Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    On the crack and delamination risk optimization of a Si-interposer for LED packaging
    ( 2014)
    Auersperg, J.
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    Dudek, R.
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    Jordan, R.
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    Bochow-Neß, O.
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    Rzepka, S.
    ;
    Michel, B.
    3D-integration becomes more and more an important issue for advanced LED packaging solutions as it is a great challenge for the thermo-mechanical reliability to remove heat from LEDs to the environment by heat spreading or specialized cooling technologies. Thermal copper-TSVs provide an elegant solution to effectively transfer heat from LED to the heat spreading structures on the backside of a substrate. But, the use of copper-TSVs generates also novel challenges for reliability as well as also for reliability analysis and prediction, i.e. to manage multiple failure modes acting combined - interface delamination, cracking and fatigue, in particular. In this case, the thermal expansion mismatch between copper and silicon yields to risky stress situations. To overcome cracking and delamination risks in the vicinity of thermal copper-TSVs the authors performed extensive simulative work by means of fracture mechanics approaches - an interaction integral approach within a simulative DoE and the X-FEM methodology to help clarifying crack propagation paths in silicon. The results provided a good insight into the role of model parameters for further optimizations of the intended thermal TSV-approaches in LED packaging applications.
  • Publication
    Basic thermo-mechanical property estimation of a 3D-crosslinked epoxy/SiO2 interface using molecular modelling
    ( 2011)
    Hölck, O.
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    Dermitzaki, E.
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    Wunderle, B.
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    Bauer, J.
    ;
    Michel, B.
    In this work we present a procedure for the construction of 3D networked epoxy moulding compounds and an estimation of basic thermodynamic properties by molecular dynamics simulations. Our investigations present part of general trend to extend failure analysis, reliability assessment and the development of packaging materials from the conventional discrete usage of simulation techniques to a more holistic approach of an interconnected multimethods- procedure, enabling bottom-up simulation of complex microsystems. Within that framework, the task at hand for detailed atomistic molecular modelling is to develop practical methods in order to take materials development as well as materials failure analysis to the nanoscale level. This paper reports a cross linking scheme for the construction of three dimensionally cross linked simulation packages and presents a first property analysis of an industry-oriented moulding compound material. First models and results are presented of model packages of ideal epoxy/silicon-dioxide interfaces.
  • Publication
    Molecular dynamics approach to structure-property correlation in epoxy resins for thermo-mechanical lifetime modeling
    ( 2010)
    Wunderle, B.
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    Dermitzaki, E.
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    Hölck, O.
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    Bauer, J.
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    Walter, H.
    ;
    Shaik, Q.
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    Rätzke, K.
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    Faupel, F.
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    Michel, B.
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    Reichl, H.
    This paper addresses the potential of molecular dynamics simulation for structureproperty correlations in epoxy-resins. This is an important topic within a multi-scale framework to lifetime prediction in electronic packaging. For that purpose, epoxy-resins with small systematic variations in chemical structure have been synthesised and then characterised by various thermo-mechanical testing methods. It was found that moisture diffusion showed the greatest response with respect to material and loading parameters such as polarity, free volume, moisture concentration and temperature. Based on a parametric study, modeling approaches of various complexity have been able to show first qualitative but then also quantitative agreement. The paper comments further on the accuracy and limits of the method and correlates the calculations with experimental structural analysis results.
  • Publication
    Interlayer cooling potential in vertically integrated packages
    ( 2009)
    Brunschwiler, T.
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    Michel, B.
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    Rothuizen, H.
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    Kloter, U.
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    Wunderle, B.
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    Oppermann, H.
    ;
    Reichl, H.
    The heat-removal capability of area-interconnect-compatible interlayer cooling in vertically integrated, high-performance chip stacks was characterized with de-ionized water as coolant. Correlation-based predictions and computational fluid dynamic modeling of cross-flow heat-removal structures show that the coolant temperature increase due to sensible heat absorption limits the cooling performance at hydraulic diameters <= 200 mu m. An experimental investigation with uniform and double-side heat flux at Reynolds numbers <= 1,000 and heat transfer areas of 1 cm(2) was carried out to identify the most efficient interlayer heat-removal structure. The following structures were tested: parallel plate, microchannel, pin fin, and their combinations with pins using in-line and staggered configurations with round and drop-like shapes at pitches ranging from 50 to 200 mu m and fluid structure heights of 100-200 mu m. A hydrodynamic flow regime transition responsible for a local junction temperature minimum was observed for pin fin in-line structures. The experimental data was extrapolated to predict maximal heat flux in chip stacks having a 4-cm(2) heat transfer area. The performance of interlayer cooling strongly depends on this parameter, and drops from > 200 W/cm(2) at 1 cm(2) and > 50 mu m interconnect pitch to < 100 W/cm(2) at 4 cm(2). From experimental data, friction factor and Nusselt number correlations were derived for pin fin in-line and staggered structures.
  • Publication
    Failure modeling of ACA-glued flip-chip on flex assemblies
    ( 2009)
    Wunderle, B.
    ;
    Kallmayer, C.
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    Walter, H.
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    Braun, T.
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    Gollhardt, A.
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    Michel, B.
    ;
    Reichl, H.
    This paper addresses the reliability of flip-chip on flex (FCOF) assemblies glued with an Ag-particle filled anisotropic conductive adhesive (ACA). As the description of FCOF failure gives still much scope for speculation, a physics of failure based approach is developed here, taking into account the changing thermo-mechanical properties of the ACA under temperature and moisture. A failure hypothesis is formulated based on the loss of contact pressure. Material analysis, material characterisation, finite element (FE) modeling and lifetime tests have been employed to establish correlations to support this failure hypothesis. It was found, that moisture plays the most important role for interconnect failure. The model is able to predict quantitative changes of force as function of loading parameters and correlate them qualitatively to the experimental mean time to failure. New insights are provided about the stress fields at the ACA bump. The model is discussed with respect to a direct prediction of failure versus time.
  • Publication
    Lifetime modelling for microsystems integration: From nano to systems
    ( 2009)
    Wunderle, B.
    ;
    Michel, B.
    Due to the rapid development of IC technology the traditional packaging concepts are making a transition into more complex system integration techniques in order to enable the constantly increasing demand for more functionality, performance, miniaturisation and lower cost. These new packaging concepts (as e.g. system in package, 3D integration, MEMS-devices) will have to combine smaller structures and layers made of new materials with even higher reliability. As these structures will more and more display nano-features, a coupled experimental and simulative approach has to account for this development to assure design for reliability in the future. A necessary "nano-reliability" approach as a scientific discipline has to encompass research on the properties and failure behaviour of materials and material interfaces under explicit consideration of their micro- and nano-structure and the effects hereby induced. It uses micro- and nano-analytical methods in simulation and experiment to consistently describe failure mechanisms over these length scales for more accurate and physically motivated lifetime prediction models. This paper deals with the thermo-mechanical reliability of microelectronic components and systems and methods to analyse and predict it. Various methods are presented to enable lifetime prediction on system, component and material level, the latter promoting the field of nano-reliability for future packaging challenges in advanced electronics system integration.
  • Publication
    Micro- and nanoreliability research in the micro materials center Chemnitz of Fraunhofer ENAS
    ( 2009)
    Michel, B.
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    Dudek, R.
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    Auersperg, J.
    ;
    Winkler, T.
  • Publication
    Thermo-mechanical reliability during technology development of power chip-on-board assemblies with encapsulation
    ( 2009)
    Wunderle, B.
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    Becker, K.-F.
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    Sinning, R.
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    Wittler, O.
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    Schacht, R.
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    Walter, H.
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    Schneider-Ramelow, M.
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    Halser, K.
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    Simper, N.
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    Michel, B.
    ;
    Reichl, H.
    In this paper we examine the thermo-mechanical reliability of polymer-encapsulated chip-on-board (COB) assemblies for power applications by simulation and experiment. Thereby the focus is set on the low cycle fatigue failure behaviour of the die-attach material under thermal cycling conditions. As die-attach material different solder materials and Ag-filled thermal adhesives have been used. The encapsulation was performed with a soft silicone-based and hard silica-reinforced epoxy-based material, respectively. An other process variable takes into account die-tilt. The study was carried out as a feasibility analysis in the course of a COB technology development. To this end lifetime models have been employed to correlate crack growth in the, i.e. attach to a computational accumulative failure criterion which allows to consistently describe ad predict quantitatively the lifetime of the assemblies. Thereby a considerable influence of the encapsulation was found. In particular it could be shown that a hard encapsulation largely increases reliability for solder die-attach.
  • Publication
    Nondestructive failure analysis and simulation of encapsulated 0402 multilayer ceramic chip capacitors under thermal and mechanical loading
    ( 2009)
    Wunderle, B.
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    Braun, T.
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    May, D.
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    Michel, B.
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    Reichl, H.
    The use of multilayer ceramic chip capacitors as integrated passive in, e.g., system in package applications needs methods to examine and predict their reliability. Therefore, a nondestructive failure analytical technique is described to detect cracks in the ceramic and the metallic layers within encapsulated 0402 surface mount device (SMD) capacitors. After choosing from techniques to reproducibly generate cracks, it is shown that an in situ capacitance measurement is a convenient method to detect these failures unambiguously. Finite element simulations support the experimental results. A reliability estimate for capacitor integrity under given loading conditions is given.