At 12:02 PM 9/24/98 -0700, Martin wrote:
...
>        2) Since a Gerber file is a series of brush strokes, there is no
>netlist information, nor component information, stored in the file. A given
>viewer might be able to high-light all overlaping brush strokes, giving the
>illusion of a net, but it couldn't identify a component so there would be no
>conection information. So, unless there has been a revision to the Gerber
>standard that I haven't heard of, you can not make a reliable net list from
>the Gerber file.
...

This answer was *mostly* correct. First of all, a Gerber viewer that was
also drill-file aware could highlight a net. It would not be an illusion,
it would actually connect copper. The program might not be able to
recognise components, but the operator would easily be able to do so, by
reading the component legend.

But this would not make a net list.

>>3)  Is there any reason why blind vias might perturb the process of
>>extracting a netlist?

I don't have a high-end Gerber editor, only the shareware viewers, which do
not track connectivity and therefore the blind via question is moot for
them. But I would expect that a high-end viewer which was layer-aware could
handle blind vias.

Now, I have many times reconstructed PCB files from Gerber. The process
involves identifying primitives that are part of components (which consist
of pads, which are usually flashes, plus outlines, which are draws, and
reference designators, which are drawn text on the legend layer) and
replacing them with real components; the real components can be made (at
least in Tango for DOS) rather easily out of the primitives which came from
the Gerber file; the pads get numbered at this point and the reference
designator is turned into text (in Tango it would always be .REFDES); this
component is placed in a library, then back on the board with the
appropriate reference designator.

Once the components have been reconstructed, Tango and many other CAD
programs can then recreate a netlist.

It is more difficult to describe than it is to do, at least for one who is
familiar with Tango. But Tango for DOS won't handle blind vias.

Theoretically, a CAD program could character-recognise the reference
designators and similarly the pad patterns and generate standard components
from this information. But it would be difficult, and I would expect the
state of the art to be conversion assistance, not automatic conversion. One
might still need, for example, to select the pads which are part of the
component and identify their style of numbering and sequence.

[log in to unmask]
Abdulrahman Lomax
P.O. Box 423
Sonoma, CA 95476

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