Highly accelerated stress test

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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

where RHs is the stressed humidity, RHo 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

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

Therefore the total acceleration factor for unbiased HAST testing is


  1. Gunn, Jeffrey E., Sushil K. Malik, and Purabi M. Mazumdar. "Highly accelerated temperature and humidity stress test technique (HAST)." Reliability Physics Symposium, 1981. 19th Annual. IEEE, 1981.

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