Highly accelerated stress test
Encyclopedia
The highly accelerated stress test (HAST) method was invented by Nihal Sinnadurai while working as a Research Engineer at British Telecommunications Research Laboratories in 1968 in order to perform highly accelerated reliability testing of electronics components that are likely to encounter humid environments during normal (ambient) operation. The method uses the principle of a non-saturating autoclave designed and engineered with no moving parts, to deliver close temperature (<1°C) and humidity (<2%RH
) control and a high reliability of the stress equipment. Nihal Sinnadurai and his team carried out many millions of device hours of reliability stress testing in HAST chambers, and arrived at a clear correlation with a humidity exponent as the stress accelerating agent.
The generic Sinnadurai-HAST (SH) Model he developed by analysing the experimentally determined data, is:
When applied to semiconductor devices, the empirical SH Model expression is:
When applied to thick-film elements, the empirical SH Model is:
where 175000 is approximately 20 years and is the required lifetime (tamb) at the ambient condition, RHs is the applied humidity stress, RHamb is the humidity at the application ambient, Ts is the applied stress absolute temperature and Tamb is the application ambient temperature.
Relative humidity
Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...
) control and a high reliability of the stress equipment. Nihal Sinnadurai and his team carried out many millions of device hours of reliability stress testing in HAST chambers, and arrived at a clear correlation with a humidity exponent as the stress accelerating agent.
The generic Sinnadurai-HAST (SH) Model he developed by analysing the experimentally determined data, is:
When applied to semiconductor devices, the empirical SH Model expression is:
When applied to thick-film elements, the empirical SH Model is:
where 175000 is approximately 20 years and is the required lifetime (tamb) at the ambient condition, RHs is the applied humidity stress, RHamb is the humidity at the application ambient, Ts is the applied stress absolute temperature and Tamb is the application ambient temperature.