On 28 Sep 2011 at 0:00, Josh Koffman wrote:

> Hi all.
>=20
> I have a question about pours/planes on a PCB. I generally deal with 2
> layer PCBs, and one thing I've never quite figured out is how to deal
> with a plane/pour. I generally route all my tracks, including ground.
> Then I create a pour, but I only connect it to ground close to the
> power input on the board. I've always understood that this is to
> minimize the possibility of ground loops. This usually means I end up
> with a bunch of pour areas that run parallel to actual ground traces.
>=20
> I've been looking at PCBs designed by other folks, and it seems
> somewhat common to do a pour, but have it named the same as the ground
> signal, so that it floods over all traces that are ground. This means
> the pour can often flood into areas that would be inaccessible
> otherwise. I will sometimes do this on very small boards.
>=20
> So...which is the better way to go? I would imagine that it's highly
> dependent on the task at hand. I'm generally not doing much in the way
> of RF (though my current board has a Bluetooth module on it). My
> processors are usually clocked at no more than 16MHz.
>=20
> Thoughts? I'm really not sure which way to go on this one.
>=20
> Thanks!
>=20
> Josh

10 times out of 9 my boards are done this way. Avoids having to
individually route GND traces, maximises GND area, etc. The idea is that
you are minimising the GND resistance in the circuit, thereby minimising
GND voltages. But: you still absolutely must pay carefull attention to
where GND currents will flow, sometimes using "slices" to seperate GND
plane areas, directing high current paths, seperating sensitive areas and
connecting back to one common GND point etc.

I usually "tidy" these things up at the end of the design, looking at how
the GND plane turned out, looking at narrow necks and "fattening" these up
where possible, adding/shifting GND vias to better places etc.

I keep the GND plane clearance greater than (2x) track to track
clearance... reduce capacitive effects, less likely to get manufacturing
shorts to GND plane etc.

--=20
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  brent.brown@clear.net.nz


--=20
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