Encapsulants silicone

Of all the commercially available organic and inorganic polymeric materials, RTV silicone elastomer has proved to he one of the most effective encapsulants used for mechanical and moisture protection of the Integrated Circuitry (1C) devices. A general overview of the RTV silicone elastomer and its commercial preparation and cure mechanism are described. Improved electrical performance of the RTV silicone encapsulant, by immobilizing the contaminant ions, such as Na, K" , Cl , with the addition of the heterocyclic poly-ethers as the contaminant ion scavengers seems to have a potential application as the contaminant ionic migration preventor in the electronic applications. 

For incorporation of crown ethers and cryptates into the RTV encapsulant system as sodium and potassium ion scavengers, the total ionic contaminants must first precisely be determined. Atomic absorption is used to measure these ions in commercial silicone RTVs and silicone fluids. Values of "10 ppm for sodium and potassium were obtained in the best samples. Chloride level was determined by potentiometric titration of the silicone with AgN03. A quantity of ion trap (either crown ethers or cryptates) was then added to the RTV silicone encapsulant, and its molar concentration was equal to the combined sodium and potassium contaminant levels. 

Figure 5. Triple-track resistor electrical testing performance of crown ethers in commercial RTV silicon encapsulants. Conditions bias, 180 V relative humidity, 96% temperature, 100°C.

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

Fig. 9. Rheology of silicone encapsulants (a) good material (b) bad material. To convert Pa-s to P, multiply by 10. To convert Pa to dyn/cm2, multiply by...

There are several US military specifications on silicones that are worthy of mention a) Silicone Compound , MIL-S-8660B (Ref 6a) which specifies requirements for a moisture and corrosion sealing compd for shells and, b) Silicone, Encapsulant, Room Temperature Curing for Space Applications , MIL-S-83384 (USAF) (Ref 15)... 

Until recently, most silicone gels provided inadequate adhesion to coated or encapsulated parts. Modern silicone encapsulants and coatings contain, however, silane "coupling agents", which are able to form a permanent water proof covalent bond to most substrates and therefore avoid failure associated with loss of adhesion to the substrate. 

Figure 1. Effect of modifier concentration on modulus of resultant silicone encapsulant.

DC resistance and AC impedance measurements were made on a commercial silicone encapsulant on aluminum... 

Some specimen surfaces were "contaminated by design" by evaporating aqueous droplets of. 01 M CaCl solution. CaCl is an hygroscopic salt that readily forms aqueous vacuoles under the polysiloxane at ambient humidities above 29.3% RH (12). It is important to note that surface impurity levels in our experiments can be traced entirely to deliberate contamination, as noted above, or to inadequate surface cleaning prior to encapsulation. To the best of our knowledge, the Amicon silicone encapsulant was free of... 

To overcome the limited thermal stability of epoxies, silicone encapsulates have been used starting in the early 2000s. Silicone is a polymer that contains Si and O thereby resembling Si02 more so than epoxy resins. This resemblance sug-... 

The multicomponent products generally do not rely on moisture penetration for cure. Their chief attribute is fast cure in very deep sections. Thus many industrial production lines that demand fast cure use a two-component sealant (including the use of silicone encapsulants for electrical components). Cure of these two-part systems can be accelerated further by additional catalyst or exposure to elevated temperatures. 

Fig. 3.4. Focus assembly for television monitor in which a hybrid circuit is encapsulated by a self-priming two-component silicone encapsulant.

Silicone encapsulants should continue to be recognised for their benefits of easy application, fire resistance and low toxicity. They are likely to play an important role in such applications as high-voltage cascades and automotive electronic modules. 

Davis, J., Protection of automotive electronic components and modules by silicone encapsulants. Proceedings of International Symposium on Automotive Technology and Automation, Stockholm, 1981. 

A new silicone encapsulant for the solar industry is available that can enable flexible thin-film modules to be laminated cost effectively using roll-to-roll processing. Marketed under the trade name ELASTOSIL Solar 2200, this new product is transparent, pourable and non-corrosive. It vulcanizes rapidly at elevated temperature and reportedly features outstanding adhesive properties. In its cured state, it can provide all types of thin-film solar cells with effective long-term protection from chemical and mechanical stresses. Web www.wacker.com... 

Polymeric encapsulation has largely displaced techniques of hermetically sealing electronic devices, due to the low cost and ease of production. However, since all polymers are permeable to some small extent to water vapour, problems of adequate protection do still occur. Interestingly, it is not the inherent permeation of water into the polymer which alone causes these problems. Rather, they arise from the presence of trace amounts of catalyst residues in the polymer, which are transported to the surface of the device by the permeating water and which there result in the formation of an aggressive electrolyte solution. This problem is of particular concern with epoxide resins and of lesser concern with silicone encapsulants. 

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