Curable silicones

Yamamoto and Minamizaki [159] disclose the use of a curable silicone based release agent blended with resin particles which swell or are soluble in organic solvent. Coatings made with such blends can be written on with solvent based inks. For example, an addition cure silicone network containing 20 wt% 0.1 p,m diameter PMMA particles exhibited both good writeability (no ink dewetting and smear free) and a low release force of 10 g/cm for a PSA tape. 

Stein, J. and Eckberg, R.P., UV Curable silicone release coatings and controlled release additives. J. Coat. Fabr., 20, 24 (1990). 

Ghu, H. K. UV Curable Silicones From Acryloxymethyldimethylacryloxysilane. In Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Eds. ACS Symposium Series 729 American Chemical Society Washington, DC, 2000 pp 170-179. 

Keohan FL, Lewis LN (1985) Heat curable silicone polyimide rubber compositions containing cyclometallized platinum phosphite compounds. US Patent 4634610 A... 

Arkles BC (1983) Thermoplastic-curable silicone blends. US Patent 4500688... 

Itoh K, Fukuda T (1978) Thermally curable silicone rubber compositions. US Patent 4164491... 

Arkles BC (1987) Manufacture of curable silicone semi-interpenetrating networks. US Patent 4714739... 

R. P. Eckberg, "Chemistry and Technology of Radiation Curable Silicone Release Coatings," in D. Satas, ed.,. Advances in Pressure Sensitive Adhesives, Satas Associates, Warwick, R.I., 1992. 

Ultraviolet-Curable Silicones for Integrated-Circuit Protection... 

The new UV curable silicones afford an attractive alternative to standard heat activated materials for integrated circuit protection where high speed automated fabrication and assembly processes are desired. Additionally, the photosensitivity of these materials present other convenient processing opportunities. 

UV curable silicones are not new.(8-9) The most common functionalities incorporated into the system to allow photocrosslinking are thiol/ene, oxirane, or reactive unsaturation such as acrylate. However, the thiol functionality is corrosive to substrates of interest for integrated circuit applications. Additionally, the resultant sulfide crosslink has a limited thermal... 

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. 

Variation of structural and compositional parameters allow modification of the physical properties to tailor performance to specific application needs. For example, the effect of ingredients added to control the modulus of two UV curable silicone polymers is presented in Figure 1. Both Polymer A and Polymer B were polydiorganosiloxanes which contained terminal reactive unsaturation. Admixture with a photosensitization system and subsequent cure afforded soft, elastomeric products. Modifier A was incorporated into Polymer A to soften the system further. As the concentration of Modifier A increased, the modulus decreased, and the resultant composition became more gel-like. In a contrary fashion, Modifier C was added to Polymer B to provide reinforcement. As the concentration of Modifier C was increased, the modulus of the resultant cured film increased, the elongation decreased, and the tensile strength went through a maximum. 

Figure 2. Modulus of UV curable silicone vs irradiation dose.

Figure 4. Photopattern process for wafer stage applied UV curable silicone coating.

Synthesis of Silicone Monomers and Intermediates. Another important reaction for the formation of Si—C bonds, in addition to the direct process and the Grignard reaction, is hydrosilylation (eq. 3), which is used for the formation of monomers for producing a wide range of oiganomodified silicones and for cross-linking silicone polymers (8,52—58). Formation of ether and ester bonds at silicon is important for the manufacture of curable silicone materials. Alcoholysis of the Si—Cl bond (eq. 4) is a method for forming sflyl ethers. HC1 removal is typically accomplished by the addition of tertiary amines or by using NaOR in place of R OH to form NaCL... 

Among the most successful of the new radiation-curable silicone coating systems are compositions Incorporating cycloaliphatic epoxyfunctional silicone polymers with compatible iodonlum salt photocatalysts (1 - S ) The syntheses, structures, UV cure response, and other properties of these materials and some of their derivatives and monomeric homologs are discussed In the balance of this chapter. Their specific application for release coatings has been described In great detail elsewhere (5.6 > and Is not the subject of this paper. 

Ganter, B., BoBhammer, Irmer, U. UV-curable silicone rabbca open up new fields. InL Polym. Sci. Technol. 40, 1-4 (2013)... 

F. Dong, S. Diao, D. Ma, S. Zhang, S. Peng, Preparation and characterization of 3-chlo-ropropyl polysiloxane-based heat-curable silicone rubber using polyamidoamine den-drimers as cross-linkers. Reactive and Pimctional Polymers, ISSN 1381-5148 96 (November 2015) 14—20. http //dx.doi.Org/10.1016/j.reactfimctpolym.2015.09.005. 

---