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PublicationWafer Level Capping Technology for Vacuum Packaging of Microbolometers( 2023-08-03)
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PublicationOn-chip integration of optical microbottles for biosensing( 2023)In the last decades, coupling strategies of optical microresonators have been intensively explored to develop highly sensitive and label-free miniaturized biosensors. This work presents an innovative semi-automatic assembly approach for glass microbottles on a photonic integrated circuit (PIC) with single-mode waveguides. Microbottles are extraordinary whispering-gallery-mode (WGM) structures with additional axial confinement of the light along the bottle shape. A high dense spectrum of resonances varying along the bottle curvature is typically observed. To excite these resonances, the evanescent field of waveguides is used, as it provides direct evanescent interaction, integration of multiple structures and mass production. Initial coupling tests in air yielded a Q factor of 104 at 1550 nm by employing an active alignment setup and a customized gripping tool. Lateral coupling tolerances of Δx = ±50 μm and Δy = ±2 μm for a bottle diameter of 180 μm were also found. An existing assembly machine including a visual system, alignment system, high precision glue dispenser and UV light was used for the identification, placement and fixation of microbottles. A highest Q factor of 105 was determined after the attachment of a microbottle. Similar results were obtained with bio-chemical modified samples. A laser cutting method was also applied for reducing the fiber length of the microbottle. In this way the hybrid PIC can be compatible with microfluidics. The dedicated assembly process is a promising tool to bring optical resonators into practical use for label-free biochemical sensing but also for other applications such as quantum sensing and communication.
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Publication3D Thin Film Metrology without Cross-Sectional Sampling( 2023)Conformal coating in high aspect ratio substrates is a crucial factor in the development of next generation 3D semiconductor devices. Conventional approaches of employing vertical high aspect ratio substrates for conformality studies have usually been restricted by the tedious analytical technique requirements. Here, we present an innovative solution for this problem by introducing lateral high aspect ratio substrates; PillarHall® LHAR4 silicon test chips together with simple, fast and accurate metrology tools. The current work also reports the non-organic adhesive approach for the integration of these chips in 300 mm wafer aiming at wafer level processing.
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PublicationFinite Element-Based Monitoring of Solder Degradation in Discrete SiC MOSFETs( 2023)Many of the reliability methods used in power electronics require extensive experimental data, resulting in long product design cycles. This work focuses on developing a simulation-driven approach to assess the reliability of a discrete silicon carbide MOSFET by monitoring 2nd level solder degradation under power cycling in the thermal and thermo-mechanical domains. Active power cycling tests are performed to determine the loading condition at which end-of-life is reached due to a 20% increase in thermal resistance. Numerical analysis using finite element simulations is conducted to gain a physical understanding of the failure criterion from a mechanical point of view. The proposed methodology aims to accelerate the quality assurance and product qualification processes of discrete power electronic devices.
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PublicationRealization, multi-field coupled simulation and characterization of a thermo-mechanically robust LiDAR front end on a copper coated glass substrate( 2023)The thermo-mechanical robustness of Advanced Driving Assistance Systems is crucial to leverage the growing market of automated driving. Especially in case of optical sensors, such as camera and Light Detection and Ranging (LiDAR) sensors, the thermo-mechanical state of the sensor front end is closely coupled with its optical performance. Deformations in the optical path, consisting of the lens elements and imager, can cause major performance degradation like defocus. Additionally, the big Coefficient of Thermal Expansion (CTE) mismatch between the commonly used FR4 substrate and large silicon (time-offlight) imagers, leads to extraordinary mechanical stress in the respective interconnects if operated under harsh automotive temperature conditions. Hence, within this work, an optical LiDAR front end on glass is realized in the form of reducedcomplexity modules (RCMs) of the transmitter and receiver path. The transmitter RCM, consisting of a variety of small glassmounted high power Vertical Cavity Surface Emitting Laser (VCSEL) diodes is tested and evaluated with respect to lifetime reliability, whereas the receiver RCM, consisting of a glassmounted large-scale imager, is firstly investigated with regard to cooling under high temperature operation.
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PublicationA Closer Look to Fan-out Panel Level Packaging( 2023)Fan-out Wafer and Panel Level Packaging are two of the dominating trends in microelectronics packaging. Both approaches with different flavors as RDL last face-up or face-down have reached maturity and are introduced in high volume manufacturing. This paper discusses warpage in detail as one key challenge in fan-out packaging and how to influence the warpage during processing of a reconfigured panel for Chip first / RDL last approach.
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PublicationDetermination of Lemaitre Damage Parameters for Al H11 Wire Material( 2023)The quality of wirebond interconnects is characterized by shear and pull tests. For such a simulation we need an adequate damage model, since a purely elasto-plastic model fails to give the full picture [1]. For the description of damage, the Lemaitre damage model is selected, because this model is already used in comparable blanking simulations [2]. In addition, the main damage-driving factor of this damage model is the equivalent plastic strain, which is known to be the suitable failure criteria for ductile materials. The model, introduced by Lemaitre in 1985, is for isotropic ductile damage [3]. It has been used and extended in many other works. Still, more than three decades later, modelling free evolving multiaxial damage is often a more scientific topic and has not yet been proven a sufficient engineering tool to investigate destructive tests by numerical simulation. Reducing the amount of tests has been and still is a demand to save time in the design process. Therefore, it is needed to further investigate the capabilities of such damage models on complex applications. Indeed, the damage parameters first need and will be determined in this study for the material used in the application.
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PublicationTSiCV Based Silicon Carbide Interposer Technology( 2023)This paper describes the research on the development on SiC Interposer technology with Through SiC Vias (TSiCV). It demonstrates a SiC Interposer with the Flip-Chip assembled Chips with different thicknesses. It gives an overview over the different approaches of via formation and describes the fabrication of a SiC Interposer. It highlights the differences between the via formation between silicon and silicon carbide. The etching of SiC itself is described and two different isolation methods for the vias are discussed. Furthermore, two different methods to access the backside of the via are presented. The via diameters between 40 μm to 120 μm have been investigated and etch rates of up to 2 μm/min were achieved. A discussion about the possibilities and limitation of the different approaches are presented.
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PublicationModification of Prony Series Coefficients to Account for Thermo-Oxidative Ageing Effects within Numerical Simulations( 2023)Ageing effects potentially limit the lifetime of electronic device and systems. To prevent failure during the desired lifetime, knowledge about the used materials is of key importance. Moreover, the change of the used materials during the expected lifetime and its impact on the functionality of the product needs to be considered.In this study, a simulation approach is discussed that can consider ageing effects caused by oxidation at elevated temperature of a printed circuit board material used for radio-frequency applications. By state-of-the-art thermomechanical material characterization, the properties are derived of samples that were stored at elevated temperature (175°C) for up to 1000 hours.Within the simulation workflow, the properties of the different aged states are defined by modifying the pristine properties. Four exponential functions are derived modifying the initial modulus, the characteristic time constants, the shift function and the coefficient of thermal expansion, all in dependency of ageing time.This new approach is compared with an approach where for each aged state a different material set is defined. The deviation between experiment and simulation becomes larger with this new approach, which was expected, since much less detailed information about the material properties are being used. However, the new approach has a major benefit of opening up the opportunity to, for example, perform sensitivity analyses in a very simple manner. Additional benefits are the gained knowledge on how the material is changing over time and the possibility to extract material properties for aged times that are not being measured.
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PublicationWarpage of Fan-Out Panel Level Packaging - Experimental and Numerical Study of Geometry and Process Influence( 2023)In order to reduce waste and cost, the trend in Fan-Out Packaging is the move to rectangular panels instead of circular wafers [1]. These panels can be made in larger formats and better utilize the space due to the rectangular shape. However, with the larger format, warpage of the panels increases and remains a challenge in Fan-Out Panel Level Packaging (FOPLP) production. Warpage occurs mainly due to the multitude of materials that undergo multiple production steps at different temperatures, which leave residual stresses induced by mismatch of thermal strains and strains due to chemical processes (e.g. cure shrinkage). These superimposed effects and the complex material behaviour still make it challenging to predict warpage numerically and control warpage during production [2], [3]. In this work, warpage of nine different variants of a 300 × 300 mm2 panels with dummy dies have been investigated experimentally and numerically. It has been shown that the numerical model can replicate warpage of the panels and the potential for numerically supported warpage adjust steps in the fabrication of the panels has been demonstrated.
