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As the trend towards the densification of integrated circuit (IC) devices continues, the complexity of interfaces involving dissimilar materials and thermo-mechanical interactions has increased. Highly integrated systems in packages now comprise numerous thin layers made from various materials. The interfaces between these different materials represent a vulnerable point in ICs due to imperfect adhesion and stress concentrations caused by mismatches in thermo-mechanical properties such as Young's modulus, coefficients of thermal expansion (CTE), and hygro-swelling-induced expansion. This study investigates the impact of thermal variations on the fracture behavior of three bi-material interfaces used in semiconductor packaging: epoxy molding compound–silicon (EMC–Si), silicon oxide–polyimide (SiO2–PI), and PI–EMC. Using double cantilever beam (DCB) tests, we analyzed these interfaces under mode I loading at three temperatures: −20 °C, 23 °C, and 100 °C, under both quasi-static and cyclic loading conditions. This provided a comprehensive analysis of the thermal effects across all temperature ranges in microelectronics. The results show that temperature significantly alters the failure mechanism. For SiO2–PI, the weakest point shifts from silicon at low temperatures to the interface at higher temperatures due to thermal stress redistribution. Additionally, the fracture energy of the EMC–Si interface was found to be highly temperature-dependent, with values ranging from 0.136 N/mm at low temperatures to 0.38 N/mm at high temperatures. SiO2–PI's fracture energy at high temperature was 42% less than that of EMC–Si. The PI–EMC interface exhibited nearly double the crack growth rate compared to EMC–Si. The findings of this study provide valuable insights into the fracture behavior of bi-material interfaces, offering practical applications for improving the reliability and design of semiconductor devices, especially in chip packaging. [ABSTRACT FROM AUTHOR]

The use of adhesive bonding for joining composites has grown due to its excellent performance compared to traditional joining methods. However, delamination remains a significant issue in adhesively bonded composite joints, often causing early failure and reducing joint performance. To address this, there is a strong interest in methods that enhance the through-thickness strength of composite substrates to reduce the risk of delamination. Various studies have suggested techniques to prevent delamination in carbon fiber reinforced polymer (CFRP) single-lap joints (SLJs). This study investigates the reinforcement of substrates to prevent delamination, often by adding a tough polymer or metal layer (called fiber metal laminates) to the top and bottom surfaces of the substrates. The effects of incorporating aluminum and film adhesive layers (each comprising 25% of the composite substrate's thickness) on the failure load and failure mode of bonded joints under different loading rates, including quasi-static (1 mm/min), high-rate (0.1 m/s), and impact (2.5 m/s) conditions, were examined. These configurations were also simulated using cohesive zone modeling (CZM) across all loading rates to predict failure load and mechanisms numerically. Under impact loading, substituting outer CFRP layers with polymer or metal layers significantly increased the failure load and energy absorption capacity. Samples reinforced with aluminum and polymer showed approximately 39% and 13% higher failure loads, respectively, compared to the reference CFRP samples under impact. In terms of energy absorption, SLJs reinforced using aluminum could dissipate energy about 15% greater than the reference CFRP SLJs. The polymer reinforcement configuration can enhance specific strength with a relatively smaller increase in weight compared to FML. This is particularly important in aerospace applications, where minimizing weight while improving performance is crucial. [ABSTRACT FROM AUTHOR]

A novel hot-melt cyclic olefin-based adhesive was designed as a transparent, non-tacky film of amorphous thermoplastic with a unique polymer micro-structure. The aim of the present paper is to assess the mechanical properties of the 0.1 mm thick COP hot-melt adhesive film through adhesive characterizations tests. The glass transition temperature was determined using dynamic mechanical analysis (DMA). For mechanical characterization, bulk and thick adherend shear specimens were manufactured and tested at a quasi-static rate, where at least three specimens were used to calculate the average and standard deviation values. Tensile tests revealed the effects of molecular chain drawing and reorientation before the onset of strain hardening. Thick adherend shear specimens were used to retrieve shear properties. Fracture behaviour was assessed with the double cantilever beam (DCB) test and end-notched flexure (ENF) test, for characterization under modes I and II, respectively. To study the in-joint behaviour, single lap joints (SLJs) of aluminium and carbon fibre-reinforced polymer (CFRP) were manufactured and tested under different temperatures. Results showed a progressive interfacial failure following adhesive plasticization, allowing deformation prior to failure at 8 MPa. An adhesive failure mode was confirmed through scanning electron microscopy (SEM) analysis of aluminium SLJ. The adhesive exhibits tensile properties comparable to existing adhesives, while demonstrating enhanced lap shear strength and a distinctive failure mechanism. These characteristics suggest potential advantages in applications involving heat and pressure across automotive, electronics and structural bonding sectors. [ABSTRACT FROM AUTHOR]

Chip packaging engineering has evolved significantly to meet the performance demands of integrated circuits (IC) and micro-electromechanical systems (MEMS). Layers, mainly composed of metals, ceramics, and polymers are utilized to safeguard circuits and facilitate electrical connections. While, mechanical testing ensures bonding properties and reliability of bi-material interfaces in these components, there is a lack of discussion on the advantages and disadvantages of different test methods. Environmental factors, notably humidity and temperature, pose significant challenges, with a gap in understanding each condition's impact on interfaces. This review aims to provide comprehensive insights into the mechanical characterization of bi-material interfaces and their response to environmental conditions. It's divided into two main parts: a review of mechanical approaches in characterizing bi-material interfaces, including strength and quasi-static fracture tests and the presentation of test results considering temperature and humidity influence. The paper highlights the effects of humidity and high temperatures on the interface fracture energy, primarily due to the properties of polymeric materials in packaging for different interfaces. Additionally, it offers a summarized approach for selecting testing setups based on the desired interface. [ABSTRACT FROM AUTHOR]

The study proposes a novel concept of a curved single lap joint (SLJ) with non- uniform adhesive thickness to reduce stress concentrations near overlap edges. Experimental and numerical methodologies investigate this joint using two adhesives: Araldite 2015-1 and AV138. Numerical models in ABAQUS predict cohesive failure in the adhesive layer. The curved configuration doesn't significantly enhance strength in SLJ using ductile adhesives, but for brittle ones, strength increased by 131% due to sensitivity to peak stresses. In conclusion, the curved SLJ effectively reduces stress concentrations and the effectiveness of this concept is linked to the ductility of the adhesive used. [ABSTRACT FROM AUTHOR]

The increasing interest in adhesives, such as pressure-sensitive adhesives (PSAs), is often held back by uncertainties regarding their long-term behavior, which includes creep behavior. However, little information exists in the literature regarding creep behavior of PSAs. In this paper, a unified phenomenological creep model for PSAs is applied in SLJs for static and cyclic creep, seeking to develop a tool to predict creep behavior of PSAs. The model was validated by comparing the predicted creep curves with experimental data. It captured the three creep phases and predicted the creep curves for different stresses and temperatures, which is uncommon in literature. [ABSTRACT FROM AUTHOR]

Three-dimensional printing is widely becoming prevalent in various industries, including the automotive sector. As this technology advances, critical structures subjected to impact loads may also be produced using additive manufacturing. A key parameter in this technique is the infill density of the printed geometry, which directly affects mechanical properties such as strength, stiffness, and ductility. Functionally graded layouts present themselves as one of the best techniques to design effective impact attenuators. The present work combines these techniques and parameters to evaluate the behaviour of geometrically graded impact attenuators produced through additive manufacturing, with different infill densities for polylactic acid (PLA) and polycarbonate (PC) materials. The results obtained show an increase in the mechanical strength for both materials and all the infill densities when compared to reference quasi-static results. [ABSTRACT FROM AUTHOR]

In response to heightened environmental awareness, various industries, including the civil and automotive sector, are contemplating a shift towards the utilization of more sustainable materials. For adhesive bonding, this necessitates the exploration of materials derived from renewable sources, commonly denoted as bio-adhesives. This study focuses on a bio-adhesive L-joint, which is a commonly employed configuration in the automotive sector for creating bonded structural components with significant bending stiffness. In this investigation, the behavior of joints composed of pine wood and bio-based adhesives was studied. Two distinct configurations were studied, differing solely in the fiber orientation of the wood. The research combined experimental testing and finite element modeling to analyze the strength of the joints and determine their failure mode when subjected to tensile loading conditions. The findings indicate that the configuration of the joint plays a crucial role in its overall performance, with one of the solutions demonstrating higher strength. Additionally, a good degree of agreement was observed between the experimental and numerical analyses for one of the configurations, while the consideration of the maximum principal stress failure predictor (MPSFP) proved to accurately predict the location for crack propagation in both configurations. [ABSTRACT FROM AUTHOR]

This study focuses on the prediction of the fracture mechanics behaviour of a highly flexible adhesive (with a tensile elongation of 90%), since this type of adhesive is becoming widely used in automotive structures due to their high elongation at break and damping capacity. Despite their extensive applications, the understanding of their fracture mechanics behaviour under varying loading rates and temperatures remains limited in the literature. In addition, current prediction models are also unable to accurately predict their behaviour due to the complex failure mechanism that such bonded joints have. This study aims to determine whether a simple triangular cohesive zone model (CZM), which predefines the crack path, can reproduce the load–displacement curves of adhesives under various temperatures and strain rates. To achieve this, a calibrated CZM is used, adapting the model for reference joints and then validating it with independent test results conducted in a wide range of loading and environmental conditions. The tests were performed at speeds between 0.2 and 6000 mm/min and at three different temperatures ranging from −30 °C to 60 °C. Mode I fracture toughness was measured using the DCB (double cantilever beam) specimens. Using a simple triangular CZM may not be optimal for predicting the mechanical response of highly flexible adhesives with complex failure mechanisms and multiple crack paths. However, by correctly adjusting the cohesive zone properties for a limited set of reference conditions, it is possible to accurately predict the mechanical response of these joints across various test speeds and temperatures, significantly reducing costs and effort. [ABSTRACT FROM AUTHOR]

This research work presents the development of a flexible tool for performing the new joining process, called hole hemming, between dissimilar materials with very different mechanical properties. This work includes the design, fabrication, and assembly of the structural, active and passive components of the hole hemming tool and the evaluation of their performance. The tool is designed to have adjustable structural and passive tool components as well as easily interchangeable active tool components. The tool is evaluated for joining the AA6082-T4 aluminum sheet with 2 mm thickness to the AZ31 magnesium sheet with 0.9 mm thickness by experimental tests. The maximum force measured during the hole flanging and hemming stages is about 55 kN and 70 kN, respectively. The experimental data is also compared to the numerical results obtained from the finite element analysis of an ideal design. The results in both stages allow concluding the developed tool meets the considered requirements and can be efficiently used for creating hole-hemmed joints between dissimilar materials. [ABSTRACT FROM AUTHOR]

Biostructures found in nature exhibit remarkable strength, toughness, and damage resistance, achieved over millions of years. Observing nature closely might help develop laminates that resemble natural structures more closely, potentially improving strength and mimicking natural principles. Bio-inspired Carbon Fiber-Reinforced Polymers (CFRP) investigated thus far exhibit consistent pitch angles between layers, whereas natural structures display gradual variations in pitch angle rather than consistency. Therefore, this study explores helicoidal CFRP laminates, focusing on the Non-Linear Rotation Angle (NLRA) or gradual variation to enhance composite material performance. In addition, it compares the strength and failure mechanisms of the gradual configuration with conventional helicoidal and unidirectional (UD) laminates, serving as references while conducting transverse tensile tests (out-of-plane tensile). The findings highlight the potential of conventional and gradual helicoidal structures in reinforcing CFRP laminates, increasing the failure load compared to unidirectional CFRP laminate by about 5% and 17%, respectively. In addition, utilizing bio-inspired configurations has shown promising improvements in toughness compared to traditional unidirectional laminates, as evidenced by the increased displacement at failure. The numerical and experimental analyses revealed a shift in crack path when utilizing the bio-inspired helicoidal stacking sequence. Validated by experimental data, this alteration demonstrates longer and more intricate crack propagation, ultimately leading to increased transverse strength. [ABSTRACT FROM AUTHOR]

The use of thin-ply composite materials has rapidly increased due to their tailorable mechanical properties and design flexibility. Considering an adhesively bonded composite joint, peel stress stands out as a key contributor leading to failure among other primary stress factors. Therefore, the reinforcement of carbon fiber-reinforced polymer (CFRP) laminates throughout the thickness could be considered as an approach to improve the joint strength. Using thin plies locally between the conventional CFRP layers in a laminate can enhance the strength, as the sudden change in stiffness means that the load transfer is not monotonous. Consequently, the following study examined the effect of altering thin plies gradually throughout the thickness on the behaviour of the CFRP laminates when subjected to transverse tensile loading. To achieve this goal, the CFRP laminates were gradually modified by using different commercially accessible prepreg thin plies, leading to an improved overall structural performance by reducing stress concentrations. Besides conducting an experimental study, a numerical assessment was also carried out utilizing Abaqus software with a Representative Volume Element (RVE) at the micro scale. The comparison of reference configurations, which involved various thin plies with different thicknesses and traditional CFRP laminates, with the suggested gradual configuration, demonstrated a notable enhancement in both strength and material cost. Furthermore, the proposed RVE model showed promising capability in accurately forecasting the strength of fabricated laminates. [ABSTRACT FROM AUTHOR]

This research aims to examine the tensile strength of a hybrid composite laminate reinforced by thin-plies when used as an adherend in bonded single lap joints subjected to high-rate and impact loading. Two different composites, namely Texipreg HS 160 T700 and NTPT-TP415, are employed as the conventional and thin-ply composites, respectively. The study considers three configurations: a conventional composite, a thin-ply, and a hybrid single lap joint. Numerical models of the configurations are developed to provide insight into failure mechanisms and the initiation of damage. The results indicate a significant increase in tensile strength for the hybrid joints over the conventional and thin-ply joints, due to the mitigation of stress concentrations. Overall, this study demonstrates the potential of hybrid laminates for improving the performance of composite joints under highrate loading and impact conditions. [ABSTRACT FROM AUTHOR]

Adhesive bonding has been increasingly employed in multiple industrial applications. This has led to a large industrial demand for faster, simpler, and cheaper characterization methods that allow engineers to predict the mechanical behavior of an adhesive with numerical models. Currently, these characterization processes feature a wide variety of distinct standards, specimen configurations, and testing procedures and require deep knowhow of complex data-reduction schemes. By suggesting the creation of a new and integrated experimental tool for adhesive characterization, it becomes possible to address this problem in a faster and unified manner. In this work, following a previous numerical study, the mode I and II components of fracture-toughness characterization were validated experimentally in two different configurations, Balanced and Unbalanced. For mode I, it was demonstrated that both configurations presented similar numerical and experimental R-curves. The relative error against standard tests was lower than ±5% for the Balanced specimen; the Unbalanced system showed higher variations, which were predicted by the numerical results. Under mode II, the Balanced specimen displayed plastic deformation due to high deflections. On the contrary, the Unbalanced specimen did not show this effect and presented a relative error of approximately ±2%. Nonetheless, it was proven that this approach to obtain such data by using a single unified specimen is still feasible but needs further development to obtain with similar precision of standard tests. In the end, a conceptual change is proposed to solve the current mode II issues. [ABSTRACT FROM AUTHOR]