Publications Search Results

Now showing 1 - 5 of 5
  • Publication
    A New Noise-Suppression Algorithm for Transient Thermal Analysis in Semiconductors Over Pulse Superposition
    ( 2020)
    Schmid, M.
    ;
    Bhogaraju, S.K.
    ;
    Hanss, A.
    ;
    Elger, G.
    This article introduces a new measurement method for noise suppression in transient thermal analysis (TTA), which is used to measure the transient thermal impedance of power semiconductors and LEDs. An additional short pulse sequence is added to the standard TTA measurement procedure. The thermal response of this additional sequence is converted into the original single-pulse response of standard TTA by superposition of previous pulses in the sequence. Applying this method, the noise before 1 ms can be significantly reduced without averaging over multiple measurement repetitions that would increase the measurement time accordingly. The noise reduction for times below 1 ms is important to resolve the thermal resistance layers close to the junction of a semiconductor. The measurement method and data analysis algorithm are developed for TTA measurements, but the principle is suitable for all linear time-invariant (LTI) systems where the system response is measured over several time decades. The algorithm was evaluated on simulated and experimental data of a power LED. With an additional sequence of only 100 ms, a signal-to-noise ratio (SNR) improvement of 15.1 dB for simulated data and 14.7 dB for experimental data was achieved. This is equivalent to averaging over 30 repetitions in the standard TTA procedure. Therefore, the new method achieves a reduction of measurement time of 97% for applications where low noise levels are required for times below 1 ms.
  • Publication
    Hybrid Cu particle paste with surface-modified particles for high temperature electronics packaging
    ( 2019)
    Bhogaraju, S.R.
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    Mokhtari, O.
    ;
    Pascucci, J.
    ;
    Hanss, A.
    ;
    Schmid, M.
    ;
    Conti, F.
    ;
    Elger, G.
    Die-attach bonding is a key process to realize high-temperature operation of power semiconductor devices. Ag sintering has been in the forefront of the research in the past decade as a suitable alternative to high temperature solders such as AuSn. However, the high cost of Ag and low electromigration resistance have been deterrants to large scale industrialization. Cu is ~100 times cheaper than Ag and more abundantly available. It is easy to process and recycle and displays mechanical, thermal and electrical properties comparable with Ag. In this contribution, the research is focused on developing Cu sintering as an alternative to Ag sintering. Different sintering pastes have been prepared in-house by combining Cu particles in micro and/or nano-scale with polyethylene glycol 600 (PEG600). The performances of the pastes have been analysed and evaluated under different bonding conditions. Shear strengths of approximately 88MPa has been achieved while working with a combination of surface modified Cu-alloy particles and PEG600 as binder. Surface modifications on the Cu-alloy particles are obtained through a selective etching of the alloying element. Sintering was performed under a bonding pressure of 20MPa, at 275°C, for 30min, under N 2 . comparison with hybrid Cu particle paste under the same experimental conditions, the result is very promising and better by a factor 2.
  • Publication
    Time Saving Averaging Algorithm for Transient Thermal Analyses over Deterministic Pulse Superposition
    ( 2019)
    Schmid, M.
    ;
    Hanss, A.
    ;
    Bhogaraju, S.K.
    ;
    Elger, G.
    Transient thermal analysis (TTA) with the measurement of the single pulse thermal impedance (Z th (t)) is a standard method to verify the thermal integrity of power semiconductors modules. For best evaluation of measured data, the signal to noise ratio (SNR) should be as high as possible. Especially in the early time domain, it is difficult to achieve high SNR because of the required high bandwidth. Most common way to increase SNR is averaging over several TTA measurement repetitions. Since the semiconductor module therefore has to reach thermal equilibrium, this solution is very time consuming. This paper introduces a new averaging algorithm for TTA, wherein several short deterministic pulses are applied to the semiconductor before standard TTA. Over superposition, the influence of the previous pulses is removed from all short pulses and averaging is possible without reaching thermal equilibrium. Result is a standard single pulse Z th (t) and not a duty cycle form of it. The algorithm is tested by simulations and experimentally using automotive LEDs to verify feasibility and demonstrate benefit. Thereby a SNR increase equivalent to 33 repetitions in standard TTA was reached.
  • Publication
    Failure Identification in LED packages by Transient Thermal Analysis and Calibrated FE Models
    ( 2019)
    Hanss, A.
    ;
    Liu, E.
    ;
    Abdullah, M.R.
    ;
    Elger, G.
    Transient thermal analysis (TTA) by experimental thermal impedance (Zth) measurements and data simulation by transient finite element (FE) simulation are suited to investigate the thermal path and mechanical integrity of electronic devices. After calibration, the FE model can be used for failure mode analysis. In this paper first a FE model for blue Flip Chip (FC) LEDs is set-up and calibrated to the experimental data. To reduce the ambiguity of the parameter identification within the calibration process caused by the relative large number of model parameters in a transient FE simulation several sets of experimental data are measured and simulated: the LED assembled on different substrates, i.e. an AlN ceramic and a standard Al-IMS board, and similar LEDs, i.e. same LED type but different sized light emitting area (1 mm 2 and 0.5 mm 2 ). The model is calibrated in the time domain using b(z), i.e. the logarithmic time derived of Zth(z= ln(t)). The least square residuum of simulated and experimental data is minimized. Different approaches of fitting are compared, i.e. fitting b(z), Zth(t) and the structure function, resulting in b(z) being a good option for the LED under investigation. The calibration is obtained by an optimizer in an automated workflow, i.e. using ANSYS coupled with optiSLang.After calibration the model is used to identify failures during accelerated stress test. An automatic TTA tester is used to detect changes of the Z th (t) during accelerated lifetime testing, e.g. temperature shock testing.By implementing failure into the calibrated model, e.g. cracks in the solder joint, delamination of the EPI from the redistribution layer and degradation of the dielectric layer of the Al-IMS, the calibrated model is fitted to the b(z) curves of the aged samples. The strength of the approach is demonstrated by extracting the quantitative changes of the physical parameters from the fitted model in an automatic way.
  • Publication
    Solder process for fluxless solder paste applications
    ( 2016)
    Hanss, A.
    ;
    Hutter, M.
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    Trodler, J.
    ;
    Elger, G.
    Fluxless soldering, i.e. residue free soldering with the aid of gaseous activation is known for many years, but only well established in the field of opto-and microwave electronics. In low cost high volume applications this technology has not yet become mainstream. In the fluxless soldering the wetting of the solder is made possible by means of an activating process gas. After the soldering process, no cleaning process is necessary because no corrosive residues are left on the circuit boards and components. Therefore soldering using solder paste without aggressive chemical ingredients has a high market potential. Expensive preforms could be replaced by paste dispensing or paste printing. In this paper, a residue free SnAgCu solder paste and a suitable soldering process is developed and presented. It is applied on high power ceramic LED packages and unpackaged flip chip LEDs which can be assembled directly on a substrate. In this paper the main paste properties such as printability of a commercial flux solder paste with those of the fluxless solder paste are compared. Likewise, the soldering results after a reflow process of these different paste systems are evaluated and compared. Different solder joint analysis methods like X-Ray, the transient thermal analysis, cross section and shear strength tests are presented in this paper. Finally a measurement technique to detect contamination on a soldered module is shown. There is a possibility that the concept and process proposed and demonstrated in this paper can reduce the production costs of electronic systems and improve the quality of soldered electronic modules.