gEDA-user: PCB gerber export problem

[Stuart Brorson]

I haven't had experience with polygons and PCB.  However, I did have a
problem once with thermals not making it to the FR-4.  It turned out
that the PCB fab house needed to set a switch on their CAM software in
order to read PCB's Gerbers properly.

The issue is that PCB exports Gerbers which use a large subset of the
facilities available in the Gerber spec.  However, some CAM programs
don't support all Gerber features, or some CAM operators don't know
how to flip the switch to enable these features.

The specific problem I had was that some of PCB's drawing was done
with "clears" -- or something like that -- which not all CAM programs
draw by default.  That's IIRC.

My heretical suggestion:  Download GCPrevue and inspect your Gerbers
with it.  GCPrevue is a very powerful freeware [1] Windoze program for
Gerber viewing.  It has never failed me.  If the polygons look bad in 
GCPrevue, the PCB has a problem.  If the polygons look good in
GCPrevue, then your CAM software needs to be configured better.

A larger issue for the PCB developers is this:  If so many CAM
programs/operators can't read our perfectly valid Gerber files, then
should we perhaps modify our Gerber output so that it can be read by
even the most creaky, antique CAM program, and be imported
successfully by the most brain-dead CAM operator?  Or maybe we need to
put a note into the autogenerated fab drawing saying "CAM with clears
enabled" or something like that?

Stuart

[1]  Free as in beer only.


On Wed, 10 Jan 2007, Matthew Sager wrote:

> I have had a similar problem when using gerbers made with PCB with Circuit
> CAM (this is the software package for LPKF mechanical etching machines).  I
> found the polygon support to be a little flaky, but I also did not use
> polygons very much.  I was only using 1 or 2 polygons per PCB and they were
> very simple (a rectangle).  So take my limited testing with a grain of
> salt.  I never did trace out where the error was, also the PCB polygon code
> has changed a lot from the last time I tried using Circuit CAM.
>
> The error I was concerned with at the time involved Circuit CAM expecting a
> certain layer name or none at all.  I did finally find an option in Circuit
> CAM to ignore layer names.
>
> Matthew
> KI4AJZ
>
> On 1/10/07, Tomaz Solc <tomaz.solc at tablix.org> wrote:
>> 
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>> Hi everyone
>> 
>> Yesterday I sent a layout I've made with PCB (exported to gerber) to our
>> faculty PCB fabrication department. Fortunately people there checked the
>> layout before actually starting the machine and warned me that it looks
>> a bit strange.
>> 
>> This is how a part of my layout looks like on their machine:
>> 
>> http://www.tablix.org/~avian/geda/pcb/gerber-problem/circuitcam.jpg
>> 
>> And this is how it looks on PCB:
>> 
>> http://www.tablix.org/~avian/geda/pcb/gerber-problem/pcb.png
>> 
>> You can see that clearance around pins and lines is missing in some
>> parts of the gerber output. Strangely, the same gerber files look OK in
>> "gerbv" viewer.
>> 
>> Does anyone have any ideas how to solve this problem? I think it's
>> highly unlikely that this would be a bug on their end.
>> 
>> I'm using PCB version 20060822. I also tried the latest CVS version but
>> that just introduced a lot more errors (clearances were all wrong and
>> some polygons don't show at all in the output)
>> 
>> Best regards
>> Tomaz
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>> 
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>