In this thesis, applying viral vectors to the heart will be researched. Optogenetics is a quickly emerging field within microbiology. With a quickly emerging field of research, solutions for applying the viral vectors in a safe, quick and easy way are required.
The current method of genepainting requires a surgical procedure. To apply viral vectors into tissue, the two other main methods of applying viral vectors are encapsulation and microneedling. Encapsulation has been shown in literature to be too novel, with some disadvantages. The decision was made to make microneedles based on the material PVA.
For the production of PVA needles, moulds were made, which are shaped similarly to the design. For this mould production, 3D printing and laser cutting were explored, out of which the 3D printed moulds showed the most reliable characteristics.
The material PVA has been made with two different production processes and materials. The first one is solely PVA, which was solidified by repeated freeze-thaw cycles, and the second one is a mixture of PVA and sucrose solidified by drying the material. The first production has been used to show that the microneedles do penetrate heart tissue; it can be used in combination with viruses, and it has a reliable production method. The second recipe involves mixing sucrose in the PVA, which has been shown to dissolve and decrease in size.
The conclusion shows that for all the aspects of localised viral vector application in the context of optogenetics, PVA microneedles are highly likely to be able to fulfil that role. This will be shown by looking at aspects such as penetration of the heart, solubility of the materials, expression rate after production, and more. ... Read more

Developing reliable and efficient power semiconductors is essential to realizing a sustainable future. Packaging materials for high-power applications are electrically overstressed, are exposed to harsh environmental conditions, and are subjected to heightened temperature swings, thereby compromising the device’s stability and longevity. In this dissertation, a series of experimental methodologies were explored for monitoring the package conditions, particularly the die-attach interface, which transmits the necessary electrical, thermal, and mechanical signals from the device to the system. Furthermore, advanced thermal management strategies were investigated to circumvent concentrated microthermal hot spots and improve the device’s power rating. ... Read more

Silicon nanopores have emerged as the cornerstone of ionic and nanofluidic channels, enabling diverse applications such as biosensing, DNA-based information storage, and nanopore batteries. Their mechanical robustness, surface functionalization versatility, and seamless integration with nanofluidic devices make them highly adaptable to advanced technologies. The three-step wet etching (TSWE) method has shown great promise in fabricating silicon nanopores. However, precise control of silicon etching and achieving reliable etch-stop remain significant challenges. This thesis investigates the controllable fabrication of single-crystal solid-state silicon nanopores with extremely small dimensions using the TSWE method. Novel methodologies are introduced to address these challenges, exploring their applications in nano-mask lithography, biosensing, and ionic field-effect transistors (FETs). By analyzing nanopore formation principle at the atomic scale, the study establishes a quantitative relationship between nanopore size and the related ionic current, enabling the fabrication of nanoslits as small as 3 nm. The research integrates heavy boron doping and electrochemical passivation to regulate etching rates and achieve precise etch-stop, significantly enhancing fabrication controllability and scalability, with potential for large-scale production. The fabricated nanopores were further utilized in ionic FETs, demonstrating three-dimensional gating to modulate surface charge density. This enabled transitions between ohmic and diode-like regimes and enhanced ionic current rectification, as validated by COMSOL simulations. Additionally, the nanopores were successfully applied in biosensing, achieving high-sensitivity detection of biomolecular translocation events. Nano-mask lithography was also demonstrated, utilizing the nanopores as hard masks for focused ion beam (FIB) lithography to achieve precise and reproducible pattern transfer. These findings underscore the potential of single-crystal silicon nanopores for advanced applications in nanofabrication, biosensing, and ionic circuit development. This work establishes a foundation for future exploration in ion transport, nanofluidics, and scalable device manufacturing. ... Read more

As integrated circuits (ICs) become increasingly miniaturized, traditional solder-based interconnects face challenges related to their thermal and mechanical performance, limiting their reliability in high-density applications. This thesis addresses the growing demands of the microelectronics industry, particularly in advanced semiconductor packaging technologies, by focusing on the development of innovative interconnect methods using metallic nanoparticles, specifically copper (Cu). The research aims to overcome these limitations by utilizing copper nanoparticle (CuNP) paste to achieve direct copper-to-copper (Cu-to-Cu) bonding through nanoparticle sintering. This technique is essential for enabling next-generation 2.5D and 3D IC architectures, which require dense interconnects for improved performance... ... Read more

This thesis systematically investigated themicrostructure evolution and mechanical behavior of sintered copper (Cu) nanoparticles (NPs) using an integrated approach combining multiscale simulations with micromechanical tests. The research addressed critical challenges in the design and optimization of sintered Cu for advanced electronic applications, with a focus on anisotropic fracture behavior, porosity-dependent properties, thermal effects, interfacial strength, particle morphology, and the role of ALD coatings.

Chapter 1 established the foundational context for this study by underscoring the significance of sintered Cu NPs in electronics packaging and identifying critical gaps in the existing literature. It defined the research objectives and outlined the thesis structure, emphasizing the necessity of an integrated experimental and computational approach to link microstructure evolution with mechanical performance.

Chapter 2 systematically investigated the influence of sintering pressure on the evolution of anisotropic microstructures in sintered Cu NPs. By integrating molecular dynamics (MD) simulations with micro-cantilever bending tests, the study revealed that uniaxial sintering pressure promoted preferential neck alignment along the loading direction, resulting in pronounced mechanical anisotropy. These findings underscored the critical role of processing parameters in governing microstructural orientation and, consequently, in tailoring the mechanical performance of sintered Cu NPs. This chapter established a foundational understanding of the process–structure–property relationships central to nanoparticle-based sintering.

Chapter 3 examined the influence of sintering pressure on densification and mechanical performance. Sintered Cu NPs exhibited a favorable combination of high strength and low elastic modulus, highlighting their suitability for electronic packaging. A two-stage deformation mechanism was identified, governed by the material’s porous architecture and heterogeneous microstructure. Initial compressive loading compacted voids and formed dense interparticle contacts, followed by plastic deformation primarily accommodated through intragranular slip.

Chapter 4 investigated the strain rate- and temperature-dependent viscoplastic behavior of sintered Cu NPs. Micro-pillar compression tests, coupled with the Anand viscoplastic model, revealed the competing effects of strain-rate hardening and thermal softening. Phase-field fracture simulations further elucidated the influence of porosity on crack initiation and propagation, providing critical insight into fracture mechanisms under varying loading conditions.

Chapter 5 focused on the interfacial strength and fracture behavior of sintered Cu NPs bonded to Cu substrates. Micro-cantilever bending tests and cohesive zone model (CZM) demonstrated that interface-notched specimens exhibited superior fracture resistance, with a stress intensity factor (KQ) of 2.88 ± 0.10 MPa·m1/2, compared to 2.12 ± 0.11 MPa·m1/2 for Cu NP-notched specimens. Simulations aligned with ex perimental results, showing that reduced fracture resistance in Cu NP-notched samples stemmed from porosity and stress concentration, while enhanced strength at the interface was attributed to strong bonding andminimized void formation.

Chapter 6 examined the effect of Cu particle morphology on densification and fracture toughness. Fracture resistance was found to be highly morphology-dependent: bimodal sintered Cu exhibited the greatest toughness, attributed to effective crack deflection and bridging. Monomodal Cu showed moderate resistance, while flake-shaped Cu displayed the lowest toughness, primarily due to weak interlamellar bonding and anisotropic porosity.

Chapter 7 revealed that the fracture toughness of sintered Cu NPs was strongly dependent on loading mode. Mode II (in-plane shear) exhibited the highest toughness due to shear-induced particle interlocking, followed by mode I (tensile) characterized by ductile tearing, and mode III (out-of-plane shear), which showed the lowest toughness due to triaxial stress and unstable crack propagation. The application of an Al2O3 coating enhanced fracture toughness across all modes, with the greatest improvement observed under shear-dominated and mixed-mode loading. The coating constrained surface deformation, delayed crack initiation, and strengthened interparticle boundaries, while preserving the intrinsic ductile fracture mechanism.

Chapter 8 concluded the thesis by synthesizing the key findings and outlining future research directions, including the mitigation of oxidation, investigation of sizedependent mechanical behavior, understanding of stiffness mismatch, and exploration of metamaterial-inspired design strategies. ... Read more

Electronic components are getting increasingly integrated into a diversity of applications, products, and industries and are becoming an essential part of them. In some cases, they are responsible for handling critical tasks (e.g., the perception system in autonomous driving) and are exposed to harsh environmental conditions (e.g., elevated temperatures). Thus, the reliable functioning of electronics is more significant than ever before. Traditional reliability qualification methods rely on the tests in specification manuals and handbooks and, therefore, hold little significance today. New methods of reliability estimation have emerged and evolved quite a lot over the past six decades. The recent ones focus on product-specific reliability, as it is often the case that identical electronic components experience non-identical operating conditions and environmental loads and, thus, have a variation in their lifetimes. Implementing Prognostics and Health Management (PHM) for electronic components is a promising way to address this challenge. Demonstrating this approach using a Digital Twin-based framework is the primary goal of this dissertation. Organised into six main chapters, this thesis lays out a generalised framework for PHM and its building blocks (in Chapter 1); presents a systematic review of the term 'Digital Twin', its state-of-the-art, definitions, and architectural models (in Chapter 2); explores the physics-of-degradation for electronics packaging and encapsulating materials and identifies two commonly observed package-associated mechanical failure mechanisms (in Chapter 3); showcases a systematic procedure to prepare a six-parameter material model reflecting thermo-oxidative ageing of Epoxy Moulding Compounds (EMC) and its effects on the thermomechanical behaviour of an electronic package (in Chapter 4); focuses on developing and testing in-situ monitoring for package-to-PCB solder interconnects of a wafer-level chip-scale package using a high-resolution piezoresistive sensor (in Chapter 5); and demonstrates a superelement-based Finite Element reduced-order modelling technique and optimises for its accuracy and efficiency (in Chapter 6). ... Read more

The increasing demand for precise light control in biomedical research, especially in fields like optogenetics and liquid crystal elastomers (LCEs), has exposed the limitations of traditional light sources regarding precision, controllability, and size. To address these challenges, this research focuses on developing miniaturized LED matrix systems capable of producing high-precision, high-power customizable light patterns essential for complex biological experiments. Two mini LED matrix systems—a 48x32 matrix and a larger 160x160 matrix—were designed and developed to achieve precise modulation of light intensity and patterns. These systems were tailored to meet the rigorous requirements of optogenetic experiments, which demand precise control over cellular activities, and to explore the potential applications in light-responsive LCEs. Controlling the light-responsive behavior of LCEs is critical for advancements in soft robotics, artificial muscles, and other applications requiring adjustable light sources. The 48x32 mini LED matrix system was successfully applied to control cardiac activity through optogenetics, demonstrating its ability to modulate light for inducing and terminating arrhythmias precisely. Additionally, its integration into LCE experiments showed promise for broader biomedical applications. Building on this success, the development of a larger 160x160 mini LED matrix system extended the technology’s applicability, supporting larger-scale experimental setups and human-sized models. By providing innovative solutions to the challenges of precise light control in biomedical research, this work opens new possibilities for experimental and clinical applications, offering significant contributions to the field. ... Read more

Sintered silver is known for its high thermal and electrical conductivity and is considered a promising die attach material for wide bandgap semiconductors at high power. This study investigates the evolution of microstructure and mechanical properties of sintered silver materials during aging in different atmospheres. The study used a combination of experimental methods, including shear tests, scanning electron microscopy, and EBSD, to evaluate the effects of air and nitrogen atmospheres on the reliability of the material. Advanced simulation methods, such as dynamic Monte Carlo and phase field methods, were combined to predict grain growth and void evolution during aging. The results show that air aging accelerates grain growth and pore aggregation, and oxidation is suppressed in a nitrogen atmosphere. These findings provide insights into optimizing the sintering process to improve the long-term stability and performance of sintered silver in semiconductor packaging applications. ... Read more

This dissertation explores the development and application of an interactive optoelectronics platform designed for the precise manipulation of heart rhythm using mini/micro LEDs, primarily within the context of optogenetic applications. The research uses advancements in LED technology for biomedical engineering, focusing on the design, fabrication, and characterization of LED matrix systems. Key objectives include the development of a 48x32
mini LED matrix system, characterized for its electrical, optical, and thermal properties, and evaluated for both interactive and scripted operations. Additionally, the thesis investigates the use of this matrix for optogenetic control of cardiac activities, including optical pacing, conduction block, and the induction and termination of arrhythmias, demonstrating the system’s capability to manipulate cardiomyocytes in vitro. Furthermore, a real-time interactive optoelectronic manipulation system is developed, featuring software for real-time
control and manipulation of optical patterns, incorporating fastmanipulation frame streaming, image processing, and customized calculations. The research also extends to designing an LED matrix of human atrial surface area and the associated driver for potential clinical applications. The conclusions underscore the feasibility and effectiveness of using LED-based optoelectronic systems for precise biological control, laying the groundwork for future biomedical research and clinical therapies, and highlighting the significance of
interdisciplinary approaches in advancing medical technologies. ... Read more

IN advancing the ’More thanMoore’ paradigm, heterogeneous integration has emerged to facilitate the creation of highly efficient, compact, and multi-functional semiconductor systems. Addressing the challenges related to power efficiency, superior performance, and integration density, low-temperature nanoparticle sintering technology has become pivotal for integrating diverse materials and components in advanced semiconductor packaging. Traditional electronic packaging materials face limitations and process complexity, making low-temperature nanoparticle sintering an attractive option. With its benefits of low processing temperatures (< 0.4 Tm), exceptional electro-thermomechanical performance, and high process flexibility, this technology is gaining increasing attention, particularly in high-power electronics packaging applications. Over the past decade, silver (Ag) sintering technology has shown promise in the power electronics industry, serving as an effective solution for high-power die-attach. However, due to the high cost of materials, efforts have been directed towards pressure reduction and exploring alternative sinter materials to reduce overall process costs. In recent years, the concept of ’all copper (Cu) interconnect’ has transcended fromlow-power to high-power applications, with low-temperature Cu nanoparticle sintering showing substantial potential as a replacement for Ag in pressure-assisted sintering. Despite this promising avenue, the understanding of sintered Cu materials remains limited, primarily due to susceptibility to oxidation issues. Comprehensive studies comparing both sinter materials, extending beyond mere shear tests, are insufficient, leaving a significant gap in our understanding. Furthermore, methodologies for characterizing the sintered structure and providing detailed insights into its thermo-mechanical behavior are notably absent. In this dissertation, molecular dynamics (MD) simulation was employed at first to study the nanoparticles’ coalescence kinetics and mechanical and chemical performance of coalesced nanoparticles. A two-hemispherical nanoparticle model was built to simulate the impact of sintering temperature and pressure on low-temperature pressureassisted coalescence. The sintering dynamics and microstructure evolution were analyzed, including neck growth, shrinkage variation, grain boundary development, and dislocation activities. Furthermore, on the basics of pressure-assisted sintered nanoparticles, uniaxial tensile tests with a constant strain rate were employed to investigate its tensile performance. Subsequently, another mechanical nanoindentation simulation was implemented in a multi-nanoparticle sintered structure. The impact of indentation position and indenter size on the nanoindentation response was investigated. At the end of the first chapter, the chemical corrosion of sulphidation on multi-Ag nanoparticles’ sintered structure was simulated by the reactive-force-field (ReaxFF) MD method. The sulphidation on the dense Ag and porous sintered structures was compared and analyzed. Moreover, the sulphidation mechanism was revealed at an atomic level... ... Read more

Microwave Induced Plasma (MIP) is an advanced decapsulation tool developed by Jiaco Instruments. The goal of this thesis is to optimise the current MIP system. There are two directions: 1. Improve the etching rate. 2. Find selectivity between different materials (Si, SiO2, SiN). The experiments are divided into two parts in total, improved cavity and CF4-based MIP machine etching selectivity experiment. The cavity experimental results demonstrate that high input power is the route to optimising MIP efficiency. Etch experiments demonstrate that the CF4/O2 gas recipe is effective in achieving etch selectivity and that temperature is a key factor influencing these etch selectivities. ... Read more

This study deals with the challenge of warpage in power modules, vital components in the rapidly expanding electric and hybrid-electric vehicle industry. The variations in temperature during manufacturing, resulting in significant warpage changes, contribute to device cracks, delamination, and reduced reliability.
The primary focus is understanding and mitigating the warpage phenomenon in power module substrates. This warpage is induced by thermo-mechanical stresses during the assembly packaging process. The investigation begins by exploring the cause of warpage change by characterizing annealed copper properties and employing 2D finite element model (FEM) analysis. The study identifies plastic strain as the dominant cause of warpage change during process steps. Subsequently, a validated 3D FEM simulation model is developed to replicate practical annealing and sintering processes. Lastly, the project delves into factor analysis to identify critical variables influencing warpage. It underscores that balancing residual copper volume is crucial in warpage reduction. Additive and subtractive manufacturing techniques establish a correlation between the removal of copper volume and warpage reduction.

This project provides comprehensive insights into the manufacturing process of AMB substrate, warpage behavior, and effective strategies for reduction, constructing a solid foundation for future manufacturing and design. ... Read more

Board-level reliability (BLR) looks at the reliability problem in the package and PCB interconnection, which is an important topic in microelectronics. The current criterion in the BLR test is to look if the connection is open, which can only detect the failure and there is no available method that can detect the degradation of the solder joints. This project mainly focuses on the degradation process of solder joints in board-level vibration tests and thermal cycle tests.

Special methods and test programs are developed tailored for two test vehicles, and some of the test results are collected and analyzed. Assisted by the failure analysis technique, the physical change of solder joints can be observed.

Findings in this study show the parameter shift during the solder joint degradation and also the mathematic model that describes the relationship between the crack of the solder joints and resistance increment.
... Read more

This dissertation investigates copper sintering as a high-temperature die-attach technology for wide bandgap (WBG) power semiconductors such as SiC and GaN. WBG devices require advanced packaging solutions to maintain performance under high power, fast switching, and elevated temperatures. The study first employs molecular dynamics simulations to elucidate sintering mechanisms, microstructure evolution, and particle size effects, showing that applied pressure promotes plastic flow, densification, and pore reduction, while substrate pinning may induce residual stresses. Next, a self-developed Cu paste was fabricated and sintered under various temperature, pressure, and time conditions. Thermal and electrical conductivity, die shear strength, and microstructural evolution were evaluated, identifying 250°C, 3 min, and 20 MPa as an optimal processing window. Mechanical characterization including indentation hardness, elastic modulus, and creep behavior demonstrates the effect of process parameters on room-temperature properties and long-term reliability. Finally, pressure-assisted Cu sintering was applied to SiC power modules and compared with Ag-sintered modules. Both static and dynamic tests, including thermal cycling and high-temperature storage, confirm that Cu-sintered modules achieve equivalent performance and reliability at lower cost. The work establishes a systematic understanding of copper sintering processes, linking simulations, materials, processing, and application, providing a robust methodology for WBG power electronics packaging. ... Read more

Power electronics are an important technology used to convert electricity from a source like a battery or high voltage DC bus to more usable forms of electricity. This has to be done efficiently, reliably and without failures which is critical in applications like electric cars or datacenters. Power MOSFETs with upcoming SiC and GaN devices are an important building block used in these converters. Hence these power MOSFET devices have to be improved continuously to get a lower on resistance (R_DSon), a better thermal dissipation and lower parasitic losses. In this thesis we will take a look at the embedding of power MOSFETs inside a PCB to obtain these improvements. This new technology needs to be evaluated in terms of reliability, failure-modes and thermal/electrical performance. By designing,
manufacturing and testing a PCB with embedded devices. During manufacturing silver sintering has been used for attaching the die to a copper coin. In the end the manufacturing has been done successfully.
Testing showed an 18% lower R_DSon and a twice as low junction to ambient thermal impedance indicating a better performance compared to regular packaging. ... Read more