NOTQIN — OT Track

First Pass Yield

2 min read

First Pass Yield (FPY)

Definition

Fraction of units that pass through a process the first time without rework, repair, or scrap. The quality metric that exposes hidden rework, unlike traditional yield (which counts reworked-then-passed as success).

Variant: Rolled Throughput Yield (RTY) — product of FPY across all process steps. RTY collapses fast as steps multiply.

Formula

FPY (single step) = Units Passing First Inspection / Units Started

RTY = FPY_step1 × FPY_step2 × ... × FPY_stepN

Required data

  • Units started at each step
  • Units passing first inspection (rejected + reworked counted as NOT first-pass)
  • Per-step traceability if computing RTY

Possible data sources

  • In-line QC sensors / vision systems
  • MES first-time-pass flag on each routing operation
  • Operator inspection logs (lower data quality)

Factory example

Wiring-harness assembly, 5 stations:

  • FPY each = 95%
  • RTY = 0.95^5 = 77.4%

If you only measure end-of-line yield and call it 96% (because rework is invisible), you’re hiding 18.6 percentage points of process loss.

Economic impact

  • Cost of poor quality (CoPQ): rework labor, scrap, retest, customer returns, scorecard hits (IATF 16949 PPM)
  • FPY trend = leading indicator of process drift (Stage 6 SPC territory)
  • Drives Control Plan + FMEA priorities

Common mistakes

  • Calling end-of-line yield “first pass” when rework loops are silent
  • Only measuring final FPY → can’t tell which step is hemorrhaging
  • Counting “reworked and passed” as a pass → hides the cost
  • Not separating defect types → can’t drive corrective action
  • Comparing FPY across products with different complexity → noise

See also

Graph View

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