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March 1999

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Subject:
From:
Jeff Seeger <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 26 Mar 1999 05:54:25 -0500
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Matthew Lamkin wrote:
> >Jeff Seeger wrote:
> > many snips for brevity <

[Matt Says >>>] done. Of course record of what is
> >done is allways taken & applied to the CAD file afterwards.

        I knew that.  But the practice is frightfully common, and
        too many people take it lightly.  No better forum than
        this to point out "good intention/bad concept".  Please
        forgive me if my humour gets dark by 5am.
> >
> >> some alterations that my CAD package could not,
> >
> >        Sure hope you have a scripting facility in that tool...
> >
> >[Matt Says >>>]  A scripting utility? what for, what would that do?

        Capture the mods/extensions for the benefit of the next
        revision.  Myself, I have enough of a time capturing
        "what I meant" once, and to do a significant edit again
        for a minor modification usually leads back to the "edit
        the gerber files" mode.  If the post-CAD tweaks can be
        captured and automated, the torturous path is less of
        a temptation.  I have found that no matter how careful
        and studious one is about back-feeding changes into the
        CAD system, a mistake is inevitable.

> >[Matt Says >>>]  My CAD package cannot create pads with a slot in them to
> >prevent the solder flowing
> >[Matt Says >>>]  over them when wave soldered. However using GC-Prevue I have
> >been able to do this with
> >[Matt Says >>>]  some clever manipulation of a bit of copper & layer merging.
>
        Well, can't visualize the case but you get the idea.  Any
        editor that can't capture what it did and repeat it gets
        used only as a viewer in our environment.  Of course, it
        really only moves the problem to a different level because
        on more complex revisions you may need to edit the script.
        Honestly we had to evolve to keeping multiple CAD tools so
        that we didn't have "can't create" problems.
> >
> >        Back to topic, I've seen difficulties w/274X - and the
> >        more complex the artwork the more likely the troubles.
> >
> >[Matt Says >>>]  I only once had problems, I usually design them out. Custom
> >apertures seemed to be
> >[Matt Says >>>]  my only problem, but only because I did not know how to
> >create them (I do now).

        Have had to gather a roster of viewers to see if we could
        get agreement.  One 274X file loaded back into source system
        just fine, but we got three different results from three dif-
        ferent readers.  Distilling the problem to a managable case
        and reading the spec showed the source tool was well behaved,
        if non-intuitive in some defaults.

        That was some time ago, and I think all the tools have improved.
        They had to.  But once in a while we encounter someone using an
        old version...
--

      Jeff Seeger                         Applied CAD Knowledge Inc
      Chief Technical Officer                  Tyngsboro, MA  01879
      jseeger "at" appliedcad "dot" com                978 649 9800

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