8.4 Containment playbook: suspect lots, line stop triggers & escape handling

When a critical defect is first detected on the floor, the primary engineering priority is Containment. Before initiating a Root Cause Analysis, it is essential to isolate the risk, define the suspect population, and establish a verified Clean Point so that production can safely resume.

Defining the suspect lot (the bracketing logic)

A “Suspect Lot” represents the volume of production that might potentially be affected by the failure. This volume is bounded by the last known good state and the current detection point.

The “Bookend” Principle:

To execute a quarantine, the temporal and physical boundaries of the risk window must be identified.

• The Start Point (Bookend A): The last verified “Good” event (e.g. a passing hourly Quality audit, a documented machine setup verification, or a verified Golden Sample run).
• The End Point (Bookend B): The moment of detection plus all current WIP (Work In Progress) presently on the line.

The Execution Logic:

Whenever the defect is continuous (e.g. a broken SMT nozzle), all production units must be quarantined backwards to Bookend A. Whenever the defect is random or intermittent and cannot be accurately bracketed, the entire shift’s production volume must be quarantined for 100% visual/electrical sorting. In environments where traceability is limited (e.g. batch-level tracking rather than individual serial numbers), it is necessary to quarantine the entire underlying Work Order.

Pro-Tip: Relying solely on estimates such as “the machine started doing this five minutes ago” must be avoided. Without hard data, the Start Point should default to the last time the process was mathematically verified as successful.

Line stop triggers (the andon protocol)

Operators must have the authority and explicit management support to stop production when issues arise. Ambiguity in this standard can lead to increased scrap.

Triggers for Immediate Auto-Stop:

1. Severity 1 Defect: Any potential safety or regulatory violation (e.g. exposed high-voltage traces, missing dielectric isolation).
2. Consecutive Failures: Three consecutive units failing the exact same test for the same defect code.
3. Yield Drop: Station First Pass Yield (FPY) dropping below 90% in any rolling hour.
4. Process Drift: A Critical to Quality (CTQ) parameter (e.g. reflow soldering temperature profile) drifting outside engineered control limits (Cₚₖ < 1.0).

The Action Command:

When any Trigger condition is met, the conveyor or machine must be stopped. Once the line is stopped, the Red Andon Light must be illuminated and the Lead Quality Engineer notified. Production should not resume until the Quality Engineer reviews the process and approves the “First Good Piece” check following any adjustment.

Escape handling (customer protection)

An “Escape” occurs when a defect bypasses all factory controls and is shipped to the customer or distribution hub. Prompt action is the most important variable in mitigating commercial impact.

Step 1: The Alert (Notification)

For any Safety or Regulatory Risk, the customer must be notified within 24 hours. For Functional or Cosmetic Risks, the customer must be notified promptly with a drafted containment plan; waiting until the root cause is discovered is prohibited.

Step 2: The Clean Point

“Safe” audited product must be visually distinguished from “Suspect” product to restore customer confidence.

• The Action: All certified safe units (those produced after an engineered fix or manually 100% screened) must be marked with a specific visual identifier (e.g. a Neon Green Dot, or a date-coded stamp) directly on the outer packaging and the unit label.
• The Communication: A formal notice detailing this specific marking convention must be sent to the customer.

Step 3: The Inventory Sweep

When an Escape is formally confirmed, these three locations must be swept immediately:

1. Finished Goods Warehouse: All outgoing shipments matching the part number must be halted.
2. In-Transit: Shipments must be recalled or diverted if possible.
3. Distributor Hubs: An immediate stock hold must be requested.

100% Sorting (the human firewall)

If a process is proven unstable, a temporary physical Firewall (a 100% Human or automated Machine sort) must be installed to protect the customer while engineering investigates the root cause.

Rules of Engagement:

• The Instruction: A rapid “One Point Lesson” (OPL / visual aid) zooming in specifically on the defect being hunted must be created, rather than relying solely on general IPC inspection criteria.
• The Efficiency: 100% manual visual sorting is visually demanding. Human inspectors must be rotated periodically (e.g. every 2 hours) to maintain high focus.
• The Exit Criteria: The Firewall must remain in place until the true Root Cause is demonstrably eliminated AND at least 3 consecutive production lots pass the firewall with zero defects.

Final Checkout: Containment playbook: suspect lots, line stop triggers & escape handling

Monitored Parameter	Engineering Rule / Threshold
Suspect Scope	Always roll back to the “Last Known Good” empirical check (Audit/Setup).
Line Stop Rule	3 Consecutive identical Fails OR any Safety Risk = Immediate Stop.
Restart Authority	An authorized Quality Engineer or Manager must approve the line restart.
Clean Point	Use visually distinct markings (e.g. Neon Green Dot) on both the unit and the master box.
Customer Notification	Safety/Regulatory issues < 24 Hours.
Firewall Exit Logic	3 Clean Lots + Verified Engineering Root Cause Fix.
Traceability Penalty	If specific failing serials cannot be identified, the entire Master Lot is presumed suspect.