Fraunhofer Institute for Reliability and Microintegration

• Three novel custom-built in-situ setups for mechanistic studies of flame retardants • Detailed decomposition mechanisms of phosphoramidate flame retardant and transformation products • Transformation of phosphoramidates reduces their flame-retardant efficacy • Gaseous P(V) species do not form PO radicals • Substrate alters decomposition mechanism—PO radicals form exclusively on it Phosphorus-centered radicals such as PO • are often proposed as key species in gas-phase flame inhibition, yet their formation under realistic thermal decomposition conditions remains unclear. This uncertainty arises from the coupling of transport, pyrolysis, and mixing processes, as well as from fragmentation of radical ions in conventional mass spectrometry. Here, steady-state in situ 18 eV electron-ionization molecular-beam mass spectrometry is combined with TG–IR, thermogravimetric analysis, microcombustion calorimetry, standardized flame tests, and quantum-chemical/statistical-rate modeling to elucidate the mode of action of a tris-phosphoramidate flame retardant (TD). TD is studied neat and when applied to cotton, between 200 and 500°C. Control pyrolysis of triethyl phosphate (TEP) and diethyl phosphoramidate (DEPAm) is performed. Neat TD decomposes to TEP and ethene without forming PO radicals. In contrast, TD-coated cotton yields DEPAm, ethanol, and PO radicals above ∼400°C. Neither isolated TEP nor DEPAm forms PO • , and calculations show unimolecular PO • formation to be unfavorable. Removing TEP by brief curing worsens flame performance, and TG–IR/TGA/MCC indicate that formation of a cross-linked phosphorodiamidate network lowers condensed-phase acidity and FR-effectiveness. Thus, suggesting that PO • formation is substrate-mediated, most likely following bimolecular pathways involving substrate released radicals, without being the principal driver of FR-efficacy.

Conventional soldering processes in microsystem packaging often induce critical thermo-mechanical stresses, caused by mismatches in the coefficients of thermal expansion (CTEs) of materials such as silicon dies, molding compounds, and substrates. Reactive multilayer systems (RMS) offer a localized heat source that can significantly reduce such stresses, thereby enabling the bonding of heat-sensitive components. To expand the technological possibilities in fabricating heterogeneous microsystems, this study investigates RMS-based bonding of low temperature co-fired ceramics (LTCC) substrates. Two experimental series were conducted. In the first, both reactive foils and deposited RMS structures were used to bond relatively large chips measuring 10 mm x 10 mm under a bonding pressure of 1.5 MPa, with ignition triggered either thermally (up to 350 °C) or resistively, supported by a temperature of 200 °C. In the second series, smaller chips measuring 3 mm x 3 mm were bonded using a reactive foil to achieve a bonding pressure of 100 MPa. Here, ignition was triggered by an electrical spark, supported by a temperature of 160 °C. The bonding interfaces and metallurgical reactions were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The results reveal significant differences between bonding LTCC substrates using prefabricated reactive foils and deposited RMS structures: prefabricated foils generate higher peak temperatures, often exceeding the thermal limits of the metallization system, whereas deposited RMS structures produce lower peak temperatures and offer better compatibility due to the ability to tailor specific parameters.

This paper presents the development and miniaturization of a high-voltage DC-DC converter module designed to power FPGA (Field Programmable Gate Array) units and sensor nodes in next generation seismic streamer systems for marine seabed analysis. The module converts a fixed input voltage of 120 V into two regulated output voltages of 12 V and 3.3 V, enabling decentralized power supply along the streamer sections. A cascaded topology using two buck converters was selected based on efficiency and thermal performance simulations with PSpice. Initial validation was conducted on prototype boards, followed by the implementation of a miniaturization concept through embedding active and passive components into the PCB’s dielectric layers. The embedded module was designed with an opening in the center to give room for passing cables as the strain relief and data/power lines. The size of the module is limited by the diameter of the stream to ≤3.5 cm. Electrical measurements confirmed a reliable performance with efficiencies of up to 77.9%, supporting the suitability of the concept for future integration into the next-generation seismic ocean streamer.

The continuous growth of data-driven applications such as 5G fronthaul, memory disaggregation, and autonomous systems demands increasingly efficient and scalable network technologies. Optical switching is emerging as a key solution due to its potential for low-latency operation, high bandwidth, and energy efficiency. However, the integration of photonic and electronic components into compact and manufacturable packages imposes significant challenges, especially at high interconnect densities. This paper presents the development and validation of a fan-out wafer-level packaging (FOWLP) approach as part of the Horizon Europe project PUNCH. The work focuses on demonstrating a scalable and precise process flow capable of integrating multiple dies, including a photonic integrated circuit (PIC) placeholder and several electronic ICs (EICs), into a common package A critical aspect of the PUNCH approach is the development of a scalable, high-performance electrical and optical packaging solution based on a 200 mm FOWLP process. The concept includes a two-layer ERDL with line/spacing of 10/10 μm, allowing short interconnects between PIC and EICs, thereby improving overall performance and reducing power consumption. The package can be connected to a high-density substrate via soldering or substrate embedding. Both approaches are evaluated within PUNCH. For the optical interface, the implementation of an optical redistribution layer (ORDL) is investigated to facilitate scalable fiber coupling, further enhancing the practicality of FOWLP for optoelectronic integration. In this work, we present the first experimental results of a FOWLP demonstrator, where multiple EICs have been integrated with a large central die, resembling the PIC, to assess manufacturability, die placement accuracy, warpage control, and electrical performance.

This paper focuses on developing a contactless jetting technique to apply a novel microparticle-based silver (Ag) sinter paste suitable for pressureless sintering of miniaturized optoelectronic components. Traditional soldering methods encounter challenges at high temperatures, which can be addressed by employing advanced sintering techniques. In these techniques, the use of adapted materials plays a pivotal role in facilitating process adaptation. We detail the optimization of a contactless jet dispensing process and analyze the influence of key parameters, such as cartridge pressure, needle lift, rising time, and open time, on the precision and reliability of material deposition. We develop a volumetric flow model to characterize the jetting process, which enables fine control over the deposited dot volume and shape. Through experimental validation using square-footprint LED dice, we demonstrate a linear correlation between open time and dot volume while highlighting falling time as a free parameter affecting dot morphology. This methodology demonstrates the potential for the accurate and efficient application of sintering pastes in optoelectronic packaging and paves the way for future advancements in microelectronic assembly.

ABSTRACT The smartphone industry faces sustainability challenges from greenhouse gas emissions and resource depletion to growing e‐waste volumes. Circular business models have been proposed as a pathway to address these issues, yet their adoption remains limited, lacking integrative assessment frameworks that connect environmental performance with business viability. This study develops and applies such a framework combining life cycle assessment, monetisation of externalities via the eco‐cost method and a structured value alignment score. Using primary data from Fairphone 5 as a case study, four scenarios with increasing levels of circularity are analysed: (S0) a linear business‐as‐usual baseline, (S1) extended use with moderate user‐led repairs, (S2) long‐life use with intensified user‐led repairs and (S3) a product‐as‐a‐service model based on manufacturer‐led refurbishment. The results demonstrate that all circular business models outperform the linear baseline in terms of both environmental impacts and monetised externalities. Incremental models that extend product lifespans through user‐led repair (S1, S2) yield significant reductions in greenhouse gas emissions (up to −46%) and eco‐costs (−36%). However, their strategic alignment is constrained by weakened consumer value propositions and original equipment manufacturing profitability. In contrast, a product‐as‐a‐service model (S3) achieves superior outcomes by internalising life cycle responsibility and aligning incentives with longevity and service quality, reflecting systemic reconfiguration of value logics. The study contributes theoretically by operationalising an integrated framework that bridges environmental metrics with strategic value dimensions to evaluate circular business models. Practically, it provides firms a structured tool for evaluating trade‐offs and advancing scalable pathways towards a sustainable circular economy.

In this paper, quartz glass hybrid bonded wafer for antenna circuit substrates at D-band frequencies is presented. The structure of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$75 \mu \mathrm{m}$</tex> thickness quartz glass layer directly bonded onto single crystal silicon base substrate having air-filled cavity allows to realize low-loss, high gain and broad bandwidth antenna. This configuration doesn't contain organic material at all, therefore, it is expected to have better reliability against harsh environment and moisture. A prototype of the cavity-backed <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1 \times 4$</tex> serial-fed microstrip patch antenna array was fabricated using this hybrid bonded wafer and achieved 13 dB antenna gain and 30 GHz bandwidth at center frequency of around 140 GHz. The realization of a large cavity enclosing the entire patch array enables much better characteristics than with a single patch. These results proved its high potential for next generation automotive radar application, etc.