Highly accelerated stress test explained

The highly accelerated stress test (HAST) method was first proposed by Jeffrey E. Gunn, Sushil K. Malik, and Purabi M. Mazumdar of IBM.^[1]

The acceleration factor for elevated humidity is empirically derived to be

AF _{H} = e ^{const ⋅ (RH ^{n} _{s} - RH ^{n)} _{o}} , 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

AF _{T} = e ^{(E _{a/k)(1/T} _{o} -1 /T _{s)}} ,

where E_a is the activation energy for the temperature-induced failure (most often 0.7 eV for electronics), k is the Boltzmann 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

AF _{HAST} = AF _{H} ⋅ AF _{T} = e ^{const ⋅ (RH ^{n} _{s} - RH ^{n)} _{o}} e ^{(E _{a/k)(1/T} _{o} -1 /T _{s)}} .

Notes and References

1. Highly Accelerated Temperature and Humidity Stress Test Technique (HAST). 19th International Reliability Physics Symposium. 10.1109/IRPS.1981.362972. Las Vegas. April 7–9, 1981. IEEE. Gunn. Jeffrey E.. Sushil K. . Malik. Purabi M.. Mazumdar. 48–51.