Labelling and tracing boards in a rack

The expensive storage failure is usually not a damaged board. It is the wrong board going back to the line: a reworked assembly that looks identical to a failed one, or a lot split across two racks and put back together wrongly. Nobody catches it in the storeroom. It gets caught at the customer.

Number the slots, not just the rack

A label on the end of a rack tells you what the rack holds. It does not tell you which board came out of which position, which is what you need when a lot is part-processed, or when three boards out of fifty failed and you want to know if they were adjacent.

Numbered slots turn a rack into a coordinate system. Board 17 is board 17 to everybody, on every shift, and a note that says "17 to 22 rejected" needs no further explanation. We stock a slot-number label set as a spare part for exactly this, because it is the cheapest traceability upgrade available.

What to put on the rack label

Keep it to what somebody needs in order to act without asking:

• Work order or lot, because that is the key everything else joins on
• Part number and revision, since revision is what gets confused
• Operation last completed, not the one coming next, which changes
• Quantity and slot range, so a short rack is visibly short
• The date it entered storage, which is the only way a floor-life clock stays honest

Make the state visible on the rack

Most mix-ups happen because two racks look the same. Colour is faster than reading: one convention for incoming, one for in process, one for hold or rework. An ESD slot stopper is also worth knowing about, because a stopper on the last used slot makes a part-full rack obvious from across the room, and stops boards migrating in transit.

Keep the clock with the boards

If a lot carries moisture-sensitive components, the floor-life clock started when the dry pack was opened, and the only place that date is useful is on the rack in front of the operator. A clock that lives in a spreadsheet is a clock nobody checks. Written on the rack, it gets read every time somebody reaches for a board.

More on what that clock governs is in baking MSD boards, and the standards behind traceability are collected in the standards reference.