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Vieillissement thermique de la structure nanoporeuse de l’Ag fritté pour le report de puces des modules d’électronique de puissance : nanotomographie in situ, rôle d’une interface et simulation du comportement mécanique

Abstract : The rapid evolution of power electronics is closely linked to the need to improve the performance and the reliability of greener transportation systems (cars, planes, etc.). The latest generation of power modules is based on SiC or GaN chips, which provide higher performance than traditional Si chips, but with a significant increase in operating temperature. As power modules are a complex assembly of different materials, all of them having different coefficients of thermal expansion, a fine re-evaluation of the evolution of the microstructures and properties over time for each material and interfaces is necessary. This is a critical issue since the systems work now at a much higher temperature. In particular, the die-attached bonding layer is a key point for the entire module reliability, as it must ensure good mechanical cohesion while being a very good thermal and electrical conductor. As the traditional bonding solutions are no longer usable for the most advanced modules, new bonding solutions need to be investigated. Among all the emerging solutions, silver (Ag) paste sintering appears to be an excellent die-attach technology because Ag has the best thermal and electrical conductivity as well as a very high melting temperature compared to other commonly used materials. However, the conditions of elaboration of the sintered Ag lead to a nanoporous microstructure, known to alter the properties of the material. Furthermore, the evolution of the nanoporous structure and properties during thermal aging is only poorly known and very often only based on 2D investigations. In this work, time resolved evolution (4D) of the nanoporous microstructure of sintered Ag during thermal aging in the range of 200°C to 350°C was monitored using in-situ X-ray nanotomography. In particular, the effect of a copper substrate (Ag/Cu) on the porosity evolution was investigated. Drastic differences in microstructural evolution were observed between pure sintered Ag samples and samples with a copper interface. Full-field numerical simulations by the finite element method have been proposed to determine the mechanical properties of sintered Ag. It appears that sintered Ag has an almost perfectly isotropic behavior with elastic properties depending mainly on the porosity. The morphology and spatial arrangement of the pores do not have a significant influence on the elastic properties.
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Submitted on : Thursday, October 13, 2022 - 2:35:01 PM
Last modification on : Friday, October 21, 2022 - 3:46:02 AM

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  • HAL Id : tel-03813616, version 1

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Kokouvi Happy N'Tsouaglo. Vieillissement thermique de la structure nanoporeuse de l’Ag fritté pour le report de puces des modules d’électronique de puissance : nanotomographie in situ, rôle d’une interface et simulation du comportement mécanique. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2022. Français. ⟨NNT : 2022ESMA0010⟩. ⟨tel-03813616⟩

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