Biegel, Paul Eric

A Framework for Decision Support in Concurrent Product Development

Concurrent product development involves techniques to help manage the simultaneous design process. A fundamental challenge of concurrent product development is how decisions can be supported by providing current, and complete yet succinct design evaluations. One approach involves a decision support framework consisting of a "design attribute hierarchy" (an ordered structure of all design attributes and sub-attributes for a product), and a "design object hierarchy" (a structure of all hardware components in a product). some issues of framework development have, however, remained and include: guidelines to determine the design attributes essential to product superiority; guidelines to assist design attribute hierarchy assembly; enhancements to ensure that attribute mappings alert high-level decision makers of design failures; specific rules to prevent erroneous mapping; a theory to develop the design object hierarchy structure; and methods to merge the design object and design attribute hierarchies. This thesis addresses these issues and explores solutions. to demonstrate how the solutions to these issues contribute to the framework's implementation, an example product that is part of a submarine weapon system is considered.

Braunberg, Gregory C. (M.S. Mechanical Engineering)

Computer Aided Infrared Thermography Using Emissivity Compensated Imaging

Infrared thermography is a full field, non-contact temperature measurement technique. The measurement of radiant energy emitted from a substance provides the basis for infrared thermography. In order to utilize infrared thermography consideration must be given to the emissive properties of the target object and to the uncertainties associated with the measurement. This paper develops a methodology for emissivity compensated infrared thermography to obtain true temperature measurements. In addition, the measurement uncertainty in the temperature measurement is developed along with guidelines for its application.

Ko, Wing Fu (M.S. Mechanical Engineering)

A Systems Engineering Approach to Design a Smart Tool Post Structure

Precision machining has received more and more industry-wide attention as dimensional accuracy becomes a significant measure of quality in a product. the key in achieving today's quality requirement is, therefore, precision of a machine tool. Since the invention of the first CNC machine tool in the 1960s, machine tool research has entered an almost stagnant stage. There are numerous reasons for the slow progress, and the lack of system-wide studies of the machine tool performance is one of them.

The research presented in this thesis focused on improving machining accuracy using a systems engineering approach. A conventional lathe during machining is taken under consideration as a machining system. The tool post is identified as a critical component in the machining system to achieve the defined machining accuracy. Smart material made actuators are used to design a new tool post structure that is capable of carrying out an active vibration control during machining.

In this thesis research, the fabrication of the designed tool post is completed. results obtained from the initial test strongly demonstrate its capability to attenuate tool vibration during machining in an active and intelligent way. Thus, the smart tool post system fulfills the design objective of achieving microscopic level machining precision on a low cost conventional machine tool platform. Suggestion on the actuator specifications are made for further improvement on vibration compensation.

Naqvi, Syed Ali Naved

Transient Thermal Stress Analysis of Plated Through Holes Subjected to Wave Soldering

The manufacture of a printed wiring board (PWB) assembly involves attaching components onto the board often using wave soldering processes. Because the PWB assembly is exposed to temperatures during wave soldering which are higher than any related operating temperature, understanding the heat transfer and potential damage mechanisms which arise during the wave soldering process is critical to quality control and reliability. In particular, cracks may be initiated during the wave soldering transient depending on the manufacturing quality of the plated through holes. Theses cracks may be arrested or masked due to the presence of solder and become manifest after operational cycling.

This paper presents a study of the heat transfer mechanisms, stresses and deformations which occur during wave soldering. a transient non-linear thermal stress analysis was conducted to study the heat transfer and potential damage mechanisms which arise during the wave soldering process. Two different kinds of models, three dimensional orthotropic and axisymmetric orthotropic are used and the results compared. Temperature an stress/strain history curves are examined to determine the impact of wave soldering operation on the fatigue life of plated through holes. the effect of factors such as the presence of innerplanes in a PWB assembly on the maximum stresses and strains developed in the PTH is investigated.

Osterman, Michael (Ph.D. Mechanical Engineering)

Placement Methods for Electronic Components on Printed Wiring Boards Based on Reliability and Routability Measures

The placement of electronic components on a printed wiring board (PWB) is a complex problem which requires tradeoffs between several goals. Traditionally, placement techniques have focused on improving routability based on minimizing the total wire length between interconnected components. However, electronic card assembly (ECA) reliability, which is measured in terms of time to failure, cycles to failure, or the hazard rates of the individual components, the interconnections, and the PWB, is also affected by component placement.

The reliability of an ECA is a function of the design, manufacture, assembly, environmental conditions, and stresses which include humidity, vibration, shock, and temperature. The temperature dependent failure of an ECA can generally be described by functions of component junction or case temperatures, threshold temperatures, temperature changes, temperature gradients, and/or temperature histories.

In this thesis, the placement problem will include reliability and routability. The placement of components for reliability will be explored based on physics of failure based on temperature failure dependency of components. Placement procedures are developed so as to minimize the total hazard rate of the components on a PWB cooled by either convection or conduction cooling technologies. Finally, a placement procedure is developed to combine placement for reliability and routability.

This effort is intended to expand the range of knowledge in electronic layout by allowing for upfront consideration of both reliability and routability. In addition, the development and verification of the mathematical theory and tools necessary for combined placement is a innovative and necessary step in remaining competitive in electronic system design.

Reinhart, Hugh Steven (M.S. Mechanical Engineering)

Automated Maintanability (M) Modeling and Analysis

This thesis examines a set of computerized techniques which can be used during the system design process to predict and utilize maintainability (M) system parameters associated with repair times, manpower requirements, and false alarm rates. Included is a description of a software module which uses statistical techniques to quantify various aspects of maintainability. The module provides the ability to create user specific elemental task databases which can be used to compile knowledge of maintenance times gained through experience with similar systems already in operation.

Hierarchical modeling techniques make it possible for M parameters to be calculated for the entire system, or any level of a subsystem without reentering the failure mode and repair data. This encourages modular design and improves the finished product by speeding the design process, allowing the analysis of more design options, and providing estimates of the operational behavior of the finished system.

Roza, Scott A. (M.S. Mechanical Engineering)

Vibrational Modeling of Wedge-lock Edge Guides

The accurate determination of the natural frequency of a printed wiring board (PWB) in its working environment is an essential part of its design. The natural frequency is critical in determining the amount of vibrational fatigue damage the board and its components will sustain.

The greatest variable in determining the natural frequency of PWBs is the type of support provided by the edge guide connectors. Traditionally, the classical types of support (free, simple, or clamped) are assumed to exist at the edges. In reality, edge guides are of a construction that limits translation and rotation but cannot completely eliminate either. Therefore, the actual natural frequency of a PWB will fall somewhere between the values calculated for simple support and clamped support.

This thesis focuses on how commonly used wedge-lock edge guides perform and affect the natural frequency of a PWB. In particular, the wedge-lock edge guides were modeled as being rigid in translation but elastic in rotation. Since the edge guides are assumed to be elastic in rotation, they can be further modeled as rotational springs with an unknown spring constant. Vibrational testing was performed on a variety of edge guides manufactured by Calmark Corporation. The analyses of the edge guide test data with a finite element program allowed the calculation of corresponding rotational spring constants (K_r). Values for K_r were then integrated into plots to produce "look-up" tables to determine K_r in any environment. This research is critical to the accurate modeling and design of PWB natural frequency.

Sharif, Irfan (M.S. Mechanical Engineering)

Effect of Dimensional Variabilities on Lead Compliance and Solder Joint Fatigue Life

Lead compliance is a critical paramenter 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 for computation of lead stiffness and prediction of fatigue life of the leaded surface mount components has been developed. Three dimensional finite element analyses are performed to obtain 12x12 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 for 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.

She, Jieyu (M.S. Mechanical Engineering)

A New Algorithm for Evaluating Complex System Reliability

An algorithm has been developed to evaluate the terminal pair reliability for complex systems. the minimal path set concept is extended to all non-target nodes, and a new concept of subpath is proposed. A subpath is a part of a path which is disjoint to the rest of the path. Subpath intersections are eventually used in path intersections. By means of a disjoint branch set technique, the partial disjoint features of subpaths are used to reduce the number of path intersections in the calculation of the system reliability. An efficient algorithm is obtained to calculate the terminal pair reliability for the directed and the undirected networks.

Vodzak, John (M.S. Mechanical Engineering)

Coupled Thermal and Vibrational Fatigue Analysis of Solder Joints for Surface Mounted Components

The combined effects of elastic and plastic strains on solder joint reliability are investigated. The dependence of fatigue life on strain amplitude is found to obey the classical generalized Coffin-Manson relationship in available experimental data. The commonly adopted approaches of relating only plastic strains to fatigue life or the total strain to fatigue life with a single power law relationship are shown to be inadequate when predicting solder joint reliability. Instead, both elastic strains and plastic strains should be considered independently, especially when the electronic assembly is subjected to a combination of large amplitude thermal loads and relatively lower amplitude vibrational loads.

A methodology is presented to evaluate the combined effects of simultaneous vibrational and thermal cycling of solder joints. The damage from the two load-types are superposed to assess the overall effective fatigue reliability of a solder joint. As a first order approximation, linear superposition rules such as Miner's rule are utilized. Reliability predictions from this simple model are compared to thermal low cycle fatigue models for three simple combined loading problems.

A simple first order mechanical model is developed to determine solder joint strains, by considering PWB deflections that are produced by vibration. The model determines solder joint strain as a function of the local radii of curvature in the PWB. Solder joint strain levels predicted by the mechanical model are shown to have amplitudes which will cause appreciable fatigue damage when compared to thermal fatigue damage.

Watts, Jonathon David (M.S. Mechanical Engineering)

Placement for Producibility and Assembly

Design for producibility describes a method by which products are designed to be compatible with the most capable manufacturing processed, equipment, and production practices available. As such, this paper develops a methodology for placing microelectronic components on mixed technology printed wiring boards as a function of the ratio of surface mounted to plated through-hole components, the component package styles used, the number of sides of the printed wiring board to be populated, and the abilities of the production equipment to be employed. Within this methodology, a procedure for selecting a global board-level assembly process plan is discussed and an automated routine for determining microelectronic component placement positions and orientations on populated and semi-populated mixed technology printed wiring boards is demonstrated. In addition, a procedure which compares the printed wiring board area required to accommodate the components with globally defined or component specific inter-component space requirements against the available printed wiring board area is described. Finally, an automated routine for generating the microelectronic component layout with acceptable inter-component spacings utilizing a force directed placement technique is proposed.