I'm *wearing* my virtual shorts right now.... good thing this is radio and
not television

-chris

-----Original Message-----
From: Don Ingram [mailto:[EMAIL PROTECTED]]
Sent: Monday, September 03, 2001 3:41 AM
To: Protel EDA Forum
Subject: [PEDA] Virtual Shorts


Just got PCB Fab Magazine & noticed that they are running 10 micron wide
traces.

Better make the virtual shorts way less than the customary 1mil

heh heh heh

Cheers

Don Ingram
[EMAIL PROTECTED]
Ph +61 7 4954 6074    UTC+10hrs
Fx +61 7 4954 6222
----- Original Message -----

From: Abd ul-Rahman Lomax <[EMAIL PROTECTED]>
To: Protel EDA Forum <[EMAIL PROTECTED]>
Sent: Saturday, September 01, 2001 7:09 AM
Subject: Re: [PEDA] Isolated "Island" on PCB


> At 06:16 PM 8/30/01 -0500, Nicholas Cobb wrote:
> >         I am making a board that has internal power and ground planes
and
> > I would
> >like to make an island that is isolated from all layers on my board. I
have
> >made a split plane of both the power and ground to have the isolated +5,
and
> >isolated gnd.  I just don't know how to keep the gnd and +5 plane from
> >invading. I have outlined my "island" with traces on the keepout layer.
>
> The keepout layer has no effect on negative layers!
>
> The most reliable way to accomplish what is desired is to ensure that the
> isolated net has a *different* net name. This, of course, would normally
be
> done on the schematic. If you don't want nets connected, don't give them
> the same name!
>
> If we want a single-point ground, there are a number of ways to accomplish
> this.
>
> 1. If the nets are *not* distinctly named and you want to leave it that
way
> (not recommended), place primitives (such as lines) on the negative layer
> to create isolating anti-copper. Leave a gap in the isolating outline.
This
> will *not* be DRC'd.
>
> 2. Use an ordinary jumper placed on the schematic; it has one net on one
> side and the other net or nets on the other side(s). The jumper is shorted
> in production. This method has an advantage that one can tinker with the
> isolation, placing, for example, a resistor or an inductor between the
> areas. We can place track to short the jumper on production boards, if
that
> is what we want. But this will produce a DRC error because of the short. I
> dislike this, because it encourages me to disregard a DRC error, a bad
> habit to develop.
>
> 3. Use a Virtual Short, which is a footprint used for the jumper which
> appears to be isolated to DRC but is actually shorted in production,
either
> because the gap between the two sides is *very* small (like 2 microinches)
> and thus disappears in real-world production, or the sides are shorted *in
> the footprint* using a non-copper mech layer assigned for this purpose.
> That layer is plotted with the jumper on all relevant layers (this is set
> up in the CAM Manager, where we can have different CAM setups for
different
> layers). The first kind of Virtual Short is described in the user FAQ in
> the filespace for [EMAIL PROTECTED]
>
> I've assumed that Mr. Cobb does not want "an island isolated from all
> layers." Rather he wants this island to have its own unique net, or he
> wants to isolate sections of +5 and gnd. If he truly wants isolation from
> all layers, he can place primitives on all negative layers (such as lines
> or fills) to blow out the section.
>
> [EMAIL PROTECTED]
> Abdulrahman Lomax
> P.O. Box 690
> El Verano, CA 95433
>

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