Encapsulants electronic devices

Wong, C. P., "Encapsulated Electronic Devices Having Improved Silicone Encapsulant", 0. S. Patent 4,271,425, June 2, 1981. 

These molding compounds were also used to encapsulate electronic devices for reliability testing. In Figures 4, 5, and 6, stable bromine CEN outperformed "state-of-the-art" resins in the bias pressure cooker device test (BPC), high temperature storage device test (HTS), and the highly accelerated stress test (HAST). 

U.K. Patent Application GB 2087 1S9A. Plastic Encapsulated Electronic Devices. 

Permeability. Blon elastomer has much less diffusion of silicon oil and water than silicon rubber under the same testing conditions (ASTM D814). Comparative permeation rates are listed on Table VI. Applications demanding low permeable materials Include Implantation of encapsulated electronic devices and silicon oll-fllled breast prostheses. 

Polyurethanes available for electronic components include Baydur CSP from Bayer which is claimed to offer high dimensional accuracy and the ability to provide complex geometries, variable wall thicknesses and excellent surface reproduction when moulded. PU and epoxy resin potting compounds are used to encapsulate electronic devices and their components to give them enhanced mechanical and electrical stability as well as providing protection from moisture, thermal or physical shock and vibration. 

Thermosetting-encapsulation compounds, based on epoxy resins (qv) or, in some niche appHcations, organosiHcon polymers, are widely used to encase electronic devices. Polyurethanes, polyimides, and polyesters are used to encase modules and hybrids intended for use under low temperature, low humidity conditions. Modified polyimides have the advantages of thermal and moisture stabiHty, low coefficients of thermal expansion, and high material purity. Thermoplastics are rarely used for PEMs, because they are low in purity, requHe unacceptably high temperature and pressure processing conditions. 

A broad variety of structural polymers is nowadays available that are suitable for applications as different as carbon fiber reinforced materials, encapsulation of electronic devices or adhesive bonding. Each of these polymers belongs to one of two classes thermosets or thermoplastics. 

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. 

Leakage. By far the majority of implanted electronic devices fail due to mechanisms of the second type (i.e. leakage). In a poorly encapsulated implant, this failure mode can cause rapid deterioration in a matter of days, hours, or even minutes. As the size of the implant designs are reduced, the risk of this type of failure is greatly Increased because due to the small dimensions involved, the time for fluid entry into the package becomes very short. 

Thin films (qv) of vitreous silica have been used extensively in semiconductor technology. These serve as insulating layers between conductor stripes and a semiconductor surface in integrated circuits, and as a surface passivation material in planar diodes, transistors, and injection lasers. They are also used for diffusion masking, as etchant surfaces, and for encapsulation and protection of completed electronic devices. Thin films serve an important function in multilayer conductor insulation technology where a variety of conducting paths are deposited in overlay patterns and insulating layers are required for separation. 

Encapsulants -for electronic devices [EMBEDDING] (Vol 9) -m electronic packaging [PACKAGING - ELECTRONIC MATERIALS] (Vol 17)... 

Single-walled carbon nanotubes are known to possess extraordinary strength.138 Mechanical properties of BN nanotubes would be worthy of exploration. Unlike carbon nanotubes, BN nanotubes are predicted to have stable insulating properties independent of their structure and morphology. Thus, BN tubes can be used as nano-insulating devices for encapsulating conducting materials like metallic wires. Filled BN nanotubes are expected to be useful in nanoscale electronic devices and for the preparation of nano-structured ceramics. 

Metallofullerenes will also become an important nanostructured material for future nanoscale electronic devices, because the band gaps of endohedral metallofullerenes, for example, can be varied between 1.0 and 0.2 eV depending on the fullerene size, the kind of metal atom(s) as well as the number of metal atoms encapsulated. 

The protection of electronic devices has been a key application for specialty silicones, and this application continues to keep pace with the rate of device development (5). Silicones are used in various ways, ranging from resinous circuit board coatings to encapsulants, with the silicone gels representing a unique solution to a diflScult problem, stress relief These dielectric gels are prepared by hydrosilation and are lightly cross-linked poly(dimethylsiloxane)s. Their modulus is extremely low, but they are elastic in their behavior. They have the stress-relief characteristic of a liquid but the nonflow property of an elastomer. These jellylike materials maintain their physical profile over the broad temperature range of-80 to 200 °C. 

Glass films are used in the semiconductor industry because of their dielectric properties, and are used for encapsulating integrated circuits and other electronic devices because they provide a hermetic seal. Glass films are formed by both reactive and non reactive deposition methods, (e.g., evaporation, sputtering, and ion implantation or ion platting for the latter). 

This class of condensation polymers is characteristically recognized by cross-linking from the reactions of epoxide groups. The products are useful as one of the best adhesives for cementing of rigid materials, and as potting compounds for physical protection or encapsulation of electronic devices. 

Typical transfer molding compositions for encapsulation of electronic devices are mixtures of an epoxy novolac resin, a phenolic resin hardener, a catalyst, large amounts of inorganic filler (e.g., Si02) flame-retardant ingredients, internal lubricants, carbon black, and sometimes other additives such as getters to trap ionic impurities (34,35), corrosion-protection materials, and stress-relief ingredients. 

The purpose of encapsulation is to protect electronic IC devices and prolong their reliability. Moisture, mobile ions, (eg., sodium, potassium, chloride, fluorides), UV-VIS and alpha particle radiation, and hostile environmental conditions are some of the possible causes of degradation or interaction which could negatively affect device performance or lifetime. Silicon dioxide, silicon nitride and silicon-oxy-nitride, commonly used as passivation layers have excellent moisture and mobile ion barrier properties and are, therefore, excellent encapsulants for devices. As for the... 

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