Czerny, Bernhard

Official Name

Czerny, Bernhard

Main Affiliation

Energie-Umweltmanagement

Akademische Titel

Mag. Dr.

bernhard.czerny@fh-burgenland.at

ORCID

0000-0001-8147-3122

Scopus Author ID

36238795900

Status

staff

Research Outputs

Visualization by Date

Now showing 1 - 10 of 13

Electro-thermal analysis of in situ vibration measurements on IGBT modules under operation conditions
(Elsevier, 2012-09-17)
Czerny, Bernhard
;
Nagl, Bernhard
;
Lederer, Martin
;
Khatibi, Golta
;
Thoben, Markus
;
Nicolics, Johann
This paper discusses different application relevant electrical loading cases of an IGBT module of a power inverter. Thereby, different operation conditions such as pulse frequencies, inverter output currents and output frequencies, as well as two different operation modes are discussed. Each load case investigation is conducted by electrical, thermal, and in situ vibration measurements. Moreover, on the base of finite element analyses a deeper insight is gained into reliability relevant thermo-mechanical behavior. For this purpose an IGBT module is operated at a load of 30% to 80% of its nominal value in order to cause representative thermo-mechanical displacements of dies and bond wires. By applying an inverter output frequency in a range of 1 to 280 Hz a temperature ripple of up to 40 K on the dies and a vertical displacement of up to 9 μm on a bond wire is observed. These results are important to improve life-time-predictions.
44 1Scopus© Citations 3
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
Thermo-mechanical analysis of bonding wires in IGBT modules under operating conditions
(Elsevier, 2012-09)
Czerny, Bernhard
;
Lederer, Martin
;
Nagl, Bernhard
;
Trnka, A.
;
Khatibi, Golta
;
Thoben, Markus
The lifetime of IGBT (Insulated Gate Bipolar Transistor) modules is limited by thermo-mechanical fatigue. Thereby bonding wires represent the critical links where damage initiation is observed. For the first time Laser Doppler Vibrometer measurements and thermal imaging were employed to determine the temperature-dependent deformations of bond wires at different frequencies under operation conditions. This should be considered as an important step to facilitate more precise life-time predictions of power modules in long term usage.
43 2Scopus© Citations 76
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
A New Approach for Evaluation of Fatigue Life of Al Wire Bonds in Power Electronics
(Elsevier, 2014-03)
Czerny, Bernhard
;
Khatibi, Golta
;
Kotas, Agnieszka Betzwar
;
Weiss, Brigitte
;
Lederer, Martin
Ultrasonically bonded Al wire bonds on Al metallization pads are widely used in power semiconductors. The required long time reliability of the devices is highly dependent on the interfacial quality of Al 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 Al 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 Al 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. © 2014 The Minerals, Metals & Materials Society.
45 1Scopus© Citations 6
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
A novel approach for evaluation of material interfaces in electronics
(2016-03-05)
Czerny, Bernhard
;
Khatibi, Golta
;
Lassnig, Alice
;
Lederer, Martin
;
Nicolics, Johann
;
Magnien, Julien
;
Suhir, Ephraim
The rapid technological advancements and market demands in electronic sector requires application of highly accelerated, still practice relevant reliability assessment methods. At present, accelerated power and temperature cycling tests count as the state of the art for qualification of the devices. However due to physical characteristics of the devices, there are limitations to accelerated thermal and power cycling tests. Further acceleration by exceeding a critical temperature or time reduction may result in occurrence of failure mechanisms other than those encountered in real application or suppressing these failures. An alternative approach for further acceleration of the testing procedures is based on the application of isothermal mechanical fatigue testing at high frequencies (AMT). The principle idea of this approach is replacement of thermally induced strains by means of equivalent mechanical strains. Based on a physics of failure approach, the relevant failure modes in the material interfaces are induced enabling detection of weak sites of the devices in a very short duration of time. In addition of time saving factor a further advantage of mechanical fatigue testing is the possibility of decoupling of thermal, mechanical and environmental stress factors for a more effective investigation and diagnosis. This paper presents an overview of our recent reliability studies on different types of electronic components by using the proposed methodology with the aim to give an insights into the advantages and some restrictions of AMT for qualification of electronic devices.
61 1Scopus© Citations 4
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 3
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
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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