A Guide to Conductive Elastomers for EMI Shielding
Conductive elastomers are essential materials used in electronic manufacturing to prevent electromagnetic interference (EMI) within and surrounding an electronic device. These elastomeric polymers reside within EMI shielding gaskets and are made in a variety of materials, each of which has unique properties and characteristics. Conductive EMI gaskets are commonly known for:
- Optimal functionality in a variety of environments and applications
- Unparalleled interference shielding
- Design flexibility
- Wide range of operating temperatures
- Several filler materials available
At KraFAB, we use Parker Chomerics EMI elastomer gaskets. There are three distinct types of elastomer materials to choose from when selecting the right gasket design for your application: silicone, fluorosilicone and ethylene propylene diene monomer (EPDM).
EMI Gasket Materials
Silicone Elastomer Gaskets
One of the key characteristics of silicone elastomer materials is their ability to withstand volatile environments. Silicone gaskets, otherwise known as rubber gaskets, can function in temperatures as low as -67ºF and as high as 572ºF. They’re also resistant to moisture and other weathering factors, UV light, oxidation, and more. Silicone is a very soft, malleable material with a low compression set, yielding additional design flexibility.
Benefits of Silicone Elastomer Gaskets for EMI Shielding
- High environmental sealing capabilities
- Functionality in extreme temperatures
- Resistant to weathering, UV radiation, oxidation and aging
- Flexibility and low compression set for optimal design flexibility
Fluorosilicone Elastomer Gaskets
Unfortunately, silicone gaskets can lose their form when exposed to certain solvents and fluids, which ultimately impacts the effectiveness of the gasket and its ability to conduct interference. Fluorosilicone can withstand this adversity, but it’s slightly less flexible than silicone. Still, the material has a relatively low compression set.
Benefits of Fluorosilicone Elastomer Gaskets for EMI Shielding
- Solvent and oil resistance
- Functionality in extreme temperatures
- Optimal compression set resistance
- Cost-efficient
Ethylene Propylene Diene Monomer (EPDM)
Ethylene propylene diene monomer gaskets are perhaps the most durable of the rubber gaskets, providing excellent conductivity and electrical insulation. They are highly resistant to environmental adversities, wear, ozone and ultraviolet radiation. EPDM gaskets are also color resistant, meaning that they won’t stain their mating surfaces. While EPDM gaskets are commonly used for NBC decontamination due to their resistance to chlorinated solvents, they shouldn’t be put in contact with most oils, halogenated solvents and concentrated acids.
Benefits of EPDM Elastomer Gaskets for EMI Shielding
- Excellent resistance to water, weather, UV radiation, oxidation and aging
- Functionality in extreme temperatures
- Color stability
- Optimal in for electrical insulation
Conductive Gasket Molding for EMI Shielding
No matter the type of gasket material chosen, each is made by curing or crosslinking the desired material into gasket form. There are several methods commonly used for curing EMI elastomers into place, described below.
Compression Molding
The compression molding process involves a pre-formed mold with a hollow cavity in the shape of the desired gasket design. The mold is filled with uncured material, put into a press and cured. Then, the design is extracted from the mold.
Injection Molding
The injection molding process is similar to compression molding. Instead of placing the material into the mold and forming it with compression, the mold is closed completely and conductive material is injected into the cavity. The injection process ensures that no more material is used than necessary, saving both time and material.
Extrusion Molding
Extrusion molding refers to the process of pushing a material through a die to create extruded cork stock. The die is a machine that uses pressure to extrude a material through a machined opening. The finished extrusion is cut to size with corners either glued or spliced together. Extrusion molding does cause the output material to swell slightly, a phenomena known as “die swell”. This can impact the functionality of the finalized gasket in certain applications.
Curious to learn more about gasket design for EMI shielding? Get in touch with our team at KraFAB today and talk with our experts about the right elastomers and molding process for your project.