BOM Revisions

When a customer sends a new BOM revision, Gerbtrace shows what changed against the previous one: quantities, designators, MPNs, values and DNP flags. Both files go through the same import as the BOM tab, so column mapping, designator ranges (C1-C4), units such as 1 Stk and MPN spelling are handled the same way.

Where to compare

• BOM tab – click Compare revisions in the toolbar. Pick the old revision (a BOM file of the project or an upload) and the new one (usually an upload). Editors can then replace the project BOM with the new file (see Replacing the project BOM).
• Compare mode – create a compare project with the old BOM in Packet 1 and the new BOM in Packet 2. The file names must look like a BOM (for example contain BOM, Bill of Materials or Stückliste) so the import classifies them. Select the matched BOM pair in the sidebar and the BOM diff replaces the canvas; Text Diff still shows the raw file text.

Column mapping

Each side is parsed with the header row and column mapping Gerbtrace detects, or with the project's stored mapping for a project file. If the new revision renames or reorders its columns, the mapping of the old revision is carried over by header name, and the summary says how many columns were mapped like the old revision. Use Columns to correct a mapping; a column can only be mapped to one field.

Columns that only number the rows (#, Pos, Item, Line, Nr.) are ignored, so a reordered BOM does not show every line as changed. Other unmapped columns are compared when both revisions have them.

How lines are matched

Gerbtrace pairs old and new lines with the strongest key first:

1. Same designator set – C1, C2, C3 and C1-C3 are the same set.
2. Overlapping designators – a line that was split, merged or regrouped.
3. Same MPN – for lines without designators, such as screws or labels.
4. Value and package – for lines without an MPN.

Lines left over are added or removed. Designator comparison ignores case and whitespace.

Reading the result

The summary counts added, removed, changed and unchanged lines. Filter by change type (Added, Removed, Quantity, Designators, MPN, Value / package, DNP, Description & other), search, or turn on Show unchanged.

• Lines – one row per matched line with the old and new values. The line column shows its position in each file after parsing (#3 → #4). Split, merged and regrouped lines are labelled.
• Designators – one row per designator: added, removed, or changed MPN, value or line.

The value comes from a Value column when the BOM has one; otherwise the description is compared as the value. Designators listed on more than one line in the same file are flagged above the table.

Export

Use Export to download:

• Excel workbook (.xlsx) – sheets for the summary, the lines and the designators.
• Changed lines (.csv) and Changed designators (.csv).

File names follow the export naming scheme, for example Board_BOM-Revision-Diff.xlsx.

Replacing the project BOM

In the BOM tab, an editor can click Replace BOM with this revision when the old side is a project BOM file and the new side is an upload. This needs the BOM and Files tabs unlocked. After you confirm:

• The old file is removed from the project and the new file is added with the column mapping used in the compare.
• The BOM tab re-imports it like any changed BOM file. Lines whose designators are unchanged keep your edits (groups, notes, pricing). A changed MPN is added next to the old manufacturer, so remove the old part where it no longer applies. Lines with new designators come in fresh, and removed lines are dropped.
• The old file is not kept. The confirmation offers Download old revision and Export diff (.xlsx) so you can keep both, and use the diff as a checklist of lines to review.