Scenario note: This is a representative, anonymized engineering scenario created to explain a control method. It is not presented as a named customer claim or a published production result.
A 200-unit pilot build included a polarized protection device near the power input. The BOM manufacturer part number was correct, but the PCB silkscreen symbol and the assembly drawing indicated opposite orientations. The centroid rotation matched one of them but did not explain the physical polarity mark.
The risk
If the line followed only the centroid file, all 200 units could have been placed consistently and still been wrong. AOI could also learn the wrong orientation if the program were built from the same ambiguous reference. The result might be a power-up failure, component damage, or a large rework lot.
The containment decision
The build was held at first article. Engineering compared the component datasheet, PCB pad numbering, schematic net connection, assembly drawing, and physical package mark. The buyer then issued one written disposition identifying the approved orientation and the affected release package.
The permanent correction
- Correct the silkscreen or assembly drawing in the next controlled PCB/assembly revision.
- Add a close-up polarity image to the assembly instructions.
- Lock an AOI reference using the approved first article.
- Record the deviation for the current lot and link it to the affected serial range.
- Add polarity reconciliation to the pre-line release checklist.
Buyer takeaway
A correct BOM does not resolve conflicting assembly information. For diodes, LEDs, electrolytic capacitors, IC pin 1, batteries, connectors, and other directional parts, require one authoritative orientation reference and stop the build when sources disagree.
Use the PCBA release-package revision guide to align the source files, or submit the package for engineering review before pilot release.