Mean time between failures, total operating hours divided by the number of failures, used for repairable equipment such as process tools, pumps and servers. When the failure rate is constant, MTBF is the reciprocal of that rate, and only about 37 percent of units are still running at a time equal to the MTBF. Fab equipment teams track it alongside MTTR, mean time to repair, to calculate tool availability.
MTBF on the wafer robot is down to 180 hours since the firmware update. That's a crash a week on every tool in the cluster.
An MTBF of 50,000 hours does not mean a part lasts 50,000 hours. With a constant failure rate, nearly two-thirds fail before then.
Also heard as
- mean time between failures
Do not mix it up with
- MTTF: MTTF applies to items that are replaced, not repaired, after their first failure.
Related terms
MTTF
Mean time to failure: expected life of a non-repairable item, the average time until its first and only failure.
Bathtub curve
Plot of failure rate over a product's life: falling early failures, a flat random period, then rising wear-out.
Weibull distribution
Flexible life distribution with a shape and a scale parameter, the standard model for fitting time-to-failure data.
FIT
Failures in time: one failure per billion device-hours, the standard unit for semiconductor failure rates.