UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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2004 - 20082

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Author: search.filters.author.Goswami, ArindamSubject: search.filters.subject.Engineering, Mechanical

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    Quantitative Hermeticity Assessment of Packages with Micro to Nano-liter Cavities
    (2008-10-07) Goswami, Arindam; Han, Bongtae; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Hermeticity is a measure of the "leak-proof ness" of packages with internal cavities and is critical for ensuring proper operation of the devices/circuits enclosed in them. The most widely used hermeticity detection technique in the industry is the helium fine leak test. The exiting conduction based governing equation is examined to investigate the volume dependant limits of the test when applied to metal sealed MEMS packages. The results clearly indicate that the test has limited applicability for small internal volumes (1 nanoliter - 1 microliter). The limited applicability of the guidelines specified in Method 1014.11 of the MIL-STD-883F document for hermeticity characterization is also characterized. To cope with these limitations, a regression analysis based procedure is developed and implemented to extract the true leak rate from the apparent leak data. While the apparent leak rate obtained directly from the He mass spectrometer changes with the test parameters, the true leak rate remains constant and this can be used as a metric to evaluate a package seal. The hermeticity of polymer sealed MEMS packages is also studied. Unlike metal sealed packages, gas transport in polymer sealed packages occurs via diffusion. A gas diffusion based model is proposed to study the hermetic behavior of these packages. An effective numerical scheme is developed to implement this model and simulate the change in cavity pressure as gas flows into or out of the cavity through the polymeric seal. An optical interferometry based leak test is developed to experimentally measure this change in cavity pressure. The experimental data is used to verify the validity of the proposed numerical scheme and the assumption of adiabatic boundary conditions made in the numerical model. An inverse method is presented to determine the two diffusion properties, diffusivity and solubility, of the polymeric seal by using the experimental data iteratively with the numerical data. The proposed method offers unique advantages over the routinely practiced/existing gas diffusion property measurement techniques.
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    IMPACT OF HARDWARE OBSOLESCENCE ON SYSTEM SOFTWARE FOR SUSTAINMENT-DOMINATED ELECTRONIC SYSTEMS
    (2004-05-04) Goswami, Arindam; Sandborn, Peter A.; Mechanical Engineering
    The last two decades have witnessed manufacturers of sustainment-dominated long field life electronic systems incorporate Commercial Off the Shelf (COTS) technology products into their systems on a large scale. Many of these products, however, have lifetimes of significantly shorter duration than the systems they are incorporated into and as a result become obsolete long before the system's intended duration of useful life is over. This problem is especially prevalent in avionics and military systems, where systems may encounter obsolescence problems even before they are fielded and always during their support life. Manufacturing that takes place over long periods of time exacerbates this problem. Many part obsolescence mitigation strategies exist including: lifetime buy, last-time buy, part replacement, aftermarket source, uprating, emulation, re-engineering, salvage, and ultimately redesign of the system. Design refresh (or redesign) has the advantage of treating multiple existing and anticipated obsolescence problems concurrently and additionally allows for functional upgrades. Hitherto, there have been studies concentrated on determining the optimum combination of different obsolescence strategies by using life cycle cost as the deciding criterion. However, these studies take into account only hardware life cycle costs. In many systems, such as avionics systems, software life cycle costs (redesign, rehosting and requalification) have a significant bearing on total life cycle cost. Thus software redesign due to part obsolescence triggered hardware redesign should also be addressed during life cycle management planning. This thesis describes a methodology and it's implementation for determining the hardware part obsolescence impact on life cycle sustainment costs for system software based on future production projections, maintenance requirements and part obsolescence forecasts. The methodology extends the MOCA (Mitigation of Obsolescence Cost Analysis) methodology/tool that determines the optimum design refresh plan during the field-support-life of the product in order to minimize life cycle cost. The design refresh plan consists of a set of design refresh activities and their respective calendar dates. The methodology incorporates the use of two software commercial cost analysis models: PRICE S and COCOMO. The methodology developed in this thesis has been validated using a Navy test case (VH-60N Digital Cockpit Upgrade Program). It has also been applied to Honeywell International, Inc.'s AS900 engine controller. The results obtained demonstrate the necessity of taking software redesign analysis into account during life cycle management planning.