Board level shields have emerged as one of the popular choices for shielding PCBs from electromagnetic interference (EMI). These shields are applied onto PCBs in such a way that they mitigate EMI without disturbing the circuitry and components. Although these shields look simple, much consideration goes into designing them. This post discusses some important design considerations for board-level shields which helps improve the overall device performance.
How to Design a Board-Level Shield?
A board-level shield (BLS) comprises a metal cage, which helps isolate board-level components and reduce EMI. These shields help improve the performance of a PCB or a device, which is why they need to be designed carefully. The following pointers will help you understand it better.
- Board Layout: As mentioned, board layout and design analysis will help in making the right shield. The shield must cover the entire board area comprising sensitive components without disturbing the wires and considering the ventilation holes and vias. This will ensure optimal protection against internal EMI. Here are some features one must consider when designing EMI shields.
-
- Configurations: Board-level shields can be designed in one or multiple-piece configurations. As the name suggests, the one-piece configuration resembles a simple metal cage. This shield and the board’s ground plane offer EMI protection on all six sides but aren’t a good choice if the components require regular repairs. In multiple-piece configurations, the shields feature multiple components such as frame and lid or shield and clips, which can be easily removed whenever repair or inspection of shielded components is required. Users can remove these shields in pieces from the places where repairs may be required.
- Corner Configurations: The shield corners help improve shield performance. However, if not properly designed, these corners may allow EMI to escape and reach the shielded components. The shields can be designed with standard corners, tight corners, welded corners, and interlocking corners.
- Ventilation Holes: These are designed just as per the ones on the board to facilitate air exchange and heat dissipation. The standard types are single and double-density holes with diameters ranging from 0.60″ to 0.120″ and beyond. These aspects are customizable.
- Shielding Materials: The material used for the board level shield should be selected based on the frequency range of the EMI and the conductivity of the material. Copper is a commonly used material owing to its high conductivity. Other metals used are silver, nickel, and gold among others. However, the best shields are those which have both conductive and non-conductive elements. The non-conductive elements include engineered thermoplastic such as polyetherimide. These plasticized metal shields are the best when it comes to shielding effectiveness and have many other benefits.
- Shield Mounting: The method of mounting the shield to the PCB should be considered to ensure proper grounding and connection to the device. Soldering the shield directly to the PCB is a common mounting method. Plasticized metal shields are absolutely lightweight and can be easily thermoformed into the desired size and shape and snap onto the board.
- Shield Removal: A board level shield must be easily removable and reusable. This facilitates reworking on a PCB such as adding or removing components, upgrading according to a new requirement, and so on. A designer must be able to remove the shield work on the board and put the shield back in place. The shield must be designed for an easy peel-off removal applying minimal force. This feature helps prevent damage to any components, vibration, and so on.
If you are an OEM that manufactures electronic or electromechanical devices or a PCB assembly, you would require good quality board level shields to reduce interference and electromagnetic coupling, both internal and external. This would certainly enhance the device’s performance. Hence, it is essential to get the best quality board-level shields. XGR Technologies offers SnapShot ™ EMI shields with isolation for a wide frequency range from below 1 GHz to 12 GHz. These shields are made of plasticized metal and are super lightweight. While they stay firmly in place, these shields can be easily removed and reinstalled in case you need to make any changes to the board. You can contact XGR Technologies team today to know more about these EMI shields or share your requirements.
