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Arrgh - PCB footprint pad dimensions!

Discussion in 'CAD' started by Leon Heller, Sep 25, 2004.

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  1. Leon Heller

    Leon Heller Guest

    Why is it that the manufacturers' footprints for SM devices nearly always
    give the dimensions between the edges of the pads? I thought it was standard
    engineering practice to give the dimensions between centres, which is what
    is required by the PCB package I use, so I have to do a few calculations
    every time I create a new SM footprint.

  2. Leon Heller

    Leon Heller Guest

    Further to the above, I've just seen a footprint which has *one* dimension
    between the *centre* of a central pad and the edge of another with *all* the
    others between the edges!!!

  3. they do that so you can learn how to use a calculator!
  4. Bob Stephens

    Bob Stephens Guest

    One of my pet peeves as well. So far I haven't screwed up the offset
    calculations on a board, but it's only a matter of time...

  5. I always try to print it out 1:1 and lay the part overtop with a new
    footprint. If there's no samples in hand, that's when problems (this
    and other kinds) tend to occur.

    Best regards,
    Spehro Pefhany
  6. Using my CAD software, when creating Patterns like this - I will usually
    also place the Package Outline information on an Assembly Layer -
    superimposing it onto the Pad Layout. I will also create little square pads
    on the Assembly Layer - that way... if something looks 'odd' it will usually
    jump out at me, and I can investigate further, correcting if necessary.

    I had a Pattern recently - for a SIM Card - that dimensioned to the plastic
    edges... and the Pad edges. That was a challenge. I think mechanicers like
    to pose interesting challenges when it comes to dimensioning parts.


    James Jackson
  7. Slav Mit.

    Slav Mit. Guest

    Hello, everybody.
    In my opinion it is worth to visit and try their PCB
    Libraries Navigator. It is free (demo) for a month period. It helps to
    design land patterns properly concerning all tolerancies. I would appreciate
    any opinions about it.
    Best Regards.
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