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4.1 Why Traceability Levels Matter

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

Traceability is the map that connects a shipped unit back to its route, materials, and decisions—so problems get isolated, not amplified. The choice between lot marks and unit serialization sets how fast RMAs (returns) get scoped and how confidently suppliers or auditors are answered. Go deeper with genealogy—linking component lots to each serial—and investigations become surgical instead of warehouse-wide. Labels, scanners, and MES (Manufacturing Execution System) turn that choice into enforceable reality, tying IDs to routes, tests, and rework history. Contracts and regulated markets often set the floor, but smart teams pick the minimum depth that protects margin and credibility. Decide it early, bake it into the Golden Data Pack, and the rest of the chapter shows how to wire it cleanly.

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: choose the minimum traceability that lets you isolate risk fast and satisfy contracts—then enforce it with labels, scanners, and MES. Lot-level keeps cost down; unit + component-lot buys precision in regulated and high-stakes markets. Either way, decide before you ramp.   


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