Utilizing Bottom Copper for Multiple Power Planes in a 4-Layer PCB Design

I’m currently working on my first 4-layer PCB design, and my stack-up is as follows:

  1. Signal traces + ground fill
  2. Ground plane, no traces
  3. 5V plane, no traces
  4. Signal traces + ground fill

While the board incorporates a few different voltages, aside from the 5V connected to most parts, they are generated and utilized in localized areas. I’m considering utilizing the bottom copper to define multiple power planes around where they are used and created. Additionally, they could serve as thermal dissipators.

However, I’m unsure if this approach is recommended or if it might cause any interference. My circuit doesn’t involve high-frequency components except for a few using 10 MHz signals. Any guidance or insights on this matter would be appreciated.

It’s common practice to use multiple layers for power planes on PCBs. You can even allocate the top layer for localized power planes if needed. With careful planning, layer 3 could also accommodate localized power planes if heat-sinking isn’t necessary. Maintain the integrity of the 0 volts ground plane as much as possible, although experienced designers may deviate from this rule based on their expertise.

You could go either way, especially with no high frequencies involved, and I don’t think you would have a problem.

I typically opt for a signal/ground/-15V/+15V stack-up for op-amps. This configuration frees up a significant amount of space on the top layer for routing signals without interference from the dual power supplies.
Keep in mind that the +5V plane on Layer 3 may experience some coupling with the small power pours on Layer 4 due to the capacitive effect between parallel layers. If your +5V line tends to be noisy, it’s advisable to place the copper pour with the low-noise voltage reference on top of the ground plane. However, if you’re not dealing with low-noise requirements, there shouldn’t be any issues.

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