IEC 60749-4:2017(E) provides a highly accelerated temperature and humidity stress test (HAST) for the purpose of evaluating the reliability of non-hermetic packaged semiconductor devices in humid environments. This edition includes the following significant technical changes with respect to the previous edition: a) clarification of requirements for temperature, relative humidity and duration detailed in Table 1; b) recommendations that current limiting resistor(s) be placed in the test set-up to prevent test board or DUT damage; c) allowance of additional time-to-test delay or return-to-stress delay.