Evaluation and Characterization of Reliable Non-Hermetic Conformal Coatings for Microelectromechanical System (MEMS) Device Encapsulation

©2000 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.The thrust of this project was to evaluate commercial conformal encapsulation candidates for low cost aerospace applications. The candidate conformal coatings evaluated in this study included silicone elastomers, epoxies, and Parylenes with bi-layer or tri-layer designs. Properties characterized in this study included mobile ion permeation and moisture ingress resistance, interfacial adhesion variation through thermal shock cycling and 85 C/85% RH aging. Surface Insulation Resistance (SIR), Triple Track Resistance (TTR) and die shear strength were used for the corresponding electrical and physical property characterizations. Parylene F displayed excellent properties for environmental protection. Silicone elastomers displayed less resistance to the harsh environment as compared to the Parylene family (N, C, D types), but it could provide advantages for low residual stress applications. The change in adhesion strength between Parylene C and silicone elastomers after exposure to thermal shock cycling or 85 C/85%RH aging for different time periods were conducted from die shear test in terms of the interfacial failure. SIR values of all the candidate materials after 1000 h exposure to 85 C/85%RH, with 100V dc for resistance measurement, range from 1 108–1 109. Leakage current values after 1000 h exposure to 85 C/85%RH, 175 V bias, are in the range of 10 9 to 10 11 Amp. The bi- or tri-layer conformal coating combination investigated in this study showed significant promise for encapsulation of the microelectromechanical system (MEMS) devices