EMI Bites: Why Traces Need to Stay Away from PCB Edges
Your PCB design might look perfect on screen, but one common oversight can turn your board into an EMI problem during certification testing: routing signal traces too close to the board's edge.
This seemingly minor placement issue can create major electromagnetic interference headaches.
But why does keeping traces near the edge cause such big problems?
- Fringe field emissions - When signal traces run close to the board edge, their electromagnetic fields can "leak" beyond the PCB boundaries, turning your board into an unintentional antenna that broadcasts interference.
- Crosstalk between traces - If you try to solve the edge problem by cramming traces tightly together away from edges, you create a new issue: traces that are too close will interfere with each other, creating noise that corrupts your signals.
The fundamental principle: Electromagnetic fields don't care about your PCB boundaries—they follow the laws of physics!
When traces are too close to edges, your carefully designed PCB becomes an EMI transmitter.
My proven strategies for clean, EMI-compliant layouts:
- Keep signal traces well inward from all board edges
- Maintain at least three trace widths of spacing between traces
- Plan your layout to balance proper trace placement with routing efficiency
- Use a solid, continuous reference plane underneath to contain electromagnetic fields
—Dario
P.S. Want more EMI control strategies to pass EMC?