How to improve EMC in multi-layer I/O module boards

Multilayer board design is an effective way to systematically improve the EMC performance of I/O modules. A typical four-layer board stack-up consists of a top signal layer, a ground layer, a power layer, and a bottom signal layer. Complete ground and power layers provide low-impedance return paths and good decoupling for signals. Six-layer or more boards can add more ground layers to form shielded cavities. During design, high-speed signal layers should be placed close to ground layers to confine electromagnetic fields within the dielectric. Power planes should be tightly coupled to their adjacent ground planes to form natural parallel-plate capacitance, providing low impedance at high frequencies.

Power planes can be segmented between different power domains, but care must be taken to ensure the reference ground plane below the segmentation gap remains intact. Dense placement of ground vias along the board edges creates a Faraday cage effect. Multilayer boards also facilitate clear zoning, such as placing analog circuitry in a corner with its own independent ground plane. Through proper stack-up design and impedance control, multilayer boards can fundamentally improve signal integrity and reduce radiated emissions.