The yield funnel: where good dies are lost between start and shipment.
Every stage passes on a little less than it received. Knowing which stage loses most tells you where to spend the next engineer.
In brief
- Yield is lost at several gates, each with its own causes.
- Measure each gate separately, or the losses blur together.
- Excursions cause the sharpest drops; how fast they close matters.
- A closure routine stops the same loss returning.
Wafers started
Wafers through the line− Scrap, breakage, misprocessing
Good dies at wafer sort− Defects, parametric fails
Units assembled− Assembly defects
Units passing final test− Test and burn-in fails
Units shippedWhat the customer receives
Proportions are illustrative, to show where loss happens. They are not measured data.
Read the funnel gate by gate
- Line yield counts wafers that survive processing. Losses here are scrap, breakage and misprocessing: handling and discipline problems as often as technical ones.
- Sort yield counts good dies per wafer. Losses come from defects and parametric drift, and show up as bin-map signatures.
- Assembly and final test lose units to attach, bond and mold defects, and to test and burn-in failures.
The excursion loop
The steepest drops come from excursions: a process that shifts without warning. The loop below is how a line stops paying for the same excursion twice.
- 01DetectSPC, inspection or a customer flags a shift.
- 02ContainHold suspect lots. Stop the bleeding.
- 03Root causeFind the cause, not the nearest symptom.
- 04CorrectFix the process, tool or material.
- 05PreventChange standard work and controls.
- 06CloseVerify with data, then release.
Most new lines are good at the first two steps and weak at the last two, because the engineers who should prevent recurrence are already on the next fire. Our consultants put the closure routine in place and hold it until it runs on its own.