8.10 Operational Metrics: FPY vs. RTY

In high-volume electronics manufacturing, standard "Yield" metrics often conceal systemic inefficiencies. A production line reporting 98% yield may still be hemorrhaging cash if that figure relies on extensive rework loops hidden from the final count.

8.10.1 First Pass Yield (FPY)

• Definition: The percentage of units that exit a process step as "Good," regardless of whether they were reworked during that step.
• The Flaw: FPY ignores the "Hidden Factory" — the unrecorded cost of re-soldering, re-testing, and touch-up.

8.10.2 Rolled Throughput Yield (RTY)

• Definition: The probability of a single unit passing through the entire process (Printing -> Placement -> Reflow -> AOI -> Test) without a single defect or rework event.
• Calculation: RTY is the product of the yields of each individual process step.
• Y_total = Y_print x Y_place x Y_reflow x Y_test
• Example: A 5-step process where each step has a 95% yield results in a final RTY of only 77% (0.95⁵).
• Mandate: RTY is the primary metric for Cost of Quality (CoQ) reduction because it exposes the cumulative impact of minor inefficiencies.

Final Checklist