Stycast 5954

Stycast 5954 is a highly filled, two-component, silicone encapsulant designed for protecting heat-generating devices in demanding environments. This red silicone system is specifically engineered to handle extreme temperature ranges from -65 to +260°C while providing high thermal conductivity and superior electrical insulation. Its “reversion resistant” nature ensures that the material remains stable and does not liquefy or degrade when exposed to high temperatures in enclosed assemblies, making it ideal for power supplies, transformers, and sensors.
The system consists of a red resin (Part A) and a white liquid hardener (Part B) mixed at a convenient 1:1 ratio by weight. In its uncured state, the mixed material has a viscosity of 35,000 mPa·s and a density of 2.45 g/cm³. It features a 90-minute pot life at 25°C, providing a generous window for processing. A significant advantage of Stycast 5954 is its ability to be cured in very large castings with virtually no shrinkage or adverse exotherm (heat generation), meaning there is essentially no limit on the size of the part being encapsulated.

The curing schedule is flexible, ranging from 20 minutes at 150°C to up to 7 days at room temperature. For peak performance, a post-cure of 2 hours at 175°C is recommended. Because this is an addition-cure silicone, it is highly sensitive to “cure inhibition”, contact with amines, tin salts, sulphur, or chlorinated rubbers must be strictly avoided as they can prevent the material from hardening. To ensure a void-free finish, vacuum deairing at 1 to 5 torr is recommended before pouring.

Once fully cured, Stycast 5954 exhibits a Shore A hardness of 85 and a thermal conductivity of 1.15 W/(m-K). It is a high-grade electrical insulator with a volume resistivity of $>1 times 1×10¹⁴ ohm-cm and a dielectric strength of 17.7 kV/mm. While the silicone naturally provides excellent release properties, adhesion to non-silicone substrates can be achieved by pre-treating surfaces with Primer S 11. Its combination of high-temperature stability and thermal management makes it a critical component for high-reliability bridge rectifiers, thermistors, and thermal probes.