Description

Molding compounds and resins are industrial plastics and polymers that are suitable for forming. They are used in injection molding, compression molding, reaction injection molding (RIM), resin transfer molding (RTM), and blow molding. Types include thermoset resins, gel elastomers, encapsulants, potting compounds, composites, and optical grade materials. Typically, products are supplied as pellets, liquids, and powders.

Types

The GlobalSpec SpecSearch Database contains material listings on these type of molding compounds and resins.

Elastomers and rubber materials are characterized by their high degree of flexibility and elasticity (high reversible elongation). They are based on a variety of different systems, including silicone, polyurethane, chloroprene, butyl, polybutadiene, neoprene, natural rubber or isoprene, and other synthetic rubber or compounds.

Composite compounds are types of resins made from two or more constituent materials with significantly different physical or chemical properties. One of these constituents is generally a strengthening phase, reinforcement fibers, toughening phase, or other specialty fillers that provide unique properties.

Thermoplastics are polymers that turn to liquid when heated and turn solid when cooled. They can be repeatedly remelted and remolded, allowing parts and scraps to be reprocessed. In most cases they are also very recyclable.

Thermosets or thermosetting plastics are polymer materials that have been irreversibly cured. They are generally stronger than thermoplastics due to polymer cross-linking and are better suited for high-temperature applications (below their decomposition points). They tend to be more brittle than thermoplastics and many cannot be recycled due to irreversibility.

Silicone molding compounds are used mainly in electrical applications because of their good chemical and electrical properties. They feature high arc resistance, high dielectric strength, and a low dielectric constant. Silicone molding compounds also provide good resistance to corona and electric breakdown, even after exposure to moisture and higher temperatures.

Most molding compounds are composite materials that consist of epoxy resins, phenolic hardeners, silicas, catalysts, pigments, and mold release agents.  A product’s chemistry and filler material help to determine key mechanical, physical, thermal, and electrical properties.

Properties

Molding compounds and resins exhibit properties based on their composition. Special consideration should be given to properties such use as temperature, coefficient of thermal expansion, tensile strength, and dielectric strength.

Use temperature is the allowable temperature range in which the compound can operate effectively which determines what environments a resin can be used in.

The coefficient of thermal expansion is a measure of the tendency of the compound to change in volume in response to temperature, which could limit space restraints under certain operating temperatures.

The tensile strength is the maximum stress a material can withstand while being stretched or pulled before necking deformation occurs.

Dielectric strength is the maximum electric field strength that a material can withstand without breaking down, and is most important when a resin is used with a semiconductor or other electrical device.

Semiconductor Encapsulating Materials

Several different types of plastic molding compounds are used to encapsulate semiconductor devices. General-purpose products are suitable as long as they provide high flexural strength and exert relatively large stresses on the encapsulated device, which typically use a thicker package type. Low-stress molding compounds are better for encapsulating thin packages. Molding resins with a high thermal conductivity are required for encapsulating high-power devices. Surface mount technology (SMT) requires a low moisture absorption rate and/or high flexural strength.