Reel-level traceability for a single board: the time window is the only workable method
One board uses several reels and one reel feeds several boards — a many-to-many relation. Reel-level traceability can only be reconstructed from loading timestamps and routing time windows.
Reel-level traceability means two things: given an SN, you can find which reels it used; given a reel, you can find which boards it went onto. What gets you there is not recording a part number for every board, but recording the usage time window of each reel on each machine.
Why the part number is not enough
A board at one station only touches the reel that is loaded at that moment. But a line has dozens of stations, a board passes dozens of them, and each station has been through several reels. If all you record is "this station used this part number", you get part-number level, not reel level.
Part-number traceability can only bound the problem: this batch of boards all used 0402-10K, which reel is unknown. The wider the bound, the higher the cost of quarantining it.
A many-to-many relation cut by time windows
The real relation looks like this:
- A reel is loaded at T1 and runs out at T2; the SN sequence produced in between belongs to it
- A board passes a station at T3, using whichever reel was loaded at that moment
So the rule is: a pass time falling inside a reel's usage window means the board used that reel.
| Data | Source | Key fields |
|---|---|---|
| Loading record | Loading scan | Station, reel barcode, load time |
| Splicing record | Splicing scan | Remaining quantity on the old reel, new reel barcode, switch time |
| Pass record | Scan at each station | SN, station, pass time |
Align the three tables on time and reel-level traceability holds. Without splicing records the window breaks at the moment of the splice, and every board after it fails to link.
How precise the window has to be
Minute-level alignment is enough, provided both loading and splicing are recorded. The typical symptoms of insufficient precision:
- Splicing records the new reel but not the end time of the old one, so two windows overlap
- The loading scan happens after the reel is seated, a few minutes later than actual availability
- Pass records only exist at shift level (reported per shift) with no per-board timestamp
The third is fatal: without per-board pass times the windows cannot be aligned, and traceability falls back to batch level.
Both directions must be supported
The system has to answer both questions; one alone is incomplete:
- Forward: this board, which reels did it use (complaints and audits)
- Reverse: this reel, which boards went onto it (incoming defects, supplier recalls)
Reverse lookup is the one used more often in practice. When a supplier batch turns out bad, the list of affected boards has to be produced within half an hour; later than that and the goods have already moved.
Write the boundary conditions down
Reel-level traceability is not universal. Three gaps are inherent and belong in the acceptance criteria from the start:
- Manual replenishment: material borrowed from another machine without a scan breaks the window
- Leftovers shared across orders: a reel used across two work orders must be split by remaining quantity, otherwise the whole order is counted as having used that reel
- Rework re-loading: a removed reel loaded again is a second use and needs its own record, otherwise the same reel shows two discontinuous windows
Frequently asked questions
FAQ
- How many barcodes does reel-level traceability need?
- Use the vendor barcode or a self-applied reel number on the material side, and only the SN and station code at the machine side. The count of barcodes is not the issue; what matters is whether loading, splicing and station pass each leave a timestamp.
- What happens when one reel spans two work orders?
- Split it by remaining quantity and cut the usage record of that reel into two segments, one per work order. The system must support carrying the remaining quantity forward, otherwise traceability attributes the whole reel to the first order.
- Can reel-level traceability work without per-board pass times?
- No. Reel-level linking depends on the pass time falling inside the reel's usage window. With shift-level data only, the windows cannot be aligned and the best you get is batch level.
- How is a large volume of traceability data stored?
- Archive by year once a table reaches tens of millions of rows. Archived data stays queryable through a separate entry point. Deleting is not recommended: automotive electronics customers usually require coverage of the product lifecycle plus the after-sales period.