces to the solder, to the chip, and to the substrate surfaces, respectively, have been considered. The simulation results indicate that rapid failing of the flip-chip modules due to delamination can be prevented effectively by using an underfill that has a high Young’s modulus at room temperature (even 20 GPa are not too high) and a CTE slightly lower than solder. Since the ultimate failure is always caused by growing of a major crack, the damage integral concept is valid for lifetime estimations even in the case of FC modules with underfill.
A New Approach to Calculate Atomic Flux Divergence by Electromigration
Authors: Sasagawa K. , Nakamura N. , Saka M. , Abe´ H.
Published: February 2008

In this paper, a new calculation method of the atomic flux divergence used to predict the formation of electromigration-induced void is proposed by considering two-dimensional distributions of current density and temperature and also simply considering the line structure of not only polycrystalline, but also bamboo line. For the verification, electromigration phenomenon near the corner of an angled polycrystalline line, which results in two-dimensional distributions of current density and temperature, is treated as an example. The usefulness of the proposed method is discussed in the light of the comparison of prediction of void formation near the corner with the experimental result.
A Thermo-Mechanical Approach for Fatigue Testing of Polymer Bimaterial Interfaces
Authors: Gurumurthy C. K. , Jiao J. , Norris L. G. , Hui C.-Y. , Kramer E. J.
Published: February 2008

We have developed a new technique that uses a noncontact fiber optic displacement sensor to investigate the crack growth along polymer interfaces under thermal fatigue conditions. This technique has been used to test the underfill/passivation interface of a direct chip attach (DCA) assembly, the thermal fatigue driven delamination of which is a major cause for failure of DCA assemblies. The sample is prepared as a multilayered cantilever beam by capillary flow of the underfill over a polyimide coated metallic beam. During thermal cycling the crack growth along the interface from the free end changes the displacement of this end of the beam and we measure this displacement at the lowest temperature in each thermal cycle. The change in beam displacement is converted into crack growth knowing the geometry of the specimen. The crack growth rate depends on the maximum difference in the strain energy release rate of the crack in each cycle and the mechanical phase angle. This paper outlines the theoretical basis of the technique and provides initial results obtained for a variety of underfills dispensed over a commercial (PMDA/ODA) polyimide. The technique was validated by comparing the crack growth measured by displacement changes with direct optical microscopy measurements of the crack length.
Forced Convection Heat Transfer Augmentation in a Channel With A Localized Heat Source Using Fibrous Materials
Authors: Angirasa D. , Peterson G. P.
Published: February 2008

A numerical model is developed for high Reynolds number forced convection heat transfer in a channel filled with randomly oriented, thin fibrous materials of high porosity. A localized isothermal heat source, flush with one of the channel walls is considered to simulate an electronic component. The inertial coefficient and the dispersion conductivity associated with high Reynolds number flows and convective heat transfer are empirically modeled from existing experimental and analytical studies. The resulting fluid flow and heat transfer relationships are presented for a relevant range of parameters, and the fundamental physical processes are explained.
Characterizing the Failure Envelope of a Conductive Adhesive
Authors: Olliff D. , Qu J. , Gaynes M. , Kodnani R. , Zubelewicz A.
Published: February 2008

This paper focuses on mechanical testing designed to determine the static failure envelope for a conductive adhesive. Samples were made by bonding copper pegs together with the conductive adhesive. The samples were then tested at various loading conditions including tension, tension shear, and compression shear. Results were analyzed in order to check for correlations between the data and the testing procedures. The statistical distribution of the data was also analyzed. Furthermore, a finite element model of the test sample was constructed and used to verify the assumptions made with respect to the interpretation of the data. The data from various loading conditions was then used to construct the static failure envelope of the material. A modified Coulomb–Mohr failure criterion was used to model the failure envelope of the conductive adhesive. This criterion contains four material constants to be determined experimentally. Once these parameters are determined, a failure envelope can be easily constructed. The envelope can then be used to predict failure at any combination of shear and normal stresses. The test results showed that the empirical data are well characterized by the modified Coulomb–Mohr failure envelope.
Damage Mechanics of Surface Mount Technology Solder Joints Under Concurrent Thermal and Dynamic Loading
Authors: Chandaroy R. , Basaran C.
Published: February 2008

In the electronic industry, the dominant failure mode for solder joints is assumed to be thermal cycling. When semiconductor devices are used in vibrating environment, such as automotive and military applications, dynamic stresses contribute to the failure mechanism of the solder joint, and can become the dominant failure mode. In this paper, a damage mechanics based unified constitutive model for Pb40/Sn60 solder joints has been developed to accurately predict the thermomechanical behavior of solder joints under concurrent thermal and dynamic loading. It is shown that simultaneous application of thermal and dynamic loads significantly shorten the fatigue life. Hence, damage induced in the solder joint by the vibrations have to be included, in fatigue life predictions to correctly predict the reliability of solder joints. The common practice of relating only thermal cycling induced inelastic strain to fatigue life can be inadequate to predict solder joint reliability. A series of parametric studies were conducted to show that contrary to popular opinion all dynamic loading induced strains are not elastic. Hence, vibrations can significantly affect the fatigue life and reliability of solder joints in spite of their small mass.
Deformation Behavior of Two Lead-Free Solders: Indalloy 227 and Castin Alloy
Authors: Whitelaw R. S. , Neu R. W. , Scott D. T.
Published: February 2008

The deformation behavior of two commercial lead-free solder alloys, Indalloy 227 (77.2Sn-20.0In-2.8Ag) and Castin alloy (96.2Sn-2.5Ag-0.8Cu-0.5Sb), over a range of strain rates (10−6 s−1 to 10−2 s−1), temperatures (–55°C to 125°C), and isothermal and thermomechanical cycling conditions is experimentally determined. The behavior of these two lead-free alloys is compared to that of 60Sn-40Pb solder. In order to minimize the number of experiments, yet capture the significant features of the deformation behavior and obtain the simple Norton power law constants, strain-rate jump tests are successfully used. This minimal test information is also shown to be sufficient to determine a complete set of material parameters for modern unified thermoviscoplastic models that can capture the dominant strain rate and temperature effects including the thermomechanical cycling behavior. As an exercise, the parameters for the Bodner-Partom model are determined for both lead-free alloys and predictions of thermomechanical cycling are shown.
A Heat Sink Performance Study Considering Material, Geometry, Nozzle Placement, and Reynolds Number With Air Impingement
Authors: Maveety J. G. , Hendricks J. F.
Published: February 2008

An impingement air flow heat sink performance study which considers the effects of geometry, nozzle-to-sink vertical placement, material and Reynolds number has been performed. The experiments consisted of varying the dimensionless nozzle-to-sink vertical distance from 2 to 12 and the Reynolds number from 1 × 104 to 5 × 104. A new carbon composite material manufactured by AlliedSignal was tested and shown to have superior heat transfer characteristics when compared to aluminum. The study also showed that optimal performance is achieved when the nozzle is placed within the dimensionless vertical distance of eight to twelve from the heat sink, and when the Reynolds number lies between 4 × 104 and 5 × 104. Both experimental and analytical estimates of the spreading resistance within the heat sinks tested were obtained.
A Damage Coupling Framework of Unified Viscoplasticity for the Fatigue of Solder Alloys
Authors: Qian Z. , Ren W. , Liu S.
Published: February 2008

A damage coupling framework is proposed with a unified viscoplastic constitutive model for the fatigue life prediction of solder alloys, including a consistent and systematic procedure for the determination of material parameters. The model also incorporates the effects of grain size and cyclic hardening/softening. The phenomenological framework of continuum damage mechanics (CDM) is modified to embed intensive researches on the ductile damage fracture by void nucleation, growth, and coalescence, based on a lower bound for the viscoplastic potential of voided materials. The damage coupling with elasticity and viscoplasticity is formulated by irreversible thermodynamic approach. The constitutive model is also extended to large deformation kinematics. The preliminary application of the model to creep damage is presented.
Effect of Temperature and Strain Rate on Mechanical Properties of 63Sn/37Pb Solder Alloy
Authors: Shi X. Q. , Zhou W. , Pang H. L. J. , Wang Z. P.
Published: February 2008

In this study, tensile tests of 63Sn/37Pb solder were carried out at various strain rates from 10−5 s−1 to 10−1 s−1 over a wide temperature range from −40°C to 125°C to study the effect of strain rate and testing temperature on the mechanical properties in a systematic manner. Based on these experimental data, a set of empirical formulae was derived by a statistical method to describe the effect of temperature and strain rate in a quantitative manner and explain the variation in the mechanical properties published in other reports. It is concluded that the empirical formulae can be used to characterize the mechanical properties of 63Sn/37Pb over a wide range of temperatures and strain rates.
J-Lead Solder Joint Thermal Fatigue Life Model
Authors: Wong T. E. , Kachatorian L. A. , Cohen H. M.
Published: February 2008

A thermal fatigue life prediction model of J-lead solder joint assembly has been developed. This model is evolved from an empirically derived formula based on modified Manson-Coffin fatigue life Prediction theory. To estimate solder joint fatigue life, nonlinear finite element analysis (FEA) was conducted using the ABAQUS™ computer code. The analysis results show that cracks are initiated and propagated from both the heel and the toe of the solder joint toward the center portion of the joint. This condition results in the solder joint fatigue life degradation and is included in the model development. The fatigue life prediction model is then calibrated to life cycling test results, which were provided by Jet Propulsion Laboratory (JPL/NASA). The developed life prediction model, combined with the nonelastic strains derived from FEA and Miner’s cumulative damage law, was used to predict the cumulative damage index of the solder joint under NASA’s thermal cycling environment (between −55°C and 100°C). The analysis results indicate that this solder joint has a 50 percent failure probability when the solder joint is exposed up to 5206 thermal cycles. To shorten the test time, a modified thermal cycling profile was proposed. This profile is the same as the NASA thermal cycling environment except using the high end of the dwell temperature at 125°C. The analysis results show that a 50 percent failure probability of the solder joint would occur after the solder joint is exposed to 3500 cycles of the NASA thermal environment and followed by 1063 cycles of the modified thermal profile. In conclusion, the developed life prediction model is recommended to serve as an effective tool to integrate the process of design selection, quality inspection, and qualification testing in a concurrent engineering process. It is also recommended to conduct a micro-section in the solder joint to verify the solder crack paths and further validate the life prediction model. When additional thermal cycles have been added into the test specimens, recalibrating this model by test is also recommended.
Application of a Genetic Algorithm to Wind Turbine Design
Authors: Selig M. S. , Coverstone-Carroll V. L.
Published: February 2008

This paper presents an optimization method for stall-regulated horizontal-axis wind turbines. A hybrid approach is used that combines the advantages of a genetic algorithm with an inverse design method. This method is used to determine the optimum blade pitch and blade chord and twist distributions that maximize the annual energy production. To illustrate the method, a family of 25 wind turbines was designed to examine the sensitivity of annual energy production to changes in the rotor blade length and peak rotor power. Trends are revealed that should aid in the design of new rotors for existing turbines. In the second application, five wind turbines were designed to determine the benefits of specifically tailoring wind turbine blades for the average wind speed at a particular site. The results have important practical implications related to rotors designed for the Midwestern US versus those where the average wind speed may be greater.
A Numerical Method for Power Plant Simulations
Authors: Carcasci C. , Facchini B.
Published: February 2008

This paper describes a highly flexible computerized method of calculating operating data in a power cycle. The computerized method presented here permits the study of steam, gas and combined plants, Its flexibility is not restricted by any defined cycle scheme. A power plant consists of simple elements (turbine, compressor, combustor chamber, pump, etc.). Each power plant componment is represented by its typical equations relating to fundamental mechanical and thermodynamic laws, so a power plant system is represented by algebraic equations, which are the typical equations of components, continuity equations, and data concerning plant conditions. This equation system is not linear, but can be reduced to a linear equation system with variable coefficients. The solution is simultaneous for each component and it is determined by an iterative process. An example of a simple gas turbine cycle demonstrates the applied technique. This paper also presents the user interface based on MS-Windows. The input data, the results, and any characteristic parameters of a complex cycle scheme are also shown.
Heat Transfer in a High-Temperature Packed Bed Thermal Energy Storage System—Roles of Radiation and Intraparticle Conduction
Authors: Jalalzadeh-Azar A. A. , Steele W. G. , Adebiyi G. A.
Published: February 2008

A model is developed and experimentally verified to study the heat transfer in a high-temperature packed bed thermal energy storage system utilizing zirconium oxide pellets. The packed bed receives flue gas at elevated temperatures varying with time during the storage process and utilizes air for the recovery process. Both convection and radiation are included in the model of the total heat transfer between the gas and the pellets. It is found that thermal radiation and intraparticle conduction do not play a major role in the overall heat transfer in the packed bed under the specified operating conditions. An uncertainty analysis is performed to investigate the propagation of the uncertainties in the variables to the overall uncertainty in the model predictions and the experimental results.
Entrainment and Mixing in Vertical Buoyant Light-Gas Plumes
Authors: Kumar R. K. , Chiang H. W. , Kalos F.
Published: February 2008

A simple model is developed to determine the entrainment coefficient and the spread of a light-gas plume in a quiescent atmosphere. Experiments performed with low-velocity saltwater/freshwater and helium-in-air jets indicate that buoyant gas plumes spread significantly faster than thermal plumes. The calculated effluent concentrations are in excellent agreement with those measured when an entrainment coefficient of 0.15 is used in the plume equations. This is significantly higher than the entrainment coefficients of 0.075 to 0.093 reported for thermal plumes.
Visualization of Formaldehyde Distribution Above Platinum Plate Catalyst by Using LIF Method
Authors: Kang W. , Fujita O. , Ito K.
Published: February 2008

Visulization has been attempted to measure formaldehyde formation during catalytic combustion of methanol/air mixtures. The visualization of formaldehyde distribution above a platinum plate in methanol premixed gas flows was carried out by a LIF (laser-induced fluorescence) method. Formaldehyde (CH2O) has fluorescence spectra in the 340.6–493.3-nm range when it is excited by the third harmonic wavelength of Nd:YAG laser (355 nm). In our study, formaldehyde was excited by a pulse laser shot and the fluorescence at wavelength of 412.2 nm was selected for investigation. By this laser technique, the time resolved instantaneous distribution of formaldehyde on the platinum plate was successfully observed. The results show that the distribution of formaldehyde fluorescence is affected by gas velocity, catalyst temperature, and especially excess air ratio. The results correspond well with the results of a mathematical modeling for formaldehyde formation over Pt, and it confirms that this method is useful for analyzing the mechanism of catalytic combustion.
Blowout Limits of a Jet Diffusion Flame in the Presence of Small Surrounding Jet Pilot Flames
Authors: Kibrya M. G. , Karim G. A.
Published: February 2008

The blowout limit of a methane jet diffusion flame is examined in the presence of a number of much smaller pilot jet flames of different fuels arranged within an experimental burner assembly in a co-flowing stream of air. It is shown that the blowout limit of the central jet flame can be extended very appreciably by increasing the flow rate through the smaller pilot jets. The basis for this extension to the blowout limit and the role of some changes in the operating parameters are discussed. It is suggested that the extension to the blowout limit observed is due mainly to the thermal contribution of the pilot jet flames.
An Investigation of the Lean Operational Limits of Gas-Fueled Spark Ignition Engines
Authors: Badr O. A. , Elsayed N. , Karim G. A.
Published: February 2008

Examination is made of the operational limits in two variable compression-ratio single-cylinder engines when operating on the gaseous fuels methane, propane, LPG, and hydrogen under a wide range of conditions. Two definitions for the limits were employed. The first was associated with the first detectable misfire on leaning the mixture, while the second was the first detectable firing under motoring condition in the presence of a spark when the mixture was being enriched slowly. Attempts were also made to relate these limits to the corresponding values for quiescent conditions reckoned on the basis of the flammability limits evaluated at the mean temperature and pressure prevailing within the cylinder charge at the time of the spark. The measured limits in the engine were always higher than the corresponding flammability limit values for the three fuels. Both of these limits appear to correlate reasonably well with the calculated mean temperature of the mixture at the time of passing the spark.
The Equivalence of Maximum Power and Minimum Entropy Generation Rate in the Optimization of Power Plants
Authors: Bejan Adrian
Published: February 2008

It is shown that to maximize the power output of a power plant is equivalent to minimizing the total entropy generation rate associated with the power plant. This equivalence is illustrated by using two of the oldest and simplest models of power plants with heat transfer irreversibilities. To calculate the total entropy generation rate correctly, one must recognize that the optimization process (e.g., the variability of the heat input) requires “room to move,” i.e., an additional, usually overlooked, contribution to the total entropy generation rate.
Modeling of the Mechanical Behavior of Materials in “High-Tech” Systems: Attributes and Review
Authors: Suhir E.
Published: February 2008

We examine some attributes of modeling of the mechanical behavior of materials and structures in microelectronics and photonics (mainly fiber optics) engineering. The merits and shortcomings of experimental and theoretical modeling are addressed, as well as the interaction between different modeling approaches. The concepts discussed are illustrated by a brief review of the published work in the field. The review is based primarily on the author’s research conducted during his work at Bell Laboratories and reflects, to a great extent, the state-of-the-art in modeling of the mechanical behavior of “high-tech” materials and structures. “The only real voyage to discovery consists not in seeking new landscapes, but in having new eyes.” [Marcel Proust, French Writer] “The Practical value of mathematics is, in effect, a possibility to obtain, with its help, results simpler and faster.” [Andrey Kolmogorov, Russian Mathematician]
Thermal Management in Direct Chip Attach Assemblies
Authors: Baldwin D. F. , Beerensson J. T.
Published: February 2008

Direct chip attach (DCA) packaging technologies are finding increasing application in electronics manufacturing particularly in telecommunications and consumer electronics. In these systems, bare die are interconnected directly to a printed circuit board. The two primary forms of DCA included chip on board (COB) where the die are attached face up and wirebonded to the substrate and flip chip on board (FCOB) where bumped die are interconnected active face down directly to low-cost organic substrates. In the current work, thermal management of four direct chip attach technologies is investigated. Experimental measurements are conducted exploring the junction-to-ambient thermal resistance and thermal dissipation paths for COB interconnection and three FCOB interconnect technologies including solder attach, anisotropic adhesive attach, and isotropic adhesive attach. A first-order chip-scale thermal design model is developed for flip chip assemblies exhibiting good agreement with the experimental measurements.
Thermomechanical Durability Analysis of Flip Chip Solder Interconnects: Part 2—With Underfill
Authors: Darbha K. , Okura J. H. , Shetty S. , Dasgupta A. , Reinikainen T. , Zhu J. , Caers J. F. J. M.
Published: February 2008

The effect of underfill material on reliability of flip chip on board (FCOB) assemblies is investigated in this study by using two-dimensional and three-dimensional finite element simulations under thermal cycling stresses from −55°C to 80°C. Accelerated testing of FCOB conducted by the authors reveals that the presence of underfill can increase the fatigue durability of solder interconnects by two orders of magnitude. Similar data has been extensively reported in the literature. It is the intent of this paper to develop a generic and fundamental predictive model that explains this trend. While empirical models have been reported by other investigators based on experimental data, the main drawback is that many of these empirical models are not truly predictive, and can not be applied to different flip chip architectures using different underfills. In the proposed model, the energy-partitioning (EP) damage model is enhanced in order to capture the underlying mechanisms so that a predictive capability can be developed. A two-dimensional finite element model is developed for stress analysis. This model accounts for underfill over regions of solder in an approximate manner by using overlay elements, and is calibrated using a three-dimensional finite element model. The model constant for the enhanced EP model is derived by fitting model predictions (combination of two-dimensional and three-dimensional model results) to experimental results for a given temperature history. The accuracy of the enhanced EP model is then verified for a different loading profile. The modeling not only reveals the influence of underfill material on solder joint durability, but also provides the acceleration factor to assess durability under life cycle environment, from accelerated test results. Experimental results are used to validate the trends predicted by the analytical model. The final goal is to define the optimum design and process parameters of the underfill material in FCOB assemblies in order to extend the fatigue endurance of the solder joints under cyclic thermal loading environments.
Effect of Heat-Spreader Sizes on the Thermal Performance of Large Cavity-Down Plastic Ball Grid Array Packages
Authors: Lau J. , Chen T. , Lee S.-W. R.
Published: February 2008

The effect of heat-spreader sizes on the temperature distribution, thermal resistance, and cooling power of a set of cost-effective cavity-down plastic ball grid array (PBGA) packages assembled on a FR-4 epoxy glass printed circuit board (PCB) is presented. The sizes of these packages are 35 × 35 mm and 40 × 40 mm with 4 and 5 rows of solder balls.
Alternative Curing Methods for FCOB Underfill
Authors: Merton M. M. , Malhotra C. P. , Nikmanesh N. , Mahajan R. L.
Published: February 2008

This paper explores the use of liquid immersion and vapor condensation curing as alternatives to conventional hot air oven curing of flip chip on board underfill. Heat transfer results suggest that both the liquid immersion and vapor condensation heating result in reduced cure times due to higher heat transfer results associated with these two techniques. Preliminary reliability studies Suggest that the two proposed rapid curing methods do not result in any increased failure rates or different failure mechanisms. In almost all the samples the failure mode was delamination of the underfill followed by solder fatigue failure.
Flow-Field Prediction in Submerged and Confined Jet Impingement Using the Reynolds Stress Model
Authors: Morris G. K. , Garimella S. V. , Fitzgerald J. A.
Published: February 2008

The flow field of a normally impinging, axisymmetric, confined and submerged liquid jet is predicted using the Reynolds Stress Model in the commercial finite-volume code FLUENT. The results are compared with experimental measurements and flow visualizations and are used to describe the position of the recirculating toroid in the outflow region which is characteristic of the confined flow field. Changes in the features of the recirculation pattern due to changes in Reynolds number, nozzle diameter, and nozzle-to-target plate spacing are documented. Results are presented for nozzle diameters of 3.18 and 6.35 mm, at jet Reynolds numbers in the range of 2000 to 23,000, and nozzle-to-target plate spacings of 2, 3, and 4 jet diameters. Up to three interacting vortical structures are predicted in the confinement region at the smaller Reynolds numbers. The center of the primary recirculation pattern moves away from the centerline of the jet with an increase in Reynolds number, nozzle diameter, and nozzle-to-target plate spacing. The computed flow patterns were found to be in very good qualitative agreement with experiments. The radial location of the center of the primary toroid was predicted to within ±40 percent and ±3 percent of the experimental position for Re = 2000–4000 and Re = 8500–23000, respectively. The magnitude of the centerline velocity of the jet after the nozzle exit was computed with an average error of 6 percent. Reasons for the differences between the numerical predictions at Re = 2000–4000 and experiments are discussed. Predictions of the flow field using the standard high-Reynolds number k-ε and renormalization group theory (RNG) k-ε models are shown to be inferior to Reynolds stress model predictions.
Determination of Fracture Toughness for Metal/Polymer Interfaces
Authors: Sundararaman V. , Sitaraman S. K.
Published: February 2008

This work focuses on the interpretation of experimental results obtained from fracture toughness tests conducted for a typical metal/polymer bimaterial interface similar to those encountered in electronic packaging applications. Test specimens with pre-implanted interfacial cracks were subjected to a series of fracture toughness tests. Interfacial fracture toughness is interpreted from the experimental results as the critical energy release rate (Gc) at the instant of crack advance. The values of Gc from the experiments are determined using direct data reduction methods assuming linear elastic material behavior. These Gc values are compared to critical energy release rate values predicted by closed-from analyses of the tests, and to critical J-integral values obtained from finite-element analyses of the test specimen geometries. The closed-form analyses assume linear elastic material behavior, while the finite-element analyses assume both linear elastic as well as elastic-plastic material behaviors.
A Statistical Mechanical Model of Electrical Carbon Fiber Contacts
Authors: Xie J. , Pecht M. , Dasgupta A. , Swift J. A. , Wallace S. J.
Published: February 2008

This paper presents a model for electrical carbon fiber contacts. In the model, a statistically distributed fiber length was considered at contact surfaces. A technique of dealing with this kind of contact surfaces with statistically determined, or specifically undeterminable, geometry was developed. The results were compared with the experimental data obtained previously. Also, the contact behaviors of electrical carbon fiber contacts were discussed and some specific contact properties, which were also observed experimentally, were clarified. A contact resistance decreasing rate was defined in a logarithmic-logarithmic scale coordinate. A constant-rate contact region was identified. The objective of this research is to provide a theoretical basis for the contact surface designs of electrical connectors.