Kent Lawrence

University of Texas at Arlington, Mechanical and Aerospace Engineering, Faculty Member

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Andrej Dujella

University of Zagreb

David Seamon

Kansas State University

KANNAN B T

SRM UNIVERSITY

Shan Gao

Shanxi University

Kiran Dasari

University of Illinois at Urbana-Champaign

Harijono Djojodihardjo

Institut Teknologi Bandung

Umit Unver

Yalova University

Sravankumar Kota

Institute Of Aeronautical Engineering

Adnan Awad

The University Of Jordan

Nasreen Kausar

Yildiz Technical University

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Papers by Kent Lawrence

Feasibility of non-linear analysis of the BEoL structure in a flip chip package under thermal shock

29th IEEE Semiconductor Thermal Measurement and Management Symposium, 2013

ABSTRACT Miniaturization and more recently convergence have been driving the industry since the i... more ABSTRACT Miniaturization and more recently convergence have been driving the industry since the invention of the transistor and integrated circuit (IC). Though the gate delay has decreased with transistor scaling, the increase in the resistive capacitive (RC) interconnect delay due to shrinking interconnect dimensions has become a serious concern for the development of future-generation electronics. To reduce the delay due to resistance R, a major technology change was the replacement of Aluminum (Al) with Copper (Cu) interconnect layers in the BEoL (Back-end-of-line). Recently, some investigators have suggested using low-k dielectric (having dielectric constant less than 4) instead of SiO2 (k= 3.9) to reduce the capacitive component in the RC delay. Low-k dielectric materials have characteristics such as low mechanical strength, hardness and adhesion, thereby making it imperative to characterize their thermo-mechanical response. Integration of Cu/low-k interconnects has become a critical reliability issue from the foundry&#39;s standpoint as well as package reliability. The thermo-mechanical stresses are induced inside the chip during various fabrication processes, field use, etc. The CTE mismatch between the various components leads to significant warpage and stresses in the metal/dielectric region of the die. In this study, a 3-D multi-level finite element (MLFE) approach has been used to examine the mechanical integrity of the Nano-scale inter-layer-dielectric (ILD) when the package is subjected to thermal shock. Since thickness of each layer in the metal/dielectric region is few orders of magnitude lower than that of the chip/substrate (at least 3 orders) it is almost impossible to analyze it at the global level. Therefore, sub-modeling technique has been leveraged to conduct a relatively accurate estimation of the mechanical behavior of the Cu/low-k region under thermal shock condition. A comparative analysis of the mechanical response of the Cu/low-k region i- done for 2 cases - 1) ILD taken as linear material (commonly used industry practice to save computational time) 2) temperature dependent non-linearity of the ILD is implemented and creep and plastic response is captured. The creep model was implemented to represent its realistic mechanical behavior. This study demonstrates the variation in the thermo-mechanical response between the 2 cases thereby addressing the importance of a non-linear analysis for such systems. The developed framework is further utilized to perform a parametric analysis for the number of BEoL layers and to study the effect of underfill properties on the structural integrity of the dielectric layers.

Optimum design of structures with multiple configurations with frequency and displacement constraints

31st Structures, Structural Dynamics and Materials Conference, 1990

ANSYS Workbench Tutorial

Fatigue Fracture of the Interlocking Nail in the Treatment of the Distal Part of the femoral Shaft Fractures

Journal of the Korean Society of Fractures, 1997

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ANSYS tutorial release 14

The eight lessons in this book introduce the reader to effective finite element problem solving b... more The eight lessons in this book introduce the reader to effective finite element problem solving by demonstrating the use of the comprehensive ANSYS FEM Release 14 software in a series of step-by-step tutorials. The tutorials are suitable for either professional or student use. The lessons discuss linear static response for problems involving truss, plane stress, plane strain, axisymmetric, solid, beam, and plate structural elements. Example problems in heat transfer, thermal stress, mesh creation and transferring models from CAD solid modelers to ANSYS are also included. The tutorials progress from simple to complex. Each lesson can be mastered in a short period of time, and Lessons 1 through 7 should all be completed to obtain a thorough understanding of basic ANSYS structural analysis. The concise treatment includes examples of truss, beam and shell elements completely for use with ANSYS APDL 14

ANSYS workbench tutorial release 14

The exercises in ANSYS Workbench Tutorial Release 14 introduce you to effective engineering probl... more The exercises in ANSYS Workbench Tutorial Release 14 introduce you to effective engineering problem solving through the use of this powerful modeling, simulation and optimization software suite. Topics that are covered include solid modeling, stress analysis, conduction/convection heat transfer, thermal stress, vibration, elastic buckling and geometric/material nonlinearities. It is designed for practicing and student engineers alike and is suitable for use with an organized course of instruction or for self-study. The compact presentation includes just over 100 end-of-chapter problems covering all aspects of the tutorials

An Algorithm for Reducing the Size of Finite Element Closed-Form Source Code Files

Volume 13: New Developments in Simulation Methods and Software for Engineering Applications; Safety Engineering, Risk Analysis and Reliability Methods; Transportation Systems, 2009

Closed-form solutions, as opposed to numerically integrated solutions, can now be obtained for ma... more Closed-form solutions, as opposed to numerically integrated solutions, can now be obtained for many problems in engineering. In the area of finite element analysis, researchers have been able to demonstrate the efficiency of closed-form solutions when compared to numerical integration for elements such as straight-sided triangular [1] and tetrahedral elements [2, 3]. With higher order elements, however, the length of the resulting expressions is excessive. When these expressions are to be implemented in finite element applications as source code files, large source code files can be generated, resulting in line length/ line continuation limit issues with the compiler. This paper discusses a simple algorithm for the reduction of large source code files in which duplicate terms are replaced through the use of an adaptive dictionary. The importance of this algorithm lies in its ability to produce manageable source code files that can be used to improve efficiency in the element generat...

Stress Concentration Factor in Sheet Metal with Permanent Plastic Deformation

55th AIAA/ASMe/ASCE/AHS/SC Structures, Structural Dynamics, and Materials Conference, 2014

Finite element simulation of bulk elastic waves in piezoceramic transducers using interdigital electrodes

SPIE Proceedings, 1995

Bulk waves can be created in a thin piezoelectric plate by applying an electrical signal to inter... more

Investigation of Morphable Wing Structures for Unmanned Aerial Vehicle Performance Augmentation

AIAA Infotech@Aerospace Conference, 2009

*† ‡ In this paper, we propose a mechanism to continuously morph a wing from a lower aspect ratio... more *† ‡ In this paper, we propose a mechanism to continuously morph a wing from a lower aspect ratio to higher and to further extremities of a gull-configuration and an inverted gull- configuration. The mechanism comprises of a linear actuator for the extension of the wing and the servo motors to obtain the gull and inverted gull configurations. The initial design and preliminary finite element representation using just beams and plates were the benchmarks to proceed for the detailed structural analysis of the complete wing. From these results the modified CAD model developed to compute the vibrational mode frequencies to avoid any resonance conditions due to the combined operation of the servo motors and the structure. The preliminary aerodynamic analysis includes using COTS tools, to obtain basic aerodynamic parameters such as the lift curve slope, drag polar and the pitching moment slope as functions of angle of attack at different Reynolds numbers. A morphable balsa wood wing assembly is being built and will be tested in the wind tunnel for moderate operating speeds scaled on the basis of operation of a small sized fixed wing unmanned aerial vehicle (UAV) at the Aerodynamics Research Center, University of Texas at Arlington. These tests include obtaining the forces and moments from a Pyramidal six-component force balance; which are in turn utilized to evaluate the co-efficient of lift, drag and pitching moment at various angles of attack.

Issues in Finite Element Modelling for Laminated Composites

Proceedings of the Tenth International Conference on Computational Structures Technology

Design for Stackability of Flash Memory Devices Based on Thermal Optimization

24th Digital Avionics Systems Conference

Convergence of computing and communications dictates building up rather than out. As consumers de... more Convergence of computing and communications dictates building up rather than out. As consumers demand more functions in their hand-held devices, the need for more memory in a limited space is increasing. Over the past few years, die stacking has emerged as a powerful tool for satisfying challenging IC packaging requirements. As stacked packaging evolves into taller stacks, what issues do

Light-Weight, Client-Side Engineering Computational Utilities

Proceedings of the Twelfth International Conference on Computational Structures Technology

Analytical/Finite-element modeling and experimental verification of spray-cooling process in steel

Metallurgical and Materials Transactions A, 1998

An atomizer is a helpful tool that can be used to tailor the cooling rate of steel from the proce... more An atomizer is a helpful tool that can be used to tailor the cooling rate of steel from the processing temperature in order to get desired properties. It is important to determine the temperature distribution in a specimen subjected to cooling by an atomized spray. A finite-element model for transient heat transfer and thermal-stress analysis is developed to determine the temperature and thermal-stress distribution. The results of the finite-element heat-transfer model are compared with a finite-difference model. The heat-transfer model describes the heat-transfer processes in an AISI 4140 steel cylinder subjected to controlled atomized spray cooling from an initial temperature of 1273 K. The temperature fields predicted by the model are used both to predict the resulting microstructure using continuous cooling transformation (CCT) diagrams and as an input for the thermal-stress model to predict the occurrence of quench cracks. The thermal-stress model incorporates temperature-dependent material properties, heat generation due to phase changes, elastoplastic behavior of steel, and the volumetric expansion associated with the formation of martensite. The results of the finite-element model are verified experimentally by recording temperature profiles, obtaining micrographs, and recording the occurrence of quench cracks. I. INTRODUCTION THE need for new materials has spurred innovation and research in metallurgical processing operations. In order to improve and optimize productivity and quality, industries such as forging, welding, casting, and heat treatment are adopting process-modeling techniques to reduce defects, scrap, design lead time, and cost. [1,2] In most forge shops, the forged parts are piled together and allowed to cool in air. This process is very slow and a large number of parts are produced before the first part is cooled down and taken for preliminary inspection. Moreover, the final product needs to be heat treated to meet the customer's specification. Therefore, if specific properties can be engineered by microstructural control of alloys during the forming process itself, it would lead to substantial economic savings. Accelerated cooling by quenching has been demonstrated as a possible method to get desired properties. [3-6] However, this method is limited to low-carbon and microalloyed steels because of the possibility of quench cracks in medium-and high-carbon and alloy steels. Microalloyed steels, by virtue of their low alloy content, are not very hardenable and do not pose a significant challenge. However, low-alloy steels contain larger amounts of alloying additions like Mo and Cr, which increase the hardenability of the steel and therefore increase the chances of quenchcrack formation. Furthermore, the quenching process does not facilitate the tailoring of cooling rates unless one uses a variety of quenching media and agitation. [7,8] Water spray cooling using jets of water was found useful R. THOMAS, Research and Development Engineer, is with Komag,

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Control Loads and Their Effects on Fuselage Vibrations

Journal of the American Helicopter Society, 1967

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Micromachined integrated pressure—thermal sensors on flexible substrates

Journal of Micromechanics and Microengineering, 2006

This paper presents the design, modeling and simulation of micromachined, integrated pressure-the... more This paper presents the design, modeling and simulation of micromachined, integrated pressure-thermal sensors on flexible polyimide substrates. Finite element simulations were performed with polycrystalline silicon as the piezoresistor material on a suspended Si3N4 layer. These piezoresistors are connected to each other in a half-bridge Wheatstone configuration using flexible aluminum interconnects. Several different designs of integrated thermal-pressure sensors as well as

Erratum: "Bending-Torsion Transfer Matrices Associated with Swept Surfaces

Journal of Aircraft, 1967

HE paper by Eugene H. Handler entitled "Tilt and vertical float aircraft for open ocean operation... more

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Design analysis of composite angle clips

Finite Elements in Analysis and Design, 1992

Attention is given to an analysis procedure for determining the maximum allowable beam pressure f... more Attention is given to an analysis procedure for determining the maximum allowable beam pressure for a composite angle clip in a beam-clip structural configuration. A quasi-isotropic laminate was used in this type. Three layups, (45 sub 10, 0 sub 10, -45 sub 10, 90 sub 10) sub s, (45, 0 -45, 90) sub 10s, and (45 sub 10, 90 sub 10, -45 sub 10, 0 sub 10) sub s, are used to study the effect of delamination and first ply failure strength. It is found that without any ply failure the (45, 0, -45, 90) sub 10s clip can sustain the highest beam pressure, and the (45 sub 10, 90 sub 10, -45 sub 10, 0 sub 10) sub s has the lowest allowable pressure among the three laminates. A critical location is identified in the composite angle clip. A modified Pagano-Pipes approximation method is used to evaluate the interlaminar normal stress at the critical location through the laminate thickness for all three layups. The (45, 0, -45, 90) sub 10s is found to be the least susceptible to delamination.

The effect of a symmetric discontinuity on adjacent material in a longitudinally vibrating uniform beam

Experimental Mechanics, 1987

free longitudinally vibrating uniform beam containing a symmetric discontinuity is presented. Bas... more free longitudinally vibrating uniform beam containing a symmetric discontinuity is presented. Based on this model, an analytical expression is developed which relates the length of the section containing the damage to the depth of the discontinuity. It thereby fixes the length of the element used to model this section of the beam. This expression was verified experimentally and shown to be material independent.

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Damage assessment based on the structural frequency-response function

Experimental Mechanics, 1988

A method is presented for determining both the amount and position of damage present in members w... more A method is presented for determining both the amount and position of damage present in members which can be modeled as longitudinally vibrating uniform beams. The method is valid for all boundary conditions, and for simplicity, is applied to the free-free case. It uses the shift in the natural frequencies of vibration, which are determined from the structural frequency-response function, caused by the damage present in the beam. These altered values of frequency are then utilized in a graphical solution technique which predicts the damage location directly and provides a parameter whose value is related to the magnitude of the damage present.

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Feasibility of non-linear analysis of the BEoL structure in a flip chip package under thermal shock

29th IEEE Semiconductor Thermal Measurement and Management Symposium, 2013

Optimum design of structures with multiple configurations with frequency and displacement constraints

31st Structures, Structural Dynamics and Materials Conference, 1990

ANSYS Workbench Tutorial

Fatigue Fracture of the Interlocking Nail in the Treatment of the Distal Part of the femoral Shaft Fractures

Journal of the Korean Society of Fractures, 1997

Download

ANSYS tutorial release 14

ANSYS workbench tutorial release 14

An Algorithm for Reducing the Size of Finite Element Closed-Form Source Code Files

Volume 13: New Developments in Simulation Methods and Software for Engineering Applications; Safety Engineering, Risk Analysis and Reliability Methods; Transportation Systems, 2009

Stress Concentration Factor in Sheet Metal with Permanent Plastic Deformation

55th AIAA/ASMe/ASCE/AHS/SC Structures, Structural Dynamics, and Materials Conference, 2014

Finite element simulation of bulk elastic waves in piezoceramic transducers using interdigital electrodes

SPIE Proceedings, 1995

Bulk waves can be created in a thin piezoelectric plate by applying an electrical signal to inter... more

Investigation of Morphable Wing Structures for Unmanned Aerial Vehicle Performance Augmentation

AIAA Infotech@Aerospace Conference, 2009

Issues in Finite Element Modelling for Laminated Composites

Proceedings of the Tenth International Conference on Computational Structures Technology

Design for Stackability of Flash Memory Devices Based on Thermal Optimization

24th Digital Avionics Systems Conference

Light-Weight, Client-Side Engineering Computational Utilities

Proceedings of the Twelfth International Conference on Computational Structures Technology

Analytical/Finite-element modeling and experimental verification of spray-cooling process in steel

Metallurgical and Materials Transactions A, 1998

Download

Control Loads and Their Effects on Fuselage Vibrations

Journal of the American Helicopter Society, 1967

Download

Micromachined integrated pressure—thermal sensors on flexible substrates

Journal of Micromechanics and Microengineering, 2006

Erratum: "Bending-Torsion Transfer Matrices Associated with Swept Surfaces

Journal of Aircraft, 1967

HE paper by Eugene H. Handler entitled "Tilt and vertical float aircraft for open ocean operation... more

Download

Design analysis of composite angle clips

Finite Elements in Analysis and Design, 1992

The effect of a symmetric discontinuity on adjacent material in a longitudinally vibrating uniform beam

Experimental Mechanics, 1987

Download

Damage assessment based on the structural frequency-response function

Experimental Mechanics, 1988

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