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I'm designing my first 6-layer board using a SIG|GND|SIG+PWR|SIG+PWR|GND|SIG stack up. This is often claimed to be the best stack up online and in literature because layers 1, 3 are closely coupled to GND on layer 2 and layers 4 and 6 to layer 5.

However looking at the standard 6-layer stack ups at JLCPCB and PCBWay it seems they don't offer this close coupling as standard stack up:

JLCPCB offers as standard for a 1.6mm board: L1 [4mil] L2 [22mil] L3 [4mil] L4 [22mil] L5 [4mil]
PCBWay offers as standard for a 1.6mm board: L1 [0.11mm] L2 [0.6mm] L3 [0.11mm] L4 [0.6mm] L5 [0.11mm]

In both these standard stack ups the layers are closely coupled in pairs (L1+L2 and so on) not in triplets (L1+L2+L3).

Is using one of these standard stack ups an issue for the "standard" 6-layer stack-up? Should I request a non-standard stack up?

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  • \$\begingroup\$ It all depends what you are doing, what frequencies and currents are involved? Is this RF, computer, what? \$\endgroup\$
    – Neil_UK
    Commented Aug 4, 2023 at 7:39
  • \$\begingroup\$ Note that traces in the middle layers are vastly better coupled to the surrounding planes (at 22/26 mils distance) than they are to each other (except broadside coupled stripline), so it doesn't make much difference for signal quality. Whether that's a problem for trace width (wider for given Zo?) or other reasons, you'll have to tell us what you're doing. \$\endgroup\$ Commented Aug 4, 2023 at 9:05

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Rick Hartley suggests the following 6-layer stack-up in this video:

1 ------Sig/Pwr------
2 ------Ground------
        (core)
3 ------Sig/Pwr------
4 ------Ground------
        (core)
5 ------Sig/Pwr------
6 ------Ground------

The coupling is done in pairs which better matches the standard stack ups of the fabricators you mentioned.

Highlights:

  • Only 3 signal layers
  • All the power pours are referencing ground
  • All the signals are referencing ground
  • Changing from layer 1 to layer 3 doesn't require a stitching via
  • Changing from layer 3 to layer 5 doesn't require a stitching via
  • Care is needed so that layer 5 signals are routed above layer 6 copper
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