OEE in a fab or OSAT: the six losses, explained.
Expensive tools are only as valuable as the good output they produce. Overall equipment effectiveness shows where the rest goes.
In brief
- OEE multiplies availability, performance and quality.
- Each factor hides two of the six standard losses.
- The bottleneck tool’s OEE sets the whole line’s output.
- Many losses are people and practice, not machine.
OEE=Availability×Performance×Quality
Planned production time
Run timeAvailability lossBreakdowns. Set-ups and adjustments.
Net run timePerformance lossSmall stops. Running below rated speed.
Fully productive timeQuality lossStart-up rejects. Production rejects.
Bar lengths are illustrative. The six losses are the standard categories used in equipment-effectiveness work.
The six losses on a semiconductor floor
Availability
Breakdowns
Unplanned downs: a failed part, an alarm nobody on shift can clear.
Availability
Set-ups and adjustments
Recipe changes, chamber seasoning, qualification runs after maintenance.
Performance
Small stops
Idle waiting for a FOUP, an operator or a material.
Performance
Reduced speed
Running below rated throughput, often to protect yield.
Quality
Start-up rejects
Monitor wafers and first units after a restart.
Quality
Production rejects
Rework and scrap during steady running.
Where to start
- Start at the bottleneck. An hour gained elsewhere is an hour of more waiting.
- Log the reason for every stop. Without reasons, OEE is a score, not a diagnosis.
- Look at shifts separately. The same tool often runs very differently by shift, which points to skills cover.
This is the volume branch of our loss tree.