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Wheeler J.M.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Armstrong D.E.J.,University of Oxford | Heinz W.,Kompetenzzentrum Automobil und Industrie Elektronik GmbH | Schwaiger R.,Karlsruhe Institute of Technology
Current Opinion in Solid State and Materials Science | Year: 2015

Nanoindentation measurement capabilities at elevated temperatures have developed considerably over the last two decades. Commercially available systems can now perform stable indentation testing at temperatures up to ∼800 °C with thermal drift levels similar to those present at room temperature. The thermal management and measurement techniques necessary to achieve this are discussed here, with particular emphasis on systems featuring independent heating of both the indenter and the sample. To enable measurements at temperatures where oxidation of the indenter and/or sample are a concern, vacuum nanoindentation techniques have also been developed. A natural extension of testing in vacuo is elevated temperature nanoindentation in situ in the scanning electron microscope, and the additional requirements for and benefits of this are discussed. Finally, several new emerging testing techniques are introduced: thermal cycling/fatigue, interfacial thermal resistance measurement and small scale transient plasticity measurements. © 2015 Elsevier Ltd.

Fellner K.,Polymer Competence Center Leoben | Antretter T.,University of Leoben | Fuchs P.F.,Polymer Competence Center Leoben | Pelisset T.,University of Leoben | Pelisset T.,Kompetenzzentrum Automobil und Industrie Elektronik GmbH
Journal of Strain Analysis for Engineering Design | Year: 2016

In printed circuit boards, thin copper layers are used as current paths. During the thermal loading of printed circuit boards, stresses arise due to the different coefficients of thermal expansion of the used materials. To be able to model the mechanical behavior of printed circuit boards under cyclic thermal loads, cyclic mechanical tests of thin copper foils under changing tensile and compression loads at different temperatures were conducted. From these experiments, the isotropic and kinematic hardening parameters were determined serving as material input data for a nonlinear isotropic/kinematic hardening model in the finite element analysis-software Abaqus. The kinematic hardening parameters were fitted in an optimization process. The isotropic hardening variables were determined based on the stress versus plastic strain relationship that was constructed incrementally from the available individual cycles. The so-obtained curve was found to be not unique, but to depend on the loading situation. Hence, different approaches for strain range memorization were evaluated. Since these approaches were developed for modeling strain-controlled tests, whereas the experimental data were obtained in a force-controlled way, a phenomenological formulation was developed and applied. The results of curvature measurements during thermal cycling were used for model validation. The experimental results and the numerical predictions are in good agreement. © Institution of Mechanical Engineers. © IMechE 2015.

Heinz W.,Kompetenzzentrum Automobil und Industrie Elektronik GmbH | Robl W.,Infineon Technologies | Dehm G.,Max Planck Institute Fur Eisenforschung
Studies in Surface Science and Catalysis | Year: 2015

During a switch event in a power semiconductor device temperature changes of up to 300 K can occur in the Cu layer. Repeated switching operations causes cyclic thermal cycling which may finally lead to thermomechanical fatigue with severe microstructural changes. In this study, the influence of the starting microstructure and film thickness (600 nm and 5000 nm) on thermomechanical fatigue was investigated for epitaxial and polycrystalline Cu films for up to 1000 thermal cycles. Severe surface roughening and a texture change (crystal rotation) are detected during thermal cycling for the polycrystalline Cu films, while the epitaxial films maintain their microstructure. Controlling the initial microstructure of a Cu layer in a device exposed to cyclic thermomechanical straining is a route to delay surface damage. © 2014 Elsevier B.V. All rights reserved.

Hochauer D.,Materials Center Leoben Forschung | Mitterer C.,University of Leoben | Penoy M.,CERATIZIT Luxembourg S.ar.l. | Puchner S.,Kompetenzzentrum Automobil und Industrie Elektronik GmbH | And 5 more authors.
Surface and Coatings Technology | Year: 2012

Alumina (Al2O3) coatings deposited by chemical vapor deposition (CVD) with different modifications and dopants are widely applied as wear resistant coatings on cemented carbide cutting tools. The aim of this work was to investigate the influence of CH4 addition on the deposition of α-Al2O3 by low-pressure chemical vapor deposition (LPCVD). The coatings were deposited at 1005°C on a TiN-TiCN base layer using a precursor gas mixture of AlCl3, CH4, CO2, HCl, H2S, and H2. Coating characterization was conducted by scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GDOES), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), glancing angle X-ray diffraction (GAXRD), nanoindentation and tribological ball-on-disk tests against Al2O3 balls. Additionally, the ball-on-disk wear tracks were investigated by Raman spectroscopy.The highest carbon doping content achieved in this study was in the range of 0.5-1.0at.%. SEM top-view images indicate a less facetted coating topography with slightly larger grains for C-doped coatings. GAXRD patterns show the α-Al2O3 modification for undoped and C-doped coatings with only minor differences concerning lattice parameters, preferred orientation and stresses. The hardness values remain at ~25GPa for both coating types. The friction coefficient decreases from 0.7 for undoped Al2O3 to 0.5 and 0.4 for the C-doped coating at room temperature and 700°C, respectively, which is attributed to the formation of a lubricious nanocrystalline graphite layer in the sliding contact. At 900°C, both coatings show a further reduction of the friction coefficient to 0.35 due to out-diffusion of titanium through the thermal crack network of the Al2O3 layer and formation of rutile. © 2012 Elsevier B.V.

Wimmer A.,Kompetenzzentrum Automobil und Industrie Elektronik GmbH | Leitner A.,Austrian Academy of Sciences | Detzel T.,Infineon Technologies | Robl W.,Infineon Technologies | And 4 more authors.
Acta Materialia | Year: 2014

In this study, the low-cycle fatigue properties (1-15,000 cycles) of electrodeposited Cu, which is frequently used as metallization in the semiconductor industry, is analyzed with respect to its microstructure. Freestanding Cu tensile samples 20 μm × 20 μm × 130 μm were fabricated by a lithographic process. The grain size of the samples was modified by using three different process conditions for electrochemical Cu deposition. All samples were subjected to cyclic tension-tension testing performed with a miniaturized stress-controlled stage in situ in a scanning electron microscope until failure occurred. The number of cycles sustained prior to failure depends on the accumulated creep strain and can be related to the failure strain in a tensile test. It will be shown that the microstructure influences the number of cycles to failure and the failure mode. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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