EMC Question of the Week: July 20, 2026

copper fill on layer 6 of a printed circuit board

A section of a single layer in an 8-layer printed circuit board is shown in the figure. Assuming this board meets its EMC requirements, this is almost certainly a layer devoted to  

  1. high-speed signals
  2. power distribution
  3. RTN
  4. GND

Answer

The best answer is “b.” The large plane areas and lack of traces suggest that this is not a plane devoted to high-speed signals. The fact that a BGA device with over 400 connections connects to at least 4 separate plane areas is a clear indication that this is not a layer devoted to RTN or GND. 

RTN and GND are both labels typically given to the net(s) that serve the purpose of returning signal currents to their source. On multilayer boards, these should normally be implemented as one or more solid planes that have no gaps. The figure in this problem shows a section of an open-source board from Texas Instruments. Their return plane (a net labeled Dgnd) is shown below.

dgnd layer of an open-source circuit board from Texas Instruments

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