5.7 Defect Taxonomy & Disposition Rules (Linked to MRB)

Ambiguity in defect classification paralyzes production lineslines. If an operator cannot instantly distinguish between a "process indicator" and allows latent failures to escape. A subjective debate over whether a scratch"functional isfailure," "Minor"they will either scrap good parts (wasting money) or "Major"pass wastesbad engineeringparts hours(risking and degrades the baseline for acceptable quality.liability). This chapter establishes a rigid,binary, physics-based taxonomy for non-conformities and defines the exactrigid logic path for their disposition,disposition. removingWe remove emotion from the decision process.process: the physics of the defect determines its fate, not the schedule pressure.

Defect Severity TaxonomyClassifications

Classify defects based on their impact on Safety,Safety, Function,Function, and Assembly,Assembly, not on the costcomponent of the component.cost.

Critical Defect (Severity 1)

• Definition: The deviation renders the product unsafeunsafe, illegal, or legally non-compliant.hazardous.
  • Impact:Physics/Risk: Risk of injury, fire, shock, or regulatory violation (e.g., creepageCreepage distance violation, exposed live part,parts, toxic material presence).(RoHS failure), or lithium battery damage.
  • Action:
    • If Critical Defect is found -> Then Quarantine entire lot immediately.
    • If Root Cause is not identified ->→ Then Stop Ship / Stop Build.Build immediately.
    • If root cause is unknown → Then Quarantine the entire lot and upstream inventory.

  Major Defect (Severity 2)

  • Definition: The deviation results in functional failure or prevents proper assembly (Form/Fit/Function).
  • Physics/Risk: Open circuits, short circuits, dimensional interference, or significant reduction in usability/reliability.
    • Impact: Product does not work,anticipated life-cycle is compromised, or unit cannot be assembled (Fit/Form/Function failure).cycle.
    • Action:
      • If functional/reliabilitydefect riskaffects ->function → Then Reject unit.
      • If systemicdefect (rate > AQL limit)limit ->→ Then Trigger SCAR (Supplier Corrective Action Request).

    Minor Defect (Severity 3)

    • Definition: TheA deviation is cosmetic or a slight departure from specificationsstandards that does not affect Function or Safety.Safety, often cosmetic or a slight process drift.
      • Impact:Physics/Risk: Visual imperfectionimperfections not visible to the end-user, or minor dimensional deviationdeviations within tolerance stacking limits.
      • Action:
        • If defect doesis notinvisible affectto customer perception ->→ Then CountLog againstfor process control (yield tracking) but continue processing.
        • If accumulation of minor defectsminors exceeds visual standardlimit ->→ Then Reject.

      Pro-Tip: Do not confuse "Minor" with "Acceptable." A Minor defect is still a non-conformance. If theyour process produces frequent Minor defects, theyour process capability (Cpk)CpK is degrading.degrading, and a Major defect is inevitable.

      Disposition Logic Gates

      Once aclassified, the defect ismust classified,be executeprocessed. Use this logic to determine the dispositionphysical basedpath onof the following logic gates. Do not invent new categories.hardware.

      1. RTV (Return to Vendor)

      • Trigger: Incoming material fails AQL inspection or functional testing.

        inspection.

      • Logic:
        • If partcomponent iscost cheaper< than shipping/inspection cost ->→ Then Scrap atlocally and credit note (with vendor expense.agreement).
        • If stock is criticalzero forand continuityline ->is down → Then 100% SortSort/Screen (charge labor back to vendor).

      2. Scrap

      • Trigger: Non-recoverable non-conformancefailure where rework is impossible or costscost > 50% of unit value.
        value

        or physics prohibits repair.

      • Logic:
        • If structuralPCB integritysubstrate is compromisedcracked, (e.g.,burned, crackedor PCB,delaminated bent chassis) ->→ Then Scrap. DO(Structural NOTintegrity is gone; do not attempt mechanicalrepair).
        • If straightening.Intermetallic Compound (IMC) is compromised by excessive heat cycles → Then Scrap.

      3. Rework (Standard)

      • Trigger: Deviation can be corrected to meet original specificationsspec using a validatedpre-validated, process.
        documented

        process (e.g., IPC-7711).

      • Logic:
        • If reworka processStandard Operating Procedure (SOP) exists and is documented ->→ Then Execute Rework.
        • If reworkno requiresSOP unprovenexists methodsor (e.g.,"creative" jumpersoldering wiresis onrequired a final board) ->→ Then Stop. Escalate to MRB.

      4. UAI (Use As Is)

      • Trigger: DeviationComponent is outsideout specof spec, but posesEngineering validates zero functional or reliability risk.

      • Logic:
        • If dimensiondeviation is outpurely ofcosmetic toleranceon an internal surface → Then UAI.
        • If deviation reduces margin (e.g., 5% less capacitance) but fitscircuit matingremains partstable ->→ Then UAI (requiresRequires Engineeringsigned Approval)deviation).
        • If visual blemish is on internal surface -> Then UAI.

      The Material Review Board (MRB) Triggers

      The MRB is the "Supreme Court" of quality. It is not a committeedaily formeeting approvingto badapprove quality;sloppy work; it is a risk assessment body for complex dispositions. Only escalate to MRB when the standard disposition logic fails or high-value risks are involved.

      EscalateWhen to MRBTrigger IF:MRB:

      1. Structural Modification: TheDisposition proposedrequires dispositioncutting changestraces, drilling holes, or adding jumper wires (changing the Fit, Form, or Function (e.g., drilling new holes, cutting traces)"Form").
      2. Reliability Risk: The defect might degrade long-term performance (e.g., oxidizedcorrosion, contacts,slight moisture exposure).
      3. High Value: The scrap cost of scrap exceeds the pre-defined threshold (e.g., > $5,2,000).
      4. Customer Impact: The deviation mightrequires bea noticeablepermanent change to the customer,drawing requiringor a deviationcustomer waiver.

      MRB Output Requirements:Output:

      • Technical Justification: Physics-A physics-based reason why the deviation is acceptable.
      • Containment: PlanA plan to prevent furtherthe productiondefect offrom this defect.recurring.
      • Expiry: The decision applies only to the specific serial numbers or lot identified.listed. It doesis not set a precedentpermanent forrule future production.change.

      Final Checklist

      ParameterControl Point	RuleCritical /Requirement	Risk ThresholdAvoided
      Critical Defect Action	Immediate Stop Build;Build Quarantineauthority Lot.delegated to Quality Techs.
      Major Defect Criteria	FailsSafety Function,/ Fit,Regulatory or Safety.Liability
      Rework ConstraintLimits	AllowedMax only2 withattempts validated,per documentedjoint/location.	PCBA instruction.Delamination / Pad Lift
      MRB Trigger (Cost)Threshold	Scrap valueCost > [Insert$X,XXX Threshold,or e.g.,Safety/Reliability $1,000].Risk.
      MRB Trigger (Risk)	AnyFinancial riskLoss to/ ReliabilityField or Safety.Failure
      UAI DocumentationAuthority	MustRequires include Engineering signature& andQuality expirationManager (Lot/Qty).Sign-off.	Unauthorized Design Change
      DispositionScrap Time LimitLogic	Non-conformingStructural materialdamage must(Cracks/Burns) be= dispositionedMandatory withinScrap.	Latent 48Field hours.Failure
      Traceability	All MRB/Rework actions recorded by Serial Number.	Recall Management