Publications

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Now showing 1 - 8 of 8
  • Publication
    Effect of the loop forming process on the lifetime of aluminum heavy wire bonds under accelerated mechanical testing
    (2024-03)
    Florens Felke
    ;
    Anne Groth
    ;
    Martin Hempel
    ;
    ;
    Golta Khatibi 
    ;
    Torsten Döhler
    ;
    Ute Geissler 
  • Publication
    Fatigue testing method for fine bond wires in an LQFP package
    (Elsevier, 2016-09) ;
    Mazloum-Nejadari, Ali 
    ;
    Khatibi, Golta 
    ;
    Weiss, Laurens 
    ;
    Zehetbauer, M. 
    A mechanical testing setup was developed to study the fatigue response of fine thermo-sonic wire bond connection in low profile quad flat packages (LQFP). The testing set-up was designed to induce pre-defined multi-axial stresses in the wire bond loops of non-encapsulated packages in order to mimic their deformation behavior during the thermo-mechanical loading. Lifetime curves were obtained up to 1.0E7 loading cycles with fatigue failure occurring in the heat affected zone of the ball bond. The experimental fatigue data in combination with extended FEA provided the basis for a Coffin Manson lifetime model. The proposed fatigue testing procedure can be applied as a highly efficient method for evaluation of various wire bonded packages by using a limited number of test samples and simultaneous testing of several wire bonds.
      69  1Scopus© Citations 12
  • Publication
    Thermo-mechanical analysis of bonding wires in IGBT modules under operating conditions
    (Elsevier, 2012-09) ;
    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
  • Publication
    Interface characterization of Cu-Cu ball bonds by a fast shear fatigue method
    (Elsevier, 2020-11) ;
    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
  • Publication
    A fast test technique for life time estimation of ultrasonically welded Cu-Cu interconnects
    (Elsevier, 2010-09) ;
    Khatibi, Golta 
    ;
    Weiss, Brigitte 
    ;
    Licht, T. 
    In this research the quality of the interconnects of the ultrasonically welded Cu terminals to the Cu substrate in the IGBT-module has been investigated. An ultrasonic resonance fatigue system in combination with a laser Doppler vibrometer and a special specimen design was used for shear fatigue testing of these large ultrasonic Cu-Cu welds (about 0.5 cm2). Fatigue life curves up to 109 loading cycles were obtained in a very short period of time. Using this technique it was possible to evaluate the fatigue strength of these interconnects for the first time. The microstructural features of the interconnects were characterized and their crack growth behaviour was studied. Fracture analysis of the fatigued specimen shows that failure occur due to the propagation of the crack beneath the welding interface into the copper substrate. Additionally performed finite element simulations offer an insight into the stress and strain concentrations during the mechanical fatigue tests. As this method is not restricted to the welding geometry, material joints with larger interconnects can be tested likewise. Thus this new technique can be used as a practical and valid fatigue testing method for evaluation of various interconnects.
      50  2Scopus© Citations 1
  • Publication
    Experimental and analytical study of geometry effects on the fatigue life of Al bond wire interconnects
    (Elsevier, 2013-09) ;
    Khatibi, Golta 
    ;
    Paul, Indrajit 
    ;
    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.
      56  2Scopus© Citations 21
  • Publication
    High resolution thermal simulation of electronic components
    (Elsevier, 2000) ;
    Nicolics, Johann 
    ;
    Musiejovsky, Laszlo 
    An efficient thermal management in electronic components is essential to minimize the influence of thermomechanically induced stress and thermal load. Frequently, thermal simulation tools are applied to reduce the number of experiments needed for thermal characterization of the semiconductor components. However, for using commercially available software packages, much effort is necessary for maintenance and for generating the thermal models. Moreover, the limitation of the node number does not allow a discretization sufficiently fine for more complex structures as in high lead count packages. In this paper, a new thermal simulation tool is presented, which allows one to create models in a very efficient way. The developed and implemented solver based on the alternating direction implicit method is efficiently processing the required high node number. Moreover, the developed thermal simulation tool is applied for the thermal characterization of a 176 lead quad flat pack (QFP-package) using a discretization with 320,000 nodes. Steady-state and transient thermal qualities of the package are investigated under boundary conditions as specified by the Joint Electronic Device Engineering Council (JEDEC). Further, results obtained by thermal simulation are compared with those established from experimental procedures. Conclusions of how this new tool can be used for thermal design optimization are derived.
      120
  • Publication
    Interface reliability and lifetime prediction of heavy aluminum wire bonds
    (Elsevier, 2016-03-01) ;
    Khatibi, Golta 
    In this study a high frequency mechanical fatigue testing procedure for evaluation of interfacial reliability of heavy wire bonds in power semiconductors is presented. A displacement controlled mechanical shear testing set-up working at a variable frequency of a few Hertz up to 10 kHz is used to assess the interfacial fatigue resistance of heavy Al wire bond in IGBT devices. In addition, power cyclic tests were conducted on IGBT modules for in-situ measurement of the temperature distribution in the devices and determination of the thermally induced displacements in the wire bond loops. Finite Element Analysis was conducted to calculate the correlation between the thermally and mechanically induced interfacial stresses in the wire bonds. These stress values were converted into equivalent junction temperature swings (ΔTj) in the devices based on which lifetime curves at different testing frequencies were obtained. Comparison of the fatigue life curves obtained at mechanical testing frequencies of up to 200 Hz with the power cycling data related to the wire bond lift-off failure revealed a very good conformity in the ranges of 50 to 160 K. A lifetime prediction model for Al wire bonds in IGBT modules is suggested by which the loading cycles to failure can be obtained as a function of ΔTj and the mechanical testing frequency. The proposed accelerated shear fatigue testing procedure can be applied for rapid assessment of a variety of interconnects with different geometries and material combinations. Decoupling of the concurrent failure mechanisms and separation of the thermal, mechanical and environmental stress factors allows a more focused and efficient investigation of the interfaces in the devices.
      59  1Scopus© Citations 35