01005 Built-in Short
AOI during fabrication will catch most pad shorts caused by etching.
THIS MONTH WE look at etching faults on PCBs. This is no ordinary set of pads. They are for an 01005 chip capacitor, the second-smallest chip component available. (Yes, there is an even-smaller size.) The 01005 component package is approximately 0.016″ by 0.008″ or 0.4mm by 0.2mm and small enough for most members of your staff.
Unfortunately, we found small copper shorts between the two mounting pads on one of our test boards that were not picked up during fabrication. The defective boards were spotted during printing trials. The nickel and gold plating are also present. As with many copper shorts, this is related to bare board etching and imaging, but they should have been picked up earlier.

It is not uncommon for bare board prototypes to miss standard AOI stages in fabrication. This was the reason in this case, as the author was in a hurry to start assembly trials. They printed and soldered fine, but the x-ray was a bit of a giveaway!

01005 pad short
Figure 1. 01005 pad short.
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Bob Willis Caricature
Bob Willis
is a process engineering consultant; His column appears monthly.