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Can anybody tell me whether the colour of the Solder Resist on a PCB makes any difference when using AOI equipment to recognise the components placed on it??

Mike
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  • I don't have direct experience with this, but I've heard that yes, that can be a pretty big problem. Your assembler will have better information on what their limitations are. – Daniel Mar 29 '18 at 16:13

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I suspect not, since the optical aspect of AOI (automated optical inspection) uses infrared light to illuminate the solder joints iirc.

If a system uses regular cameras to deduce correct orientation of parts, I could see contrast between the solder mask and the components being a consideration. However, I think such a system requires some programming and positional registration to be effective anyway, so that's probably not a significant concern.

Truth is, you should talk to your assembly house about it, as it probably depends on the specifics of their equipment and experience.

vicatcu
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  • Aren't they very likely to use regular cameras too, given that they want to spot things like wrong IC markings? I don't see how you could do that with IR. – Lundin Mar 29 '18 at 13:46
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From my (limited) experience in working on AOI machines - yes, it makes a difference. Especially with white soldermask.

Of course this will probably depend on the machine, but I had problems with detecting correct positions of (oddly shaped) elements and bridges between leads on white soldermask. But I think it would be best, to consult your PCB assembler and ask if it is a problem (for their machines).

It also depends how much "in-depth" will they go with the scan. If they will do just a basic scan - to only check if the elements are placed - this should not be a problem. But if the do "full" scan - checking solder fillets, bridges etc. - I think it could be problematic.

desqa
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