EMI shielding plastics refer to specialized plastic materials designed to block or reduce electromagnetic radiation or radiated electromagnetic interference (EMI) that can disturb the operation of or sometimes damage electrical and electronic devices/equipment. These plastics are commonly used to construct plastic enclosures for electronic devices (e.g., smartphones & laptops) to protect them from electromagnetic interference (EMI) or radio frequency interference (RFI).

Figure: EMI shielding plastic and its one application shown

EMI is defined as the disturbance or interference to the operation of electrical and electronic equipment and systems caused by unwanted radiation signals emission from nearby equipment or natural causes (e.g., lightning). The EMI can also impact human health. The RFI is a type of EMI that occurs in the radio frequency spectrum and interferes with radio communication systems such as radio, TV systems, and wireless communications. EMI shielding plastics can be used employed to protect devices from EMI/RFI. These plastics are generally made by using two approaches:

• Conductive Metal Coating on the Plastic
• Incorporating conductive fillers into the plastic matrix (known as conductive plastics).       

In EMI shielding applications, the EMI shielding plastic enclosure surrounds (covers) a device and creates a Faraday cage effect, which blocks or attenuates electromagnetic radiation by reflecting and absorbing the incident electromagnetic wave energy. This action prevents external EMI/RFI signals from entering the enclosure while also preventing any EMI/RFI signals generated by the enclosed device from leaking out. Thereby, the shielding plastic enclosure ensures that the electronic device operates properly without disturbing nearby equipment or affecting people’s health, enhancing the device's electromagnetic compatibility (EMC).

Note: EMI shielding plastic enclosures can serve as a lightweight alternative to metal enclosures in the consumer and automotive industries, providing excellent shielding effectiveness while reducing overall weight.

Applications: 

Shielded plastic enclosures are used across various industries to protect devices from EMI/RFI, including: 

• Housing consumer electronics such as smartphones, laptops, and other devices.
• Medical equipment housing to protect sensitive medical instruments.
• GPS Devices, shielding against interference that could disrupt location signals.
• Aerospace and Automotive equipment housing.
• Defense and Military, providing shielded housings for mission-critical components. 
• Analytical Instruments, ensuring precision and accuracy in sensitive measurement devices. 

Key Benefits of EMI Shielded Plastic Enclosures:

• Cost Reduction: Generally more economical than metallic options.
• Weight Reduction: Serves as a lightweight alternative to metallic enclosures in some EMI shielding applications.
• Ease of production
• Improved Design Freedom: Offers options for integral and multiple colors, soft-touch finishes, and complex designs.

How are EMI shielding plastics produced?

Conventional plastics are non-conductive, with a resistivity in the range of 10¹⁵–10¹⁸ Ω•cm, making them unsuitable for EMI shielding applications. However, there are two common methods used to make plastics suitable for EMI shielding:

1. Conductive Metal Coating on the Plastic Surface: In this method, a conductive metal coating (such as silver, copper, or nickel) is applied to the surface of conventional plastic to provide EMI shielding. Various coating methods can be utilized, including conductive paints, ion plating,  electroplating, electroless plating, vacuum metallization, and foil laminates or tapes.

2. Incorporating Conductive Fillers into the plastic matrix: In this method, the base plastic material is embedded with conductive materials (called conductive fillers) such as nickel, aluminum, copper-coated glass fibers, silver-coated conductive fillers, nickel-coated graphite fibers,   silver-coated spheres, brass fibers, and aluminum alloy flakes. The conductive fillers provide conductivity properties to the plastic and make it suitable for EMI shielding applications.

Conclusion:

EMI shielding plastics are special plastic materials commonly used as enclosures for electronic devices. These plastic enclosures can replace metallic enclosures in the consumer and automotive industries to reduce weight while still offering excellent EMI shielding effectiveness. These plastics are produced by either applying a conductive coating on the plastic surface or incorporating conductive fillers into the base plastic material. EMI shielding plastics provide effective EMI/RFI protection for electronic devices used in various industries, including consumer electronics, automotive, aerospace, telecommunications, military, and more.