TL;DR

Rising false calls are usually a library threshold that needs re-tuning, an illumination change, or a conveyor vibration issue. Audit the top false-call component families first.

What you might see

false fail rate above baseline on production line
operator override rate increasing
specific component families generating most false calls
false call pattern correlated with board position on conveyor

Likely causes

Tap to mark as ruled out

Inspection library threshold set too tight for the current paste and component variation
Illumination module brightness change altering reflectance readings
Conveyor vibration causing slight board movement during image capture
Component packaging lot change with different body color or marking

Required tools

Koh Young SPC reporting tool
Known-good reference boards for re-teach
Illumination calibration target
Torque driver for rail clamps

Safety first

Do not modify inspection thresholds without running a validation lot. A threshold change that reduces false calls can also increase real defect escapes.

Procedure

7 steps · ~60 min

1
Export the false call report from the Koh Young SPC tool and rank by component reference, part number, and failure mode.
2
Focus on the top 3 component families generating the most false calls.[1]
3
For each, run the library re-teach wizard using a sample of 30 or more known-good boards to recapture the baseline measurement distribution.[1]
4
Check the illumination intensity reading in the system diagnostics. Replace any LED illumination module that reads below the minimum calibrated value.
5
Inspect the conveyor rail clamps and verify the board is held firmly during scan. Tighten any loose rail clamp.
6
Verify the PCB support pins are set correctly for the board. Insufficient support under large components can cause micro-vibration during imaging.
7
Run a validation lot of 20 boards after the library change and compare the false call rate to the baseline. Accept the change only if the false call rate drops without increasing the escape rate.

Sources

Koh Young Koh Young Zenith Alpha / Aurora AOI / X-Ray Inspection general technical documentation, Koh Young
Koh Young AOI system general library calibration and SPC procedures (general)

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