At 11:10 PM 4/27/01 +0100, Terry Harris wrote:
>On Fri, 27 Apr 2001 07:55:37 -0400, you wrote:
> >> Bottom line, the format is a netlist as we understand a net list plus the
> >> physical location and dimensions of the pads.
>I hope it isn't that simple - testers, particularly roving probe testers
>only test continuity from each end of a 'net' + any stubs. For testing
>non-continuity (shorts) they don't bother looking for shorts between nets
>which don't get close to each other. You need more than a netlist and pad
>locations to figure out net ends, stubs, and net proximity.

Sure. However, Gerber plus IPC-D-256 gives you what you need, I would 
think. The physical geometry of the gerbers tells you what is close to 
what. The net list identifies the nodes.

As I recall, there is a field in IPC-D-356 for identifying a net midpoint. 
That *would* be a tad more complicated to generate.

>While Gerber is not an ideal format for generation of connectivity
>information at least it is a standard and one that PCB houses are going to
>get from all customers.

Sure. But while it is an understatement to say that it "is not ideal for 
generation of connectivity information." I'd think that the fabricator 
could generate what was necessary for probe testing from the gerber. The 
probe tester does not need to know what the node names are.

>If you choose to supply the board house with additional information then it
>is your problem if it is wrong - and you are going to be less familiar than
>the board house is with the conversion tool and less able to 'tune' it to
>suit their tester
>I think it would be more useful to be able to check a conectivity netlist
>against a Protel design, the PCB house gives you the netlist generated from
>Gerbers the way they think they plotted them. That would check the
>connectivity netlist and Gerbers and check them before they have made a
>batch of possibly bad PCBs.

If IPC-D-356 is generated from the PCB file, it could be merged with the 
Gerber data to allow the regeneration of a true net list as we know one. 
And then we could use our ordinary netlist comparison tools.

Since IPC-D-356 does include a full net list (except that parts are only 
identified by reference designator), it should be possible to compare it 
with the Gerber directly. It would not be difficult to make a 
tool/procedure in Protel that would do this. (Generate components and their 
pads from IPC-D-356, and then import the gerber to appropriate copper 
layers. Vias could be generated from IPC-D-356 or from unassigned flashes 
and drill data. At this point, once Update has been run, any violations 
should be immediately detected by DRC. I haven't considered negative 
layers.... but that should also be possible.

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

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