UV curable silicones

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. 

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. 

Typical Physical Properties of UV Curable Silicone for Integrated Circuit Protection... 

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

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

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

Dworak, D. P. Soucek, M. D., Effect of Mixed Sol-Gel Precursors on the Metal-Oxo Phase Within a UV-Curable Silicone Hybrid Material. Macromol. Chem. Phys. 2006, 207,1230-1232. 

Ostreich, S., UV-curable silicones (pp. 397-403), Proc. RadTech Europe, Basle, 2001. 

Takahashi, M Irifune, S. and Ohba, T Development of EB/UV curable silicone-aaylate for release coatings (pp. 564-567), Proc. RadTech Asia, Yokohama, 1997. 

A facile preparation of acrylate terminated silicones by the condensation reaction between the readily available silanol terminated silicone fluids and acryloxymethyldimethylacryloxysilane is described. The simplicity of the reaction provides a practical route for the preparation of UV curable silicones. The surprising ease of the reaction between the silane and silanol is attributed to the possible hypervalent silicon transition state even though Si-NMR evidence suggests the silane is tetracovalent. 

Scheme 2. Shin-Etsu s preparation of UV curable silicones with multiple acrylate...

Ostreich S. UV-curable silicones. In Proceedings of the RadTech Europe. Basle 2001 397-403. 

Takahashi M, Irifune S, Ohba T. Development of EB/UV curable silicone-acrylate for release coatings. In Proceedings of the RadTech Asia. Yokohama 1997 564—567. 

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