[sdiy] Ground planes

[Neil Johnson]

Hi,

David Ingebretsen wrote: 
> Is there any value to adding a ground plane fill to a PCB for the typical
> types of circuits for audio module? How about one on both sides of a two
> sided PCB? Is there any difference in putting it on the top versus bottom?

For audio its questionable.  I do it on my boards for two reasons: cosmetic (a copper plane on the top side gives a more uniform appearance) and ease of routing the ground nets, especially so on through-hole boards.

Otherwise since we're dealing with relatively low frequencies the electrical benefits of a ground plane are not that great.  If you want low-noise there are much better design techniques than blindly relying on a ground plane.  If anything, if used incorrectly ground planes (and power planes) can make things worse.

Oh, and it doesn't matter which side the ground plane is on.

> I'm getting ready to send a board off to be made. It's easy to add it, but
> I'm not sure the theory behind it other than even with "thermals", it's a
> pain to solder pads connected to a ground plane. 

How many spokes do you have on your thermals?  And how wide are your antipads?

> I've noticed some PCB's I've purchased have them, but many don't and I
> haven't heard any artifacts either way.

At audio frequencies its unlikely you'll hear any benefit.  If you're aim is low noise then much better to carefully route the signal path (including the signal ground) between circuit blocks, and keep power and signal grounds separate, and have a single ground point.  And be very careful who you share grounds with (i.e. everything that plugs in - differential is best here).

A good read on ground planes (and other PCB layout tips) for high-frequency stuff:

http://www.analog.com/library/analogdialogue/archives/39-09/layout.html

Cheers,
Neil
--
http://www.njohnson.co.uk