> thanks to all who responded.  i've absorbed some of it and i'm still
> chewing on the rest.

that's what we're here fer..... ;-)

> there was also talk about just deleting the mask where the heat sink
> goes, and a polygon "pour" or "fill" was suggested here.  i have never
> done this before.

in the PCB editor, try a Place->Fill or a Place->Polygon Plane...  just like
you would Place->Track (but make sure you have the soldermask layer of
choice selected on the layer tabs below for convenience...)

you gotta love protel...

> i know very little about gerbers and how to manipulate them.

gerbers tend to be simple text files and also have an associated aperture
file....

gerbers contain x,y coordinates and such information for primitives like
pads and traces (tracks in protel)....

the aperture files contain a list of associations, say a pad dimension or
style, associated to a "code".  If you have, on your board, 53 pads with
dimension 10 mil by 30 mil, then that dimensioning might be associated to a
single code, say "11" for example.  Then for other things like tracks that
are 10 mil wide, it may have a different code as well...   basically the
aperture file collates and lists all unique styles of primitives found on
your board layout and associates code names to them....

then the gerber file just lists the x,y location (and some other things) and
uses one of the code names for the proper primitive to be "placed" at that
x,y location on the photoplot....

in theory, for a photoplotter, the gerbers instruct the plotter to move a
light source over a piece of film to the different x,y locations.  The
aperture "wheel" is like those Disney/Kodak paper wheels in your kid's
binocular slide viewer (with the little advance-to-the-next-slide lever on
the side).  The wheel has all of your apertures that either get
flashed/drawn on the film at the proper x,y location.... The light source
shines through the aperture selected on the wheel to expose the film with
that primitive at that x,y...

then the developed film (negative) is used to photo-expose "resist" on your
copper-clad fiberglass board for acid etching...  the exposed portions of
resist are baked on with this photosensitive process and keeps the copper
underneath it intact during etching, the rest of the unexposed resist (where
the photo-negative obscures the photo-exposing light)gets washed off,
exposing bare copper to be etched away.... (although there are other
details/caveats here that I wont get into for now...)

ultimately, gerbers are files that you do not want to edit by hand in the
text file domain... rather use a graphical viewer programme to manipulate it
graphically... but if you want to leave out a layer, then that's even
easier...  CAMtastic might suite that purpose....

there's a pretty accurate (maybe not as detailed as some would like) quickie
description of the board fab phase...  I used to do all the above steps by
hand years ago... now I farm it out to the fab house....  It's a better use
of my time and money ;-)

Cheers,
-chris

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