Encapsulants and Potting Compounds

Encapsulants and potting compounds are resins or adhesives that are used to encapsulate circuit boards and semiconductors, fill containers of electronic components, and infiltrate electrical coils. They provide environmental protection, electrical insulation and other specialized characteristics. Encapsulants and potting compounds belong to a broader category of electrical resins and electronic compounds that includes adhesives, greases, gels, pads, stock shapes, gaskets, tapes, and thermal interface materials. Most potting compounds are based on polymeric resins or adhesives; however, materials based on ceramic or inorganic cements are often used in high temperature applications. Some encapsulants and potting compounds are designed to form a thermally conductive layer between components or within a finished product. These thermally conductive products are used between a heat-generating electrical device and a heat sink to improve heat dissipation.

There are many types of encapsulants and potting compounds. Common potting compounds and casting resins are used to fill compartments or pockets that contain electronic components. Encapsulants seal or cover circuits; typically, encapsulant layers are less than 100 mils thick. Molding compounds are suitable for fabrication processes such as injection, compression, and blow molding; film extrusion; reaction injection molding (RIM); and resin transfer molding (RTM). Gap filling or underfill compounds are used to fill in gaps or spaces between two surfaces to be bonded or sealed. Glob top or daub-type compounds are used to insulate semiconductor dies or other electronic components on printed circuit boards (PCB) without encapsulating the entire assembly. Low viscosity resins or varnishes are used to impregnate coils or coat wires. Adhesives and die bonding encapsulants and potting compounds are thermal interface materials that are used to join components.

Encapsulants and potting compounds are based on a variety of chemical systems. Examples include polyamide, polyamide-imide (PAI), polybutadiene, polycarbonate (PC), polypropylene (PP), polyurethane (PUR), silicone, vinyl, and polyvinyl chloride (PVC). Epoxy resins exhibit high strength and low shrinkage during curing. Polymers are used widely and include liquid crystal polymer (LCP) and polyolefin. Fluropolymers such as polytetrafluorethylene (PTFE) and polyvinylidene fluoride (PVDF) provide superior chemical resistance. Various polyester products, including terphthalate and polyethylene terephthalate (PET), are also available. Some thermosetting resin bonds are based on the melamine formaldehyde system. Others are based on the phenol formaldehyde system. 

Important specifications for encapsulants and potting compounds include electrical, thermal, mechanical, processing, and physical properties. Electrical properties include electrical resistivity, dielectric strength, and dielectric constant or relative permittivity. Thermal properties include service temperature, thermal conductivity, and coefficient of thermal expansion (CTE). Mechanical properties include flexural strength, tensile strength, and elongation. Processing and physical properties for encapsulants and potting compounds include viscosity, process or curing temperature, process or cure time, and pot life. 

Encapsulants and potting compounds vary in terms of features. Many products that are designed for electrical and electronics applications provide protection against electrostatic discharge (ESD), electromagnetic interference (EMI), and radio frequency interference (RFI). Materials that are electrically conductive, resistive, insulating, or suitable for high voltage applications are also available. Flame retardant products reduce the spread of flames or resist ignition when exposed to high temperatures. Thermal encapsulating and potting compounds and thermal interface materials that use a phase change are able to absorb more heat from electronic devices or electrical components.

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