3.2 Serialization and identity lifecycle

A Serial Number (SN) is not a sticker; it is the Primary Key of your physical reality. If two units on the floor share the same ID, or if an ID is generated but never applied to hardware, the integrity of your database collapses.

Identity is a state machine. A Serial Number must be managed through a strict lifecycle from “Birth” to “End of Life” to prevent data corruption.

Identity syntax rules

Before generating a single ID, the syntax must be clearly defined. “Smart” numbers (which embed logic like the Date or Line into the string) often become problematic or break down over time as processes change.

Structure: A random or sequential Unique Identifier (UID) must be used. Context (like the Date, Line, or Product) must be stored as attributes in the database, rather than embedding them in the character string.
Alphabet: Using Base-34 (excluding the letters I and O to prevent visual confusion) should be considered.
Constraint: When a Serial Number contains special characters (like /, \, or :), the system might struggle to process it. These characters routinely break URL strings in web-based reporting tools.

The lifecycle state machine

An Identity is not static. It moves through distinct states.

1. Create (minting)

The generation of the string in the database.

Rule: The Unit_ID column needs a UNIQUE constraint in the database schema.
Risk: “Ghost IDs” must be treated seriously. For example, if 1,000 labels are pre-printed and the printer jams, there are effectively 50 “Created” IDs in the database that do not exist on the floor.
Control: When a label is destroyed or misprinted, an operator should scan it to “Void/Scrap” immediately to maintain alignment between physical and digital states.

2. Assign (binding)

The moment the ID is applied to the hardware.

Laser Marking (Preferred): The laser requests an ID from the MES, marks the board, and verifies the read. When the read fails, the system should reject the board. It is generally unsafe to assume a mark is legible without explicit optical verification.
Labeling: An Operator scans the printed Label, and the MES links that Label to the Production Order.

3. Split (depaneling / inheritance)

In electronics, you manufacture a “Panel” (1 Parent) containing multiple “Circuits” (N Children).

The Problem: Reflow data belongs to the Panel. The customer buys the Circuit.
The Logic:
- Step 1: Track Panel_ID through SMT.
- Step 2: At Depaneling (Router), trigger the Split Event.
- Step 3: MES auto-generates Circuit_IDs (if not pre-marked) or reads existing Circuit_IDs.
- Step 4: Inheritance: All process data (Temperatures, Times) from Panel_ID is copied/linked to every Circuit_ID.

4. Merge (aggregation / packing)

The inverse of splitting. Grouping individual units into a parent container (Tray, Box, Pallet).

Logic:
- The Operator scans the Box_ID (Parent).
- The Operator scans the Unit_IDs (Children).
- Constraint: When the specific Unit_ID status is not “Passed,” the system should actively block the operator from adding that unit to the box.
Traceability: The Box_ID acts as a proxy. Scanning the Box reveals all the contained Units.

5. Reassign (carrier logic)

A distinction must be made between Product ID (Immutable) and Carrier ID (Reusable).

Product ID: Once assigned, it never leaves the product.
Carrier ID (Pallet/Tray): This can be unbound and reused for different products.
Logic: When a unit is removed from a carrier, the system should break the digital link (e.g. by setting the Carrier_ID to Null).

6. Relabel (damage control)

Labels occasionally get damaged. Replacing them requires a controlled, high-risk operation.

The Cardinal Rule: It is poor practice to generate a new identity for an existing product. Instead, the original Serial Number (SN) must be reprinted.
Procedure:
1. A Supervisor authenticates the request.
2. The Operator scans the old 2D code (if readable) or manually enters the Serial Number (SN).
3. The MES validates the current status of that Serial Number (SN).
4. The Printer produces a Duplicate label.
5. Audit Log: The system records an event like “Reprint event for Serial Number (SN):123 by User:“ABC"".

7. Scrap (the end)

When a unit is destroyed, its digital twin should also transition to a terminal state.

Action: Transition the State to “Scrapped”.
Constraint: When a Serial Number is marked as Scrapped, the system should block any future processing attempts using that ID.
Re-Use: The SN of a scrapped part must not be recycled. That SN is permanently retired.

8. Rework (the loop)

Sending a unit back through a previous step to correct a defect.

Logic: The prior failure history must not be deleted; instead, the new rework history must be appended.
State: Transition the unit to an “In Rework” status.
Validation: When the rework is complete, the unit should re-pass the specific Quality Gate that originally flagged the failure.

Final Checkout: Serialization and identity lifecycle

Category	Control	Rule
Uniqueness	Constraint	Database Unit_ID requires a Globally Unique constraint.
Depaneling	Inheritance	100% of Panel data flows down to the Child Circuits after a split.
Relabel	Immutable Identity	Damaged labels are Reprinted (Same SN), rather than Replaced (New SN).
Aggregation	Quality Gate	An operator cannot pack (Merge) a unit unless its State is “Pass”.
Carriers	Hygiene	Carrier IDs are cleared (unbound) before starting a new production run.
Scrap	Finality	Scrapped IDs are blacklisted and not re-used.
Format	Readability	Avoid ambiguous characters (O/0, I/1) to ensure an ISO Grade C minimum readability.