The unbiased highly accelerated stress testing (HAST) is performed for the purpose of evaluating the reliability of non-hermetically packaged solid-state devices in humid environments. It is a highly accelerated test which employs temperature and humidity under non-condensing conditions to accelerate the penetration of moisture through the external protective material (encapsulant or seal) or along the interface between the external protective material and the metallic conductors which pass through it. Bias is not applied in this test to ensure that the failure mechanisms potentially overshadowed by bias can be uncovered (e.g. galvanic corrosion). This test is used to identify failure mechanisms internal to the package and is destructive. NOTE This test is a complete rewrite of the test contained in Clause 4C of Chapter 3 of IEC 60749 (1996) (without bias voltage).