8.2 Internal MRB & quarantine discipline

The Material Review Board (MRB) process is a formal engineering investigation, not simply a repair area or a storage space for production mistakes. Every item placed in the MRB cage represents a failure of process controls upstream. The engineering goal is clear: Segregation must be maintained. If a known non-conforming part can be mistaken for a good part and re-introduced to the production line, the Quality System has a significant vulnerability. The MRB Cage serves as the organizational boundary separating a production anomaly from a potential customer escape.

Physical segregation (the red cage)

Quarantine is not just a digital status in the ERP system; it requires physical handling on the factory floor. Electronic blocking alone is often insufficient, as operators may not check the broader ERP status when staging materials for the SMT machine.

The “Red Cage” Standard:

• The Physical Barrier: The Quarantine area should be a locked wire cage or a distinctly separated room with controlled access.
• The Visual Logic: Suspect MRB material must be tagged with a visible RED “Non-Conforming” label upon detection.
• The Inventory Gap Risk: Whenever material is placed in the cage, it must be electronically transferred to the formal “MRB” or “Blocked” storage location in the ERP system within the same shift. The Engineering Risk: When the physical state and the digital state drift out of sync, Planning routines may schedule new production against known bad inventory, leading to line-down events when those materials are unavailable.

The MRB hierarchy (disposition logic)

The MRB is a data-driven decision-making body. The lead Quality Engineer or Quality Manager typically holds the final technical vote. The standard logic must be used to disposition material effectively:

• Disposition: Return to Vendor (“RTV”)
  • Trigger: A supplier material defect is confirmed.
  • Action: A SCAR (Supplier Corrective Action Request) along with a formal Debit Memo must be issued. The material must be moved to the Shipping Dock promptly.
• Disposition: Scrap
  • Trigger: The product cannot be recovered economically or functionally safely.
  • Action: The PCBA must be Mutilated before disposal. Discarding intact PCBs in a standard dumpster is discouraged, as they might be harvested for high-value components and sold on the secondary market. A hole must be drilled through the main BGA or the unit appropriately destroyed.
• Disposition: Rework
  • Trigger: A known, recoverable process defect (e.g. a missing mechanical screw, a single cold solder joint).
  • Requirement: A step-by-step Rework Instruction (WI) must be documented and approved by Manufacturing Engineering before a technician begins work. A verbal “Just fix it” instruction is insufficient and risks introducing latent field failures.
• Disposition: Use As Is (UAI)
  • Trigger: A cosmetic defect or a minor mechanical deviation that affects physical form but has zero impact on functional fit or safety.
  • Requirement: A mandatory Engineering Deviation Waiver signed by the ultimate Design Authority (the customer or the Chief Engineer). The Quality department should not approve a UAI alone.

MRB aging & velocity (the “graveyard effect”)

A common issue in MRB management is the “Graveyard Effect”—bad parts enter the cage and remain unresolved indefinitely. This obscures WIP costs and the true factory yield data.

The 30-Day Limit:

• Whenever a disposition discrepancy remains open for > 30 days, the MES should default the financial status to SCRAP. The Logic: If Engineering or the Supplier hasn’t resolved the root cause in a month, the material is generally irrecoverable. Investing resources in tracking it must be stopped.
• The Metric: Track the “Average Days in MRB.” An engineering target is usually < 7 Days.

Scrap security (gray market protection)

High-value silicon (CPUs, FPGAs) and completed sub-assemblies can be targets for theft. Scrapped electronic material should be managed with a clear chain of custody.

• The Protocol: The destruction of high-value manufacturing scrap (Main CPUs, expensive Memory blocks, fully completed PCBAs) should be witnessed by a Quality auditor.
• Certificate of Destruction (CoD): This is required for proprietary or branded OEM material before the container is emptied.

Final Checkout: Internal MRB & quarantine discipline

Control Element	Monitored Requirement	Engineering Rule
Access Control	Physical Cage Lock	Quality Personnel Only (Electronic Key/Badge access).
Identification	Physical Tagging	Red Tag attached immediately upon the failure event.
UAI Decision	Formal Deviation	Engineering Signature Required (No verbal approvals).
Aging Limit	Velocity Tracking	> 30 Days in the cage demands a disposition (typically Scrap).
Rework Control	Formal Documentation	An approved, step-by-step Work Instruction (WI) is required before reworking the board.
Disposal Control	Silicon Security	The boards must be mutilated or crushed to prevent component resale.