bluuebunny/crossref_metadata_2025 huggingface dataset:
The Child Welfare System and State Intervention in Families: From Historical Patterns to Future Questions
Authors: Reich Jennifer A.
Published: April 2008

The child welfare system remains one of the most important welfare institutions in regulating family life and meanings of gender. However, it has largely escaped sociological analysis. This article provides a framework for thinking about the meanings of state intervention in family life and describes the legal and procedural machinations of the system by providing an overview of the history of the system. In doing so, this article elucidates the complex and contradictory mandates the child‐protective services system and its actors face and raises several questions or quandaries that remain under‐explored and deserving of analytical attention.
Special Issue: Evolutionary perspectives on salmonid conservation and management
Authors: Waples Robin S. , Hendry Andrew P.
Published: April 2008

This special issue of Evolutionary Applications comprises 15 papers that illustrate how evolutionary principles can inform the conservation and management of salmonid fishes. Several papers address the past evolutionary history of salmonids to gain insights into their likely plastic and genetic responses to future environmental change. The remaining papers consider potential evolutionary responses to climate warming, biological invasions, artificial propagation, habitat alteration, and harvesting. All of these papers consider how such influences might alter selective regimes, which should then favour plastic or genetic responses. Some of the papers then go on to document such responses, at least some of which are genetically based and adaptive. Despite the different approaches and target species, all of the papers argue for the importance of evolutionary considerations in the conservation and management of salmonids.
Development of microsatellite markers for the grapevine fungal pathogen Phaeomoniella chlamydospora
Authors: SMETHAM GABRIELLE , ADES PETER , FORD REBECCA
Published: April 2008

Twenty polymorphic microsatellite markers from microsatellite‐enriched genomic DNA of the grapevine fungal pathogen, Phaeomoniella chlamydospora, were developed and characterized. The markers were used to genotype isolates from Australia and from Europe/Eurasia. The number of alleles per locus ranged from two to 11. Gene diversity per locus ranged from 0.08 to 0.63 among Australian isolates, and from 0.2 to 0.77 among isolates from Europe/Eurasia, demonstrating the suitability of these markers for population genetic studies of P. chlamydospora. Eighteen of the 20 markers also amplified a product in the closely related Phaeoacremonium aleophilum.
FORECASTING THE SOUTH AFRICAN ECONOMY WITH GIBBS SAMPLED BVECMs
Authors: Gupta Rangan
Published: April 2008

The paper uses the Gibbs sampling technique to estimate a heteroscedastic Bayesian Vector Error Correction Model (BVECM) of the South African economy for the period 1970:1‐2000:4, and then forecasts GDP, consumption, investment, short and long term interest rates, and the CPI over the period of 2001:1 to 2005:4. We find that a tight prior produces relatively more accurate forecasts than a loose one. The out‐of‐sample‐forecast accuracy resulting from the Gibbs sampled BVECM is compared with those generated from a Classical VECM and a homoscedastic BVECM. The homoscedastic BVECM is found to produce the most accurate out of sample forecasts.
ADJUSTING SOUTH AFRICA'S FISCAL BALANCE FOR TERMS‐OF‐TRADE EFFECTS
Authors: Swanepoel Jan A.
Published: April 2008

Standard output gap‐based calculations and interpretations of the cyclical component of the fiscal balance may convey a misleading picture in countries such as South Africa which experience substantial movements in their terms of trade. This paper therefore adjusts South Africa's general government primary balance for terms‐of‐trade effects by means of an alternative calculation of the transitory component based on a measure of the real income gap rather than the real output gap. The results indicate that measures of the cyclical component of the budget balance based on real income and real output gaps generally yield broadly similar results over history, but during exceptional periods of rapid changes in commodity prices, the measures can be very different.
CURRENCY BOARD ARRANGEMENTS AS A SUPER‐FIXED ALTERNATIVE IN THE CHOICE OF EXCHANGE RATE REGIME1
Authors: Wessels Buks
Published: April 2008

Currency board arrangements (CBAs) are currently widely proposed as a super‐fixed exchange rate solution to exchange rate volatility. This paper researches the nature, operation, benefits and disadvantages of CBAs. Benefits comprise improved policy credibility, lower inflation and interest rate levels, increased economic growth, increased foreign capital flows, and sharply reduced currency speculation. These are compared with the shortcomings of CBAs, such as the absence of a lender of last resort, real exchange rate misalignments and their consequences for the economy. The paper identifies the type of country that would be the most likely candidate to benefit from a CBA.
Combined Vibrational and Thermal Solder Joint Fatigue—A Generalized Strain Versus Life Approach
Authors: Barker D. , Vodzak J. , Dasgupta A. , Pecht M.
Published: April 2008

The combined effects of elastic and inelastic strains on solder joint reliability are investigated. Experimental data from high-cycle fatigue tests of solder are combined with data from low-cycle fatigue tests to obtain a plot of total strain amplitude against cycles to failure. The generalized Coffin-Manson fatigue equation is used to describe this relationship. The transition fatigue life of approximately 7000 cycles indicates that elastic strains play a significant role in the fatigue damage of solders at a life of 103 cycles or higher. The results suggest that the commonly adopted approach of relating only inelastic strain, or the total strain, to fatigue life with a single power law relationship may be inadequate when predicting solder joint reliability. Instead, both elastic strains and plastic strains should be considered, especially when the electronic assembly is subjected to a combination of large amplitude thermal loads and relatively lower amplitude vibrational loads. A methodology is presented to evaluate the combined effects of simultaneous vibration and thermal cycling of solder joints. This combined loading situation is simulated by superposing the effects of the vibrational and thermal loads. The damage due to each load-type acting individually is determined and then superposed to assess the overall effective fatigue life of the joint. As a first order approximation, a linear superposition rule is utilized, Miner’s rule. Reliability predictions from this simple superposition model are then compared to standard low cycle thermal fatigue models.
Solder Joint Reliability — Design Implications From Finite Element Modeling and Experimental Testing
Authors: Charles H. K. , Clatterbaugh G. V.
Published: April 2008

An extensive finite element modeling and experimental testing program has been carried out to determine the most optimum design parameters for solder joints in surface mount applications. Although the analysis and testing (power cycling and thermal cycling) has been carried out for a variety of package styles, particular attention will be paid to the result for leadless ceramic chip carriers. This package is particularly useful in certain high performance military and commercial applications. Analysis and experimentation indicate that increased fatigue life under power cycling can be attained by fabricating solder joints with large fillets and low standoff heights. The large fillet geometry significantly reduces harmful stress concentrations while increasing the net cross-sectional area within the joint. Both factors tend to improve the fracture toughness of the joint. The temperature and frequency dependencies of solder joint fatigue life under power cycling testing is discussed. The observed frequency dependence can be minimized by eliminating harmful tensile strain components thus reducing harmful stress relaxation and tensile induced oxygen embrittlement of grain boundaries. Temperature cycling studies indicate joints with slightly higher standoffs and low fillet angles are more resistant to cyclic fatigue than pillar type joints which tend to focus shear strains at the interfaces. Solder joints can be tapered to improve overall reliability but, in most cases, tapering will provide only a small increase in fracture toughness of the joint through the elimination of stress concentrations. Additional fatigue life increases can be obtained only through an enlargement of the joint cross-sectional area. Aspects of the above results will be presented in detail along with design guidelines for creating high reliability solder joints for various application scenarios.
Oxidation of (Pb, Sn) and (Pb, In) Alloys
Authors: Konetzki R. A. , Zhang M. X. , Sluzewski D. A. , Chang Y. A.
Published: April 2008

The oxidation of (Pb,Sn) and (Pb,In) single-phase alloys and the Pb-Sn eutectic was studied using Auger electron spectroscopy (AES) and a scanning Auger microprobe (SAM). The oxidation of the single-phase alloys results in a structure which has been called “an oxide inversion layer”, where the amount of solute in the oxide increases with depth into the oxide layer, reaches a maximum, then decreases to its value in the bulk alloy. The solute content of the oxide is noticeably higher in the region surrounding grain boundaries, due to the enhanced diffusion of the solute. Grain boundary oxidation is also observed in the single-phase alloys. The oxidation kinetics of both the single-phase (Pb,Sn) alloys and the eutectic alloy are logarithmic at 22° C and 90° C, but become parabolic at temperatures greater than 120° C. Pb-3.0 at. percent In alloys follow logarithmic oxidation kinetics up to 150°C and parabolic kinetics between 175°C and 250°C.
Sensor Technology for ZIF Connectors
Authors: Chikazawa T. , Lim C. K. , Luu H. V. , Toda M. D. , Vogelmann J. T.
Published: April 2008

A zero insertion force (ZIF) connector was designed with the requirement of maintaining a specified contact normal force and wipe sufficient to achieve reliable electrical performance. In order to evaluate the design during its development and to monitor its quality during full scale production, a nondestructive sensor was developed to measure the force and wipe simultaneously. The sensor was built into a steel coupon, and assembled in a benchtop fixture that facilitates ease of alignment and measurement of the contact springs. The coupon can also be mounted on a printed circuit card to enable “in-situ” measurement of connectors assembled in the electronic “cage-like” package. Prior to sensor availability, the connector vendors as well as IBM had other methods of measuring contact force and wipe. These measures had varying accuracies, and were difficult to correlate. The sensor described in this paper was duplicated in order for the vendors and IBM to have a consistent measurement tool.
Solder Joint Formation in Surface Mount Technology—Part I: Analysis
Authors: Heinrich S. M. , Elkouh A. F. , Nigro N. J. , Lee Ping S.
Published: April 2008

An analytical model of solder joint formation during a surface mount reflow process is developed in the present paper, and the solution is obtained in an explicit integral form. For two limiting cases—infinitesimal and infinite solder areas—the solution is expressed in closed form. Numerical results illustrate the influence of the process parameters (surface tension, density, and cross-sectional area of the molten solder, and the contact angles between the solder andpretinning) on joint shape and overall fillet dimensions. Comparisons between theoretical predictions and laboratory data show excellent agreement.
Solder Joint Formation in Surface Mount Technology—Part II: Design
Authors: Heinrich S. M. , Nigro N. J. , Elkouh A. F. , Lee P. S.
Published: April 2008

In this paper dimensionless design curves relating fillet height and length to joint cross-sectional area are presented for surface-mount solder joints. Based on an analytical surface tension model, the advantage of these dimensionless curves is that they may be used for arbitrary values of solder density and surface tension. The range of applicability of previously developed approximate formulae for predicting joint dimensions is also investigated. A simple example problem is included to illustrate the use of both the design curves and the approximate formulae.
Packaging Architecture Considerations of High Density Multi-Chip Electronic Packages Via System Optimization
Authors: Krusius J. P.
Published: April 2008

Multi-chip packaging of high density CMOS based systems is analyzed using package system simulation, a new systematic methodology for design and trade-off studies of electronic packages in order to examine future trends. Technology parameters for a representative CMOS chip, multi-chip package (MCP), and printed wiring board technology are defined. Six key MCP parameters are optimized using simulated annealing. A large number of different optimum MCP’s for minimum system cycle time have been found. Based on this set key packaging parameter relationships are derived and associated future trends discussed. Finally, the significance of these trends to mechanical engineers is outlined.
An Investigation of the Passive Cooling of Table Model Television Receivers
Authors: Yuki M. S. , Parsons J. R. , Krane R. J.
Published: April 2008

Economic and reliability considerations lead to the adoption of passive techniques for cooling by a combination of natural convection and radiation heat transfer. In order to facilitate the cooling by natural convection, thermal design engineers commonly incorporate vent openings in the walls of a receiver cabinet. Unfortunately, natural convection flows in complex, vented enclosures are presently not well understood and designers must employ “cut and try” methodologies to determine the sizes and locations of vent openings. Since vent openings are expensive to incorporate in consumer electronic products, it was decided to develop the techniques that would enable thermal designers to minimize the number of vent openings in a TV cabinet and maximize the effectiveness of those vents that are employed. Thus, the present study represents the first step in a rational program to develop the tools that will enable engineers to optimize the thermal design of a table model television receiver. In this initial work, experiments were performed to determine the effects of vent size and location on component cooling in a representative table model receiver. Vents were systematically blocked until the set was operated in a completely sealed condition. Measurements of component, air, and cabinet wall temperatures and the results of flow visualization experiments were used to assess the effects of various combinations of vent openings on the natural convection cooling of the receiver. Results indicate that: (1) the present design of the vent system of a representative, commercially available table model television receiver is adequate, but has not been optimized, and (2) significant improvements in the design of the vent could be achieved; that is, improved component cooling could be obtained with fewer vent openings. The results of this work, which should be directly applicable by thermal designers, will also serve to experimentally verify numerical models of the natural convection flows through television receivers that are currently under development.
Numerical Modeling of Forced Convection Heat Transfer for Modules Mounted on Circuit Boards
Authors: Agonafer D. , Moffatt D. F.
Published: April 2008

Numerical simulation of the fluid and heat transfer characteristics of electronic modules mounted on circuit boards is performed using a commercial finite-control-volume code, PHOENICS. The model is used to simulate the experimental data for flow over blocks simulating electronic modules from published sources of data. The Reynolds numbers considered in both studies vary from 1000 to 7000. The numerically computed heat transfer coefficient agreed with the experimental data in the fully developed region within 8 percent. However, the results were quite sensitive to the transverse grid distribution for flow rates in the turbulent regime. Guidelines are suggested in the effective use of the commercial code for such classes of problems.
Predicted Stresses in Wire Bonds of Plastic Packages During Transfer Molding
Authors: Suhir E. , Manzione L. T.
Published: April 2008

An analytical stress model is developed for the evaluation of flow induced stresses in wire bonds of plastic packages during molding. We limit our analysis to the stresses acting in the plane of a wire bond. These stresses can possibly result in liftoff of the ball bond from the bonding pad of the integrated circuit. The main purpose of the analysis is to evaluate the effect of the wire bond configuration. It is shown that the stresses in wire bonds are proportional to the square of the ratio of the wire-bond span to the diameter of the wire. This explains the difficulty in molding assemblies with long wire bond spans. We also showed that wire configurations, characterized by nonzero slope angles at the ends, result in lower stresses than conventional wire shapes, where the wedge bond to the electric lead forms a zero angle. The obtained results are useful when designing plastic package assemblies and/or choosing the appropriate wire bond loop height and span.
Mechanical Engineering Issues and Electronic Equipment Reliability: Incurred Costs Without Compensating Benefits
Authors: Leonard C. T.
Published: April 2008

Temperature is widely viewed as a major influence on failures of electronic equipment. Failure Prediction Methodology (FPM), such as MIL-HDBK-217 is an often quoted reference describing the temperature influence, often depicted as being exponential in effect, affecting wide classes of electronic component parts. The FPM concept of a constant failure rate that is accelerated by various environmental influences is widely applied beyond its validity. Misapplications of the reliability models in current use may cause failure avoidance efforts such as temperature reduction and parts quality selections not to yield anticipated overall results. The cost and complexity effects can be significant: temperature reduction, for example, can result in expensive system implementations in some cases whose costs and complexities may exceed the anticipated benefits in reliability. Due to industry wide continuing improvements in component quality over the years, the continuing quest for electronics reliability should change emphasis from attention to electronic parts to activities that address assembly and processes. This paper discusses the ways the temperature ingredient of reliability and similar concepts may be currently applied, with examples to illustrate disparities between anticipations and realizations. Alternate approaches are offered and their possible implementations are discussed.
High and Low-Cycle Fatigue Damage Evaluation of Multilayer Thin Film Structure
Authors: Oshida Yoshiki , Chen P. C.
Published: April 2008

A five-layered (Cu/Cr/Kapton® /Cr/Cu) metallic thin film structure was subjected to a completely reversed bending fatigue cycling with a wide ranges of applied strain amplitudes from 0.25 percent to about 30 percent. A new model for determination of the number of cycles to fatigue failure NF was proposed for single-crack and multi-crack formations. Within a strain amplitude ranging from 1 to 10 percent, a Manson-Coffin’s relationship was recognized for both the number of cycles to crack initiation NC and NF with exponents of 0.39 and 0.51, respectively. Selected fatigued test samples were further subjected to X-ray diffraction line analysis for dislocation density (ρ) calculation, which was related to the number of fatigue cycles N and strain amplitude (Δ εT) in an empirical formula. It was also found that dislocation densities accumulated up to both Nc and NF were related to applied strain amplitudes. Consequently, if applied strain amplitude is known and progressive change in dislocation density is measured, one can predict the remaining fatigue life as well as fatigue cycles which were already consumed.
Closing of Surface Flaws Under Compressive Loading
Authors: Warren W. E. , Amos D. E.
Published: April 2008

The plane elastic deformation of a notched half-plane which is compressed by a flat rigid surface is investigated. The stress and displacement fields of this notched halfplane are felt to be representative of the conditions occurring in the neighborhood of a flaw on the surface of a compressed circular O-ring. O-rings are often installed as environmental seals in electronic components, and the results of this analysis indicate that minor surface flaws do not threaten the integrity of O-ring seals under normal installation conditions. Compressing the O-ring reduces the notch surface opening and pushes the notch surface toward the rigid compressing plate. Both of these effects reduce the notch void volume and the possibility of seal leakage.
Thermal Stresses and Free-Edge Effects in Laminated Beams: A Variational Approach Using Stress Functions
Authors: Yin Wan-Lee
Published: April 2008

A variational method involving stress functions is used to determine the interlaminar stresses and the free-edge effects in a laminated beam under a temperature loading. The stress function in each layer is approximated by a cubic polynomial function of the thickness coordinate. The equilibrium equations, the traction boundary conditions, and the continuity conditions of the interlaminar stresses are exactly satisfied in this analysis, while the compatibility equations and interfacial continuity of the tangential strains are enforced in an averaged sense by applying the principle of complementary virtual work. The method is highly efficient and accurate. A thermal stress analysis for a three-layer beam using only eight eigenfunctions yield results that are comparable in accuracy to finite-element solutions involving thousands of degrees of freedom.
Thermoelastic Solutions for a Finite Substrate With an Electronic Device
Authors: Lau J. H.
Published: April 2008

Sneddon and Lockett obtained a fairly general solution to the steady-state thermoelastic problem for the thick plate (Sneddon and Lockett, 1960). In particular, they have obtained the exact solutions for axially symmetrical temperature distributions on the upper surface of the thick plate. In this note, their exact solution will be applied to an electronic problem, namely, a chip on a substrate with finite thickness. Emphasis is placed on the generation of dimensionless charts for the temperature, displacement, and stress distributions in the substrates. These charts are not only useful for designing substrates but also can be used to verify finite element analysis procedures.
Low Cycle Fatigue of Sn96 Solder With Reference to Eutectic Solder and a High Pb Solder
Authors: Solomon H. D.
Published: April 2008

This paper describes the 35°C and 150°C low cycle fatigue behavior of Sn96 solder (96.5 Sn/3.5 AG), the tin silver eutectic. There is a considerable amount of anecdotal information which says that this solder is superior to eutectic solder in its fatigue resistance. This study generally supports this assertion, but not for all plastic strain ranges. This solder has an excellent balance of strength, ductility and fatigue life under strain cycling. Furthermore, it is also shown that this solder is superior to a high Pb solder (92.5 Pb/2.5 Ag/5.0 Sn). The only drawback of the tin silver eutectic is that it has a higher melting point than the melting point for the Sn/Pb eutectic (221°C versus 183°C), and this requires a higher soldering temperature. This higher temperature necessitates some process alterations in order to use this solder.
Asymptotic Expansions for the Thermal Stresses in Bonded Semi-Infinite Bimaterial Strips
Authors: Lee Mikyoung , Jasiuk I.
Published: April 2008

The plane elasticity problem of two semi-infinite bimaterial strips, that undergo constant temperature change, is considered. Following Bogy (1968), we use Airy stress function method, Mellin transform, and conformal mapping to investigate the asymptotic behavior of stresses at the interface near the edge of two strips.
A Creep/Relaxation Model Which Exhibits Chaotic Instability—Comparison With Solder Data
Authors: Russell S. J.
Published: April 2008

A mathematical model of creep/relaxation was developed which allows non steady-state behavior, incorporates a modification of the customary steady-state stress versus creep rate power law in order to account for higher rate instability (super-plasticity effect), and uses a discrete time step which is assumed to depend crucially on the grainy structure of solder. In simplest form, the model is transformed into a classic discrete logistic model of population dynamics whose chaotic instability has been extensively studied. A “chaos parameter” is identified which is shown to depend upon time step (grain size) and relaxation of load (dwell). Dynamic behavior of Sn63-Pb37 solder was studied in both bulk and joint forms at various initial loads and constant temperatures. The prediction of instability after dwell was confirmed in both forms. Since both depend upon grain size, dwell time, and relate to instability, a close relationship between the chaos parameter and solder fatigue is suggested.
Fatigue Properties of Microelectronics Solder Joints
Authors: Nir N. , Dudderar T. D. , Wong C. C. , Storm A. R.
Published: April 2008

Low cycle fatigue studies of solder joints designed and fabricated to represent generic interconnection structures typical of what might be used in packaging microelectronics have been carried out to assist in the development of a better understanding of the fundamental mechanical properties that determine the reliability of such structures. These studies involve micro scale joints (micro-joints) of both eutectic and 95/5 Pb/Sn solders fabricated by several different processes. In addition to a discussion of the results of recent tests reflecting specified loss-of-strength failure criteria and extensive post-test failure mode analysis of, primarily, 95/5 Pb/Sn micro-joints, descriptions of (1) the design and fabrication of the custom shear test vehicles and (2) the high-resolution electro-mechanical loading system used to apply cyclic loadings under isothermal conditions will be presented. This computer controlled system provides for the application of fully or partially reversed shear strains (with or without dwells) to either prototypes or custom test vehicles, and can be operated to maintain either total or plastic strain control during cycling.
The "Smeared" Property Technique for the FE Vibration Analysis of
Printed Circuit Cards
Authors: Pitarresi J. M. , Caletka D. V. , Caldwell R. , Smith D. E.
Published: April 2008

The primary objective of this paper is to investigate the accuracy of the finite element (FE) smeared properties approach for the determination of the mode shapes and frequencies of a printed wiring board (PWB) populated with electronic modules. Smearing of the material and/or structural properties is a recognized means of reducing a complicated structure to a less complicated approximation. Comparisons of both the natural frequencies and mode shapes are made between the smeared FE model and those obtained from vibration testing. The extent of correlation between the mode shapes is characterized by the modal assurance criterion (MAC). Since the intent of this study is to examine the effectiveness of the smearing technique, free boundary conditions are assumed. It is shown that the smearing technique can produce good correlation of both natural frequencies and mode shapes of PWBs populated with modules. A case study of a PWB with both surface mount technology (SMT) and pin-in-hole (PIH) components is presented.
Reliability Monitoring in Drilling Electronic Circuit
Boards
Authors: Hocheng H. , Jiaa C. L.
Published: April 2008

The purpose of the current study is to provide a monitoring scheme for evaluating the reliability of drilling of electronic circuit board (ECB) made of FR4 composite materials. The ECB is a laminated mechanical structure. Delamination often occurs at the hole exit during drilling. The resulted delamination deteriorates the long-term performance of the ECB when subject to mechanical and/or thermal loading. Acoustic emission can monitor the extent of this damage. A linear relationship exists between the size of delamination and the energy level of emitted signal when the proposed signal processing technique is used. The results contribute to higher quality ECB’s and can be applied in the manufacturing stage in an automated manner.
Temperature Dependence of the Mechanical Properties of GaAs Wafers
Authors: Hu Jun Ming , Pecht Michael
Published: April 2008

GaAs is known to have superior electronic properties and greater photovoltaic conversion efficiency compared to elemental semiconductors such as silicon and germaniumn. Mechanical properties of GaAs at different temperatures are now necessary to incorporate into the design models for the GaAs die attach and substrate architecture for microelectronic packages. These properties are also required to aid in defining reliability and screening specifications. This paper presents the experiment results on various material properties of GaAs wafer over the temperature range of − 75°C to 200°C. Material properties determined from testing include the modulus of elasticity, the modulus of rupture, the critical value of stress intensity factor, and the coefficient of thermal expansion. The importance of fracture assessment in semiconductor devices is also discussed.
Quasi-Static Modeling of the Self-Alignment Mechanism in Flip-Chip Soldering—Part I: Single Solder Joint
Authors: Patra S. K. , Lee Y. C.
Published: April 2008

A three-dimensional mathematical model simulating the self-alignment mechanism in the flip-chip soldering of a single joint has been developed. Based on the principle of energy minimization, it calculates the quasi-static surface profiles defined by the size of the solder pads, the solder volume, the surface tension coefficient, the vertical loading and the misalignment. The model is capable of calculating initial, intermediate and final profiles and their associated restoring forces during the solder reflow. It can provide the guidelines to improve the assembly yield and the stress-related reliability of the flip-chip soldering technology.
Development of Hermetic Microminiature Connectors
Authors: Neilsen M. K. , Andrews L. A. , Monroe S. L. , McCollister H. L.
Published: April 2008

Miniaturization of hermetic packages has provided the incentive to develop a new family of hermetic microminiature connectors. Microminiature connectors, with a pin spacing of 1.27 mm, have previously been available only in the nonhermetic form. New microminiature connectors with compression seal materials, 304 Stainless Steel housings, Alloy 52 pins, and TM-9 Glass insulators, were examined because compression seals are currently used in larger hermetic connectors and are typically designed to create a residual compressive stress state in the insulator during manufacturing. The new microminiature connectors with compression seals were evaluated analytically with two and three-dimensional finite element models and experimentally by fabrication of prototype connectors. The finite element analyses predicted the development of undesirable tensile stress in the insulator during manufacture and identified the mechanism responsible for the generation of tensile stress in the glass. The experimental investigation confirmed the existence of undesirable tensile stress in the glass with the observation of crack development during manufacture. Since the design requirements would not allow the geometric modifications needed to manufacture crack-free connectors with compression seals, insulator materials that generate a matched seal with 304 Stainless Steel housing were developed. Connectors with these matched seals were successfully manufactured.
A Note on the Determination of the Thermal Stresses in Multi-Metal Beams Subjected to Temperature Variations
Authors: Cifuentes A. O.
Published: April 2008

This technical note shows that the determination of the stresses induced in multi-metal beams by temperature changes reduces to solving a linear system of equations. This system of equations has a very particular structure that allows one to obtain a closed form solution easily.
An Experimental Investigation of Deformation of Plated Holes for a Single 30-210-30°C Thermal Cycle
Authors: Gross T. S. , Perault J. A. , Watt D. W.
Published: April 2008

The out-of-plane displacement field around two plated holes with different pad diameters in an FR-4 printed wiring board was measured for a single 30°C–210°C–30°C temperature cycle using electro-optic holographic interferometry. At the end of the temperature cycle, the outside edge of the pad was raised above the level of the laminate and the inside edge was depressed below the level of the laminate. This indicates that the barrel is plastically deformed in compression to a total strain of approximately 0.58–0.66 percent which is well above typical yield strains of 0.2 percent. The smaller diameter pad was inclined more than the large diameter pad, but the residual compressive strain in the barrel was roughly the same. Both the residual compressive strain and the inward inclination of the pad are in conflict with the predictions of most finite element models of plated hole deformation. However, there were cracks at the pad-barrel interface which are not included in finite element models. The residual compressive deformation of the barrel is attributed to inelastic deformation of the FR-4 matrix at the high end of the thermal cycle. The stress in the barrel was estimated using an approximate elastic analysis of pad deflections. The estimated stress for different hole diameters for the same pad diameter was roughly proportional to the ratio of their barrel plating cross-sectional areas for a 30–150°C temperature change. The elastic analysis is shown to predict (unrealistic) tensile barrel stresses at the end of the full temperature cycle.
A Numerical Lead Frame Compliance and Stress Model
Authors: Goldmann Lewis S.
Published: April 2008

A new method is presented to compute the mechanical compliance and thermal stress in surface mount leads of arbitrary shape. It involves expressing the profile polynomially by a computer-generated spline curve, and numerically integrating the generalized Castigliano formulas. Comparisons to data in the literature, generated by standard analytical and experimental techniques, show excellent agreement. An example is presented to show typical results obtainable by using the model.
Modeling Complex Inelastic Deformation Processes in IC Packages’ Solder Joints
Authors: Busso E. P. , Kitano M. , Kumazawa T.
Published: April 2008

Large scale three-dimensional finite element analyses of 68 and 44 pin types Quad Flat I-Leaded packages subjected to −55°C to 150°C temperature cycling are performed to predict the way in which inelastic strains and microstructure evolve in the solder joints. A new set of unified constitutive equations, which correctly accounts for the inelastic strain rate dependency on stress, temperature, and microstructure (internal stresses) and the evolution of the latter with deformation, was used to model the solder joints’ thermo-mechanical behavior. Estimates of the critical inelastic strain ranges in the solder joints were obtained from the calculated inelastic deformation histories. The range of inelastic strain associated with each thermal cycle is small and practically unaffected by the observed ratcheting of the cycles toward positive strains due to the non-zero mean cycle stresses. By combining the numerical results with fatigue life data obtained from leads subjected to the same thermal loading, a fatigue life relation for mean failure probability of the IC packages’ solder joints has been proposed. The analysis correctly predicts the critical locations for crack initiation.
Investigation of Thermomechanical Properties of Low Temperature Cofired Ceramic
Authors: Hu J. M. , Barker D. , Ghoshtagore R. , Pecht M.
Published: April 2008

Thermomechanical properties of low temperature cofired ceramic substrates in the range of operational temperatures are necessary to incorporate into the design models for multichip modules and other electronic packages. These properties are also required in assessing reliability and aiding in screening and qualification procedures. This paper presents the test methods and experimental results on various thermomechanical properties of low temperature cofired ceramic over the the temperature range of −55°C to +250°C. Material properties determined from the tests include the modulus of elasticity, the modulus of rupture, the fracture toughness, and the coefficient of thermal expansion.
Influence of Surface Mount Lead End Geometry on Fatigue Life
Authors: Gupta Vineet K. , Barker Donald B.
Published: April 2008

The local coefficient of thermal expansion (CTE) mismatch between compliant surface mount component leads and the solder that is used to attach the components to a printed wiring board can dramatically influence the thermal fatigue life of the solder joint. To quantify the contribution of the local CTE mismatch to the overall thermal fatigue damage of the solder joint, a finite element thermal fatigue simulation using an energy partitioning technique is used to compare four different lead end shapes. The four lead configurations considered are J-lead, and three gullwings leads; one with the foot parallel to the board surface, one with the foot sloped slightly downward towards the board, and one with the foot sloped slightly upward. The dimensions of the leads are purposely chosen so that the in-plane compliance is equal for the different lead shapes, only the shape of the lead end varied. Comparisons are first made with equal solder joint heights and then the solder height of the gull-wing lead is varied between 0.05 to 0.23 mm (2 to 9 mils). The influence of the solder wetting angle is also investigated.
A Fractional-Factorial Numerical Technique for Stress Analysis of Glass-To-Metal Lead Seals
Authors: Mathieu Barry , Dasgupta Abhijit
Published: April 2008

Fracture of glass seals in metallic hermetic electronic packaging is a significant failure mode because it may lead to moisture ingress and also to loss of load carrying capacity of the glass seal. Seal glasses are intrinsically brittle and their fracture is governed by the stresses generated. This study investigates stresses in lead seals caused by handling, testing, mechanical vibration, and thermal excursions. Loads considered are axial tension, bending, and twisting of the lead. More general loading can be handled by superposition of these results. Factorial techniques, commonly used in multi-variable Design of Experiments (DoE), are used in conjunction with finite element parametric simulations, to formulate closed-form regression models which relate the maximum principal stress within the glass seal to the type of loading and geometry. The accuracy of the proposed closed-form equations are verified through analysis of residuals. The analysis reveals the sensitivity of the magnitude of the seal stress to design variables such as the materials and geometry of the seal, lead, and package. Manufacturing-induced problems such as defects and flaws are not considered. An additional purpose for presenting this study is to illustrate the use of design of experiment methods for developing closed-form models and design guidelines from simulation studies, in a multi-variable problem.
Failure Analysis of No-Clean and Water-Clean Solder Joints 0.4 mm Pitch, 256-Pin Plastic Quad Flat Pack
Authors: Govila R. K. , Pao Y.-H. , Larner C. , Lau J. , Twerefour S. , Erasmus S. , Dolot S.
Published: April 2008

Printed circuit boards populated with twenty-five 0.4 mm pitch, 256-pin plastic quad flat packs (QFP) containing no-clean and water-clean solder joints were subjected to thermal cycling in order to induce thermal fatigue failure. QFPs failed from a minimum of 0.27 cycle to a maximum of 5310 cycles. Solder joints in both types of units were examined in the scanning electron microscope, and a relative comparison of the extent of fatigue damage is presented. The failure associated with cracking in the eutectic composition Sn/Pb solder initiated at the stress concentration sites. Crack propagation continued either along the pin-solder interface or solder-pad interface and ultimately resulted in the separation of the pin/pad junctions. In addition, a qualitative and quantitative comparison of the resulting solder micro-structure and the failure mode between the no-clean and the water-clean QFP solder joints was made and discussed.
Effects of Substrate Conductivity on Convective Cooling of Electronic Components
Authors: Choi C. Y. , Kim S. J. , Ortega A.
Published: April 2008

The coupled conduction and forced convection transport from substrate-mounted modules in a channel is numerically investigated to identify the effects of the substrate conductivity. The results presented apply to air and two-dimensional laminar flow conditions. It was found that recirculating cells as well as streamwise conduction through the substrate play an important role in predicting convective heat transfer from the printed circuit board (PCB) and modules and in determining the temperature distributions in the PCB, modules, and fluid. The dimensionless temperature and the local Nusselt number along the interface between the fluid and the module or PCB are rather complicated, and therefore, predetermined simple boundary conditions along the solid surface may be inappropriate in many conjugate heat transfer problems. In general, the results show that the maximum temperature within heat sources can be greatly reduced by increasing the conductivity of the PCB. The effectiveness of the use of highly conductive materials for PCB, however, depends on the distance between the heat generating modules on the PCB. In addition, finite thermal resistance between the module and the PCB would serve to diminish the PCB conduction effects, thereby reducing the effectiveness of the enhancement afforded by increased conductivity.
A Multi-Kilowatt Immersion-Cooled Standard Electronic Clamshell Module for Future Aircraft Avionics
Authors: Jimenez Peter E. , Mudawar Issam
Published: April 2008

A new type of immersion cooled module, the BTPFL-C2, was developed for thermal management of future high flux avionics while conforming to the geometrical constraints of existing military modules and avionic enclosures. The BTPFL-C2 houses two circuit boards separated by a flow distribution plate and employs two sleeveless quick connection coolant couplers. The flow distribution plate supplies the coolant inside the module into parallel narrow channels formed between the distribution plate and the surfaces of the chips. Theoretical predictions of the thermal performance of the BTPFL-C2 were substantiated by experimental data using a test module populated with ten chips. Increasing the coolant subcooling at the module inlet was found to decrease pressure drop across the module, decrease the coolant flow rate requirements, and extend the upper cooling limit of the BTPFL-C2. These results reveal the BTPFL-C2 is capable of dissipating an order of magnitude more heat than today’s most advanced avionic module. At an inlet subcooling of 40.3°C, the BTPFL-C2 could dissipate over 3000 W using only about 0.051 kg/s (0.50 gpm) of Fluorinert FC-72 and a pressure drop of only 2.8 kPa (0.41 psi).
Transient Phenomena in Compressor Stations During Surge
Authors: Botros K. K.
Published: April 2008

Transient phenomena are generally inherent in the operation of compressor stations: These are either fast or slow transients. A model describing the governing equation for the gas dynamics, control system, compressor and turbine shaft inertias has been developed. The effect of these inertias is manifested by an example of a compressor station operating near the surge control line. Another example deals with a station that has a cooler placed in the recycle path. This alters the rate at which the compressor shaft decelerates upon shutdown and may cause backward spinning depending on the relative magnitude of the shaft inertia with respect to the cooler volume. Backward spinning of compressor shaft has detrimental effects on dry seals and is undesirable. It was found that by keeping the recycle valve closed upon shutdown, the rate of shaft deceleration will be reduced.
Compressor Fault Identification From Overall Performance Data Based on Adaptive Stage Stacking
Authors: Mathioudakis K. , Stamatis A.
Published: April 2008

In the present paper a method for the identification of faulty stages in a multistage compressor is presented. The values of overall compressor parameters, namely mass flow rate, pressure ratio, and efficiency, at different operating points are the input data to the method. Employing these data, the method gives the location and the number of faulty stages, as well as the amount of deviation from intact condition performance. It is shown that the kind of fault that has caused stage performance deterioration can be identified. Features of the method, such as generality of applicability, input data requirement, and reliability of the findings, are discussed.
First- and Second-Law Analysis of Steam-Turbine Cogeneration Systems
Authors: Habib M. A.
Published: April 2008

The paper presents an analysis of a cogeneration plant. The performance of the plant is compared to a conventional plant with separate production of process heat and power. The analysis is first- and second-law based and, therefore, quantifies the irreversibilities of the different components of each plant. In the cogeneration plant, the heat required in the boiler can be obtained either from fuel firing (condensing or back-pressure turbine plant) or from exhaust gases of a simple gas turbine (gas turbine cogeneration plant). The present study compares the two methods. The influence of the heat-to-power ratio and the process pressure on the thermal efficiency, utilization factor, and irreversibilities of the different components of each plant is presented. The results show that the total irreversibility of the cogeneration plant is lower by 38 percent compared to the conventional plant. This reduction in the irreversibility is accompanied by an increase in the thermal efficiency and utilization factor by 25 and 24 percent, respectively. The results show that most irreversible losses are due to boiler.
An Infrared Pyrometry System for Monitoring Gas Turbine Blades: Development of a Computer Model and Experimental Results
Authors: de Lucia M. , Lanfranchi C.
Published: April 2008

This work describes the development of a computer modeling system for infrared pyrometry measurement of gas turbine blade temperature. The model accurately evaluates apparent target emissivity and temperature on the basis of the radiation heat fluxes exchanged at steady-state conditions. Experimental testing conducted on gas turbine models in a controlled-temperature furnace has shown that the reliability of the target emissivity prediction effectively reduces one of the major causes of error in infrared pyrometry.