Defect in diode(Reverse Polarity)

Do you mean that your machine is placing the part backwards? Or the part is reversed internally? Like the Cathode mark is painted wrong?

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There could be several reasons - wrong part setup, wrong program, wrong machine placement. Solution will be to measure part before placement.

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incoming material. bad feeder. set rotate before recognition

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Sounds like a feeder or pick issue.

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If it was only 1 or 2 components on a reel that were backwards, I would lean more likely the cause just being the component was wrong direction in Tape from factory.

Not much you can do from a Pick & Place perspective, generally.. Most machines use binary vision or similar, which means they're only looking for lead characteristics and don't check for polarity. Moreover, the polarity mark is on top of the component so machines that due have this ability, generally are limited to LEDs or ICs where a marking is present on the bottom.

I wouldn't be too worried unless it was becoming common. Your QC / AOI should catch this to prevent it from ever getting to the customer.

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We use NPM and CM machines. What we've seen is the part will stick to the top tape on occasion and get flipped, either upside down, or reverse. Adjust the tape/cover so the top tape is pulled while the part is still under the cover. This is usually the fix for us.

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Possibly operator reloading rejected parts into tape/feeder in wrong orientation.

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