EMI Bites

If you're battling random resets, frozen boards, or EMC test failures, chances are these common pitfalls are at play.

I've compiled my top 10 mistakes that trip up even seasoned designers—rooted in overlooking electromagnetic fields and parasitics.

Remember, think fields, not electrons, to channel energy properly and avoid black magic fixes.

- Not choosing the appropriate stackup for your board.

This sets the foundation. Wrong layer pairs mean fringe fields escape, crosstalk spikes, and you're back to respins. Always pair layers wisely—don't skimp here.

- Traces spaced too closely, promoting crosstalk.

Fields from one trace invade neighbors, causing noise on buses or resets. Maximize spacing or tighten coupling to the return reference plane (RRP) to confine those fields.

- Not mitigating parasitic effects from routing.

Trace inductance, via placement gone wrong, or impedance mismatches—these parasites kill performance. Shift to frequency-domain thinking to spot and squash them early.

- Not minimizing current loop size.

Large loops act as antennas for radiated emissions. Keep the RRP close to shrink loops and contain differential-mode currents—EMI issues drop dramatically.

- Not adding protection and/or filtering to each in/out.

Unfiltered I/Os let external noise couple in or emissions leak out. Filters help, but they're no substitute for solid layout—design to prevent, not just patch.

- Separating "grounds."

Forget splitting planes—it's a myth that invites noise. Use a continuous RRP and smart partitioning to keep analog, digital, and power currents from mixing.

- Not adding return vias next to signal vias.

Signal vias without nearby returns create inductance spikes and field leaks. Stitch them properly to maintain low-impedance paths and field containment.

- Poor component placement.

Overlooked placement leads to internal EMI chaos. Partition your board (analog/digital/power/I/O) guided by the schematic—get this right, and you're halfway to compliance.

- Not designing controlled impedance signal traces.

Signals care about impedance, not net names. Ensure continuous paths free of discontinuities to prevent reflections and distortions that turn into EMI nightmares.

- Creating antenna-like structures that promote EMI emissions and susceptibility.

Traces, pours, or cables forming unintended antennas radiate or pick up interference. Keep designs simple, visualize field paths, and avoid unnecessary complexities.

Master these, and EMC becomes predictable physics, not trial-and-error. Spot them in your next layout review to save time, money, and headaches.

To electromagnetic enlightenment,

–Dario

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