acceleration factor (A, AF)

For a given failure mechanism, the ratio of the time it takes for a certain fraction of the population to fail, following application of one stress or use condition, to the corresponding time at a more severe stress or use condition.

NOTE 1 Times are generally derived from modeled time-to-failure distributions (lognormal, Weibull, exponential, etc.).

NOTE 2 Acceleration factors can be calculated for temperature, electrical, mechanical, environmental, or other stresses that can affect the reliability of a device.

NOTE 3 Acceleration factors are a function of one or more of the basic stresses that can cause one or more failure mechanisms. For example, a plot of the natural log of the time-to-failure for a cumulative constant percentage failed (e.g., 50%) at multiple stress temperatures as a function of 1/kT, the reciprocal of the product of Boltzmann’s constant in electronvolts per kelvin and the absolute temperature in kelvins, is linear if one and only one failure mechanism is involved. The best-fit linear slope is equal to the apparent activation energy in electronvolts.

NOTE 4 The abbreviation AF is often used in place of the symbol A.

References

JEP122E, 3/09
JEP143B.01, 6/08
JESD74A#, 2/07
JESD85#, 7/01
JESD91A#, 8/01
JESD94A, 7/08