In the United States, the provision of gerber files is, as has been noted,
standard. Many fab houses will not accept anything else.
In the U.S., Protel is a minority CAD system (though certainly there are a
lot of licenses). For fab houses to be able to accept Protel files,
obviously they need a license. And do they need a license for every other
system out there.
The only universal standard for photoplots, practically speaking, is
gerber. And every fab house has tools for dealing with gerber, with editing
it if they need to do so, etc. Often these tools are quite sophisticated.
I told a story on the main list about a Protel license sale I lost because
the company was accustomed to sending PADS files to their fabricator. There
was little reason for this, since the fabricator could have easily accepted
gerbers. I can think of only one justification: if the fabricator makes
changes, they can become part of the permanent board file. And I don't like
that, that it is the fabricator making final design decisions. I'd want to
be consulted, and if I am being consulted, I can quickly change the board
and generate new gerber.
Fabricators will change the gerbers anyway, and it would assume that they
would do this with gerber, not with the original board file, which would
introduce tremendous confusion. We set up hole sizes on a board at nominal;
they will adjust these to meet fabrication realities. Our supplied gerber
and drill files are a *specification.*
So why are CAD files supplied sometimes? I work with a fabricator who often
gets them. Why? Because the designers are engineers who really don't know
what they are doing, and they do not clean up their designs, they leave it
to the fabricator. He builds the cost for this into what he quotes them.
Sometimes he has an outside designer do the work; I've occasionally been
that designer.
How about a board where the engineer did not know how to make footprints so
the whole board is part footprints -- where the footprints were in the
standard library -- and part raw primitives? Naturally, the engineer
checked the board by drafting another engineer and they sat there and read
off connections to each other. And, naturally, there were errors remaining
on the board.
Did they know how to generate gerber? Barely, not well.
There are plenty of errors that can be made in the reduction of design
files to gerber. Some of these are errors in design choice taking place in
setting up the gerbers, that is, they are not clear in the design file.
Whose responsibility are they?
When a fabricator makes a mistake plotting the gerber or following the
other design specifications, it is typically clear whose mistake it is. It
gets murkier when design files are supplied.
Yes, if you have a long-standing relationship with the fabricator, they
might take on the task of reducing the files to gerber. But then you can be
locked into that fabricator; it's not necessarily good for the company. If
you supply gerber, you can ask another fabricator for a quote at any time.
The gerber files are also commonly requested by assemblers.
All these people should not be altering design files, and it is easy --
once you know how to do it -- to supply gerber and Excellon drill files and
BOMs and pick-and-place files. Again, they all have tools to deal with
these, they have to. They don't have to have Protel or Eagle or whatever
their customer might be using.
In Australia, many or most fabricators might have Protel, certainly. But
what if you want to send your boards to Malaysia, to get a quote from a
house that does not have Protel? Are they out of the running simply because
they don't have your CAD system? Much as I like Protel, I would not judge
the quality of a fabricator based on whether or not they had this
particular CAD software! If they did not have a good gerber editor, I
*would* be concerned.
[EMAIL PROTECTED]
Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433
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