EMC Question of the Week: February 26, 2018
On circuit boards that have a layer devoted to "ground" it is very important to,
- minimize the number of via holes in this layer
- minimize the diameter of all via holes
- provide isolated ground areas for each supply voltage
- all of the above
- none of the above
Answer
The best answer is "e. none of the above". The number and size of via holes in a ground plane is generally not an issue. Via diameters are typically much smaller than a wavelength (even at frequencies up to a few GHz). As long as via holes don't connect to each other forming slots, currents can flow freely around them.
Providing isolated ground areas for each supply voltage is usually a very bad idea. Most boards with a layer devoted to "ground" should have one solid plane that serves as a common return path for all the single-ended circuits on the board. In rare situations where it becomes necessary to isolate current returns to avoid common-impedance coupling (e.g. certain audio circuits), a separate return trace or plane should be located on another layer of the board.
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