What an SMT material error-proofing system is: three levels by blocking capability
A material error-proofing system checks feeder, part number and substitution before placement and blocks on mismatch. Blocking falls into scan prompt, scan-and-lock, and scan-and-lock plus splice verification.
A material error-proofing system checks that feeder, part number and substitution rules agree before mounting, blocks the action when they do not, and keeps a record. It does not improve placement quality; it solves one thing: wrong material does not enter the line.
Three actions that let wrong material in
Wrong material is not a single mistake but any one of three actions left unchecked:
- First loading: a reel placed on the wrong feeder. Most plants scan here already, so problems are limited.
- Splicing: a reel runs out and a new one of the same part number is loaded. The part number matches but batch and vendor may not, and the action is fast and often skipped.
- Substitution: a registered substitute goes on when the main part is short. A system that only validates the main part number either alarms on all of these or gets bypassed.
Of the three, first loading accounts for only part of the problem; splicing and substitution are the chronic gaps. Whether a system is adequate comes down to whether it covers the last two.
Three levels, and what they actually block
| Level | Method | What it blocks | What it misses |
|---|---|---|---|
| 1 | PDA or station terminal scans, compares feeder and part number | Wrong feeder, wrong part number | The alarm can be ignored; splicing and substitution are outside the check |
| 2 | A failed scan locks the machine until resolved | As above, and cannot be ignored | Splice actions not connected; false alarms when substitution rules are unmaintained |
| 3 | Locks the machine and brings splicing, substitution and leftovers into the check | All three actions, with timestamps throughout | Operators scanning under another person's account, which needs access control and audit |
Most plants stop at level 2, because level 2 only solves the visible problem. Level 3 depends on the feeder table carrying main-to-substitute relations; without them the system can only match part numbers one to one and will raise false alarms on every substitution.
Four kinds of data the system must keep
Blocking is the immediate action; data is what can be checked later. A usable system keeps at least:
- Feeder-to-part mapping: generated by work order, model and side, and reissued at changeover
- A scan record for every reel: who scanned which reel onto which feeder, and when
- Splice records: remaining quantity on the old reel, new reel barcode, splice time
- Substitution records: which substitute part was used and whether it was on the allowed list
Only with all four can the system answer the question audits ask most: which reels went into this board.
Three inputs to prepare before go-live
- Feeder table: exportable by model and side, ideally with a substitute column. Without one the system has to be built by hand, and that work falls on the customer.
- Part numbers and substitution rules: substitutes must distinguish full substitution from conditional substitution, such as only for specific work orders.
- Barcode rules: whether the reel barcode carries part number, batch and quantity. Barcodes with a serial only need an extra mapping table.
With these incomplete the system can still go live but will not block accurately, which is the most common cause of rework in implementation.
When not to start with a system
Lines with low single-shift output, a fixed model and fewer than ten changeovers a year can hold the error rate down with a paper feeder table and two-person verification. There the benefit is audit documentation rather than error-proofing itself, and it can wait until a customer asks for traceability.
Frequently asked questions
FAQ
- Does a material error-proofing system need extra hardware?
- It depends on the level. Level 1 needs an industrial PDA or a station terminal; level 2 must be able to lock the mounter, which needs an equipment interface or an IO signal; level 3 also covers the splice action and usually involves lit racks or a handheld scanner.
- What if the operator ignores the alarm?
- Level 1 relies on management, level 2 and above rely on the lock: nothing proceeds and the machine cannot start until it is resolved. When selecting a system, "can the alarm be ignored" is a harder criterion than any feature list.
- How should substitutes be configured to avoid false alarms?
- Maintain main-to-substitute relations in the feeder table with the substitution conditions noted. Validate feeder, part number and substitution permission together at the scan, and release only substitutes on the allowed list.
- Can it run without an electronic feeder table?
- Yes, but the table has to be built by hand first, and the effort scales with the number of models. For plants with many models and frequent changeovers, digitalise the feeder table first; otherwise maintenance cost will exceed the benefit.