Czerny, Bernhard

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Official Name
Czerny, Bernhard
Main Affiliation
Akademische Titel
Mag. Dr.
Email
bernhard.czerny@fh-burgenland.at
ORCID
Scopus Author ID
36238795900
Status
staff

Research Outputs

2023 2023 2022 2022 2021 2021 2020 2020 2019 2019 2018 2018 2017 2017 2016 2016 2015 2015 2014 2014 0.0 0.0 1.0 1.0 2.0 2.0 3.0 3.0 4.0 4.0 5.0 5.0 6.0 6.0

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    Publication
    Accelerated mechanical fatigue interconnect testing method for heavy wire bonds in power modules
    (2017-05-11)
    Czerny, Bernhard 
    Every new development in device performance and packaging design, due to new materials and design changes can influence the device reliability drastically. High performance and high reliability demands in power electronics over several decades and a short time to market development, raise the need for very fast reliability testing methods. In this study a mechanical fatigue testing method is presented for evaluating the interfacial fatigue resistance of heavy Al wire bonded interconnects in high power modules. By separating the concurrent thermal, mechanical and environmental failure mechanisms a selective investigation of the desired failure mode is possible. The setup is designed to reproduce the thermo-mechanical shear stresses by mechanical means, while provoking the same lift-off failure mode as in power cycling tests. With a frequency variable test setup of a few Hz up to several kHz, measurements from 1E3 up to 1E8 and determining the influence of the testing frequency on the fatigue life were possible.
      55  1
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    Publication
    Simulation of stress concentrations in wire-bonds using a novel strain gradient theory
    (Elsevier, 2013-04-14)
    Czerny, Bernhard 
    ;
    Lederer, Martin 
    ;
    Nagl, Bernhard 
    ;
    Trnka, A. 
    ;
    Khatibi, Golta 
    ;
    Thoben, Markus 
    Fatigue failure of wire-bonds is one of the key factors limiting the lifetime of power electronic devices. In IGBT (insulated gate bipolar transistor) modules, wire-bonds are exposed to repeated temperature changes leading to thermo-mechanical stresses in the constituent materials. Due to the geometry, stress concentrations arise at the interfaces of aluminum wires and silicon chips. In the framework of classical continuum mechanics, these stress concentrations show the characteristics of stress singularities. Nevertheless, IGBT modules reach lifetimes of about 30 years under service conditions. Therefore, it seems that classical continuum mechanics exaggerates the stress concentrations occurring at the material transitions. Hence, it is the subject of the present investigation to calculate more realistic stress distributions using a novel strain gradient theory.
      38  1Scopus© Citations 1
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    Publication
      80  1
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    Publication
    Reliability of Cu wire bonds in microelectronic packages
    (Elsevier, 2017)
    Czerny, Bernhard 
    ;
    Mazloum-Nejadari, Ali 
    ;
    Khatibi, Golta 
    ;
    Lederer, Martin 
    ;
    Nicolis, Johann 
    ;
    Weiss, Laurens 
    In this study the thermo-mechanical response of 25 μm Cu wire bonds in an LQFP-EPad (Low Profile Quad Flat Exposed Pad) package was investigated by numerical and experimental means. The aim was to develop a meth odology for fast evaluation of the packages, with focus on wire bond fatigue, by combining finite element analysis (FEA) and mechanical fatigue testing. The investigations included the following steps: (i) simulation of the warp age induced displacements in the encapsulated LQFP-176-Epad package due to temperature changes, (ii) repro ducing the thermally induced stresses in the wire bond loops in an unmolded (non-encapsulated) LQFP package using an accelerated multiaxial mechanical fatigue testing set-up under the displacement amplitudes deter mined in case (i) and determination of the loading cycles to failure (Nf), (iii) FEA of the experiments performed in (ii) based on the boundary conditions determined in (i) to calculate the states of stress and strain in the wire bonds subjected to multiaxial mechanical cyclic loading. Our investigations confirm that thermal and mechanical cyclic loading results in occurrence of high plastic strains at the heat affected zone (HAZ) above the nail-head, which may lead to fatigue failure of the wire bonds in the packages. The lifetime of wire bonds show a propor tional relation between the location and angle of the wire bond to the direction of loading. The calculated accu mulated plastic strain in the HAZ was correlated to the experimentally determined Nf values based on the volume weighted averaging (VWA) approached and presented in a lifetime diagram (Δd-Nf) for reliability assessment of Cu wire bonds. The described accelerated test method could be used as a rapid qualification test for the deter mination of the lifetimes of wire bonds at different positions on the chip as well as for related improvements of package design.
      61  1Scopus© Citations 20
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    Publication
    In situ vibration measurements on power modules under operating conditions
    (Elsevier, 2012-04-16)
    Czerny, Bernhard 
    ;
    Nagl, Bernhard 
    ;
    Lederer, Martin 
    ;
    Trnka, A. 
    ;
    Khatibi, Golta 
    ;
    Thoben, Markus 
    The subject of this investigation was determination of thermo-mechanically induced displacement of the components inside a power module under operation conditions. It is well known that lifetime of insulated gate bipolar transistor (IGBT) modules is limited by thermo-mechanical fatigue. Wire bonded interconnects inside the IGBTs count as critical sites where crack initiation and failure is observed. In this study the temperature dependent periodic deformation of wire-bonds under operating conditions was determined by using a laser Doppler vibrometer (LDV) and thermal imaging camera. Furthermore finite element analyses (FEA) were conducted to obtain the strain values needed for lifetime assessments.
      43  1Scopus© Citations 6
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    Publication
    Step-by-Step Building of a Four Dimensional Fatigue Compatible Regression Model including Frequencies
    (2021-12)
    Czerny, Bernhard 
    ;
    Castillo, Enrique 
    ;
    Fernández Lavín, Alfonso Antonio 
    ;
    Blasón, Sergio 
    ;
    Khatibi, Golta 
    ;
    Zareghomsheh, Mohammad 
    The purpose of this research is to develop a model, with emphasis on compatibility conditions and model building, valid for high cycle fatigue design components such as wind turbines, automobiles, high speed railways and aeronautical material. In this work, we have added the frequency as one more variable to an existing fatigue model that already includes maximum stress, stress ratio and lifetime. As a result, a model and estimation method has been proposed and a random variable V has been identified, which, allows the accumulated damage and the probability of failure to be assessed for any load history in terms of stress levels, stress ranges and frequencies. Finally, the model is validated using a large set of real experimental data.
      197  1
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    Publication
    Fatigue life time modelling of Cu and Au fine wires
    (2018-05-25)
    Czerny, Bernhard 
    ;
    Khatibi, Golta 
    ;
    Mazloum-Nejadari, Ali 
    ;
    Delshadmanesh, Mitra 
    ;
    Lederer, Martin 
    In this study, the influence of microstructure on the cyclic behaviour and lifetime of Cu and Au wires with diameters of 25μm in the low and high cycle fatigue regimes was investigated. Low cycle fatigue (LCF) tests were conducted with a load ratio of 0.1 and a strain rate of ~2e-4. An ultrasonic resonance fatigue testing system working at 20 kHz was used to obtain lifetime curves under symmetrical loading conditions up to very high cycle regime (VHCF). In order to obtain a total fatigue life model covering the low to high cycle regime of the thin wires by considering the effects of mean stress, a four parameter lifetime model is proposed. The effect of testing frequency on high cycle fatigue data of Cu is discussed based on analysis of strain rate dependency of the tensile properties with the help of the material model proposed by Johnson and Cook.
      70  1Scopus© Citations 9
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    Publication
    A rapid test for reliability of heavy wire bonds
    (Konradin-Verl. Kohlhammer, 2019-04-17)
    Czerny, Bernhard 
    ;
    Seidl, Siegfried 
    Bond-Drahtverbindungen müssen über mehrere Dekaden und unter hohen thermomechanischen Belastungen zuverlässig halten. Dafür sorgt ein Bondtester mit einem extrem schnellen automatischen Qualitätstest zur Lebensdauerbestimmung der Bond-Drahtverbindungen.
      60  1
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    Publication
    Towards adequate qualification testing of electronic products: Review and extension
    (Elsevier, 2014-12-03)
    Czerny, Bernhard 
    ;
    Khatibi, Golta 
    ;
    Lederer, Martin 
    ;
    Magnien, Julien 
    ;
    Suhir, Ephraim 
    ;
    Nicolics, Johann 
    Electronic product manufacturers are constantly seeking efficient, cost-effective and trustworthy accelerated test (AT) methods to keep up with the today's market demands. At present, accelerated temperature cycling testing is viewed as the state of the art for reliability assessment of electronic products. Accelerated mechanical fatigue testing has been proposed recently as a novel concept and an attractive cost-effective and time-saving qualification alternative for electronic devices. The principle idea of this approach is replacement of thermally induced loading with equivalent and adequate mechanical loading. Using mechanical fatigue testing set-ups, the devices under test can be subjected to single or multi-axial cyclic loading conditions at high frequencies. As a result, physically meaningful lifetime curves can be obtained. The suggested methodologies and procedures enable one to detect the vulnerable sites of the devices in a very short time. Exemplary results for power semiconductor products demonstrate the applicability of the proposed method for qualification of first and second level interconnects. The advantages and limitations of the proposed concept are addressed and discussed in detail.
      41  1