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PADS, ASCII output question: Scale factor?

Discussion in 'CAD' started by Joerg, May 16, 2007.

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  1. Joerg

    Joerg Guest

    Hello Folks,

    We weren't able to sort this out. The layouter said this is the usual
    file that SMT assemblers use to program their pick&place machines but
    the assembler said they can't use it since the scale factor or data
    format for the coordinates is unknown. PADS was set to the American
    dimensioning of "mils" (1/1000th of an inch). Contacting Mentor resulted
    in no help. Here is one example from the ASCII file:

    R75.2 R66.2
    -190690500 289179000 1 381000 1024 TEARDROP N 90 90
    -190690500 287274000 31 381000 512 TEARDROP P 90 90

    What does "-190690500 289179000" mean in terms of mils, or millimeter?
  2. That actually looks like gerber info to me.

    I just generated a pick and place file out of Protel99SE, here's what part
    of it looks like:

    Designator Footprint Mid X Mid Y Ref X Ref
    Y Pad X Pad Y TB Rotation Comment
    U33 SO-8 1790mil 310mil 1915mil
    385mil 1915mil 385mil B 180.00 LM2672M-5.0
    U34 SO-8 840mil 310mil 965mil
    385mil 965mil 385mil B 180.00 LM2672M-5.0
    R304 0805_-_100MIL 4275mil 4605mil 4320mil
    4605mil 4320mil 4605mil B 180.00 6.04k
    R302 0805_-_100MIL 3555mil 4335mil 3600mil
    4335mil 3600mil 4335mil B 180.00 10.0k
    R301 0805_-_100MIL 3555mil 4235mil 3510mil
    4235mil 3510mil 4235mil B 360.00 10.0k
    U54 SO-18_WIDE 3380mil 11330mil 3170mil
    11130mil 3170mil 11130mil B 360.00 ULN2803AFW
    U53 SO-18_WIDE 3380mil 9730mil 3170mil
    9530mil 3170mil 9530mil B 360.00 ULN2803AFW

    They don't really need the P&P file. It just makes it a little faster to
    program the machine.

  3. Joerg

    Joerg Guest

    Thanks, Chris. Maybe the layouter generated the wrong file. Anyhow,
    since he's traveling now they went ahead and started programming the
    machine by hand. Over 500 parts...
  4. Hal Murray

    Hal Murray Guest

    They don't really need the P&P file. It just makes it a little faster to
    What's the error rate on "hand" programming?

    Reducing sources of errors seems like a good idea to me.
  5. Joerg

    Joerg Guest

    It's surprisingly low. In the late 80's it was all hand-programming and
    the errors were usually zero. But we do not have a choice here because
    the layouter can't be reached right now and the stuffed boards must be
    at the client Monday morning.

    It's 80% analog and I'll find a stuffing mistake pretty quickly. The
    only drag would be that we'd then have to correct it about 40 times.
  6. Marra

    Marra Guest

  7. My machine uses mechanical centering (vs laser centering) and tends to be
    off a little from the values the P&P file generates anyway. Manual
    programming is actually done with the camera, so placement errors are not
    really an issue. Most boards are easy to program manually, so not having the
    P&P file is not really a big deal.

  8. Joerg

    Joerg Guest

    Which brings up a question: Do you do contract assembly? Looked on your
    web site but it's under construction.
  9. Joerg

    Joerg Guest

    Sure, but what is the scale factor to get to inches, or millimeters?
    When we measured by hand and using a Gerber viewer the results totally
    did not corroborate the numbers in the PADS file.
  10. Joerg,
    The ASCII output is in PADs "basic units". If you have a PADs manual
    there is usually a section in the rear of the manual (at least the older
    manuals) that explains the basic ACSII format output and I believe it may
    also explain the basic units measure. Today it is maybe in a PDF or text
    file in one of your install directories or just left uninstalled on your
    original install CD.

    From memory (I haven't used PADs consistently for more than 8 years) the
    basic units are something like 254 microinches (or was it 25.4 microinches).
    It is the base unit of measure that the PADs database uses and allows them
    to easily convert metric to inches and back again without round-off errors.
    You should be able to look at a component or two, do some math and confirm
    the basic unit measure knowing the components real location from the
    database zero-zero point.

    The line that you quoted would seem to be a trace between R75 Pin 2 and
    R66 Pin 2, with teardropping. The first line will be the location of the one
    end start point and the second line will be the location of the end point.
    The "-190690500 289179000" are the base unit measures, the other data
    relates to both trace width and the teardrop sizing and orientation. That is
    my best recollection anyway.
  11. Joerg

    Joerg Guest

    Thanks, Brad. Now I know where to look for the next round. Or actually
    where our layouter could look because I don't have PADS.

    I just wish Mentor had told our assembler that (our layouter was
    traveling so he couldn't call them). But they more or less brushed him
    off. Anyhow, now they have programmed the machine by hand and the boards
    are coming off the reflow this afternoon.
  12. JeffM

    JeffM Guest

    ....and has been for >3 years.*/

    Already has all the business he can handle??
  13. Joerg

    Joerg Guest

    Well, sometimes you need a domain only for communications. Email, FTP
    and so on. My web site isn't that hot either but for now good enough.
    Promise to spiff it up some, but only when the workload eases off a bit.

  14. I do small volumes of control electronics, but so far it's just been my own
    stuff. I can certainly look at your boards to see if I could run them
    though. You can email me direct for more info.

  15. Joerg

    Joerg Guest

    I'll do that when the next round comes. It's mostly fine-pitch SMT
    stuff, up to 6U VME sizes (but not full length), some TSSOP and 0603.
    Occasionally I have to drop down to 0402 sizes.

  16. The people I traditionally sell to aren't real interested in websites.
    Somehow I manage to stay busy...

  17. My machine can handle boards up to 12"x10", and passives down to 0603.
    0402's take a special feeders which I don't have. I've never tried TSSOP's
    on it, but I can place 50mil pitch IC's no problem. No BGA's or anything
    requiring x-ray inspection though.

    Incidentally, if you're ever shopping for a P&P machine, laser centering is
    a must. Mine uses the older mechanical jaws to square the parts on the head
    before placement. It's effective, but it's also the primary limitation when
    placing smaller than 25mil pitch parts.

  18. Joerg

    Joerg Guest

    Same here. The only thing they sometimes want to look at is what
    services can be provided.
  19. Joerg

    Joerg Guest

    My boards are rarely larger than that. But TSSOP would be 25mil pitch.
    And I stay away from BGAs whenever possible because they are all but

    But I won't shop for P&P machines, I'll leave that work to the experts
    like you. Or, as the poker players say, you've got to know when to
    fold'em ;-)
  20. Hawker

    Hawker Guest

    There is a way to interpret that, but I use an unsupported script under
    VB scripts in Layout to make my X-Y sheet. Some 3rd party programs that
    some assemblers use can directly read a PADS ASCII file, that is why
    they asked for that, but apparently yours cannot so use the built in
    script under VB scripts.

    BTW I thought you were on the PADS ListServer as well. Probably get
    better answers there than here.

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