Your last paragraph is exactly what I want to do. I wanted the island to be
isolated from everything. Placing fills on the planes worked great.
Nick Cobb

-----Original Message-----
From: Abd ul-Rahman Lomax [mailto:[EMAIL PROTECTED]]
Sent: Friday, August 31, 2001 4:09 PM
To: Protel EDA Forum
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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