PCB Design Overall Best Practices?

General Electronics
2

Too many to list really, but I’ve done a Design for EMC course by Keith Armstrong only a year or so ago. Since striving for EMC also results in good signal and power integrity, there’s a lot of value and I’m happy to share some nuggets:.

  • Tie shields to GND via a 0Ohm resistor. The old 1M/10n in parallel is a common misconception to avoid odd shield/GND ground loops within a single cable which are mostly a non-issue in modern systems, and a direct GND tie (at both ends!) will give best EMC performance. Worst case, the fit option means you can play around (in applications with multiple cables that are shielded, all bets are off and there’s no way of knowing what option works best - but generally the 0Ohm direct shunt is a good place to start).
  • At the end of the design, top and bottom GND fills is a great idea if there is decent free space (ie no point if it is split very badly) followed by via stitching. A solid GND plane gives anywhere from 10 to 20dB reduces EMI noise floor, so even a split GND fill won’t hurt.
  • For 4 layer or more boards, a VCC/GND plane gives basically 10n free bypass capacitance globally. So when placing bypasses, go for higher (100n, 1u) or lower (1n) value depending on your IC
  • Parallel bypassing (1u/100n/10n) does not give the frequency response you would expect (ie their frequency responses don’t just perfectly multiply due to ESR/ESL of each). If you have a current-hungry fast device (say, an ESP32) a Pi filter will give much better results
  • Fit option for your plated mounting holes. Common-mode currents are the main cause of EMC issues, and you never know where they could be coming in and out of your system
  • Ferrite beads have very specific and high Qs. This means if you choose just 1, it could either not be enough or actually make things worse. Consider choosing them carefully, and using several in series for critical power lines.

Take these as-is, I’m not here to debate. I’m sure some of them will spice up controversy, as these topics can be polarising. But I’ve seen the calculations, the simulations, and the before/after testing to prove them (that’s why you pay thousands for the course for). They’ve worked well for me. So I stick by them :slight_smile:

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