audioeaglepcb-design
I am designing motherboard for my preamplifier project and I want to setup PCB as follows:
What is the Eagle Design Rule Setup for such a board?
You've got lots of little proximity issues and shorts that Eagle's DRC should have pointed out to you. Did you run the DRC? When you do, it's best to use the design rules provided by the board house you plan to use. For example, here's OSH Park's design rules (scroll half way down the page). They even provide a .dru file to use directly as your DRC.
I've circled in orange the problems that I could see. As whatsisname suggested, it'd be more helpful if you provided the schematic as well.
I haven't used Eagle in a while, but if I remember correctly, at the bottom left of the screen after you hit the ratsnest button, it will tell you how many airwires are remaining. I expect the airwires are still there, but since the nearest ground connection is directly beneath the pads then they're vertical (not showing up very well when viewing from the top or bottom). Unless this is a new feature in Eagle 7 (doubtful) then you will still need to create vias next to the pins that need to connect to ground.
Best Answer
Why?
Obviously, a perfect analysis requires much more detail about your design than I have access to at the moment, but here are some general considerations.
A lower-inductance stack-up
I'm generally loathe to describe things as "analog" and "digital". Really, you should be classifying circuits by impedance and frequency (but that's a different topic).
The PCB is a 3D structure. If you want to minimize cross-talk, pick-up, and EMI, you need to minimize the current-paths' loop-area.
Allocating layers to functions as you have suggested results in much larger distances between the outgoing track (power-supply to load) and the return path (load to power-supply) as the return (should be) on the ground plane and that plane will be far from your signal layers.
You want to allocate functions laterally (same layer) and place that layer as close as possible to the ground plane as you can get it.
In virtually all of the "standardized" prototyping processes, the bulk of PCB thickness is in the core (the middle). So layers 1-2 and layers 3-4 are much closer together than 2-3.