A BOM and placement file can contain the same number of rows while describing different components. One may omit a reference, duplicate another, or belong to a different assembly variant. Compare their reference sets before upload and resolve every difference against the intended build.
JLCPCB’s BOM/CPL troubleshooting guide identifies inconsistent and repeated designators as distinct issues. Use that distinction in your own checks: a missing reference and a duplicated reference require different investigations, even when their effects cancel in a total count.
Normalize without changing meaning
Expand grouped BOM references into individual designators. Trim accidental surrounding whitespace and preserve the original values for review. Do not silently rename references, remove punctuation, or change case unless the export and receiving format explicitly define that transformation.
Create three sets: references intended to be fitted, references in the BOM, and references in the placement output. Keep intentional non-placement, mechanical items, and manually installed components in explicit categories according to the assembler’s requirements. They should not vanish merely to make two files match. Assign each excluded item a reason and an owning operation so its installation or deliberate omission remains visible in the overall build plan.
Review the differences
| Finding | Question to resolve |
|---|---|
| Fitted reference missing from BOM | Which part is the assembler expected to procure or receive? |
| Fitted reference missing from placement | Is it omitted accidentally or handled by another operation? |
| Placement reference absent from the intended build | Is the export from another variant or revision? |
| Reference repeated | Is there a duplicate row, grouping error, or panel convention? |
Check quantity independently. A grouped BOM line should contain the expected number of unique references per board, and the order quantity should not be confused with the per-board population. If panel data is used, define who expands unit placements across the array.
Confirm identity after matching
- Resolve all set differences with a documented disposition.
- Verify each fitted reference maps to the intended part number.
- Check side, position, and orientation in the assembly preview.
- Confirm the portal’s accepted population matches the intended variant.
- Save the accepted files and preview with the release revision.
A perfect set match does not prove correct coordinates or components. It establishes only that the named positions are accounted for. Continue with part matching and orientation review before approving assembly.
Regenerate both files from the controlled source after corrections. Avoid maintaining a manually edited placement file beside an unchanged design. The reannotation review explains why all identity-dependent outputs must move together after reference changes.
Move from reading to a build-ready project
Use the fabrication and assembly checklists to prepare drawings, production files and test requirements.
Open the DFM checklist