Microelectronics, humidity protection

The protection of microelectronics from the effects of humidity and corrosive environments presents especially demanding requirements on protective coatings and encapsulants. Silicone polymers, epoxies, and imide resins are among the materials that have been used for the encapsulation of microelectronics. The physiological environment to which implanted medical electronic devices are exposed poses an especially challenging protection problem. In this volume, Troyk et al. outline the demands placed on such systems in medical applications, and discuss the properties of a variety of silicone-based encapsulants. 

The original intent of this project was to identify and/or perfect vendor-supplied, state-of-the-art hydro-phobic polymer sealants, such that the end product could meet military criteria for hermeticity in hybrid microelectronic devices. Solubility and diffusivity constants and permeabilities for several types of hydrophobic polymers were determined. Data from the laboratory and theory from literature both indicate that moisture impermeable polymers are not attainable, at least to meet military standards. The project objective was then redirected towards finding a means of passivating the surface of a microelectronic device against moisture. It was found that interface modification, i.e., passivation of the chemically reactive surface species, provides significant protection in high temperature and humidity environments. Plasma polymerization of hexamethyIdi-silazane (HMDS) afforded phenomenal protection to moisture sensitive thin film nichrome resistors even under the most severe test conditions. 

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