2.5 MES: Comprehensive Traceability and Data Management

In electronics manufacturing, documentation and traveler control form the backbone of traceability. Each unit's record is more than a log — it is the authoritative account of every process, inspection, and rework step, ensuring that nothing is hidden and no board goes untracked. When maintained with discipline, the traveler prevents duplication, enforces re-inspection after repairs, and provides the evidence needed to prove both compliance and quality. By consolidating all history into a single controlled system, manufacturers turn individual fixes into collective process knowledge while safeguarding customer trust.

2.5.1 The Traceability Mandate

The primary goal of the traveler system (managed by the Manufacturing Execution System, MES) is to give every unit a complete, auditable history from raw materials to the final packaged box.

• Unbroken History: Every unit (Serial Number, SN) must have a verified record of every step passed and every process recipe used.
• Rework Control: Any repair action must be logged, forcing a mandatory re-inspection route to prove the fix was effective before the unit can proceed.
• Shadow Data Prevention: The MES must be the single source of truth. No paper notes, side spreadsheets, or chat logs are acceptable for quality-critical data.

House Rule: No scan, no move. The physical movement of the board must be mirrored by an electronic scan and status update in the MES.

2.5.2 Mandatory Traceability Data (MES Records)

The electronic record must be comprehensive and auto-populated by machine interfaces whenever possible to create a complete genealogy for each Serial Number (SN).

Bucket	Required Fields (Managed by MES)
Identity & Context	Product & Revision, Serial Number (SN), Work Order (WO)/Lot, Variant.
Genealogy (Inputs)	PCB lot, stencil ID, paste lot, component lots for critical parts (BGAs, power), feeder/fixture IDs.
Process Recipes	Printer/PnP/Oven/AOI/AXI/Test recipe version IDs (the exact versions used).
Inspection Results	SPI/AOI/AXI image links, ICT/FCT logs, reflow profile plot link.
Disposition	Current status (WIP/HOLD/REWORK/PASS/SCRAP), and the station that set that status.
Rework History	Ticket ID, defect code, action, parts replaced, attempt count, and evidence images.

2.5.3 Status Control and Routing

A simple status model ensures automatic and correct routing, preventing boards from bypassing critical re-inspection gates.

Status	Meaning	Set By	Allowed Next Step(s)
WIP (Work In Process)	In process; no recorded fails.	Auto on start/step scan.	Next routed step.
NG-QUAR (Quarantine)	Unit contained; fail recorded.	Auto on test/inspection fail.	Only Rework or MRB.
REWORK	Under repair with open ticket.	Repair Tech claim.	Re-Inspect/Re-Test for the failing gate(s).
MRB (Material Review Board)	Needs board-level disposition decision.	QE/PE set.	Scrap / Use-as-is / RTV / Rework.
PASS	All required gates cleared.	Final test station.	Pack $\to$ Ship.

Routing Rule: After a status of REWORK, the MES must automatically insert the failing test station (e.g., ICT, FCT) back into the route. The board cannot proceed until that gate is successfully passed again.

2.5.4 Rework Ticket Mandates

The rework ticket serves as the primary log for all repair activity and must be auto-generated upon the first failure scan.

• Essential Fields: Log the SN, Refdes, the controlled Defect Code, and Action Taken (what was swapped, what flux/temps were used).
• Attempt Tracking: The ticket must explicitly track the attempt count (per component or site) and the number of heat cycles (if BGA/QFN rework limits apply).
• Verification: The ticket must list the required verification step(s) (e.g., AXI check, FCT spot check) and link the digital proof (image/log) before closure.

2.5.5 Genealogy and Component Replacement

When a component is replaced, the unit's permanent genealogy record must be updated instantly to maintain traceability down to the part level.

• New Part Scan: The new part number and lot/date code must be scanned and linked to the board's SN in the MES.
• Removed Part Log: The old part's lot number should be flagged as removed, providing a complete record for any future supplier quality audit or field failure investigation.
• Security Items: If unique identifiers (firmware hash, MAC addresses, encryption keys) are altered during rework, the new values must be logged and verified by the test system.

2.5.6 Final Packaging and Audit Controls

Final documentation ensures that the product shipped is the product verified, locking down the last steps of the process.

• Board-to-Box Mapping: The packer must scan all board SNs and link them to the final Box SN. The system must block pack-out if this map is incomplete or if any board has an open ticket.
• Traveler Backup: In the event of an MES outage, use pre-printed barcoded travelers as a temporary, physical backup. All data collected on paper (timestamps, actions, signatures) must be back-entered into the MES immediately upon system recovery.
• Guardrails: The MES must block actions that create shadow data (e.g., automatically importing images from AOI/AXI directly to the ticket, preventing manual upload to non-audited systems).

Final Checklist

Mandate	Criteria	Verification Action
Start/Move Control	No scan, no move enforced across all gates.	Operator must scan SN to move status from WIP to NG-QUAR or PASS.
Rework Traceability	Ticket logs Defect Code, Action, Attempt Count, and Profile ID.	Technician must scan new part lot/date for genealogy updates.
Verification Gate	Board must re-pass the failing test station (ICT, FCT) after any repair.	MES must automatically insert required re-inspection steps into the routing.
Final Genealogy	All critical part lots, firmware version, and test logs are linked to the Serial Number.	The final Board-to-Box Map must be complete and locked at pack-out.
Documentation Health	Dashboard reports Aging Tickets (open $\gt 24$ hours) and Reprint Reasons for labels.	System permissions prevent non-qualified personnel from setting PASS status.