A serial number is an identity, even when it contains only digits. If a spreadsheet removes its leading zeros or changes a long identifier, measurements can become associated with the wrong PCB. Protect identity columns before using a CSV file for yield analysis, retest reconciliation, or supplier reporting.
Microsoft’s guidance on leading zeros and large numbers explains that Excel can convert numerical text and recommends preserving appropriate columns as text during import. A display format that merely adds zeros is different from retaining the original identifier.
Define identity fields in the export contract
Mark unit serial numbers, lot codes, attempt identifiers, station names, and revision codes as text fields. Do not decide the data type by inspecting a few sample rows. A code that happens to be numeric in one production run may contain letters or punctuation in another.
Retain the original export as a read-only analysis input. Work on a separate copy or controlled import query. If an identifier has already lost characters, adding zeros afterward may not recover it reliably: the intended width may vary, and long numerical identifiers may have suffered additional changes.
Run an identity round-trip check
| Example pattern | Risk to inspect |
|---|---|
| Leading zeros | Zeros disappear when interpreted numerically |
| Long digit string | Stored digits differ from the source text |
| Letter E between digits | Code is interpreted as scientific notation |
| Date-like revision or lot code | Text becomes a calendar date |
Use synthetic identifiers representing the actual naming rules, without borrowing real customer serial numbers for software tests. Import them using the intended workflow, export the result, and compare the complete character strings with the source. Checking only what fits visibly in a narrow spreadsheet cell is insufficient.
Protect joins and summaries
- Verify identity columns before merging files.
- Count unmatched and multiply matched records.
- Inspect differences involving whitespace or letter case.
- Apply only normalization rules permitted by the identity specification.
- Retain the source value alongside any normalized comparison field.
Do not use fuzzy matching to silently reconcile production identities. A near match may represent a different physical unit. Route ambiguous cases for investigation with the original scan, test record, and manufacturing reference available.
Close the review with the import procedure and an example file that demonstrates preserved identities. Repeat the round-trip check after changes to the spreadsheet version or downstream parser. The measurement-unit guide covers the numerical columns, which need their own explicit conversion rules rather than the text treatment used for serial numbers.
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