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Browsing by Author "Collins, Gustina B."

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    Design, Fabrication and Testing of Conformal, Localized Wafer-level Packaging for RF MEMS Devices
    Collins, Gustina B. (Virginia Tech, 2006-06-05)
    A low-cost, low-temperature packaging concept is proposed for localized sealing and control of the ambient of a device cavity appropriate for Radio-Frequency (RF) Micro- Electro-Mechanical (MEMS) devices, such as resonators and switches. These devices require application specific packaging to facilitate their integration, provide protection from the environment, and control interactions with other circuitry. In order to integrate these devices into standard integrated circuit (IC) process flows and minimize damage due to post-fabrication steps, packaging is performed at the wafer level. In this work Indium and Silver are used to seal a monolithic localized hermetic pack- age. The cavity protecting the device is formed using standard lithography-based processing techniques. Metal walls are built up from the substrate and encapsulated by a glass or silicon lid to create a monolithic micro-hermetic package surrounding a predefined RF microsystem. The bond for the seal is then formed by rapid alloying of Indium and Silver using a temperature greater than that of the melting point of Indium. This ensures that the seal formed can subsequently function at temperatures higher than the melting temperature of pure Indium. This method offers a low-temperature bonding technique with thermal robustness suitable for wafer-level process integration. The ultimate goal is to create a seal in a vacuum environment. In this dissertation, design trade-offs made in wafer-level packaging are explained using thermo-mechanical stress and electrical performance simulations. Prototype passive microwave circuits are packaged using the developed packaging process and the performance of the fabricated circuits before and after packaging is analyzed. The effect of the package on coplanar waveguide structures are characterized by measuring scattering parameters and models are developed as a design tool for wafer-level package integration. The small scale of the localized package is expected to provide greater reliability over conventional full chip packages.
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    Laser Processing of Polyimide on Copper
    Collins, Gustina B. (Virginia Tech, 2001-05-08)
    While work using a laser for processing a polymer dielectric is currently being studied, the purpose of this thesis is to present an effective and economical approach using laboratory equipment that is most commonly used and available for the processing of materials including polymers and metals. The use of a laser allows for a more cost effective and flexible method for processing polyimide over other wet and dry processes. This thesis represents the results of research on the laser processing of polyimide on copper. The research examines the effect of the laser processing parameters using a CO2 laser. The parameters examined include the pulse width, repetition rate, and number of pulses. The processed samples include freestanding Kapton with no adhesive layer, freestanding Kapton with an adhesive layer, and Kapton with adhesive layered on copper. The laser processing used a single laser shot with the parameters being varied over a series of shots fired. The effect of the parameters was observed over large and small ranges. The characteristics of processed freestanding samples were graphically presented along with captured images. The results demonstrate that the laser processing of polyimide is strongly dependent on the laser pulse width and that the optimum value from these experiments suggest the use of a pulse width of 60ms for using a CO2 laser. From these results, further considerations for the laser processing of polyimide on copper were given.