bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolutionary effects of alternative artificial propagation programs: implications for viability of endangered anadromous salmonids
Authors: McClure Michelle M. , Utter Fred M. , Baldwin Casey , Carmichael Richard W. , Hassemer Peter F. , Howell Philip J. , Spruell Paul , Cooney Thomas D. , Schaller Howard A. , Petrosky Charles E.
Published: April 2008

Most hatchery programs for anadromous salmonids have been initiated to increase the numbers of fish for harvest, to mitigate for habitat losses, or to increase abundance in populations at low abundance. However, the manner in which these programs are implemented can have significant impacts on the evolutionary trajectory and long‐term viability of populations. In this paper, we review the potential benefits and risks of hatchery programs relative to the conservation of species listed under the US Endangered Species Act. To illustrate, we present the range of potential effects within a population as well as among populations of Chinook salmon (Oncorhynchus tshawytscha) where changes to major hatchery programs are being considered. We apply evolutionary considerations emerging from these examples to suggest broader principles for hatchery uses that are consistent with conservation goals. We conclude that because of the evolutionary risks posed by artificial propagation programs, they should not be viewed as a substitute for addressing other limiting factors that prevent achieving viability. At the population level, artificial propagation programs that are implemented as a short‐term approach to avoid imminent extinction are more likely to achieve long‐term population viability than approaches that rely on long‐term supplementation. In addition, artificial propagation programs can have out‐of‐population impacts that should be considered in conservation planning.
Development of eight polymorphic microsatellites for a Zn/Cd hyperaccumulator Sedum alfredii Hance (Crassulaceae)
Authors: HUANG HUI‐RUN , SHU WEN‐SHENG , MAO ZHI‐BIN , GE XUE‐JUN
Published: April 2008

Sedum alfredii is a Zn/Cd hyperaccumulator distributed in East Asia. A total of eight polymorphic microsatellite markers were developed. These loci were screened in 25 individuals from one heavy metal‐tolerant population and one nontolerant population, respectively. The average allele number of these markers was 5.25 per locus, ranging from two to nine. Population‐specific alleles were found at each locus. The observed and expected heterozygosities ranged from 0.000 to 0.640 and from 0.451 to 0.819. Significant deviation from Hardy–Weinberg equilibrium was detected at both the species and the population level. No significant linkage disequilibrium was detected at population level.
Isolation and characterization of microsatellite loci in Pimelodus maculatus (Siluriformes: Pimelodidae)
Authors: PAIVA ANA LUIZA B. , KALAPOTHAKIS EVANGUEDES
Published: April 2008

To evaluate genetic variability in Pimelodus maculatus, a small migratory catfish common in South America, we isolated and characterized several microsatellite markers from individuals collected from a population in the River Grande (Brazil). A total of 11 loci were obtained and analyzed. All the loci were polymorphic, with the number of alleles ranging from three to 27 per locus. Observed and expected heterozygosities ranged from 0.5 to 0.89 and from 0.53 to 0.95, respectively. These polymorphic markers can be used as effective tools to study the genetic structure in populations of this species.
PPAR γ regulates MITF and β‐catenin expression and promotes a differentiated phenotype in mouse melanoma S91
Authors: Grabacka Maja , Placha Wojciech , Urbanska Krystyna , Laidler Piotr , Płonka Przemysław M. , Reiss Krzysztof
Published: April 2008

Melanoma represents one of the most rapidly metastasizing, hence deadly tumors due to its high proliferation rate and invasiveness, characteristics of undifferentiated embryonic tissues. Given the absence of effective therapy for metastatic melanoma, understanding more fully the molecular mechanisms underlying melanocyte differentiation may provide opportunities for novel therapeutic intervention. Here we show that in mouse melanoma S91 cells activation of the peroxisome proliferator activated receptor (PPAR) γ induces events resembling differentiation, such as growth arrest accompanied by apoptosis, spindle morphology and enhanced tyrosinase expression. These events are preceded by an initial transient increase in expression from the Microphthalmia‐associated transcription factor gene, (MITF) promoter, whereas exposure to a PPAR γ ligand‐ ciglitazone that exceeds 8 h, causes a gradual decrease of MITF, until by 48 h MITF expression is substantially reduced. Beta‐catenin, an MITF transcriptional activator, shows a similar pattern of decline during ciglitazone treatment, consistent with previous reports that activated PPAR γ inhibits the Wnt/β‐catenin pathway through induction of β‐catenin proteasomal degradation. We suggest that the PPAR γ‐mediated β‐catenin down‐regulation is likely to be responsible for changes in MITF levels. The data suggest that PPAR γ, besides its well‐established role in mesenchymal cell differentiation towards adipocytes, might regulate differentiation in the melanocytic lineage.
TBX3 and its splice variant TBX3 + exon 2a are functionally similar
Authors: Hoogaars Willem M.H. , Barnett Phil , Rodriguez Mercedes , Clout Danielle E. , Moorman Antoon F.M. , Goding Colin R. , Christoffels Vincent M.
Published: April 2008

Tbx3, a member of the conserved family of T‐box developmental transcription factors, is a transcriptional repressor required during cardiogenesis for the formation and specification of the sinoatrial node, the pacemaker of the heart. Both the TBX3 and the highly related TBX2 genes are also associated with several cancers, most likely as a consequence of their powerful anti‐senescence properties mediated via suppression p14Arf and p21CIP expression. In melanoma, the TBX2 gene is frequently amplified and inhibition of Tbx2 function leads to senescence and up‐regulation of p21CIP, a Tbx2 target gene. Tbx3 + 2a is a splice variant containing an extra 20 amino acids encoded by exon 2a inserted into the highly conserved T‐box DNA‐binding domain. We find here that Tbx3 + 2a is evolutionary conserved and that similar insertions are largely absent from the T‐box domains of other T‐box factors. Tbx3 + 2a has been reported to lack DNA‐binding ability and act as a functional antagonist of Tbx3. By contrast, we now demonstrate that both Tbx3 and Tbx3 + 2a bind the consensus T‐element, the p21CIP1 promoter, and the Nppa cardiac target gene. Both isoforms also function as repressors of p21CIP1 and Nppa promoter activity and interact with homeobox factor Nkx2‐5. When ectopically expressed in the embryonic heart of mice, Tbx3 and Tbx3 + 2a both suppressed chamber formation and repressed expression of cardiac chamber markers Nppa and Cx40. The results suggest that in the assays used, Tbx3 and Tbx3 + 2a are functionally equivalent and that like Tbx2, Tbx3 may also function as an anti‐senescence factor in melanoma.
Role of nodal signaling and the microenvironment underlying melanoma plasticity
Authors: Postovit Lynne‐Marie , Margaryan Naira V. , Seftor Elisabeth A. , Hendrix Mary J. C.
Published: April 2008

The incidence of melanoma has increased dramatically over the last 50 yr, and although melanoma accounts for only 10% of all skin cancers, it is responsible for over 80% of skin cancer deaths. Recent studies have uncovered critical molecular events underlying melanocytic transformation and melanomagenesis. Among these noteworthy observations are the acquisition of stem cell‐associated proteins, such as the Notch receptors and Nodal, which have also been implicated in melanoma progression. For example, we have demonstrated that Nodal expression is limited to invasive vertical growth phase and metastatic melanoma lesions, and that inhibition of Nodal signaling promotes the reversion of metastatic melanoma cells toward a more differentiated, less invasive non‐tumorigenic phenotype. In addition, molecular cross‐talk exists between the Notch and Nodal signaling pathways. Interestingly, the acquisition of stem cell‐associated plasticity is often acquired via epigenetic mechanisms, and is therefore receptive to reprogramming in response to embryonic microenvironments. Here, we review the concept of melanoma plasticity, with an emphasis on the emerging role of Nodal as a regulator of melanoma tumorigenesis and progression, and present findings related to epigenetic reprogramming.
Thermomechanical Behavior of Multilayer Structures in Microelectronics
Authors: Daniel I. M. , Wang T.-M. , Gotro J. T.
Published: April 2008

Linear thermoelastic lamination theory was used to determine the state of residual stresses and warpage in multilayer structures following elevated temperature curing. The inputs necessary are the mechanical and thermal properties of each layer, the stacking sequence of layers, and the irreversible chemical deformation taking place during curing of the polymeric matrix layers. The predictions were verified experimentally with a woven-glass/epoxy material. The basic mechanical and thermal properties and polymerization shrinkage were determined for the unidirectional layer. Subsequently, the warpage was measured for a [06/906] antisymmetric cross-ply laminate by means of the shadow moire´ method. Experimental results were in good agreement with the theoretical prediction.
Realistic Modeling of Edge Effect Stresses in Bimaterial Elements
Authors: Eischen J. W. , Chung C. , Kim J. H.
Published: April 2008

A classic paper by Timoshenko in 1925 dealt with thermal stresses in bimetal thermostats and has been widely used for designing laminated structures, and in contemporary studies of stresses in electronic devices. Timoshenko’s analysis, which is based on strength of materials theory, is unable to predict the distribution of the interfacial shear and normal stresses known to exist based on more sophisticated analyses involving the theory of elasticity (Bogy (1970) and Hess (1969)). Suhir (1986) has recently provided a very insightful approximate method whereby these interfacial stresses are estimated by simple closed-form formulas. The purpose of the present paper is to compare three independent methods of predicting the interfacial normal and shear stresses in bimaterial strips subjected to thermal loading. These are: 1.) Theory of elasticity via an eigenfunction expansion approach proposed by Hess, 2.) Extended strength of materials theory proposed by Suhir, 3.) Finite element stress analysis. Two material configurations which figure prominently in the electronics area have been studied. These are the molydeneum/aluminum and aluminum/silicon material systems. It has been discovered that when the two layers are nearly the same thickness, the approximate methods adequately predict the peak values of the interfacial stresses but err in a fundamental manner in the prediction of the distribution of stress. This may not be of concern to designers who are interested mainly in maximum stress alone. However, it has been shown that if one layer is relatively thin compared to the other, the approximate methods have difficulty in predicting both the peak value of stress and its associated distribution.
Modeling Thermal Stress Behavior in Microelectronic Components
Authors: Scott G. C. , Astfalk G.
Published: April 2008

Thermal stress cracking is a significant mechanical failure mode in microelectronic components. This failure results from elevated stresses in components exposed to elevated temperatures due to the mismatch of thermal and mechanical properties of the constituent materials. The underlying mechanism responsible for these elevated stresses is not well understood. Therefore, we developed general mathematical and computational techniques for modeling the evolution of these stresses. As a test vehicle, we applied these techniques to thermal stress evolution in multilayer ceramic capacitors (MLCC). Thermal stress cracking has been implicated in significant, industry-wide problems associated with the cracking of these components. The model is used to solve for the transient development of thermal and mechanical gradients across the two spatial dimensions of the MLCC mid-plane. Material types with different thermal and mechanical properties and the interfaces between the material types are specifically included in the model. The stress field solutions are used to indicate when and where mechanical failure is expected to occur. The solutions of the model equations have been obtained using special partial differential equation solvers implemented on a CONVEX C120/220 supercomputer. The model is used to investigate the effects of MLCC termination geometry and material properties on the evolution of thermal stresses.
Elasticity Analysis to Aid in Extracting Thin Film Elastic Moduli From Continuous Indentation Data
Authors: Stone D. S.
Published: April 2008

This article provides elasticity solutions to the indentation of a bilayer by three-sided and four-sided indentors. These solutions aid characterization of thin film elastic moduli through continuous indentation techniques. The solutions are expressed in closed-form, and can be numerically evaluated on a small computer; additionally, graphs of some of the solutions are provided to aid in rapid data analysis. Simulations of unloading compliance, C, versus 1/A1/2 (A = projected area of indent) are compared with experimental data. The data are taken from measurements of single crystal Si, polycrystalline Al, and 1 μm Al deposited on Si. The elasticity analysis is used in the measurement of the elastic modulus of a sodium borosilicate glass, and the same glass but with a damaged surface layer introduced by suspension in an acid solution.
Prediction of Surface Temperature and Heat Flux of a Microelectronic Chip With Jet Impingement Cooling
Authors: Wang X. S. , Dagan Z. , Jiji L. M.
Published: April 2008

In this paper, a previously developed analytic solution is applied to the conjugate heat transfer problem of jet impingement cooling of a microelectronic chip. The analysis is used to predict the surface temperature and heat flux distributions of a chip cooled by a laminar impinging FC-77 liquid or water jet with uniform heat flux dissipation at the heated bottom of the chip. Results are presented for two jet diameters of 0.5 and 1 mm. It is shown that, for a constant Reynolds number, the surface temperature is lower when the jet diameter is smaller. On the other hand, when the jet diameter is increased, the surface temperature and heat flux distributions are more uniform. Water jet impingement cooling shows much lower surface temperature and much higher heat transfer coefficient than FC-77 jet cooling. The thermal resistance for FC-77 liquid jet is 6 times larger than that for a water jet.
How Long Should Be a Beam Specimen in Bending Tests?
Authors: Suhir E.
Published: April 2008

We assess the effect of shear on the deflections of beam specimens in three-point and four-point bending tests. The analysis is based on an analytical stress model using energy considerations. Numerical examples are carried out for polymeric specimens and for glass gel specimens. It is concluded that shear may not be considered in three-point bending tests if the length-to-height (or the length-to-diameter) ratio is greater than, say, 12. In the case of four-point bending it is also important that the distance between the external forces applied in the beam’s span be significantly smaller than the specimen’s length. It is recommended that this distance does not exceed half the specimen’s length.
The Creep-Fatigue Interaction in Solders and Solder Joints
Authors: Stone D. S.
Published: April 2008

Two models are proposed for relating the metallurgy of the solder to the growth of fatigue cracks through solder joints. These models illustrate how different aspects of the creep behavior can contribute to the so-called “creep-fatigue interaction”. The first model treats fatigue crack growth through the solder, far from the interface between solder and substrate. Either an intragranular or intergranular path may be taken depending upon conditions of loading. Intragranular fatigue dominates when the cycle frequency is high, in which case failure life is governed by the Coffin-Manson law. Intergranular failure occurs at low frequencies because grain boundary sliding at low frequencies allows the grain boundaries to become exposed to the atmosphere, which in turn causes oxidation. This model predicts the effects of frequency, strain amplitude, and grain size on fatigue life. In the second model, the fatigue crack travels within the interface region between solder and substrate. Here, the strain introduced in the solder joint during fatigue is not relevant; instead, the stress transferred to the interface is more important. The second model considers the effect of solid solution concentration on fatigue life. The predictions of both models agree reasonably well with published fatigue data from solders and solder joints.
A Mechanistic Model for Solder Joint Failure Prediction Under Thermal Cycling
Authors: Wong Boon , Helling D. E.
Published: April 2008

A mechanistic model for eutectic Pb/Sn solder life predictions has been developed and applied to leadless surface mount solder joints. This model can quantitatively describe both crack initiation and crack propagation processes in the solder. There are four parts to this model: a crack initiation model, a crack propagation model [1], a microstructural coarsening model and an analysis of the deformation in the solder during thermal cycling. By merging these models together, it is possible to predict the time to crack initiation and the time to failure of these solder joints. Solder joint life predictions show good agreement with data obtained on thermally cycled surface mount leadless chip resistors.
Isothermal Fatigue of 63Sn-37Pb Solder
Authors: Cutiongco E. C. , Vaynman S. , Fine M. E. , Jeannotte D. A.
Published: April 2008

The effects of aging, strain range, hold time at maximum strain and temperature on the isothermal fatigue life of bulk 63Sn-37Pn solder samples over the total strain range (Δ εT) from 0.3 to 3.0 percent (tension-tension) and within the temperature range of 25° C to 100° C were studied. The cycles to failure (Nf) were defined as the number of cycles at which the ratio of the maximum tensile stress to the maximum compressive stress starts to drop appreciably. Fatigue life increases rapidly after a day or two of aging after heat treatment at 150° C for 2 hours followed by air cooling but levels off after a week. The log of fatigue life decreases linearly with increasing log of plastic strain range above Δ εT = 0.6 percent. Hold time at maximum strain dramatically decreases the cycles to failure, however, an increase of hold time more than a few minutes eventually leads to a constant Nf. Temperature variation from 25°C to 100° C was found to have little effect on the fatigue life of the solder in tests with and without hold time. Separation of Pb-rich and Sn-rich phases and cracking of the Sn-rich phases are the main modes of fracture under all conditions used. Damage is concentrated along crisscrossing shear bands oriented approximately 45 deg to the load direction.
Assembly Stiffness and Failure Criterion Considerations in Solder Joint Fatigue
Authors: Wilcox J. R. , Subrahmanyan R. , Li Che-Yu
Published: April 2008

The ramifications of the definition of failure on solder joint fatigue life are discussed in terms of two considerations: (1) the dependence of the measured damage parameter (load drop or resistance increase) on the solder joint area and (2) the time profile of solder joint area. The latter is influenced by the applied displacement profile, the assembly stiffness, the deformation properties of the solder joint, and the dependence of rate of fatigue damage accumulation on its driving force. Experimental data are presented to illustrate the influence of these considerations on failure criterion. An integral methodology is used for the description of damage accumulation. Representative simulations are performed that demonstrate failure criterion effects on apparent fatigue life. Isothermal mechanical displacement controlled cyclic loading is emphasized. The principles presented may also be applied to thermal cycling of solder interconnects.
Analysis of Parameters Influencing Stresses in the Solder Joints of Leadless Chip Capacitors
Authors: Shah M. K.
Published: April 2008

The purpose of this study was to evaluate parameters such as solder joint standoff and fillet heights, termination cap length, chip eccentricity, chip rotation, etc. that influence stresses in the solder joints as well as the leadless chip capacitors. This analysis covers COG and X7R ceramic chip capacitors on multi-layer FR-4, and G-30 PWB or Alumina substrates. From the values of the stresses computed, it appears that (i) the stand-off height should be at least 100μm (.004 in.) (ii) the solder fillet height should be around half the chip thickness, (iii) the chip eccentricity on the mounting pad should be restricted to 8 percent of the chip length and (iv) chip rotation should be within 3.5 deg, while maintaining minimum solder stand-off height of 100μm (0.004 in.). The recommendations given here should be used only as preliminary design guidelines and not as a substitute for design and analysis or the requirements of manufacturing standards.
Isothermal Fatigue Behavior of Sn-Pb Solder Joints
Authors: Summers T. S. E. , Morris J. W.
Published: April 2008

Isothermal fatigue data were collected for the compositions 5Sn-95Pb, 20Sn-80Pb, 40Sn-60Pb, 50Sn-50Pb and 63Sn-37Pb within the binary Sn-Pb system. All of these compositions are commercially available and include those most commonly used. Because Sn-rich solders are rarely used, they were not investigated here. The fatigue life was defined by a 30 percent load drop. The solders were tested in a double shear configuration joined to copper at 75° C. The displacement rate chosen was 0.01 mm/min, which corresponds to a strain rate of 1.5 × 10−4s−1 for our specimen configuration, over a 10 percent plastic strain range. Additionally, the microstructural changes during fatigue are presented. The various solder compositions studied exhibit strikingly different as-solidified microstructures. These differences are discussed in terms of their effect on the isothermal joint failure mechanism and joint isothermal fatigue life.
Analysis of Insertion Force in Elastic/Plastic Mating
Authors: Yamada S. E. , Ueno H.
Published: April 2008

A simulation of an insertion of a solid pin into a slot between two opposing compliant beams is attempted. As a particular feature, the elastic-plastic deformation of the slot during the insertion is incorporated, as such a situation often occurs in electronic system interconnection. Each instance of the insertion process is considered as a static equilibrium of the insertion force and the contact force (including the frictional force). The equilibrium position of the deflected beams and the pin can be obtained as the point satisfying the following two conditions: 1) at the contact point, the contact force direction is offset from the normal direction to the contact points by the friction angle and, 2) the present positions of the contact points (one on the beam and the other on the pin), and their tangent angles must coincide exactly with each other. The simulated insertion force and depth relation agrees well with the real measurement.
Enhancement of Critical Heat Flux From High Power Microelectronic Heat Sources in a Flow Channel
Authors: Mudawar Issam , Maddox Douglas E.
Published: April 2008

Several surface augmentation techniques were examined in an investigation of enhancement of critical heat flux (CHF) from a simulated electronic chip to a fluorocarbon (FC-72) liquid in a vertical channel. A parametric comparison of boiling performances is presented for a smooth surface and for surfaces with low-profile microgrooves, low-profile microstuds, and high-profile pin fins. Critical heat fluxes as high as 361 W/cm2 were achieved using a combination of moderate flow velocity, high subcooling and surface enhancement. A semiempirical model constructed previously for CHF from a smooth discrete heat source to saturated or subcooled liquid flow, was found successful in correlating CHF data for the three enhanced surfaces.
Effects of Heat Intensity, Size, and Position of the Components on Temperature Distribution Within an Electronic PCB Enclosure
Authors: Du Z.-G. , Bilgen E.
Published: April 2008

Natural convection heat transfer has been studied in a sealed small PCB enclosure of three heated components which are mounted on a PCB plate within a large console cooled by vented airflow. A two-dimensional laminar flow model is used with appropriate boundary conditions. Detailed influences of each parameter, such as intensity, size, and position of the heaters on temperature and flow distributions within the enclosure have been studied. The favorable component arrangements for various cases have been determined.
Mechanical Modeling of Multilayered Films on an Elastic Substrate—Part I: Analysis
Authors: Erdogan F. , Joseph P. F.
Published: April 2008

In this paper the basic residual stress problem for multilayered or multiple films on an elastic substrate is considered. The stresses may be caused by a homogeneous temperature variation or slow thermal cycling and by far field mechanical loading. The films are approximated by orthotropic membranes and the substrate is assumed to be an elastic continuum. The interfacial zone is modeled by either an ideal interface or a homogeneous shear layer. The primary interest in the paper is in examining stress concentrations or singularities near the film ends. For the two interface conditions considered, this is done by varying the film/substrate contact angle. Also studied are strain energy release rate for the propagation of an interfacial crack and the direction and the magnitude of the maximum cleavage stress for a possible crack initiation in the substrate. The basic modeling and analysis are considered in Part I. Part II of the paper is devoted to the presentation and discussion of the results.
Thermal Analysis of a Ceramic Package for Microelectronic Applications
Authors: Rajala H. , Renksizbulut M.
Published: April 2008

Thermal analysis of a ceramic microelectronic package has been performed for six configurations under prescribed free and forced convective conditions. The corresponding three-dimensional temperature fields, and thus, the complex heat flow patterns within the package have been determined. The predicted temperatures compare favorably with the experimental data obtained using a 44-lead quad package. It is observed that, in forced convection, there is no significant reduction in the junction temperatures when the package is mounted in the cavity-down configuration. In free convection, filling the cavity with helium also results in small reductions in temperatures. On the other hand, conditions existing at the back surface of the board have a fairly significant effect on the junction temperature. Although essentially negligible in the forced convection cases, thermal radiation accounts for about one-fifth of the total heat transfer from the package in the free convection cases.
The Thermal Capacity Effect Upon Transient Natural Convection in a Rectangular Cavity
Authors: Khalillolahi A. , Sammakia B.
Published: April 2008

Transient natural convection in a rectangular enclosure is analyzed using a finite difference scheme. The enclosure is adiabatic and filled with water. The buoyancy induced flow is generated by a flat vertical uniform flux surface that has a finite thermal capacity. The full two-dimensional equations representing conservation of mass, momentum, and energy are solved in their time-dependent form. The solution technique used is a modified finite difference procedure very similar to Simple Arbitrary Lagrangian Eulerian (SALE) technique. Two values of surface thermal capacity are investigated, each resulting in a different flow regime during the transient. At short times a simple one-dimensional conduction regime is found to occur. As the leading edge effects arrive at any downstream location the conduction regime is terminated and true convection effects set in. At intermediate times a different flow regime is detected, namely a steady two-dimensional regime that approaches the steady state similarity solution for a similarly heated surface immersed in an infinite fluid medium. Excellent agreement is found with previous analyses and measurements during the early and intermediate transients.
Natural Convection From a Column of Flush Heat Sources in a Vertical Channel in Water
Authors: Joshi Y. , Knight D. L.
Published: April 2008

Natural convection from a single column of eight in-line, rectangular heat sources flush mounted on one wall of a vertical channel immersed in water was examined. Input power to each heating element was varied from 0.2–2.0 W for channel spacings in the range of 1.5–15.0 mm, as well as with the shroud removed. Flow visualization in two mutually perpendicular vertical planes was carried out both with and without the shroud for each power level. Component temperature measurements were made using thermocouples embedded within the substrate. By suitably accounting for the increasing convected energy downstream, a single heat transfer correlation was obtained for all channel spacings larger than 3 mm. For smaller channel spacings, the component center temperatures increased substantially above the correlation. To investigate the effect of heater spacing, temperature measurements in the absence of shroud were also made with only selected components powered. As the spacing between successive heated components was increased to twice of the fully heated configuration, the upstream effects on component heat transfer become negligible. Further increase in spacing resulted in a weak enhancement in heat transfer downstream. Comparison of the present data with existing experimental studies and new computations revealed significant influence of the heater and substrate material thermal properties on the transport.
Parametric Investigation Into the Effects of Pressure, Subcooling, Surface Augmentation and Choice of Coolant on Pool Boiling in the Design of Cooling Systems for High-Power-Density Electronic Chips
Authors: Mudawar I. , Anderson T. M.
Published: April 2008

A high power electronic chip was simulated experimentally to investigate upper cooling capabilities using a variety of pool boiling enhancement techniques. Parametric effects of system pressure, subcooling, surface augmentation, and choice of coolant on boiling heat transfer from a vertical 12.7 × 12.7 mm2 flat surface were examined. The two fluorocarbon coolants tested, FC-72 and FC-87, resulted in similar boiling curves, but FC-87 significantly reduced chip surface temperature for a given heat flux. Increasing pressure enhanced boiling performance and critical heat flux slightly. However, the significant increase in chip temperature, and the practical problems associated with packaging electronic hardware in a pressurized environment precluded pressurization as a viable enhancement option. Subcooling was very effective in increasing critical heat flux and significantly reducing bubble size and growth of the bubble boundary layer on the chip surface. Surface augmentation was also effective in enhancing critical heat flux; however, some surface geometries promoted noticeable temperature excursion at incipience.
Double-Sided “Velcro-Type” Input/Output Contactor Interface Design: Mechanical Behavior of Elastic Contactors
Authors: Suhir E.
Published: April 2008

Mechanical behavior of the contactors in a double-sided “velcro-type” area array connection system is analyzed and discussed. Such a system can be utilized in electronic packaging as an effective high density input/output connector interface. We conclude that low-modulus high-strength metallized polyimides can be regarded as suitable materials for the application in question, while even the strongest metals turn out to be insufficiently flexible and strong to be considered as attractive candidates for super-high-density interconnections.
Forced Convection Air Cooling of Simulated Low Profile Electronic Components: Part 2—Heat Sink Effects
Authors: Lehmann G. L. , Pembroke J.
Published: April 2008

Forced convection air cooling of an array of low profile, card-mounted components has been investigated. A simulated array is attached to one wall of a low aspect ratio duct. This is the second half of a two-part study. In this second part the presence of a longitudinally finned heat sink is considered. The heat sink is a thermally passive “flow disturbance”. Laboratory measurements of the heat transfer rates downstream of the heat sink are reported and compared with the measured values which occur when no heat sinks are present. Data are presented for three heat sink geometries subject to variations in channel spacing and flow rate. In the flow range considered laminar, transitional and turbulent heat transfer behavior has been observed. The presence of a heat sink appears to “trip” the start of transition at lower Reynolds numbers than when no heat sinks are present. A Reynolds number based on component length provides a good correlation of the heat transfer behavior due to variations in flow rate and channel spacing. Heat transfer is most strongly effected by flow rate and position relative to the heat sink. Depending on the flow regime (laminar or turbulent) both relative enhancement and reductions in the component Nusselt number have been observed. The impact of introducing a heat sink is greatest for flow rates corresponding to transitional behavior.
Effect of Polarity on Heat Transfer in the Ball Formation Process
Authors: Huang L. J. , Jog M. A. , Cohen I. M. , Ayyaswamy P. S.
Published: April 2008

Ball formation is the first step in wire bonding of semiconductor chips to their lead frames. An electric discharge melts the wire and surface tension causes the melt to roll up into a ball; the ball is subsequently pressed onto the proper bond pad on the chip to make a ball bond. In the ball bonding process, the electrical discharge characteristics, the associated heat transport, and the wire material determine the nature of the ball formed. The discharge shows sensitivity to the polarity of the wire. Experiments with upscaled aluminum and copper wires in air at reduced pressure show that the heat transfer to the wire associated with the discharge is significantly greater when the wire is the anode than when the wire is the cathode. These experiments included temperature measurements in real time made by fine thermocouples implanted in upscaled wires. In aluminum the anode wire receives twice as much energy from the arc as the cathode wire. In copper the anode wire receives three times as much energy from the arc as the cathode. Our conclusions are also reinforced by metallographic examination of sectioned balls.
Study on the Laminar Mixed Convective Heat Transfer in Three-Dimensional Channel With a Thermal Source
Authors: Shaw Heiu-Jou , Chen Wen-Lih , Chen Cha’o-Kuang
Published: April 2008

In this paper, the mixed convective heat transfer phenomena in a three-dimensional channel with one heating-element is studied. A general-purpose computer program is developed to analyze the flow field and temperature distribution in the channel. In order to ensure the accuracy of result, numerical computation is performed by using the alternating direction implicit (A.D.I.) method based on the SIMPLER algorithm. This paper deals with fundamental heat transfer phenomena in “L.S.I.” package, which is used extensively in microelectronic equipment. The influences of Reynolds number and Grashof number on the Nusselt number of the heating-element are discussed. In order to make it easier for readers to understand the phenomena studied in this paper, three-dimensional streaklines and three-dimensional isothermal surfaces are presented.
Effect of Component Layout and Geometry on the Flow Distribution in Electronics Circuit Packs
Authors: Azar K. , Russell E. T.
Published: April 2008

An experimental investigation was conducted to study the impact of component layout and geometry on flow distribution on a circuit pack. The experiment was conducted in a water tunnel using aluminum blocks to simulate various electronic components. The experiments were conducted for laminar and onset of transition Reynolds numbers. Diluted ink was used as the flow visualization vehicle. The study looked at flow over single component, multiple component, and fully loaded circuit packs. The study drew a number of conclusions including the flows were highly three dimensional, and location and orientation of components with large aspect ratio will significantly affect circuit pack flow distribution.
Understanding the Cyclic Mechanical Behavior of Lead/Tin Solder
Authors: Tien J. K. , Hendrix B. C. , Attarwala A. I.
Published: April 2008

For lead/tin solders, room temperature is hot enough that deformation is controlled by creep. Creep deformation is thermally activated and is a function of time. Therefore, the appropriate parameters which can describe cyclic behavior are the ones which are functions of temperature and time, such as strain rates, ramp rates, and hold times. The traditional cyclic loading parameters of strain amplitude and stress amplitude are inadequate and can even be misleading as they do not take into consideration the rate at which strain or stress was applied. In addition to permanent creep strains, anelastic strains are also stored as a function of time during cyclic loading. Anelastic strains are recoverable and thus can be nondamaging. During cyclic loading, anelastic strains are stored along with creep strains during the time spent on load. If the hold times in accelerated cycling are shortened to the extent that a significant portion of the total strain stored during on-load is anelastic (around 3 seconds) then the damage storage rate decreases rather than accelerating. These factors need to be considered both when accelerated testing is contemplated and in the development of life prediction equations.
A Systems Approach to Solder Joint Fatigue in Spacecraft Electronic Packaging
Authors: Ross R. G.
Published: April 2008

Differential expansion induced fatigue resulting from temperature cycling is a leading cause of solder joint failures in spacecraft. Achieving high reliability flight hardware requires that each element of the fatigue issue be addressed carefully. This includes defining the complete thermal-cycle environment to be experienced by the hardware, developing electronic packaging concepts that are consistent with the defined environments, and validating the completed designs with a thorough qualification and acceptance test program. This paper describes a useful systems approach to solder fatigue based principally on the fundamental log-strain versus log-cycles-to-failure behavior of fatigue. This fundamental behavior has been useful to integrate diverse ground test and flight operational thermal-cycle environments into a unified electronics design approach. Each element of the approach reflects both the mechanism physics that control solder fatigue, as well as the practical realities of the hardware build, test, delivery, and application cycle.
Stiffness and Fatigue Study for Surface Mounted Module/Lead/Card Systems
Authors: Engel P. A. , Caletka D. V. , Palmer M. R.
Published: April 2008

Modules attached to circuit cards by peripheral J- and gullwing leads were studied for their behavior under flexure. Three aspects of mechanical behavior were focused upon: the stiffness of the system, the forces arising in the leads, and the fatigue strength of the latter. The effective stiffness of a module-reinforced circuit card was measured experimentally in several configurations (load on card and load-on-module, double-sided and stacked). The leaded attachments were in two parallel rows. Analytical modeling of these tests were performed considering the leads as a continuous elastic foundation connecting the module and the card; test results were corroborated. Experiments were also conducted to establish the elastic and elastoplastic range of lead stiffness in three perpendicular directions: in two shearing planes and axially. The latter was the stiffest and most significant direction, motivating much of the present analysis. For lead force, the analytical procedure yielded values which were confirmed by finite element computation methods described previously by Engel (1990). Fatigue tests were performed on both J- and gullwing leads. Solder joints failed in the former, while lead failures occurred in the latter.
Transient Thermal Stress Analysis of a Plated Through Hole Subjected to Wave Soldering
Authors: Barker D. , Pecht M. , Dasgupta A. , Naqvi S.
Published: April 2008

During a typical wave soldering operation a plated through hole (PTH) is exposed to temperatures which are higher than any rated operating temperatures. Understanding the heat transfer and the potential PTH damage mechanisms, which arise during the wave soldering process, is critical to PTH quality control and reliability. In particular, cracks may be initiated during the wave soldering transient and become manifest only after operational cycling. This paper presents a transient nonlinear thermal stress analysis of a nonsolder filled PTH that is subjected to a typical wave soldering process. A full three-dimensional orthotropic analysis and an axisymmetric analysis with cylindrically anisotropic properties are used and the results compared. Temperature and stress/strain history curves are examined to determine the impact of the wave soldering operation on the PTH fatigue life. The effect of PWB innerplanes on the PTH maximum stress and strain is also investigated.
Interfacial Shear and Peel Stresses in Multilayered Thin Stacks Subjected to Uniform Thermal Loading
Authors: Pao Yi-Hsin , Eisele Ellen
Published: April 2008

An analytical approach has been developed to evaluate the interfacial shear and peel stresses in multilayered thin stacks subjected to uniform temperature variation. The approach, which is based on an extension of Suhir’s bimetal thermostat model, provides a system of coupled linear second order differential equations used in solving for the interfacial stresses. Once these stresses have been determined, the normal stress in each layer and the deflection of the stack can be readily obtained. Two numerical examples are used to demonstrate the capability of the approach. The first example deals with a five-layered symmetric double-shear solder joint. The results are compared to a nonsymmetric three-layered solder joint to study the effect of bending and the interactions of material properties. One of the interesting features observed is that the maximum interfacial shear stress does not necessarily occur at the edge. The other numerical example is a four-layered transistor stack mounted on a substrate. The structural behavior is analyzed, and the effect of geometric dimension is examined. The present approach is shown to provide more accurate results than those of others based on the same assumptions. In addition, applications of the approach to more general stack configurations are also discussed.
Automated Finite-Element Mesh Generation for Surface Mount Technology Solder Joints
Authors: Read D. T. , Lucey G. K.
Published: April 2008

The ultimate goal of this work is an improved method to assess the significance of anomalies in surface mount technology (SMT) solder joints, by relating them to field performance and reliability. The fitness-for-purpose approach can be applied to SMT solder joints by relating specific characteristics or flaw indications in individual solder joints to their likelihood of failure, through finite element analysis. An effort is underway to automate the finite element modeling of actual solder joints by generating meshes from optical and X-ray inspection data in the form of thousands of surface points. Computer programs have been written to convert these surface points to finite element meshes. Two trial data sets have been meshed, one from an X-ray laminography system and one from a machine vision system.
Fatigue Analysis of a Planarpak™ Surface Mount Component
Authors: Sharif I. , Barker D. B. , Dasgupta A. , Pecht M. G.
Published: April 2008

This paper discusses the thermo-mechanical fatigue life analysis of an analog Avantek Planarpak™ surface mount device where the entire base of the component is soldered directly to the printed wiring board. The critical thermal stresses and strains are analyzed with the help of two and three-dimensional finite element models. The effect of solder voids and incomplete bonding is also investigated. The paper also shows how fatigue life estimations can be made using q generalized form of the Manson-Coffin equation even though the maximum solder attach stresses are found to be elastic.
Stress Analyses of Flip TAB Interconnects in Multi-Chip Module
Assembly
Authors: Nagaraj Ben , Mahalingam Mali
Published: April 2008

Flip Tape Automated Bond (FTAB) interconnect is one of the leading candidates for device to substrate interconnection in a high performance Multi-Chip Module (MCM). The TAB interconnect becomes a structural member in the MCM assembly, bearing both “mechanical” and “thermal” loads. Further, to accomplish high thermal performance in the assembly, physical contact to the device may be made under substantial contact pressures. The device may be supported by elastic structures to redistribute the interconnect forces. Finite Element Methods (FEM) are used to analyze the structural behavior of TAB interconnects under (i) the applied mechanical load to the device and (ii) the thermal loads due to the heat dissipation in the device. Variation of the force components on the TAB interconnects and the maximum failure criterion based on the stresses in the interconnects are reported. Effect of the support area and the modulus of the supporting element on the interconnects are discussed. Generic design guidelines are presented for flip TAB interconnect based MCM assembly.
Statistical Energy Analysis for Electronic Equipment
Authors: Lu L.
Published: April 2008

Vibration response of electronic equipment analyzed by a simple mathematical model or a finite element model can only provide a limited system response calculation. Application of the Statistical Energy Analysis (SEA) was extended to the calculation of the vibrations of individual components. In order to demonstrate the applicability of SEA to instrumentation vibration analysis at high frequency ranges, an 8-component electronic box was chosen for test and analysis. There was good agreement between tested and analytical results in the frequency averaged sense.
A Study of Forces and Motion Generated During Pulsed Laser Welding of Optical Packages
Authors: Rangwala S.
Published: April 2008

This paper presents an analysis of forces and motions generated during interaction of pulsed laser energy with materials. The effects of this interaction on the subsequent dynamics of the material receiving this energy have important implications in the manufacture of laser diode packages. Small motions which occur during laser welding of the package assembly can cause serious losses in the amount of coupled power, thus degrading the performance of the package. This work is aimed at understanding how these movements occur. Various quantities such as force, acceleration and coupled power variations were measured during a laser welding operation. These measurements establish that significant thermal stress waves are generated during the welding process. However, the final relative motion between cylindrical specimens which are butt-welded by a laser beam occurs due to rapid cooling and shrinkage of the weld pool at the interface of the two specimens.
Elastoplastic Analysis of Bimaterial Beams Subjected to Thermal Loads
Authors: Cifuentes A. O.
Published: April 2008

The problem of determining the stresses in a bimaterial beam subjected to a thermal load is considered. One beam layer is assumed to be linear while the second layer is assumed to be elastoplastic. A simple analytical solution is derived and compared against results obtained with finite elements.