| Created: 10/19/99 |
Argento, Christopher W. (M.S. Mechanical Engineering)
Forced Convection Air Cooling of a Commercial Electronic Chassis: Experiments and Computations
The primary objective of the present study is to examine the suitability of commercial software for system level electronic packaging design. For the study a commercial-off-the-shelf (COTS) electronics, fully-populated, 20-slot, VMEbus chassis was used. The study consisted of an initial experimental phase followed by detailed computational studies. The experimental program involved thermocouple measurements of component surface temperatures at several locations and pressure drops measurements across selected regions for total operating power levels of 423 to 846 W for volumetric flow rates between 0.05 and 0.14 m3/s. Computational models of the experiment were created using FLOTHERM software and analyzed for recorded test conditions. Modeling techniques and experimental measurements are discussed and comparisons with computational predictions are provided.
Bhagath, Shrikar (M.S. Mechanical Engineering)
Mechano-Stochastic Modeling of Connector Reliability
This thesis presents the development of an initial, "first-cut", mathematical model for the prediction of electrical interface reliability trends. The model pertains to gold plated contacts subject to loss of normal force and environmental corrosion with time. Stress relaxation over time and temperature in the base metal of the contact is accounted for. Utilizing the results of Mixed Flowing Gas (MFG) tests, the model can be used to estimate the statistical contact resistance at a particular load (normal force), aging and operating temperature in the class II and III environments. An attempt is made to correlate experimental data with the classical Holm's equation and to introduce time dependence into the equation. Wear in the gold plated contact finishes is also modeled.
Evans, Jillian (M.S. Mechanical Engineering)
Qualification and Quality Assurance of 3-D Technology
This work presents a comparison study of three dimensional (3-D) packaging and interconnection technology. the study identifies four generic types of 3-D technology currently available and overviews the materials, fabrication and assembly processes used for each type. The data are tabulated for easy comparison. In addition, the reliability aspects of 3-D technology were explored. Potential failure mechanisms, and the critical stresses which may activate these failure mechanisms, are discussed. Quality assurance practices and methods of rework are also reviewed. Existing reliability test data is discussed and additional tests, based on the identified failure mechanisms, are recommended.
Gohari, Kamran (M.S. Mechanical Engineering)
Effect of Temperature and Humidity Cycling on FR-4, BT and CE Printed Wiring Boards
An experimental investigation was conducted to study any degradation characteristics of Flame retardant (FR-4), Bis- maleimide (BT) and Cyanate Ester (CE) printed wiring board materials subject to four cycling experiments: 25 to 85øC temperature cycling, 25 to 150øC temperature cycling, 25 to 200øC temperature cycling, and a combined temperature and humidity cycling test of 25 to 85øC with 20% to 85% relative humidity. Environmental scanning electron microscope photography was used to study degradation effects. Resin/fiber interface debonding was observed in these studies. Debonding occurred primarily on the edges of the fiber-glass bundles. Explanations involve the moisture sorption of epoxy, the coefficient of thermal expansion mismatch between the epoxy-resin and glass-fiber, and the geometry of glass- fiber bundles.
Hwang, Ten-ken (Ph.D. Materials and Nuclear Engineering)
Monte Carlo Reliability Model for Monolithic Microwave Integrated circuits (MMICs)
In order to predict and assess the reliability of MMICs, a new reliability model has been developed which includes the interactions among individual devices, components and subsystems. The failure rates of the MMIC components are set to be more realistic as time- dependent rather than time-invariant. A methodology is developed to simulate the reliability of MMIC systems which are indicative of a general interactive multi-stage system. Correlated (dependent) relations among MMIC components have been estimated through circuit analysis by SPICE. Thereafter, the Monte Carlo techniques were applied in order to develop the model and two types of MMIC circuits based on existing experimental data were examined in order to validate the model.
The MMIC Monte Carlo reliability simulation for both dependent (modified by a weighing factor) and independent (based on Mil-HDBK method) for TIA, EG-6101 LNA, EG-6010 LNA and EG-6203 power amplifier based on discrete component data have been performed. The results indicate that the estimation of MMICs' life including interactions between FETs is much closer to experimental data than the estimation without taking into account the interactions. Therefore, the MMIC can be applied MMIC reliability prediction and more closely predicts the results obtained by testing the full MMIC circuit. The computer simulation program has been developed for MMIC reliability prediction. Techniques for obtaining correlations within MMICs to be used in reliability prediction are also presented.
Kuo, Jong-Shyang (M.S. Mechanical Engineering)
Temperature Dependent Performance Simulation and Failure Mechanisms of Heterostructure Field Effect Transistors and Inverter Circuits
In order to investigate high temperature characteristics of the heterostructure field-effect transistor (HFET), a model for the temperature dependence of current-voltage characteristics of HFET is developed. More complicated functional elements are often designed as simple extensions to the basic inverter. Therefore, the temperature dependence of forward-transfer characteristics of two different HFET-based inverters are analyzed by the developed temperature dependent model and AIM-SPICE. Finally, the primary failure mechanisms and failure modes of the HFET are described. The current-voltage characteristic collapses caused by the failure mechanisms, such as AlGaAs/GaAs interdiffusion and gate degradation, are simulated with the developed temperature dependent model.
Lall, Pradeep (Ph.D. Mechanical Engineerin)
The Influence of Temperature on Microelectronic Device Failures
Steady state temperature plays a major role in the design, reliability assessment, stress screening, and derating of microelectronic devices. The device reliability is presently modeled by an arrhenius which predicts that the device reliability decreases exponentially with increase in steady state temperature. State of art reliability modeling criteria cannot be used to assess the temperature sensitivity of device design, forcing use of temperature reduction as a major reliability improvement measure. In this dissertation the temperature dependence of microelectronic device failures and electrical parameter variation have been evaluated in the temperature range of -55 to 125øC. Investigations on temperature dependencies have been used to derive design specific thermal derating guidelines to evaluate the operating limits of temperature and non-temperature stresses. Derating guidelines will enable the evaluation of reliability improvement achieved by varying the operating temperature and non-temperature operating stresses, and allow the design team to explore cost- effective options by derating other stresses, rather than always choosing steady-state temperature, which often has the penalty of added cost and weight.
Mathieu, Barry (M.S. Mechanical Engineering)
Stress Analysis of Glass Lead Seals Under General Mechanical Loading
In many metallic electronic packages, glass-to-Metal leadseals complete the hermetic seal, mechanically support the leads, and electrically insulate the leads from the conductive metal package. Fracture of the glass seals may result in moisture ingress to the package and may potentially decrease the load carrying capacity of the glass seal. Fracture is initiated by loading applied either through the leads or package. Loads applied through the lead occur during, handling, testing, mechanical vibration, and thermal excursions. Examples of loading through the package occur during pressure leak testing and handling. This study investigates stresses in lead seals resulting from loads applied through the lead only. Loads considered are axial tension, bending, and twisting of the lead. Superposition techniques can be used for general loading. The stresses are determined using finite element simulations of the individual loading conditions. The analysis reveals the sensitivity of the magnitude of the seal stress to seal, lead, and package geometry. Dimensions of the lead, package wall thickness, lead pitch, and radius of the hole in the package for the lead seal are considered. In addition, response analysis is used to formulate pseudo closed form equations to relate the maximum principal stress to the type of loading and geometry. The accuracy of the proposed closed-form equations are verified through analysis of residuals. This study also provides novel applications of designing of experiment techniques in multi-parameter simulation studies.
Ramappan, Vijay (M.S. Mechanical Engineering)
A Numerical Simulation of Selected Manufacturing Variabilities in Plated Through Holes
Plated holes (PTH) failures are typically due to thermo-mechanical stresses caused during manufacturing (solder reflow), screening, and operation. The magnitude of these stresses are influenced significantly by the presence of manufacturing defects, such as plating irregularities and resin smears, leading to premature wearout failure in the field. The quality of the PTH is defined as the extent of manufacturing variabilities in its geometry and material properties, that influences the design-life. Quality is dependent on consistent and repeatable techniques for drilling, cleaning (including etchback), and metallizing the hole. The critical defects addressed are the de-adhesion or the hole-wall pull-away of the copper barrel in the PTH from the dielectric material and plating nodules or plating offsets in the barrel. The associated failure mechanism is the buckling of the copper barrel during the cooling down cycle after solder reflow, when large compressive and bending strains can be generated on the copper barrel. The stresses and strains due to buckling in the PTH are analyzed using a non-linear, elastic-plastic finite element analysis. The stress-strain hysteresis during the temperature cycling is tracked and the strain range is computed. The strain history is then used to calculate the fatigue life using the Coffin-Manson model incorporating the effects of residual stresses. It is then established that the plating offsets are the primary causes for the PTH barrel to buckle and the effects of variation of this critical defect on the fatigue life is studied using design of experiments. A closed form relationship between the critical manufacturing parameter - plating offset, the PTH geometry and the fatigue life is developed through analysis of the factor effects and residuals.
Wu, Xin (Ph.D. Mechanical Engineering)
An Experimental Study of Polyimide Films Used in High Density Interconnects
The study investigated the mechanical and thermomechanical behaviors of polyimide films used in high density interconnects under various conditions and produced experimental results that can be used in the finite element simulation for the interconnect. These objectives were accomplished by: