Steve Gregory wrote:
>
> Hi all,
>
> We're having a board lay-out done outside, and as with new designs, I
> will get asked to look at the preliminary gerbers to see if I can see
> anything out of place that might need changing.
>
> I looked the the gerbers that were given to me and the first think I
> noticed was that on some IC footprints, there was 1 rectangular pad,
> then 9 pads where the corners were rounded, then a rectangular pad,
> and on and on...
>
> snip <

        Hi Steve,

        You may find this useful.  Around or about my fifth or sixth
        CAD platform, I developed this rule when loading software:

        step 1, load software
        step 2, delete vendor supplied library
        step 3, continue with installation and adaptation

        As to the mix/match of pad shapes, recently we inherited a
        part with a "datasheet" footprint, with oblong pads on the
        corner pins of a four-sided part to cure an interference.
        The rest of the pins were rectangular, with an elongated pin
        to indicate #1.

        Sure enough the pin 1s had too much solder, with the corner
        pins all insufficient.  Sure, a closer look and a second
        try at the stencil may well have cured this but should that
        be necessary????

        Lesson?  Use a standard, stick with it and refine interpre-
        tation over time.  You do not know with certainty what a CAD
        or component vendor had in mind for a process when they set
        up that footprint, unless of course they tell you in great
        gory detail - and you agree.

        Best Regards,
--

      Jeff Seeger                         Applied CAD Knowledge Inc
      Chief Technical Officer                  Tyngsboro, MA  01879
      jseeger "at" appliedcad "dot" com                978 649 9800

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