Increasing the reliability of aluminum wirebonds by thermal treatments: analysis and implementation

• Published in: IEEE journal of emerging and selected topics in power electronics 2023-06, Vol.11 (3), p.1-1
• Main Authors: Pichon, Pierre-Yves, Brandelero, Julio, Lelesle, Johan, Ouhab, Merouane, Quemener, Vincent
• Format: Article
• Language: English
• Subjects: Aluminum; Crack propagation; Electrothermal modelling; Gate Driver; Heat treatment; Insulated gate bipolar transistors; Mechanical factors; Metallization; Microstructure; Nanoindentation; Physics of Failure; Recrystallization; Reliability; Reliability Analysis; Semiconductor devices; Temperature Control; Temperature measurement; Wirebonds; Wires
• ISSN: 2168-6777; 2168-6785
• DOI: 10.1109/JESTPE.2022.3231963

In this work we studied the effect of a post-bonding thermal treatment on thick aluminum wirebonds lifetime in IGBT power modules during power cycling at different temperature swings. A reliability improvement of up to 44% is demonstrated for the bonds located at the center of the chip and seeing the highest thermal treatment temperature. The physical phenomena occurring during the thermal treatments and during power cycling are studied using microstructure analysis (Scanning Electron Microscopy techniques) and nanoindentation. Softening of the material results from recrystallization and/or recovery during thermal treatment, whereas during power cycling the thermal treated material hardens due to strain accumulation and defect formation. Despite the hardening our data suggests a decrease in crack growth rate at the second half of the testing time. We implemented an approach for applying thermal treatments during typical operating conditions in a converter by controlling the off-state losses of a device in a multichip configuration. The stability and the limits of this approach are studied experimentally and described by an electrothermal model. This study allows us to conclude on a realistic process window for online thermal treatments, by considering both material constrains and practical temperature control limits.