Dear Dwight Harm,
"Dwight Harm" <[EMAIL PROTECTED]> on 2001-05-18 03:03:17 PM, getting
frustrated, wondered:
>All the vias seems well inside the boundaries. I did find that if I delete
>all the vias, the warning goes away. Putting just one via back gets the
>warning.
>
>As another experiment, I tried changing the net assigned to the split plane
>(on my ground plane) to No Net, and to some random net. In both cases the
>warning did not change, nor were additional warnings issued, which seems
>odd, since the vias would be causing a short between two nets.
>
>I'm not even sure what Protel means by "overlapping". The top & bottom
>polygons, and the inner plane splits, all have identical (I think!)
>boundaries.
>
>Dwight.
You probably already know all this, but let me try to explain it anyway to get
it all clear in my head.
My understanding is that you can place the first split plane (a polygon) on a
power plane pretty much anywhere you feel like. The copper on that layer
*inside* the polygon is assigned the split plane's net; the copper *outside*
that polygon (off to infinity) is assigned the (default) power plane's net.
You can place as many other split planes on a power plane as you like (although
I've never actually tried more than 3), as long as those polygons do not overlap
each other. (it's OK if the vertices of one split plane are exactly on top of
the vertices of another). If the polygons did overlap each other (Venn diagram),
then it would be ambiguous what net the copper in that overlap area should have.
That's what the ``overlapping split planes'' error is supposed to signify. If
one polygon was *completely* inside another one, it's intuitively obvious what
Protel ``should'' do, but that software hasn't been written yet.
The "overlapping" only applies to split planes on the same layer. The split
planes on one layer ("power plane") are completely independent of polygon pours
on a different layer ("bottom layer"), and completely independent of split
planes on a different layer ("ground plane").
You could email it to me or one of the other people who have volunteered to look
at problems.
p.s.: Is chopping up the internal planes really helping ? According to
http://www.geocities.com/Heartland/Hills/5131/thermal.htm
,
``in the still-air environment ... double-sided heat sinks provided no advantage
perhaps because ... the board is thin enough that it does not insulate the heat
sink. Rather, heat is conveyed to the air from both sides of the heat sink even
when a single-sided unit is used.''
If putting copper on the bottom layer doesn't help compared to leaving it off, I
don't see that doing complicated things on the internal layers are going to make
any difference.
--
David Cary
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