菲特：長期失效率的單位，定義為每10⁹個器件小時發生一次故障，每1000個小時發生一次PPM（百萬分之一），或每1000個設備運行100萬小時發生一次故障。

平均無故障時間（MTTF)，是系統的預計失效時間。對于不可修得的系統，MTTF相當于其故障時間分布的平均值。

The calculation of product life

Below is the calculation process of product life under 55℃.

According to Arrhenius model:

AFT = exp((Ea/k)×(1/Tu - 1/Ts)) = tu/ts

AFT = Acceleration factor due to

tu = Time at use temperature (e.g. 55°C)

ts = Time at stress temperature (e.g. 150°C)

k = Boltzmann's Constant (8.617 x 10-5 eV/°K)

Tu = Temperature at Use (°K)

Ts = Temperature at Stress (°K)

Ea = Activation Energy (e.g. 0.7 ev)

X2 = Chi Squared Distribution, value depends on number of failures and confidence interval

TDH (Total Device Hours) = Number tested × Test hours

The failure rateλ is calculated by using the formula:

λ = [X2 /(2×TDH ×AFT)] ×109

MTTF (Mean Time to Failure) = 1/λ

MTBF: Mean time between failure, is the expected time between two successive failures of a system. Therefor, MTBF is a key reliability matric for a system that can be repaired or restored.

MTTF: Mean time to failure, is the expected time to failure of a system. Non-repaired systems can fail only once. Therefore, MTTF is equivalent to the mean of its failure time distribution.

MTTR: Mean to Restoration.

MTTF =∑T1/ N

MTTR =∑(T2+T3)/ N

MTBF =∑(T2+T3+T1)/ N

MTBF= MTTF+ MTTR

For non-repairable system, MTBF=MTTF.