Room temperature vulcanized encapsulants

Improved Room-Temperature Vulcanized (RTV) Silicone Elastomers as Integrated Circuit (IC) Encapsulants... 

This structure has superior water-resistant properties in comparison to conventional polyols used for PU synthesis. Room temperature cures are easily obtained with typical urethane catalysts. Short chain diols, fillers and plasticizers may also be used in their formulations in order to vary physical properties. Formulations usually with NCO/OH ratio of 1.05 are used for this purpose. Such urethanes are reported to be flexible down to about -70 °C. HTPB is regarded as a work horse binder for composite propellants and PBXs. HTPB also successfully competes with widely used room temperature vulcanizing (RTV) silicones and special epoxy resins for the encapsulation of electronic components. HTPB-based PUs are superior in this respect as epoxy resins change their mechanical properties widely with temperature. 

These are typically represented by the chemical structure shown in Fig. 12.1. This structure has superior water-resistant properties to that of the conventional polyols used in polyurethane synthesis and it successfully competes with both them and room temperature vulcanizing (RTV) silicones on this basis, especially as the principal application market is the encapsulation of electronic components. Epoxy resins, widely used for encapsulation, change their mechanical properties widely with temperature and hydroxy-terminated polybutadiene-based urethanes are superior in this respect. 

RTV silicone elastomer, an organosiloxane, is one of the most effective encapsulants used for temperature cycling and moisture protection of IC devices. Since World War II, silicones (organosiloxane polymers) have been used in a variety of applications where properties of high thermal stability, hydrophobicity, and low dielectric constant are necessary, e.g., as encapsulants or conformal coatings for integrated circuits. In 1969 it was demonstrated that room temperature vulcanized (RTV) silicones exhibited excellent performance as moisture protection barriers for IC devices and a number of different RTV silicone have been adapted For use in the elec-tronics industry... 

The major use of silicone elastomers is in aircraft where high and low temperature properties and electrical insulation characteristics are utilized, e.g., gaskets, sealing strips, ducting and cable insulation. Liquid room-temperature vulcanizing silicone elastomers are used for the encapsulation of electronic and electrical equipment. 

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