Czerny, Bernhard

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

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    A new approach for evaluation of fatigue life of al wire bonds in power electronics
    (Elsevier, 2014-02-16)
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    Khatibi, Golta 
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    Lederer, Martin 
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    Kotas, Agnieszka Betzwar 
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    Weiss, Brigitte 
    Ultrasonically bonded A1 wire bonds on A1 metallization pads are widely used in power semiconductors. The required long time reliability of the devices is highly dependent on the interfacial quality of A1 wire and the bond pad. Reliability of wire bonds is commonly assessed by thermal and power cycling tests. Accelerated mechanical fatigue testing can be used as an alternative to these time consuming procedures. In the present study, lifetime of thick A1 wedge bonds on Si substrates was investigated using a novel mechanical fatigue testing technique operating at high frequencies and elevated temperatures. The influence of microstructure, testing temperature and frequency on lifetime of A1 wire bonds was investigated. Finite element analysis was applied to calculate the stress distribution at the interfacial region and to establish life time prediction curves. The results of mechanical isothermal fatigue curves were compared and correlated with thermal cycling data of Al wire bonds. Copyright © 2014 by The Minerals, Metals & Materials Society.
      1Scopus© Citations 2  131
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    Simulation of stress concentrations in wire-bonds using a novel strain gradient theory
    (Elsevier, 2013-04-14)
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    Lederer, Martin 
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    Nagl, Bernhard 
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    Trnka, A. 
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    Khatibi, Golta 
    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.
      1Scopus© Citations 2  61
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    A Rapid Reliability Assessment Method for Fine Wire Bonds in Power Electronic Packages
    (IEEE, 2024-09-25)
    Walter, Thomas
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    Khatibi, Golta 
    Scopus© Citations 1  40
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    Towards adequate qualification testing of electronic products: Review and extension
    (Elsevier, 2014-12-03)
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    Khatibi, Golta 
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    Lederer, Martin 
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    Magnien, Julien 
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    Suhir, Ephraim 
    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.
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      2  81
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    Versatile ultrasonic fatigue testing method with variable load ratio for small scaled samples
    (2019-05-16)
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    Gasser, Christoph 
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    Khatibi, Golta 
      1  74
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    In situ vibration measurements on power modules under operating conditions
    (Elsevier, 2012-04-16)
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    Nagl, Bernhard 
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    Lederer, Martin 
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    Trnka, A. 
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    Khatibi, Golta 
    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.
      1Scopus© Citations 7  58
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    Experimental and analytical study of geometry effects on the fatigue life of Al bond wire interconnects
    (Elsevier, 2013-09)
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    Khatibi, Golta 
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    Paul, Indrajit 
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    Thoben, Markus 
    The reliability of power electronic devices is mainly limited due to thermo-mechanical fatigue of the internal bond wire interconnections. The bond wire shape is already defined at the design stage of the device. Thus preliminary lifetime assessments become more and more important in order to satisfy the high quality demands and the short time to market of the devices. In this study a fast experimental test setup is used in order to determine the lifetime of a large number of wire bond shapes. Furthermore an analytical model is applied to calculate optimized wire bond shapes for a given set of parameters. The results of this investigation should help to optimize the shape parameters at an early stage of development using the presented analytical model in combination with the fatigue tests. © 2013 Elsevier Ltd. All rights reserved.
      2Scopus© Citations 26  92
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    BAMFIT - Accelerated Mechanical Fatigue Interconnect Test
    (2018-01-01)
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    Seidl, Siegfried 
      1  115
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    Interface characterization of Cu-Cu ball bonds by a fast shear fatigue method
    (Elsevier, 2020-11)
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    Khatibi, Golta 
    A highly accelerated shear fatigue testing method is presented to test the long-term reliability and reveal the bonded interface of thermosonic Cusingle bondCu ball bonds. The method is an adaptation to a new industrial fatigue tester (BAMFIT) and can be conducted without an intricate specimen preparation. This method induces mechanical cyclic shear stresses to the Cu nailhead in order to initiate fatigue fracture until lift-off, revealing the actual bonded interface. This study compares the fatigue resistance of Cu wire bonded to coarse and fine grained Cu and Al metallization. The fatigue experiments are accompanied by nano indentation tests, shear tests and finite element analysis. The fatigue results showed the best performance for Cu bonds on coarse grained Cu pads (metallization), followed by those bonded on fine grained Cu while the Cusingle bondAl nailheads failed at least a decade earlier than Cusingle bondCu bonds. Annealing the specimens prior to testing resulted in slight increases in the number of loading cycles to failure (Nf) for Cu bonds as well as for Cusingle bondAl bonds, while the scattering in Nf for Cu bonds increased. Nevertheless the calculated endurance limit of the fatigue data decreases with increasing annealing stages, due to a change in the fracture probability curve. With the ability to compare the fatigue behaviour of the bonded interface within minutes, this method is most suitable for rapid qualification at an early stage of development.
      2Scopus© Citations 7  101