I've always designed my two layer boards with ground planes top and bottom.
However, I noticed a board lately with the ground plane on the top layer and a power plane on the bottom layer.
This can obviously make things a bit simpler but I was wondering if it's better to stick to two ground planes or if this is normal practice for two layer boards?
My boards do have some RF components but no long traces from them (a few mm run from a BNC header to a daughter board for composite video and another few mm run from a RN42N bluetooth module to a SMA connector).
I, like you, have settled with top and bottom ground planes.
So far, I have not had any reason to stop doing so.
Even high speed ECL designs worked well.
The only thing I am adamant about is separate ground planes for digital and analog circuits.
If things have worked in the past for you, continue to use top and bottom ground plains.
My take on this is that if the power and ground are decoupled frequently you can use power plane to join
bits of ground-plane at RF (decoupling) frequencies - rather than have a via between ground planes on each
side you have a decoupling capacitor... This can simplify distribution of power and allow both planes to be
broken into islands so long as their decoupling cap connections stitch everything together at high frequencies.
MarkT:
rather than have a via between ground planes on each side you have a decoupling capacitor
There is a rather cunning trick for this.
You have a hole in the PCB to fit a SMD capacitor which is inserted through the hole so that one connection "land" is on each side, and solder it in place.
Paul__B:
There is a rather cunning trick for this.
You have a hole in the PCB to fit a SMD capacitor which is inserted through the hole so that one connection "land" is on each side, and solder it in place.