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

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Now showing 1 - 10 of 39
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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.
      45  1
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      57  1
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      63  1Scopus© Citations 21
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    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
    Interface characterization of Cu-Cu ball bonds by a fast shear fatigue method
    (Elsevier, 2020-11)
    Czerny, Bernhard 
    ;
    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.
      80  2Scopus© Citations 4
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    Publication
    Loop formation effects on the lifetime of wire bonds for power electronics
    (2020-03-24)
    Czerny, Bernhard 
    ;
    Ribbeck, Hans-Georg von 
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    Doehler, Torsten 
    ;
    Khatibi, Golta 
    ;
    Geissler, Ute 
    In the present work, the influence of loop forming aspects on the reliability of US-bonded aluminium heavy wires was studied, combining three measurement techniques, for the first time: Laser confocal microscopy based wrinkling characterization, accelerated lifetime measurements BAMFIT and destructive pull tests. The focus of this study was the systematic investigation of the heel region of the wire bond depending on process parameters and especially on the loop geometry regarding durability and lifetime. As first results, effects reducing durability were identified which are not apparent in normal testing and a recommendation for the use of reverse movements can be given.
      69  1
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    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
    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
    Reliability analysis of Cu wire bonds in microelectronic packages
    (Elsevier, 2016-04-18)
    Czerny, Bernhard 
    ;
    Mazloum-Nejadari, Ali 
    ;
    Khatibi, Golta 
    ;
    Lederer, Martin 
    ;
    Nicolics, Johann 
    ;
    Weiss, Laurens 
    In this study the thermo-mechanical response of 25 μm Cu wire bonds in an LQFP-EPad package was investigated by numerical and experimental means. The aim was to develop a methodology for fast evaluation of the packages, with focus on wire bond fatigue, by combining FEA and mechanical fatigue testing. The investigations included the following steps: (i) simulation of the warpage induced displacements in the encapsulated LQFP-176-Epad package due to temperature changes, (ii) reproducing 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 determined 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 proportional relation between the location and angle of the wire bond to the direction of loading. The calculated accumulated plastic strain in the HAZ was correlated to the experimentally determined Nf values based on the volume weighted averaging (VWA) approach 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 determination of the lifetimes of wire bonds at different positions on the chip as well as for related improvements of package design.
      62  1Scopus© Citations 4
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    Publication
    Cyclic robustness of heavy wire bonds: Al, AlMg, Cu and CucorAl
    (Elsevier, 2018-09)
    Czerny, Bernhard 
    ;
    Khatibi, Golta 
    Development of advanced electronic packages can be drastically affected by implementation of new materials. The ever increasing demands for high performance and reliable power electronics, raise the need for rapid robustness evaluation of interconnects. In this study the lifetime of heavy wire bonded interconnects, fabricated with different wire material types Al, AlMg, Cu and Al coated Cu (CucorAl) bonded onto direct copper bonded ceramic substrates was investigated. The tests were performed using an accelerated mechanical fatigue testing system, which allows to determine the lifetime of the interconnects with regard to wire bond lift-off failure in a short period of time. Thus, the influence of ultrasonic power variation and the impact of aging on the performance of wire bonds with different material combinations was studied. Cu wire bonds showed clearly the best fatigue performance as well as static shear strength followed by AlMg and Al bonds. Increasing the ultrasonic power results in a higher fatigue resistance of CucorAl in comparison to pure Al wires. In certain cases, the results of the fatigue experiments and static shear tests were found to be contradictory. The presented results suggest that accelerated mechanical fatigue testing can be used as an additional fast method for qualification of interconnects and assessment of the influence of wire material, bond parameter and aging.
      60  1Scopus© Citations 27