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I have a 4 layer PCB with the following planes...

  1. Connector (Top): Holds all traces going from connectors to components.
  2. Signal
  3. Ground: Coper filled completely.
  4. Power (Bottom): Coper filled for +15V and traces for -15V

Does it matter if the bottom layer is the power layer and that the ground layer is adjacent to it on the 3rd layer?

Some notes about the design:

  • Uses +15V -15V
  • Signal is audio with some op amps.
  • Basically building simple audio mixer, nothing fancy.
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  • \$\begingroup\$ This is called the "stack up" and may depend on the required trace thickness, signal speeds, board house, etc. There are a lot of ways to stack up a PCB. \$\endgroup\$ – Ron Beyer Jan 5 at 5:42
  • \$\begingroup\$ Yes understood, but based on the above description/restrictions, I don't have many choices anyways. I moved the power and ground in the middle but thats about it. My design is 15V and it's audio, nothing else. \$\endgroup\$ – user432024 Jan 5 at 6:03
  • \$\begingroup\$ Does this answer your question? The best stack-up possible with a four-layer PCB? \$\endgroup\$ – Huisman Jan 5 at 6:04
  • \$\begingroup\$ Searc this site on "layer stack up"... there are lots of Q/A about it \$\endgroup\$ – Huisman Jan 5 at 6:04
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It depends on your design requirements, such as highest signal frequency and EMC (electro-magnetic compliance). But in general for audio type signals it doesn't matter too much. The power plane will act like a ground plane next to signal layers, so you want to use as much copper as possible on the power planes as well. If your traces need to match a specific impedance, then you'll need to calculate trace size based on the dielectric and board thickness. There are good trace calculators on the web. I'll provide an example below. Or you will need a good layout CAD program which can computer trace impedance based trace dimensions and how far away the underlying ground/power plane is.

For a simple audio circuit like you have you really probably don't need to worry about trace impedance too much assuming your trace lengths are far shorter than a 20 Khz or so wavelength (20 KHz has a wavelength of about 15 km!).

Trace Impedance Example Using EEWeb Trace Calculator:

  • Board Type FR4: dielectric constant = 4.7
  • Layer thickness (between layers): 40 mil
  • Copper thickness: 1 mil
  • Trace Width: 50 mil
  • Resulting Impedance: 61 ohms

Layer Stackup

I would definitely modify the layer stack up as follows:

  1. Top connectors and signal traces
  2. Power
  3. Ground
  4. Signal

The above is typically what is seen. I like to have the signal layers on the outside in case any ECs (engineering changes) are needed. It is easy to modify traces on the outside, but not inside.

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  • \$\begingroup\$ Ok cool. Thanks. The longest trace I have is about 10cm if even. And using KiCad defaults for trace sizes. \$\endgroup\$ – user432024 Jan 5 at 6:30
  • \$\begingroup\$ EMC stands for electromagnetic compatibility. \$\endgroup\$ – Huisman Jan 5 at 6:41
  • \$\begingroup\$ @Huisman - I have seen it used for both. For example Electromagnetic Compliance \$\endgroup\$ – Otto Caldwell Jan 5 at 7:08
  • \$\begingroup\$ Better provide another link, they provide a Core Compliance Tasting Services. Anyway, I think you need to test the ability of electrical equipment and systems to function acceptably in their electromagnetic environment (compatible with the environment) and if successful, you may comply to legislation \$\endgroup\$ – Huisman Jan 5 at 7:15

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