Why the BOM and the released revision keep drifting apart

It rarely starts with a big mistake. A buyer swaps a resistor for an equivalent because the original is out of stock, and the edit lands in the working Excel file. The ECO follows late, or never.

Meanwhile the traveler on the floor still lists the old part, stores picks what that traveler says, and the line loads whatever stores handed over without asking why.

Three documents now describe three different boards. The first person to notice is usually an operator holding a reel that does not match the pick list, after the kit is built. A quiet edit becomes a stopped line.

Most houses hold four copies. There is the customer file, the internal costed file, the one inside the pick and place program, and the one printed on the traveler. Each changes on its own schedule. Nobody owns the set. That is the root cause.

ECOs add a second layer. An ECO may be approved but not yet applied, or applied to the BOM but not to open work orders, so boards already in kitting get caught first.

Reference designators cause special trouble. A line reading C12 to C18 in one file and seven separate lines in another will not compare cleanly, so a manual check misses it.

Pick one active job. Pull the customer BOM, the internal BOM, the program file and the traveler, then compare them line by line for part number, quantity and reference designators.

Write down every difference. Ask who changed it and when, because the pattern shows which handoff is leaking, and it is often the step between engineering and purchasing. Start at that handoff.

Do this for three jobs. One job can be an accident while three show a habit, and the feeder setup file of the pick and place machine often carries the oldest copy. Nobody opens it until loading day.

Keep one released record per assembly, with a revision letter and a state of draft, released or obsolete, and let only released revisions attach to a work order. Drafts stay out of the shop.

Make the ECO the only way to change a released BOM, and have it list the affected work orders and the stock on hand of the old part. Someone chooses use up, rework or scrap.

Print the traveler from the work order, never from a loose file, then check again when stores kits the job and when the line starts the run.

Software helps because it can refuse. A system that lets a work order use only a released revision removes a whole class of errors that training alone never will.

Even without software, a weekly review works.

Name one owner for the released record. Engineering usually fits best, while purchasing may propose alternates but never publish them, and that single owner answers when two documents disagree. This week, take your three most active jobs and list the revision on each of the four documents, starting with the job nearest to its ship date.