Assembly - December 2008 - (Page 49) ASSEMBLY Dispensing RTVs Cushion the Ride Silicones are best dispensed with automated equipment. oom-temperature vulcanizing silicones (RTVs) are amazing materials. As their name implies, they cure at room temperature in hours or days, depending on the formulation. They are thermoset materials: Once cured, they can’t be transformed back R to their original state regardless of what attacks them. This makes them excellent for hostile environments where other materials may degrade. Some unique RTVs never fully cure. These are “self-healing” materials. When this type of RTV is damaged, new material under the damaged surface starts to cure. This type of material is typically used in critical military and automotive applications. RTVs can be formulated in a wide range of consistencies, from 5,000 centipoise—the consistency of honey— to a no-slump paste that is virtually solid. Thick RTVs are thixotropic. That is, they are gel-like at rest, but fluid when agitated or pressured. RTVs solve many challenges for assemblers of equipment destined for rugged use. They resist moisture and chemicals, and they cushion electronic assemblies, fasteners, switches and Silicones are thermoset materials: Once cured, they can’t be transformed back to their original state regardless of what attacks them. By Bill Boyd Equipment Program Manager Specialty Coating Systems Inc. Indianapolis Because of their thermal and chemical stability, RTV silicones are ideal for coating circuit boards that will see service in extreme environments. www.assemblymag.com December 2008 / ASSE M B LY 49 http://www.assemblymag.com
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