Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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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.

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Simulation Based Analysis of Secondary Effects on Solder Fatigue

2009 , Dudek, R. , Doering, R. , Bombach, C. , Michel, B.

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Investigations of Reliability of Lead-Free Solder Joints

2008 , Faust, W. , Poller, T. , Dudek, R. , Michel, B.

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Publication

Thermal test- and field cycling induced degradation and its Fe-based prediction for different SAC solders

2008 , Dudek, R. , Faust, W. , Ratchev, R. , Roellig, M. , Albrecht, H.-J. , Michel, B.

A study of the performance of different Sn based solder alloys applied for large to small sized solder interconnects was undertaken. From the theoretical and experimental investigations on creep, fatigue and brittle fracture behaviors the paper focuses on the low cycle fatigue performance in test and field thermal environments. Special focus was put on a newly developed highly creep resistant solder alloy "Innolot" (SnAg3.8Cu0.7Bi3.0Sb1.4Ni0.2). In addition to results of previous studies on lead free materials, particularly their longterm durability and their microstructure-properties dependence was addressed. Phenomenological models based on finite element analyses including solder creep behaviors were applied to study the component and cyclic regime dependent creep straining and creep dissipation in several joints to assess solder failure. For this purpose, creep properties of several solders were measured for ball-type joint sized specimens.

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On the crack and delamination risk optimization of a Si-interposer for LED packaging

2013 , 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. Therefore, the authors performed extensive simulative work to overcome cracking and delamination risks in the vicinity of thermal copper-TSVs by means of fracture mechanics approaches. Especially, an interaction integral approach is utilized within a simulative DoE and X-FEM is used to help clarifying crack propagation paths in silicon. The DoE-based response surface methodology provided a good insight into the role of model parameters for further optimizations of the intended thermal TSV-approaches in LED packaging applications.

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Micro- and nanoreliability research in the micro materials center Chemnitz of Fraunhofer ENAS

2009 , Michel, B. , Dudek, R. , Auersperg, J. , Winkler, T.

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Reliability of Several Sn-Based Solders under Test- and Field Fatigue Loadings

2008 , Dudek, R. , Ratchev, R. , Faust, W. , Michel, B.

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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.

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FEA Based Reliability Prediction for Different Sn-Based Solders Subjected to Fast Shear and Fatigue Loadings

2008 , Dudek, R. , Kaulfersch, E. , Rzepka, S. , Röllig, M. , Michel, B.

Recent studies revealed that there is no simple ldquodrop inrdquo solution for the lead-free replacement of SnPb joints, instead different Sn-based solders are advantageous for different use conditions, which can be dominated either by drop loading or by thermal cyclic loading in harsh use conditions. By way of high-speed shear testing reliability assessments of components during drop and shock events can be studied in a simplified manner. Dynamic 3-D finite element simulations have been performed applying explicit FEA to replicate the shear tests virtually. It was shown in this way that SAC 1305 solder outperformed SAC 387 solder. The low cycle fatigue behavior of different SAC alloys is additionally of interest. Fatigue life predictions require both the constitutive description of the lead-free solders and a fatigue hypothesis linked to the material selected. Based on recently measured creep properties the solder joint creep strain and creep dissipation responses were analyzed for several components and thermal cycling conditions. The results based upon non-linear finite element calculations indicate different trends for creep strain and energy dissipation: while the first is clearly increasing with lowered alloying Ag-content, the latter is almost stable and does only slightly vary. Furthermore, these trends are different for different test- and field cycling conditions as well as the different components studied.

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Challenges for multi-scale modeling of multiple failure modes in microelectronics packaging

2008 , Auersperg, J. , Dudek, R. , Vogel, D. , Michel, B.

Design for thermo-mechanical reliability of electronics components on the basis of parameterized Finite Element Models and DoE/RSM-approaches (Design of Experiments/Response Surface Methods) are more and more performed for optimizations at early phases of the product development process. This is especially the case for electronic components in the fields of RF (Radio Frequency), optoelectronics, high temperature, and power applications, which are often exposed to extreme thermal environmental conditions, mechanical shock and vibrations. Additionally, a continuous industry drive for miniaturization and function integration forces the development of feature sizes down to the nanometer range and the introduction of new high-tech, nano-particle filled or nano-porous materials. These developments cause new challenges for reliability analysis and prediction, i.e. the development of multiple failure criteria for combined loadings including residual stresses, interface delamination, cracking and fatigue of interconnects simultaneously. That's why, the authors face up to multiscale modeling approaches, damage and fracture mechanics approaches on the basis of continuum mechanics, and measurement techniques of material properties in the miniaturized range addressed. Evaluations of residual stresses, especially of thin films, resulting from several manufacturing steps are an important precondition for high-quality FEA-based RSM/DOE-simulations towards robust designs, too.

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