Development of Conformal PDMS and Parylene Coatings for Microelectronics and MEMS Packaging

There is a growing demand in the development of small-scale devices in microelectronics and microelectromechanical systems (MEMS). Packaging and reliability of such devices are of great concern as they introduce a number of unique packaging issues that are distinct and different from typical electronic packaging applications. In addition, the packaging or encapsulation 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 protective coatings can provide an innovative solution for some of the aforementioned issues. Polymers have indeed shown such a potential for use either as a standalone coating, or an intermediate layer for the subsequent harder, stiffer coatings. In this study, we explore processes and properties of the three coating systems: i) PDMS, ii) Parylene (para-xylylene), iii) Parylene/PDMS. In particular, parylene coating on PDMS is a focus of this study. The parylene coating having much higher mechanical properties than PDMS provided a way to enhance the surface properties of this PDMS. Proper surface modification of PDMS via oxygen plasma seemed to be essential to generate desirable microstructures of parylene coating. Mechanical properties of such coatings are systematically examined via a nanoindenter. The dynamic nanoindentation is also employed to assess viscoelastic properties, as well as depth-dependent mechanical properties. While characterizing the films using the nanoindentation, the substrate effect influenced the indentation data. In addition, extensive surface characterizations are carried out using atomic force microscope (AFM), scanning electron microscope (SEM), and optical microscopy.Copyright © 2005 by ASME