The How and why of Biased Humidity Tests with Copper Wire

HAST at 110 or 130 °C is often the biased humidity test of choice when qualifying copper wire, due to its short execution time. However, failure mechanisms, like corrosion, can be over-accelerated during HAST compared to a milder test like THB at 85 °C. This is especially the case under certain conditions (e.g. high bias or electrical fields) due to changes in material behavior during the HAST test. In this paper, an approach to determine an acceleration model is proposed based on an observed incubation time before the onset of corrosion. Although HAST at 130°C combined with high electrical field is an extremely stressful test condition, delaying incubation until well beyond the JESD47 requirement of 96h (or AEC Q006 requirement of 192 h for copper wire) can be achieved. Parts that pass this test condition have a large robustness margin in electronic packages.