Examples of operating conditions

We were contacted by one user in Kyoto City about a defect leaking out, and we visited the site to review the settings.

Under the circumstances, white defects could not be removed due to the "setting to not see black defects and darken the lighting" in order to forcibly secure the yield. Therefore, the data was re-created and the good registration was performed again.

Results,
Objects: 10 imaging & inspection per frame
Number of registered good samples: Approximately 160 images for the same lot
Detection level: Confirmed that a defect sample of several pixel size can be detected.
Special note: When NG is detected, retry only once.
Good product rate during one day of operation: approximately 85% (frame by frame)
The data is shown in the following table.
At first glance, this may seem low, but if the number of inspections is considered, the good rate is 98.4%. Considering the fact that there are sometimes streaks in the substrate that are indistinguishable from defects, this is a good figure.

The results of the meeting with the person in charge at the site this time are as follows,
(1) No parameter adjustments will be made to ensure a good quality rate.
(2) The brightness of illumination is not changed.
(3) There is considerable lot-to-lot image variation (mainly due to the glossiness of the material surface), and if this is absorbed by the good registration, microdefects will not be detected. Therefore, when the good quality rate drops, we consider that lot-to-lot variation has occurred and re-register the good products.
This is what we are talking about.

As is the case with various other samples, the lot-to-lot variation is greater than one might expect. This is obviously greater than the luminance variation of the lighting.
I believe that many imaging systems operate with "settings that do not decrease the good rate when the lot changes (because it is hard to re-set)," but this level means that defects smaller than the lot-to-lot variation are not detected. I think this is very dangerous.

I think it is necessary to "construct an imaging system that does not change images even if the lot changes" or to "allow easy tuning of settings even if the lot changes. Automatic tracking?"　I hope there is a way to determine if that tracking is correct....