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Institut für Struktur- und Funktionskeramik

Life time of multilayer ceramic systems (FMCS)

Fig. 1: a) Soldered multilayer LTCC-modul on a PCB,
b) Cross-section of a module subjected to very high number of temperature cycles; a crack has originated at the edge junction ceramic – solder joint, and propagated through the ceramic.

Modern electronic systems ( functional multilayer ceramic systems; FMCS) are in general composed of a mix of materials (ceramics, metals and polymers), as seen in Fig. 1a, which have very different electrical, thermal and mechanical properties. During processing and in service they suffer from large temperature changes and the mismatch in thermal expansion coefficients (CTE mismatch) causes the development of significant internal stresses which may limit the system reliability (see Fig. 1b). Another cause for failing may also be mechanical stresses due to vibrations. The aim of this project is to analyse the mechanical reliability of functional multilayer ceramics systems with three focus points.

  • First the characterisation of multilayer components must consider the influence of the layered structure (e.g. properties and distribution of the layers) on their mechanical properties.
  • The second point is related to the interconnects (i.e. solder joints) employed to integrate the multilayer components into FMCS. The aim is to characterise t he thermo-mechanical behaviour of the Solder Joint at the relevant length scale and temperature under low and high cycle loading.
  • The third focus will be the generation of a parametric FE model to account for the strains and stresses in the FMCS under certain thermo-mechanical conditions. The properties of the involved materials measured at different temperatures, relevant length scales and actual geometries will be the input for the model. The evaluation of the internal stresses due to the combination of materials in the FMCS (e.g. Component – Solder Joint – Substrate) caused by temperature changes will be attempted aiming to validate the FE results. Fractographic analyses of sample specimens (with special attention to interfaces) will also be performed to identify the failure of FMCS which along with the FE results will be utilised to give design recommendations of the complete system.

The project will be carried out in close cooperation with the company EPCOS (Deutschlandsberg) and the company CONTINENTAL (Regensburg, Germany) as well as with the Department of Materials Physic (DPM, Leoben) and the Group of Physics of Nanostructured Materials at the University of Vienna (UW, Vienna).