Velderrain M.,NuSil Technology
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012
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 (C 6H 5) and trifluoropropyl (CF 3CH 2) 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 40 0 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. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
Reilly B.,NuSil Technology
Rubber World | Year: 2012
Not only are there many different types of adhesives, there are also several types of silicone adhesives. Your choice of a silicone adhesive, whether a one part RTV adhesive, a two part adhesive, a film adhesive or a pressure-sensitive adhesive, should depend on the substrates you are using and the application(s) you are undertaking. While silicone adheres well to a variety of substrates on its own, primers and other preparations do help improve adhesion. Because finding the most suitable adhesive and/or primer can be difficult, NuSil offers custom formulation of primers and adhesives, as needed. Especially when communicating unique requirements, having a good relationship with your material supplier can be helpful.
Velderrain M.,NuSil Technology
AIP Conference Proceedings | Year: 2011
Growth in the solar industry has resulted in newer technologies, specifically concentrator photovoltaic (CPV) modules, to explore using new types of materials such as silicone encapsulants. CPV and LCPV module designs are to achieve the most efficient energy conversion possible however it is equally important to demonstrate long term reliability. Silicone is a material of interest due to its thermal stability and ability to absorb stresses incurred during thermal cycling. The refractive index of clear silicone adhesives is advantageous because it can be optimized using phenyl groups to match BK7 glass and other substrates to minimize light loss at the interfaces but it is relatively unknown how the optical properties change over time possibly yellowing in such a harsh environment. A 1.41 silicone encapsulant is compared to a 1.52 refractive index silicone. Optical Absorption (300 nm-1300 nm), Water Vapor Permeability, Moisture Absorption and effects of oxidation at elevated temperatures will be compared of these materials to aid the engineer in choosing a silicone for their CPV application. Non-phenyl containing 1.41 RI silicones have been used for several years for bonding solar arrays in the satellite industry. Phenyl groups on the siloxane polymer can change various properties of the silicone. Understanding how phenyl affects these properties allows the engineer to understand the benefits and risks when using a RI matching silicone to minimize light loss versus a non-phenyl containing silicone. © 2011 American Institute of Physics.
Burkitt B.,NuSil Technology
Rubber World | Year: 2012
Fluorosilicone's advent into the commercial marketplace offers opportunities for manufacturers to pursue new applications for silicones in the automotive, aircraft and general markets. The unique properties of fluorosilicones provide a solution for products that need broad operating temperatures, fuel resistance and long-term reliability. Initially, the silicone polymer is produced, and silica is added as a reinforcing filler to improve the physical properties of the elastomer. This mixture is called a base. Acting similarly to gravel in concrete, silica reinforces the cured silicone polymers through van der Waals forces and hydrogen bonding between hydroxyl groups on the silica surface and the siloxane backbone of the polymer. Within the flurosilicone family, several formulations are available that can be adjusted to fit specific applications. The breadth of material choices for these types of applications is attributable to advances in fluorosilicone technology based on trifluoropropyl methylpolysiloxane polymers.
Velderrain M.,NuSil Technology |
Lindberg M.,NuSil Technology
44th International Symposium on Microelectronics 2011, IMAPS 2011 | Year: 2011
Silicones have been used for decades in aerospace and other harsh environments where temperature extremes are common. As the level of sophistication increases for electronic devices to serve these industries where failure is not an option, the material supplier has to also be able to meet these needs. Silicones are polymeric materials composed primarily of repeating silicon and oxygen bonds, known as siloxanes, which can be optimized for various chemical and physical properties by incorporating different organic groups onto the silicon atom. Employing advanced processing techniques to the siloxane system can also greatly reduce mobile siloxane molecules to reduce contamination that can cause electronic failures during assembly or operation. Siloxane based polymeric systems are also unique polymers compared to standard organic based materials in that they have a large free volume that imparts a low modulus which absorbs stresses during thermal cycling as well as not degrading at continuous operating temperatures up to 250 C. They are also slightly polar which allows the incorporation of fillers to impart a variety of unique properties. Filler technology is also a rapidly growing enterprise where fillers with various particle sizes and shapes can be added to silicones to impart key properties such as maintaining electric conductivity at elevated temperatures. This paper will explain fundamentals of silicone chemistry and processing related to getting the optimal performance in harsh environments. A case study comparing two different electrically conductive fillers and how they can influence the electrical conductivity at elevated temperatures will be presented.