Interface delamination is one of the most important issues in the microelectronic packaging industry. Silver filled die attach is a typical adhesive used between the die and copper die pad for its improved heat dissipation capacity. Delamination between die attach and die pad will severely impact the heat conduction and result in product failure. In order to predict this delamination, interface properties should be characterized. Tri-material, copper-die attach-EMC, samples are made according to the package processes. A four point bending test system is established in order to perform delamination tests at different temperatures using a universal tester Zwick/Roell Z005. In addition, a Keyence optical system is mounted to capture a series of pictures during the delamination processes. This will provide the delamination geometry information needed for determining the interface properties. Four point bending tests have been performed at room temperature, 40, 60, 85, and 150ºC respectively. In addition pre conditioning sample are also tested at room temperature and 85ºC respectively after 48 hours pre conditioned at 85ºC/85%RH. . Experiments show that the ¿critical delamination load¿ decreases steadily with temperature increasing. Experiments also show moisture has no effects on the ¿critical delamination load¿ compared with the dry samples tested at the same temperatures. This means that moisture has no effects on the interface toughness between copper and die attach. To quantify the interface properties, numerical simulations of the four point bending test have been performed by using a finite element model comprising cohesive zone elements which will describe the transient delamination process during the four point bending tests. Correspondently, the interface toughness decreases from 26.5J/m2 at room temperature to 1.9J/m2 at 150ºC as calculated from the cohesive zone element model. These results show that temperature has a large effect on the interface toughness. By means of an extensive model parameter sensitivity study, combined with the measured delamination length in horizontal direction along the copperdie attach interface at room temperature critical opening value has been determined.@en

In this paper, a fast moisture sensitivity level (MSL) qualification method and a fast moisture characterization method are discussed. The fast moisture characterization uses a stepwise method to obtain more reliable and more material moisture properties. The established relationships for moisture diffusion coefficients and moisture saturation levels with respect to the temperature and relative humidity can be used to predict moisture properties in the MSL range. Fast moisture sensitivity level qualification is accomplished with the aid of simulation combined with the characterized moisture diffusion properties. Moisture absorption processes at different conditions are simulated using a 3D model at conditions according to the moisture sensitivity test levels. Simulation of weight change at different condition and simulation of local moisture concentration are performed and compared between different conditions. Simulations show that at 696 h preconditioning time at 30°C/60%RH for MSL level 2a can be decreased to 42 h at 85°C/85%RH. Time required for package reliability and moisture sensitivity analysis is largely shortened.@en

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

Moisture induced failures in the plastic encapsulated packages are one of the most important failure mechanisms in microelectronics. These failures are driven by the mismatch between different material properties, such as CTA, CME (Coefficient of Moisture induced Expansion) and degradation of interface strength caused by moisture absorption of polymer materials. Therefore, it is critical to know how much moisture exists in packaging materials, the moisture distribution in the package and hygro-mechanical effects on the package. In this paper moisture diffusion, moisture distribution and hygro-mechanical effects are simulated at the following conditions: 85°C/85%RH, 60°C/60%RH and 85°C/dry, 60°C/dry using 2D SiP (System in Package) finite element model.@en

Behavior of epoxy resin is critical for performance and reliability of electronic packages. The ability to predict properties of cross linked epoxy resin prior to laboratory synthesis will facilitate the materials design. Theoretical studies in this field face a big challenge because there is no conventional way to build atomistic models of specific polymers, which form a network. Molecular dynamics (MD) is a potentially powerful method that can simulate the materials at atomic scale and it can be used to describe the performance and properties of a wide range of systems. In the present work, the properties of the cross-linked epoxy resin compound were predicted by MD simulations. Periodic amorphous structures of the cross-linked epoxy resin compound were simulated at various temperatures. The correlation of the glass transition temperature (Tg) and properties of the cross-linked epoxy resin coumpound were investigated. The results show that Tg can be estimated by the plot of densities and non-bond energy at different temperatures. The Tg predicted was in agreement with the experimental data, which shows that MD simulation is an effective tool to estimate the properties of crosslinked epoxy resin.@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

Moisture induced failure in plastic encapsulated packages is one of the most important failure mechanisms in microelectronics. This failure is driven by the mismatch between different material properties such as CTE, CME (Coefficient of Moisture induced Expansion) caused by moisture absorption in plastic packaging materials. Therefore, it is important to know moisture effects on mechanical properties of plastic packaging materials, especially CME. Moisture induced expansion can be calculated using epsilon = beta times C, here epsilon is the strain, beta is the CME and C is the moisture concentration. Traditionally using the combined TGA (Thermal Gravimetric Analyzer) technique, the CME of plastic packaging materials is characterized. TGA is used to measure the weight change and TMA is used to measure the length change. By combining both the TMA and TGA measurements, the CME can be determined. This method is often used in industry and it is observed that the CME value is often overestimated. In order to get precise CME values a high precision DMA (Dynamic Mechanical Analyzer) is used to measure the length change of a sample while a humidity generator is used to regulate the relative humidity. Therefore, temperature and relative humidity are controlled in the DMA chamber and can be used to measure the length change under different relative humidity conditions. CME values measured by the DMA plus humidity method are much lower than that of the TGA/TMA method. In order to find out which method is more reliable, a third experiment was done. A bi-material sample is created to verify our measured CME value. TDM equipment (oven + camera system to detect vertical displacement of the sample) is used to measure the warpage of the bi-material sample. Using our measured CME value, finite element model simulation result shows that the hygro-mechanical warpage of the model fits well with TDM test result.@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

Time to market is becoming one of the most important factors because of the fierce market competition. However, traditional reliability and interface toughness characterization tests take a very long time. For example, moisture sensitivity level assessment (MSL 1) will take 168 hours pre conditioning at 85C/85%RH and tradition thermal cycling takes even longer time. The long preconditioning times are chosen to ensure that also the thicker section of a package are completely saturated. Thinner packages, however, are already saturated after one to two days. In this study, we therefore investigated whether it would be possible to speed up the qualification process by shortening the preconditioning time. We focus in particular on the interface toughness. From our four point bending test and analysis, it is found that temperature has great effects on the interface toughness and moisture also has small effects on the interface toughness. In order to do the fast qualification test, thermal shock cycling tests combined with moisture absorption are performed. Experiments show that moisture can speed up the delamination.@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

Generally, the viscoelastic properties of packaging materials used in the simulation models are obtained from the materials after postcuring. However these properties were observed to change during humidity conditioning and the thermal cycling. Two kinds of packaging materials are tested, one is molding compound and another is underfill. All samples are cured according to the curing procedure, postcured at 180ºC. Before the test, first the samples are pre-dried at 125ºC for 24 hours and then preconditioned at 60ºC/60%RH for 40 hours. Secondly, one reflow at 260ºC. Finally, all samples are subjected to thermal cycling. Thermal cycling temperature range is from -65ºC to 150ºC and every cycle is finished in 30 minutes. For the DMA test, a TA instrument Q800 is used. Test results show the glass modulus, rubber modulus and glass transition temperature increase with the number of thermal cycles. This change in materials after humidity and thermal treatment is here referred to as aging. The finite element software Marc is used to simulate the internal change of stress and displacement. The simulation result shows that the total warpage has increased a little at the corner of passive die, which is where the critical cracks and crazes were found in our qualification tests. And the Von Mises stresses increase after thermal cycling.@en

We propose a molecular modeling method which is capable of modeling the mechanical impact of the porosity and pore size to the amorphous silicon-based low-dielectric (low-k) material. Due to the electronic requirement of advanced electronic devices, low-k materials are in demand for the IC backend structure. However, due to the amorphous nature and porosity of this material, it exhibits low mechanical stiffness and low interfacial strength, as well as inducing numerous reliability issues. The mechanical impact of the nano-scaled pore, including the porosity ratio and pore size, is simulated using molecular dynamics on the mechanical stiffness and interfacial strength. A fitting function is formulated based on the continuum homogenous theory and atomic interaction in nano-scale. The simulation results are fitted into analytical equations based on the homogenous theory.@en

Since recent years, the micro-electronic industry changes the material usage, design and structure, in order to satisfy the customer demands of the higher performance and smaller size. One of the examples is the change of the basic materials from Al/SiO2 to Cu/low-k in IC interconnect structure. As a
consequence, new reliability issues at device/product level have been discovered, and most of the failure modes have the characteristics of multi-scale: the failure of the um or nm induces the malfunction of the device/product. The conventional approach of the failure prediction can be achieved by the well-developed continuum scale theory, e.g., finite element method. Moreover, the nano-meter scaled simulation is demanded in order to link the macro physics to
the micro scale. This paper will demonstrate the capability of the molecular simulation of predicting the nano-scaled stiffness and atomic scale failure. @en

We propose an amorphous/porous molecular connection network generation algorithm for simulating the material stiffness of a low-k material (SiOC:H). Based on a given concentration of the basic building blocks, this algorithm will generate an approximate and large amorphous network. The molecular topology is obtained by distributing these blocks randomly into a predefined framework. Subsequently, a structural relaxation step including local and global perturbations is applied to achieve the most likely stereochemical structure. Thus, the obtained mechanical properties of the low-k materials have been verified with the experimental data.@en