Conductive Adhesives and Compounds

Conductive adhesives and compounds provide an electrically and/or thermally conductive path between components. Electrically conductive adhesives and compounds provide low resistivity and are used to prevent electrostatic discharge (ESD), electromagnetic interference (EMI), and radio frequency interference (RFI). They are also used in thick film metallization and electrical interconnections. To improve heat dissipation, thermally conductive adhesives and compounds are applied between a heat-generating electrical device and a heat sink. These products are designed to form a thermally conductive layer, either between components or within a finished product. Both electrically conductive and thermally conductive adhesives and compounds are available in many forms. Examples include adhesive and casting resins, molding and potting compounds, greases and pastes, encapsulants, and conformal coatings.

There are many chemical systems and filler materials for conductive adhesives and compounds. Some chemical systems contain acrylics, elastomers, natural or synthetic rubbers, epoxy resins, ceramic or inorganic cements, silicone compounds, vinyl systems, polyamides, or polyimides. Other chemical systems contain thermoset bismaleimide (BMI) resins, cellulosic or cellulose compounds, fluoropolymers, or liquid crystal polymers (LCPs). Commonly used chemical systems also include polybutadiene, polycarbonate (PC), polyethylene (PE), polyester, polyolefin, polypropylene (PP), polysulphide, and polyurethane (PU, PUR). For filler materials, some conductive adhesives and compounds contain aramid fiber, chopped fiber, carbon powder, or graphite powder. Other products contain glass fillers, metal fillers, or inorganic compounds. Unfilled products are also available. Typically, these raw materials are used as starting components for the production of finished adhesives and compounds.

There are several curing technologies for conductive adhesives and compounds. Typically, thermoplastics and thermoset resins are cured using heat or heat and pressure. Vulcanization, a thermosetting reaction, uses heat and/or pressure in conjunction with a vulcanizing agent to produce materials with greatly increased strength, stability, and elasticity. Some materials cure or vulcanize at room temperature. Others cure with radiation, electron beam irradiation, visible light, or ultraviolet (UV) light. Single component curing systems consist of a resin that hardens through the application of heat or a reaction with surface moisture. Two-component and multi-component curing systems for conductive adhesives and compounds consist of two or more resins and a hardener, crosslinker, activator or catalyst. 

Selecting conductive adhesives and compounds requires an analysis of physical, mechanical, thermal, electrical, and optical properties. Physical properties include viscosity, gap fill, melt flow index (MFI), and water absorption. Melt flow index (MFI) is the output flow occurring in a 10-minute period through a standard die while a fixed pressure is applied via a piston to a 190° C melt. Mechanical properties for conductive adhesives and compounds include tensile strength, tensile modulus, and elongation. Thermal properties include temperature range, deflection temperature, thermal conductivity, and the coefficient of thermal expansion (CTE). Resistivity, dielectric strength, and dielectric constant are important electrical properties. Optical properties include index of refraction, a measure of the speed of light in a material, and transmission.   

Conductive adhesives and compounds are used in many industries and applications. Some products are used in the manufacture of printed circuit boards (PCBs). Others are designed for electrical power and high voltage products such as generators, transformers, circuit breakers, and motor assemblies. Specialized conductive adhesives and compounds meet military specifications (MIL-SPEC) or are suitable for aerospace applications. Products for automotive and optoelectronic applications are also available. Flame retardant materials resist ignition or reduce the spread of flames when exposed to high temperatures. Flexible or dampening materials form a layer that can bend without cracking or delaminating.

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