RE: [PROTEL EDA USERS]: Multiple GND nets and I want no plane connection for one of them...

["D. Chris Mackensen" <dcm@blueskydevice.com>]

> >Hey... I was going to ask the question where I have multiple
> different GND
> >nets and I do not want some of the pads to connect to the GND plane
> >(separate higher current return to a starred ground connection).
> >
> >But I was able to make a pad class and make a rule for plane
> connect style
> >(no connect) with this pad class... works pretty slick...  so I guess I
> >answered my own question...
>
> There is a better way, in my opinion, which is to use separate
> nets on the
> schematic for each leg of the ground which should be isolated from the
> others.

Actually, yes I agree... I was worried about shorts (even though not
necessarily critical but we don't like quasi GND loops).... I actually did
it in two passes after playing with it for a short while.... The first pass
I had the separate GND nets in the schematic.  Loaded the nets, routed, then
I tied the 2 GND nets together on the PCB at the star point and the got the
expected DRC error.  Then I went back to the schematic and tied the two GND
nets together.  Then reloaded the nets/updated the PCB and with a little
playing with pad classes, was able to make sure the two high current pads
were not connected to the GND plane as well....  Luckily it was only 2 pads
I had to worry about...

> This is a part having a footprint with two pads (or more) which are
> separated from each other in the PCB database by perhaps .004 mil. Yes, 4
> micro-inches.

yes, I have seen this now that I recall.... It was actually on an allegro
board where sense lines had to be run separately from a DCDC converter (same
concept)...  I think the new PE14 version of allegro will have this feature
native without faking it.  But given the huge price for allegro (and its
complexity and general unautomated pain to use) I think I'll stick with
Protel for my projects here at home...

Thank you,
-chris