At 01:43 PM 3/27/01 -0500, Thomas Sprunger wrote:
>I am trying to find a way to place text and components on ground planes 
>(or polygon fills) and to make them an absence of copper (or Anti Copper 
>in Orcad). Is this possible in the PCB portion of Protel?

Anything is possible, even if we don't know how to do it.... :-)

A polygon pour will avoid and pour around track on its layer which is not 
assigned to its net. Gerber plots reduce strings to track. These facts can 
be used to produce negative text.

Protel has no true anti-copper attribute for primitives. Such primitives 
would have fairly drastic impact on many routines, I would think, so I 
would not expect it soon. However, positive-negative merges have been 
suggested and if Protel moves in this direction, it will become possible to 
have anti-copper. Normally we think of a photoplot merge as being 
subtractive-additive, i.e., the anticopper primitives are written to 
subtract copper from a solid layer, and then the normal primitives are 
written to add positive features. But anticopper as Mr. Sprunger is 
conceiving it would require additive-subtractive, or 
subtractive-additive-subtractive; eventually in the process negative shapes 
are drawn or flashed to remove copper from a solid region.

RS-274X supports such procedures, but Protel does not, because it is 
essentially more complex.

But we can make negative text, as I indicated above.

Photoplot some text. Import the plot, which will create track primitives 
representing the text. With appropriate clearance settings, pour copper 
around it; do not remove dead copper and, of course, the net for the 
polygon pour must be different from that of the track primitives (which 
will be no-net ordinarily). Lock the polygon and delete the original 
imported track. This block could be made into a component if you want to be 
able to move it about. A net can be assigned to it by Update or global edit.

I have not experimented with layer-specific keepouts for this except to 
find that layer specific keepouts cannot be created by global edit. Others 
have complained about this so perhaps we will see such a feature in the 
future. For now, one could manually check keepout for each track primitive 
reduced from the string and this would eliminate the necessity of deleting 
it. One could  modify such primitives en masse in the ASCII database itself 
(or in a spreadsheet???).

keepout fills can also be placed to create open blocks in a pour, and 
keepout arcs to create open circles.

As to strings on inner planes, that is extremely simple. Just place the 
strings. Any primitive placed on a negative layer, such as an inner plane, 
is anti-copper already. Protel has no other negative copper layers; the 
solder mask is a negative layer, though.

Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433

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