Stretchable electronics offer potential application areas in biological implants interacting with human tissue, while also facilitating increased design freedom in electronics. A key requirement on these products is the ability to withstand large deformations during usage without losing their integrity. Experimental observations show that delamination between the metal conductor lines and the stretchable substrate may eventually lead to short circuits while also the delaminated area could result in cohesive failure of the metal lines. Interestingly, peel tests show that the rubber is severely lifted at the delamination front caused by its high compliance. To quantify the interface in terms of cohesive zone properties, these parameters are varied such that the experimental and numerical peel-force curve and rubber-lift geometry at the delamination front match. The thus obtained interface properties are used to simulate the delamination behavior of actual three-dimensional stretchable electronics samples loaded in tension.@en

The first part of this paper deals with the analysis of layer buckling and delamination of thin film multilayer structures that are used in flexible display applications. To this end, 250 nm thick indium tin oxide (ITO) layers have been deposited on a 200 µm thick high temperature aromatic polyester substrate (Arylite) with a 3 µm silica-acrylate hybrid hard coat (HC). Typical buckle morphologies are determined from two-point bending experiments, in which geometries are measured after straightening of the sample. Finite element simulations have been performed to estimate the corresponding interface properties and compressive strains in the layers, and to illustrate the effect of sample straightening on the buckle geometry. The second part considers the fracture sensitivity analysis of an active matrix Thin Film Transistor (TFT) display containing 512 x 256 pixels, with a typical pixel dimension of 160 x 160 µm. Due to the large scale differences between the display and the TFT patterning a multi-scale modelling framework has been developed, which allows to include realistic material stacks and a detailed pixel geometry. The resulting patterning effect shows an anisotropic behaviour at both the pixel level and the global display level due to the multi-scale approach. Using the Area Release Energy (ARE) method an energy-based failure criterion has been utilised to analyse cohesive failure at several (critical locations in the pixel geometry. Specifically, the sensitivity to tunnelling cracks in the dielectric layers is considered, which have been experimentally observed in comparable TFT samples that are subjected to tension. This local failure analysis allows for the identification of critical regions within the pixel geometry, which strongly depend on the location within a pixel.@en

Stretchable electronics offer potential application areas in biological implants interacting with human tissue. Furthermore, they facilitate increased design freedom of electronic products. Typical applications can be found in healthcare, wellness and functional clothes. A key requirement on these products is the ability to withstand large deformations during usage without losing their integrity (i.e. large stretchability). One of the possible basic designs for stretchable electronics is to interconnect small rigid semiconductor islands with thin metal conductor lines on top of a highly deformable substrate, such as a rubber material. In this case, large stretchability must also be provided by these thin metal conductor lines. The adhesion of the conductor lines to the rubber substrate is of major importance from a reliability point of view. Experimental observations show that delamination between the metal conductor lines and the stretchable substrate may eventually lead to short circuits while also the delaminated area could result in cohesive failure of the metal lines. To understand and quantify the behavior of the copper-rubber interface, peel tests are performed and analyzed by means of experiments and numerical simulations. Interestingly, experimental observations show that the rubber is severely lifted at the delamination front caused by its high compliance. To quantify the interface properties, numerical simulations of the peel test have been performed by developing a finite element model comprising of cohesive zone elements by which the transient delamination process during the peel test is described in detail. By means of an extensive model parameter sensitivity study combined with the measured peel-force curves and the rubber-lift geometry at the delamination front, the final set of model parameters has been determined. Finally, the thus obtained model parameters are used to simulate the delamination behavior of actual three-dimensional stretchable electronics samples loaded in tension.@en

Debonding of polymer-metal interfaces often involves both interfacial and cohesive failure. This paper extends the investigation of Yao and Qu presented in [Yao Q, Qu J. Interfacial versus cohesive failure on polymer-metal interfaces in electronic packaging - effects of interface roughness. J Electr Packag 2002; 124; 127-34] towards a numerical fracture mechanics model that is used to quantitatively predict the relation between cohesive and adhesive failure on a metal-polymer interface. As example, an epoxy-aluminum interface is investigated. The competition between adhesive and cohesive failure depending on surface roughness parameters will be studied. Understanding of these phenomena could enable the optimization of interface properties for different applications.@en

The first part of this paper deals with the analysis of layer buckling and delamination of thin film multi-layer structures that are used in flexible display applications. To this end, 250 nm thick indium tin oxide (ITO) layers have been deposited on a 200 µm thick high temperature aromatic polyester substrate (Arylite¿) with a 3 µm silica-acrylate hybrid hard coat (HC). Typical buckle morphologies are determined from two-point bending experiments, in which buckle widths and heights are measured after straightening of the sample. Finite element simulations have been performed to estimate the corresponding interface properties and compressive strains in the layers, and to illustrate the effect of sample straightening on the buckle geometry. The second part considers the fracture sensitivity analysis of an active matrix Thin Film Transistor (TFT) display containing 512 x 256 pixels, with a typical pixel dimension of 160 x 160 µm. Due to the large scale differences between the display and the TFT patterning a multi-scale modelling framework has been developed, which allows to include realistic material stacks and a detailed pixel geometry. The resulting patterning effect shows an anisotropic behaviour at both the pixel level and the global display level due to the multi-scale approach. Using the Area Release Energy (ARE) method an energy-based failure criterion has been utilised to analyse cohesive failure at several (critical) locations in the pixel geometry. Specifically, the sensitivity to tunnelling cracks in the dielectric layers is regarded, which have been experimentally observed in comparable TFT samples that are subjected to tension. This local failure analysis allows for the identification of critical regions within the pixel geometry, which strongly depend on the location.@en

Thermo-mechanical reliability issues are major bottlenecks in the development of future microelectronic components. Numerical modeling can provide more fundamental understanding of these failure phenomena. As a result, predicting and ultimately preventing these phenomena will result in an increased reliability of current and future electronic products. In this paper, delamination phenomena occuring in Cu/low-k back-end structures, buckling-driven delamination in flexible electronics and peeling tests on stretchable electronics will be modeled and validated by experimental results. For the Cu/low-k back-end structues, failure sensitivity analysis is performed by the recently developed Area Release Energy (ARE) method while transient delamination processes are described by cohesive zone elements in the critical regions. For the latter, a dedicated solver is applied that is able to deal with brittle interfaces. For the flexible and stretchable electronics applications, cohesive zones are used to characterize the interface properties by combining numerical results with experimental measurements.@en