Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

Filters
10
Reset filters

Settings
Now showing 1 - 10 of 10
  • Publication
    Thermo-mechanical characterisation of thin sputtered copper films on silicon: Towards elasto-plastic, fatigue and subcritical fracture-mechanical data
    ( 2018)
    Wunderle, B.
    ;
    May, D.
    ;
    Zschenderlein, U.
    ;
    Ecke, R.
    ;
    Springborn, M.
    ;
    Jöhrmann, N.
    ;
    Pareek, K.A.
    ;
    Heilmann, J.
    ;
    Stiebing, M.
    ;
    Arnold, J.
    ;
    Dudek, R.
    ;
    Schulz, S.
    ;
    Wolf, M.J.
    ;
    Rzepka, S.
    Thin metal layers, especially those made of copper, are omnipresent in today's packaging applications as e.g. RDL structures, conductor traces on flexible and stretchable substrates, chip finishes or terminal metallisation, serving electrical, thermal or mechanical purposes. During operation, thermo-mechanical stress will cause failures in the Cu layers and interfaces over time. As Cu is very process and size dependent, its resistance to fatigue failure needs to be characterised with samples which have undergone identical processing steps as those in the real application. For that purpose, simple specimens and fast testing routines are necessary, some of which may need special loading stages for varying the load variables of interest such as stress amplitude and temperature. This paper addresses fatigue characterisation of thin Cu films on silicon under typical processing conditions on simple and inexpensive but industry-grade samples. Along with them, custom built test stands have been used to handle those specimens appropriately within a specimen-centred approach.
  • Publication
    Coupled electro-thermo-mechanical analyses on power cycling induced loadings in sintered silver IGBT-modules with and without overmolding
    ( 2016)
    Dudek, R.
    ;
    Döring, R.
    ;
    Rzepka, S.
    ;
    Stegmeier, S.
    ;
    Ehrhardt, C.
    ;
    Rittner, M.
    ;
    Rudzki, J.
    The reliability challenges of inverter modules with insulated-gate bipolar transistors (IGBTs) and diodes silver sintered to DBC substrates and copper wire bonded were investigated in a project called ""ProPower"". It was one aim to find out possible failures when the modules are subjected to different kinds of power cycling. Coupled finite element (FE-) analyses are reported to understand the thermo-mechanical stresses that cause these failures. Initial parametric FE-studies on passive thermal cycles revealed that missing decoupling between the mismatched stacked materials, which previously was guaranteed by the soft solder, leads to coupling of thermo-mechanical stresses not only dependent on stack geometry but also on mounting conditions. Hence, a system view on the stress situation is required and was realized in FEA by including the full assembly with heatsink mounting, bonding wires, by including intrinsic stress due to processing and by different types of active loading, and in particular also of combined temperature and power cycling. Different parametric variations were studied, e.g. the effect of overmolding. Power cycling induced failure modes from testing are related to critical stresses and proposals for ""physics of failure"" based lifetime modeling are made.
  • Publication
    Investigations on power cycling induced fatigue failure of IGBTs with silver sinterea interconnects
    ( 2015)
    Dudek, R.
    ;
    Doring, R.
    ;
    Rzepka, S.
    ;
    Ehrhardt, C.
    ;
    Hutter, M.
    ;
    Rudzki, J.
    ;
    Osterwald, F.
    ;
    Eisele, R.
    ;
    Stegmeier, S.
    ;
    Weidner, K.
    ;
    Rittner, M.
    Because of the need for electronics use at temperatures beyond 150 deg C, new high temperature interconnection technologies emerge, like silver sintering and copper wire bonding. In the project PROPOWER inverter modules with IGBTs and diodes mounted on DBC substrates were investigated as a prototype. Analyses were made to study the effects of the new interconnect technologies on fatigue failure. It is one basic question for the replacement of solders by sinter silver to what extend the failure behaviour depends on the kind of loading, that means passive thermal cycling versus active thermal cycling, and how it relates to solder fatigue failure. These questions were addressed by passive thermal cycling and in particular by different kinds of power cycling. Failure modes different from those observed with traditional interconnection technologies were detected. Finite element (FE-) analyses were made to understand the thermo-mechanical stresses, which cause these failures.
  • Publication
    Electro-thermo-mechanical analyses on silver sintered IGBT-module reliability in power cycling
    ( 2015)
    Dudek, R.
    ;
    Döring, R.
    ;
    Rzepka, S.
    ;
    Ehrhardt, C.
    ;
    Günther, M.
    ;
    Haag, M.
    New demands on the thermo-mechanical design of sintered silver interconnections emerge. Development of this inter-connection technology and both experimental and theoretical studies on their reliability were subjects of the project ""PROPOWER"". The focus of this paper is on theoretical analysis of thermo-mechanical reliability risks of a project demonstrator, an insulated-gate bipolar transistor (IGBT) module, subjected to power cycling loadings. Coupled electro-thermal-mechanical analyses have been carried out using the finite element method (FEM). Introduction of a new interconnect material means at the same time introduction of a new constitutive behavior and new failure modes. As the material stiffness increases, the decoupling effect of compliant solder layers reduces and intrinsic mechanical stresses increase in the whole power stack. This leads on one hand to less low cycle fatigue in the interconnect, as plastic dissipation is reduced, but on the other hand to higher failure risks like brittle cracking and sub-critical crack growth. However, if early brittle failure can be avoided by appropriate designs, the new interconnection technology allows an increase in fatigue reliability of several hundred percent. Based on the complex theoretical framework simulation results are validated by testing in order to achieve trustworthy thermo-mechanical reliability predictions. Failures like chip metallization damage and the different damage mechanisms of the die bond if either solder or sinter silver is used are related to the different stress situations in the module.
  • Publication
    Investigations on power cycling induced fatigue failure of IGBTs with silver sintered interconnects
    ( 2015)
    Dudek, R.
    ;
    Döring, R.
    ;
    Rzepka, S.
    ;
    Ehrhardt, C.
    ;
    Hutter, M.
    ;
    Rudzki, J.
    ;
    Osterwald, F.
    ;
    Eisele, R.
    ;
    Stegmeier, S.
    ;
    Weidner, K.
    ;
    Rittner, M.
    Because of the need for electronics use at temperatures beyond 150??C, new high temperature interconnection technologies emerge, like silver sintering and copper wire bonding. In the project PROPOWER inverter modules with IGBTs and diodes mounted on DBC substrates were investigated as a prototype. Analyses were made to study the effects of the new interconnect technologies on fatigue failure. It is one basic question for the replacement of solders by sinter silver to what extend the failure behaviour depends on the kind of loading, that means passive thermal cycling versus active thermal cycling, and how it relates to solder fatigue failure. These questions were addressed by passive thermal cycling and in particular by different kinds of power cycling. Failure modes different from those observed with traditional interconnection technologies were detected. Finite element (FE-) analyses were made to understand the thermo-mechanical stresses, which cause these failures. To simulate the power cycle loading most realistic, coupled electro-thermal-mechanical analyses were carried out which are in the focus of this paper. The simulation results are compared to failures found by testing.
  • Publication
    On the crack and delamination risk optimization of a Si-interposer for LED packaging
    ( 2014)
    Auersperg, J.
    ;
    Dudek, R.
    ;
    Jordan, R.
    ;
    Bochow-Neß, O.
    ;
    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
    Degradation of moulding compounds during highly accelerated stress tests - A simple approach to study adhesion by performing button shear tests
    ( 2012)
    Pufall, R.
    ;
    Goroll, M.
    ;
    Mahler, J.
    ;
    Kanert, W.
    ;
    Bouazza, M.
    ;
    Wittler, O.
    ;
    Dudek, R.
    High temperature storage can degrade moulding compounds for chip encapsulation to such an extent that the adhesion to surfaces like copper (lead frames) or polyimide (chip coating) decreases drastically causing delamination. Also during normal operation of electronic components heat is generated locally (bond wire or chip surface) degrading the moulding compound and reducing the adhesion which in extreme cases can destroy the metallisation or the bond wires.
  • Publication
    Solder joint reliability in automotive applications: Describing damage mechanisms through the use of EBSD
    ( 2010)
    Steller, A.
    ;
    Pape, U.
    ;
    Dudek, R.
    Due to the large scatter in data that have been gathered over the past years to describe the reliability behavior of lead-free solder joints, a precise correlation of aging condition to the resulting damage appearance could not yet be established. Recent research has shown, that a key to a more profound understanding of damage mechanisms can be offered through the analysis of recrystallization processes in the solder joints. Electron Backscatter Diffraction (EBSD) is a valuable analysis method to obtain quantitative data on grain properties. In this paper the results of detailed EBSD measurements on SnAg3.0Cu0.5 solder joints of chip resistors are therefore presented. Correlations between recrystallization behavior and applied loading profile are generated and verified through FEM-simulations. It is recommended to employ sophisticated data mining tools like Support Vector Machines to support data interpretation of the various parameters offered by EBSD.
  • Publication
    Simulation based analysis of secondary effects on solder fatigue
    ( 2009)
    Dudek, R.
    ;
    Doering, R.
    ;
    Bombach, C.
    ;
    Michel, B.
    Secondary effects on thermal fatigue of solderjoints, which frequently have been neglected, were studied by means of the finite element method (FEM). Based on a semi-empirical approach to predict fatigue life by evaluating the cyclic accumulated equivalent creep strain or energy density, effects of organic boards intrinsic properties on solder joint fatigue were investigated. Aspects of more realistic FR-4 board modelling were studied, in particular concerning its in-plane anisotropy and intrinsic warpage behaviour. Intrinsic board warpage was measured on test board level as well as for boards from series production. High intrinsic warpage was in particular found for several test boards. The effects for the worst case scenario observed so far were analysed for both first level and second level interconnects. The change in predicted fatigue life varied between 30% and 500%, the latter most critical effects were found at large QFN components. Another secondary effect studied was to include the frequently neglected interfacial intermetallics into FEM. It turned out that for components with relatively large standoff like LFBGAs the effects were actually negligible, but for the highly miniaturized components like chip resistors CR0201 they are the decisive factor.
  • Publication
    Micro- and nanoreliability research in the micro materials center Chemnitz of Fraunhofer ENAS
    ( 2009)
    Michel, B.
    ;
    Dudek, R.
    ;
    Auersperg, J.
    ;
    Winkler, T.