Research Outputs

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Now showing 1 - 10 of 39
  • Publication
    Investigation on the Lifetime of Copper Wire Bonds in Electronic Packages under Thermal and Mechanical Cyclic Loading
    (Elsevier, 2018-09-18) ;
    Lederer, Martin 
    ;
    Mazloum-Nejadari, Ali 
    ;
    Khatibi, Golta 
    ;
    Weiss, Laurens 
    ;
    Nicolics, Johann 
    In this study, the results of simulative and experimental investigations regarding thermal cycling (TC) of a LQFP (Low Profile Quad Flat Exposed Pad) with embedded copper wire bonds are discussed. The focus of this study is to analyze cyclic thermal and mechanical loading at high plastic strain in the heat affected zone (HAZ) above the nail-head, which may lead to fatigue failure of wire bonds in the packages. Thereby, a comparison with multiaxial mechanical test results obtained in a previous study will be drawn [1]. Indeed, the lifetime diagrams for these two methods show a clear correlation. Convincing agreement was found on experimental and on theoretical level. The described accelerated test method can be used as a rapid test for the determination of the lifetimes of wire bonds at various positions on the chip. Moreover, our testing method leads to conclusions, which enable improvements of package design.
      63  1Scopus© Citations 3
  • Publication
    Thermomechanical Reliability Investigation of Insulated Gate Bipolar Transistor Module
    (Elsevier, 2018-05-16) ;
    Khatibi, Golta 
    ;
    Liedtke, Magnus 
    ;
    Nicolics, Johann 
    Though, significant efforts have led to high solder joint quality, thermomechanical fatigue and delamination of the solder joints are still considered as one main failure cause in Insulated Gate Bipolar Transistor (IGBT) power modules. Frequently used test procedures such as accelerated power cycling and thermal cycling allow to rate reliability and to predict lifetime under assumed power load conditions. However, these tests are less capable of detecting the root physical failure cause. In this paper a non-destructive thermal method to observe the successive effect of solder layer fatigue is suggested and discussed. Somewhat similar to power cycling, the method is based on an accelerated temperature cycling process where the power component is self-heated. The resulting change of thermal conductivity of the solder joint due to degradation is detected by contactless temperature measurement. First metallurgical analyses confirm the degraded solder structure as cause of the thermal changes due to aging.
      53  1Scopus© Citations 6
  • Publication
    Step-by-Step Building of a Four Dimensional Fatigue Compatible Regression Model including Frequencies
    (2021-12) ;
    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.
      198  1
  • Publication
    Highly Accelerated Mechanical Lifetime Testing for Wire Bonds in Power Electronics
    (IMAPS, 2022-06) ;
    Khatibi, Golta 
    This article presents various experimental studies on fatigue evaluation of wire bond interconnects and interfaces in electronic devices using an accelerated mechanical fatigue testing system. This dedicated experimental setup is designed to induce fatigue failure in the weak sites of the wire bond by reproducing the thermomechanical failure modes occurring during operation. An exceptional highly test acceleration is achieved by increasing the mechanical testing frequency into the kHz regimen enabling the determination of lifetime curves in a very short time. A com parison of this method to conventional testing methods such as power cycling, a shear testing exploits the potential of customized accelerated mechanical testing. Exemplary studies on the degra dation and fatigue failure of heavy Al wire bonds typically used in power electronics and novel Cu wire bonds are presented and advantages and some restrictions of the proposed method are discussed.
      107  1
  • Publication
    Wire bond degradation under thermo- and pure mechanical loading
    (Elsevier, 2017-09) ;
    Pedersen, Kristian Bonderup 
    ;
    Nielsen, Dennis A. 
    ;
    Khatibi, Golta 
    ;
    Iannuzzo, Francesco 
    ;
    Popok, Vladimir N. 
    ;
    Pedersen, Kjeld 
    This paper presents a fundamental study on degradation of heavy Al bond wires typically used in high power modules. Customized samples are designed to only consist of Al bond wires on standard Si diodes. These samples are subjected to pure mechanical and passive thermal cycling to investigate the bond degradation behavior on a simple system as well as compare these two test methods. Although an appreciable difference in fracture behavior is observed between these two methods, both provide correlation between the number of cycles and degree of degradation, especially in the case of the passive thermal test. To enable investigation of degradation rate a large number of bond interfaces is analyzed and they are found to follow conventional accepted fracture laws like Paris-Erdogan. With additional work this could enable the possibility of obtaining empirical parameters to be used in actual physics based lifetime laws.
      49  1Scopus© Citations 16
  • Publication
    Application of in-situ non-invasive failure detection methods for wire bonds
    (2020-09-15) ;
    Chavan, Vinayak 
    ;
    Gasser, Christoph 
    ;
    Rosc, Jördis 
    ;
    Khatibi, Golta 
    Two in-situ failure detection methods by measuring acoustic emissions and transducer responses are presented to investigate the wire bond degradation failure during a highly accelerated mechanical fatigue test. This BAMFIT fatigue test is used to induce cyclic shear stresses in the bond interface until wire bond lift-off, operating at 60 kHz. The task was to incorporate non-invasive failure detection to identify the degree of degradation prior to end of life as an extension to the BAMFIT method and a possible quality control method. The acoustic emission investigations uses a Fabry Perot interferometer to detect high frequency emissions in the vicinity of the wire bond and detecting changes in the first three harmonics to identify a bond degradation. The transducer response approach observes systematic changes in the vibration and the damping behavior of the coupled resonance system by using the transducer as a piezo sensor. The results have shown that defective bond interconnect can be identified as early as ~50% of end of life, using high power but very short vibration pulses, and at ~80% for low power and completely non-invasive pulses. The obtained responses from the presented methods were correlated to the degree of degradation of the bond wire interface, by completing BAMFIT tests until end of life, cross section analysis as well as non-destructive X-ray computer tomography.
      68  1Scopus© Citations 2
  • Publication
    Fatigue life time modelling of Cu and Au fine wires
    (2018-05-25) ;
    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
  • Publication
    A rapid test for reliability of heavy wire bonds
    (Konradin-Verl. Kohlhammer, 2019-04-17) ;
    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
  • Publication
    Accelerated mechanical fatigue interconnect testing method for heavy wire bonds in power modules
    (2017-05-11)
    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.
      56  1
  • Publication
    Loop formation effects on the lifetime of wire bonds for power electronics
    (2020-03-24) ;
    Ribbeck, Hans-Georg von 
    ;
    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