Another Land Pattern Mixup

Here’s an interesting error that doesn’t show up very often. Notice that the opening in the solder mask matches about what the copper land pads should be, but the pads themselves are really tiny. To start with, it’s not an exact match. It would fit the part a little better if the pads were closer together, but more than that, the pads are just the wrong size. The stencil looks okay and the solder mask opening looks okay (except that it’s a little too too wide).

I’m not really sure what went wrong here. Maybe one person started making a custom library part and someone else finished it, or maybe the component was changed between starting and finishing the library part.

If the stencil photo looks like it’s made of cloth — it’s not. We just photographed a CRT view of it.

Duane Benson
Need more chocolate.

4 thoughts on “Another Land Pattern Mixup

  1. There use to be a CAD system that showed an X,Y in the aperture report that wasn’t the pad size.

    X was the pad size (either round or square) and Y was the length of the draw to create the pad.

    .050 x .010 = .050 x .060 Pad
    .050 x .030 = .050 x .080 Pad

    I’m guessing someone either didn’t recognize this or had trouble with the math.

  2. This where having your solder mask opening and the pad size the same and having your fabricator adjust the solder mask opening commensurate with their processes, withing guidelines set by the fabrication drawing, as per IPC7351. Saying that I once had to change a pad size on a board, and only did the copper layers when I re did the gerbers, lets just say there was a slight gap around the pad exposing the 0V copper pour, which didn’t endear me to the production department.

  3. Could even be a translation error of the gerber data, particularly if it’s a re translation of older RS-274D with a human-interpreted aperture table though this is rare these days with RS-274X and ODB , and modern CAM software like Genesis.

  4. This is exactly WHY I take the extra time to manually go through my gerbers (mostly I use Pentalogix Viewmate) online before I send them out. I specifically look at 1) pads vs soldermask opening, 2) pad vs. paste mask, and 3) soldermask opening vs silkscreen designation. If you take the time you can, most often times, spot these issues. Yes, it does take time, but remember, this particular case (small pads) is NOT something your fabricator will flag (e.g. it is not a manufacturing DRC issue for them).
    Again, take the time, process the data (gerbers) on your end first, then submit the data.
    No, you will not be able to catch these issues ALL THE TIME, but you can minimize the problems – by using care.
    Good day.

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