Thin Ceramic Substrate Research Articles

Analysis, Design and Realization of a Furnace for In Situ Wettability Experiments at High Temperatures under X-ray Microtomography.

In this study, we analyzed the problem of a compact furnace, to be used for in situ experiments in a cone-beam X-ray microtomography commercial system. The design process was accomplished and outlined through its main steps, until the realization of a prototype. The furnace was conceived to carry out wettability experiments at temperatures up to 700 °C and under inert atmosphere on sessile droplets of a molten metal alloy, with a few millimeters diameter, posed on a thin ceramic substrate. X-ray imaging of the molten droplet is expected to permit an accurate three-dimensional reconstruction of the droplet profile and a robust estimation of the related quantities (such as the contact angle and the surface tension) utilized for the assessment of metal-ceramic joints by brazing. The challenges faced during this project, mostly related to the constraints of the setup, and the novel solutions implemented were discussed also with the support of analytical and numerical tools, in terms of interaction of X-rays with matter, geometry and working principle, heat transfer and insulation, material selection.

Influence of structural factors on thermal stress in skutterudite-based thermoelectric module

Thermoelectric (TE) modules for power generation usually operate under high temperatures and large temperature differences, which inevitably introduce thermal stress in the modules. Suppressing the thermal stress is then one of the important issues for improving the service reliability of TE modules. In the past decades, various approaches have been developed for the design optimization of TE module primarily being focused on the enhancement of conversion efficiency, while the influence of structural factors on the module’s mechanical reliability is often overlooked. In this work, we proposed a multi-objective optimization strategy by using the finite element method to evaluate the structural reliability of a TE module, which integrates the module mounting mode, configurational structure of ceramic substrates, thickness of ceramic substrates and electrodes, cross-sectional shape of TE legs, and gaps between [Formula: see text]- and [Formula: see text]-type legs. As a typical sample, the thermal stress of an 8-pair skutterudite (SKD)-based TE module with the framework dimensions of 20 × 22 × 12 mm3 was well studied under the service conditions. The results reveal that a split structure of ceramic substrates and a pressing mounting mode with 2 MPa pressure on the module’s hot-side can significantly reduce the thermal stress in the module. Meanwhile, increasing the gap distance between [Formula: see text]- and [Formula: see text]-type legs, rounding the square column shaped legs, using thin ceramic substrate and thick electrode also can relieve the thermal stress somewhat. The simulation gives a comprehensive solution to reduce the thermal stress and enhance the module’s service reliability for the practical applications through structure optimization.

Inkjet Printing on a New Flexible Ceramic Substrate for Internet of Things (IoT) Applications.

In this article, the optimization of printing properties on a new, flexible ceramic substrate is reported for sensing and antenna applications encompassing internet of things (IoT) devices. E-Strate® is a commercially available, non-rigid, thin ceramic substrate for implementing in room temperature and high-temperature devices. In this substrate, the printing parameters like drop spacing, number of printed layers, sintering temperature, and sintering time were varied to ensure an electrically conductive and repeatable pattern. The test patterns were printed using silver nanoparticle ink and a Dimatix 2831 inkjet printer. Electrical conductivity, high-temperature tolerance, bending, and adhesion were investigated on the printed samples. The three-factor factorial design analysis showed that the number of printed layers, sintering temperature, sintering time, and their interactions were significant factors affecting electrical conductivity. The optimum printing parameters for the thin E-Strate® substrate were found to be 20 μm drop spacing, three layers of printing, and 300 °C sintering temperature for 30 min. The high-temperature tolerance test indicated a stable pattern without any electrical degradation. Repetitive bending, adhesion test, and ASTM tape tests showed adequate mechanical stability of the pattern. These results will provide insight for investigators interested in fabricating new IoT devices.

Early-Stage Detection of Melanoma Skin Cancer Using Contactless Millimeter-Wave Sensors

Studies show that the early (stage I) diagnosis of cancer increases the survival rate of patients, and significantly reduces treatment costs. Millimeter-wave radars can detect skin tumors based on the difference between the electrical properties of melanomas and healthy skin tissues. This paper proposes a low-power multitone continuous-wave radar design at 77GHz for biomedical imaging applications, to be used for skin cancer detection. The sensor implementation is based on a low-cost Miniature Hybrid Microwave Integrated Circuit (MHMIC) design. The entire sensor was integrated on a 0.127mm thin ceramic substrate. Two 16-element patch antenna arrays are implemented in the transmitter and receiver modules. The receiver is a six-port homodyne quadrature down-converter. The integrated power detectors are fabricated using HSCH-9161 Schottky diodes. The sensor was encapsulated in a metallic fixture with dimensions 35 by 45mm. Two cascaded amplifier circuits are designed and implemented for amplifying baseband voltages at the output of each power detector. The proposed radar design has the ability to detect the dielectic properties of tissues, making it suitable for the detection of melanomas with an accuracy on the order of tens of microns.

Broadband <inline-formula> <tex-math notation="LaTeX">$E$ </tex-math> </inline-formula>-Band WR12 to Microstrip Line Transition Using a Ridge Structure on High-Permittivity Thin-Film Material

A rectangular WR12 waveguide to microstrip line (MSL) transition using a very thin high-permittivity ceramic substrate ( $\varepsilon _{r} = 9.9$ and $h = 127 \,\,\mu \text{m}$ ) is presented and analyzed. The proposed configuration uses a gradually extending metal ridge over a thin-film MSL to ensure electric field transformation, and an accurate impedance matching, while maintaining a good electrical contact, without any soldering or gluing. The fabricated prototype has been successfully tested in terms of insertion and return losses. The obtained results exhibit a bandwidth of more than 37% at −10 dB with an insertion loss of 1.5–2.7 dB, over the entire 60–90-GHz frequency band. The design simplicity and suitability for high-permittivity thin-film substrates, as well as the very broadband operation capability, enable it to be easily integrated with various planar monolithic microwave integrated circuits/miniaturized hybrid microwave integrated circuits microstrip circuits for different millimeter-wave applications.

Catalytic combustion in a plate type combustor to achieve uniform temperature distribution

Optimization of a catalytic combustor constructed using thin honeycomb ceramic substrates is reported herein. Honeycomb ceramic catalytic combustor is capable of providing heat to a dimethyl ether (DME) reformer, which is an essential requirement for an endothermic reforming process. The function of the proposed catalytic combustor is to maintain a uniform temperature distribution up to 500 °C. A fixed-bed flow reactor type combustor was set to operate under atmospheric pressure, and Pt/γ-Al2O3 catalyst was coated on the cordierite substrate (600 cell per square inch(cpsi)). Experimental variables considered in this study include the composition of multi-catalyst blocks, flow distributor, excess air ratio, space velocity, exit area ratio of the burner, and type of fuel. While performing the parametric study, the space velocity was selected in the range of 18000-27000 h-1 to ensure stable combustion (root mean square error (RMSE) < 10). For catalytic combustors employing C3H8 as fuel, optimized T-shaped and SiC foam distributors comprising three catalyst blocks with 50 % minimum area ratio of the combustor outlet were deemed as the best design combination in terms of superior combustion performance with temperature uniformity and no exhaust pollutants. For catalytic combustors fueled with DME, temperature variation on the surface of the combustor could be maintained within 17.6 °C of the reference temperature value.

Next Generation Ceramic Substrate Fabricated at Room Temperature

A ceramic substrate must not only have an excellent thermal performance but also be thin, since the electronic devices have to become thin and small in the electronics industry of the next generation. In this manuscript, a thin ceramic substrate (thickness: 30–70 µm) is reported for the next generation ceramic substrate. It is fabricated by a new process [granule spray in vacuum (GSV)] which is a room temperature process. For the thin ceramic substrates, AlN GSV films are deposited on Al substrates and their electric/thermal properties are compared to those of the commercial ceramic substrates. The thermal resistance is significantly reduced by using AlN GSV films instead of AlN bulk-ceramics in thermal management systems. It is due to the removal of a thermal interface material which has low thermal conductivity. In particular, the dielectric strengths of AlN GSV films are much higher than those of AlN bulk-ceramics which are commercialized, approximately 5 times. Therefore, it can be expected that this GSV film is a next generation substrate in thermal management systems for the high power application.

Design of improved ring Wilkinson power divider for millimetre wave applications

An improved millimetre wave microstrip power divider is presented. This circuit enhanced the conventional Wilkinson power divider (WPD) performance by adding transmission lines between the transformer arms and the resistor to reduce inherent undesirable mutual coupling. The proposed power divider design parameters show more stability over a wider frequency band compared to other valid design solutions. For comparison purposes, the proposed power divider along with the WPD are designed at 61 GHz using high permittivity thin ceramic substrate. The measurement results of the proposed circuit demonstrate improved bandwidth with high input/output matching and isolation of −15 and −24 dB, respectively, in the whole frequency band of 10 GHz. Furthermore, the excess insertion loss is reduced by 20% compared to the conventional one.

A Compact V-Band Planar Gap-Coupled $4\times 1$ Antenna Array: Improved Design and Analysis

In this paper, a broadband 60-GHz millimeter-wave $4\times 1$ microstrip patch antenna array using the gap-coupled technique is presented and analyzed. In order to meet the challenging requirement of reduced size related to this kind of technique, and facilitate the integration with other integrated passive or active devices, the proposed antenna array has been designed on a thin ceramic substrate ( $\varepsilon _{r} = 9.9 $ and $h = 127~\mu \text{m}$ ), using an miniature hybrid microwave integrated circuits (MHMIC) fabrication process. The proposed structure is based on a modified shape of a gap-coupled patch element with curved radiating edges. For further analysis, the performances of the latter in terms of impedance bandwidth, gain, and radiation efficiency were investigated and compared with a conventional structure of a rectangular gap-coupled patch antenna. The obtained results clearly show that the proposed gap-coupled array structure provides an improved bandwidth (7%) and an enhanced gain (10.7 dB), while maintaining a reduced size (5.2 mm $\times9.5$ mm). All these benefits make it an attractive candidate for the future integrated millimeter-wave RF front-end circuits; it can, however, be connected directly to various MHMIC passive circuits, or active devices through using the wire bonding technology, on a standard thin-film alumina substrate.

Performance comparison of 60 GHz printed patch antennas with different geometrical shapes using miniature hybrid microwave integrated circuits technology

This study presents a comparative study of several printed antennas having different shapes of the patch (rectangular, square, triangular, trapezoidal, circular, elliptical, and annular ring), suitable for 60 GHz wireless applications. All these microstrip patch antennas have been designed and fabricated on a very thin ceramic substrate to enable a high level of integration with other integrated circuits including passive circuits (such as power dividers, hybrid couplers, and passive filters), and active circuits (such as low noise amplifier (LNA), radio frequency (RF) mixers, and frequency multipliers). In that event, all of those circuits will be incorporated on a single and very small planar substrate to reduce overall size, and to avoid lossy millimetre-wave connectors. To analyse and compare the performances, advanced design system of Keysight Technologies was used for circuits design and simulation. This comparison is based on the obtained results particularly in radiation characteristics and inputs return loss, by determining the main associated parameters such as the bandwidth, voltage standing wave ratio, gain, directivity, efficiency, and cross-polarisation level. This comparative study would be very helpful for RF design engineers to select suitable antenna geometry while designing microstrip patch antenna arrays at 60 GHz millimetre-wave band.

Thermal and Electrical Characterizations of Ultra-Thin Flexible 3YSZ Ceramic for Electronic Packaging Applications

Abstract This paper presents thermal and electrical characterizations of an ultra-thin flexible 3YSZ (3 mol% Yttria Stabilized Zirconia) ceramic substrate to explore its potential for electronic packaging applications. The thicknesses of the ultra-thin 3YSZ substrates were 20 μm and 40 μm. The flexible thin ceramic substrate can provide not only better modulus for higher robustness in manufacturing, especially in Z-axis direction of modules, but also low thermal resistance for high density 2D (two dimensional) / 3D (three dimensional) power module packaging applications. To better understand the thermal and electrical properties of the ultra-thin flexible ceramic, different measurements were employed. Thermal conductivity was measured at different temperatures by 3-omega method, the results were verified by thermo-reflectance measurement at room temperature. Relative permittivity was measured from 100 Hz to 10 MHz, with dielectric losses determined by dielectric spectroscopy. The dielectric breakdown of the ultra-thin flexible 3YSZ was measured, from room temperature to 150 °C. Weibull analysis was performed on 20 measurements for each temperature. The test results showed that the thermal conductivity of 3YSZ decreased from 3.3 W/mK at 235 K to 2.2 W/Mk at 600 K. The relative permittivity decreased from 30.9 to 27.3 for higher frequencies for both substrates with different thickness. The temperature-dependence of relative permittivity and dielectric loss was studied. The results showed that these two parameters increased slowly from −65 °C to 150 °C, but more repidly from 175 °C to 250 °C. The dielectric breakdown decreased at higher temperature, from 5.76 kV to 2.64 kV for thickness of 20 μm, 7.84 kV to 3.36 kV for thickness of 40 μm. SEM (Scanning Electron Microscopy), EDS (Energy-dispersive X-ray Spectroscopy) and XRD (X-ray Powder Diffraction) analysis was performed to compare the microstructure of 3YSZ ultra-thin substrate and that of AlN (Aluminum Nitride) substrate. The microstructure of 3YSZ consisted of smaller round particles and that of AlN contained larger columnar particles. FEA (Finite Element Analysis) simulations were also applied to demonstrate the thermal properties of 3YSZ in simplified model of power modules. Though the measurement results showed that it did not meet expectations for high temperature power modules, the present work showed potential applications of the ultra-thin 3YSZ substrates in low voltage power modules, LED modules.

Alumina ceramic slot antenna for UHF RFID tag embedded in vehicles

ABSTRACTTo address the metallic interference problem in vehicular RFID (radio‐frequency identification) applications, this letter proposes a novel alumina ceramic slot tag antenna (ACSTA). The proposed antenna consists of a grounded thin alumina ceramic substrate and a slotted top layer rectangular patch, and the all four sides of the substrate are shorting walls. The slot can be equivalent to a horizontal magnetic current flow, so an excellent radiation performance is achieved according to the electromagnetic image theory. Meanwhile, due to the existence of the ground plane, the influences of metallic objects behind the ground to the tag antenna impedance can be maximally reduced. Combined with a commercial chip, this ACSTA is fabricated and measured, and the thickness of the novel tag is only 1mm. The tag antenna offers a half power coefficient bandwidth of 6.9% (0.87–0.93 GHz) with a stable gain about 3.6 dBi, and a similar half power coefficient bandwidth of 6.9% (0.89–0.95 GHz) with a gain about 4.8 dBi when it is attached to an 100 × 100 mm2 metallic plate, respectively. Moreover, the experimental results show that the maximum read range is about 27 or 30 m without or with a same attached 100 × 100 mm2 metallic plate, respectively. Simulation and measurement results show that the operating frequency band of the ACSTA covers US legal UHF RFID (902—928 MHz) band, and so it is a quite suitable candidate for vehicular RFID applications. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1150–1154, 2016

Precision dicing of hard materials with abrasive blade

The present work shows the experiments on dicing of high alumina substrates using abrasive blades. The technology used by modern electronic components is based on narrow and thin ceramic and single crystal substrates. One of the techniques used to obtain these products is to dice a larger substrate using an abrasive blade to generate low damages and high productivity called dicing process. Samples with high alumina (99.8 %) were diced with diamond abrasive blades in a creep feed process. The process parameters were changed as cuts 1 to 3 mm deep were made. The feed speed varied from 1 to 19 mm/s and the blade rotation varied from 10,000 to 30,000 rpm. The blade wearing as well as the linearity and the quality of dicing were analyzed. Higher blade rotation increases the blade stiffness and on these experiments a more stable cutting process was achieved at 30,000 rpm. The removal material mechanism was also explored comparing the chipping between silicon and the high alumina specimens.

Considerations for On-Wafer Millimeter-Wave Measurements on Thin Ceramic Substrate

This paper presents an on-wafer millimeter-wave circuit’s characterization build on thin ceramic substrate having a high relative permittivity. An RF short circuit, designed with a quarter-wavelength radial stub, is used in load design and launch transition. To improve the design accuracy of electromagnetic (EM) tools, the dielectric constant of the ceramic substrate is extracted using measurements of several pairs of microstrip lines combined with EM simulations. The largest deviation obtained, compared with the mean value over the frequency band, is less than 1%. Thus, a new six-port circuit is designed and characterized using a millimeter-wave probe station. A comparison between the measurement and simulation results, using extracted manufacturer-recommended relative permittivity, is conducted. The six-port $q_{i}$ points’ location is close to the simulated and theoretical ones over the frequency band of interest. As demonstrated in this paper, the substrate permittivity extraction has improved the design accuracy of the millimeter-wave circuits. Excellent performance of this circuit in terms of matching, isolation, and amplitude and phase balance is obtained.

Study on electromigration in flip chip lead-free solder connections with 40 μm or 30 μm diameter on thin film ceramic substrates

Electromigration comprises one of the processes affecting the long-term reliability of electronic devices; it has therefore been the focus of many investigations in recent years. In regards to flip chip packaging technology, the majority of published data is concerned with electromigration in solder connections to metallized organic substrates. Hardly any information is available in the literature on electromigration in lead-free solder connections on thin film ceramic substrates. This work presents results of a study of electromigration in lead-free (SAC305) flip chip solder bumps with a nominal diameter of 40 μm or 30 μm with a pitch of 100 μm on silicon chips assembled onto thin film Al2O3 ceramic substrates. The under bump metallization (UBM) comprised of a 5 μm thick electroless nickel immersion gold (ENIG) layer directly deposited on the AlCu0.5 trace. The ceramic substrates were metallized using a thin film multilayer (NiCr-Au(1.5 μm)-Ni(2 μm) structure on the top of which wettable areas were produced with high precision by depositing flash Au (60 nm) of the required diameter (40 μm or 30 μm). All electromigration tests were performed at the temperature of 125 °C. Initially, one chip assembly with 40 μm and one with 30 μm solder bumps was loaded with the current density of 8 kA/cm2 for 1,000 h. The assemblies did not fail and an investigation with SEM revealed no significant changes to the microstructure of the bumps. Thereafter seven chip assemblies with 40 μm solder bumps and five assemblies with 30 μm bumps were subjected to electromigration tests of 14 kA/cm2 or 25 kA/cm2, respectively. Six of the 40 μm-assemblies failed after 7,000 h and none of the 30 μm-assemblies failed after 2,500 h of test duration so far. Investigation of failed samples performed with SEM and EDX showed asymmetric changes of microstructure in respect to current flow. Several intermetallic phases were found to form in the solder. The predominant damage of the interconnects was found to occur at the cathode contact to chip; the Ni-P layers there showed typical columnar Kirkendall voids caused by migration of Ni from the layers into the solder. Failure of the contacts apparently occurred at the interface between Ni-P and solder. In summary, the results of the study indicate a very high stability of lead-free solder connections on ceramic substrates against electromigration. This high stability is primarily due to a better heat dissipation and thus to a relatively low temperature increase of the ceramic packages caused by resistive heating during flow of electric current. In addition, the type of the metallization used in the study seems to be more resistant to electromigration than the standard PCB metallization as it does not contain a copper layer.

Additive Technologies for Ceramic MEMS Sensors

The application of MEMS technology for the fabrication of MOX sensors with low power consumption becomes now a very important trend in gas sensor design. However, traditional silicon technology has some evident disadvantages, when applied in high-temperature devices produced in limited batch. We present our attempt to combine the advantages of ceramic MEMS technology (high working (600°C) and technological treatment (1000°C) temperature, chemical stability at high temperature) with the advantages of additive technologies for the fabrication of functional elements of gas sensor (heaters, sensing, and catalytic layers). We developed conductive silver, gold and platinum nanoparticle (10–30nm) inks usable in ink and aerosol jet printers and demonstrated the possibility to fabricate narrow conductive lines of microheaters and electrodes of sensor (line width ∼ 35μm). The combination of jet printing onto thin ceramic substrate with laser cutting enables the fabrication of advanced cantilever type sensors operating in pulsing heating mode.

Piggyback resistive Micromegas

Piggyback Micromegas is a novel readout architecture where the anode element is made of a resistive layer on a ceramic substrate. The resistive layer is deposited on the thin ceramic substrate by an industrial process which provides a large dynamic range of resistivity (106 to 1010 MΩ/□). The particularity of this new structure is that the active part is entirely dissociated from the read-out element. This gives a large flexibility on the design of the anode structure and the readout scheme. Without significant loss, signals are transmitted by capacitive coupling to the read-out pads. The detector provides high gas gain, good energy resolution and the resistive layer assures spark protection for the electronics. This assembly could be combined with modern pixel array electronic ASICs. First tests with different Piggyback detectors and configurations will be presented. This structure is adequate for cost effective fabrication and low out gazing detector. It was designed to perform in sealed mode and its long term stability has been extensively studied. In addition perspectives on the future developments will be evoked.

Complete Characterization of Novel MHMICs for V-Band Communication Systems

This paper presents the characterization results of several new passive millimeter wave circuits integrated on very thin ceramic substrate. The work is focused on the design and characterization of a novel rounded Wilkinson power divider, a 90° hybrid coupler, a rat-race coupler, and a novel six-port (multiport) circuit. Measurements show the wideband characteristics, allowing therefore their use for multi-Gb/s V-band wireless communication systems.

Performance of a Compact Dual Six-Port Millimeter-Wave Network Analyzer

This paper presents a millimeter-wave network analyzer incorporating two six-port correlators for the measurement of the reflection and transmission coefficients of a device under test in the frequency band 59-61 GHz. An instrumentation integrating the hardware and software resources, including advantages such as robustness, compactness, relatively low cost, small size, and real-time operation, is developed. The millimeter-wave part of the system is implemented on a thin alumina ceramic substrate. The proposed solution eliminates the need for complex heterodyne schemes and for bulky tuning mechanisms generally found in dual six-port network analyzers. Associated to this system, an explicit calibration procedure is proposed. The performance, in terms of measurement accuracy, is evaluated by comparing the results obtained from the system proposed with those given by a conventional network analyzer.

Optimization of laser cutting processes using design of experiments

We report on the optimization of laser cutting of thin Al2O3 ceramic layers using a design of experiment (DOE) approach. DOE allows to separate the most important influencing factors on the targeted cutting process, to clarify their interaction, to reduce the overall amount of parameter sets that need to be examined and to identify the optimized parameter regions, respectively. Using both, a continuous wave 500 W fiber laser and a 200W CO2 laser, we have optimized and compared the cutting of 250μm thin Al2O3 ceramic substrate layers applying a commercial DOE software. Our results demonstrate the potential of DOE to optimize laser material processes.