BOM revision control: rev letters, change logs and matching Gerbers

A bare board has a revision, usually printed in copper or silkscreen. A BOM has a revision. An assembly may have a third. They move at different speeds: changing a resistor value changes the BOM but not the board, while re-routing changes the board and often the BOM. Conventions differ between companies. What matters is that the record says which BOM revision belongs with which board revision, for example BOM D with board B.

A workable rule: bump the BOM letter for any change to an MPN, a quantity, a designator list or a DNP state, anything that could alter what is bought or placed. Description typos can follow a looser rule if you write it down.

A typical Gerber set describes the bare board, not the parts, so the match is made by checking. Confirm that the revision text in the board data equals the BOM's board revision. Then compare designators: every populated BOM designator should appear in the placement file, and the placement file should hold nothing that the BOM does not list as populated or DNP. Expect a short list of explainable exceptions, such as fiducials, mounting holes and logos. An unexplained designator on either side means the files come from different designs.

Board revision B is already released. A review changes R14 from 10K to 4.7K and sets C9 to DNP, so the BOM moves from revision B to revision C while the board stays at B. The log row records both changes, the reason and the approver. The file is saved as SN-210_BOM_revC.csv, with revision C written inside it. The diff against the previous BOM should show those two lines and nothing else. A third difference means the log is incomplete, or someone edited the file by hand. Once C is released it is not edited: the next change is revision D.

• Names like final_v2_NEW.xlsx. They say nothing about order or approval.
• Revision in the name only. The file name says C and the contents are still B.
• Silent edits after a quote. The BOM changes with no new letter, so the quote and the build disagree. See BOM for assembly quotes.
• Renumbered designators. Re-annotation changes designators with no physical change, so an older BOM no longer fits the new board.
• One half re-exported. New Gerbers with the old BOM, or the reverse.
• No log. A spreadsheet edited by several people, with nothing recording who changed what.

Some industries and customers set their own record-keeping rules for BOM changes. This guide describes common practice, not compliance advice.

BOMParser does not track revisions and does not compare two BOMs. What it gives you is a stable shape: every PDF BOM becomes the same ten CSV columns, so two revisions can be compared in a spreadsheet or a diff tool. The validation report records the file name, page count, totals and time of each conversion, and the checks show whether a revision's own arithmetic holds. Convert a file on the BOM to CSV page; pricing lists the plans. Free: one BOM every 24 hours, ten sheets or fewer, no registration. A free run stops at sheet 10 of a longer BOM. Redeem a code and the ceiling rises to 150 sheets.