bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of the Growth and Collapse of Voids in Viscous Solids
Authors: Lee B. J. , Mear M. E.
Published: April 2008

The growth and collapse of isolated voids in power-law viscous matrix materials are investigated. The study is restricted to axisymmetric remote stressing and to voids which are initially spheroidal with the axis of symmetry of the voids coincident with the axis of symmetry of the remote loading. Particular attention is given to the evolution of initially spherical voids, but the effect of initial void shape on subsequent void evolution is also investigated. For linearly viscous matrix materials, the voids evolve through spheroidal shapes and the work of Budiansky et al. (1982) provides the desired information about the history of void shape and volume. For nonlinear matrix materials, the void evolution is idealized as proceeding through a sequence of spheroidal shapes, and the rate of deformation for a given instant is evaluated using a Ritz procedure developed by Lee and Mear (1992). The results of the study demonstrate that the history of void volume and void shape is influenced significantly by the material nonlinearity, the remote stress state and the initial void aspect ratio.
Stress Fields in a Continuous Fiber Composite With a Variable Interphase Under Thermo-Mechanical Loadings
Authors: Mikata Yozo
Published: April 2008

Stress fields in a continuous fiber composite with a variable interphase subjected to thermomechanical loadings are studied by using a four concentric circular cylinders model. An exact closed form solution is obtained for the stress field in the interphase in a series form using Frobenius method in a certain case. Numerical results are presented for FP fiber/Al 6061 composite with interphase, and carbon fiber/Al 6061 composite with interphase. It is found that the variableness of the thermoelastic constants in the interphase has significant effects on the stress distributions in the interphase. Therefore, this will, in turn, affect the initiation of cracks in the interphase.
Nonlocal Behavior of Elastoplastic Metals: Theory and Results
Authors: Muller D. , Lemoine X. , Berveiller M.
Published: April 2008

In this paper, a nonlocal theory based upon crystalline plasticity is used in case of a dislocation cell structure induced during plastic straining and represented by a two-phase material. By describing convective dislocation motion (which appears to be a basic feature of hardening) and storage mechanisms, under some simplifying assumptions, numerical simulations exhibit significant effects on the intragranular heterogeneization, as well as on global results like the Bauschinger effect.
Damage Mechanics of Two-Dimensional Woven SiC/SiC Composites
Authors: Shan Hui-Zu , Pluvinage Philippe , Parvizi-Majidi Azar , Chou Tsu-Wei
Published: April 2008

The paper reports an analysis and modeling of the damage behavior of two-dimensional woven SiC/SiC composites. The damage mechanics analysis originally developed by Ladeveze and coworkers for polymeric and C/C composites are adopted and extended for ceramic matrix composites. The experimental findings of the coauthors reported in a companion paper provides the data for analytical modeling. The damage model assumes quasi-isotropic elastic behavior of the undamaged SiC/ SiC composites as well as orthotropic damage development (e.g., matrix microcracking, interfacial debonding, and fiber fracture). The model utilize two damage variables which are determined from experimental data; and the constitutive relation takes into account the difference in damage development between tension and compression in the principal material directions. The validity of the theory is demonstrated by the prediction of damage evolution of a SiC/SiC specimen under four-point bend test based upon the experimental data of tension and compression tests. A finite element method coupled with damage is adopted for the flexural analysis. The predictions agree quite well with experimental results.
Dislocation Punching From Ceramic/Metal Interfaces
Authors: Taya M. , Mori T.
Published: April 2008

Relaxation of misfit strains at interfaces between two different materials by dislocation punching is studied analytically by focusing on two types of interfaces: planar and nonplanar. As an example of planar type interface, the case of metal coating/ ceramic substrate system is studied while ceramic filler/metal matrix composite system is examined as an example of a nonplanar interface. Based on the present analytical model, the condition for dislocation punching for each interface is established. Validity of the dislocation punching model is verified by comparing the analytical results with limited experimental results, resulting in a good agreement.
The Effective Properties of Composite Materials With Constant Reinforcement Density by the Linear Mori-Tanaka Method
Authors: Zuiker J. R. , Dvorak G. J.
Published: April 2008

In its original form, the Mori-Tanaka method estimates constant overall properties of statistically homogeneous composite materials subjected to uniform overall stresses, strain or temperature changes, from averages of local fields in the phases. To permit applications involving large overall stress and/or temperature gradients, and functionally graded materials with a variable reinforcement density, the method has been extended to linearly variable overall and local fields by Zuiker and Dvorak (Composites Engineering, Vol. 4, 19–35, 1994) as a first step toward application of the method to statistically inhomogeneous materials with variable reinforcement density. Here, the effective properties are examined in detail. Non-zero components of the stiffness matrix are shown to satisfy invariance requirements and to vary with reinforcement volume fraction and size of the representative volume. It is shown that the linear and constant field approaches provide different estimates of overall properties for small representative volumes, but nearly identical estimates for large volumes.
Parameter Analysis for Time-Dependent Low-Cycle Fatigue Life
Authors: Yamaguchi Koji , Kobayashi Kazuo , Ijima Kiyoshi , Nishijima Satoshi
Published: April 2008

Temperature and strain rate dependences of low-cycle fatigue life can be represented by a modified Larson-Miller parameter. The parameter P is written by P=T(logN25−Alog ε˙ + B), where T is temperature, N25 is fatigue life, ε˙ is strain rate, and A and B are constants. In the analysis, each data of several kinds of engineering materials from ferritic steels to austenitic stainless steels are used. These are the authors original data published in the documents of NRIM Fatigue Data Sheets. The result of 304 stainless steel has been compared with statistical analysis result by Diercks adopted in a design code. The fatigue life curves represented by the proposed parameter analysis fitted well test data in high-cycle region as well as ones in low-cycle region.
Detection of 1 mm Fatigue Crack Initiation Using Strain Waveform
Authors: Makabe Chobin , Kaneshiro Hideo , Nishida Shin-ichi , Urashima Chikayuki
Published: April 2008

It is very difficult to monitor fatigue crack initiation at all parts of machine equipment day after day. In this study, a method of continuous monitoring for fatigue crack initiation is examined which uses the strain waveform of running machine. A notched section of the equipment is taken as the inspection point because many fracture accidents originate in fatigue cracks initiated from such a notch. Fatigue crack initiation can easily be detected by observation of the waveform of a strain function composed of the strains in the vicinity of the notch, because it changes shape on crack initiation. This change of the waveform is brought about by the change of the compliance of the material due to the crack closure behavior. It is found that crack initiation detection is improved by spectral analysis of the waveform.
Multiaxial Low-Cycle Fatigue Damage Evaluation Using A. C. Potential Method for Alloy 738LC Superalloy
Authors: Isono Yoshitada , Sakane Masao , Ohnami Masateru , Fujiyama Kazunari
Published: April 2008

This paper studies tension/torsion multiaxial low-cycle fatigue lives and creep-fatigue damage evaluation for Alloy 738LC superalloy. Tension/torsion creep-fatigue tests were carried out using hollow cylinder specimens and multiaxial creep-fatigue lives were obtained. The Mises’ equivalent strain correlated the multiaxial low cycle fatigue lives within a factor of two scatter band. An a.c. potential method is developed to detect the creep-fatigue damage associated with crack nucleation and extension. A.c. potentials at high frequencies accurately detect the creep-fatigue damage from the early stage of life while those at low frequencies detect that in the final stage of life. A.c. potentials at high frequencies detect the crack density, defined as the total crack length per unit area, and maximum crack length more sensitively than those at low frequencies.
Strain-Rate Sensitivity, Relaxation Behavior, and Complex Moduli of a Class of Isotropic Viscoelastic Composites
Authors: Li J. , Weng G. J.
Published: April 2008

A micromechanical principle is developed to determine the strain-rate sensitivity, relaxation behavior, and complex moduli of a linear viscoelastic composite comprised of randomly oriented spheroidal inclusions. First, by taking both the matrix and inclusions as Maxwell or Voigt solids, it is found possible to construct a Maxwell or a Voigt composite when the Poisson ratios of both phases remain constant and the ratios of their shear modulus to shear viscosity (or their bulk counterparts) are equal; such a specialized composite can never be attained if either phase is purely elastic. In order to shed some light for the obtained theoretical structure, explicit results are derived next with the Maxwell matrix reinforced with spherical particles and randomly oriented disks. General calculations are performed for the glass/ED-6 system, the matrix being represented by a four-parameter model. It is found that, under the strain rates of 10−7/hr and 10−6/hr, randomly oriented disks and needles at 20 percent of concentration both give rise to a very stiff, almost linear, stress-strain behavior, whereas inclusions with an aspect ratio lying between 0.1 and 10 all lead to a softer nonlinear response. The relaxation behavior of the composite reinforced with spherical particles is found to be more pronounced than those reinforced with other inclusion shapes, with disks giving rise to the least stress relaxation. The real and imaginary parts of the overall complex moduli are also established, and found that, as the frequency increases, the real part of the complex bulk and shear moduli would approach their elastic counterparts, whereas for the imaginary part, the increase shows two maxima, and then drops to zero as the frequency continues to increase. Finally, the complex bulk modulus is examined in light of the Gibiansky and Milton bounds, and it is found that, for all inclusion shapes considered, this modulus always lies on or within the bounds.
The Effect of Matrix Constitutive Model on Residual Thermal Stresses in MMC
Authors: Brayshaw James B. , Pindera Marek-Jerzy
Published: April 2008

A thermomechanical analysis of advanced composites in a wide temperature range is presented. This analysis is based on the micromechanics method of cells. An incremental formulation of the micromechanics model is developed to facilitate the use of various inelastic constitutive theories. These theories incorporate time-dependent and temperature-dependent features for modeling different types of metal matrices. The constitutive models include the Bodner-Partom unified theory of viscoplasticity, the incremental plasticity model, and a power-law creep model. The effect of the cooling rate, taking into account temperature-dependent matrix properties, on residual thermal stresses is subsequently investigated for a SiC/Ti composite using the different models for the matrix phases. Predictions generated using the micromechanics method are compared with available results of finite-element analysis.
Closure of a Nuclear Waste Repository Deeply Imbedded in a Stratified Salt Bed
Authors: Xu Wei , Genin Joseph
Published: April 2008

The Waste Isolation Pilot Plant (WIPP) is a repository vault, mined deep into a salt strata. It eventually closes in on itself, encapsulating its contents. At room temperature salt may be regarded as a linear, isotropic, viscoelastic material. In this study, using triaxial compression test results on salt, we determine the relaxation functions and set up the boundary value problem for the encapsulation mechanism of a salt vault. Closure of the repository as a function of time is determined using a three-dimensional finite element model. The Tresca failure criterion is used to predict the stability of the repository. Finally, the study is validated by comparing our results to in-situ measured data.
The Adiabatic Heat Transfer Coefficient and the Superposition Kernel Function: Part 2—Modeling Flatpack Data as a Function of Channel Turbulence
Authors: Anderson A. M. , Moffat R. J.
Published: April 2008

This paper describes an investigation of the forced convection heat transfer and pressure drop characteristics of a regular in-line array of flatpacks for several channel heights and inlet velocities. The work has both practical and theoretical interest since it relates to technical problems now faced by the electronics industry, and it embodies one of the most general heat transfer problems: nonuniform heat release from nonuniform geometries. To predict operating temperatures in situations where the wall temperature distribution is nonuniform, one must use superposition. Both the adiabatic heat transfer coefficient, had and the superposition kernel functions, g* are required. The problem can be solved using superposition directly (had and g*) or indirectly (using had and g* to calculate the correct value of hm). Either way the superposition data is required. This work presents the first full set of superposition data for flatpack arrays. Part 1 presents heat transfer and pressure drop results and part 2 presents a model for heat transfer that is based on the maximum turbulence fluctuations in the channel.
Heat Transfer Enhancement by Flow Destabilization in Electronic Chip Configurations
Authors: Amon C. H.
Published: April 2008

Numerical simulations of the flow pattern and forced convective heat transfer in geometries such as those encountered in cooling systems for electronic devices are presented. For Reynolds numbers above the critical one, Rc, these flows exhibit a traveling wave structure with laminar self-sustained oscillations at the least stable Tollmien-Schlichting mode frequency. Supercritical oscillatory flow induces large-scale convective patterns which lead to significant mixing and correspondingly heat transfer augmentation. Three techniques of heat transfer enhancement by flow destabilization are compared on an equal pumping basis: active flow modulation, passive flow modulation and supercritical flow destabilization. It is found that the best enhancement system regarding minimum power dissipation corresponds to passive flow modulation in the range of low Nusselt numbers. However, supercritical flow destabilization becomes competitive as the requirement for a higher Nusselt number begins to dominate the design choices.
Theoretical and Experimental Investigation of Laser Drilling in a Partially Transparent Medium
Authors: Nowak T. , Pryputniewicz R. J.
Published: April 2008

An investigation of pulsed, laser drilling in a partially transparent medium was conducted. The study included both theoretical and experimental analyses. The theoretical analysis included development of a computer simulation to model the laser drilling process—a three-dimensional finite difference solution with temperature-dependent thermal properties, finite sample geometry, and experimentally determined laser beam characteristics. Both qualitative and quantitative correlation of the theoretical and experimental results was good with successful prediction of hole shapes and minimum error in the theoretically predicted cross-sectional areas of the laser-drilled holes ranging approximately ± three percent over the range of energies per laser pulse considered in this study. Results of calculations and experiments demonstrated the importance of the shape and irradiance distribution of the incident laser beam on the quality of laser-drilled holes in Al2O3 samples.
Thermal Strain Measurements of Solder Joints in Second Level Interconnections Using Moire Interferometry
Authors: Guo Yifan , Woychik Charles G.
Published: April 2008

Low cycle fatigue of solder joints is one of the major kinds of failures in second level interconnections of an electronic package. The fatigue failure is caused by thermal strains which are created from a mismatch of coefficients of thermal expansion (CTE) that occurs between two levels of packaging. As the package approaches smaller dimensions, measurements of thermal strains in the solder interconnections become very difficult. In this paper, moire interferometry technique was applied to evaluate the thermal strains in the second level interconnections for both conventional pin-in-hole (PIH) packages and surface mount components. The coefficient of thermal expansion of each component was measured. Thermal strain distributions in the solder interconnections were determined, and reliability issues were discussed. The strains in solder joints of the PIH components were much higher than those of the stacked surface mount components. Even though the surface mount components had a lower inherent strength, their overall mechanical reliability was much higher since they had practically no localized strain concentrations.
Influence of Selected Design Variables on Thermo-Mechanical Stress Distributions in Plated-Through-Hole Structures
Authors: Bhandarkar S. M. , Dasgupta A. , Barker D. , Pecht M. , Engelmaier W.
Published: April 2008

Failure of plated-through-holes (PTHs) due to thermomechanical stresses is a well established cause of failure of multilayer printed wiring boards (MLBs). This paper uses the finite element method (FEM) to examine the nature of the stress distribution within the PTH structure when the MLB is subjected to thermal loads. Guidelines are laid out for realistic modelling of material properties and boundary conditions in the FEM model. Parametric studies are conducted to study the qualitative effect of several geometric parameters on the critical stresses in the PTH. Both traditional glass-epoxy (FR-4) MLBs and highly anisotropic Kevlar-polyimide MLBs are examined. Differences in behavior observed between the two materials underline the pitfalls in extending the standard design thumbrules for standard FR-4 MLBs to other MLB materials. The purpose here is to provide guidelines for the reliable design of PTHs. Actual fatigue life predictions are deferred to a later paper.
Design Parameters and Practical Considerations in the Two-Phase Forced-Convection Cooling of Multi-Chip Modules
Authors: Gersey Christopher O. , Willingham Thomas C. , Mudawar Issam
Published: April 2008

Forced-convection boiling was investigated with a dielectric coolant (FC-72) in order to address some of the practical issues related to the two-phase cooling of multi-chip modules. The module used in the present study featured a linear array of nine, 10 × 10 mm2, simulated microelectronic chips which were flush-mounted along a 20-mm wide side of a rectangular channel. Experiments were performed with a 5-mm channel gap (distance between the chip surface and the opposing channel wall) at eight orientations spaced 45 degrees apart. Two other channel gaps, 2 and 10 mm, were tested in the vertical up flow configuration. For all these configurations, the velocity and subcooling of the liquid were varied from 13 to 400 cm/s and 3 to 36°C, respectively. Changes in orientation did not affect single-phase or nucleate boiling characteristics, but did have a major impact on CHF. Upflow conditions were found to be the best configuration for the design of two-phase cooling modules because of its inherently stable flow and relatively high CHF values. The CHF value for the most upstream chip in vertical upflow agreed well with a previous correlation for an isolated chip. Combined with the relatively small spread in CHF values for all chips in the array, this correlation was found to be attractive for design purposes in predicting CHF for a multi-chip array. To achieve a given CHF value, it is shown how the strong CHF dependence on velocity rather than flow area allows for a reduction in the required flow rate with the 2-mm, as compared to the 5-mm gap, which also required a smaller flow rate than the 10-mm gap. This reduction inflow rate was significant only with subcooled conditions corresponding to high CHF values.
Investigation and Prediction of Creep and Creep-Like Behavior of Solids by Laser Methods
Authors: Cherstvov E. V. , Mokhel A. N. , Salganik R. L. , Soutorshin V. N.
Published: April 2008

Problem of investigation of creep and creep-like behavior of solids in both prediction and micromechanical features is considered in connection with possibility of laser-aided measuring velocities and displacements of sufficiently small regions on natural (without its any special marking and treatment) surface with high enough accuracy and time resolution.
Thermal Stress Analysis of Pin Grid Array Structures: Pin and Solder Joint Problems
Authors: Engel Peter A. , Wu Kee Rong
Published: April 2008

The role of the solder joint as an elastic foundation is investigated first for structural analysis of the pin. Failure mechanisms are discussed. For various pin cross sections, guidelines for computing the foundation constant by analytical and finite element methods are established. Exact expression are derived for the pin stress. The solder stress (radial pressure or tension) is found by an approximate contact analysis. Elasto-plastic pin analysis, for excessive thermal mismatch, is effected by an iterative method. The variation of the plastic domain is examined for various size and material parameters. Axial forces in the presence and absence of pin plasticity are investigated, and the overall effect on the PGA is discussed.
Thermal Stress Analysis of Pin Grid Array Structures: Module and Card Interactions
Authors: Engel P. A. , Webb J. R.
Published: April 2008

While primary thermal stress analysis of pin grid arrays considers a nonflexible card and module delineating the structure, in this paper we consider the stress relief (resulting in a “secondary” force system) afforded by bending and stretching of the delineating plates. The primary axial force F, plate moments, M1, M2, and shear V are considered acting in radial planes, and the secondary pin forces P are solved by stipulating compatibility of deformations at the two pin ends. A collocation technique is used to evaluate the plate equations in polar symmetry. The contributions of transverse plate compliances, and in-plane compliances are evaluated numerically for a 50 mm ceramic module, and compared with known experimental force measurements.
Predicted Bow of Plastic Packages Due to the Nonuniform Through-Thickness Distribution of Temperature
Authors: Suhir E. , Manzione L. T.
Published: April 2008

Warpage of molded plastic packages becomes a more serious consideration as their size increases. In this analysis we develop an analytical stress model for the evaluation of the thermally induced bow of large plastic packages due to the nonuniform distribution of temperature in the through-thickness direction after the molding cycle. This model enables one to determine the effects of the package geometry and material properties on the induced warpage. We show that the bow of the package is proportional to the edge length squared, and is inversely proportional to the package thickness. We show also that the coefficient of thermal expansion (contraction) of the molding compound has a strong effect on the bow, while its Young’s modulus has a small effect. The performed experimental work has indicated that different procedures for handling the packages after molding result in different temperature gradients leading to different bows. The obtained results are useful in the selection of the appropriate molding compound and rational physical design of thick plastic packages, as well as in the optimization of the handling procedures after molding and post-curing.
Drill Wear Monitoring in Circuit Board Manufacturing Using Drilling Forces and Their Spectra
Authors: Ramirez Ciro N. , Thornhill R. Joe
Published: April 2008

The potential application of indirect tool wear monitoring methods in circuit board drilling is discussed. Monitoring methods are discussed and the state of tool wear monitoring research is presented. The nature of cutting forces developed in drilling FR-4 is examined using a simple numerical model of drilling which explains the structure of drill vibration spectra. The spec ta of predicted forces are shown to have nonzero amplitudes only at multiples of the fundamental frequency of the drill. Experimental spectra are presented which agree with these predictions.
Fluid Flow Modeling and Simulation for the Coaxial Cable of the LEASAT Antenna System
Authors: Yeh Hsien-Yang , Yeh Hen-Geul
Published: April 2008

A preliminary fluid flow modeling, analysis, and simulation of the gas pressure profile within a 259 cm long coaxial cable is presented. This coaxial cable is part of the antenna system of the LEASAT satellite. To eliminate the possibility of any corona or arcing phenomenon inside the coaxial cable during operation of the satellite, it is necessary to not only prove experimentally but also show analytically that the gas pressure inside the cable drops down and stays below 0.01 Ton within 24 hours after the satellite enters into its orbit. In this paper, only the analytical work is discussed. The continuum fluid mechanics and the kinetic theory of gases are applied for modeling and analysis. Computer simulation is done by using an IBM XT and the results are presented.
Interlaminar Stresses in Layered Beams
Authors: Mirman B.
Published: April 2008

An effective numerical procedure is developed for calculation of interlaminar shear and peeling stresses in layered beams. This procedure is based on the Built-up-Bar theory.
Application of Linear Assignment Model for Planning of Robotic Printed Circuit Board Assembly
Authors: Ji Z. , Leu M. C. , Wong H.
Published: April 2008

A planning method is presented for achieving shorter working-in-process and thus better productivity of printed circuit board assembly. This method finds the optimal sequence of component placement (and insertion) and near-optimal arrangement of feeders. For placement of components on a printed circuit board with a set of given feeder locations, the sequencing problem is shown to be equivalent to, and therefore solvable as, a linear assignment problem, which involves assigning n components to m feeders with the objective to minimize the total assembly time. A heuristic approach based on a linear assignment model is employed for arrangement of feeders. An example is provided to illustrate the solution generated by the proposed method.
A Shape Optimal Design Methodology for Packaging Design
Authors: Rajan S. D. , Nagaraj Ben , Mahalingam Mali
Published: April 2008

Shape optimal design methodology has been used as a design tool in the automotive and aerospace industries for quite some time now. In the present work the hybrid natural shape optimal design approach is used along with a nonlinear programming (NLP) technique to find the optimal shapes of electronic packaging components. The design problems are formulated as min-max problems and linear and materially nonlinear finite element analyses provide the function values. The applicability of the developed methodology is illustrated using a design example that deals with the packaging design of a plastic pad array carrier digital package. The results indicate that the methodology can be used either as an effective way of evaluating different design alternatives or refining existing designs.
A Conjectured Solder Fatigue Law Based on Nonlinear Dynamics
Authors: Russell S. , Caroselli R. , Mason J. , Shah M.
Published: April 2008

A discipline of nonlinear dynamics (Chaos Theory), not traditionally used in the study of solder, is applied here in developing a conjectured general form for fatigue based on creep. Solder joint data are analyzed which demonstrates two strain-rate regimes. In the literature, this is recognized as related to the two modes of grain boundary and matrix creep. In this paper, the behavior is treated as a “bifurcation” and a quadratic normal form identified which addresses qualitative features of the observed data. The resulting mathematical model is transformed into a quadratic map (difference equation) which is a classic paradigm for chaotic motion. This model addresses not only the two distinct rate regimes but also an unstable intermediate range of erratic motion which is observed in the data. Correlation between solder fatigue behavior and onset of model instability regarding effects of solder dwell (model relaxation) and solder grain size (assumed to be associated with model time increment) has been discussed in previous work. This has motivated examination of the classic Coffin-Manson (C.M.) low cycle fatigue law for elastic, plastic deformation in terms of appropriate quadratic maps. The result is a “curve-fit” representation of the C.M. forms in terms of map parameters. In particular, a simple relationship appears to exist between the “universal slopes” of the C.M. law and the “universal” Feigenbaum constant δ = 4.66920..., so called because it is associated with a wide class of maps which includes the quadratic as a special case. With this approach, a conjectured form of solder fatigue law under creep deformation is generated. General properties of the resulting form are discussed and compared with some of the fatigue models currently in use.
Wetting Dynamics of Molten Solder Alloys on Metal Substrates
Authors: Singler T. J. , Clum J. A. , Prack E. R.
Published: April 2008

Preliminary results from solderability studies are used to elucidate the physicochemical aspects of solderability, in particular the relationship between liquid composition and wetting. Spreading front morphology is discussed and a possible mechanism for observed rapid spreading sequences is advanced. That mechanism is based on solubility of metallization in one of the solder components (Sn). A composition study of a spreading sequence exhibiting a precursor film is presented along with a discussion of the role of the film in the overall wetting process. Segregation of the Pb and Sn alloy components during the spreading is discussed in terms of surface energy concepts, and the microscopic features of the substrate.
Isothermal Fatigue of LCC/PWB Interconnections
Authors: Solomon H. D.
Published: April 2008

This paper describes the isothermal fatigue of leaded chip carrier to PWB interconnections. A split board technique was used to test the behavior of the Kovar leads and Sn63 solder joints made between a 64 IO leaded chip carrier and a PWB. The leads and solder joints were subjected to proscribed deflections at 35°C or 125°C and at frequencies of 0.33 Hz or about 0.002 Hz. At 35°C and 0.33 Hz, the failures were primarily in the Kovar lead, but when the cycling frequency was decreased to about 0.002 Hz, the failures developed in the Sn63 solder joint between the lead and the PWB. At 125°C, the failures were in the solder, even when the cycling frequency was 0.33 Hz. In addition to studying the influence of temperature and cycle frequency, this paper also compares the behavior of leaded joints to that of leadless joints and illustrates the superiority of the leaded joints.
Experimental and Analytical Studies of 28-Pin Thin Small Outline Package (TSOP) Solder-Joint Reliability
Authors: Lau J. , Golwalkar S. , Erasmus S. , Surratt R. , Boysan P.
Published: April 2008

The reliability of 0.5 mm pitch, 28-Pin Thin Small Outline Package (TSOP) solder joints has been studied by experimental temperature cycling and a cost-effective 3-D nonlinear finite element analysis. Temperature cycling results have been presented as a Weibull distribution, and an acceleration factor has been established for the failure rate at operating conditions. Thermal fatigue life of the corner solder joints has been estimated based on the calculated plastic strain, Coffin-Manson equation, and isothermal fatigue data on solders. A correlation between the experimental and analytical results has also been made. Furthermore, failure analysis of the solder joints has been performed using Scanning Electron Microscopy (SEM) and an optical method.
Effect of SMC Lead Dimensional Variabilities on Lead Compliance and Solder Joint Fatigue Life
Authors: Barker D. B. , Sharif I. , Dasgupta A. , Pecht M. G.
Published: April 2008

Lead compliance is a critical parameter in optimal design and interconnection reliability of surface mount leaded components. The cyclic force transmitted to the solder joint in surface mount leaded components is controlled in part by the lead compliance. In this paper a methodology is presented for the computation of lead stiffness and the prediction of fatigue life of the leaded surface mount components. Three-dimensional finite element analyses have been performed to obtain the 12 × 12 stiffness matrices for both the PQFP gullwing and PLCC J leads and solder joints. These stiffnesses are then used in predictive fatigue life equations to estimate the fatigue life. The stiffness matrices and diagonal lead stiffnesses form the basis for identifying more failure resistant packages. Variabilities in lead and package dimensions provided by different vendors, manufacturing to JEDEC standards, are identified and their adverse effects on solder joint fatigue life are studied with the help of finite element parametric analyses. Eighty different finite element analyses are performed to study the effect of change in lead length, height, width and thickness on the lead stiffness and solder joint fatigue life for both the PQFP and PLCC attachments. Finally recommendations are made in order to obtain a better control on component fatigue life.
Refined Variational Solutions of the Interfacial Thermal Stresses in a Laminated Beam
Authors: Yin W.-L.
Published: April 2008

Efficient and accurate solutions of the interlaminar stresses in a layered beam under a temperature loading are obtained by a variational method using stress functions and the principle of complementary virtual work. Polynomial expansions of the fifth or lower degrees are used to approximate the variation of the stress functions in the thickness direction of each layer. Comparison of the solutions of the various orders with the existing numerical and analytical solutions indicates that the variational solutions converge rapidly as the degree of the polynomial expansion increases and that even the lowest-order variational solutions yield satisfactory results for the interlaminar stresses. Over short segments of the interface adjacent to the free edge, the resultant forces of the interlaminar normal and shearing stresses are given by the first-order derivatives of the stress functions. These global measures of the severity of interlaminar peeling and shearing action are predicted accurately by the lowest-order variational solution.
Effect of the Nonlinear Behavior of the Material on Two-Point Bending of Optical Glass Fibers
Authors: Suhir E.
Published: April 2008

We evaluate the effect of the nonlinear stress-strain relationship on the maximum curvature and maximum stress in optical glass fibers subjected to two-point bending. The analysis uses an assumption that this relationship, obtained experimentally for the case of uniaxial tension (Mallinder and Proctor, 1964; Kraus, Testardi, and Thurston, 1979, Glaesemann, Gulati, and Helfinstine, 1988), holds in the case of compression as well, and is applicable also to bending deformations. We show that the shift in the neutral axis due to the nonlinear stress-strain relationship has a significant effect on the maximum stress, while its effect on the maximum curvature is small and need not be considered. We show also that this relationship, obtained for elastic strains, not exceeding 5 percent, cannot be applied for very large strains, and therefore the future experimental work should include the evaluation of the nonlinear behavior of the material, both in tension and compression, for higher strains and for high strength fibers (such as, for instance, fibers protected by metallic coatings). The obtained results can be helpful in the analysis of optical glass fibers subjected to two-point bending.
Onset of Transition in the Flow Over a Three-Dimensional Array of Rectangular Obstacles
Authors: Garimella S. V. , Eibeck P. A.
Published: April 2008

Onset of transition is investigated in the flow over an array of protruding elements mounted on the bottom wall of a rectangular water channel simulating flow passages between adjacent circuit boards in computers. The element dimensions are held constant while the channel height and the element spacing are varied. Flow visualization and turbulence measurements are used to determine transition Reynolds numbers, which compare well with previous results obtained from heat transfer data. The complicated, three-dimensional flow field causes transition to be a function not only of flow rate and array geometry but also of location in the array. Transition occurs in the fully developed region of the array at a channel height-based Reynolds number of 700 for a channel height of 1.2 element heights, increasing to 1900 for a channel height of 3.6 element heights. However, when Reynolds number is defined based on element height, transition occurs at the same Reynolds number of 550 for all channel heights. Increasing the stream wise spacing between elements causes transition to occur at lower Reynolds numbers.
An Approximate Thermal Contact Conductance Correlation
Authors: Antonetti V. W. , Whittle T. D. , Simons R. E.
Published: April 2008

An approximate thermal contact conductance correlation which does not depend upon the surface asperity slope was developed. Published surface texture data for 65 specimens were used to establish a relationship between the average roughness and the RMS asperity slope, which was then used to develop a new approximate thermal contact conductance correlation. The investigation was conducted for a range of surface roughness typical of contacting surfaces. Comparison to limited test data and to 2080 simulated contact joints, indicates the new approximate thermal contact conductance correlation has an expected RMS error of approximately 23 percent.
Effects of Adhesion and Delamination on Stress Singularities in Plastic-Packaged Integrated Circuits
Authors: van Vroonhoven J. C. W.
Published: April 2008

The reliability of plastic-packaged integrated circuits is severely affected by the occurrence of delamination. Several types of electrical and mechanical failures are introduced as a result of the delamination, such as metal smear, pattern shift, open channels, passivation cracking, and fracture of the plastic encapsulation. An analysis on the basis of fracture mechanics is applied to wedges of two dissimilar elastic media as a model for the interfaces between silicon chip and plastic mould compound. The stress state inside the encapsulation and in the vicinity of the edges of the silicon chip is characterized by a stress-singularity parameter. It is shown that loss of adhesion aggravates the singular behavior of the strees components and that delamination induces higher stresses inside the packaging material. This will lead to crack initiation in the plastic encapsulation and also to more rapid crack growth in comparison with undamaged devices. This stress-singularity approach provides an explanation for the observed relation between the occurrence of delamination and the increase of the failure frequency in plastic-encapsulated integrated circuits. The thermal effects that arise during the temperature cycling tests are also investigated. For uniformly distributed temperatures it is shown that the stress singularity is determined by the elasticity constants and by geometric effects and that it does not depend on thermal influences.
Application of Impedance Spectroscopy for On-Line Monitoring of Solder Paste
Authors: Herman C. R. , Skormin V. A. , Westby G. R.
Published: April 2008

The technique of impedance spectroscopy is suggested for industrial monitoring of solder paste in the surface mount assembly process. Being an on-line implementable technique, it has the potential of giving valuable insight to the manufacturing characteristics of solder paste and can facilitate application of statistical process control methods. This exploratory study evaluates impedance spectroscopy as a monitoring tool and focuses on key topics which can lead to the creation of on-line standards for solder paste. The presented technique is supported by experimental results and statistical analysis.
Local Characteristics of Convective Heat Transfer From Simulated Microelectronic Chips to Impinging Submerged Round Water Jets
Authors: Sun H. , Ma C. F. , Nakayama W.
Published: April 2008

An experimental study was performed to investigate the local characteristics of heat transfer from vertical simulated micro-chips to impinging submerged circular water jets. The effects of jet velocity, and nozzle-to-plate spacing were studied in the range of Re = 5.0 × 103 ˜ 3.6 × 104. Heat transfer rates at the stagnation point and local heat transfer distributions were correlated. Transition from laminar to turbulent flow was observed.
Nucleate Boiling and Critical Heat Flux From Protruded Chip Arrays During Flow Boiling
Authors: Gersey C. O. , Mudawar I.
Published: April 2008

The effects of chip protrusion on the forced-convection boiling and critical heat flux (CHF) of a dielectric coolant (FC-72) were investigated. The multi-chip module used in the present study featured a linear array of nine, 10 mm x 10 mm, simulated microelectronic chips which protruded 1 mm into a 20-mm wide side of a rectangular flow channel. Experiments were performed in vertical up flow with 5-mm and 2-mm channel gap thicknesses. For each configuration, the velocity and subcooling of the liquid were varied from 13 to 400 cm/s and 3 to 36° C, respectively. The nucleate boiling regime was not affected by changes in velocity and subcooling, and critical heat flux generally increased with increases in either velocity or subcooling. Higher single-phase heat transfer coefficients and higher CHF values were measured for the protruded chips compared to similar flush-mounted chips. However, adjusting the data for the increased surface area and the increased liquid velocity above the chip caused by the protruding chips yielded a closer agreement between the protruded and flush-mounted results. Even with the velocity and area adjustments, the most upstream protruded chip had higher single-phase heat transfer coefficients and CHF values for high velocity and/or highly-subcooled flow as compared the downstream protruded chips. The results show that, except for the most upstream chip, the performances of protruded chips are very similar to those of flush-mounted chips.
Solder Joint Creep and Stress Relaxation Dependence on Construction and Environmental-Stress Parameters
Authors: Ross R. G. , Wen L. C. , Mon G. R.
Published: April 2008

Creep strain is probably the most important time-dependent damage accrual factor affecting solder joint reliability. Under typical multi-hour loading conditions, creep-induced strain is a complex function of solder metallurgical structure, solder temperature, loading time per cycle, the applied stress, and the spring constant of the combined part/lead/board system. The complex system level creep-fatigue interactions involved in electronic part solder joints are shown to be a strong function of the relative stiffness ratio κ, which is the ratio of the stiffness of the combined solder-lead system to the stiffness of the solder element by itself. For a leadless chip package, κ is close to unity. For a compliant leaded package, κ is typically in the 0.01 to 0.0001 range. Important environmental stress dependencies, including the effects of operating temperature, displacement amplitude due to thermal and mechanical cycling, and cyclic frequency of loading are investigated for different levels of k. Understanding the sensitivity of solder strain range to relative stiffness and these key environmental parameters is important to understanding the behavior of alternative packaging concepts and to achieving robust electronic packaging designs and testiong approaches.
Modeling the Vibration Restraints of Wedge Lock Card Guides
Authors: Barker D. B. , Chen Y. S.
Published: April 2008

One of the most dominate parameters that influence the calculation of a PWB’s natural frequency is the boundary conditions along the edges of the board. A series of experiments was conducted with Calmark three and five-part wedge locks to determine the boundary condition restraint offered by these commonly used card guides. The wedge locks were modeled as simple supports preventing transverse deflection of the plate edge and as linear elastic springs restraining the rotation of the plate edge. The rotational spring constant for the wedge lock was then calculated in an semi-inverse manner by measuring the natural frequency response of a well-characterized plate.
Estimating the Vibration Fatigue Life of Quad Leaded Surface Mount Components
Authors: Barker D. B. , Chen Y. S. , Dasgupta A.
Published: April 2008

This paper discusses the assumptions and details of the fatigue life calculations required to predict the fatigue life of quad leaded surface mount components operating in a vibration environment. A simple approximate stress analysis is presented that does not require complex finite element modeling, nor does it reduce the problem to a simple empirical equation or rule of thumb. The goal of the new method is to make PWB vibration solder joint reliability information available to the designer as early as possible and in an easily understood and implemented manner.
Analytical Solutions of Stresses in a Cylindrical Plate Due to Polynomial Radial Temperature Distributions
Authors: Wu Frank F. H.
Published: April 2008

Thermal stress is a significant contributor to a component’s failure during manufacturing processes. In the electronic industry, for example, it is very common that components experience an extensive number of nonuniform, local heating cycles throughout its life time. In order to promote reliability, components are put through burn-in which creates a very nonuniform temperature distribution. In order to reduce cost, reworkability is considered to be a necessary option for the manufacturing processes to achieve high yield; these rework processes usually require localized heating. In addition, due to certain functionality requirements, materials with different coefficients of thermal expansion are cast together. The thermal mismatch caused by nonuniform temperature and/or different coefficients of thermal expansion will create thermal stress which could result in the cracking of the components. The fracture often initiates on the interface between the different materials or at the free edge of the surface. To make the problems mathematically tractable, the problems here are simplified as linear thermo-elastic and axisymmetric. It is concluded that the displacement distribution is one order higher than the temperature distribution if the temperature is a polynominal function of the radial distance from the center of a disk. The solutions also show the effect of the edge boundary conditions on the stress level; namely a certain degree of constrained edge support will reduce the tensile stress around the edge of the plate. This will reduce the failure rate of the plate, particularly for a brittle material. Finally, a numerical finite element solution for a square plate with a localized heating source is given to demonstrate the applications of the analytical solutions to fixture design during the process development.