Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    Parametric FE-approach to flip-chip reliability under various loading conditions
    ( 2004)
    Wunderle, B.
    ;
    Nüchter, W.
    ;
    Schubert, A.
    ;
    Michel, B.
    ;
    Reichl, H.
    In this paper we focus on the thermo-mechanical reliability of flip-chip assemblies which are, in addition to periodic thermal loads, constrained by mechanical boundary conditions caused by the attachment of a heat-spreader. Whereas mechanically unconstrained flip-chip assemblies have been in the focus of reliability studies for a long time, the loading induced by additional mechanical constraints and hence the impact on solder bump reliability is still largely unknown. So a comprehensive study was carried out comprising FE-simulations for lifetime prediction and thermal cycling tests for experimental verification. For this purpose a tool for modular parametric FE-model generation was developed. The experiments do coincide with the simulative prediction with good accuracy, allowing for the first time a distinct statement about the reliability of flip-chip packages with attached heat-spreaders. As a result we have found that in general all additional constraints on the chip do reduce its lifetime. A distinct ranking has be obtained as a function of the specified variables. Eventually design guidelines are given.
  • Publication
    Reliability assessment of flip-chip assemblies with lead-free solder joints
    ( 2002)
    Schubert, A.
    ;
    Dudek, R.
    ;
    Walter, H.
    ;
    Jung, E.
    ;
    Gollhardt, A.
    ;
    Michel, B.
    ;
    Reichl, H.
    Due to environmental awareness, and the health hazards involved in using lead in solders, large efforts to develop lead-free soldering have been made in recent years. Sn-Ag alloys are expected to be one of the best candidate lead-free solders. Furthermore, from a reliability viewpoint, there has been interest in improved thermal fatigue resistance of solder interconnects. In this study, two lead-free solder alloys (Sn96.5Ag3.5, Sn95.5Ag3.8Cu0.7) were investigated in comparison to lead-containing solder alloys (Sn63Pb37, Sn59Pb40Ag1). These investigations were focused on mechanical and physical properties (coefficient of thermal expansion, stress-strain curves at different strain-rates) as well as on the microstructural appearance of the solders. The mechanical and thermomechanical behavior of the solders were examined by TMA, DTMA, tensile tests, and creep tests. Constant-load creep tests were performed on the specimens at temperatures from 20 degrees C to 150 degrees C. Steady-state strain rates spanned seven orders of magnitude ranging from 10/sup -11/ s/sup -1/ to 10/sup -4/ s/sup -1/. The second step is a reliability study of flip-chip assemblies on FR-4 (high T/sub g/ material) with three different underfill materials and with Sn63Pb37, Sn96.5Ag3.5, and Sn95.5Ag4.0Cu0.5 bumps, undergoing thermal cycles from - 55 degrees C to 125 degrees C and -55 degrees C to 150 degrees C. The deterioration (characterized by electrical resistance and SEM) are described. Furthermore, it is shown that the material parameters obtained from the tests will increase the precision of finite-element analysis for reliability studies of microelectronic packages with lead- free solder interconnects.
  • Publication
    a46Parametric FE-approach to flip chip reliability under various loading situations
    ( 2002)
    Wunderle, B.
    ;
    Nüchter, W.
    ;
    Schubert, A.
    ;
    Michel, B.
    ;
    Reichl, H.
  • Publication
    Numerical and experimental investigations of large IC flip chip attach
    ( 2000)
    Schubert, A.
    ;
    Dudek, R.
    ;
    Leutenbauer, R.
    ;
    Coskina, P.
    ;
    Becker, K.-F.
    ;
    Kloeser, J.
    ;
    Michel, B.
    ;
    Reichl, H.
    ;
    Baldwin, D.
    ;
    Qu, J.
    ;
    Sitaraman, S.
    ;
    Wong, C.P.
    ;
    Tummala, R.
    A study was conducted to investigate the reliability of large FCOB assemblies through both thermal cycling tests and numerical simulation. Samples with IC sizes from 10 mm to 40 mm were prepared and subjected to thermal cycling (AATC -55°C/+125°C0 to verify the simulation results with the experimental findings.
  • Publication
    Experimental and numerical reliability investigations of FCOB assemblies with process-induced defects
    ( 2000)
    Schubert, A.
    ;
    Dudek, R.
    ;
    Kloeser, J.
    ;
    Michel, B.
    ;
    Reichl, H.
    ;
    Hauck, T.
    ;
    Kaskoun, K.
    To develop comprehensive design guidelines, models and experiments cannot overlook process-induced imperfections in the flip chip on board (FCOB) assemblies. The following items were noted as being significant factors which were used for modeling and by thermal cycling tests: (a) varying stand-off-heights and alternative bump sizes, (b) underfill-particle settling, (c) underfill-void effects, (d) underfill-to-bump coverage, (e) asymmetrical fillets vs. symmetrical fillets. A detailed numerical and experimental reliability study of perfect and imperfect flip chip assemblies has been completed. Experimental studies of the failure modes and of the mean cycles to failure are in good agreement with the failure modes and life time, as predicted by FEM for the different technological variants. A hierarchy of influences was worked out in three levels (important, medium, negligible). Most important imperfections resulting in a strong reliability decrease are particle settling, a symmetrical fillets and small and big voids.
  • Publication
    Package reliability studies by experimental and numerical analysis
    ( 2000)
    Schubert, A.
    ;
    Dudek, R.
    ;
    Michel, B.
    ;
    Reichl, H.
  • Publication
    An efficient approach to predict solder fatigue life and its application to SM- and area array components
    ( 1999)
    Dudek, R.
    ;
    Nylen, M.
    ;
    Schubert, A.
    ;
    Michel, B.
    ;
    Reichl, H.
  • Publication
    Flip chip solder joint reliability
    ( 1999)
    Schubert, A.
    ;
    Dudek, R.
    ;
    Vogel, D.
    ;
    Becker, K.-F.
    ;
    Kloeser, J.
    ;
    Michel, B.
    ;
    Reichl, H.
  • Publication
    Thermo-mechanical reliability of flip chip structures used in DCA and CSP
    ( 1998)
    Schubert, A.
    ;
    Dudek, R.
    ;
    Vogel, D.
    ;
    Michel, B.
    ;
    Reichl, H.
    The continuing demand towards high-density and low profile integrated circuit packaging has accelerated the development of flip chip structures as used in direct chip attach (DCA) technology and chip size packages (CSP). The advantages in density, cost and electrical performance are obvious. Solder joints, the most widely used flip chip interconnects, have a relatively low structural compliance due to the large thermal expansion mismatch between silicon die and the organic substrate. This causes high thermally induced creep strain on the interconnects during temperature cycling and leads to early failure of the solder connections. The reliability of flip chip structures can be enhanced by applying an epoxy-based underfill between the chip and the substrate, encapsulating the solder joints. However, over ranges of design, process, and material parameters, different failure modes are observed with significant dependence on material properties and geometry. Nonlinear finite element analysis for flip chip structures is carried out to investigate the reliability impact due to a number of selected design and material parameters. Especially two fundamental issues are addressed, namely, the optimization of thermomechanical properties of underfill materials and manufacturing process-induced defects.