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Pressure-volume-temperature and wave propagation studies of polyimide films
This dissertation presents an investigation of the mechanical, thermal, and physical properties of polyimide coatings and films. In the electronics industry, polyimide coatings are commonly found as dielectric interlayers for high density multi-chip modules. As a film, polyimides are used as flexible printed circuit boards. Therefore, complete understanding of their properties can be important for material selection and reliability prediction. In addition, better comprehension of their processing can aid in improving the properties of the polyimides. Orthotropic linear elasticity theory has been used to characterize several thin polyimides including novel fluorinated polyimides. Using a commercially available Pressure-Volume-Temperature (PVT) Apparatus, the bulk compressibility and volumetric thermal expansion of the polyimides were measured. In combination with other techniques such as vibrational holographic interferometry, high pressure gas dilatometry, tensile testing, and thermomechanical analyzer, the out-of-plane Young's Modulus and out-of-plane coefficient of thermal expansion were determined. As a result, knowledge of the in-plane and out-of-plane elasticity coefficients and coefficients of thermal expansion can help in designing finite element models that predict the reliability of complex microelectronic devices. Similar characterization studies were done on poly(ethylene terephthalate) and bisphenol A polycarbonate. From the initial PVT experiments on polyimides, irreversible densification was observed for some thermally cured polyimide films which were subjected to high pressures and temperatures. Using optical microscopy, wide-angle x-ray diffraction, and density measurements, studies were done to probe the changes associated with this densification behavior. The findings suggest that polyimides used as dielectric interlayers in multi-chip modules may crystallize under highly constrained situations and high temperatures. Tenter frame processing is typically used to produce highly oriented polymer films. However, past studies have revealed that better quality polyimide films may be achieved by controlling its stress state during the tentering process. Therefore, the mathematics are detailed for measuring the complete state of stress in a polyimide film using wave propagation theory. Preliminary experimental research has involved a laboratory scale setup consisting of a means for inducing wavefront propagation, non-contact fiber-optic displacement sensors for detecting the wavefront, and an oscilloscope and computer for collecting and interpreting data.
Chen, Michael John, "Pressure-volume-temperature and wave propagation studies of polyimide films" (1998). Doctoral Dissertations Available from Proquest. AAI9823725.