EMI Bites: Hidden Problems in a "Perfect" PCB
Your PCB might look flawless to the naked eye, but small design mistakes can create big electromagnetic interference (EMI) headaches when it's time for certification testing.
The biggest troublemakers?
Impedance mismatches, poor layer transitions, leftover stubs, and crosstalk between traces.
But why exactly do these seemingly minor issues cause such major problems?
- Impedance mismatches - When traces connect at junctions with different impedances, signals bounce back instead of flowing smoothly, creating unwanted reflections.
- Poor layer transitions - Moving signals between PCB layers without proper stitching vias means there's no stable reference point for the signal to follow.
- Stubs - These leftover trace segments act like tiny antennas, broadcasting electromagnetic noise into the environment.
- Crosstalk - When traces run too close together (less than three trace widths apart), they interfere with each other, creating noise that corrupts signals.
Here's the key insight:
Signals follow the laws of physics, not your design intentions!
Even the most carefully planned PCB can become an EMI nightmare if these fundamentals aren't addressed.
My go-to solutions for clean, EMI-compliant designs:
- Use point-to-point routing for direct signal paths
- Add stitching vias at every layer transition
- Eliminate all unnecessary stubs
- Maintain proper spacing between traces
-Dario
P.S. Want more EMI control strategies to pass EMC?