Highly accelerated stress test

The highly accelerated stress test (HAST) method was first proposed by Jeffrey E. Gunn, Sushil K. Malik, and Purabi M. Mazumdar of IBM.

The acceleration factor for elevated humidity is empirically derived to be

${\displaystyle AF_{\text{H}}=e^{{\text{const}}\cdot (RH_{\text{s}}^{n}-RH_{\text{o}}^{n})},}$

${\displaystyle {\text{const}}}$ is a value which normally goes from 0.1 to 0.15

where RH_s is the stressed humidity, RH_o is the operating-environment humidity, and n is an empirically derived constant (usually 1 < n < 5).

The acceleration factor for elevated temperature is derived to be

${\displaystyle AF_{T}=e^{(E_{\text{a}}/k)(1/T_{\text{o}}-1/T_{\text{s}})},}$

where E_a is the activation energy for the temperature-induced failure (most often 0.7 eV for electronics), k is Boltzmann's constant, T_o is the operating temperature in kelvins, and T_s is the stressed temperature.

Therefore the total acceleration factor for unbiased HAST testing is

${\displaystyle AF_{\text{HAST}}=AF_{\text{H}}\cdot AF_{T}=e^{{\text{const}}\cdot (RH_{\text{s}}^{n}-RH_{\text{o}}^{n})}e^{(E_{\text{a}}/k)(1/T_{\text{o}}-1/T_{\text{s}})}.}$