Radiation-curing siloxanes

TABLE 16. Functional siloxane radiation cure systems... 

SiHcone mbber has a three-dimensional network stmcture caused by cross-linking of polydimethyl siloxane chains. Three reaction types are predominantiy employed for the formation of siHcone networks (155) peroxide-induced free-radical processes, hydrosdylation addition cure, and condensation cure. SiHcones have also been cross-linked using radiation to produce free radicals or to induce photoinitiated reactions. 

Typical physical properties obtainable with UV cured silicones are provided In Table I. Incorporation of reactive unsaturation into the silicone polymer backbone In combination with a photosensitization system provided the photocure capability. Properties of a standard heat-cured encapsulant developed for use on semiconductor devices, Dow Corning HIPEC R-6103, are provided for comparative purposes. Clearly, introduction of a photocrosslinking mechanism into a siloxane type composition has afforded the desired result. The one-part, solventless, UV curable silicone composition cured rapidly upon exposure to UV radiation, providing a cured composition which has retained the typical properties that make silicones so attractive for protection of semiconductor devices. 

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