Board-level shielding (BLS) refers to the use of metal cages or enclosures on printed circuit board (PCB) to protect sensitive electronic components from electromagnetic interference (EMI) and radio frequency interference (RFI) and reduce crosstalk issues in the PCB. The metal enclosure acts as a Faraday cage, blocking electromagnetic radiation signals from entering or exiting the shielded area of the PCB. This protects the critical circuits and components within the enclosure from external EMI/RFI disturbances and also protects other circuits and components near the shielded enclosure and nearby electronic devices from internally generated EMI/RFI by the enclosed components and circuits. 

Board level shielding is used in various electronics applications, including mobile phones & tablets, 2-in-1 notebooks, medical devices, routers, wireless meters, game consoles, point of sale (POS) equipment, wireless speakers, wearables & IoT, drones, servers, and a wide range of electronic devices.

Figure: Board-level shielding and one-piece, two-piece shield design shown

The metal enclosures providing board-level shielding are made of conductive materials such as aluminum, stainless steel, nickel-silver, cold-rolled steel, beryllium copper, and phosphor bronze. These metallic cages are available in one-piece, two-piece, multi-cavity designs and custom configurations to offer BLS. They come in a variety of material options, shield sizes, surface mounting, and through-hole mount configurations, with customization options available. Board level shielding or PCB level shielding, is an EMI shielding technique that significantly contributes to improving the EMC performance of the electronic device.

Board-level shield design Configurations

One-piece shield design: In a one-piece shield solution, a single continuous piece of metal is used to cover the components and circuits needing protection. For a surface mount shield, the metal cage is attached or soldered to the PCB using alignment pins. In the case of a through-hole shield, it is attached to the PCB using mounting pins. It is a simple & economical shielding solution. This shield solution is also available in a multi-plane cover design. This type of shield is usually used where access to the covered components for repair is not necessary.

Figure: One-piece shield design configurations

Pros of one-piece shield solution:

• Simpler design and lower cost
• Easier to assemble and disassemble, suitable for automated assembly processes.
• Provides effective shielding with minimal seams, reducing EMI/RFI leakage and interference.
• The multi-plane cover design is used to cover irregular height components under one shielded enclosure/cover. 

Cons of one-piece shield design:

• Once installed, it can be difficult to access the components underneath the metal enclosure for testing, debugging, or repair.
• Removal and reinstallation can be cumbersome/difficult and may risk damage to the PCB or components.

Two-piece shield design: The two-piece shield solution consists of a metal frame that is soldered/attached to the PCB and a removable metal cover (or lid) that fits onto the frame. Two-piece shields are ideal for applications where frequent access to the shielded components is required, such as during prototyping, testing, and field repairs. This shielding solution is available in the following configurations:

• Two-piece surface-mount shield with alignment pins.
• Two-piece through-hole shield with mounting pins.
• Two-piece surface mount with no pins.
• Two-piece surface-mount shield with castellated edges.
• Two-piece shield configuration with a multi-plane cover.

Figure: Two-piece shield design configurations

Pros of two-piece shield solution:

• Provides easier access to the shielded components for testing, debugging, and repair without having risk to board damage by removing the entire shield.
• Allows for multiple re-entries without damaging the shield or the PCB.
• Flexible design options, such as different cover styles for specific applications.

Cons of two-piece shield solution:

• Typically complex to manufacture, more expensive, and assemble compared to one-piece solutions.

Multicavity shield design: The multi-cavity shield design is a compartmentalized shield that combines multiple shields into one cover. It saves board space, reduces shield weight, and lowers overall costs. This shielding solution typically features a two-piece design with inner walls (frames) strategically placed and covered by a single removable metal cover.

Figure: Multi-cavity design

Peel shield design: The Peel shield design features an easy-to-remove or peelable top section for accessing components and circuits. The top section can be removed by hand with minimal force using a hook scriber or tweezers, eliminating the need for labor-intensive desoldering. This approach prevents damage to the board and components, thereby reducing the risk of increased scrap. After repair, the shield's top can be resealed using a replacement cover. The Peel shield is more economical and ideal for situations where infrequent access to shielded components is required.

Figure: Peel shield design

Key features of board-level shielding solutions

• Available in standard one-piece, two-piece, multi-plane, multi-cavity designs, peel shield design, and custom configurations.
• Available in Surface-mount, through-hole, snap fit, and clip mounting options.  
• Available in unlimited board shield sizes and configurations.
• Designs available to use in extreme shock and vibration applications.
• Allowing pick-and-place automation.
• Can be provided in tape-and-reel or tray packaging.

Board-level shielding is an effective way to suppress EMI/RFI on circuit boards to ensure proper functioning of electronic devices.

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