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7.1 Operational Metrics: FPY, RTY, & Cost of Quality (CoQ)

In high-volume electronics manufacturing, standard "Yield" metricsis oftena concealvanity systemic inefficiencies.metric. A production line reporting 98%99% yieldOutput mayYield can still be hemorrhagingbankrupting cashthe company if that40% figureof reliesthose onunits extensiverequired rework loops hiddento frompass. As a Quality Director, you must distinguish between making product and fixing product. Operational metrics are not just for accounting; they are the finalpressure count.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?"

  • Definition:Formula: The(Units percentagePassed of/ unitsUnits thatEntered) exit* a100
  • Use processCase: stepCapacity asPlanning. "Good,"It regardlesstells ofyou whetherif theyyou werecan reworkedmeet duringthe thatshipping step.schedule.
  • The Flaw:Danger: FPY ignoresallows rework. If an operator re-tests a board 3 times to make it pass, FPY sees a "Pass." It hides the "Hidden Factory" — the unrecorded cost of re-soldering, re-testing, and touch-up.instability.

2. Rolled Throughput Yield (RTY)

  • Definition:– The Reliability Metric

RTY measures the probability of a single unit passing through the entire processvalue (Printing -> Placement -> Reflow -> AOI -> Test)stream without a single defecttouch-up, rework, or reworkre-test. event.This is the truth metric.

  • Calculation: RTY is= theY(print) product× Y(place) × Y(reflow) × Y(test)
  • The Math of theFailure:
    • If yieldsyou ofhave 5 process steps, each individualat process95% step.yield (which sounds good):
    • YtotalRTY = Y0.95 × 0.95 × 0.95 × 0.95 × 0.95 ≈ print77%.
    • Reality: xNearly Yplace x Yreflow x Ytest
    • Example: A 5-step process where each step has a 95% yield results1 in a4 finalunits RTYare ofbeing onlyreworked. 77% (0.955).
    • Mandate: RTYThis is thewhy primary"95% metricyield" foris unacceptable in complex systems.

3. Cost of Quality (CoQ) reduction– becauseThe itFinancial exposesMetric

Quality is not free, but Poor Quality is expensive. CoQ is the cumulativetotal financial impact of minorthe inefficiencies.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.
  • The Rule: $1 spent on Prevention saves $10 in Correction and $100 in Failure.

Decision Logic: Which Metric When?

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

Final Checklist

Metric

CalculationFocus FocusArea

Critical Warning Sign

Strategic ValueAction

FPY

Single Station Output / Input

> 98% but High OT

CapacityInvestigate Planningre-testing (Throughput)loops

RTY

ProductSystem of all Step YieldsIntegrity

< 90%

ProcessStop ImprovementLine (True& Cost)Fix Root Cause

Scrap Rate

Material Loss

Variance > 0.5%

InventoryAudit VarianceRed Bins / Trash

CoQ

Financial Health

Failure Cost > Appraisal

Shift budget to Prevention

DPMO

DefectsProcess Per Million OpportunitiesCapability

Rising Trend

SixReview Sigma BenchmarkingTraining/Calibration


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