What Is EMI Shielding and Why Is It Important for PCB Design?

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Jun 13, 2022|Manufacturing Excellence, Product Innovations and Design

In EMI shielding, critical circuits are covered using metal shields that protect from radiation and absorption of EMI. Discover why it is important for PCB design!

In this article, we will discuss what is EMI, what causes it, why you should avoid it, and what measures you can take to keep your electronics safe. We discuss the best options in the market and the pros and cons of each one

What Is Electromagnetic Interference (EMI)?

Have you ever noticed when you are listening to the radio and someone’s cellphone goes off, how you seem to hear static coming out of your speakers? This is not a coincidence. What you are experiencing is an interruption of your radio signal because of the cellphone signal coming from the cell tower.

EMI or Electromagnetic Interference happens when the source of one signal interrupts another signal. This type of interference is not benign, and it goes beyond interrupting your favorite song. 

EMI can damage circuits through induction, electrostatic coupling, or conduction. As a result, exposure to EMI can result in a device being unable to perform as expected or even fail.

Types of EMI

There are two types of EMI:

• Narrowband EMI

• Broadband EMI

Narrowband EMI occurs within a narrow band of frequencies (or even a single frequency). This EMI is produced by radios, TV stations, and cell phones. It can happen intermittently or continuously. Although disruptive, this type of EMI will not damage equipment, unlike broadband  EMI which occurs in a wider spectrum and can damage electronic devices. broadband EMI can be caused by things like a motor, car ignition, defective fluorescent lights, defective power lines, or a jet engine. This kind of EMI affects electronic devices by mixing up the signals these devices are supposed to receive.

The most common broadband EMI occurs over radio frequencies. The energy radiated by circuits, power lines, lightning, lamps, etc. can all generate this interference.

This type of EMI is noticeable when electronic devices stop working as they should. At home, it can cause interference with your electronics, but in an industrial setting, it can damage hardware, lost data, and affect productivity.

Where does EMI come from?

EMI can be produced to any of the following sources:

Natural sources of EMI

This type of EMI is caused by natural sources, such as Lightning strikes, solar flares, cosmic noise, static and atmospheric electricity, dust and snowstorms, and the sun.

This type of EMI can happen suddenly and impact electrical equipment if it is not protected appropriately and it can affect military equipment or transportation. Weaker EMI, such as the one produced by snowstorms can disrupt phone signals.

Residential EMI

This type of EMI comes mainly from wireless devices or electronic appliances, too. While this type of EMI doesn’t cause permanent damage, it can disrupt and lead to poor performance of other electronics.

Residential EMI can be caused by cell phones, laptops, Wi-Fi devices, baby monitors, blue tooth devices, microwaves, or toaster ovens, to name a few. The more electronic devices we add to our home, the more sources of EMI we will find.

Another factor that may influence man-made EMI is the quality of the electronics. The better the performance of the electronics, the higher the frequencies at which they operate, and the higher the risk for EMI.

Industrial

This EMI is produced at a larger scale and can cause severe interference. This type of EMI can come from sources as varied as electric motors or generators, cellular networks and telephone transmissions, television, radio and satellites, the power grid, railroads, or medical equipment just to name a few sources.

The Importance of EMI Shielding 

EMI shielding is important to protect sensitive electronic designs from signals and to prevent stronger signals from interfering with nearby electronics. Having a PCB design checklist can help you remember what needs protecting, and how.

EMI affects sensitive electronics and affects different sectors, including personal and industrial electronics, and even critical military and emergency systems, so it is crucial to ensure that electrical systems are shielded against EMI in every possible way.

What is EMI Shielding and How Does it Work? 

EMI shielding covers critical circuits with metal shields that protect them from radiation and the absorption of electromagnetic signals that can cause EMI.

EMI shields absorb the interference and create a flow of current in the metal used in the shield, which is then transferred to the ground plane.

EMI Shielding in PCBs 

Shielding in PCBs is used in medical, communication, and military applications. They are often used in the stages that are most vulnerable to EMI: Input, output, and amplifier.

To avoid common circuit board problems, ensure that they are covered with metal shields to protect them from the radiation and absorption of EMI. They do this by isolating the circuit or components from the rest of the board.

PCB Shielding Methods

Shielding a design means it needs to be encapsulated on both sides by a layer of material that will absorb EMI. These layers are connected to the ground to dissipate the EMI.

Bend Requirements:

Shielding alters the thickness of the flexible circuit. The minimum bend capacity is a function of thickness, so shielding will reduce the bend capacity of the design.

Bend requirements may be static (bend once to fit) or dynamic (bends many times). 

Controlled Impedance:

These requirements mean that the shields must have electrical characteristics that comply both with EMI requirements and performance since reference planes need to achieve the necessary controlled impedance values. 

Shielding Materials

The effectiveness of an EMI shield is determined by the materials used in the shield. The material is chosen depending on the type of circuit and how often it is going to be operated.

Silver Ink Shields:

Silver ink is used to print objects that can conduct electricity. These are flexible, one-component inks that adhere to a great variety of media, like plastics and composite materials.

Copper Layer Shields

Copper is the most reliable metal for EMI shielding. It reduces both magnetic and electrical waves. It has a higher rate of conductivity, which makes it very effective as an EMI shield.

Shielding Films

These films are corrosion-resistant and flame retardant. They are ideal to shield around corners and odd shapes because they’re flat.

Conclusion

EMI can be a major cause of malfunction in electronics. When designing a PCB, it is crucial to pay attention to which shielding technique is the most appropriate, to ensure the optimal functioning of your system.