The unbiased highly accelerated stress testing (HAST) is conducted to assess the reliability of non-hermetically sealed solid-state devices under humid conditions.
This is a highly accelerated testing procedure that utilizes elevated temperatures and humidity in non-condensing conditions to expedite the penetration of moisture through the external protective material, such as an encapsulant or seal, or along the interface between this material and the metallic conductors that traverse it. No bias is applied during this test to allow for the detection of failure mechanisms that may be masked by bias, such as galvanic corrosion.
The primary objective of this test is to pinpoint failure mechanisms that are internal to the package, and it is a destructive process.
Note: This test represents a comprehensive revision of the testing procedure found in Clause 4C of Chapter 3 of IEC 60749 from (1996), conducted without the application of bias voltage.
