A Primer for HAST: Highly Accelerated Stress Testing

HAST Chamber: Highly Accelerated Stress Testing
DES’s HAST Chamber

The HAST acronym stands for Highly Accelerated Temperature/Humidity Stress Test and is sometimes shortened to Highly Accelerated Stress Testing. HAST makes use of accelerated temperature and humidity conditions to precipitate failures which could be caused by long term exposure to humid environments.

HAST has been developed to replace Temperature-Humidity-Bias (THB) testing which has typical conditions of 85 ⁰C and 85 % RH along with a bias voltage applied to the sample. A typical THB test time would be 1000 hours. HAST uses increased test temperatures of 110 to 130 ⁰C which decreases the test time to as low as 96 hours compared to a THB test. Thus, by choosing HAST over THB for an accelerated reliability test, testing can be completed in days, not weeks.

HAST utilizes a positive pressure inside the test chamber along with temperatures above 100 ⁰C and controlled humidity. This requires that the chamber be tightly sealed to prevent leaks so that the test conditions can be maintained. Testing can be performed with or without a voltage bias on the samples.

For a biased test, a DC voltage is applied to the samples. The samples are connected to wires or sockets located inside of the test chamber. Wires inside of the chamber pass through a sealed feedthrough where they are connected to power supplies located outside of the chamber. The bias can be continuous or cyclic DC voltage. Note that cyclic DC voltage is not the same as AC voltage.

Common standards used for HAST are JESD22-A110, JESD22-A118, IEC 60068-2-66. Typical test conditions are:

Temperature [dry bulb °C] Relative Humidity [%] Temperature [wet bulb, °C] Vapor Pressure [kPa (psia)] Duration [hours]
130 85 124.7 33.3/230 96
110 85 105.2 17.7/122 264


Delserro Engineering Solutions, Inc. (DES) has many years of experience performing HAST testing and can assist customers in setting up a test using the proper test conditions. So, if you do not know what test conditions that you should use or what specification to choose then we will help you because we are HAST experts!

Contact us or call 610.253.6637 to find out what DES can do for you!

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3 thoughts on “A Primer for HAST: Highly Accelerated Stress Testing”

  1. How do you correlate that 1000hrs of 85C/85%RH THB is equivalent to 96hrs for HSTL? Any mathematical model?

  2. how do you correlated 96hrs equivalnt to 1000hrs when 130’C//85% RH. What is the mathematical model you used? thanks.

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