Vieillissement de joints brasés pour l’électronique de puissance : caractérisation métallurgique et simulation numérique du comportement mécanique

Abstract : The new mechatronic technologies can significantly reduce the energy consumption and gas emissions of personal cars, by introducing rupture innovations in electrified powertrains complementarily or alternatively to combustion engines. The power electronics assemblies used in starter-alternator systems use solder joints which need to be substituted with lead-free solder in agreements with international standards. This thesis contributes to the metallurgical and mechanical characterization of two tin-based lead-free solder joints. These joints are produced industrially with a Die Laser Soldering process which leads to heterogeneous solidification microstructures, poorly reproducible, multiphased, and with defects. The objective of this thesis is to provide a better understanding of the solder joints lifetime during thermomechanical aging. Thermal aging generates stresses and plastic deformation due to the mismatch in the coefficients of thermal expansion between the different layers of the assemblies. Isotropic constitutive laws were identified from an experimental database of tensile tests on bulk specimens. Those constitutive laws were used in finite element simulations in order to assess the negative effect of the solder joint porosity, inherent flaw traced back to the soldering process. Aging tests coupled with observations of the microstructure evolution have shown the influence of tin grains orientation on crack initiation. The heterogeneity of the microstructure prevents us from proposing a representative volume element of the materials. An inverse method has been implemented in parallel with the development of an in situ bending test bench under a profilometer in order to build the first steps for the mechanical characterization of industrial solder joints.
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Samuel Jules. Vieillissement de joints brasés pour l’électronique de puissance : caractérisation métallurgique et simulation numérique du comportement mécanique. Matériaux. Ecole Nationale Supérieure des Mines de Paris, 2015. Français. ⟨NNT : 2015ENMP0018⟩. ⟨tel-01924513⟩

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