Created: 10/19/99

CALCE EPSC Graduate Student Theses (1992)

Agarwal, Rakesh K. (Ph.D. Mechanical Engineering)

Prediction of Thermal, Dielectric and Thermo-Mechanical Properties of Woven-Fabric Composites for PWB Substrate Materials

In this study, analytical models are developed to predict the effective orthotropic constitutive properties of plain-weave fabric-reinforced composite laminates. A homogenization scheme is applied to formulate a boundary value problem (BVP) in a unit-cell exploiting the two-scale asymptotic behavior of the laminate due to the periodic repeat pattern in the construction of the woven fabric. Laminate effective thermal conductivity, complex dielectric permittivity and coefficient of thermal expansion are obtained by solving the formulated BVP both analytically and numerically, as functions of constituent material properties, fiber volume fraction, and weave style. The analytically predicted effective properties are compared with values obtained from fully three dimensional finite element simulations, with predictions from existing models in the literature and with experimentally determined values. Performance maps indicating the interactions among the properties are presented for various material systems.

Arora, Ajay K. (M.S. Mechanical Engineering)

Design Guidelines for Lid Seals and Lids of Hermetic Microelectronic Packages

This work presents physics of failure based guidelines for hermetic lid/lid seal design. Potential failure mechanisms of lids and lid seals are identified as overstress failures including excessive lid deflection, lid fracture and seal fracture; and wearout failures including fatigue of seal under temperature cycling and vibration loads, and corrosion of the lid and seal. Models for the identified failure mechanisms are presented. All the above information is utilized to present complete guidelines for the design of lid seals including methodology for selection of appropriate lid sealing process, selection of lid and seal materials, and determination of seal/lid geometry and dimensions. The recommended qualification and quality assurance procedures are also outlined.

Balakrishnan, Sudha (M.S. Mechanical Engineering)

A Concurrent Approach to Printed Wiring Board Assembly Design

This thesis presents an integrated approach for the concurrent design and analysis of printed wiring board assemblies. The fundamental assembly design processes of component selection, component placement and board architecture selection is extended to address the issues of reliability, producibility, testability, maintainability and life cycle costs concurrently with design for functionality. A design flow chart identifies the various design steps, enumerates the relevant concurrent issues at each step, describes the nature of analysis to be performed, and shows feedback loops to facilitate optimization of the design parameters. Design inputs required for a concurrent approach are also discussed.

Bhandarkar, Sarvotham M. (Navin) (Ph.D. Mechanical Engineering)

Thermomechanical Analysis and Fatigue Life Prediction of Multilayer PWB PTHs

Thermomechanical analyses are performed to investigate fatigue failures of PTHs in rigid organic multilayered boards subjected to temperature cycling. The relative severities of several geometric and material parameters on critical stresses in the PTH are investigated through linear parametric studies. Nonlinear analyses of stress and strain through finite element methods (FEM) are used to predict the fatigue lives of PTHs. The numerical results compare well with experimental data. This dissertation also includes thermomechanical constitutive characterization of fabric-reinforced composite boards. Orthotropic effective thermomechanical properties, variation of properties with fiber volume fraction, and nonlinear behavior due to matrix nonlinearity /progressive damage in the transverse yarn are studied. Characterization of unidirectional yarn bundles that constitute the fabric weave is performed through a Mori-Tanaka scheme. The scheme can address imperfect and damaged interfaces, radial variations in interphase properties and multiple coatings on fibers.

Bonadies, Gary (M.S. Mechanical Engineering)

A Computer Integrated Product Development Environment: An Implementation of Concurrent Engineering for the Conceptual Design of Electronic Systems

With the knowledge that global competition requires the reduction of the product development cycle time and a lowered product cost, the implementation of concurrent engineering into the daily workings of all product developments becomes more necessary than ever. The acceptance that the majority of a product's life cycle cost is determined during the conceptual design stage emphasizes the importance of the development and implementation of concurrent engineering methodologies into the conceptual design stage of product development. The Computer Integrated Product Development Environment (CIPDE) supports the implementation of concurrent engineering into the conceptual design process. CIPDE incorporates a methodology as well as an integrating framework with services which provides unambiguous product information to all disciplines simultaneously. The environment links the product information to requirements, design intent, and implementation plans. CIPDE's unique architecture is a combination of a multilayered and a horizontal/vertical implementation. The layered approach of CIPDE allows for the optimization of the environment by providing for the integration of existing frameworks or tools. The management and facilitation of the conceptual design process within a concurrent engineering environment is addressed by the modular software environment developed. The modular software framework accomplishes the conceptual design by administration of the framework and module activities, and the management of the information and the design process. An example is provided to illustrate the conceptual design process operating within CIPDE. Several recommendations are made regarding the future work required to continue the implementation of concurrent engineering into the conceptual design process.

Chen, Yeong-Shu (Ph.D. Mechanical Engineering)

Predicting the Vibration Fatigue Lives of Electronic Components Mounted on a Printed Wiring Board

This dissertation discusses an algorithm for predicting the vibration fatigue lives of electronic components mounted on a printed wiring board (PWB) during the system design stage. The algorithm is based on accurately modeling the PWB's boundary supports so that the natural frequencies and mode shapes can be determined. The PWB's deflection and it's radius of curvature can then be calculated for the prescribed random vibration loading condition. The attach deflections and attach or solder joint stresses are then obtained by applying a force equilibrium on a component mounted on the PWB. Basquins high cycle fatigue relation is then used to determined the fatigue life. The presented method can be easily implemented on a personal computer or low end workstation as a design tool. In order to more accurately model a PWB's boundary conditions, an experimental program was conducted to evaluate the restraint offered by commonly used wedge lock card guides. A simple analytical solution to approximate the attach deflection from the local radius of curvature of the PWB is derived. For simplifying the description of the deformed PWB geometry, some basic assumptions are made. The effects of these assumptions are studied by comparing the results with the finite element analysis solutions. The correction factor for current algorithm is then obtained.

Harris, David (M.S. Mechanical Engineering)

Fuzz Button Design Variation and Performance Effects

The contact resistance as a function of deflection and load were experimentally determined for Beryllium/Copper (BeCu) and Molybdenum (Mo) fuzz button contacts, as a function of wire diameter, button diameter, and button density. Wire diameters of 0.001 and 0.002 inches and fuzz button diameters of 0.020 and 0.040 inches for the BeCu buttons were tested. The 0.001 inch wire diameter manufactured in a 0.020 diameter Mo fuzz button was the only configuration available in this metal system. For the BeCu and Mo buttons, 20 and 25% density buttons were tested. The research showed that for both metal systems the maximum observed deflection of the fuzz buttons varies between 0.010 and 0.020 inches at loads of 100-200 grams with contact resistances of less than 0.020 Omega. Specific values for each button contact configuration are presented in the form of design guidelines for applications in solderless electronic modules.

Johnson, Scott David (M.S. Mechanical Engineering)

Experimental Determination of Mechanical Properties of Single Crystal Gallium Arsenide (GaAs) Wafers

Mechanical properties of single crystal electronics grade Gallium Arsenide (GaAs) wafer material were experimentally determined. Both bare unprocessed GaAs wafers and processed metallized GaAs wafers were tested. Modulus of Elasticity, Modulus of Rupture, and opening Mode Fracture Toughness data were collected for various crystal orientations and over various temperatures. Finally, a finite element analysis model of the metallized GaAs wafer configuration was created to study the distribution of stresses induced by mechanical flexural loading. Modified configurations were then modeled for comparison with the original configuration. Variations in GaAs substrate and back side metallization thicknesses were studied to identify configurations with stresses lower than those found in the specimens tested in this study.

Lawton, Douglas (M.S. Mechanical Engineering )

Interface Heat Transfer and Wedgelock Assemblies

This thesis investigates interface heat transfer and the factors that influence the mechanism of transferring heat between two surfaces in contact. This thesis compares empirical results for interface joint thermal conductance with predicted performance utilizing a more practical contact conductance correlation. The empirical data contained in this thesis indicates that measured values for the thermal joint conductance are 4 to 5 times lower than values predicted with the more practical contact conductance correlation. This thesis also challenges the assumption commonly made for most conductance correlations that the two surfaces in contact are nominally flat. Interface heat transfer is significantly influenced by flatness, while most contact conductance correlations neglect the influence of flatness. This thesis also investigated the performance of devices called wedgelocks, which are mechanical clamps that provide the pressure needed to promote interface heat transfer on conduction cooled electronic modules. The results indicate that the greater the number of segments in the wedgelock assembly, the higher the clamping force for a given screw torgue and the more even the distribution of the clamping force. In addition, the effect that wedgelock surface finish has on performance was investigated in this thesis. The results indicate that, while the surface finish impacts the clamping force generated by the wedgelock, there is less than a 5øC improvement in interface temperature rise, for a module dissipating 100 Watts, between the candidate wedgelock finishes evaluated.

Mofid, Nabil (M.S. Mechanical Engineering)

Transient Thermal Stress Analysis of Surface Mounted MLC Capacitors Subjected to Wave Soldering

Due to the demands for smaller component size, higher component density, increased use of automation, and lower manufacturing costs, the usage of surface mount components has increased dramatically in recent years. Cracking of MLC capacitors during the wave soldering operation due to thermal stresses caused by differential stress inside the capacitor, different amount of temperature along the length and height, is a major problem. This paper presents a transient thermal stress analysis of MLC capacitors subjected to wave soldering process. A two-dimensional analysis is used and temperature and stress /strain curves will be examined to determine the impact of wave soldering on MLC capacitor crack.

Pusarla, Chandrasekhar (Ph.D. Mechanical Engineering)

Design Guidelines for Flip-Chip Bonding for Hermetic Microelectronic Packages

This thesis work involves the development of design guidelines for flip-chip bonded interconnects. The study identifies all the potential failure mechanisms associated with flip-chip bonds and then presents models to assess their effects on the reliability. These failure mechanisms are governed by the materials, geometries, manufacturing and assembly processes, power cycles and usage environments. A physics of failure approach is then employed to realize complete design guidelines (including material selection criteria and geometry design rules), which can meet the functional requirements and prevent potential failure mechanisms.

Verma, Shailendra (M.S. Mechanical Engineering)

Screening Guidelines for Electronics at the Assembly Level

Screening is a process to detect or precipitate defects in devices to reduce field failures. The thesis develops a general methodology of the screening process to not only eliminate defective devices but also use the process as a design development tool. It is required that a specific screen be developed for a specific failure site and mechanism to realize an effective screen. In this thesis screens are developed for solder joints by studying its physics of failure. The manufacturing defects are identified and modeled to calculated the stresses required to precipitate the defective solder joint.

Zhang, Zhan (M.S. Mechanical Engineering)

Project Planning and Scheduling in a Concurrent Engineering Environment

A project planning and scheduling methodology is developed to bring the engineering change process into the planning stage of a product. This methodology is aimed at bringing all the product development activities into consideration at the project planning stage itself in order to execute the engineering changes and improve quality. The inherent problems of sequential design are eliminated by incorporating producibility analysis, reliability analysis, and maintainability analysis into the planning phase. The study develops a standard monitoring node system, project planning, and scheduling methodology. The standard monitoring node system is developed to design quality into the product by Taguchi methods. In order to ensure that engineering changes are considered in the planning phase, the standard monitoring nodes are distributed to the product development process through aggregate planning. The planning method discussed in the research provides a way to reach the work load driven planning in a concurrent engineering environment. A dynamic scheduling is developed to determine when to apply the resources and to estimate the completion times of the design activities precisely.

Zhu, Lily Hui (M.S. Electrical Engineering)

High Temperature Modeling and Thermal Character istics of GaAs Mesfets on Diamond Heat Sinks

Based on the ZTC bias point theory developed for MOSFET, the existence of ZTC bias point is verified for GaAs MESFETs in the present research, and the theoretical location of the ZTC bias point has been determined. The maximum drain current and transconductance points are found, and their relationship to the ZCT bias point is discussed. A second contribution of this research is the study of the high temperature behavior of GaAs MESFETs with diamond heat sinks. The thermal resistance of this device structure is measured by infrared microscopy. The peak junction temperature has been identified in this research by both experimental measurements and computer aided thermal analysis. This work represents the first verification of experimentally determined ZTC bias points with a device physics temperature dependent FET model.