8.1.3. Failure Rates
The Soft Error Rate (SER) or SEU reliability is expressed in Failure in Time (FIT) units. One FIT unit is one soft error occurrence per billion hours of operation.
- For example, a design with 5,000 FIT experiences a mean of 5,000 SEU events in one billion hours (or 114,155.25 years). Because SEU events are statistically independent, FIT is additive. If a single FPGA has 5,000 FIT, then ten FPGAs have 50,000 FIT (or 50K failures in 114,155.25 years).
Another reliability measurement is the mean time to failure (MTTF), which is the reciprocal of the FIT or 1/FIT.
- For a FIT of 5,000 in standard units of failures per billion hours, MTTF is:
1 ÷ (5,000 ÷ 1 Bh)=1 billion ÷ 5,000 = 200,000 hours = 22.83 years
SEU events follow a Poisson distribution and the cumulative distribution function (CDF) for mean time between failures (MTBF) is an exponential distribution. For more information about failure rate calculation, refer to the Intel FPGA Reliability Report.
Neutron SEU incidence varies by altitude, latitude, and other environmental factors. The Quartus® Prime Pro Edition software provides SEU FIT reports based on compiles for sea level in Manhattan, New York. The JESD89A specification defines the test parameters.
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