At 03:02 PM 5/19/2002 -0700, Embedded Matt wrote:
>1. I placed an arc on the plane (my board is circular)
>to form a circle all the way around the edge of the
>board.  The idea is to keep the plane away from the
>edge of the board.  The assigned net for the arc is
>"No Net".  Is this the correct procedure for keeping
>the plane away from the edge of the board?

Yes. The only way to blow out (clear of copper) the edge of the board for 
power planes is to place primitives to be plotted at the same time (i.e., 
on the same layer or on a merged mech layer).

There is an annoying warning generated by DRC, however, that there are 
primitives on the plane layer. This warning is generated because the 
presence of such primitives, if unintentional and in certain positions, 
could break nets. Placing the edge blowout on a mech layer and setting the 
plane photoplot(s) specially in CAM Manager to merge with that layer would 
be a solution. Obviously, one must still be careful not to break nets with 
the edge blowout.

>2. The arc is 50 mils wide.  Since I placed the arc
>directly on top of the board outline, I expect to get
>25 mils of clearance from the board edge to the plane.
>  In general, is that enough clearance?

Yes, it is conservative but it is also what I routinely use.

>3. I have split the plane into multiple nets.  The
>tracks that indicate the boundaries are 45 degree and
>90 degree tracks.  Recall I have an arc on my board
>edge.  Because the 45/90 tracks and the arc are not
>"compatible", the tracks extend outside of the arc to
>avoid tiny slivers of plane near the board edge.  Is
>there a better way to do this?  For example, can I
>define the regions with mostly 45/90 tracks but add an
>arc at the board edge to complete the region?  Will
>the way I have done this likely confuse the board

Not the board house, as long as the desired outline is clearly specified 
somewhere, but it might confuse DRC. I forget if arcs can be used for 
facets of the split plane polygons, but definitely one should use the 
polygons and not use free primtives, it was not completely clear to me what 
Matt is using. I do suggest keeping all plane split edges inside the board 
outline created by  the drawn blowout. Since the latter is being drawn with 
a 50 mil track, which would be unnecessarily large for a plane split (I 
might use 20 or 24 mils), it is easy to bring a split to and into the edge 
blowout without taking the split beyond the nominal board edge.

Small slivers on an inner plane would generally be harmless, I would not 
put a great deal of effort into eliminating them. However, if you leave 
only a very thin path between one part of a split section and another, this 
could be a problem.

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