Influence of Moisture Absorption on Power Cycling Capability of IGBT Modules

Power cycling test (PCT) is one of the most important tests to evaluate the packaging reliability of power electronics, which is much closer to the actual working condition when coupled with moisture stress. With Si-IGBT modules packaged in EasyPACK, it was observed that Devices Under Test (DUTs) reached a saturation state of moisture absorption approximately 60 hours after the start of temperature/humidity storage in 85°C/85% Relative Humidity (RH) environment by monitoring the DUTs' weight gain. Then three groups of experiments [Group 1: DUTs without preaging; Group 2 and Group 3: DUTs were preaged with storage in 85°C/85%RH environment for 256 and 500 hours respectively] were designed to investigate how the power cycling capability of devices would be affected by continued storage after saturation. Experimental results show that the power cycling lifetime of devices decreases significantly after 85°C/85%RH storage, but it does not decrease further after the saturation is reached. Further analysis of the failure mechanism of the devices shows that solder layer aging is almost not affected by continued storage after saturation, but bond wire degradation is deepened, resulting in an increase in the onvoltage drop of devices at the early stage of the PCT.