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

2008 , Auersperg, J. , Wunderle, B. , Dudek, R. , Walter, H. , Michel, B.

Design studies 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. That is why electronics components especially in the field of RF (Radio Frequency), optoelectronics, high temperature and power applications are often exposed to extreme thermal environmental conditions, mechanical shock and vibrations. However, a continuous industry drive for miniaturization and function integration forces the development of eature sizes down to the nanometer regime. Simultaneously, the well known thermal expansion mismatch problem of the several materials, residual stresses generated by several steps of the manufacturing process and various kinds of inhomogeneity attribute to interface delamination, chip cracking and fatigue of interconnects, in particular. The applied methodologies typically base on classical stress/strain strength evaluations or/and life time estimations of solder interconnects using modified Coffin-Manson approaches. Recent studies show also how the evaluation of mixed mode interface delamination phenomena, classical strength hypotheses along with fracture mechanics approaches and thermal fatigue estimation of solder joints can simultaneously be taken into account. Over and above that, new materials will be introduced especially in Back-end of line (BEoL) layers of advanced Cu/Low-k 90, 45, ..., 22 nanometer CMOS (Complementary Metal-Oxide Semiconductor) technologies. So, black diamond-I or black diamond-II as new materials are increasingly porous and interconnect materials or new functional layers come up as nano-particle filled high-tech compounds. Thus, it is to be checked whether it can be handled as homogeneous materials anymore. For sure, this will have most important impacts on the thermo-mechanical performance of the total IC (Integrated Circuit) tack. The problems appearing during packaging of CMOS-ICs at least showed that IC and package reliability are strongly interacted. Thus, the challenge for simulations in this field is not only the wide range of structural dimensions but also, the different approaches that have to be combined: Molecular or atomistic level simulations and "conventional" Finite Element Analysis (FEA) with global-local modeling, substructuring as well as fracture and damage mechanics, cohesive zone models, viscoelasticity, plasticity and creep of homogeneous constitutive models. Furthermore, it is known that multiple failure modes competitively act simultaneously wherefore, design optimizations have to incorporate all failure modes that are essential for the overall reliability. Moreover, considering that variables of the simulation models are naturally stochastic parameters leads to the consequence that all results show also scattering. First steps towards robust designs show the potential of the utilized FEA-based RMS/DOE approach to evaluate the thermo-mechanical reliability of various electronics assemblies in a more complex way giving at the same time a more solid basis for design optimizations.

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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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