PCB electromagnetic shielding is a design technique used to isolate sensitive electronic components or signal paths from external electromagnetic interference (EMI) and prevent internal EMI from radiating to the environment. This is critical in high-density PCBs—common in smartphones, medical devices, and aerospace electronics—where closely packed components and high-frequency signals increase the risk of interference, leading to performance degradation or failure.

Shielding materials and structures are selected based on the frequency range of concern. For low frequencies (below 1 GHz), conductive metals like copper, aluminum, or steel are effective, as they reflect electromagnetic waves. For high frequencies (above 1 GHz), materials with high conductivity and permeability—such as nickel-iron alloys or conductive foams—are used to absorb and attenuate waves. Shielding can take various forms: conductive enclosures (Faraday cages) around sensitive components, copper tape or foil applied to PCB layers, or integrated shield cans (solderable metal boxes) that cover specific ICs or modules.

The design of the shield must ensure complete enclosure to prevent EMI leakage. Seams and gaps are critical—even small openings (e.g., for connectors or vents) can compromise shielding effectiveness, as EMI can radiate through gaps larger than 1/20th of the wavelength of the interfering signal. To address this, gaskets made of conductive elastomers or EMI mesh are used to seal gaps, ensuring electrical continuity between shield components. Grounding the shield to the PCB’s ground plane is essential, as it provides a low-impedance path for absorbed EMI to dissipate, preventing it from re-radiating.

Integrated PCB shielding techniques include using dedicated shield layers within the board stack-up. These layers are solid copper planes connected to ground, positioned between analog and digital sections to block crosstalk. For example, in a mixed-signal PCB, a shield layer between the microprocessor (digital) and sensor circuitry (analog) prevents high-speed digital noise from interfering with low-level analog signals. Vias (plated through-holes) are used to connect shield layers vertically, forming a 3D barrier around sensitive areas.

Shielding effectiveness is measured in decibels (dB), with higher values indicating better attenuation. Testing standards like IEEE 299 or MIL-STD-285 define methods to quantify performance, ensuring shields meet application requirements—for example, medical devices may require 60+ dB attenuation to avoid interference with patient monitoring systems. By implementing effective electromagnetic shielding, PCBs can maintain signal integrity, comply with EMC regulations, and operate reliably in noisy environments.