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From: Abd ul-Rahman Lomax <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: RE: [PROTEL EDA USERS]: Just a hole
Date: Fri, 09 Feb 2001 18:26:47 -0800

At 01:54 PM 2/9/01 -0800, Andrew Lowy Sybrandy wrote:
 >I still have a one question:
 >
 >1. Why is it important to change the X and Y size to zero before production.
 >It was said this prevents "flashing" from within the Gerber file, but I
 >don't know what that means.

The idea is that if the pad size is set to zero, nothing would be "flashed"
for it. The term "flashed" goes back to the time when a photoplotter
aperture consisted of a piece of film with the desired pattern (like a
filled circle, for example) on it. To cause a circle to appear on the film,
the film, or the head with the aperture, or optics, one of them, was moved
to the proper position and the light behind the film was turned on and then
off. In a phototypesetter I worked with, not an entirely different animal,
the film was on a drum and the apertures -- letters in this case -- were on
another drum rotating at fairly high speed. At the appropriate time, a
flash tube inside the high speed drum was given its high-voltage jolt and,
presto, the film chemistry was activated, awaiting development.

Gerber was designed in that kind of an environment. The film or aperture
disk or drum was moved to a position. To create a single shape
corresponding to the shape on the aperture set, you'd see a command to turn
the light off, then X and/or Y position commands and then a command to turn
the light on. If it was only a flash, the light would be turned off before
moving to a new location. If it was not turned off, moving to the new
location caused a line to be drawn. That's a "draw."

As to the question, I discourage setting pad sizes to zero under just about
any conditions, and I also discourage any procedure that requires changing
things after DRC. But one would do it to cause the pad to not appear on the
film. I think there are better ways, some of which have been described by
others.


Abd ul-Rahman Lomax
LOMAX DESIGN ASSOCIATES
PCB design, consulting, and training
Protel EDA brokering (resale) services
Sonoma, California, USA
(707) 939-7021, efax (419) 730-4777
[EMAIL PROTECTED]
[EMAIL PROTECTED]


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