PCB Stackup/Ground Planes/Tradeoffs

[mspagon]

I need +Power, -Power, 2 routing layers, and a ground plane. However, I don't know how to choose my stack-up? If someone could explain all the different possibilities along with the trade-offs I'd really appreciate it. I'm concerned with things such as cost and routing difficulty and EMI and all that good stuff.

ALSO: what are the disadvantages of having +power and -Power share one ground plane?


In my book it says Top/Ground/+Power/-Power/Ground/Bottom. But more layers increase the cost, right?

So couldn't you have Top/Power/Ground/Bottom?

What about Top/+Power/Ground/-Power/Bottom? I'm assuming it's bad to have the power rails next to your routing and its better to have the ground on near the routing for shielding purposes?

Thanks so much,

Michael

 

[asimlink]

Hi Michael,

I would suggest you to read following topics on PCB Stack Design:
http://www.hottconsultants.com/techtips/pcb-stack-up-1.html

In PCB design you use even numbers of pcb layers.
Although you can use separate layer for every voltage and ground but this approach will increase cost of the pcb manufacturing.

These days embedded processors and FPGA use multiple voltage rails. Therefore these days it is very common practice to use split planes. A split plane is a copper layer which has several areas dedicated for different voltages. During split plane design you must give enough clearance to high voltage power rails. And you must not cross the highspeed nets over plane splits. Therefore you will need to design your split plane in a shape that caters all the emc related problems.

In your case a four layer pcb maybe good enough. Here is how your 4 layer pcb stack would look like:
1. Top Signal
2. GND Plane
3. Power Split plane (+p, -p, etc)
4. Bottom Signal

If your pcb has high speed signals then you should read following:
http://www.hottconsultants.com/techtips/tips-slots.html
http://www.hottconsultants.com/techtips/split-gnd-plane.html

I would suggest you to read all pcb design / emc related topics from following link:
http://www.hottconsultants.com/tips.html

Let me know if you still have any problem.

Regards