4.1 Why Traceability Levels Matter

~~Lot vs unit serialization, genealogy depth, and compliance/customer returns.~~

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surface.

4.1.1 What “traceability” really means (in 30 seconds)

Traceability ties a finished unit (or a lot of units) back to who built it, when, where, with which materials, and what happened to it along the way. Your genealogy model defines how deep that link goes—unit-level only, unit→subassemblies, or all the way to component lots. Pick the right depth and you’ll solve returns surgically instead of recalling a warehouse.

4.1.2 Levels (compared side-by-side)

Level	What you serialize	Genealogy depth captured	Typical cost/complexity	When it fits	The risk you can’t control
None	Nothing	None	$ (cheapest)	Internal prototypes, lab builds	You can’t isolate a bad batch at all.
Lot-level	Work order / date code on labels	Process route + line/shift + materials by lot	$$	Stable consumer builds where defects are rare and escapes are obvious	If one unit fails, you often quarantine the whole lot.
Unit-level (serial number)	Unique SN per PCA/product	Full route + operator/station + test results per unit	$$–$$$	Most volume products; strong RMA handling	You may still lack component-lot links unless you log them.
Unit + component-lot genealogy	SN and every critical component lot used	End-to-end: materials, processes, tests per unit	$$$ (discipline + data)	Regulated / safety markets; tight customer contracts	More scanning & data quality work; requires MES discipline.

You’ll wire whatever level you choose into labels/markings, the encoded data spec, and the scanners/MES links later in this chapter (4.2–4.5).

4.1.3 How the right level pays off during a return (RMA)

Scenario A — You have unit serialization + genealogy.

Customer gives SN. You pull its build route, test logs, and component lots in minutes; scope impact to specific SNs or lots, not a whole quarter. Close the loop in MES.

Scenario B — Lot-level only.

You can time-box the issue to an order/shift/date code, but you’ll likely quarantine more units than necessary while you sort root cause.

Scenario C — No traceability.

You’re guessing. Expect broad quarantines, longer downtime, and thin evidence for suppliers or customers.

4.1.4 Compliance & customer contracts (why “deeper” may be mandatory)

Some industries and customers require tighter genealogy (think medical devices, safety-critical, high-reliability). Your quality system (ISO 9001, ISO 13485) and customer specs will call out what must be recorded and for how long. If they say component-level traceability, that’s your floor.

Also note: high-risk components often come with traceability and Certificate of Conformance expectations from approved sources—your genealogy should preserve those links to the component lot.

4.1.5 What to capture at each depth (a practical map)

Lot-level: work order/date code, line, shift, reflow profile ID, paste lot, panel ID.
Unit-level: add the unit SN, ICT/FCT results, AOI/AXI images/flags, rework records that update serial status (no “ghost” fixes).
Unit + component-lot: on top of the above, scan critical component lots (e.g., BGAs, power devices, safety parts) at issue—either at kitting or placement—and link to the unit SN in MES.

Where it lives: IDs live on labels/marks (what & format in 4.3), are read by scanners on the line, and flow via APIs to MES/ERP—that’s how you eliminate “shadow spreadsheets.”

4.1.6 Make the decision explicit (before PVT)

State your chosen traceability level in the Golden Data Pack and the label/traceability spec (what’s encoded, where, and when to scan). Include BOM rev if customers care about visible configuration.
Configure MES routes/operations/WIP states to enforce the scans you expect; if it’s not required at the station, it won’t happen under pressure.

Bottom line:Conclusion: chooseEstablishing the minimumproper traceability thatlevel letsbefore youproduction isolatelock-in riskensures fastissues are contained swiftly and satisfycompliance contracts—thenis enforcemet without overspending. By enforcing it withthrough labels, scanners, and MES.MES, Lot-levelmanufacturers keepsgain costboth down;risk unit + component-lot buys precision in regulatedisolation and high-stakescustomer markets. Either way, decide trust.before you ramp.