Low-temperature Co-fired Ceramic Materials Research Articles

Co-sintering of a ceramic-metal bilayer: Coupled experimental, analytical and numerical approaches

The co-sintering behavior of a ceramic-metal bilayer is carefully investigated. This bilayer is composed of a gold film deposited by screen-printing on a silica-based low-temperature cofired ceramic (LTCC) layer. First, behaviors of both materials in free sintering are finely characterized. LTCC exhibits a viscous flow sintering mechanism, whereas the densification mechanism of gold is controlled by grain boundary diffusion (with an identified apparent activation energy of 101 ± 15 kJ mol−1). Free sintering of gold is also marked by a two-step densification process due to its large bimodal particle size distribution. A methodology is proposed to estimate gold viscosity at high temperatures directly from raw experimental data in free sintering, without performing dedicated mechanical characterizations. Based on the constitutive laws identified for LTCC and gold materials, analytical and numerical models of the bilayer co-sintering process are built. During co-sintering, stresses generated by densification kinetic mismatch between gold and LTCC are progressively relaxed by camber phenomenon. Calculated evolutions of camber in co-sintering are compared to curvature monitoring by ombroscopy. Finite element simulation in 3D fits well with the experimental data, whereas the analytical solution strongly underestimates camber rates. This shows that the simplified numerical approach suggested here leads to a robust numerical model, faithfully describing thermomechanical interactions occurring in co-sintering within the ceramic-metal bilayer.

Preparation of Sol-Gel-Derived CaO-B2O3-SiO2 Glass/Al2O3 Composites with High Flexural Strength and Low Dielectric Constant for LTCC Application.

Low-temperature co-fired ceramic (LTCC) substrate materials are widely applied in electronic components due to their excellent microwave dielectric properties. However, the absence of LTCC materials with a lower dielectric constant and higher mechanical strength restricts the creation of integrated and minified electronic devices. In this work, sol-gel-derived CaO-B2O3-SiO2 (CBS) glass/Al2O3 composites with high flexural strength and low dielectric constant were successfully prepared using the LTCC technique. Among the composites sintered at different temperatures, the composites sintered at 870 °C for 2 hours possess a dielectric constant of 6.3 (10 GHz), a dielectric loss of 0.2%, a flexural strength of 245 MPa, and a CTE of 5.3 × 10-6 K-1, demonstrating its great potential for applications in the electronic package field. By analyzing the CBS glass' physical characteristics, it was found that the sol-gel-derived glass has an extremely low dielectric constant of 3.6 and does not crystallize or react with Al2O3 at the sintering temperature, which is conducive to improving the flexural strength and reducing the dielectric constant of CBS glass/Al2O3 composites.

High‐frequency and intrinsic dielectric properties of β‐CaSiO3 and its application: the microstrip patch antenna

AbstractDesigning and fabricating antennas that exhibit low losses and are compact, lightweight, and highly radiation efficient are challenging in the wireless‐communication field. In this study, we simulated and fabricated microstrip patch antennas using β‐CaSiO3 low‐temperature co‐fired ceramic (LTCC) as dielectric resonator substrate. Compact ceramics that show good microwave dielectric properties (a relative dielectric constant [εr] of 6.57, high‐quality factor [Q × f] of 35 086 GHz [@14.85 GHz], and temperature coefficient of frequency [τf] of −33.56 ppm °C−1 for the optimal composition) were obtained when Li2O–CaO–B2O3–CuO glass was added to β‐CaSiO3 and sintered at 950°C. The high‐frequency properties of these composite ceramics reveal that the dielectric constant and dielectric loss are stable in the 38−58 and 70−90 GHz ranges, respectively. Furthermore, a circularly polarized antenna fabricated using a CaSiO3‐based ceramic shows a high radiation efficiency (92.04%) and gain (3.35 dBi) at a center frequency of 2.5 GHz. These β‐CaSiO3 composite ceramics offer promising prospects for high‐frequency use as well as in mobile communication applications. This study provides insight for the development of innovative antennas with new LTCC materials.

Sintering Behavior, Microstructure and Microwave Dielectric Properties of Li2TiO3-Based Solid Solution Ceramics with Lithium Fluoride Addition for Low-Temperature Co-Fired Ceramic Applications

Nowadays, low-temperature co-fired ceramic (LTCC) technology has become one of the main forms of manufacturing electronic devices. However, a majority of microwave dielectric ceramics are not suitable as LTCC materials due to their high sintering temperatures. Developing novel LTCC materials with good microwave dielectric properties is extremely urgent. In this paper, an LiF sintering aid was added to Li2Ti0.8(Co1/3Nb2/3)0.2O3 (LTCN) ceramics to explore new LTCC materials. The sintering behavior, microstructure and microwave dielectric properties of LTCN + x wt% LiF ceramics were investigated in detail. The results indicated that the addition of LiF increased the degree of disorder in the LTCN matrix, transforming it from a monoclinic to a cubic crystal system. The ceramics exhibited relatively dense and homogeneous microstructures at the sintering temperature of 950 °C as the LiF doping amount was not less than 2 wt%. By LiF doping, the quality factor (Q × f) value was significantly enhanced due to the improved microstructure. Meanwhile, the temperature coefficient of resonant frequency (τf) of LTCN ceramics was successfully regulated to the near zero value owing to the negative τf characteristic of LiF. Excellent microwave dielectric properties of dielectric constant (εr) = 19.01, Q × f = 144,890 GHz, τf = −1.52 ppm/°C were obtained when the sample doped 3 wt% LiF was sintered at 950 °C for 3 h. Furthermore, the good chemical compatibility of the LTCN-3 wt% LiF ceramic with silver electrodes suggested that the ceramic was a potential material for LTCC applications.

Temperature-stable Ba0.8Sr0.2CuSi2O6 microwave dielectric ceramics for LTCC application achieved with the addition of LBSCA and LBBS glass

Ba0.8Sr0.2CuSi2O6 ceramics have a low dielectric constant, which is useful for low-latency 5G communication. To enable the preparation of Ba0.8Sr0.2CuSi2O6 low-temperature co-fired ceramic (LTCC) materials, LBSCA and LBBS were used in this paper to reduce the sintering temperature of Ba0.8Sr0.2CuSi2O6. The effects of LBSCA and LBBS on the phase composition, densification, microscopic morphology, and vibrational characteristics of the ceramics were investigated by X-ray diffraction, scanning electron microscopy, density measurements, and Raman spectroscopy, and the causal factors influencing the microwave dielectric properties with the addition of glass were analyzed. It was found that 0.4 wt% LBSCA glass and 1 wt% LBBS glass reduced the sintering temperature to 925 °C, and these prepared ceramics had excellent microwave dielectric properties. The ceramic prepared with 0.4 wt% LBSCA glass had an εr value of 7.672, Q × f value of 37193 GHz, and τf value of −14.93 ppm/°C, while the ceramic prepared with 1 wt% LBBS glass had an εr value of 7.512, Q × f value of 32136 GHz, and τf value of −13.92 ppm/°C. The phase composition of the ceramics did not significantly change, indicating that neither glass reacted with the ceramics. The εr value was affected by both density and Raman shift, the trend in the Q × f values was consistent with the density, and the τf value decreased with increasing glass content, which was attributed to the liquid phase generated by the glass in the ceramic. In addition, co-firing these glass-doped ceramics with Ag at a low temperature resulted in good chemical compatibility. Combined with the near-zero τf, these results demonstrate the excellent promise of these two ceramics as alternative materials for LTCC microwave devices and their application in 5G communication.

Terahertz spectra of selected low-temperature cofired ceramics: A comparative study

Low-temperature cofired ceramics (LTCC) which exhibit low dielectric permittivity and low dielectric loss are promising platforms for emerging terahertz devices and systems including high-speed telecommunications. This study focuses on the analysis of the terahertz spectra of novel low dielectric permittivity LTCC materials, such as copper and zinc borates, zinc silicates, and lithium-containing dielectrics. Furthermore, their sintering conditions and THz characteristics were compared with the results presented for other materials in our previous works and those reported in literature, including selected microwave dielectric properties. The effect of sintering aids (AlF3-CaB4O7 and CuBi2O4) on the dielectric properties of Li2WO4, LiBO2, and 75 wt.% CuB2O4–25 wt.% Cu3B2O6 composite was also investigated. XRD patterns and SEM images illustrate single phase composition and dense microstructure of the tested ceramics. We describe in details the time-domain spectroscopy setup used to measure the dielectric properties of the developed materials in the 0.1–3 THz range.

Glass-free Li2SiO3-LiF ceramics with high thermal conductivity

In the past few decades, Low temperature co-fired ceramics (LTCC) technology with high thermal conductivity had been developed to meet the requirements of high-density integrated devices packaging. This work investigates the effect of LiF sintering agent on the densification, microstructure and thermal conductivity of LTCC material (Li 2 SiO 3 +4 wt% Al 2 O 3 -x wt% LiF (x = 1,2,3,4)). The enhanced densification and a high thermal conductivity value of 11.36 W/mK are achieved when adding 2 wt% LiF and sintered at 940 ℃. Besides, the phonon-dispersion relation of Li 2 SiO 3 lattice indicates that the anharmonicity interaction between low-frequency phonons are the primary factor in reducing the thermal conductivity of material. Furthermore, the Raman spectra were used to analyze the phonon scattering mechanism of all samples. The addition of the LiF changes the full width at half maximum (FWHM) which is inversely proportional to the phonon mean free path. And the reduced FWHM of Raman spectra implies higher thermal conductivity of ceramics. Base on the above results, the novel glass-free high thermal conductivity and low sintering temperature Li 2 SiO 3 + 4 wt% Al 2 O 3 -2 wt% LiF ceramic was prepared successfully with great potential in high heat conduction LTCC materials. This work could bring new insights for exploring novel high thermal conductivity ceramic materials.

Low-loss and temperature stable (1-x)Ba3P2O8-xMg2B2O5 composite ceramics with low sintering temperature

In this study, the Ba3P2O8 and Mg2B2O5 were fabricated by the solid-state reaction method separately, and the (1-x)Ba3P2O8-xMg2B2O5 (x = 0.2–0.4) low-temperature co-fired ceramic (LTCC) materials were obtained in the sintering temperature range of 880–960 °C. The phase compositions, microstructures, elemental compositions, and microwave dielectric properties of the (1-x)Ba3P2O8-xMg2B2O5 composite ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and TE01δ mode dielectric resonator method, respectively. The results revealed that the Mg2B2O5 phase and Ba3P2O8 phase could coexist well in the (1-x)Ba3P2O8-xMg2B2O5 composite ceramics without formation of any new phases. The abnormal grain growth of Ba3P2O8 grains was inhibited by the addition of Mg2B2O5. In addition, through composition of Ba3P2O8 and Mg2B2O5, the temperature coefficient of resonant frequency (τf) and quality factor (Q×f) were effectively optimized, and the sintering temperature was reduced to 880–960 °C. The optimal performance of 0.8Ba3P2O8-0.2Mg2B2O5 composite ceramic was achieved at a sintering temperature of 920 °C, τf = −1.9 ppm/°C, Q×f = 61,250 GHz, and a low permittivity εr = 10.7. The chemical compatibility test demonstrated that the composite ceramic could coexist well with silver, which indicated that the 0.8Ba3P2O8-0.2Mg2B2O5 composite ceramic is a candidate LTCC material with wide application prospects.

Preparation of an environment-friendly LTCC material by using waste soda-lime glass and natural volcanic ash

Glass/ceramic composites applied in the field of low-temperature co-fired ceramics (LTCC) were successfully prepared at 670–710 °C by using waste soda-lime glass (WG) as a binder and natural volcanic ash as a ceramic raw material. Based on the theories of suppression and supplementary network effects, alkaline-earth metal ions (R2+, R = Mg, Ca, Sr, and Ba) and B2O3 were applied to improve the dielectric properties of WG and composites, respectively. The influence of R2+ on the crystal phase evolution, microstructure, mechanical, dielectric, and thermal properties of WG-volcanic ash-based composites were systematically investigated. By doping 2.5 wt% Ba2+ to the environment-friendly LTCC composites, physical properties i.e., εr of 4.86 at 1 MHz, tan δ of 6.32 × 10−3, coefficient of thermal expansion of 8.72 × 10−6/°C, and thermal conductivity of 1.04 W/(m·K) are obtained. It is worth mentioning that the environment-friendly LTCC composite uses WG with a low glass transition temperature to reduce the sintering temperature and a tiny amount of a modifier to adjust the dielectric performance instead of synthesizing specific crystals by adding lots of chemical reagents. These, in turn, do not only have the potential to be used in the LTCC packaging technology but also have significance for sustainable development. Additionally, because of good chemical compatibility between aluminum and the composites, the environment-friendly LTCC composites with ultra-low sintering temperature have the potential ability to lower the cost of LTCC packaging materials.

Distortion of an LTCC Bilayer during Constrained Sintering: Comparison between Ombroscopic Imaging and Modeling.

A complete methodology combining experiments and modeling has been developed to investigate the constrained sintering of low-temperature cofired ceramic (LTCC) systems. The thermomechanical and sintering behavior laws, previously identified for the selected commercial LTCC material, were implemented in a finite element model. The reliability and validity range of the built model has been investigated thanks to the development of a specific distortion experience. The distortion generated during the constrained sintering of a porous LTCC layer deposited on a dense one has been monitored in situ by ombroscopy. The measured camber evolution was compared with numerical results. The camber phenomena predicted numerically and observed experimentally are very similar, characterized by the onset of distortion around 918 K and a similar evolution during heating. However, at high temperatures (around 1100 K), the simulated camber slightly differs from the experimental one. It seems to be related to the damage to the dense LTCC layer by microcracking.

Modification of CaO–B2O3–La2O3 glass powder and its application in low-temperature co-fired ceramic substrate

CaO–B2O3–La2O3 (CBL) glass is widely used in high-frequency packaging and co-firing with highly conductive metal electrodes as a new lead-free glass/ceramic system in low-temperature co-fired ceramic (LTCC) materials due to its multiple advantages, such as low softening point, controllable crystallisation properties, and chemical stability. The silane coupling agent, KH-570, was used as a surface modifier for preparing modified CBL glass powder to obtain a tape-casting slurry with low viscosity and excellent stability in a polymethyl methacrylate binder system; this system achieved better co-firing compatibility between the composite and Ag electrodes. In this study, the modification mechanism of the silane coupling agent with the powder is elucidated. The effects of the modified powder on the kinetic stability and rheological properties of the slurries were investigated. A slurry with a solid content of 39.6 vol% and lowest viscosity of 1500 mPa s could be obtained with the addition of 2 wt% KH-570. In particular, the uniformity of tape-casting slurry was observed during tape casting, leading to a difference in the density of green tapes, which increased from 2.45 (without KH-570) to 2.61 g/cm3 (with 2 wt% KH-570), and the tensile strength increased to 5.11 MPa. Simultaneously, the micromorphology and surface roughness of the green tapes and substrate were analysed by scanning electron microscopy and atomic force microscopy. The results showed an improvement in densification and a decrease in Ra after modification, resulting in the sintered substrate obtaining a higher density of 3.06 g/cm3 and a lower dielectric loss of 9.8 × 10−4 (12 GHz). The excellent co-firing compatibility between green tapes and silver paste at 850 °C was confirmed by energy-dispersive X-ray spectroscopy. In this study, high-quality LTCC materials were manufactured by coupling modification, with their stable performance ensuring their wide application.

Manufacturing of a 70 × 70 mm2 LTCC strip electrode readout for Gas Electron Multiplier detectors

Introduced by Fabio Sauli in 1997, the Gas Electron Multiplier (GEM) technology is commonly used in many high energy physics experiments. It has proven unique value in many scientific domains and adaptability to new research tasks. Typically, the GEM detectors are made with polyimide films (GEM foils and readout plate), halogen-free FR4 epoxy resins (supporting and stretching structures), conductive copper layers, etc. Because of outgassing and ageing, those components release in time residues of dust, moisture, and vapors. The residues pollute the gas mixture and consequently degrade the detector's working parameters. To avoid such a problem, devices can be constantly flushed by pure gas from an external source. This solution is not optimal for autonomous space detectors because of volume and weight limitations. The paper describes the successive work to develop an autonomous GEM detector without a gas mixture circulation system. As a solution, the use of Low-Temperature Cofired Ceramics (LTCC) materials was proposed and validated. The dedicated LTCC readout plates were manufactured and tested, and results are presented.

Solid-State-Activated Sintering of ZnAl2O4 Ceramics Containing Cu3Nb2O8 with Superior Dielectric and Thermal Properties

Low-temperature co-fired ceramics (LTCCs) are dielectric materials that can be co-fired with Ag or Cu; however, conventional LTCC materials are mostly poorly thermally conductive, which is problematic and requires improvement. We focused on ZnAl2O4 (gahnite) as a base material. With its high thermal conductivity (~59 W·m−1·K−1 reported for 0.83ZnAl2O4–0.17TiO2), ZnAl2O4 is potentially more thermally conductive than Al2O3 (alumina); however, it sinters densely at a moderate temperature (~1500 °C). The addition of only 4 wt.% of Cu3Nb2O8 significantly lowered the sintering temperature of ZnAl2O4 to 910 °C, which is lower than the melting point of silver (961 °C). The sample fired at 960 °C for 384 h exhibited a relative permittivity (εr) of 9.2, a quality factor by resonant frequency (Q × f) value of 105,000 GHz, and a temperature coefficient of the resonant frequency (τf) of −56 ppm·K−1. The sample exhibited a thermal conductivity of 10.1 W·m−1·K−1, which exceeds that of conventional LTCCs (~2–7 W·m−1·K−1); hence, it is a superior LTCC candidate. In addition, a mixed powder of the Cu3Nb2O8 additive and ZnAl2O4 has a melting temperature that is not significantly different from that (~970 °C) of the pristine Cu3Nb2O8 additive. The sample appears to densify in the solid state through a solid-state-activated sintering mechanism.

Metallization, Material Selection, and Bonding of Interconnections for Novel LTCC and HTCC Power Modules.

Ceramic baseplates are important elements in the power modules of electric drives. This paper presents low-temperature cofired ceramic (LTCC) and high-temperature cofired ceramic (HTCC) materials for the fabrication of three-dimensional power modules. The silver-based metallization and power module assembly are presented, together with aluminum-based power wire bonding and an industrial procedure to achieve high solderability and bondability. The results of the bond tests using different metallization materials, especially cost-effective ones, are presented, together with the assembly of the power modules. The best results were achieved with Ag metallization and 380 µm Al wire and with Ag–Pd metallization and 25 µm Al wire, both on an LTCC base. The paper concludes with a dual-pulse electrical test of the power modules, which proves the quality of metallization, the type of material selected, and the correctness of the wire bonding and assembly.

Machine Learning-Assisted Materials Design and Discovery of Low-Melting-Point Inorganic Oxides for Low-Temperature Cofired Ceramic Applications

The fabrication of low-temperature cofired ceramics (LTCCs) densified at a low sintering temperature (<900 °C) is energy-saving and environmentally friendly. However, finding novel LTCC materials by the trial-and-error method is time-consuming and costly. The LTCC materials often have low melting points, so it is feasible to discover high-performance LTCC materials out of the low-melting-point ceramics. A two-stage machine learning framework was adopted to establish the melting-point prediction model for inorganic oxides. Chemical compositions were used as features in stage 1 modeling; while in stage 2, more features were integrated according to domain knowledge to optimize the prediction model. Stage 2 model built by an artificial neural network algorithm shows the best performances with R2 = 0.7968 and root-mean-square error = 247.4 (K). Three features, including formation energy per atom (fepa), theoretical density (d), and number of atoms (na), were extracted as the decisive characteristics of inorganic oxides. The melting point demonstrates positive correlations with the absolute value of fepa and d. The na acts as a “recessive gene” because its contribution is indirect but necessary. The physical relationships between features and the melting point were also discussed. Furthermore, the LTCC inorganic oxides often have melting points lower than 1400 °C statistically. This criterion was verified by the reported LTCC/ultra-LTCC materials. The melting points of materials in the prediction set consisting of ∼3600 inorganic oxides were calculated by the ML model, and thus, the underlying LTCC materials could be screened out efficiently.

Design and preparation of BaO–Al2O3–SiO2–B2O3/Quartz LTCC composites with tailored coefficient of thermal expansion

In this work, by focusing on widespread problem of thermal mismatch caused by different coefficients of thermal expansion (CTE) in electronic packaging materials, low-temperature co-fired ceramic (LTCC) materials with tunable CTE values were designed. By substituting Ba2+ with Sr2+ and replacing quartz with alumina and zirconia, respectively, BaO–Al2O3–SiO2–B2O3/quartz LTCC composites with CTE of 7.05–9.52 × 10−6/°C were developed. Results show that major crystalline phases of LTCC composite materials are quartz and hexacelsian. By replacing quartz with alumina or zirconia, sintering behavior and subsequently thermal expansion and dielectric properties were modulated. On the other hand, substituting Ba2+ with Sr2+ can be beneficial to the densification of composite materials. The introduction of Sr2+ triggered mixed alkali effect and hindered the crystallization of hexacelsian phase, which can further improve mechanical properties. Finally, sandwich structure module of BaO–Al2O3–SiO2–B2O3/quartz with gradient CTE values was obtained, which showed potential for electronic packaging with sustained thermal compatibility under cyclic temperatures.

Soft magnetic, gyromagnetic, and microstructural properties of BBSZ-Nb2O5 doped NiCuZn ferrites for LTCC applications

The development of 5G technology places higher performance requirements on low-temperature co-fired ceramic (LTCC) materials. Here, a solid phase method was used to prepare BBSZ-Nb2O5 doped Ni0.22Cu0.31Zn0.47Fe2O4 samples, and the effects of doping 0.3 wt% BBSZ and different contents of Nb2O5 (x = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.1 wt%) on the microstructure as well as the soft magnetic and gyromagnetic properties of the resulting samples were studied. The doping with Nb2O5 promoted crystal lattice expansion and densification under low temperature sintering conditions. The sample containing an Nb2O5 content of x = 0.9 had the highest measured μ′ value of 212.6, which had increased by 15.9% relative to x = 0.1. Moreover, the measured Ms was the maximum value of 32.61 emu/g and ΔH reached the minimum value of 280 Oe for the x = 0.9 sample, which were 25.5% higher and 32.0% lower than those measured for the x = 0.1 sample, respectively. At x = 1.1, ε′ had the minimum value of 21.4, which was 21.6% lower, and Hc reached the maximum value of 30.8 Oe, which increased by 7.6%. This reduction in ΔH for the doped NiCuZn samples makes them promising materials for use in microwave gyromagnetic devices or as antenna substrates based on LTCC integration technology.

Temperature stability of low-temperature fired (1-x) ZnTiNb2O8-xCuTiNb2O8 microwave dielectric ceramics

In this study, (1-x) ZnTiNb2O8-xCuTiNb2O8-0.4 wt%LBSCA (0 ≤ x ≤ 0.4) microwave dielectric ceramics prepared by solid-state sintering were investigated to obtain low-temperature co-fired ceramic (LTCC) materials with near-zero resonant frequency temperature coefficient. X-ray diffraction (XRD) pattern and Rietveld refinement results reveal that with the increase in x value, main phase of ceramics is transformed from ZnTiNb2O8 to ZnNb2O6 and new phases (CuTiNb2O8 and Ti3O5) are formed at x ≥ 0.3. The microwave dielectric properties are affected with the appearance and increase in content of the secondary phase. Scanning electron microscope (SEM) images indicate that sample grains are relatively uniform and dense at x = 0.2. Raman shift obtained from Raman spectra explain changes in dielectric constant. Results reveal that the desirable dielectric properties were obtained by sintering at 875 °C with x = 0.375: εr = 35.01, Q×f = 19449 GHz, and τf = -0.3 ppm/°C, and the highest Q×f value (~38711 GHz) was obtained by sintering at 900 °C with x = 0.2 in the study.

Ultra-low permittivity ULTCC composite materials

A method to realize ultra-low temperature co-fireable ceramic composites with ultra-low permittivity is presented in this work. Hollow glass microspheres with a size of 10–100 μm were used as a filler in a tape based on lithium molybdate (Li2MoO4) ceramic to introduce controlled porosity and reduce the relative permittivity of the sintered product. A lamination pressure of only 1.25 MPa was sufficient to produce samples with uniform structure and without delamination. Differential scanning calorimetry and thermogravimetric analysis were used to optimize the sintering temperature profile of the material. The microstructure of the samples was investigated with field emission scanning electron microscopy, and the dielectric properties with a split post dielectric resonator. Compatibility of the composite ceramic with silver was tested by applying thick-film-printed electrodes and post-firing them on the surface. Samples sintered at 540 °C exhibited a relative permittivity of 1.4–5.40 and a loss tangent of 10−3–10−4 at 5 and 10 GHz. The method shows interesting possibilities to significantly reduce processing temperatures compared to conventional low-temperature co-fired ceramics materials and to obtain the extremely low permittivity that is especially required for future high-frequency applications.

Study of mixing process of low temperature co-fired ceramics photocurable suspension for digital light processing stereolithography

The Low Temperature Co-fired Ceramic (LTCC) materials are highly used for high frequency devices required for high-speed data communications, representing an attractive material for electronic applications with a direct industrial applicability. The development of a photocurable LTCC suspension for Digital Light Processing Stereolithography (DLP-SLA) technology is presented in this work. The LTCC suspension, with an optimal solid load of 40.4 vol%, was characterized along its preparation regarding the rheological behaviour, dispersant content, particle size distribution in function of milling time and photocuring properties in a visible light range. The effect of the particle size change, through ball milling, on viscosity and photocuring behaviour was studied, achieving an optimal mixing range time, which highlights the importance of the manufacturing standardization of the photocurable suspensions. The optimized suspension presents a viscosity of 3.6 Pa s at shear rate of 2 s−1, a sensitivity of 41 μm and a critical energy dose of 15 mJ cm−2. The printing process was successfully achieved, demonstrated by some defect-free printed pieces.