For high temperature interconnection sintered silver can be used, however, it induces new demands on the thermo-mechanical design. That issue requires knowledge on the thermo-mechanical reliability of silver sintered devices, the subject of this paper. Material characteristics of the sinter layers are needed for simulation, which are addressed in the first part of the paper. Based on material properties of pure silver, for sintered silver with different porosities effective material characteristics have been derived by use of a micromechanical cell model. Shear loadings with in-situ deformation analyses have also been made to investigate sintered silver behavior. A complicated dependence on processing, temperature, and deformation rate is seen. Based on different effective constitutive models for the sintered interconnects, stress loadings are studied for a power module, an IGBT on DCB substrate, for passive and active thermal cycling. For the passive cycle complex interactions of the different layers of the stack are observed, which are not seen in a module with soft solder bonding. This result can be attributed to the missing decoupling by the soft soldering layer. Failure risks are evaluated by both conventional FEA and cohesive zone modeling. A quite different stress situation is depicted for active power cycling. The situation is even more complex and it is obvious from the simulations, that active power cycling can induce failure modes different from passive cycling
Cellular metals, particularly aluminium foams, are increasingly used in automotive, railcar and aircraft industries due to their advantages such as low density, comparatively high stiffness, noise damping or non‐flammability. From this point of view a new powder‐compact forming and foaming technique has been developed to manufacture 3D‐aluminium foam sandwich (AFS) parts for components of railcars without glued joint between the foamed core layer and both cover sheets. Three different stages of foam expansion have been analysed to describe the material properties. We have characterised samples made of plane AFS panels by compression, bending and shear tests. The shear strain is optically measured by digital image correlation to estimate the shear modulus of foamed sandwiches. Furthermore, these experimentally determined values and curves are the basis for the verification and optimisation of finite element models by design of experiments. As a result of this work, recommendations could be derived for improving technological parameters.
The aim of this paper is to get insight into measurement uncertainties for thermomechanical measurements performed using a piezoresistive silicon-based stress sensor in a standard microelectronic package. All used sensors have the same construction, were produced in the same technological processes at the same time, yet the measurement results show significant distribution. The possible causes for this phenomenon are discussed in this paper. Additionally, Finite Element Method (FEM) model is created and validated, what enables a study of sensitive parameters influencing the measurement uncertainties.
KurzfassungDas Optimieren der mechanischen und tribologischen Eigenschaften keramischer Schichten basierte auf den Ergebnissen von Vorversuchen, in denen überwiegend Agglomeratpulver der Systeme Al2O3/TiO2 bzw. Al2O3/ZrO2 zur Anwendung gekommen sind. Das Erreichen der erforderlichen Oberflächenqualität der plasmagespritzten Schichten erfolgte durch eine Schleif- und Polierbearbeitung. Die Untersuchungsergebnisse der Haftfestigkeit und des gravimetrischen Verschleißes der Schichten zeigen, dass die Mischkeramiken Al2O3(70%)/TiO2(30%) und Al2O3(57,5%)/ZrO2(42,5%) die Favoriten für eine weiterführende Schichtoptimierung darstellen. Die Optimierung der Schichtstruktur und -eigenschaften beinhaltet im Schwerpunkt das weitere Homogenisieren der Schichtmorphologie bei gleichzeitiger Erhöhung der Adhäsion.
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