Silicone encapsulating and potting materials

Applications of silicone materials for potting and encapsulation are discussed. After introductory notes on general requirements and alternative materials, a description is given of the good dielectric characteristics and thermal endurance of the silicones. Reference is made to their comparatively high cost and, for some applications, limited physical strength. Silicone fluids are then described, with a note on their chemical structure. Graphs illustrate the variation of permittivity and vapour pressure with viscosity, and the effects of frequency and temperature on power factor and permittivity. Following a section on compounds, an account is given of silicone rubbers, especially of the cold-curing types. The lengthening of pot life for the catalyzed materials by adding solvent or silicone fluid is illustrated graphically. A newly developed silicone gel with novel self-healing characteristics is then described. After describing the use of silicone resin-based cements to encapsulate wire-wound resistors, and solventless silicone resins for encapsulating and potting other components, the paper concludes by referring to present and future requirements. It is considered that improved physical properties which are expected to arise from current research are the most important requirement.