Acceleration factor: definition

Beginner

How many times faster a stress test ages a chip compared with normal use.

Novice

How many times faster a stress ages a part than normal use: time to fail in use divided by time to fail under stress. For temperature, the Arrhenius model gives $\mathrm{AF} = \exp\!\left[(E_{\mathrm{a}}/k)(1/T_{\mathrm{use}} - 1/T_{\mathrm{stress}})\right]$ , with temperatures in kelvin, $E_{\mathrm{a}}$ the failure mechanism’s activation energy and $k$ Boltzmann’s constant.

Expert

Each failure mechanism has its own activation energy and voltage dependence, so one AF for a whole product is an approximation. Moving $E_{\mathrm{a}}$ across its typical 0.3–1.5 eV range changes the AF by orders of magnitude.