What is EMI/RFI Shielding?

Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) are forms of disturbance that can affect electronic devices by disrupting their normal operation. EMI refers to the unwanted noise or signals that interfere with the performance of an electronic circuit, often caused by other electronic devices, power lines, or natural phenomena. RFI is a specific type of EMI that occurs in the radio frequency spectrum, typically from 10 kHz to 300 GHz, and can interfere with wireless communication and signal processing.

EMI/RFI shielding is the practice of protecting electronic devices and circuits from these interferences by using materials and techniques that block or reduce the electromagnetic fields that cause interference. Shielding is essential to ensure that electronic devices function correctly without being disrupted by external or internal sources of electromagnetic energy. The need for shielding has grown with the increasing complexity and sensitivity of modern electronics, especially in environments with high electromagnetic activity, such as industrial facilities, medical devices, and wireless communication systems. There are two main types of EMI: 

• Radiated EMI: This type of interference is transmitted through the air and can affect nearby devices. It typically originates from high-frequency circuits or devices with poor shielding. 

• Conducted EMI: This interference travels through electrical conductors, such as power lines or signal cables, and can affect the circuits connected to these conductors. 

How do EMI/RFI Shields Work? 

EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) shields function by creating a physical barrier that prevents unwanted electromagnetic signals from entering or exiting sensitive areas of an electronic device. 

In essence, EMI/RFI shields work by combining reflection, absorption, and conduction to block or reduce unwanted electromagnetic interference, creating a protective barrier that maintains the integrity and performance of electronic devices. The effectiveness of the shielding is measured by how much attenuation it provides, often quantified in decibels (dB).

There are three key aspects of creating a barrier:

1. Absorption: The shielding material absorbs electromagnetic waves as they interact with it. Conductive materials, like metals, have free electrons that respond to the electromagnetic field by oscillating, which converts the energy of the EMI/RFI into heat, thereby dissipating it. Magnetic materials, like ferrites, can absorb high-frequency interference and convert it into a small amount of heat, further reducing the strength of the unwanted signal. 

2. Reflection: The shielding material reflects the electromagnetic waves away from the protected area. When an electromagnetic wave encounters a conductive surface, such as a metal shield, a portion of the wave is reflected back toward its source. This reflection occurs because the electric fields induce currents in the shielding material that oppose the incoming wave, creating a counteracting electromagnetic field. This reflection prevents the electromagnetic waves from penetrating the shielded area, thus protecting the internal components from external EMI/RFI. 

3. Redirection/Conduction: Shielding can also redirect electromagnetic energy by providing a path for the interference to follow. For example, in cable shielding, the interference is conducted along the shield to a ground point, where it can be safely dissipated without affecting the internal signal lines. This technique helps to isolate the sensitive parts of an electronic device from areas where interference might be more prevalent. 

EMI/RFI shields often function like a Faraday cage - a continuous conductive enclosure that surrounds the sensitive components. The Faraday cage blocks external electromagnetic fields by distributing them around the exterior of the cage, preventing the fields from penetrating the interior. Inside the shielded enclosure, the electric fields cancel out due to the conductive nature of the material, thus creating a neutral zone where electromagnetic interference is minimized.

Effective EMI/RFI shielding often involves proper grounding. The shield is connected to a ground point, which provides a low-impedance path for the interference to flow into the earth, away from the protected circuitry. Grounding ensures that any stray electromagnetic energy that does manage to enter the shielded area is quickly and efficiently removed, reducing the potential for interference. 

What are the key functions of an EMI/RFI Shield? 

EMI shields play a crucial role in protecting electronic devices from unwanted electromagnetic disturbances. These shields serve multiple functions to ensure the reliable operation of electronic systems. Below are the key functions of EMI/EMC shields: 

1. Prevention of External and Internal Interference: Shields block external electromagnetic fields and contain the device's own emissions, preventing interference with both internal and nearby external components. 

2. Crosstalk Reduction and Signal Integrity: Shields isolate circuits to minimize crosstalk and preserve the quality of electrical signals, ensuring reliable operation of high-speed and sensitive electronics. 

3. Environmental Protection and System Reliability: Beyond electromagnetic shielding, some designs also protect against physical environmental factors, contributing to overall system durability and reliability. 

4. Compliance: Shields help devices meet regulatory standards for electromagnetic emissions. 

What are the different types of materials used in EMI/RFI shields? 

EMI/RFI shield employs conductive, magnetic, or materials with both properties. The following are the types of materials used: 

1. Conductive Metals: Common materials include aluminum, copper, stainless steel, nickel-silver, and tin-plated steel. These materials are chosen for their high electrical conductivity, which makes them effective at reflecting and absorbing electromagnetic waves. 

2. Magnetic Materials: Ferrites and other magnetic alloys are used to absorb high-frequency interference, especially in applications where magnetic fields are a concern. 

3. Composite Materials: In some cases, a combination of materials is used to provide both electrical and magnetic shielding, optimizing performance across a wide range of frequencies. 

What are the different types of EMI/RFI shielding?

As electronic devices become increasingly miniaturized and wireless technology proliferates, the challenges of electromagnetic interference (EMI) and radio frequency interference (RFI) have grown more complex. These challenges can occur at various scales, from individual components on a PCB to entire rooms or buildings. To address these issues effectively, it is crucial to understand the different types of shielding required to protect against EMI/RFI. EMI shielding can be categorized into three primary types - Package Level Shielding, Board Level Shielding and Device/Room Level Shielding. We have elaborated on each of these shielding types below.

1. Package Level Shielding: Package level shielding is the most fundamental form of EMI protection, focusing on shielding individual components or integrated circuits (ICs). The goal at this level is to prevent electromagnetic fields generated by a component from interfering with nearby components or circuits. 

Key Approaches to Package Level EMI/RFI Shielding:

• Metal Stamping/Canning: Historically, individual components were surrounded by metal enclosures made from materials like aluminum. While effective, this method was cumbersome, added significant weight, and increased manufacturing costs. 

• Conductive Paints: Today, conductive paints are preferred for package-level shielding due to their lightweight nature and ease of application. These paints can be applied directly onto components, forming an effective EMI shield. The advantages include: 

  • Ultra-thin Application: Paints can be applied as thin as 8 µm, reducing bulk. 

  • Flexibility and Toughness: These paints offer durability and excellent adhesion, even under extreme environmental conditions. 

  • Cost-Effectiveness: Conductive paints are less expensive than traditional metal canning and reduce labor costs. 

2. Board Level Shielding: Moving up from the package level, board-level shielding focuses on protecting the entire PCB or specific portions of it. This approach involves surrounding the PCB or certain areas with a metallic enclosure, which prevents EMI from escaping the board and blocks external EMI from affecting the circuits. Click here to see Board Level EMI/RFI Shielding Enclosures on everything RF.

Source: Masach, a manufacturer of Board Level RF Shields

Key Approaches to Board-Level EMI/RFI Shielding:

• Metal Enclosures: Initially, metallic housings were used to enclose the PCB fully. This method, while effective, added unnecessary weight and increased production costs.

• Plastic Housings with Conductive Coatings: To reduce costs and weight, designers now often use plastic materials, such as ABS, coated with conductive paint. This method retains the effectiveness of metal shielding while being lighter and more economical.

• Conductive Paints: Specialized paints designed for board-level shielding offer a practical solution for reducing EMI. These paints are lightweight, easy to apply, and adhere well to most plastic surfaces.

3. Device and Room Level Shielding 

When EMI/RFI protection needs to extend beyond individual components or boards, device and room level shielding comes into play. This level of shielding is essential for protecting entire devices or rooms from EMI/RFI interference. 

Device Level Shielding: In some cases, it is necessary to shield the entire device. For example, electric vehicle (EV) car batteries may require full shielding to prevent EMI from affecting the vehicle's electronics. The device is enclosed in a housing coated with conductive paint to prevent EMI from leaking out or entering the device. 

Example of device level shielding
Room Level Shielding: EMI protection can be extended to rooms, such as server rooms, surgical rooms, or airplane cockpits, where sensitive equipment is used. Conductive paints, particularly water-based variants, are ideal for room-level shielding. These paints have low odor, low VOC content, and can adhere to drywall without the need for a primer.

EMI/RFI shielding is a critical consideration in the design and production of modern electronic devices. Whether at the package, board, or device/room level, effective shielding ensures that devices can operate without interference and maintain their electromagnetic compatibility (EMC). The choice of shielding technique—whether using traditional metal enclosures or modern conductive paints—depends on the specific application and the scale of the EMI/RFI challenge. As technology continues to advance, the need for effective and scalable shielding solutions will only grow, making it a vital area of focus for designers and engineers.