EMI Shielding in PCB Design: Unlocking Efficient Circuits

Why is electromagnetic interference (EMI) shielding in PCB design important?

PCBs have EMI shielding to prevent signals from damaging components and disrupting system functionality. It’s also crucial to stop potential EMI signals from radiating outward, which can cause other devices to lose data, malfunction, or fail.

EMI shielding is particularly vital in the military, medical, and communication industries. 

• Military: Protects high-speed data transmission, radar, and communication networks, ensuring safe and reliable functionality. It also guards against electromagnetic pulse attacks.

• Medical: Safeguards MRIs, patient monitoring systems, and infusion pumps, ensuring proper functionality and patient safety.

• Communication: Enhances performance and maintains the integrity of cell phone and RF communication signals.

Types of EMI shielding for PCBs

• Component shielding: Individual components, like integrated circuits (ICs) or radio frequency (RF) modules, are covered with metal cans to prevent EMI leakage and isolate them from external EMI. 

• Board shielding: A metal shield fully or partially encases the PCB, covering sections prone to EMI radiation. Ground planes (conductive layers) also help contain EMI. 

• Narrowband shielding: Protects the PCB from narrow EMI frequency ranges using tuned filters or materials designed for specific frequencies.

• Broadband shielding: Shields the circuit against a wide range of frequencies using metal foils or conductive meshes to weaken or block unwanted signals.

• Cable shielding: Wrapping cables in braided metal sheaths or foil wraps protects signals from EMI and contains any EMI produced within the cable.

Where does EMI come from?

EMI is everywhere in our environment, originating from natural, industrial, and residential sources. Understanding these sources is crucial to prevent potential circuitry damage.

Natural sources of EMI

Common natural sources of EMI include lightning, dust storms, and solar activity. 

• Lightning strikes: Electromagnetic radiation from lightning can cause surges in power and communication lines, disrupting electronics and radio communications. 

• Dust storms: Static charge build-up on dust particles can lead to electromagnetic interference, affecting electromagnetic wave propagation—especially in frequencies over 10 GHz. This is why 5G (or higher) communication systems are especially at risk of EMI from dust storms.

• Solar activity: EMI occurs when charged particles from the sun interact with the earth’s magnetic field, affecting phone lines, power lines, long ground wires, and other long conductors. Electromagnetic radiation from solar flares is also known to disrupt power grids, GPS, and satellites.

Industrial sources of EMI

Common industrial sources of EMI include power grids, TV transmitters, railroads, and cellular network towers.

• Power grids: High current loads, faults, or low-quality components create electromagnetic noise, which can transfer into any connected electronics that lack proper EMI shielding.

• TV transmitters: Broadcast RF signals (VHF and UHF bands) may cause EMI in unshielded devices in the vicinity of those transmissions (40–60 miles), especially if transmission equipment is faulty.

• Railroads: High currents used for traction generate electromagnetic fields that can interfere with communication and signal equipment. Rail-related EMI can also originate from switches in power or track systems.
  
• Cellular towers and wireless networks: RF signals can disrupt nearby electronics operating at similar frequencies. 

Residential EMI sources

Common residential sources of EMI include WiFi networks, computers, cell phones, and Bluetooth devices.

• WiFi networks: As WiFi operates at 2.4 or 5 GHz, it can interfere with other devices in the same frequency range. Note that multiple WiFi devices near each other emit more signals, which can degrade wireless network performance.

• Computers and laptops: High-speed processing in computers and laptops generates EMI that may affect sensitive devices. They also rely on RF signals for Bluetooth and wireless connectivity, causing additional EMI.

• Cell phones: Circuits and processors in mobile devices release electromagnetic radiation, potentially interfering with nearby unshielded devices.

• Bluetooth-enabled devices: Short-range RF signals used in Bluetooth connectivity can potentially interfere with nearby wireless devices operating in the same frequency band (2.4 GHz).

How to reduce EMI and increase EMC in your PCB design?

Optimizing your PCB’s design can significantly reduce EMI and improve electromagnetic compatibility (EMC).

• Minimizing trace length: Shorter trace lengths reduce signal travel time, thereby lowering EMI risks. 

• Avoid routing over split planes: Split planes can cause longer, inconsistent return paths, which in turn cause EMI. To prevent this issue, route traces over unbroken ground planes instead.

• Limit vias usage: Fewer vias reduce the risk of signal path EMI radiation. If vias are necessary, correctly match and place them in order to minimize signal integrity issues.

• Isolate high-speed traces: Separating high-speed traces from low-speed traces can prevent crosstalk, which is a major cause of EMI. Guard traces or ground planes can further isolate high-speed trace signals.

• Separate analog from digital circuits: Place analog and digital circuits on separate grounds and use shielding to prevent noise interference and ground loops.

• Avoid sharp-angled traces: Use rounded traces with angles less than 45 degrees to reduce impedance changes and prevent EMI-causing reflections.

Board-level electromagnetic shielding vs. enclosure-level electromagnetic shielding techniques

The choice between board-level or enclosure-level PCB shielding depends on the specific needs of your application.

Board-level electromagnetic shielding

Board-level electromagnetic shielding is a method that safeguards specific areas or components of a PCB from EMI. It achieves this through direct shield integration on the board.

This type of shielding involves placing a metal cover or can over specific circuits or components, protecting specific traces or planes from surrounding signals. Conductive coatings can be added to components or traces for additional protection from EMI. 

Board-level shielding is more precise and localized than the alternative, enclosure-level shielding.

Enclosure-level shielding

Enclosure-level shielding uses a shielded casing to protect the entire PCB from EMI. This approach is suitable for applications that are subject to a significant amount of electromagnetic noise.

Enclosure-level shielding works by surrounding the electronic system in a steel or aluminum enclosure that functions like a Faraday cage—preventing internally generated EMI from radiating out while, preventing external electromagnetic fields from entering the device. Applying a nickel or copper-based paint to the internal surface enhances the shielding effect.

Enclosure-level shielding offers comprehensive EMI protection for the entire system. However, it’s not as precise as board-level shielding and may increase the size and weight of the device.

What are other PCB design methods that shield from EMI?

To boost the shielding capability of your PCB and enhance its resilience, consider the following design techniques.

Select the correct shielding material for your PCB

Copper layer shields are extremely effective at safeguarding the PCB against EMI. The highly conductive material minimizes electrical and magnetic waves.

Copper layer shields are ideal for impedance control but are less flexible and more costly.

Silver shields have a silver conductive ink layer atop the insulating film covering the PCB layout. This material is best if the circuit doesn’t require impedance control.

Silver ink shielding involves additional materials and steps, which can increase the fabrication cost.

A third material option, shield films are thin, bendable, and offer high EMI shielding. They comprise a special laminate layer on top of the protective layer.

Shield films make flexible PCBs more rigid and reliable while protecting the circuitry from moisture and chemicals. 

Understand the bend requirements of your PCB

Shielding increases PCB thickness and reduces flexibility, even with multi-layer PCBs, as it involves the addition of materials like copper, conductive polymers, or aluminum.

PCB applications that require flexibility, such as wearable devices, should have thin, shielded PCBs. This ensures the circuit remains undamaged, even after repetitive bending.

The bend radius is related to the thickness, so if a PCB’s shielding is thick enough, then its minimum bend radius will increase.

A high bend radius may cause copper cracks, layer delamination, or shield damage—so design for the lowest bend radius to ensure durability.

Understand the impact of controlled independence values

Shields must bond to the circuit ground to ensure they don’t function like antennas.

This forces EMI to move away via the provided low-impedance path. Shields must also have the right conductivity and thickness to prevent EMI at various frequencies from impacting the PCB.

Higher decibel (dB) ratings, absorption, and reflection all indicate better shield effectiveness.

Shielding materials should match the PCB’s performance and EMI requirements, so always consider their physical properties, frequency response, and attenuation level.

Final thoughts on EMI shielding in PCB design

EMI shielding is essential to protect PCBs from harmful signals and prevent EMI leakage.

Effective shielding makes a significant difference in enhancing performance and maintaining signal integrity. 

Selecting appropriate shielding materials and techniques is critical for optimal protection.

By making the right choice, you can ensure your PCB works reliably even in environments with high electromagnetic interference.

Looking for ways to safeguard your circuits against EMI? Contact WellPCB today to start your project with effective EMI shielding solutions.