.png)
Here are 5 simple steps to find EMI issues early in your PCB design process:
1. Check the stackup.
The stackup is the foundation of everything.
If the stackup is not correct, EMI will devour you alive.
The reason for this is that EMI, or Electromagnetic Interference, either received or emitted, strongly depends on PCB geometries.
The way EM fields are contained is by creating boundaries for them.
This is why the first thing to ensure is that the stackup provides the right boundaries to contain the fields.
2. Analyze the return path.
That's right, the return path is as critical as the signal path.
This is one of the most common misconceptions, and it's one I also fell for at one point.
The truth is, when the signal current propagates forward, it simultaneously propagates backward.
The displacement current is established within the dielectric, and the current loop is maintained throughout the entire signal propagation.
If we interrupt one of these paths, the loop is either open (no signal propagation), or it is enlarged (forced to find alternative ways to stay closed).
This is directly related to emissions from your board.
I also discuss this more in-depth in my articles and courses.
3. Analyze the layout.
This is extremely important. Emissions are simply the result of uncontained fields; there is no black magic.
The reason we want to double (and triple) check the layout is to optimize for short trace lengths, small signal-return loops, sufficient space between traces to avoid coupling, continuous impedance characteristics, the use of return vias to contain fields when crossing between layers, etc.
4. Find out the parasitics.
Or they will find you.
This is one of the most innocent mistakes we can make.
We need to watch out for parasitic capacitance, inductance, resistance, and anything that can create alternative paths for the signal and its harmonics.
If we don’t account for parasitics, we risk creating common-mode currents, which are highly efficient at generating EMI.
Don't assume that your components and conductors will work as ideally described, because they usually don't.
5. Avoid antenna-like structures.
This means not only paying attention to the layout but also component placement.
If the component placement is incorrect, especially regarding connectors and their cables, you risk creating antenna-like structures that can become potential radiators or receivers of EMI.
Always keep in mind the dipole and loop antenna structures, as these are the most common ones.
This also means to keep an eye for the copper pours and their resonances.
I hope this helps you save your board from another EMI nightmare.
Dario