7.1 Operational Metrics: FPY, RTY, CoQ & Review Cadence

In high-volume manufacturing, standard "Yield" is a vanity metric. A production line reporting 99% Output Yield can still be bankrupting the company if 40% of those units required rework loops to pass. As a Quality Director, you must distinguish between making product and fixing product. Operational metrics are not just for accounting; they are the pressure gauges of the "Hidden Factory"—the invisible rework engine that consumes labor and reduces component reliability.

The Metrics Hierarchy

1. First Pass Yield (FPY) – The Capacity Metric

FPY measures the efficiency of a single station. It answers: "How many good units came out versus how many went in?"

• Formula: (Units Passed / Units Entered) *× 100
• Use Case: Capacity Planning. It tells you if you can meet the shipping schedule.
• The Danger: FPY allows rework. If an operator re-tests a board 3 times to make it pass, FPY sees a "Pass." It hides the instability.

2. Rolled Throughput Yield (RTY) – The Reliability Metric

RTY measures the probability of a unit passing the entire value stream without a single touch-up, rework, or re-test. This is the truth metric.

• Calculation: RTY = Y(print) × Y(place) × Y(reflow) × Y(test)
• The Math of Failure:
  • If you have 5 process steps, each at 95% yield (which sounds good):
  • RTY = 0.95 × 0.95 × 0.95 × 0.95 × 0.95 ≈ 77%.
  • Reality: Nearly 1 in 4 units are being reworked. This is why "95% yield" is unacceptable in complex systems.

3. Cost of Quality (CoQ) – The Financial Metric

Quality is not free, but Poor Quality is expensive. CoQ is the total financial impact of the quality system.

• * Good Cost (Investment):

  • * Prevention: Training, FMEA, Fixture Design.

  • * Appraisal: Calibration, Testing, Inspection labor.

• Bad Cost (Loss):
  • Internal Failure: Scrap, Rework, Re-testing, Downtime.
  • External Failure: RMA, Warranty, Liability, Brand Damage.

Pro-Tip: The Rule:rule of thumb is 1-10-100. $1 spent on Prevention saves $10 in Correction and $100 in Failure.

Review Cadence (The Pulse)

Data without a review schedule is just digital noise. Establish the following cadence to turn metrics into action.

1. Daily (Tactical Review)

Who: Line Lead, Quality Engineer, Production Supervisor.

Trigger: Shift Start / Shift End.

Focus: FPY & Scrap.

• Logic:
  • If Top 3 Defects are the same as yesterday -> Then Stop Line. The containment failed.
  • If Scrap > $500/shift -> Then Quarantine the bin for Root Cause Analysis (RCA).

2. Weekly (Corrective Review)

Who: Quality Manager, Engineering Manager, Operations Manager.

Trigger: Monday Morning Meeting.

Focus: RTY & Open CAPAs.

• Logic:
  • If RTY trend is down (despite stable FPY) -> Then Audit the rework stations. Operators are fixing defects without logging them.
  • If CAPA is overdue -> Then Assign resources immediately.

3. Monthly (Strategic Review)

Who: VP of Operations, Plant Director, Quality Director.

Trigger: Monthly Operations Review (MOR).

Focus: CoQ & Supplier Performance.

• Logic:
  • If Failure Cost > Appraisal Cost -> Then Your process is reactive. Shift budget from "Inspection" to "Prevention" (Training/Jigs).

Decision Logic: Which Metric When?

• IFIf you are measuring Line Throughput (can we ship?): ->
  • THENThen Monitor FPY.
• IFIf you are measuring Process Stability (is the process healthy?): ->
  • THENThen Monitor RTY. A drop in RTY precedes a drop in FPY.
• IFIf RTY < 90%: ->
  • THENThen Stop the line. The rework loop is introducing latent thermal stress to the components (reducing life).
• IFIf CoQ > 5% of Revenue:Revenue ->
  • THENThen The process is economically unsustainable. Initiate major Corrective Action.

Final Checklist

MetricParameter	FocusRule Area	Critical/ Warning Sign	Strategic ActionThreshold
FPY Target	Single Station Output	> 98% butper Highstation OT	Investigate(typical re-testing loopsSMT).
RTY Alert Limit	System< Integrity90% triggers Engineering intervention.
<Daily 90%Review	StopReview LineTop &3 FixPareto Rootdefects Causebefore shift start.
Weekly Review	Review RTY trends and CAPA closure rate.
Monthly Review	Review CoQ ratios (Prevention vs. Failure).
Scrap Limit	Material Loss	Variance > 0.5%	Audit Redrequires Bins / Trashexplanation.
CoQData Integrity	FinancialManual Health	Failuremodification Costof >test Appraisal	Shiftlogs budgetis togrounds Prevention
DPMO	Processfor Capability	Rising Trend	Review Training/Calibrationdismissal.