bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shearing Deformation in Partial Areal Arrays: Analytical Results
Authors: Heinrich S. M. , Shakya S. , Lee P. S. 
Published: March 2022

Abstract
Simple, closed-form expressions, based on elasticity theory, are derived for determining the location and magnitude of the maximum shearing displacement in a partial areal array of solder joints. Both uniform and non-uniform thermal loadings are considered, as is the heterogeneity of the component, which often arises due to different values of coefficient of thermal expansion (CTE) and elastic properties among the module’s constituent materials. The model is based on the assumptions that (a) the square geometry of the array and component may be replaced with an equivalent axisymmetric geometry and (b) the stiffness of the solder joints is negligible with respect to that of the component and substrate. The “soft joint” assumption corresponds to low-modulus solders or to thermal excursions occurring at high temperatures or low frequencies, for which significant stress relaxation occurs in the solder. For arrays exhibiting higher stiffness characteristics, the model yields conservative estimates of shearing displacement. Results indicate that, unlike homogeneous-component models under uniform temperature changes, the critical joints are not necessarily at the outer corners of the array. Other candidate locations predicted by the model (and observed in experimental and numerical studies) include the inner corner joints and any joints positioned beneath the die corners. The analytical results, also presented graphically, are found to depend on only three dimensionless parameters: the ratio of inner to outer array dimension, the ratio of die size to outer array dimension, and a “mismatch parameter,” which depends on the material, geometry, and loading characteristics of the problem. The results can be used to quickly determine the location and magnitude of peak shearing displacement in the array, possibly minimizing or eliminating the need to perform expensive and time-consuming finite element macroanalyses on entire assemblies involving hundreds of joints. Thus, the analyst may proceed directly to a detailed finite element microanalysis of the critical joint for fatigue life estimation, using the calculated shearing displacement as a required boundary condition in the finite element model.
The Effect of Underfill Delamination on the Reliability of Flip Chip Modules
Authors: Rzepka Sven , Korhonen Matt A. , Meusel Ekkehard , Li Che-Yu 
Published: March 2022

Abstract
The stresses occurring in the solder joints during thermal loads have been studied by finite element analysis in order to determine the effect of underfill delaminations on the reliability of FC modules and to evaluate the feasibility of lifetime estimations by the damage integral method. Besides the cases of no underfill and perfect adhesion, underfill delaminations at various interfaces to the solder, to the chip or to the substrate surfaces have been considered. The analysis included four different types of epoxy underfill, three kinds of substrates (alumina, FR-4, and flexboard), and two different tin lead solders (Pb97Sn and eutectic SnPb). The major findings are as follows. (i) The stress analysis has to be based on models that include the inelastic behavior of solder. Otherwise, even the qualitative trends might be wrong. (ii) The major beneficial effect of the underfill is its ability to create a compressive stress within the solder joint that suppresses the tensile stress concentration, which otherwise would lead to opening crack mode conditions at the side of the solder joints. The tensile stress is created by bending, which is a result of the global shear deformation due to the expansion mismatch between chip and substrate. (iii) Since the compressive stress can still be generated, delaminations from solder surfaces are not critical. (iv) When soft underfill is used, an extreme tensile stress concentration is created in the solder at the edge of the bond pad when the underfill is delaminated from the adjacent chip or substrate surfaces. This leads to a complete failure of the FC module very rapidly. (v) Using hard underfill that has a lower CTE than solder, however, the tensile stress in the joint can be kept at a safely low level even when adhesion to chip passivation or substrate is completely lost. Thus, it is possible to design FC modules, for which delaminations are not disastrous. (vi) Since the ultimate failure is always caused by growing of a major crack in the solder or at the underfill/chip interface, the damage integral concept can be applied to all kinds of FC modules, i.e. with or without underfill, to estimate the time to failure.
Some Mechanics Issues Related to the Thermomechanical Reliability of Flip Chip DCA With Underfill Encapsulation
Authors: Gall Carole A. Le , Qu Jianmin , McDowell David L. 
Published: March 2022

Abstract
The objectives of this research were to address some reliability issues in flip chip applications by characterizing the stress and strain response of a flip chip assembly under various loading conditions. In particular, the issue of fundamental limits on chip size was addressed and the importance of appropriate material models and constitutive relationships was assessed. Linear thermoelasticity models, metal plasticity models, viscoelasticity models and creep models were implemented. Finally, parametric studies were performed to optimize some of the elastic properties of the underfill.
It has been shown that (1) the chip major dimension is not the limiting factor in determining the maximum chip size for underfilled flip chip interconnections; (2) non-linear material behavior (e.g., creep, viscoplasticity, etc.) and detailed geometry need to be considered in the modeling to accurately predict the stress and strain fields; (3) there is an window for selecting optimal thermal expansion coefficient and modulus values which minimize stress and strain fields in the solder and silicon chip.
Effect of Thermal Residual Stress on the Measurement of the Adhesion Between Polyimide and Underfill Using an Asymmetric Double Cantilever Beam Specimen
Authors: Jiao Jinbao , Gurumurthy Charan K. , Kramer Edward J. , Sha Yan , Hui Chung-Yuen , Børgesen Peter 
Published: March 2022

Abstract
An asymmetric double cantilever beam (ADCB) technique was used to measure the interfacial adhesion of polyimide passivation to underfill materials. A thin layer of polyimide was coated on a standard diglycidyl ether of bisphenol-A (DGEBA) epoxy plate as one of the beams and an underfill epoxy was flowed over the polyimide film and cured to form the second beam. Due to the large difference in the coefficients of thermal expansion (CTE) between the two beams, a new term in critical strain energy release rate GT caused by the thermal residual stress becomes significant. This fact has been demonstrated experimentally by varying the thickness ratio of the two beams. The interfacial fracture energies of different underfill materials with polyimide were also measured. The results indicate that the effect of thermal residual stress must be taken into account in the calculation of critical strain energy release rate to achieve the realistic interfacial fracture energy Gc*.
Investigation of Interfacial Fracture Behavior of a Flip-Chip Package Under a Constant Concentrated Load
Authors: Wang Jianjun , Lu Minfu , Zou Daqing , Liu Sheng 
Published: March 2022

Abstract
In this paper, the interfacial fracture behavior of a flip-chip package subjected to a constant concentrated line load was investigated using a unique 6-axis submicron tester coupled with a high density laser moiré interferometry. The real-scale three-point bending flip-chip specimen, capable of measuring the crack growth rate (along the interface) and the interfacial fracture toughness was developed. The results show that the crack propagation along the interface of the passivated silicon chip/underfill under a constant concentrated load can be categorized into three stages: (1) stable crack propagation stage, (2) unstable crack propagation stage, and (3) quasi-crack arrest stage. There exist two obvious transition points between the stable crack propagation stage and the unstable crack propagation stage, and between the unstable crack propagation stage and the quasi-crack arrest stage. The moiré interferometry technique was used to monitor and measure the crack length during the test. The crack growth rate along the interface of the passivated silicon chip/underfill was calculated in terms of the load line deflection vs. time curve obtained from the test. In addition, the relationship between the crack length and the load line deflection was calibrated by using finite element analysis. The near tip displacement fields of the flip-chip package was also determined by the same method. The energy release rate was computed by using these near tip displacement variables through an analytical expression derived by authors. The interfacial fracture toughness Gc was determined by the energy release rate corresponding to the crack length at the quasi-crack arrest stage measured in the test. The interfacial fracture toughness Gc and the phase angle ϕ of the flip-chip package considered at the interface where the passivated silicon chip meets the underfill are about 35 J/m2 and −65° respectively.
Investigation of Underfill Adhesion in Plastic Flip-Chip Packages
Authors: Dai Xiang , Brillhart Mark V. , Ho Paul S. 
Published: March 2022

Abstract
The adhesion performance of underfill/printed circuit board (PCB) and underfill/chip interfaces are crucial for the reliability of plastic flip-chip packages. Delamination at either of these interfaces can drastically reduce the ability of the underfill to reinforce the flip-chip system resulting in premature assembly failure. This paper presents reproducible experimental techniques based on fracture mechanics for quantitatively determining the interfacial performance of underfill/polymer substrates and underfill/chip junctions. These techniques can be employed to rapidly evaluate new materials and process modification impact on adhesion performance of plastic flip-chip assemblies.
Fracture and Damage Evaluation in Chip Scale Packages and Flip-Chip-Assemblies by FEA and MicroDAC
Authors: Auersperg Jürgen , Schubert Andreas , Vogel Dietmar , Michel Bernd , Reichl Herbert 
Published: March 2022

Abstract
The thermo-mechanical reliability of electronic packages such as flip chip assemblies and chip scale packages is one of the most important conditions for adopting these technologies in industrial applications. On the other hand, various kinds of inhomogeneities, localized stresses and thermal mismatch between the silicon die and the substrate lead to interface delaminations, chip cracking and fatigue of solder interconnects.
The contribution shows the use of nonlinear finite element simulations with respect to the nonlinear, temperature and rate dependent behavior of the different materials used (metals, polymeric and solder materials) and the combination with experimental investigations. The development and application of failure models (e.g. thermal fatigue, life time prediction by Coffin-Manson type equations, integral fracture mechanics approaches — J–, J^–, ΔT*– integral — and evaluation of critical regions) is explained, in detail.
Furthermore, the simulation of damage growth in solder interconnects by an automatic adaptive finite element technique is performed. Inherent local damage models allow us to study the correctness of crack- and damage models. For this reason, some results have been compared to micrographs from damaged interconnects and to strain measurement results obtained by experimental methods. In particular, the microDAC measurement method is a powerful tool which inspects the displacement fields on the basis of the gray scale correlation method applied to micrographs from scanning electron microscopy, laser scanning microscopy and optical microscopy.
The application of those combined investigations should help to better understand the failure mechanisms especially in solder joints and directly support further applications for enhancing the thermo-mechanical reliability of advanced electronic assemblies.
Free-Edge Stress Intensity Factors for Edge-Loaded Bimaterial Layers
Authors: Klingbeil Nathan W. , Beuth Jack L. 
Published: March 2022

Abstract
Structures composed of bonded layers of dissimilar materials are common in a variety of applications. Designing such structures to resist debonding at free edges is often of critical importance. In this work, the problem of initiation of free-edge debonding is considered for use in designing debond-resistant layered structures. It is well known that the local elastic stress fields near the free edge of bonded dissimilar quarter planes can exhibit singular behavior, with the power of the stress singularity determined by the material mismatch. A fracture mechanics-type approach is adopted here which assumes that the local interface tractions governing initiation of debonding can be characterized by the power of the stress singularity and a suitably defined stress intensity factor. The global problem considered in this study is that of a bimaterial strip composed of isotropic layers with a uniform edge pressure applied to the top layer. A dimensionless free-edge stress intensity factor is introduced from which stress intensity factors can be derived for either uniform edge or thermal loadings applied to either or both of the layers. Finite element results are presented for the dimensionless free-edge stress intensity factor over a wide range of material mismatches and relative layer thicknesses. Trends in the dimensionless stress intensity factor are used to identify strategies for designing debond-resistant bimaterials. Finally, the trends are shown to be well approximated by the analytically calculated stress resultants transmitted across the interface, which suggests a simplified approach for designing debond-resistant multilayer structures.
Direct Measurement of the Adhesive Fracture Resistance of CVD Diamond Particles
Authors: Kamiya Shoji , Takahashi Hironori , Saka Masumi , Abé Hiroyuki 
Published: March 2022

Abstract
Diamond film produced by chemical vapor deposition (CVD) is being used in the electronics industry because of its excellent properties. In order to measure the adhesive strength of CVD diamond, external load is directly applied in a scanning electron microscope to the CVD diamond particles which sparsely appear on silicon substrate in the early stage of deposition. These particles are called nuclei when they are small and grow into contact with each other to form polycrystalline CVD diamond film. Diamond film was supposed to adhere to the substrate at only these discrete nucleation points, which might result in weak adhesive strength. We measure the maximum load, as the adhesive fracture resistance, required to scratch off the particles with 2–13 μm diameter. Adhesive fracture resistance is found to increase with the diameter of the particle. Hence we conclude that CVD diamond does not adhere only at the nucleation points but that the whole contact area to the substrate is responsible for its adhesive strength.
Two Interpretations of Rigidity in Rigid Body Collisions
Authors: Chatterjee Anindya , Ruina Andy L. 
Published: March 2022

Abstract
We distinguish between, and discuss the applicability of, two levels of rigidity in rigid-body collision modeling.
For rigidity in the strong, force-response, sense collisional contact deformations must be highly localized. The bodies then move according to 2nd order rigid-body mechanics during the collision. Incremental collision laws and most collision models using continuum mechanics for the contact region depend on force-response rigidity.
For rigidity in the weaker, impulse-response, sense the deformations need not be localized but displacements during the collision need to be small everywhere. Only the time-integrated rigid-body equations, involving before-collision and after-collision velocities, then need apply. Although a force-response rigid body is also impulse-response rigid the converse is not true. Algebraic collision laws depend only on impulse-response rigidity. Elastic vibration models of collisions are also generally consistent with impulse-response rigidity.
Strength and Stability Analyses of Retaining Structure Models for the Fracturing Fluid Characterization Facility
Authors: Striz Alfred G. , Thakore Keyur 
Published: March 2022

Abstract
Millions of dollars are spent annually on hydraulic fracturing for oil and gas well stimulation. Various researchers have proposed models to optimize the stimulation treatment, with limited success due to a lack of understanding of the behavior of critical parameters in the models, especially the fracturing fluids. Thus, the Gas Research Institute and the U.S. Department of Energy are sponsoring a project at the University of Oklahoma to investigate fracturing fluids in a large physical fracture model, the Fracturing Fluid Characterization Facility (FFCF). This simulator was initially expected to consist of a parallel plate simulator as large as 16 ft high by 100 ft long, with an internal pressure as high as 1200 psi, to determine critical fluid parameters under full-scale operating conditions. A smaller and more economical version of the simulator (7 ft high by 9 1/3 ft long) has since been built and moved to its own facility. As the reaction forces of the originally intended structure were tremendous (over 275,000,000 lbf for a full-scale simulator), structural analyses were essential.
Thus, static strength and stability (buckling) analyses were performed on various full-scale models and on the smaller final version of the pressure retaining structure for the FFCF simulator. An interior segment of each structural model consisting of the pressure chamber and the reaction beam/ plate/tie rod assemblies was modeled in detail and analyzed by the finite element method using the industry standard code MSC/NASTRAN together with the MSC/XL pre- and postprocessor. In addition to the linear analyses for all models, a material nonlinear analysis was run for Model 1. General buckling analyses by the finite element method were performed on square plates and on retaining structure plates with various boundary conditions to determine the influence of these conditions on the critical buckling loads. Finally, the full final model was analyzed for buckling proving the stability of the design.
Simplified Methodologies for the Characterization of Fatigue Crack Propagation in Metallic Structural Materials
Authors: Soboyejo Alfred B. O. , Soboyejo Winston O. 
Published: March 2022

Abstract
In several important engineering applications, the need to develop simplified mechanistically-based methodologies has become a significant factor in the development of appropriate techniques in the choice of suitable components, structures and infrastructures. Several metallic structural materials which have been used in such systems have suffered severe structural damages, due to the initiation of fatigue cracks, and in several instances, these have resulted in catastrophic structural and mechanical failures. In addition to the above, the importance of environmental and climatological considerations, including the effects of other essential variables, which can contribute significantly to fatigue crack initiation, propagation and structural failures, need to be addressed and incorporated into the formulation of any new methodologies, which may be proposed to solve the practical engineering problems in this field.
The successful results of recent research work in this field are hereby presented, in order to provide practically acceptable and simple engineering methodologies, which can provide the much needed solutions to problems in several structural and mechanical engineering design applications. The important technical contributions from the recent results of engineering research in this field are hereby presented in this technical paper.
An Integrated Micro/Macro Approach for Structural Analysis of Laminate Composites With Applications to Turbine Blades
Authors: Ávila Antonio F. 
Published: March 2022

Abstract
An integrated micro/macro mechanical procedure for structural analysis of unidirectional metal matrix composites is proposed. The micromechanical analysis is performed via the Composite Cylinder Assemblage model (CCA) or the Representative Volume Element approach (RVE). The macroscopic stress-strain relation is based on a modification of the Vanishing Fiber Diameter theory (VFD), and the concept of “smeared” finite element. The fibers are considered to be linear elastic, and the matrix viscoplastic behavior is described by the Bodner and Partom model. The overall composite behavior is assumed to be elastic-viscoplastic.
Two types of material systems are employed, namely, SCS-6/Ti-15-3 and SCS-6/Tiβ21-S. Both set of material systems exhibit isotropic and/or kinematic hardening under specific conditions of temperature and loading. The proposed methodology is validated with experimental and analytical results available in the literature. After the validation process, this methodology is applied to a 3-D finite element model of a [0/90]2s SCS-6/Tiβ21-S turbine blade tip. Aerodynamic and centrifugal loading are considered acting at the same time. The turbine blade tip inelastic strain field is presented.
Simulation of Deformation in Nial Single Crystals
Authors: Yang Chulho , Kumar Ashok V. 
Published: March 2022

Abstract
Deformation of NiAl single crystals during tensile testing was simulated using finite element analysis to investigate the modes of localized deformation. The effect of varying the loading direction with respect to lattice was studied to understand the deformation mechanism. Three-dimensional finite element models of tensile testing were created to study the effect of latent hardening when multiple slip systems are active. In particular, necking, neck diffusion and kink band formation were studied and the material and geometric characteristics that influence the deformation mode were investigated.
Vibration Control of Tubes With Internally Moving Loads Using Active Constrained Layer Damping
Authors: Ro J. , El-Din K. S. , Baz A. 
Published: March 2022

Abstract
The vibration of a flexible tube with internally moving load is controlled using patches of Active Constrained Layer Damping (ACLD) bonded to the tube surface. The damping characteristics of the tube/ACLD system are modeled by Golla-Hughes-McTavish (GHM) method in order to predict the tube response in the time domain. The transient response of tube/ACLD system is calculated using the finite element method. The predicted response is compared with that of a tube controlled with conventional Passive Constrained Layer Damping (PCLD) treatments. Such comparisons are essential in quantifying the individual contribution of the active and passive damping components to the overall damping characteristics of the system.
The predictions of the finite element model are validated experimentally using a cantilevered PVC plastic tube treated with an ACLD patch placed parallel to the tube longitudinal axis. The tube vibration due to an internally moving load is controlled by the ACLD patch using a simple velocity feedback controller. The effectiveness of the controller in damping out the tube vibration is determined experimentally and theoretically for different control gains. Close agreement is obtained between theory and experiments. The results obtained suggest the effectiveness of the ACLD treatment in controlling the vibration of precision pointing systems such as weapon systems.