Thermal Compounds and Thermal Interface Materials

Thermal compounds and thermal interface materials form a thermally conductive layer on a substrate, either between components or within a finished product. Thermally conductive resins, tapes, adhesives, greases, and compounds are often used between a heat-generating electrical device and a heat sink to improve heat dissipation. Two-part or multi-component systems consist of resins or a resin and hardener, crosslinker, activator, or catalyst. Curing technologies use heat, heat and pressure, radiation, or ultraviolet (UV) light. Some UV systems employ a secondary curing mechanism to complete the curing of adhesive regions that are shielded from UV light. For example, electron beam (EB) technologies use radiation to penetrate materials that are opaque to UV light. Thermal compounds and thermal interface materials are used in a variety of industries, especially in the manufacture of electronic components and semiconductors.

There are a variety of thermal compounds and thermal interface materials. 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. Double-sided thermal interface tapes and pads, substrates, and shapes are often used as electrical insulators. 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). Filled resins are composites that consist of a resin reinforced with fibers or particulates. Adhesives and die bonding compounds are thermal compounds and thermal interface materials that are used to join components. Typically, adhesives require a clean surface. Grease and oil compounds seal joints, openings, and fittings. Vacuum sealants have low vapor pressures to prevent outgassing. 

Thermal compounds and thermal interface materials use a variety of chemical systems. Examples include acrylics and polyacrylates, epoxy resins, polybutadiene, polycarbonate (PC), polypropylene (PP), polyurethane (PUR), silicone, vinyl, and polyvinyl chloride (PVC). Materials based on ceramic or inorganic cements are often used in high temperature applications. 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 polyeylene 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 thermal compounds and thermal interface materials 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 (CFE). Mechanical properties include tensile strength and elongation. Processing and physical properties include viscosity, process or curing temperature, and process or cure time.

Thermal compounds and thermal interface materials vary in terms of applications and features. Products that are designed for electrical and electronics applications often provide protection against electrostatic discharge (ESD), electromagnetic interference (EMI), or radio frequency interference (RFI). Materials that are electrically conductive, resistive, insulating, or suitable for high voltage applications are also available. Flame retardant materials reduce the spread of flames or resist ignition when exposed to high temperatures. Thermal 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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