Electronic – PCB stackup ambigous percent number

An advantage of a local power plane is that you can leave all the power routing out of your signal layers and in stead focus on the coupling, routing and impedance control of your signals.

Other than that the best advice is always based on your complete and exact design, so I'll tell you some of my preferences and their reasons, and leave them for you to consider.

For reasons of know-variables I prefer to keep no other layers between the GND and important signals, so in complex designs I try to make as many Signal layers directly next to a ground that fits my stack-budget (of course I'm not spending the money for 16 layers on each design I make!). And if I can only get 1 reliable layer like that, I make sure that layer has only signals and hosts at least the signals that are most important or highest frequency.

For the distances of the stack-up you best call the fab you are having the PCB made at, they know what they can do and what they stock. Once you have those numbers you can use them for your impedance control if you need to.

They can also tell you how accurate their PrePreg procedure is. If it's not very accurate or the layer it is spread on has a lot of copper areas and a lot of gaps as well (this makes PrePreg harder to get uniform) sometimes you will want your Signal and GND on either side of a normal plate, to be able to perform good impedance control. If that is a demand you might want to go for your first choice, but swap the "SIG" and "Sig/Pwr/Gnd" layers.

Another thing you put in your title is Analogue, if you have high-fidelity requirements of analogue signals you are not going to regret splitting your Analogue and Digital power domains completely, including the ground planes and only connecting them at the power-input of your board. You'll be thanking yourself for the extra effort once you find you measure very little digital noise in your analogue signals.

Well hopefully you don't have 1" spacing between your layers because that's a heck of a thick board :) You can use layer 3 for small local power planes and routing but the consequences I can think of would be the following:

• Traces on layer 4 will reference the reference plane on layer 2 if there is no reference plane below them on layer 3. As you say the distance is greater, you won't be able to get reasonably sized traces and maintain the same impedance you have on layer 1. Well unless the over all thickness is very small, but in a 4 layer board it won't be.
• Your radiated emissions will increase because your loop area is increased
• Traces on layer 3 will reference layer 2
• Places where your traces on layer 4 cross your power planes will result in impedance discontinuities and reflections. Depending on your speeds this may or may not be an issue for you. I'd advise avoiding this, and where possible only cross traces on layer 3 and 4 orthogonally (like a plus sign).
• Traces from layer 3 and 4 can couple to one another easily so avoid long parallel runs between the layers just as you would on a single layer.