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IEC 60319: Electronic Component Reliability Data — Predicting Future Failures From Historical Failure Rates
A Resistor Has a Failure Rate of 0.1 FIT — How Is That Number Statistically Derived?
IEC 60319:1999 specifies electronic component reliability data presentation and collection. FIT (Failure In Time, failures per 10⁹ device-hours) is the universal language of component reliability. But the statistical methodology behind a single FIT value is far more complex than a simple division.
| Metric | Unit | Definition |
|---|---|---|
| FIT | failures/10⁹h | Failure rate of 1×10⁻⁹/h |
| MTBF | hours | Mean Time Between Failures = 1/λ |
| γ (Confidence) | % | Typically 60% or 90% — FIT must state confidence level |
“0.1 FIT at 60% confidence” and “0.1 FIT at 90% confidence” are fundamentally different — the former means there is a 40% probability the true failure rate exceeds 0.1 FIT. In safety-critical systems (aviation, medical, nuclear), reliability data must state the confidence level. IEC 60319 mandates every reliability data point include sample size, test conditions, confidence level, and data source.
TNLab — A FIT value is not absolute. Reliability data without a stated confidence level is meaningless.
