Effect of residual stress on the delamination response of film-substrate systems under bending

The effect of residual stress on the delamination behaviour of thin films is examined under four-point bending. Elastic film-substrate systems with and without the addition of a superlayer are analysed by constructing closed-form expressions for the energy release rate at steady-state delamination. The analytical results obtained with these expressions are compared to finite element results based on cohesive zone modelling, showing an excellent\u3cbr/\u3eagreement. The closed-form expressions correctly reduce to simpler forms for film-substrate systems without residual stresses, and further include the special case of spontaneous delamination under the presence of a critical residual stress only. The closed-form expression for the elastic film-substrate system without a superlayer is used for indicating errors in alternative analytical expressions presented in the literature. Subsequently, the contribution of substrate plasticity to the delamination resistance is studied by means of\u3cbr/\u3efinite element analyses for a range of (relative) film thicknesses and various values of the (relative) interfacial strength. For a compressive residual stress the delamination response typically is characterised by a transition from large scale yielding to small scale yielding under increasing film thickness, while for a tensile residual stress the limit of small scale yielding may not be reached at large film thickness when the interfacial strength is relatively high. Furthermore, stress relaxation induced by large scale yielding diminishes the\u3cbr/\u3einfluence of the residual stress on the delamination resistance under bending

Thermomechanical multiscale modelling of substrates

\u3cp\u3eFor the thermomechanical analysis of mutlilayer substrates, detailed FE is not feasible. To capture all features, the number of elements necessary would lead to extreme computational loads. To overcome this, an elementwise homogenization method utilizing multiple representative volume elements is presented. Employing a global-local step it is still possible to obtain accurate values for local quantities of interest. The approach is demonstrated for thermal and mechanical problems. For the mechanical case the procedure is validated by a confrontation with experimental results showing the ability of the technique to indicate potential problem areas using the global/homogenized step and predict failure sites using the local step.\u3c/p\u3

Cohesive zone modeling for structural integrity analysis of IC interconnects

Due to the miniaturization of integrated circuits, their thermo-mechanical reliability tends to become a truly critical design criterion. Especially the introduction of copper and low-k dielectric materials cause some reliability problems. Numerical simulation tools can assist developers to meet this challenge. This paper considers the first bond integrity during wire bond qualification testing. During testing, metal peel off may occur. This mechanical failure mode is caused by delamination of several layers of the interconnect structure. An interfacial damage model is employed for simulating delamination. However, the fact that the considered interfaces are brittle triggers some reported numerical difficulties. This paper illustrates the potential of the interface damage mechanics approach for simulating metal peel off and it highlights the computational aspects to be developed to render a practically applicable approach

Multi-scale experimental analysis of rate dependent metal-elastomer interface mechanics

A remarkable high fracture toughness is sometimes observed for interfaces between materials with a large elastic mismatch, which is reported to be caused by the fibrillar microstructure appearing in the fracture process zone. In this work, this fibrillation mechanism is investigated further to investigate how this mechanism is dissipating energy. For that purpose, thermoplastic urethane(TPU)-copper interfaces are delaminated at various rates in a peel test experimental setup. The fracture process zone is visualized in situ at the meso scale using optical microscopy and at the micro scale using Environmental Scanning Electron Microscopy (ESEM). It is shown that the geometry of the fracture process zone is insensitive to the delamination rate, while the interface traction scales logarithmically with the rate. This research has revealed that, the interface roughness is shown to be pivotal in initiating the fibrillation delamination process, which facilitates the high fracture toughness. The multi-scale experimental approach identified two mechanism responsible for this high fracture toughness. Namely, the viscous dissipation of the TPU at the high strain levels occurring in the fibrils and the loss of stored elastic energy which is disjointed from the propagation due to the size of the process zone

2D phase field modeling of sintering of silver nanoparticles

The sintering mechanism of silver nanoparticles is modelled by incorporating surface, volume and grain boundary diffusion in a phase field model. A direction-dependent tensorial mobility formulation is adopted, capturing the fact that diffusion mainly occurs along the directions tangential to the surface of the particle. A finite element framework is applied to solve the governing equations in a fully coupled implicit manner, and the developed framework is demonstrated for particle sintering of equal and unequal sizes as well as at different temperatures. The obtained results are compared with experimental observations, whereby it is shown that the developed material model adequately describes the sintering mechanism of silver nanoparticles

Image-based interface characterization with a restricted microscopic field of view

\u3cp\u3eAccurate characterization of adhesion properties in microelectronic systems is challenging due to (1) the far-field load application that often falls outside the microscopic field of view, (2) the ultra-small loads associated with specimen deformation, and (3) the load-case and specimen dependent interface response. To overcome these challenges, a generic method based on Integrated Digital Image Correlation (IDIC) is proposed, which identifies cohesive zone model parameters (of an arbitrary model not intrinsic to the identification method), by correlating images of a delaSavemination process from a restricted field of view at the microscopic scale, whereby far-field loading data cannot be exploited.To quantify the effects of potential error sources on the performance of the proposed IDIC-routine, virtual experimentation is first conducted. Inaccurate application of boundary conditions in the FE-model of IDIC is thereby shown to be the most critical source of error. Subsequently, a real double cantilever beam (DCB) experiment has been analyzed as a well-defined test-case for characterization of adhesion properties. Since the Young's modulus of the bulk material is generally well known, the imaged, elastically deforming bulk material acts as a force sensor. External load measurement can therefore be omitted from the identification process, thereby rendering the interface identification method independent of the particular test method. The implemented IDIC-algorithm is shown to be robust for accurately identifying the two cohesive zone parameters of interest: the work of separation G\u3csub\u3ec\u3c/sub\u3e and the critical opening displacement δ\u3csub\u3ec\u3c/sub\u3e\u3c/p\u3

Performance assessment of integrated digital image correlation versus FEM updating

\u3cp\u3eFull-field identification methods can adequately identify constitutive material parameters, by combining Digital Image Correlation (DIC) with Finite Element (FE) simulation. It is known that interpolation within the DIC procedure is an important error source for DIC-results. In this study, the influence of these errors on the eventual identification results is investigated. Virtual experiments are conducted from which constitutive parameters are identified by two approaches: the commonly used method of Finite Element Model Updating (FEMU) and the more recent method of Integrated Digital Image Correlation (IDIC), in which the utilized interpolation functions are varied, and the influence on the identified parameters is investigated. It was found that image-interpolation has a significant effect on the accuracy of both methods. However, the observed differences in results between the two methods of FEMU and IDIC cannot be explained by interpolation errors.\u3c/p\u3