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Bernhard Wunderle,
K.-F. Becker,
R. Sinning, O. Wittler,
R. Schacht,
H. Walter,
M. Schneider-Ramelow,
K. Halser,
N. Simper,
B. Michel,
H. Reichl
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ABSTRACT: In this paper we examine the thermo-mechanical reliability of polymer-encapsulated chip-on-board (COB) assemblies for power
applications by simulation and experiment. Thereby the focus is set on the low cycle fatigue failure behaviour of the die-attach
material under thermal cycling conditions. As die-attach material different solder materials and Ag-filled thermal adhesives
have been used. The encapsulation was performed with a soft silicone-based and hard silica-reinforced epoxy-based material,
respectively. An other process variable takes into account die-tilt. The study was carried out as a feasibility analysis in
the course of a COB technology development. To this end lifetime models have been employed to correlate crack growth in the,
i.e. attach to a computational accumulative failure criterion which allows to consistently describe ad predict quantitatively
the lifetime of the assemblies. Thereby a considerable influence of the encapsulation was found. In particular it could be
shown that a hard encapsulation largely increases reliability for solder die-attach.
Microsystem Technologies 04/2012; 15(9):1467-1478. · 0.93 Impact Factor
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ABSTRACT: This work presents an investigation of interfacial interaction between an industrial grade epoxy molding compound and a native silicon dioxide layer usually found at chip surfaces. The free surfaces of both solid materials were subjected to an experimental contact angle analysis of three different liquids (water, diiodomethane and glycerol). Results are compared to interaction energies found by analysis of molecular models of the interfaces, yielding reasonable agreement. Results of the simulation furthermore allow a qualitative prediction about the influence of water at the interface between chip and molding compound.
Electronic Components and Technology Conference (ECTC), 2011 IEEE 61st; 07/2011
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ABSTRACT: 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.
Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE), 2011 12th International Conference on; 05/2011
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ABSTRACT: An investigation of interfacial interaction has been performed between an industry oriented epoxy molding compound Epoxy Phenol Novolac (EPN) and its filled variety EPN<sup>F</sup> (with silica particles) and a native silicon dioxide layer (SiO<sub>2</sub>) usually found at chip surfaces. The free surfaces of both solid materials were experimentally analysed by contact angle measurements of three different liquids (water, methylene-iodide (MI) and glycerol). Results are compared to interfacial energies obtained by analysis of the interfaces in bimaterial molecular models, yielding reasonable agreement. A qualitative prediction regarding the influence of water on the interfacial strength between chip and molding compound is attempted.
Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE), 2011 12th International Conference on; 05/2011
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ABSTRACT: It is well known that high temperature storage can degrade moulding compounds for chip encapsulation to such an extent that the adhesions to surfaces like copper (lead frames) or polyimide (chip coating) decreases drastically causing delamination. 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 bond wires.
Electronic System-Integration Technology Conference (ESTC), 2010 3rd; 10/2010
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B. Wunderle,
M.A. Ras,
M. Klein,
R. Mrossko,
G. Engelmann,
D. May, O. Wittler,
R. Schacht,
L. Dietrich,
H. Oppermann,
B. Michel
[show abstract]
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ABSTRACT: As the demand for new thermal technologies and materials has been increasing over the years to provide thermal solutions to the next generation of power electronics, microprocessors and high-power optical systems also thermal characterisation methods have to keep up with the pace of this development with respect to resolution and accuracy. Within the EU-funded project ldquoNanopackrdquo we have developed both bulk and interface technologies to reduce thermal resistance using Ag-based materials and low-T and low-p processes to render them eligible for the electronics industry. New processes to generate nano-enhanced surface structures as well as thermo-compression bonding are examined within this paper. Along with these processes especially designed test stands are described which are able to extract the effects achieved by the technological advances.
Thermal Investigations of ICs and Systems, 2009. THERMINIC 2009. 15th International Workshop on; 11/2009
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ABSTRACT: The nanoindentation experiment is an established technique for the determination of hardness and Young's modulus of thin films. This standard data set is not sufficient to be used as input to finite element simulations , because elastic-plastic material data is being required for analysis of reliability of metal layers. Therefore stress-strain curves are being determined by fitting the force displacement curves of the experiment with a finite-element model. Additionally this approach enables a solution for the so called substrate effect, because the stiffness of the substrate can be considered in the fitting model. This known approach is being applied and tested on thin (< 500 nm) gold layers deposited on silicon. It is shown that even for indents that exceed 10% of the film thickness a good sensitivity for Young's modulus can be reached, but for the plastic data the results are not unique and a range of plastic properties can be fitted. It is shown, that this problem of the method can be solved by correlation of the indent profiles.
Thermal, Mechanical and Multi-Physics simulation and Experiments in Microelectronics and Microsystems, 2009. EuroSimE 2009. 10th International Conference on; 05/2009
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ABSTRACT: Current developments and trends in microelectronics are focused on thin layers and novel materials. This leads to application of different test and measurement methods, which are capable to measure basic mechanical properties of such materials on micro-scale and nano-scale. The presented project focuses on application of the nanoindentation technique in order to extract the basic elastic and elasto-plastic mechanical properties of aluminium through analytical and numerical approaches. The results allowed to select the most appropriate elastoplastic material model that would be capable of fitting the experimental and numerical results. According to the performed analysis it was concluded that Ramberg-Osgood model fulfil the above criteria and can be used to predict the nanoindentation results in case of very thin aluminium layers.
Thermal, Mechanical and Multi-Physics simulation and Experiments in Microelectronics and Microsystems, 2009. EuroSimE 2009. 10th International Conference on; 05/2009
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ABSTRACT: Interfacial adhesion between the Epoxy Molding Compound (EMC) and the copper-based leadframe is one of the major concerns in the qualification of plastic packages. Since the conventional shear testing methods used in industry do not consider the residual stresses in the shear samples, they are only used as a qualitative testing method for the EMC qualifications. However, since these tests are based on the maximum force leading to interface delamination, they may cause erroneous results because of neglecting process-induced stresses, which may alter the required force needed to break the samples at the interface. Even classical fracture mechanics, based on mechanical load leading to crack propagation, may not fully characterize the interfacial fracture toughness, because the residual stresses available in the sample impede or facilitate the crack progress, depending on the state of the stresses at the crack tip. The aim of this work is to propose an effective selection criterion for finding the most suitable epoxy molding compound in terms of the intrinsic interfacial adhesion. The effect of residual stresses on the interfacial fracture toughness was investigated by performing an empirical approach to calculate the amount of the cure shrinkage by warpage measurement of the bi-material beams. The effective cure was implemented in the Finite Element Analysis (FEA) of the experimental fracture test to estimate the real interface adhesion. It was observed, that the proper molding compound candidate to fulfill the adhesion requirements was not the one which showed the maximum fracture force and material selection may be done wrongly, if the process-induced stresses are not considered in the FEA of the fracture tests.
Thermal, Mechanical and Multi-Physics simulation and Experiments in Microelectronics and Microsystems, 2009. EuroSimE 2009. 10th International Conference on; 05/2009
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ABSTRACT: This paper investigates different stress and strain measurement methods usable during packaging of electronic systems. By applying stress measurement chips, embedded fiber optic Bragg grating (FBG) sensors and pressure sensitive multilayers it is possible to determine the stress condition on the surface of silicon chips, on various substrates and within epoxy polymers.
Electronics System-Integration Technology Conference, 2008. ESTC 2008. 2nd; 10/2008
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ABSTRACT: Obtaining material data for thin metal layers is a mayor issue in the reliability assessment of microelectronic products. Therefore a method for obtaining elastic-plastic material data is analyzed and discussed in this paper. It is based on the nanoindentation of a film on a silicon substrate and the modeling of it. Thus it becomes possible to fit specific material models to the indentation experiment. Results are shown for two AlSiCu layers.
Electronics System-Integration Technology Conference, 2008. ESTC 2008. 2nd; 10/2008
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ABSTRACT: In this paper new characterization equipment for thermal interface materials is presented. Thermal management of electronic products relies on the effec-tive dissipation of heat. This can be achieved by the optimization of the system design with the help of simulation methods. The precision of these models relies also on the used material data. For the determi-nation of this data an experimental set-up for a static measurement is presented, which evaluates thermal conductivity and interface resistance of thermal inter-face materials (e.g. adhesive, solder, pads, or pastes). A qualitative structure-property correlation is pro-posed taking into account particle size, filler content and void formation at the interface based on high resolution FIB imaging. The paper gives an overview over the set-up and the measurement technique and discusses experimental and simulation results.
10/2007;
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ABSTRACT: The knowledge of deformation and fatigue behaviour is vital for understanding reliability problems and builds the basis for mechanical simulations, which quantify strains, stresses and even product life-times. The focus of this paper is the AuSn interconnect in the form of eutectic AuSn and fine pitch flip-chip interconnects consisting in this example of an Au-phase and a zetha-phase. In the fist place local elastic-plastic properties are analysed by nanoindentation giving information about the process influences on material properties. To analyse the fracture, damage and fatigue behaviour of eutectic AuSn interconnects, special set-ups have been developed. Normal lap shear samples enable the analysis under pure mechanical load and thermal lap shear specimen enable the analysis under combined thermal and mechanical load. Thus different failure modes are outlined, which can be the focus for further quantitative analysis
Electronics Packaging Technology Conference, 2006. EPTC '06. 8th; 01/2007
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ABSTRACT: The 3D-packaging technology makes it possible to stack the PCBs on top of each other and thus make full use of the third dimension. A unique space between the stacked PCB layers enables a reproducible technology without shortcuts or unconnected bumps. New applications in 3D-PDB-packages, called PCBMEMS can be realized with the combination of electric bumps and solder rings. The paper shows a fluidic cooled 11-PCB-layer with high power components. Water channels in the PCB-package dissipate the heat from the inside of the package to the environment. Heat dissipation is a bigger challenge for stacks of 3D-packages than for normal printed circuit boards (PCBs). This research paper investigates some design suggestions for a better heat dissipation. On the basis of this research paper, it becomes possible to choose the best suited PCB design. The experimental results were compared to thermal simulation results. The results of the measurements and FEM simulations show how important it is to combine the electrical and geometrical functions of 3D packages with a thermally optimized PCB design. A better heat spreading and conduction in a 3D package makes the stack more reliable at higher power dissipation
Electronics Systemintegration Technology Conference, 2006. 1st; 10/2006
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[show abstract]
[hide abstract]
ABSTRACT: This paper investigates the thermo-mechanical reliability of inter-chip-vias (ICV) for 3D chip stacking after processing and under external thermal loads relevant for the envisaged field of application (mobile, automotive) by Finite Element simulation. First the materials are characterised by nano-indentation to determine elasto-plastic data. Finite Element simulations are used to reproduce these data and to extract local material properties like E-modulus and yield stress. Accumulated plastic strain is used as failure indicator under periodic thermal loading of an ICV. Geometrical, material and process-related parameters are varied to obtain first design guidelines for this new technology. The locations of stress and strain accumulation are given.
MRS Proceedings. 12/2005; 970.
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ABSTRACT: In the paper we present an approach based on this principle to design reliable thermal management solutions for high power applications. Thermal and thermo-mechanical reliability are measured and calculated for a flip-chip mounted die with a hot-spot using reverse-side micro-channel water cooling as cooling concept. Hereby the methodology starts by material characterisation and consistent numerical implementation. Then a numerical parametric study as to geometrical features and interface materials is carried out by coupled fluidic-thermal analysis in order to evaluate the most promising variant for optimum thermal performance within the employed technology. For experimental verification a computer-controlled closed-loop thermal-fluidic testing set-up was constructed. Good correlation was found between measured, simulated and analytical results.
Thermal and Thermomechanical Phenomena in Electronic Systems, 2004. ITHERM '04. The Ninth Intersociety Conference on; 07/2004
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ABSTRACT: A modular and parametric approach to FE-modelling is presented which allows rapid virtual prototyping for MEMS and other microelectronics packages with respect to some topical reliability issues: Thermal management and thermo-mechanical fatigue. Thereby the method of automatic model generation by modular parametric modelling is outlined and some examples featuring the required solution techniques are given. This simulation procedure forms part of a comprehensive design optimisation process in the field of predictive engineering.
Design, Test, Integration and Packaging of MEMS/MOEMS 2003. Symposium on; 06/2003
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[show abstract]
[hide abstract]
ABSTRACT: Cracks inside polymeric packaging materials, which are used for
protection and isolation of electronic components, can lead to failure
of the whole system. In this presentation, the loading situation of
cracks inside the polymer of encapsulated metal structures is analysed.
The analysis is based on finite element simulations of thermally induced
stresses. In a first approach, a linear elastic material model is
assumed in combination with the application of linear elastic fracture
concepts. The load of the crack is shown to be influenced by geometrical
factors like its own initial form and length. Moreover, the occurrence
of delamination in the interface between the metal and polymer can be
very important, as it severely influences the crack front inside the
polymer. The results of this analysis are compared to experimental
observations and show good correlation. It is shown how the model can be
improved by the application of a viscoelastic material model for the
encapsulation material
Polymers and Adhesives in Microelectronics and Photonics, 2001. First International IEEE Conference on; 02/2001
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B. Wunderle,
T. Braun,
D. May,
A. Mazloum,
M. Bouazza,
H Walter, O. Wittler,
R. Schacht,
K.-F. Becker,
M. Schneider-Ramelow,
B Michel,
H. Reichl
[show abstract]
[hide abstract]
ABSTRACT: 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.
13th International Worshop on THERMal INvestigations of ICs and Systems, Budapest, Hungary 17-19 September 2007, p. 104-109.
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[show abstract]
[hide abstract]
ABSTRACT: Obtaining material data for thin metal layers is a mayor issue in the reliability assessment of microelectronic products. Therefore a method for obtaining elastic-plastic material data is analyzed and discussed in this paper. It is based on the nanoindentation of a film on a silicon substrate and the modeling of it. Thus it becomes possible to fit specific material models to the indentation experiment. Results are shown for two AlSiCu layers.
Fraunhofer IZM.
