bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Interface Roughness on Fatigue Crack Growth in Sn-Pb Solder Joints
Authors: Shang J. K. , Yao Daping
Published: February 2008

The effect of interface roughness on fatigue crack growth was studied by examining the contribution of crack-surface sliding to the fatigue crack growth resistance of the interface in 63Sn-37Pb solder joints. Model interfaces with different values of roughness were produced in Sn-Pb/Cu joints by systematically varying the morphology of the intermetallic phase at the interface. Fracture mechanics analysis was conducted to calculate the crack-sliding resistance as a function of interface roughness, contact zone length, the shear strength of the solder, and elastic properties of bi-materials. The results were compared to the variation of fatigue crack growth threshold with interface morphology.
Impact of Tapering on Interfacial Stresses
Authors: Mirman Boris
Published: February 2008

The reduction of interfacial thermal stresses is estimated for a bimaterial strip tapered at the edges. Simple equations for this stress reduction are proposed.
Life Prediction of Solder Joints by Damage and Fracture Mechanics
Authors: Ju S. H. , Sandor B. I. , Plesha M. E.
Published: February 2008

Much research has been done on Surface Mount Technology (SMT) using the Finite Element Method (FEM). Little of this, however, has employed fracture mechanics and/or continuum damage mechanics. In this study, we propose two finite element approaches incorporating fracture mechanics and continuum damage mechanics to predict time-dependent and temperature-dependent fatigue life of solder joints. For fracture mechanics, the J-integral fatigue formula, da/dN = C(δJ)m, is used to quantify fatigue crack growth and the fatigue life of J-leaded solder joints. For continuum damage mechanics, the anisotropic creep-fatigue damage formula with partially reversible damage effects is used to find the initial crack, crack growth path, and fatigue life of solder joints. The concept of partially reversible damage is especially novel and, based on laboratory tests we have conducted, appears to be necessary for solder joints undergoing cyclic loading. Both of these methods are adequate to predict the fatigue life of solder joints. The advantage of the fracture mechanics approach is that little computer time is required. The disadvantage is that assumptions must be made on the initial crack position and the crack growth path. The advantage of continuum damage mechanics is that the initial crack and its growth path are automatically evaluated, with the temporary disadvantage of requiring a lot of computer time.
Analysis and Modeling of Lead Coplanarity Distributions
Authors: Buratynski E. K.
Published: February 2008

Lead coplanarity is defined as the height of a packaged device lead above the seating plane on which the device rests. The yield of a mass reflow surface mount soldering assembly process depends on lead coplanarity since, clearly, an excessive coplanarity is likely to produce an “open” between the lead and circuit pad. Furthermore, even if a marginal joint is obtained, excessive coplanarity can lead to reliability problems. Since these issues become more important as lead sizes decrease and pitches are refined, it is important to achieve a better understanding of coplanarity. This report analyzes the nature of 86,016 coplanarity measurements of 0.4 mm pitch, 256 I/O QFP devices. Four components to the coplanarity are identified and the distribution of each is modeled. When the four components are recombined, the result is a probability distribution for coplanarity. This information is required as input to an assembly yield model where parameter variations and tolerances are analyzed to predict surface mount yields.
A Numerical Simulation of Conjugate Heat Transfer in an Electronic Package Formed by Embedded Discrete Heat Sources in Contact With a Porous Heat Sink
Authors: Fedorov A. G. , Viskanta R.
Published: February 2008

A physical/mathematical model has been developed to simulate the conjugate heat transfer in an actively cooled electronic package. The package consists of a highly conductive substrate with embedded discrete heat sources that are in intimate contact with a porous channel through which a gaseous coolant is circulated. The flow in the porous medium is analyzed using the extended Darcy model. The nonequilibrium, two-equation model which accounts for the near wall thermal dispersion effects was used for the heat transfer analysis. The concept of the general energy equation for the entire physical domain was employed as a method of solving numerically the conjugate system. The model has been validated by comparing the predictions with available experimental data for a similar system. A parametric study has been performed to examine the effects of some of the most important model parameters on the thermal performance of porous heat sink.
Finite Element Modeling of Three-Dimensional Solder Joint Geometry in SMT
Authors: Lee T. S. , Choi T. P. , Yoo C. D.
Published: February 2008

The three-dimensional geometry of a solder joint associated with a surface mount electronic packaging process is modeled by employing a height function, z = ζ(x, y), and applying the finite element solution procedure. A rigorous formulation based on the variational methodologies is derived in two-dimensional integral form so that the standard numerical techniques for plane problems can be applied. The appropriate finite element formulation and corresponding solution procedures are devised. Numerical examples representing circular and rectangular pads are tested for validation of the developed simulator and illustration of its overall capability. The method presented in this paper shows a remarkable alternative method to the complete three-dimensional finite element approach. The developed method eliminates the difficulties associated with setting up three-dimensional brick meshes or adjusting the shape of the joint body to determine the equilibrium geometry of a soldering joint.
Conjugate Heat Transfer With Buoyancy Effects From Micro-Chip Sized Repeated Heaters
Authors: Yu D. , Ameel T. A. , Warrington R. O. , Barron R. F.
Published: February 2008

Laminar mixed convection heat transfer across five in-line microchipsized heaters, surface mounted on printed circuit board (PCB), was investigated by the weighted residual finite element method. The effects of axial heat conduction within the PCB for both mixed convection and pure forced convection are reported. The flow regime considered was 200 ≤ Re ≤ 800 and 0 ≤ Gr ≤ 58,000. Internal heat generation was included in the microchip-sized blocks in order to accurately model the thermal response to predict the maximum temperature rise. On the outer PCB walls, convective heat transfer conditions were given. Thermophysical and transport properties based on materials used in the electronics industry, including orthotropic thermal conductivity in PCB, were used. The flow and solid domains were solved simultaneously. A sensitivity study of PCB heat transfer coefficients, isotropic thermal conductivity, thermal conductivity variations, and spacing effects was performed. The mixed convection transient heating process was compared with the steady-state formulation to estimate the influence of flow oscillation in heat transfer. It was found that the maximum temperature rise in the microchips predicted by pure forced convection was, at most, 10 percent higher than that predicted by mixed convection. The difference in maximum temperature between the trailing and leading chips in the array was 30 percent.
Thermomechanical Response of Materials and Interfaces in Electronic Packaging: Part I—Unified Constitutive Model and Calibration
Authors: Desai C. S. , Chia J. , Kundu T. , Prince J. L.
Published: February 2008

The disturbed state concept (DSC) presented here provides a unified and versatile methodology for constitutive modeling of thermomechanical response of materials and interfaces/joints in electronic chip-substrate systems. It allows for inclusion of such important features as elastic, plastic and creep strains, microcracking and degradation, strengthening, and fatigue failure. It provides the flexibility to adopt different hierarchical versions in the range of simple (e.g., elastic) to sophisticated (thermoviscoplastic with microcracking and damage), depending on the user’s specific need. This paper presents the basic theory and procedures for finding parameters in the model based on laboratory test data and their values for typical solder materials. Validation of the models with respect to laboratory test behavior and different criteria for the identification of cyclic fatigue and failure, including a new criterion based on the DSC and design applications, are presented in the compendium paper (Part II, Desai et al., 1997). Based on these results, the DSC shows excellent potential for unified characterization of the stress-strain-strength and failure behavior of engineering materials in electronic packaging problems.
Effect of Component Heterogeneity on Global CTE Mismatch Displacement in Areal-Array Solder Interconnects
Authors: Heinrich S. M. , Shakya S. , Lee P. S.
Published: February 2008

An analytical model is developed for the problem of a thermally loaded electronic assembly consisting of a nonhomogeneous component attached to a substrate by means of an areal array of solder joints. The component is heterogeneous in the sense that the interior, or “die”, portion and the exterior, or “carrier”, portion may have different elastic moduli, different coefficients of thermal expansion, and/or different temperature excursions. Analytical results are presented for determining (a) the location of the critical joint(s) in the array, defined as those experiencing the maximum shearing displacement due to global CTE mismatch, and (b) the magnitude of the maximum shearing displacement. The critical joint location and the (dimensionless) peak displacement are shown to depend on only two parameters: one involving the material, geometric, and loading characteristics of the component and substrate, the other being the ratio of the die dimension to the array dimension. The stiffness of the solder array is neglected in the model; thus, the results should be valid for (a) thermal/power cycling of low-modulus solders (relative to component and substrate materials), and (b) high-temperature, low-frequency thermal/power cycling, for which a large degree of stress relaxation occurs in the solder. The results may also provide conservative estimates for situations involving stiffer arrays.
Thermomechanical Finite Element Analysis of Problems in Electronic Packaging Using the Disturbed State Concept: Part 1—Theory and Formulation
Authors: Basaran C. , Desai C. S. , Kundu T.
Published: February 2008

Accurate prediction of the thermomechanical cyclic behavior of joints and interfaces in semiconductor devices is essential for their reliable design. In order to understand and predict the behavior of such interfaces there is a need for improved and unified constitutive models that can include elastic, inelastic, viscous, and temperature dependent microstructural behavior. Furthermore, such unified material models should be implemented in finite element procedures so as to yield accurate and reliable predictions of stresses, strains, deformations, microcracking, damage, and number of cycles to failure due to thermomechanical loading. The main objective of this paper is to present implementation of such an unified constitutive model in a finite element procedure and its application to typical problems in electronic packaging; details of the constitutive model are given by Desai et al. (1995). Details of the theoretical formulation is presented in this Part 1, while its applications and validations are presented in Part 2, Basaran et al. (1998).
Advanced Heat Exchange Technology for Thermoelectric Cooling Devices
Authors: Webb R. L. , Gilley M. D. , Zarnescu V.
Published: February 2008

Thermoelectric coolers (TEC) are potentially ideal devices to cool electronic components or small electronic enclosures. However, practical heat exchange can limit the COP and restrict the range of useful applications. The TEC must reject heat from the hot side to the ambient, which is typically air. The COP can be increased by reducing the hot-side temperature, which requires a high-performance heat exchanger. An understanding of the heat sources in the TEC is presented, and relations are presented to define the hot-side thermal resistance required to operate at desired operating conditions. A novel air-cooled thermosyphon reboiler-condenser system has been developed that promises significantly higher COP for thermoelectric coolers than is possible with current heat exchange technology. This heat exchanger design concept is described and compared to conventional technology.
Solder Joint Formation Simulation and Component Tombstoning Prediction During Reflow
Authors: Wu X. , Dou X. , Yeh C.-P. , Waytt K.
Published: February 2008

The failure of electrical devices associated with solder joints has become one of the most critical reliability issues for surface-mounted devices. Solder joint reliability performance has been found to be highly dependent on the solder joint configuration, which, in turn, is governed by bond pad size, alloy material, and leadframe structure, as well as solder reflow characteristics. To investigate tombstone effects causing solder joint failure during leadless component reflow process, this work has focused on (1) developing a numerical model for the simulations of the solder joint formation during the reflow process, and (2) determining possibility that a tombstone effect for the leadless component may occur by analyzing the force and torque in the problem. Using this methodology, the tombstone effect associated with different pad geometry configurations and solder paste amount has been analyzed through the application of the public domain software tool Surface Evolver. Simulations show that the tombstoning is very sensitive to pad/component geometry design, solder surface tension, solder paste volume, wetting area, and wetting angle. This model simulation can be used to determine optimal solder paste volume, pad geometry configurations, and solder material for avoiding tombstone effects.
Analysis of Bending and Shearing of Tri-Layer Laminations for Solder Joint Reliability
Authors: Buratynski E. K.
Published: February 2008

For solder joint reliability reasons, direct chip attach technology uses an underfill material to restrict the movement of the silicon die relative to the substrate due to differences in their coefficients of thermal expansion. Modeling the fatigue life of a solder joint assembled with this technology requires a shear strain versus applied shear stress relationship. The direct chip attach configuration can be modeled as a tri-layer lamination that bends and shears with temperature excursions from the stress-free temperature. The present analysis formulates an axisymmetric, tri-layer, elastic material stress model with finite radii for the silicon die and underfill layer and an infinite sized substrate layer. A closed form solution to the shear distributions at the interfaces and the bending of the lamination is presented. This solution is a function of the reactant forces exerted by solder joints and forms the basis of a fatigue life model.
Forced Convective Liquid Cooling of Arrays of Protruding Heated Elements Mounted in a Rectangular Duct
Authors: Gupta A. , Jaluria Y.
Published: February 2008

Experiments are performed to study forced convection water cooling of arrays of protruding heat sources with specified heat input. Each array has four rows, with three elements in each row. The arrays are mounted at the top or at the bottom of a rectangular channel. The Reynolds number, based on channel height, is varied from around 2500 to 9000. Flow visualization and temperature measurements revealed that the flow over the arrays was fully turbulent, even at the smallest Reynolds number. Different channel heights (ranging from 3 to 4 times the height of each element), different heat inputs to the modules, and different streamwise spacings between the elements are employed. The spanwise spacing between the elements is kept constant. It is found that the average Nusselt number is higher for smaller channel heights and streamwise spacing, at constant Reynolds number. The effect of buoyancy on the average heat transfer rate from the arrays is found to be small over the parametric ranges considered here. A small variation in the heat transfer coefficient is found in the spanwise direction. The observed trends are considered in terms of the underlying transport processes. The heat transfer data are also correlated in terms of algebraic equations. High correlation coefficients attest to the consistency of results. The data are compared with previous air and water cooling studies, wherever possible, and a good agreement is obtained.
Random Change of Vibration Modes in Thermosonic Bonding
Authors: Kang S.-Y. , Chuang K. , Lee Y. C.
Published: February 2008

Thermosonic bonding is being widely used for wire bonding and tape automated bonding (TAB). It is also being developed for flip-chip assemblies. The bonding process is sensitive to system parameters such as ultrasonic frequency, bonding tool length, and friction. One of the process control challenges is to prevent the random change of vibration modes. The change from an axial to a bending mode excitation may reduce the ultrasonic vibration amplitude at the bonding interface and result in poor bond quality. In this work, we have studied the random mode change effected by tool length, friction, and the frequency window selected for the power generator. In one case, the mode change was not observed when the tool end extended 2.32 cm below the longitudinal axis of the bonding horn. In the other case, however, the resonant frequency switched between 58.4 and 60.0 kHz when the tool moved 0.31 cm downward with all other system parameters held constant. Such a frequency shift resulted in a change of vibration amplitudes between 1.63 and 0.55 μm. Different random mode changes measured were explained by our theoretical models consisting of a modal analysis for the system and a vibration model for the tool. The models generated a guideline to prevent mode change by selecting the right system parameters.
Applications of Digital Speckle Correlation to Microscopic Strain Measurement and Materials’ Property Characterization
Authors: Lu H.
Published: February 2008

The method of digital speckle correlation is introduced, and so is the hardware system to implement the method. The advantages and the features of the technique are discussed, and application examples are given. Owing to the high spatial resolution that this technique can achieve, the method is especially useful in measuring small areas of an object, or a small component in an assembly, whether the surfaces under probing are planar or not. The applications have proved that the technique is a promising tool for the reliability study of microelectronic packages.
The Effects of Material Properties on Heat Dissipation in High Power Electronics
Authors: Lu T. J. , Evans A. G. , Hutchinson J. W.
Published: February 2008

The role of the substrate in determining heat dissipation in high power electronics is calculated, subject to convective cooling in the small Biot number regime. Analytical models that exploit the large aspect ratio of the substrate to justify approximations are shown to predict the behavior with good accuracy over a wide range of configurations. The solutions distinguish heat spreading effects’ that enable high chip-level power densities from insulation effects that arise at large chip densities. In the former, the attributes of high thermal conductivity are apparent, especially when the substrate dimensions are optimized. Additional benefits that derive from a thin layer of a high thermal conductivity material (such as diamond) are demonstrated. In the insulating region, which arises at high overall power densities, the substrate thermal conductivity has essentially no effect on the heat dissipation. Similarly, for compact multichip module designs, with chips placed on both sides of the substrate, heat dissipation is insensitive to the choice of the substrate material, unless advanced cooling mechanisms are used to remove heat around the module perimeter.
Performance Analysis of Double Stack Cold Plates Covering All Conditions of Asymmetric Heat Loading
Authors: Pieper R. J. , Kraus A. D.
Published: February 2008

Double stack, force-cooled cold plates, which are used as electronic chassis, are investigated for all conditions of unequal temperature and heat loading. A closed form solution that relates the plate temperatures to composite heat loads is derived. This analysis covers all regimes of operation. In particular, this includes the previously ignored regime in which no adiabatic point exists anywhere on either of the fins connecting cover and splitter plates. The heat dissipating advantage of the double stack structure, over a similarly designed single stack structure, is predicted with the analysis presented in the paper.
A Two-Body Formulation for Solder Joint Shape Prediction
Authors: Renken F. P. , Subbarayan G.
Published: February 2008

Solder shape prediction is essential for accurate fatigue life determination and joint design optimization. In the present paper, a new solution approach using the surface tension theory is developed to simultaneously predict standoff height, wetted surface area, contact angles, and solder shape by including energy effects between a molten solder body and an arbitrarily shaped solid body. Existing models for solder shape prediction do not appear to determine all characteristics including joint standoff height, wetted surface area, and contact angles simultaneously. A general two-body axisymmetric finite element code is developed and coupled with a constrained optimizer to solve four illustrative examples. These examples include the shape of a sessile droplet on a fixed pad, a flip-chip joint, a sessile droplet on a free surface, and a typical ceramic ball grid array solder joint. In all four examples, the results predicted by the present approach compare favorably with available experimental and numerical results.
Process Induced Stresses of a Flip-Chip Packaging by Sequential Processing Modeling Technique
Authors: Wang J. , Qian Z. , Liu S.
Published: February 2008

In this paper, a nonlinear finite element framework was established for processing mechanics modeling of flip-chip packaging assemblies and relevant layered manufacturing. In particular, topological change was considered in order to model the sequential steps during the flip-chip assembly. Geometric and material nonlinearity, which includes the viscoelastic properties of underfill and the viscoplastic properties of solder alloys, were considered. Different stress-free temperatures for different elements in the same model were used to simulate practical manufacturing process-induced thermal residual stress field in the chip assembly. As comparison, two FEM models (processing model and nonprocessing model) of the flip-chip package considered, associated with different processing schemes, were analyzed. From the finite element analysis, it is found that the stresses and deflections obtained from nonprocessing model are generally smaller than those obtained from the processing model due to the negligence of the bonding process-induced residual stresses and warpage. The stress values at the given point obtained from the processing model are about 20 percent higher than those obtained from the nonprocessing model. The deflection values at the given points obtained from the processing model are usually 25 percent higher than those obtained from the nonprocessing model. Therefore, a bigger error may be caused by using nonprocessing model in the analysis of process-induced residual stress field and warpage in the packaging assemblies.
Potential Failure Sites in a Flip-Chip Package With and Without Underfill
Authors: Madenci E. , Shkarayev S. , Mahajan R.
Published: February 2008

In this study, the effect of underfill on the level of stress concentrations is investigated and possible failure sites are identified by using a global/local finite element approach. The global elements capture the exact singular behavior of the stresses near the geometric and material discontinuities. Application of the strain energy density criterion indicates the possible failure sites and how they shift due to the presence of underfill.
Experimental Study on Electric-Current Induced Damage Evolution at the Crack Tip in Thin Film Conductors
Authors: Bastawros A.-F. , Kim K.-S.
Published: February 2008

The time dependent temperature distribution induced by electric current heating in a double edge cracked, unpassivated thin aluminum or gold film interconnect lines is monitored using a high resolution infrared imaging system. A pure aluminum or gold film, with a thickness of 0.2 μm, is deposited by high vacuum evaporation coating and patterned into test structures of varying widths. The operative mechanisms of mass transport are assessed in view of the monitored temperature profile. The pre-cracked aluminum film shows fine crack growth towards the positive electrode, which originates from the initial crack tips. The crack-tip temperature is close to melting, during propagation. After the initial crack propagation, a hot spot is formed between the two elongated cracks, and leads to failure. The crack growth generates a backward mass flow towards the negative electrode. The gold film shows a different pattern, in which the original cracks propagate towards each other with a slight tilt towards the negative electrode. The tip temperature is lower than the melting temperature. These time dependent failure mechanisms are rationalize using a proposed critical current intensity factor and a normalized current intensity rate, similar to the fracture toughness KIC for brittle fracture.
A Global Multidimensional Sensitivity Analysis of Electronic Systems Subjected to Time-Dependent Excitations
Authors: Jensen H. A. , Cifuentes A. O.
Published: February 2008

This technical note presents a global sensitivity analysis method for the dynamic response of electronic systems considering several design parameters at the same time. The method is an extension of a previous method presented by the authors for the one-dimensional case (only one design variable at a time was considered subjected to uncertainty). The method is expected to be useful in the design, analysis and qualification of electronic components.
Effect of Edge and Internal Point Support of a Printed Circuit Board Under Vibration
Authors: Lim G. H. , Ong J. H. , Penny J. E. T.
Published: February 2008

This paper presents an investigation into the vibration of a PCB that is supported on its three edges by two wedge retainers and a plug-in connector. Using a vibration test fixture to couple the PCB structure to an electromagnetic shaker, experiments were conducted to determine its dynamic response. The wedge retainer and connector are modeled as simply supported condition with appropriate rotational spring stiffnesses along their respective edges. It is found that these supports behave somewhere between the simply supported and clamped boundary conditions and provide a percent fixity of 39.5 percent more than the classical simply supported case. It is further found that a single internal point constraint that would yield the maximum fundamental frequency is located at the intersection of the nodal lines of mode 2 and mode 3. This has the effect of significantly increasing the PCB’s fundamental frequency from 68.4 Hz to 146.9 Hz, or 115 percent higher.
Mechanical Deformation in Conductive Adhesives as Measured With Electron-Beam Moire´
Authors: Drexler E. S. , Berger J. R.
Published: February 2008

Two forms (paste and film) of isotropically conductive adhesives (CAs) were mechanically loaded in shear mode. The specimens were instrumented with crossed-line gratings so that normal and shear displacements could be measured. The CA paste specimen failed outside the observed region at a stress 28 percent below the manufacturer’s predicted value. In the observed region there were no normal strains, only shear strains restricted to the CA. In the film specimen the conducting particles began breaking away from the matrix epoxy at very low loads. However, the specimen continued carrying the additional loading increments until the load was transferred to the adjacent material.
Fundamental Factors in the Design of a Fast-Responding Methanol-to-Hydrogen Steam Reformer for Transportation Applications
Authors: OhI G. L. , Stein J. L. , Smith G. E.
Published: February 2008

Improving the dynamic response of the steam reformer in a fuel cell power plant designed for transportation applications will enable the power plant to operate in a transient manner with a reduced need for supplementary batteries and their associated cost, weight, and life cycle limitations. As a method of seeking improvements to the dynamic response, a sixth-order dynamic model of a steam reformer is used with a design optimization process to determine the values of the steam reformer design parameters which will yield the fastest response time to a step input in hydrogen demand under a variety of initial conditions. Results of this analysis suggest that a steam reformer designed to have a maximum output of approximately 12,600 mol/h of hydrogen and optimized for fast response could have response times on the order of 15–20 s. A sensitivity analysis suggests that this response can be achieved primarily by reducing the thermal capacity of the reformer and improving the rate of heat transfer to the gaseous constituents within the reformer. With a steam reformer response time on the order of 15–20 s, supplementary energy storage devices, such as the ultracapacitor and flywheel, become more feasible. These devices are attractive because they have superior life cycle and power density characteristics when compared with traditional chemical batteries.
Criteria for Economic Optimization of an Absorption System Using Sources of Low Temperature
Authors: Hernandez F. , Izquierdo M.
Published: February 2008

An absorption system, reduced to the equivalent combined system of three-heat-source heat pump, is optimized with economical criteria. The multiparameter thermodynamic function η combines the COP and rate of pumping, and determines that optimum. Values of μ = 0, μ = 1, and μ > 1 define three different cases of application for different markets.
Fluid Flow in a Skewed Annulus
Authors: Haci M. , Cartalos U.
Published: February 2008

A novel, realistic treatment of annular flow in an oil well is developed. The fluid flow in an annuuls with an inclined or S-shaped inner pipe is considered. The model covers laminar and turbulent flow regimes and the results are experimentally verified. The study predicts axial and angular velocities and frictional pressure losses. The frictional pressure losses are shown to be higher than in the corresponding concentric annulus when the inner pipe is severely S-shaped. However, for typical drilling well geometries, the frictional pressure losses are found to approach the eccentric annular predictions asymptotically. Thus, the study finds the average eccentricity of a vertical or near vertical well, which is a difficult parameter for the engineer to estimate. The results of the study are of practical importance where high annular frictional pressure losses are encountered, such as in slim holes and coiled tubing operations. The frictional pressure losses in complex annular geometries are presented in an easily usable form.
Three-Dimensional Effects of Solder Joints in Micro-Scale BGA Assembly
Authors: Zhu J.
Published: February 2008

Micro-scale BGA has attracted more and more interest due to their high performance/area ratio. This technology is especially important for mobile personal equipment, such as cellular phones and laptop computers. With the decrease of solder ball sizes, the reliability problem becomes the major concern for the package design, which requires more powerful tools to address this issue. Finite element method is a useful tool for packaging design and analysis. For some BGAs, the critical solder balls are sometimes not located at a symmetric plane and the deformations in three directions will affect the distribution of stress/strain in these solder balls. Therefore, a full three-dimensional analysis is necessary to address these effects. However, it is almost impossible to run a three-dimensional single finite element model to consider all design details even with simplified material properties, not to mention creep constitutive law. Therefore, the global/local modeling technique provides an alternate way, which can simplify the modeling work’ Significantly, reduce the computational time, and enhance the crucial information at critical locations. In this study, the global/local technique was used to study a micro-scale BGA assembly and to investigate the three-dimensional effects of stress/strain distribution inside the solder joints. It was found that the maximum creep strain is not located at the plane passing through the package center and solder joint axis. It was also found that the position of maximum creep strain will shift during first several cycles, but will stabilize after the fourth cycle. This result is also helpful in evaluating the reliability of the critical solder joints in micro-scale BGA assemblies.
Energetic Fuels for Combustion Applications
Authors: Segal C. , Shyy W.
Published: February 2008

New fuels with high-energy-density are desirable for many combustion applications. Two types are reviewed in this paper, namely, mixtures resulting from addition of certain metallic or nonmetallic elements to conventional hydrocarbon fuels, and newly synthesized hydrocarbon fuels with strained molecular conformations or more densely packed molecular structures. Despite the favorable effects of high-energy content, these materials often exhibit low reactivity and their ability to improve the performance of practical combustion systems relies strongly on their interaction with the dynamics of the surrounding fluid flow. The intensity of the combustion processes of these materials is dictated, in general, by the melting, evaporation, pyrolysis, mixing, and exothermic reactions processes. Unlike other conventional hydrocarbon fuels, all these processes time scales are often comparable with each other, causing difficulties to devise simpler theoretical models to predict the combustion characteristics. Both the advances made in recent years and the needs for future research and development in the field of energetic fuels are discussed.
A Revised Decomposition Method for MILP Problems and Its Application to Operational Planning of Thermal Storage Systems
Authors: Yokoyama R. , Ito K.
Published: February 2008

A revised decomposition method for solving large-scale mixed-integer linear programming (MILP) problems with block angular structure is presented to efficiently conduct the operational planning of thermal storage systems. The fundamental algorithm adopted here is composed of solving large-scale linear programming (LP) master problems by the Dantzig-Wolfe decomposition method and small-scale MILP subproblems by the branch and bound method, and these problems are solved repeatedly until an optimality or suboptimality criterion is satisfied. As one of the revision strategies to improve computation efficiency, a two-phase approach is introduced, by which a next LP master problem can be solved efficiently by utilizing the results of a previous one. An illustrative example on a heat supply system for district heating and cooling is given to show the effectiveness of the above revision strategy. A practical example on a heat supply system with multiple thermal storage tanks for brewing is also presented.
An Experimental and Analytical Study of Single-Phase Liquid Flow in a Horizontal Well
Authors: Yuan H. , Sarica C. , Miska S. , Brill J. P.
Published: February 2008

A new test facility was designed and constructed to simulate flow in a horizontal well with a single perforation. A total of 635 tests were conducted with Reynolds numbers ranging from 5000 to 60,000 with influx to main rate ratios ranging from 1/5 to 1/100, and also for the no-influx case. The flow behavior in a single-perforation new friction expression for a single-perforation horizontal well was developed. A new simple correlation for the horizontal well friction factor was developed by applying experimental data to the general friction factor expression. The new friction factor correlation and experimental data were compared with the Asheim et al. (1992) data and model, and showed that the new correlation performed better than the Asheim et al. (1992) model.
Exergonomic Optimization of an Air-Conditioning System
Authors: Cammarata G. , Fichera A. , Mammino L. , Marletta L.
Published: February 2008

In this paper, exergonomic theory is applied to an air-conditioning system for optimization purposes. The investigation is addressed to an all-air system with air recirculation, The thermodynamic cycle includes a mixing plenum, a cooling and heating coil, chiller, and heater. The thermodynamic model is stated according to recent formulations of exergy for moist air streams, while the economic model is based on cost balance equations and real cost data for mechanical equipment. The objective function to minimize includes the following decision variables: fresh to total air rate, coefficient of performance for the chiller, inlet temperature of water for the cooling and the heating coils, temperature difference of the same streams. For the exergonomic optimization, the authors followed the approach proposed by Tsatsaronis (1984). The optimum configuration is obtained through an iterative procedure aimed at the design improvement. The results show that there is considerable room for improvement with respect to a system based on typical design parameters.
Improving the OTEC Power Plant Performance by Metal Hydride Energy Systems
Authors: Gambini M.
Published: February 2008

A new system to improve the present OTEC (ocean thermal energy conversion) power plant performance is here presented. This is a metal hydride energy system operating as a “temperature upgrading” device which allows an increase of the OTEC plant working fluid temperature at the turbine inlet. The integrated MHTUP (metal hydride temperature upgrading)—OTEC plant has been investigated, taking into account the dynamic operations of MHTUP system and the OTEC pumping power increase due to the water circulation in the MHTUP system. The results show an increase in the OTEC net power of about 20 percent and the technological feasibility of the proposal. The large amounts of metal hydride and of heat transfer surface required by MHTUP system involve a critical situation from an economical point of view. The further analysis, particularly regarding the performance optimization and new plant arrangement of the MHTUP system, have to be developed in order to attain the economical feasibility of the proposal.
Effects of Heating on Two-Dimensional Mixing Layers
Authors: Butuk N. , Gollahalli S. R.
Published: February 2008

Transverse profiles of temperature and the mean velocities in the streamwise direction in a horizontal shear layer are presented. The variation of vorticity thickness along the streamwise coordinate is examined for the cases when both streams were at room temperature and when the top stream was heated to 360 K. The similarity of the velocity field is observed only near the plane of the interface of the two streams in both cases. The vorticity thickness-velocity ration correlation agrees well with the data available for the isothermal shear layers. The heating of one stream was not found to significantly influence the vorticity thickness, which is explained by the counteracting influences of viscosity and density changes.
Gas-Liquid Stratified-Wavy Flow in Horizontal Pipelines
Authors: Chen X. T. , Cal X. D. , Brill J. P.
Published: February 2008

Gas-liquid stratified-wavy flow with low liquid loading is common in natural gas transmission pipelines and offshore gas pipelines. This specific case of two-phase pipe flow has been studied experimentally and theoretically in the present paper. The interfacial behavior during air-kerosene stratified-wavy flow in a 77.9-mm-dia 420-m-long pipeline was observed carefully. The gas-liquid interface usually exhibits a concave downward curved configuration. The liquid film-wetted wall fraction, liquid holdup, and pressure drop were also measured. A mechanistic “double-circle” model and a correlation for interfacial friction factor, required as a closure relationship in the model, have been developed. The new model gives significantly improved predictions for both liquid holdup and pressure drop during gas-liquid stratified-wavy flow in horizontal pipelines.
Optimization of the Storage Process for a Cool Thermal Storage System
Authors: Abraham M. M. , Annamalai K. , Claridge D. E.
Published: February 2008

The storage process for a static-water ice-on-coil cool thermal storage system is difficult to model analytically, based on the dynamic behavior of ice production. Systems that utilize a vapor-compression cycle, with the tank acting as an evaporator, further complicate an analytical model due to the two-phase heat transfer throughout the storage tank. This analysis presents a simplified model of the storage process for a static-water ice-on-coil storage tank acting as an evaporator in a vapor-compression cycle. Specifically, the storage process is optimized by minimizing the amount of compressor work required to freeze water at 0°C. Optimization variables are refrigerant evaporating temperatures and tank heat exchanger sizing. The dynamics office production and two-phase heat transfer are simplified by assuming the overall heat transfer coefficient remains constant throughout the storage process. An average value for the overall heat transfer coefficient may be substituted and still provide useful results. A second law analysis utilizing the irreversibility developed during cool storage is also presented. The model is then used in side-by-side comparisons of compressor work, tank heat exchanger efficiency, and irreversibility, as functions of evaporating temperature, for several heat exchanger sizes.
Exergy Evaluation of Two Current Advanced Power Plants: Supercritical Steam Turbine and Combined Cycle
Authors: Jin H. , Ishida M. , Kobayashi M. , Nunokawa M.
Published: February 2008

Two operating advanced power plants, a supercritical steam plant and a gas-steam turbine combined cycle, have been analyzed using a methodology of graphical exergy analysis (EUDs). The comparison of two plants, which may provide the detailed information on internal phenomena, points out several inefficient segments in the combined cycle plant: higher exergy loss caused by mixing in the combustor, higher exergy waste from the heat recovery steam generator, and higher exergy loss by inefficiency in the power section, especially in the steam turbine. On the basis of these fundamental features of each plant, we recommend several schemes for improving the thermal efficiency of current advanced power plants.
Acoustic Enhancement of the Rate of Heat Transfer Over a Flat Plate-An Experimental Investigation
Authors: Preston J. M. , Johnson W. S.
Published: February 2008

Increasing the rate of heat transfer can improve product quality and lower energy cost for many energy systems. Pulsating fluid flow has been used to increase the rate of heat transfer in some situations. Specifically, sound waves below the audible limit, termed infrasound, have been used to increase the rate of heat transfer from small-diameter wire rods. This study examined the effects of infrasound on the rate of heat transfer from a flat plate. A standing sound wave is formed in the neck of a Helmholtz resonator and may be enhanced by producing sound waves at the resonant frequency at or near the neck of the resonator. In this study, a standing wave of infrasound was produced in a rectangular channel by two loudspeakers driven sinusoidally by a function generator at the resonant frequency of the system. The top of the channel was formed by a copper plate maintained at a constant temperature. Thermocouples placed along the centerline of the channel measured the temperature of the air inside the channel and heat flux gages mounted on the inside surface of the copper plate were used to measure the local rate of heat transfer from the plate to the air inside the channel. Air flow inside the channel was produced by a centrifugal blower and varied by an inlet damper. The use of infrasound increased the rate of heat transfer by approximately an order of magnitude when compared to natural convection. Infrasonic enhancement of the rate of heat transfer over a two-dimensional region in forced convection was more effective in the laminar flow regime, for Reynolds numbers based on the hydraulic diameter between zero and 10,000. Typically for laminar flow, infrasound increased the rate of heat transfer up to five times the rate of heat transfer without infrasound. For turbulent air flow, however, the increase of the rate of heat transfer was almost negligible. The effect of infrasound on the rate of heat transfer was shown to depend on the air velocity inside the channel, the hydraulic diameter of the channel, and the sound pressure level inside the channel. The temperature of the copper plate over the limited range tested did not significantly affect the heat transfer coefficient. The speakers used were limited to a maximum sound pressure level of 121 dB, while infrasonic generators are capable of producing sound pressure levels over 170 dB.
The Effects of Burner Geometry and Fuel Composition on the Stability of a Jet Diffusion Flame
Authors: Papanikolaou N. , Wierzba I.
Published: February 2008

The effect of the burner configuration and fuel composition on the stability limits of jet diffusion flames issuing into a co-flowing air stream is presented. Circular and elliptic nozzles of various lip thicknesses and aspect ratios were employed with methane as the primary fuel and hydrogen, carbon dioxide, and nitrogen as additives. It was found that the effects of nozzle geometry, fuel composition, and co-flowing stream velocity on the blowout limits were highly dependent on the type of flame stabilization mechanism, i.e., whether lifted or rim-attached, just prior to blowout. The blowout behavior of lifted flames did not appear to be significantly affected by a change in the nozzle shape as long as the discharge area remained constant, but it was greatly affected by the fuel composition. In contrast, attached flame stability was influenced by both the fuel composition and the nozzle geometry which had the potential to extend the maximum co-flowing stream velocity without causing the flame to blow out. The parameters affecting the limiting stream velocity were studied.