Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    Investigation and Modeling of Etching Through Silicon Carbide Vias (TSiCV) for SiC Interposer and Deep SiC Etching for Harsh Environment MEMS by DoE
    ( 2022)
    Mackowiak, Piotr
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    Erbacher, Kolja
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    Schiffer, Michael
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    Manier, Charles-Alix
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    Töpper, Michael
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    Ngo, H.-D.
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    Schneider-Ramelow, M.
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    Lang, K.-D.
    This article presents prime results on process development and optimization of dry etching of silicon carbide (SiC) for via formation and deep etching for SiC-based microsystems. The investigations and corresponding results of the process developments enable the first realization of a full SiC-based technological demonstrator composed of a SiC-interposer with a flip chip mounted deep etched micro electromechanical system (MEMS) SiC Device. By optimizing the process, etch depth of 200 μm with an etch rate of up to 2 μm /min can be achieved for via etching. In addition, a design of experiments (DoEs) with a total of 29 experiments with seven factors was done to characterize the deep etching of large areas into the SiC. Hereby, vertical sidewalls with low micromasking, low microtrenching and an etch rate of up to 4 μm /min could be achieved. The findings and optimized processes were implemented to develop on the one hand a 200- μm -thick SiC interposer with copper metallization. On the other hand, a SiC-MEMS Device was manufactured with a deep etched cavity in SiC bulk wafer forming by the end a 50- μm thin membrane. The results demonstrate the ability of etching monocrystalline SiC with a high etch rate, enabling new fundamental topologies/structures and packaging concepts for harsh environments MEMSs and high-power electronics. The developed etching technologies demonstrate and enable various applications for 3-D Integration with wide bandgap substrates taking advantage of the superior electrical and mechanical properties of SiC.
  • Publication
    High-k dielectric screen-printed inks for mechanical energy harvesting devices
    ( 2022)
    Leese, H.S.
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    Tejkl, M.
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    Vilar, L.
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    Georgi, L.
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    Yau, H.C.
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    Rubio, N.
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    Reixach, E.
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    Buk, J.
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    Jiang, Q.
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    Bismarck, A.
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    Hahn, Robert
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    Shaffer, M.S.P.
    There are a range of promising applications for devices that can convert mechanical energy from their local environment into useful electrical energy. Here, mechanical energy harvesting devices have been developed to scavenge low-frequency energy from regular biomotion such as joint movement and heel strike. Specifically, these harvesters exploit novel printed nanocomposite dielectric inks in combination with commercially available conductive elastomers to develop a low cost, high performance embodiment of a variable capacitance mechanism device. The filler of the nanocomposite dielectric ink, consists of high-k dielectric nanoparticles (barium titanate and strontium doped barium titanate) functionalised with poly(methyl methacrylate) to improve the interface with the epoxy matrix. Characterisation by thermogravimetric analysis coupled to mass spectrometry and X-ray photoelectron spectroscopy confirmed the successful covalent grafting of up to ca. 16 wt% poly(methyl methacrylate) onto the dielectric nanoparticle surfaces, with a thickness of approximately 14 nm, measured by transmission electron microscopy. The dielectric inks were screen printed onto copper-polyimide foils, resulting in large area and flexible five to twenty-micron thick films with dielectric constants up to 45. Nanoparticle polymer functionalisation improved the homogeneity and stability of the inks. Using these screen-printed dielectrics with the commercial conductive elastomer, the mechanical energy harvester prototype demonstrated high mechanical cycling stability and low leakage current. It provided a promising power density of 160 μW cm-3, at low frequency (0.5 Hz), over a 1000 cycles, making the device suitable for wearable applications. This type of harvester has two advantages over the state of the art: it is mechanically flexible for integration into wearables and can be produced at low cost with printing methods. This journal is
  • Publication
    Experimental and simulative study of warpage behavior for fan-out wafer-level packaging
    ( 2022)
    Dijk, Marius van
    ;
    Huber, Saskia
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    Stegmaier, Andreas
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    Walter, Hans
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    Wittler, Olaf
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    Schneider-Ramelow, M.
    Controlling warpage effects in fan-outwafer-level packaging (FO-WLP) is of key importance for realizing reliable and cost-efficient system in packages (SiPs). However, warpage effects can occur during the manufacturing process, caused by a combination of different processing temperatures, different materials, and the changing properties of the materials (e.g. polymerization and related cure shrinkage). One approach to controlling warpage could be realized by assessing a numerical simulation workflow of the FO-WLP process chain, in which the relevant material properties and geometry are used as input. Since there are many different steps included in the FO-WLP process, accompanied by complex material behavior, this workflow is not straight-forward. In the present paper, the first FO-WLP processing steps are investigated in detail by performing extensive thermo-mechanical material characterization, temperature-dependent warpage measurements, and numerical simulations. The investigation focuses on two epoxy mold compound (EMC) materials with completely different physical properties. The warpage measurements of bi-material (EMC and silicon) samples reveal an irreversible effect after passing certain processing temperatures, which are significant for final warpage at room temperature. A new approach to measuring the coefficient of thermal expansion (CTE) is discussed, using a temperature profile based on the temperature in the process, instead of the three identical temperature ramps suggested by the typical standards. This new approach makes it possible to determine possible shrinkage effects. Within the simulation model, the hysteresis effect observed in the experiment is taken into account by adding a shrinkage strain as well as changing the CTE values during the process. A very good agreement between the experiment and simulation is achieved, which is shown for several demonstrators with different epoxy mold compound materials and thicknesses.
  • Publication
    Low-Temperature Processible Highly Conducting Pastes for Printed Electronics Applications
    ( 2022)
    Scenev, V.
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    Szalapak, J.
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    Werft, Lukas
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    Hoelck, Ole
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    Jakubowska, M.
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    Krshiwoblozki, Malte von
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    Kallmayer, Christine
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    Schneider-Ramelow, M.
    Scalable additive manufacturing of printed electronics is a growing field accompanied by increasing demands for reliable and integrable functional flexible printed electronic devices. Herein, a novel type of electrically conducting silver-based pastes for additive manufacturing is demonstrated. These pastes are designed for stencil- and screen-printing and can be post-processed at very low temperatures, at ambient. Furthermore, printed lines made with the pastes exhibit an electrical sheet resistance below 60 mΩ sq-1 even after room temperature and only 25 mΩ sq-1 after two minutes of curing at 90 °C.
  • Publication
    Interconnecting embroidered hybrid conductive yarns by ultrasonic plastic welding for e-textiles
    ( 2022)
    Dils, Christian
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    Kalas, D.
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    Reboun, J.
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    Suchy, S.
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    Soukup, R.
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    Moravcova, D.
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    Krshiwoblozki, Malte von
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    Schneider-Ramelow, M.
    This article presents a novel approach for the electrical interconnection of embroidered conductive yarns with each other at defined cross-points using ultrasonic spot welding. The electrically conductive yarns are made of silver-coated copper microwires plied with polyester filament fibers into a hybrid embroidery yarn. In this study we evaluated the influence of different material properties (number of microwires of conductive yarn, fabric substrate, and adhesive film), the embroidery designs of contact pads, and the main parameters of the welding process (energy, force, amplitude, and tools) on the welded interconnection. The results were evaluated by the process yield and the contact resistance of the welded contacts. The electrical contacts were then tested for long-term reliability (elevated temperature and humidity, temperature shock change, bending, washing and drying) and analyzed. In addition, the contacts were examined with scanning electron microscopy (SEM) and micro-computed tomography and in the form of cross-sections with optical and SEM techniques to discuss interconnection and failure mechanisms. The results show that ultrasonic spot welding can enable the production of highly reliable interconnections of textile-integrated conductive yarns with contact resistances of a few milliohms that are resistant to mechanical, environmental, and washing conditions, leading to potential new manufacturing processes of e-textiles.