Parylene-PDMS Bilayer Coatings for Microelectronic and MEMS Packaging
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0968-V07-07
Parylene-PDMS Bilayer Coatings for Microelectronic and MEMS Packaging Hyungsuk Lee and Junghyun Cho Mechanical Engineering, SUNY at Binghamton, Vestal Pkwy East, Binghamton, NY, 139026000 ABSTRACT Current microelectronic devices and microelectromechanical systems (MEMS) require that packaging costs be reduced with more enhanced device performance. In addition, the packaging materials are often exposed to harsh environments, for which their performance is drastically degraded. Importantly, such devices become lighter and smaller, precluding the use of conventional packaging materials and schemes. Given that, surface coatings can provide an alternative solution for some of the aforementioned issues. Polydimethylsiloxane (PDMS) is a good candidate material in many encapsulating applications but its surface must be effectively protected due to its poor surface properties. In this study, the PDMS surface is coated with the parylene-C film through a vapor-phase deposition. Proper surface modification of PDMS is then essential to generate desirable interfacial adhesion and performance between the parylene-C and the PDMS. Effects of plasma treatment were examined in this study to evaluate their effectiveness on the surface modification of the PDMS. In order to explore mechanical performances of the bilayer coatings, dynamic nanoindentation and feedback-control nanoindentation testings were employed. In addition, extensive surface characterizations are performed with atomic force microscope (AFM) and optical microscope (OM). INTRODUCTION PDMS, the room-temperature vulcanized (RTV) silicone-based elastomers, is one of the most effective encapsulants used for temperature cycling and moisture protection of electronic devices [1, 2]. It is easy to fabricate, inexpensive, transparent and biocompatible. In particular, by using a PDMS solution of low viscosity, conformal coating is achievable at the surface of the device with complex geometries. But the surface mechanical properties are weak and chemical/ mechanical performance are not yet satisfactory for use in harsh environments [3]. Parylene-C has shown a great promise as a conformal coating onto any geometrical shape of the surface even with holes and cracks. Parylene-C coatings also have a low permeability to moisture and gases such as nitrogen, oxygen, and carbon dioxide. There are several different types of parylenes available; namely, type C, N, D and F that have been considered in many commercial applications such as dielectric films and encapsulation of semiconductor devices [4]. Among those candidates, parylene-C coating has a lower gas permeability and diffusivity than the others [5]. This good barrier characteristic of parylene-C is attributed to the polarity of the chlorine atom attached to the phenyl ring, which increases the intermolecular forces. In addition, parylene-C is very ductile so that the conformality can be better than the other types [6]. It has, however, shown poor adhesion and a difficulty in growing thick coatings. We therefore explore p
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