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Thoughts on having AOI catch components that are supposed to be non populated???

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#68264

Thoughts on having AOI catch components that are supposed to be non populated??? | 21 February, 2013

Has anyone used their AOI to try to catch components that may be inadvertently placed in a location it shouldn't be? Every once in a while our equipment may drop a part onto a PCB and that part will adhere to pad. So the question has been brought up on using the AOI to inspect non populated pads on the PCB. I can understand the concept of teaching the blank area where the part should be and using that and on pattern match if there is a difference the machine would stop. But in real world does this create a lot of false call situations? Do a lot of people use their AOI in this manner?

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#68266

Thoughts on having AOI catch components that are supposed to be non populated??? | 21 February, 2013

It is a very interesting thought. However, teach all positions on the PCB might be challenging if you don't have them in the file. I think it is a smart think for OEMs as they would have all the resources to control their files. For CEM I don't see it working.

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Pete B

#68267

Thoughts on having AOI catch components that are supposed to be non populated??? | 21 February, 2013

We are a CEM and do exactly what you describe i.e. teach the image of a non-populated part and apply to all no-fits for that package style. Works very well with our equipment (Yestech)provided the visual signature of all your parts are sufficiently different.

Regarding teaching unpopulated locations - if you describe the part as a generic no-fit, for example NOFIT1206, NOFIT0805 etc. and incorporate that description into your CAD BOM as a part number for all applicable circuit references then you can automatically import them during program generation as all no-fit locations are normally included into the PCB CAD data.

Hope this helps.

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#68330

Thoughts on having AOI catch components that are supposed to be non populated??? | 28 February, 2013

I have been doing this since day one of getting the AOI. It just seemed logical. I don't know what type of AOI you have, but what I have found works best is to use solder inspection to catch parts that are loaded into a no-load location. Move the solder inspection boxes closer to the body to inspect for the end-caps of the component. The end caps should show up as white under a histogram algorithm, thereby failing the inspection if a part is loaded in that location that is supposed to be unpopulated. Another option is to use solder inspection in the normal inspection position. Except your white total would be expected to be high for no-loads instead of low. So your minimum score would have to be higher in this case (60-100). I've tried both. Using the end caps has worked better for us. But you will have to experiment with your system to see what works best. The problem with using negative templates is you can't plan for a particular part to be loaded in a particular location, so I have avoided this type of inspection. I should also mention, the above suggestion of using solder inspection for end-caps works very well for inspecting dark bodied parts with low contrast, such as MOVs. But since I am looking for an end cap, my score range would change from 0-60 (no load inspection) to 60-100 (presence/absence inspection).

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