Eagle PCB - Layer Stack Settings

[David]

Hi all,
Just a quick question. I am trying to set-up a 4 layer board in eagle for production at PCB cart with the following layers:

1. Signal
2. GND
3. VCC
4. Signal

Does anyone know the correct settings? I think its something like (1*2+3*16)?

Dave

[Simon]

shouldn't GND and VCC be the outer layers ?

[EEVblog]

shouldn't GND and VCC be the outer layers ?

Not usually, no.
GND and VCC on the inner layers is standard practice.
Advantages are you get physical access to the signal layers, far fewer vias (greater reliability, better controlled signal integrity), no crosstalk between signal layers, better power plane signal integrity (no cutouts for components), and greater bulk capacitive coupling between VCC and GND.
External EMC issues are usually moot. Only in special cases would you have no traces and all plane top and bottom.

Dave.

[David]

I emailed PCB Cart asking for there default stack-up so thought I'd post it here if anyone else was wondering:

Normal layer stack up: 1.6mm thickness/ four layer?
 
----------------- copper weight
~~~~~~~~~~~ 7628/ prepreg
============= 1.2mm1/1
~~~~~~~~~~~ 7628/ prepreg
----------------- copper weight
 
If I am correct the layer settings should be: (1+2*3+16) where * represents a core layer and + prepreg.

Dave

[jahonen]

It does not matter for the PCB fabricators how the PCB software is configured (unless you want to send the work file to them), they need only four gerber files for the copper layers plus solder masks top/bottom and optional silkscreens. Rest is pretty irrelevant, although there might be some recommended practices with particular software where the PCB layers should be located internally. For example in PADS, copper layers are always 1 to n, where n is the number of PCB layers. 1 is the top layer and n is the bottom.

Regards,
Janne

[stewartallen]

I use the following layer settings for 4 layer boards.  This specifies 4 layers with vias drilled though all the layers. ie no blind vias

(1*2+15*16)

If you have a look on the Eagle Help files, under Design Rules->Layers there is a explanation of the syntax with examples for more advanced uses.