GROUNDED: Your PCB, EMC/EMI, and SI Nuggets

"Dario, can’t we just slap on a ferrite bead or add some shielding if we fail?"

Sure, sometimes that works. But most of the time?

It’s just a Band-Aid on a much bigger problem.

Here’s the truth:

If your stackup design is wrong, fixing it later with quick patches can be hard, expensive, and sometimes impossible.

Why?

Because poor design decisions at the start often can’t be easily integrated into production workflows.

The root of the problem is simple: The basic principles of electromagnetic wave propagation were not respected.

Two Approaches to Stackup Design:

Stackup #1:

- Focuses on channeling electrons through the copper.

- Assumes electrons are the energy being transmitted as signals.

- Uses the RRP (reference return plane) as a "current sink" and "EMI shield."

Stackup #2:

- Focuses on channeling electromagnetic fields in the space around the conductors.

- Contains and guides the energy within the stackup, preventing it from radiating out.

- Uses the RRP to create a low-impedance return path and establish a proper reference potential.

The Results?

Stackup #1:

- High crosstalk between layers.

- Signals struggle to find the lowest impedance return path.

- Excess energy leaks out as EMI, creating unnecessary noise and compliance headaches.

Stackup #2:

- Lower EMI because the electromagnetic fields are contained and controlled.

- Better signal integrity thanks to low-impedance return paths.

- A design that respects the physics of energy flow, not outdated ideas about electrons.

The Takeaway:

Stop thinking about electrons.

Start thinking about energy and electromagnetic fields.

Patches like ferrite beads and filters can help, but they won’t save a poorly designed stackup.

If we want to avoid costly failures, we need to get it right from the beginning.

Want to level up your EMI knowledge?

I offer private 1-on-1 live training on EMC/EMI design.

Learn how to think like an EMI specialist and build boards that pass compliance the first time.

👉 Book your customized training here: fresuelectronics.com/training

-Dario

P.S. EMI is simple, not easy.