4.3 What to Encode & How
Encoding is where traceability turns into data that systems can trust. The choice of what to include—serial numbers, BOM revisions, lot/date codes, or line details—defines how precisely issues can be isolated later. Equally important is how the information is carried: 1D barcodes excel at long-range scans on rails and boxes, while compact 2D codes with error correction keep unit IDs readable through reflow, coating, and handling. Standards like GS1/ISO make codes interoperable across suppliers and customers, while human-readable text ensures audits and debugging don’t stall. Together, these decisions transform a printed mark into a reliable pointer to a unit’s full genealogy.
4.3.1 The data dictionary (what every code should carry)
Pick the smallest set that meets your traceability level (from 4.1) and customer/contract needs, then lock it in your Labeling & Traceability spec in the Golden Data Pack.
Core fields (most builds)
- SN (serial number) — unique per unit (or panel ID if lot-level).
- BOM Rev / Config ID — exposes which bill-of-materials revision the unit matches. Many customers require this on the visible label.
- Work order / Lot / Date code — lets you quarantine precisely when needed.
- Line / Station / Shift (compressed) — helps triage escapes fast.
Optional fields (add only if they earn their keep)
- Variant / Feature flags (if one PCB serves multiple SKUs).
- Regulatory or customer IDs (if contracts dictate).
- Checksum or internal record key used to join with MES/ERP.
4.3.2 1D vs 2D (and which standards to speak)
1D barcodes (Code 128, etc.) are great for long, scannable strings and line-of-travel readers on rails and boxes.
2D codes (DataMatrix, QR) pack more data into less space and survive damage thanks to built-in error correction. Use them on the PCB when space is tight. Choose a GS1/ISO flavor when customers want global consistency. Put the choice (1D vs 2D, symbology, field order) in your label spec so scanners and MES parse it the same way.
Rules of thumb
- Prefer DataMatrix/QR on the PCB for compact, durable unit IDs; keep Code 128 for cartons/pack-out where space is abundant.
- Keep a quiet zone around every code and size modules for your cameras; verify readability in your scanning step (4.5).
4.3.3 Human-readable lines (for eyes and audits)
Always pair machine codes with a human-readable string (SN and minimal context like WO/Rev). It saves time in debug and still passes audits when a scanner fails. Put formatting examples in the spec and keep them consistent with what MES expects.
4.3.4 Error correction & verification (don’t skip this)
- 2D codes include error correction by design; pick a level that tolerates your real world (solder splatter, cleaning, coat glare).
- Add a verify step to your route: print/laser → scan to grade → apply/accept. Failures block WIP and open a reprint flow; successes write the record via API so there’s no “shadow spreadsheet.” (Details in 4.5.)
4.3.5 Where each code lives (and why)
- Panel rail: big 1D or 2D for upstream/downstream station scans.
- PCB (unit): compact 2D (SN + Rev + WO/Date) in a consistent corner with high contrast (from 4.2).
- Box/pack-out: customer-facing 1D/2D per contract; mirror core fields and include shipping IDs. Tie all of them back to the same record in MES/ERP.
4.3.6 Put it in writing (spec template)
Your Labeling & Traceability spec should state:
- Symbologies allowed (1D/2D; GS1/ISO where required) and data field order/lengths.
- Human-readable format and fonts.
- Placement (rail vs PCB vs box) and minimum clearances/quiet zones.
- Verification step (scanner grade threshold, reprint flow) and API mapping to MES/ERP objects.