Most PNP machines and AOI machines shuld have a X out feature.
For us we use to use whiteout pens to mark the badsense spot. Now atm we use white lables, becuase there is no dry time.
The lables have there own issues, They cause overpasteing issues on naboring circuts so we probably will not be sticking with them. Likely we will move to white paintmarker.
We loose about 15 seconds of production per a panel in PNP checking for xouts, Our mirtec AOI machine is the worst offender here, Loosing about 1/3 of max volume on a simple layout, and about 1/8 on a complex layout, just to check for Xouts.(assuming panel fids, 2 pictures a circuit, + 1 more for xout) (assuming 5 pictures a circuit + 2 per module fids, add a xout)
You also have other costs, about 1/4 of the X out circuts get populated on 1 side or the other by 1 or more PNP machines, for various reasons. The AOI machine will sometimes scan a Xout resulting in hundreds to thousands of false positives.
Also there are a lot of counting issues with X out panels. It sounds so simple to just count how many circuits are done and subtract the Xouts, but it probably doubles or triples the time to count a run, and you cant always trust the PNP machine's count due to missed X Outs.
There a headache but i cant see us ever not having them.