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PCB related question

Discussion in 'Electronic Design' started by [email protected], Mar 15, 2007.

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  1. Guest

    Hi everyone,
    Here's the dilemma. We want to ensure accurate positioning of a SMT

    We can specify better accuracy on the drilling of the pcb (for
    alignment pins) and place fiducials on the board for AOI pick and

    However, we want a visual feedback after assembly.

    I've proposed putting a pattern on the foil with 1 mil steps and a
    reference mark.

    A kind of vernier if you will. I'll be putting a big shape so it's
    easily manufactured, but how well will 1 mil steps come out?

    Anyone every tried this? Does this have a name?

    And yes, I will be calling our PCB shop.
  2. You will not be able to get 1 mil traces on your PCB. How small you can go
    depends on the board house, and copper thickness, but I would expect no
    smaller than 6-8 mils. If you choose this path, you will need to leave some
    soldermask off the spot where you want to view the traces.

    Does your SMT connector have alignment pins on it? That should take care of
    any drifting in reflow...

  3. And they will tell you they can't do 1mil traces. 3-4 mil maybe if you
    pay them.

    How much positional accuracy do you need on this connector?

    If you have physical allignment pins on the connector then I can't see
    why you need to even check the allignment after assembly?...

  4. Guest

    I'm not really asking for 1 mil traces. I'm drawing a solid piece of
    copper of about 100x50 mils, but it has steps on it that change by 1
    mil. It looks like stairs. I figure that there will be enough of a
    difference on average to serve as a visual reference. There are no
    features below 10 mils on my copper piece.
    It does, and it doesn't. We are having all kinds of problems.

  5. This will etch out as a diagonal line. Even if the traces are 10 mil, you
    are asking for 1 mil resolution...

    What kind of problems? If there is an alignment locator on the part, and you
    have an alignment hole on the board, it seems reasonable that you should get
    some decent accuracy. Is the locator hole too large? Are you using too much
    paste and floating the parts? What kind of problems specifically?

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