-----Urspr ngliche Nachricht-----
Von: Brad Velander [mailto:[EMAIL PROTECTED]]
Gesendet: Freitag, 17. Mai 2002 18:08
An: 'Protel EDA Forum'
Betreff: Re: [PEDA] Too many hole sizes


Are there any IPC Certified designers who can confirm or deny the need for a
fab dwg?
        What is the current IPC comment on the issue, come on guys I know
you're out there! Is the fab dwg not just part of the "complete" fabrication
information, what is the IPC training telling you guys to do about fab dwgs
these days? This is a test, are you a IPC man/woman or a mouse?

Georg,
        here is the best example that I can give. Contrary to some very
opinionated individuals, not all PCB inspectors have computers, nor CAD
software, nor the training to operate CAD software, in a 'LOT' of PCB
fabrication shops. Trust me, I have been in and out of many PCB shops in 3
States and one Province for over 20 years. We aren't talking about the
Merixs, Tycos or Praegitzers here, just normal small - med size fab shops.
How does this inspector check drill sizes or locations? From manually
reading the numeric information? Is the fabricator CAM shop supposed to make
a drill drawing for him? Do you trust the fab shop to generate this drawing,
if they make a mistake who's fault is it, you didn't supply the required
information so they were forced to generate their own? They are not perfect,
neither are you but you didn't even have a chance to check/inspect their
handiwork! What can they use for even their trained CAM operators to confirm
the correctness of the information which they are viewing on their computer
screens?

        When the PCB is received at your company's (or your assembly shop's)
loading dock, who checks it for valid hole sizes, dimensions or other
details? Is this a fully trained CAD operator, with system software to deal
with all forms of CAD data or a simple minimally trained inspector with some
pin gauges, calipers and the ability to read a technical drawing? If you
don't supply them with a Fab dwg, do you get called to the loading dock to
check the boards upon arrival because you are the only one in your company
who can access and use the electronic data files?

        Here some other very good examples for you Georg. Where do your
drill files locate themselves within you board outline? Where are any of the
holes with respect to the board outline? What are the dimensions of your
board outline? Does everybody go into the CAM files again and again to
generate their own measures of these items? Isn't that lost repetitive
operations that could be done just once, checked, verified and appropriately
tolerance by the individuals who understand the design? What tolerances
would be allowed by differing individuals who take their own absolute
measures of the CAD data in the file? The CAD data is absolute isn't it? Are
the fabricated parts absolute without tolerance? I wish.

Sincerely,
Brad Velander.

< snip >

Hi Brad,

this was a hit to the weakest point.

First, to the question file or drawing. For the drill drawing it is
absolutly clear
for the board house what I want, wether I send a file or a drill drawing
file. I agree with you, that
some other people need the drawing to check against the board.
For the outline, I send a mech - layer with a company template like any
other mechanical drawing
with all dimensions and tolerances added.
To help the guys from the board shop, the outline of the board is a 0.3mm
line. All other lines and text
are not 0.3mm. They told me, that they can mill along the drawn outline, the
dimensions are helpful for check
purposes.



What is more important, and made me a bit nervous, the checks of the sample
boards and the series boards.
Till now, we do only a few checks.
Imagine, somebody changes a drill with the wrong diameter in a volume
production. Your assembly -line reports
that they cannot mount the pth connector, but lots of boards are already
reflow mounted and soldered. Your board
supplier surely excuses a lot and perhaps replaces the blank boards, but the
rest is up to you or your company.
( the same is for wrong outline, thickness of the board, material or labels
( UL )).

To the question:
 I have to make a checklist for protos and volume blank boards. Have you
such a list or just
ideas, what all to check. ?

Georg



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