Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    Reliability modeling & test for flip-chip on flex substrates with Ag-filled anisotropic conductive adhesive
    ( 2008)
    Wunderle, B.
    ;
    Kallmayer, C.
    ;
    Walter, H.
    ;
    Braun, T.
    ;
    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 Model for Flip-Chip on Flex using Anisotropic Conductive Adhesive under Moisture and Temperature Loading
    ( 2008)
    Wunderle, B.
    ;
    Kallmayer, C.
    ;
    Walter, H.
    ;
    Braun, T.
    ;
    Michel, B.
    ;
    Reichl, H.
    This paper addresses the reliability of .ip-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 .elds at the ACA bump. The model is discussed with respect to a direct prediction of failure versus time.
  • Publication
    Non-destructive failure analysis and modeling of encapsulated miniature SMD ceramic chip capacitors under thermal and mechanical loading
    ( 2007)
    Wunderle, B.
    ;
    Braun, T.
    ;
    May, D.
    ;
    Mazloum, A.
    ;
    Bouazza, M.
    ;
    Walter, H.
    ;
    Wittier, O.
    ;
    Schacht, R.
    ;
    Becker, K.-F.
    ;
    Schneider-Ramelow, M.
    ;
    Michel, B.
    ;
    Reichl, H.
    The use of multi-layer 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 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.
  • Publication
    Conformal coating and patterning of 3D structures on wafer level with electrophoretic photoresists
    ( 2007)
    Fischer, T.
    ;
    Töpper, M.
    ;
    Jürgensen, N.
    ;
    Ehrmann, O.
    ;
    Wiemer, M.
    ;
    Reichl, H.
    Process technology for electronic packaging and MEMS is being confronted with higher topography on the wafer due to higher complexity of the devices. Especially spin coating of photoresists has severe limitations when dealing with larger three-dimensional features leading to excessive thickness in the bottom and inadequate thickness at the top of these features. One method to overcome the limitations of using spin-coated liquid photoresists on wafer surfaces with extreme topography is the electrophoretic deposition of photoresists. The electrophoretic resist coating process is based on the electrodeposition of either a negative tone or a positive tone photoresist from an aqueous solution onto a conductive seed layer. In the aqueous resist emulsion the ionized polymer forms charged micelles comprising solvent, dye, and photoinitiator molecules. When an electric field is applied micelles migrate by electrophoresis towards the corresponding electrode and form on the surface a self-limiting, insulating film. This electrode is the wafer that is supposed to be coated. The electrophoretic deposition is finished very quickly, usually after 10 sec. The coating experiments were mainly performed in a new ED resist coater, developed by MECO Equipment Engineers B.V. This coater is based on semiautomatic single wafer operation. The resulting layer thickness is mainly affected by the applied voltage and the temperature during the deposition. Final resist layer thicknesses between 3-20 µm are obtained in dependence of the applied voltage, the bath temperature, and the used resist type. Cavities, 300-400 µm deep, obtained on Si wafers either by wet chemical etching or by dry plasma etching were conformally coated with electrophoretic resists from Rohm and Haas Electronic Materials (RHEM). It is shown that especially the top corners of the cavities are well covered with photoresist even after the full lithographic process.
  • Publication
    Localized stress measurements - a new approach covering needs for advanced micro and nanoscale system development
    ( 2007)
    Vogel, D.
    ;
    Gollhardt, A.
    ;
    Sabate, N.
    ;
    Keller, J.
    ;
    Michel, B.
    ;
    Reichl, H.
    The paper presents a recently developed method of measuring frozen elastic stresses in micro components and devices. The approach bases on stress release at the component surface by focused ion beam (FIB) milling. Stresses are deduced from the experimentally determined deformation field around the FIB milling pattern, applying reasonable stress hypotheses and appropriate modeling of the stress release field. Because of the local nature of ion milling and the limited material volume affected by deformation, the method suites to very local stress measurement. Commonly, spatial resolution is achieved in a range from submicron to some tens of microns. Residual stresses in membrane types MEMS structures have been measured and results are reported. A broader group of potential applications is expected for non-membrane structures in micro-/nanosystems or their packaging. Possible approaches for those cases are discussed, considering comparison of measured deformation fields with either analytical solutions of the mechanical problem or with finite element simulations.