Obtaining accurate measurements of mechanical properties at cryogenic temperatures, especially near liquid helium temperatures, can be difficult to obtain experimentally. A range of polymer materials are used in devices that would require those materials to be exposed to these extreme cryogenic temperatures. Therefore, it is important to predict how these materials will behave at these temperatures. The research presented here suggests parameterized mathematical fits to predict different mechanical properties (creep compliance and modulus) for three core polymers of dielectric laminate films and an epoxy underfill to temperatures approaching 4 Kelvin. The thermoplastic polymers used were etched from Ultralam 3850HT (a liquid crystal polymer or LCP), Pyralux AP 8525R (a polyimide), and Pyralux TK185018R (a laminate of polyimide and Teflon). Vespel SP-1 was used for validation of the polyimide fit. MasterBond EP29LPSP is a thermoset epoxy often used for underfill in computer chip packaging. Three fitting methods were featured including time-temperature superposition (an Arrhenius method), a cubic fit and a sigmoidal fit. All of these materials were experimentally tested using dynamic mechanical analysis from room temperature to about 130K, and the fits projected that behavior to 4K. Anisotropy was supported for the LCP, presumably because the crystallites exhibited some degree of orientation, by data for the modulus, but not the creep compliance data. This would indicate that modulus is more sensitive to crystallite orientation. The epoxy modulus did not plateau as expected, and this was attributed to low temperature movement of the methyl groups in a bisphenol A component, which if the transition was broad might not appear as an abrupt change in modulus but rather a continuous drift upwards. In summary, the fitting equations reported here can be used to predict properties at 4K for such polymers and aide in device design for devices operated in a liquid helium or similar extreme cold environment.
|Advisor:||Stretz, Holly A.|
|Commitee:||Johnson, Wayne, Padmanabhan, Venkat, Rice, Cynthia, Wilson, Chris|
|School:||Tennessee Technological University|
|School Location:||United States -- Tennessee|
|Source:||DAI-B 82/2(E), Dissertation Abstracts International|
|Subjects:||Chemical engineering, Polymer chemistry, Materials science|
|Keywords:||Cryogenic, Mechanical properties, Polymer chemistry, Time-temperature superposition|
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