Document Type

Thesis - University Access Only

Award Date

1997

Degree Name

Master of Engineering (ME)

Department / School

Electrical Engineering

Abstract

The increased use of thin film polymers in microelectronic applications has resulted in the need to better understand their chemical, thermal, mechanical and electrical properties. Of particular interest are changes in mass and viscoelasticity during curing of new high temperature polymers. Due to the limitations of existing test methods, a highly sensitive technique that can monitor mass and viscoelastic changes in thin polymer films during curing is needed. The objective of this work was to develop and test a surface acoustic wave (SAW) based system for studying the gravimetric and thermo-mechanical properties of polyimide and polyimidesiloxane thin films up to 400 °C. A secondary goal was to develop a thick film heater for controlling the temperature of the SAW sensor. Critical technical issues in this work were: the development of methods for electrical connections to the SAW sensor and thick film heater which can withstand the high operating temperatures; development of a nitrogen purged chamber to contain the heater and sensor; and the ability to separate temperature and viscoelastic effects in the SAW response from those of mass changes. The theoretical effects of mass and viscoelastic changes of acoustically thin and thick polymer films on SAW velocity and attenuation were also examined. An etched foil heater that operated at temperatures up to 500 °C was used for most of the tests. Connectors were successfully attached to the thick film heaters using a brazing process from Dupont which had a maximum operating temperature of 320 °C. A heater fabricated on bare alumina failed at 250 °C due to cracking of the substrate while a heater fabricated on a direct bond copper substrate operated to 425 °C. Gold ball bonding provided electrical connections to the SAW sensor that were used up to 400 °C. The system developed in this work was capable of measuring the mass loss due to water outgassing during cure thin polymer films to 2 % of total polymer mass in a temperature range of 20 to 400 °C. It could also measure the apparent glass transition temperature of acoustically thin films, and film resonance for acoustically thick films. The principle limitations of the system are the limited accuracy of temperature compensation and the ability to separate mass loss effects from viscoelastic effects. This system can provide a powerful technique for thin polymer film analysis but the user must have a clear understanding of polymer properties and the system limitations.

Library of Congress Subject Headings

Acoustic surface wave devices

Thin films

Polymers

Format

application/pdf

Number of Pages

158

Publisher

South Dakota State University

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