HAST is an environmental reliability test that includes a combination of high temperature, humidity, and pressure with or without electrical bias. HAST is used to accelerate the stresses of the traditional THB (temperature humidity bias) test in a controllable manner. It is this controlled acceleration of corrosion-type failures that differentiate HAST from regular THB or Autoclave. Unlike THB, HAST includes high pressure to accelerate corrosion-type failures thus uncovering flaws in packaging seals, materials, and joints between the packaging materials and pins.
HAST testing corresponds to the THB test in that failures are caused by the same mechanism. The resulting failures occur at proportional rates and a correlation can be found between activation energies. This duplication of failures occurs in far less time than THB or standard 85/85 testing. With electrical devices/components having become more reliable, several thousand hours of THB testing, for example, cannot catch the weaknesses that HAST can, and in a much shorter period of time.