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EMI Shielding Plastics: A Lightweight Alternative to Shielding Metal Cans

Author Cadence System Analysis

Key Takeaways

  • In EMI shielding plastics, shielding agents are applied to the plastic enclosure surrounding sensitive circuits. 

  • There are generally two approaches to using plastics for EMI shielding—coating with conductive metals and blending with conductive materials.

  • Coating plastics with conductive metals is a well-established method of EMI shielding in consumer electronics and the automotive industry.

Plastic enclosures in electronics              

When designing electronics, we give due importance to weight. Design iterations are made to optimize space and weight without disturbing the sound operation of the circuit. In electronic circuits, the metal enclosure incorporated for electromagnetic interference (EMI) shielding adds considerable weight. However, these enclosures cannot be eliminated because they protect circuits from incoming EMI as well as prevent outgoing EMI.

Advancements in the field of plastic technologies include EMI shielding plastics, a new trend in the electronics industry that replaces shielding cans or Faraday’s cages with plastic enclosures. EMI shielding plastics are lightweight and provide good EMC to shielded circuits.

Let’s take a closer look at EMI shielding plastics and their advantageous characteristics.

EMI Shielding 

As the use of microprocessors increases, the demand for EMI shielding also increases. These shields play a significant role in enhancing the electromagnetic immunity of devices. 

Why Do Devices Need Protection Against EMI?

EMI can cause electronic device failures. EMI subjects electronic devices to latch-ups, mis-triggers, burn-outs, etc. It is the main hindrance in power electronic circuits, where the interference is capable of damaging control signals. 

Traditional Shielding Methods

Considering all these effects, traditional circuit design methods require placing sensitive circuits inside metal cans or enclosures to shield them from EMI. These metal enclosures are grounded so that EMI-driven current on the metal is not allowed to interfere with the shielded circuit. Unfortunately, metal enclosures increase the weight of electronic devices. EMI shielding plastics are an excellent alternative that can solve the weight issues associated with EMI metal shields. 

EMI Shielding Plastics

Today, using EMI shielding plastics is a common, effective EMI prevention method. This EMI mitigation technique uses shielding agents applied to the plastic enclosure surrounding a sensitive circuit. The type and form of shielding agent is selected depending on the electromagnetic interference immunity required and the size of the molded plastic part. For EMI shielding, conductive coatings are used to fill the plastic enclosure in EMI shielding plastics. 

Approaches in EMI Shielding Using Plastics

There are generally two approaches to using plastics for EMI shielding.

  1. Coating with conductive metal - A well-established method of EMI shielding in the consumer electronics and automotive industries. A variety of coating techniques can be used, including ion plating, vacuum metallization, conductive plaints, electroplating, foil laminates, and tapes.
  2. Blending with conductive materials - Plastics can be made conductive by blending them with conductive fillers. The conductive fillers aid the plastic in achieving desirable shielding properties. Common conductive fillers include copper-coated glass fibers, nickel-coated graphite fibers, silver-coated conductive fillers, aluminum, nickel, silver-coated spheres, brass fibers, and aluminum and aluminum alloy flakes.

Properties of the Conductive Plastics Used in EMI Shielding 

Some of the property requirements of the conductive plastics used in EMI shielding are:

  • High shielding effectiveness
  • Low through resistance
  • High conductivity
  • High permeability
  • High tensile strength
  • High flexural strength
  • Low density
  • UL-94 flammability rating  
  • High-temperature withstanding abilities
  • Corrosion-free

Using EMI shielding plastics technology is one of the best alternatives to using metal enclosures to protect devices from damaging EMI. Conductive plastic materials have excellent shielding effectiveness and electrical, mechanical, and physical stability compared with metal shields.  Cadence software offers design tools that help designers implement EMI shielding in circuit boards. 

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