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 (LTCCs) 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 & times; 10 mm under a bonding pressure of 1.5 MPa, with ignition triggered either thermally (up to 350 C-degrees) or resistively, supported by a temperature of 200(degrees)C. In the second series, smaller chips measuring 3 & times; 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( degrees)C. The bonding interfaces and metallurgical reactions were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. 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.

Overheating poses major challenges in miniaturized electronics, especially as their power consumption increases. For this reason, thermal management is a necessity for efficient electronics, and its optimization is a central task in the design especially for miniaturized compact electronics. On the other hand, recovering this waste energy could be beneficial for battery-free electronics such as wireless sensors and devices located in remote environments, where the charging or changing of batteries are challenging and delicate tasks. Furthermore, batteries are known for their storage capacity degradation over time and environmental pollution. This paper presents the design, development, demonstration, and validation of an innovative 2-in-1 heat management and recovery system for autonomous electronic devices. The design incorporates the use of thermal vias as in-package heat management and vertical thermocouples, enabling simultaneously management and recovery of the heat emitted from a Si-chip. The proposed design is fabricated in Low Temperature Co-fired Ceramic (LTCC) technology, allowing the creation of a monolithic package containing miniaturized multilayer microvias in the range of 90 mu m using different materials to act as embedded thermal management and vertical thermocouples, simultaneously. The design consists of 20 lateral (Ag/Co) and 21 vertical (Ag/AgPd) micro-TEGs connected electrically in series in the system. The hybrid TEG is made by combining thick- and thin-film technologies, favoring the use of different materials and technologies with high power factors for further improvements in the field of thermal energy harvesting. The proposed design allows the management of 67 % of the IC temperature by reducing it from 246 C to 80 C using Ag and AgPd thermal vias. At the same time, the system recovers the lost thermal energy to generate 37.5 mu W of electrical power at a temperature difference of 58 C. The proposed approach allows simultaneously transitioning into green and sustainable battery-free electronics and enhances the devices reliability by maintaining thermal stabilization in a miniaturized devices using a monolithic package.

The deposition of reactive multilayer systems (RMSs) is investigated on low‐temperature cofired ceramic (LTCC) substrates having different surface morphologies. In this study, the morphologies of RMS layers that are deposited on glass‐ceramic LTCC substrates are analyzed. Different surface morphologies are prepared through pretreatments of the LTCC surface. The considered surfaces encompass an untreated natural LTCC surface, a modified sintered LTCC surface by laser ablation, a surface with a deposited metallization layer, and finally, a surface with an additional solder layer put on the deposited metallization layer. The different pretreatments lead to significant differences in the roughness of the LTCC substrates, resulting in different reaction velocities and peak temperatures on the various surface morphologies after the RMS's reaction. As a result, different grades of structural integrity (liftoff, crack formation) between the reacted RMS layer and the LTCC are observed.

Numerical computational fluid dynamics simulations have been performed on 2D sandwich models to compare the performance of low-temperature cofired ceramics (LTCC)/LTCC and Si/Si sandwiches used in reactive bonding. In the sandwich model layers of solder, silver and a reactive multilayer used to bond the substrates are modeled. Additional to this, the surrounding air environment is also modeled. For simulating the heat released by the multilayer system, a user-defined function in the form of a square wave is written for the heat source with a defined width, corresponding to the reaction width, and this propagates at a fixed speed. Two sandwiches, one with LTCC/LTCC, and the other with Si/Si, are simulated and their response analyzed in terms of the solidification/melting of the solder and their respective time-temperature histories. In this article, it is shown that numerical computational fluid dynamics simulations reveal that low-temperature cofired ceramics (LTCC)/LTCC assemblies experience significantly higher temperatures than Si/Si during reactive bonding, due to LTCC's lower thermal conductivity. This leads to prolonged solder melting, increased stresses, and potential bonding issues. In these findings, it is suggested that optimizing solder thickness and reactive multilayer system deposition could address these thermal challenges, which are difficult to measure experimentally.image (c) 2024 WILEY-VCH GmbH

This publication introduces a new interposer made from a thin glass substrate and a multilayer LTCC compound. Combination of these two material classes into an interposer substrate enables the application of thin-film and thick-film technology in one substrate. In this study thin $(\mathbf{100}-\mathbf{200}\ \boldsymbol{\mu} \mathbf{m})$ Borosilicate glass AF45® is applied. The glass substrate includes through glass vias, filled with Au-paste to provide the electrical connection from the glass surface to the underlying electrical structures on the LTCC uppermost layer. The multilayer LTCC green tapes DuPont™ 9K7 are prepared with ground structures on the uppermost layer. After the final lamination of the LTCC-multilayers to the glass, a sintering step causes the mechanical joint of the two materials as an interposer substrate. To demonstrate the Glass-LTCC-Interposer for HF-applications, microstrip line, coplanar waveguide and ring resonator were simulated, designed and fabricated. For the fabrication of fine lines and spaces, the semi-additive technology applying Auresinate paste in combination with Au-galvanic deposition was utilized. Finally, the realized structures were characterized up to 60 GHz. The HF-investigations of the realized structures on the glass-LTCC-interposer confirm the accuracy of this structuring method. Furthermore, these investigations approve the new interposer as a proper substrate for HF-applications.

To improve the understanding of reactive multilayer systems as a joining process computational fluid dynamics (CFD) simulations have been performed and compared with experimental measurements made using a pyrometer. These CFD simulations consist of a shoebox model which contains different layers. The layers in the model are an Ni/Al reactive multilayer, low temperature co-fired ceramic (LTCC) substrate and the surrounding air environment. To simulate the heat released by the multilayer system, a user defined function of probability density function (PDF) form was written for the heat source. The peak energy intensity, reaction width and reaction speed can be controlled via the PDF to adapt the simulation to the real model.

This paper discusses the application of reactive bonding for the area of L ow Temperature Cofired Ceramics (LTCC) assemblies. The goal is to reduce the thermal-mechanical stresses during soldering by transferring heat only locally to the solder joints without heating the entire component. Such a reactive multilayer system (R MS) consists of alternating nanolayers (10 - 300 nm) of at least two metal components which produce an exothermal reaction after ignition. Although the deposition of an RMS is established on silicon substrates for the use in micro-electromechanical systems (MEMS), it is very challenging to create them on LTCC substrates. One of the main obstacles is to over come all issues connected with the significant roughness, because it is not an optimum territory to deposit nanolayers. In this paper, different methods like chemical mechanical polishing (CMP) and laser ablation, to modify the surface morphology, are presented. A direct relation between the morphology and the exothermal reaction can be observed. In addition, 3-D Computational Fluid Dynamics (CFD) simulations were conducted to analyze the process in more detail. These simulations make use of a shoebox model with different layers and an adjustable user-defined function for the heat release of the RMS to adapt the reaction front velocity and the combustion temperature to the experimental values.

In order to introduce new bonding methods in the area of electronic packaging a theoretical analysis was conducted, which should give substantial information about the potential of reactive multilayer systems (rms) to create sufficient local heat for joining processes between silicon chips and ceramic substrates. For this purpose, thermal CFD (computational fluid dynamics) simulations have been carried out to simulate the temperature profile of the bonding zone during and after the reaction of the rms. This thermal analysis considers two different configurations. The first configuration consists of a silicon chip that is bonded to an LTCC-substrate (Low Temperature Co-fired Ceramics) using a bonding layer that contains an rms and a solder preform. The reaction propagation speed of the reactive multilayer was set to a value of 1 m/s, in order to partially melt a solder preform underneath a silicon chip. The second configuration, which consists only of the LTCC-substrate and the rms, was chosen to study the differences between the thermal outputs of the two arrangements. The analysis of the CFD simulations was particularly focused on interpretations of the temperature and liquid fraction contours. The CFD thermal simulation analysis conducted contains a melting/solidification model which can track the molten/solid state of the solder in addition to modelling the influence of latent heat. To provide information for the design of a test-substrate for experimental investigations, the real behaviour of Pt-100 temperature probes on the LTCC-substrate was simulated, in order to monitor an actual bonding in the experiment. All simulations were carried out using the ANSYS Fluent software.

This paper presents the characterization of Al-Ni reactive multilayer systems (RMS) sputtered on LTCC substrates featuring different surface morphologies. All samples were able to ignite, followed by self-propagating exothermic reaction along the LTCC substrate surfaces which were simultaneously monitored using high velocity pyrometer and camera measurements. The adhesion of the ignited RMS was improved on LTCC substrates having surface roughness more than about 600 nm. A reduced influence of the substrate roughness on the measured temperatures was detected for these samples as well as measurements of their reaction velocities clarify a higher impact of different surface roughness. The promising results suggest that the reaction properties and the wave propagating directions can be controlled during reactive bonding or soldering of several applications in the field of electronic packaging by manipulating the substrate morphologies, e.g. using laser ablation on bonding areas.

This paper presents passive components and embedded low-pass filter (LPF) using Low Temperature Co-fired Ceramic (LTCC) materials and advanced picosecond laser structuring. These components and the LPF are well suited for multilayer System-in-Package (SiP) and Multi-Chip-Module (MCM) applications, e.g. wireless mobile applications focusing on 5G frequency bands. The passive components were measured, working up to 40 GHz and offering good RF performances. The LPF structure, consists of these passives, achieved a measured insertion loss lower than 0.6 dB up to 20 GHz, and a return loss of less than -13 dB in the pass-band of the LPF. The 3 dB frequency was 27.4 GHz. The whole LPF occupies a substrate area of 1.3 × 0.7 × 0.09 mm 3 without probe tip ports and transitions. The LPF structures in a LTCC package suit well for 5G-band applications due to the compact dimensions and the good RF performance.

In this paper we describe the architecture and design of a non-blocking 4×4 switch matrix module for mm-wave satellite communications, where flexible signal distribution becomes increasingly relevant. Following the successful on-orbit verification of a blocking 4×4 switch matrix for a reconfigurable Ka-band input multiplexer aboard the planned German Heinrich Hertz mission, the non-blocking switch matrix module offers relevant advantages in terms of signal routing and total power consumption. The non-blocking switch matrix utilizes hybrid-integrated precision laser-trimmed Wilkinson power splitters and low microwave-loss absorptive transistor-based SPST-switches.

3D Multi Material (3D mm ) printing of LTCC materials in combination with functional metallic inks based on powder bed structuring is a new and innovative technology which enables the fabrication of electronic components and upcoming circuits, cost efficiently in small series, offer rapid prototyping capabilities as well as will feature less geometrical restrictions during design process compared to other common technologies soon. Recent material compositions of the ceramic powder mixture, binder and functional ink were developed and utilized successfully using an experimental 3D printer. Characterizations of 3D printed ceramic compounds and functional inks exhibit adequate physical and electrical properties. Furthermore, the material powder composition facilitates compatibility to SMT (surface mounting technology) and to common packaging technologies applying a screen printing step which enhance additional functionality of 3D printed electronic devices.

This chapter discusses the general requirements for microwave applications. Substrates for microwave circuits are required to have a low dielectric loss tangent (tan δ < 0.001 across the range of frequencies of interest) and high frequency and temperature stability of permittivity. Multilayer ceramic technologies such as low temperature co-fired ceramic (LTCC) offer options to implement three-dimensional waveguide, biasing, and control structures and components in addition to better shielding opportunities in the substrates. The chapter provides an overview about different technologies to structure the lateral conductor pattern on LTCC tapes and substrates. The use of LTCC is a promising technology for the realization of satellite payload modules and subsystems, since it provides good microwave performance, multilayer capabilities with three-dimensional microwave circuitry and high wiring densities, moderate production costs, and hermetic packaging. Cavities in the LTCC are used to align the monolithic microwave integrated circuits (MMIC) surface to the substrate surface.

The paper presents a novel manufacturing process which offers a high structure resolution and a high density of electrical contacts on Low Temperature Co-Fried Ceramic (LTCC) for silicon chip assembly. To provide of the small pitch of contacts screen printed gold thick films are laser structured with a picosecond laser ablation machine. Laser structured thick film contact pads have dimensions of 59 μm by 59 μm and laser drilled 50 μm vias are used to provide vertical electrical contacts to laser structured thick film lines on the inner layers. The internal structures are laser structured to provide a high line density. To demonstrate the usability of the laser structured contact pads for the chip assembly a silicon test chip is manufactured in thin film technology having gold pads with dimension of 60 microns by 60 microns. Gold stud bumps were placed on the chip pads using a thermosonic ball-wedge bonder and a 25 μm gold wire. The test chip is mounted on the laser structured surface of the LTCC by means of thermo-compression flip chip bonding. A daisy chain structure was realized on the surface of the test chip and on the LTCC to measure the electrical interconnections between the test chip and the LTCC package. The geometrical shape is measured by laser scanning microscopy (LSM). To ensure the functionality and to exclude internal failures (e.g. shorts) the samples are scanned with X-ray inspection.

Highly substrate integrated microwave circuits for space applications require a high metal pattern accuracy for transmission line structures and components. Within this work an embedded 60 GHz strip line filter is used as a demonstrator device to compare four fine line structuring processes for multilayer Low Temperature Cofired Ceramics (LTCC). Fine line screen printing (type I), resinate thin film patterning (type II), laser patterning in green state (type III) and laser patterning of fired screen printed thick films (type IV) are compared regarding pattern tolerances, electrical performance and process implementation capability. All substrates were manufactured using a subsequent tape-on-substrate process (ToS) to embed the filter. The filter measurements exhibit an insertion loss of 4 dB at centre frequencies of nearly 60 GHz for all variations.

Polarimetric radio wave processing becomes of increasing interest for very high-data rate wireless transmission and for short-range radar at millimeter-waves (mm-W). This goes along with the huge bandwidth of 7 to 9 GHz, which is available worldwide in the 60 GHz unlicensed band. In this paper, we propose a 60 GHz ultra-wideband (UWB) polarimetric multiple-input-multiple-output (MIMO) sensing system architecture and polarimetric signal processing for short-range communications and radar. Demonstration measurements were made by using an UWB radar interface. By measurements in multipath rich environments it is demonstrated that tap-wise polarimetric filtering in delay domain can enhance the 60 GHz link budget by filtering some paths and then reducing shadowing due to human activity. Additionally, optimum MIMO polarimetric filtering is proposed to reduce heavy clutter for mm-W radar, increasing by about 30 dB the signal-to-clutter-plus-noise-ratio.

Ultra-wideband (UWB) techniques are suitable for wireless broadband short range communication as well as precision radio sensors. The internationally available license-free upper ECC-band (Electronic Communications Committee) provides a bandwidth of 2.5 GHz in the range from 6.0 - 8.5 GHz. This paper presents a specialized antenna optimized for remote sensing in this frequency band. The antenna features compact dimensions, high robustness versus production tolerance, and will be utilized for remote monitoring of vitality aspects of elderly people at home.

This article presents a low‐loss fully embedded bandpass filter (BPF) using low‐temperature co‐fired ceramic (LTCC) for multilayer System‐in‐Package (SiP) and Multi‐Chip‐Module (MCM) applications, for example, wireless applications for the unlicensed 60 GHz band. Critical coupling gaps of conventional bandpass filters in this frequency range, which are not suitable for screen printing, could be eased by introducing coupling plates in adjacent layers. The four‐layer BPF is designed for Du Pont's 9k7 LTCC system, and occupies a substrate area of 5.6 × 2.1 × 0.42 mm3 including transitions and a shielding via fence. The filter, including the two grounded coplanar waveguide transmission line (CPWg) to stripline transitions, has a measured insertion loss of 1.5 dB at the center frequency 58 GHz, and a return loss of less than −10 dB over the 11 GHz 3 dB passband.

This paper presents two different wire-bond transitions, a wideband from DC up to 67 GHz and a narrowband, working at the free-licensed ISM band around 60 GHz, which are suitable for multilayer System-in-Package (SiP) and Multi-Chip-Module (MCM) applications. An aluminium oxide ceramic (Al2O3) RF test chip is assembled in a small cavity on the low temperature cofired ceramics (LTCC) material DuPont 9k7. An automatic ball-wedge bonder is used for thermosonic gold wire bonding. A return loss better than -10 dB from DC up to 54 GHz for the wideband and better than -10 dB for the narrowband transition, having a 6 GHz bandwidth in the 60 GHz ISM band, as well as an insertion loss of <;1 dB at 60 GHz were achieved for both transitions during measurements.

This paper presents two different novel methods to manufacture optimized cavity structures, which are suitable for multilayer System-in-Package (SiP) and Multi-Chip-Module (MCM) applications, in the new low temperature cofired ceramic (LTCC) material Du Pont 9k7. In contrast to standard manufacturing, the improved DP 9k7 cavities show almost perfectly orthogonal cross sections and straight edges, achieved by applying special cavity inlays or cast silicone. Ball-wedge bond wires and wedge-wedge ribbons are implemented directly to the cavity rim successfully. Therefore, these cavities are suitable for very short bond wires in complex RF systems and the introduced techniques are very promising for future applications using DP 9k7.