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School of Materials Science and Engineering

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Author: Pike, Randy T. × Author: Wong, C. P. × Author: Wu, Jiali × Item Type: Publication ×

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Now showing 1 - 3 of 3
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    Evaluation and Characterization of Reliable Non-Hermetic Conformal Coatings for Microelectromechanical System (MEMS) Device Encapsulation
    (Georgia Institute of Technology, 2000-11) Wong, C. P. ; Wu, Jiali ; Pike, Randy T. ; Kim, Namsoo P. ; Tanielian, Minas H.
    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.
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    Novel Bi-Layer Conformal Coating for Reliability Without Hermeticity MEMS Encapsulation
    (Georgia Institute of Technology, 1999-07) Wong, C. P. ; Wu, Jiali ; Pike, Randy T.
    A flexible, smooth, and low profile conformal coating was developed to accomplish the encapsulation of a microelectromechanical system (MEMS) device that will be applied to sense the static pressure on aircraft during real flight testing. The encapsulant should be able to protect the MEMS device and the multichip module (MCM) from adverse environmental conditions, i.e., mechanical shock, temperature fluctuation, engine fuel and oil contamination, and moisture/mobile ion permeation. Presently, conventional packaging schemes for electronics cannot satisfy this specific outdoor application, and a new encapsulation combination has been designed in accord with the requirement of reliability without hermeticity (RWOH). A bi-layer structure was selected because of property limitations of a single material. Pliable elastomeric silicones, are typically flexible, water repellant, and abrasion resistant. The silicone encapsulant will be first applied to planarize the MEMS surface and function as durable dielectric insulation, stress-relief, and shock/vibration absorbers over a wide humidity/temperature range. To compensate for the deficiency of silicone on engine fuel/oil contamination, Parylene C is to be deposited afterward. This bi-layer coating can achieve excellent bulk properties, such as moisture and mobile ion barrier resistance, chemical compatibility, and electrical insulation characteristics. However, the poor adhesion of Parylene C to silicone greatly restricts its application. To address this problem, silane coupling agents were used as an adhesion promoter. Significant adhesion im provement was achieved by placing an interlayer silane coupling agent to provide interfacial bonding to the silicone elastomeric surface and the Parylene C film. Furthermore, a possible mechanism of adhesion enhancement will also be presented in this study. Index Terms— Bi-layer conformal coating, micro-electromechanical system (MEMS), multichip module, Parylene C, reliability without hermeticity (RWOH), silane coupling agent, silicone elastomer.
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    Use of Compliant Adhesives in the Large Area Processing of MCM-D Substrates
    (Georgia Institute of Technology, 1998-10) Wong, C. P. ; Wu, Jiali ; Pike, Randy T.
    Large area substrate processing is a key solution for improving the productivity of multichip module deposition (MCM-D) technology. This project is focused on high temperature polymeric adhesives for attachment of silicon tiles to suitable pallets to facilitate large area film processing of MCM structures. Current polymeric high temperature adhesives are predominately polyimide-based that are not reworkable, which places an obstacle to remove the coated substrates and to reuse the high cost pallets. However, an approach will be presented in this paper to address this demand by introducing thermally cleavable links in the thermoset polyimide-amide resin. A series of novel reworkable high temperature (in excess of 350–400 ℃) adhesives have been developed, that can meet the requirements of adhesion, viscosity, thermal stability, and reworkability of the MCM-D production. Furthermore, scanning electron microscopy (SEM) microstructure images are presented for intuitive reworkability analysis.