EMI Bites: Why Copper Pours Are Often a Poor Choice for Return Paths
EMI Bites: Why Copper Pours Are Often a Poor Choice for Return Paths
A common misconception is that copper pours are great return paths in PCB design and that they serve to avoid EMI.
While usable in some cases, copper pours, especially those segmented and with antenna-like structures, typically increase current loop sizes and parasitic inductance, leading to elevated EMI emissions.
These copper pours often create high-impedance paths, forcing return currents through suboptimal routes and generating common mode noise.
The optimal solution is a dedicated Return Reference Plane (RRP) layer adjacent to the signal layer.
This ensures a low-impedance, uniform (and preferable) path for return currents, minimizing loop size, reducing parasitic inductance, suppressing emissions, and enhancing EMC compliance and signal integrity.
-Dario
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