PCB Shields

Electromagnetic interference (EMI) causes unwanted interference in the electrical path of the circuit, thereby affecting its functioning. It may make a device to operate poorly or stop working completely. As the sizes of printed circuit boards are reducing, the concern regarding EMI is increasing. Electronic systems featuring PCBs carry different interconnects, I/O cables, and integrated chips. Interconnects imitate antennas when operated at high frequencies and produce EMI, which affects the functioning of systems. PCB shielding is the method of using a non-conductive interior surface to prevent EMI/EMC in the PCB and electronic device as a whole.

 What is EMC/EMI in PCB?

EMC is a term for the electromagnetic compatibility of a device. This refers to the degree to which the device will perform effectively in its electromagnetic environment. This is the safest environment where it is assumed that the electromagnetic emissions will not interrupt or affect the performance of the nearby device or the device’s own operation. The disturbance caused by the electromagnetic emission is known as electromagnetic interference.

Sources of Electromagnetic Emissions in PCB

There are two primary sources of electromagnetic emissions – conducted and radiated emission. The conducted emission is named so, because it occurs through the cables and power input lines. However, radiated emissions occur due to switching devices, power and communication lines, and electrostatic discharges. The radiated emissions often propagate through the air to other nearby devices. One of the most common examples are laptops or mobiles interfering with aircraft electronics.

Electromagnetic emissions may occur from various sources such as ground and power planes, high-frequency traces, and poor decoupling practices.

How Unshielded Electronic Devices May Be Affected by EMI?

EMI can induce noises, cross talk, and ground bounce, which may lead to performance issues. These performance issues may lead to catastrophic damages if not addressed and attended properly. The following are a few consequences of using unshielded electronic devices.

• Failure of electronic components
• Communication disruptions
• Wireless device interruptions
• Software defects or errors
• Corruption of sensor data

To avoid these issues, PCB designers incorporate EMI and EMC design reduction guidelines in the design phase. Trace separation, using vias, routing differential traces closely, using shunt traces and guards for clock lines, avoiding stubs in high-frequency and sensitive traces, using full ground plane and ground grids, and so on are a few common design rules adopted. However, EMI can still be a big concern in spite of all these design considerations. In such cases, PCB shielding can be effective. PCB shielding is created on the principle of the Faraday Cage.

Working Principle of PCB Shielding  

PCB shielding using Faraday Cage becomes quite necessary when the system features multiple PCBs. Or if the device contains many components, they may stick and act as antennas. A Faraday cage is an enclosure made of conductive materials, which block electromagnetic fields from leaving or entering the electrical circuit. In simple terms, the Faraday Cage is a board-level shield that is attached to the ground plane of PCB.

Traditional PCB Shielding Techniques Discussed

The utilization of PCB shielding techniques aims to safeguard electronic components on the PCB by preventing the negative impacts of electromagnetic interference (EMI) and radio frequency interference (RFI). The following are a few popular traditional PCB shielding techniques used by PCB designers:

• PCB shielding metal cans: Made of metal, these PCB shielding covers appear like a replica of large metal cans used for storing or protecting sensitive items. These metal cans are often soldered directly onto the PCB during reflow or attached after reflow with small clips that are soldered to the board during reflow. They can also be designed as fixed clips, which are  soldered onto PCB.
• PCB shielding frames and covers: These PCB shielding techniques resemble a cover and are used for shielding PCBs and ensuring the isolation of components. Like metal cans, the shielding frame is typically soldered to the PCB during reflow and the cover snapped onto the frame after reflow. The PCB shielding frame and covers can be used to shield single or multiple components, depending on your requirement. PCB shielding frame and covers are made in multiple designs, such as multi-wall shielding, perforated shields, and so on.
• Conductive Coatings and Paints: Conductive silver, copper, or nickel paints can be applied to PCB surfaces or enclosures, effectively shielding complex geometries. When combined with traditional methods like metal cans or frames, they enhance overall shielding performance in lightweight or compact applications.
• Conductive Gaskets and Elastomers: Conductive gaskets made from materials like fabric-over-foam or silicone provide effective shielding at PCB housing interfaces, especially where frequent access to shielded components is required, ensuring robust EMI protection without compromising accessibility.
• Embedded PCB Shielding Layers: Internal shielding layers, such as copper or carbon, can be integrated into multilayer PCB designs to suppress EMI at the board level. This is particularly useful in compact designs where space constraints limit the use of external shields.
• Grounding Strategies: Proper grounding, including via stitching, ensures a low-impedance path between the shield and the PCB ground plane, minimizing EMI coupling. This technique is critical for maintaining effective EMI suppression throughout the design.
• Hybrid Shielding Solutions: Combining traditional PCB shields cans with conductive coatings or layered materials with different EMI-blocking properties enhances shielding performance, especially in environments with high EMI exposure.
• Optimized Shield Placement: Conducting an EMI analysis during PCB design helps identify areas requiring shielding, ensuring critical components like RF modules, oscillators, and signal traces are effectively protected, reducing interference at the source.

As the name suggests, these shields are made of metal and are attached to PCBs to protect them from EMI. PCB EMI shields are made from the following types of metals.

• Aluminum
• Steel
• Tin
• Brass
• Copper Alloys
• Silver
• Nickel

Generally, tin-covered aluminum and steel are used for making PCB shielding metal cans. These metal enclosures may feature holes that help in heat management. The shields also provide the shielding effect of a conductive cover. Generally, these shields are designed to completely cover the components, but they leave no options for power and grounding or inputs or outputs. To mitigate this, PCB shielding metal cans are supplemented with EMI mesh, gaskets, and films.

Typical Shortcomings of Traditional PCB Level Shielding Techniques 

Board-level EMI shields have been around for many years and are very much in demand. However, the following shortcomings cannot be ignored altogether.

• Consume excess space
• Metal cans and additional safety measures add to the overall PCB weight
• Difficult to rework, inspect, and remove
• Two-piece shields lower the effectiveness of shielding
• Rigidity of these cans can limit the PCB designs

XGR Technologies SnapShot® EMI shields are designed to overcome these typical shortcomings and they assure excellent EMI shielding performance.

How SnapShot® EMI Shields Assure Better PCB Shielding

SnapShot PCB shields offer a unique and superior alternative to traditional PCB shields. SnapShot shields are custom PCB shields designed for each application. XGR engineers will work with you to design a custom PCB shield based on the layout of your PCB and circuitry requiring shielding. With this approach, you can have a shield designed around your board layout vs. having to layout your board to accommodate an “off the shelf” shield. The following pointers will help you understand it better. SnapShot PCB shields are superior to traditional PCB shields in the following areas:

• SnapShot® EMI shields can be custom designed to meet the size and shape of PCB layouts.
• These EMI shields can be thermoformed to virtually any shape, such as single and multi-cavity for high-density board design, multiple height profiles with a single shield, low profile with zero clearance required between inner shield surface and components, dog house openings to allow clearance of RF traces , and so on.
• SnapShot® PCB shields are designed to withstand vibration, shock, aging, and moisture. These EMI shields are tested extensively against mechanical shock, bump, vibration, thermal shock, dry heat aging, and moist heat aging.
• Our PCB shields can be easily installed after the reflow. These EMI shields can be easily removed and replaced with no additional heat during repairs without causing damage to the board.
• The PCB level shielding is made of lightweight, thin non-ferrous engineered polymer, which is metallized with tin on the outer surface.
• This lightweight composition is ideal for applications where low weight is important.
• SnapShot® outperforms competitive PCB shields in shielding effectiveness from below 1 GHz to 12 GHz.
• These PCB shields assure consistent isolation across a wide frequency range.
• The PCB EMI shield features a non-conductive interior, which helps reduce electromagnetic coupling and eliminate shorting threats.

Applications of PCB EMI Shields

Our PCB shields have been successfully installed in the following applications:

• Medical electronics
• GPS based devices
• Handheld scanners
• Mobile computing
• Drones and avionics
• Network computing
• Avionics
• Wearable electronics

Do you have specific application needs or wish to receive a sample of SnapShot® PCB EMI shield? Then, feel free to contact us today. Our sales team will happily find you a SnapShot® PCB shielding solution that meets your shielding challenges.