Designing low permeability, optical-grade silicone systems: guidelines for choosing a silicone based on transmission rates for barrier applications

Michelle Velderrain

doi:10.1117/12.910642

6 February 2012 Designing low permeability, optical-grade silicone systems: guidelines for choosing a silicone based on transmission rates for barrier applications

Michelle Velderrain

Author Affiliations +

Proceedings Volume 8280, Advances in Display Technologies II; 82800O (2012) https://doi.org/10.1117/12.910642
Event: SPIE OPTO, 2012, San Francisco, California, United States

Abstract

Unprotected electronic components exposed to moisture from high humidity may fail due to corrosion of metal leads or other unfavorable reactions on chemically sensitive components. This is of high interest for silicones that encapsulate Light Emitting Diodes (LEDs) dies. For these applications, moisture and oxygen may react with materials, such as phosphor, used to make white LEDs for back-lighting applications and decrease or change the light output and color over time. Of the polymeric adhesives and sealants commercially available, silicones are used for their thermal stability, clarity, and comparably low modulus that provides stress relief during thermal cycling. In addition, silicones are also known to be very permeable to low molecular weight gases such as water vapor and oxygen. Recently, several types of silicones were tested for the oxygen and water vapor transmission rates, and it was found that they can have drastically different results. Silicone properties strongly affecting permeability are polymer backbone chemistry, crosslink density and fillers. Phenyl (C₆H₅) and trifluoropropyl (CF₃CH₂) groups are used to optimize the refractive index of optically clear silicones. The effect of chemical composition on the water vapor transfer rate (WVTR) and the oxygen transfer rate (OTR) at 40⁰ C and 90% Relative Humidity was investigated on several silicones with various refractive indices and compared to polydimethylsiloxane (PDMS) with similar durometers. It was found that polymer backbone chemistry had a significant influence on the permeation rates and will assist in material selection when designing for low-permeable barriers to improve package reliability.

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Michelle Velderrain "Designing low permeability, optical-grade silicone systems: guidelines for choosing a silicone based on transmission rates for barrier applications", Proc. SPIE 8280, Advances in Display Technologies II, 82800O (6 February 2012); https://doi.org/10.1117/12.910642

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