Why Use Cans for EMI Shielding on PCB?

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The smart gadgets and electronic devices around us produce massive unwanted electromagnetic energy. If not controlled, these signals and waves can interfere with the operation of other nearby electronic equipment. The signals generated by electrical devices are known as electromagnetic and radio frequency interference (EMI and RFI). It is imperative to control both EMI and RFI to ensure the optimal performance of electronics. And the best way to prevent both ingress and egress of electromagnetic energy is EMI shielding.

Electromagnetic shielding is the technique of controlling incoming or outgoing emissions of electromagnetic frequencies (EMF).  This process involves surrounding electronics and cables with conductive or magnetic materials to minimize the impact of EMI/RFI. With the help of EM shielding, sensitive electronics can be guarded against electromagnetic frequencies (EMF). The metal enclosures used for shielding helps in controlling EMI radiations by keeping the harmful interference out and unwanted emissions inside the device.

To ensure the optimal functioning of your PCB design, it is crucial to use the right type of shielding technique. In most of the electronics, metallic mesh shields are used to protect one component from affecting another inside a particular device. For the highly sensitive electronic circuits, ‘can shields’ are used for controlling EMC – Electro-Magnetic Compatibility.

What is a Shield Can?

At board level, EMI shield cans, also known as cages, covers, or lids are applied selectively to the problem areas of a circuit. The shield cans are metal boxes that are directly attached to the Printed Circuit Board for tackling components with emissions. The metal enclosure of the can is useful to prevent unwanted radiation from entering or leaving the covered region. EMI can shield are available in different metals such as steel, aluminum, silver, brass, copper alloys, nickel, and tin-plated plastic. The type of metal used depends on the application and budget. The ‘can shields’ are mounted directly to the PCB to isolate the required circuitry. The cans provide board level shielding and for thermal management, the can shields have a grid of holes in the metal.

When to Use a Shield Can?

At the time of designing a PCB, the priority should be to control emissions with good design practices. The design engineers should make use of techniques such as grounding and short traces to ensure minimal emissions. However, when it’s not possible to control EMI through design, shielding is the best way for EMI management. Shields should be applied over the RF output, or inputs and amplifier stages in a circuit. These components are most likely to be affected by/cause EMI. The high-speed components like oscillators can also be shielded to prevent them from creating interference across the board.

Shielding cans provide a cost-effective method for applications such as radio systems, wireless equipment, and consumer electronics. Can shield is useful for applications like telecoms base stations, radio communications, and data processing. You need to mount the can into the SMT clips by pushing it. The shield cans are also easy to remove and repair, as well as can be made resistant to shock and vibration.

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