In qualification of automotive ICs, what is the main reason HAST (a biased test in pressurized water vapor at around 130 °C and 85% RH) is sometimes used instead of the temperature humidity bias test (THB) run at 85 °C and 85% RH for 1000 hours?

Answer: A. It accelerates failures such as corrosion caused by moisture ingress, shortening a 1000-hour test to around 100 hours

HAST (Highly Accelerated Stress Test) is a method that tests at temperatures above 100 °C under pressure while maintaining high humidity. Raising the temperature and water vapor pressure speeds the movement of moisture through the package mold compound to the chip, accelerating electrode corrosion, increased leakage current and similar failures. For example, it is common to run about 96 hours at 130 °C and 85% RH as an evaluation equivalent to 1000 hours at 85 °C and 85% RH. It has nothing to do with evaluating soft errors or dry conditions.