Global Standards for the Microelectronics Industry
ACCELERATED MOISTURE RESISTANCE - UNBIASED HAST
The Unbiased HAST is performed for the purpose of evaluating the reliability of nonhermetic packaged solid-state devices in humid environments. It is a highly accelerated test which employs temperature and humidity under noncondensing 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 that pass through it. Bias is not applied in this test to ensure 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.