Abd ulRahman Lomax wrote:

> Actually, Protel import, while the information would be valuable, is *not*
> the best check of file accuracy. CAMtastic is much, much better for this.
> If RS-274X output is used, it is almost one-button to bring all the gerbers
> into CAMtastic, and only a few seconds more to bring in the *drill*
> information.
>
> >   I always check my Gerber files
> >by importing back into Protel, and catch a number of common mistakes
> >in setting up apertures, hole sizes, board outline and plot legends, etc.
> >I do this mostly because it is the fastest way to check the Gerbers.
>
> Unfortunately, it does not really check the gerbers, because Protel made
> mistakes in gerber implementation, and Protel might well repeat these
> mistakes in the other direction. The most famous one is the incorrect
> implementation of octagonal pads. (I forget if this one looks okay on
> import.) An independent gerber viewer, particularly the kind of CAM program
> that a fabricator might be using, is much better.
>
> There is one problem with CAMtastic, however. The resolution is limited.
> Not a problem until one is working with pretty small dimensions, however.
> If one really needs high accuracy, in the submil region, I'd be sure to
> verify the viewer. Protel does better on this, it does not break down until
> the microinch region.

Yes, I know there are risks in all this, but I often DO view things with just
a couple pads filling the whole screen, and then sometimes measure the
gaps between planes and pads.  All I can say is I haven't gotten in trouble
with this.  If the board maker finds something and refers it back to me, I
can always see it on the imported Gerbers, and then fix whatever it might
be and regenerate.  So, I've never experienced a flaw that could not be detected
by careful examination of the imported gerber files just using Protel.
I've gotten to the point that my board fab rarely has anything to squawk
about, and errors are generally present in the schematic or schematic library
information, too.

I do not use octagon pads, which seem to be a holdover from the optical
aperture wheel on the original Gerber photoplotter, to prevent diagonal
lines from having faded edges.  I guess some tight zig-zag BGA grids
might benefit from these pads, though.

Jon


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