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

Many PCB designers overcomplicate layer stackup design, especially when it comes to EMI control.

I often hear about outdated stackups that simply don’t work with today’s high signal bandwidths.

A classic scenario I see is a product being retrofitted with new ICs or ASICs, only to fail EMC compliance tests.

Designers are baffled, saying, “We just swapped the old IC for a new one with the same pinout and functions—how is this possible?”

In most cases, the problem was already there; you just didn’t notice it.

The original stackup was often designed with the cheapest combination possible, giving little thought to EMI.

Swapping in a modern IC with faster rise times or higher frequencies exposes those flaws.

To avoid this, I rely on a fundamental principle for bulletproof stackups: layers always come in pairs.

Every signal layer (or power layer, for that matter) needs an adjacent return or reference plane.

The closer these planes are, the tighter the electromagnetic fields stay, reducing loop area and preventing them from spreading out to cause trouble.

Follow this rule, and choosing a stackup becomes surprisingly simple.

Break this principle without understanding the “why” and “how,” and you’ll pay the price—even if you think you’re saving on layer count.

A little foresight here can save you a lot of headaches later.

-Dario

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