7.2 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 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?

• If measuring Line Throughput (can we ship?) -> Then Monitor FPY.
• If measuring Process Stability (is the process healthy?) -> Then Monitor RTY.
• If RTY < 90% -> Then Stop the line. The rework loop is introducing latent thermal stress (reducing life).
• If CoQ > 5% of Revenue -> Then The process is economically unsustainable. Initiate major Corrective Action.

Final Checklist

Parameter	Rule / Threshold
FPY Target	> 98% per station (typical SMT).
RTY Alert Limit	< 90% triggers Engineering intervention.
Daily Review	Review Top 3 Pareto defects before shift start.
Weekly Review	Review RTY trends and CAPA closure rate.
Monthly Review	Review CoQ ratios (Prevention vs. Failure).
Scrap Limit	Variance > 0.5% requires explanation.
Data Integrity	Manual modification of test logs is grounds for dismissal.