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., ε_r 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.     

Low temperature and microwave dielectric properties of TiO2/ZBS glass composites

TiO₂ based ceramic/glass composites were prepared by a non-reactive liquid phase sintering (NLPS) using zinc borosilicate (ZBS) glass having the deformation temperature of 588 °C. The compounds of Zn₂SiO₄ and Zn₄B₆O₁₃ were formed after the sintering process, indicating that the ZBS glass was a non-reactive one in this system. For TiO₂/50 vol% ZBS glass composite, the two-stage sintering behavior was conducted as the sintering temperature increased. The former might be correlated to the NLPS process and the latter appeared to be related to the crystallization. The dielectric constant (?_r) was mainly affected by the porosity and obeyed the logarithmic mixing rule. The quality factor (Q × f₀) showed an increase and then a steep decrease after the maximum at 850 °C. TiO₂/50 vol% ZBS glass composite sintered at 900 °C demonstrated 36 in the dielectric constant (?_r) and 7500 GHz in the quality factor (Q × f₀) for an application to LTCC filters.     

Low temperature sintering and characterization of La2O3-B2O3-CaO glass-ceramic/LaBO3 composites for LTCC application

An interesting attempt to develop low temperature sintering glass-ceramic/ceramic composite based on La₂O₃-B₂O₃-CaO (LBC) glass-ceramic and LaBO₃ ceramic, which was reported to be the main crystalline phase precipitated from La₂O₃-B₂O₃-based glass-ceramics, has been taken. The sintering behavior, phase evolution, microstructures and dielectric properties of LBC/LaBO₃ composites have been studied. The densification of LBC/LaBO₃ composite is achieved by partially reactive sintering. The LaBO₃ filler is directly involved in the sintering process of glass/ceramic composite as additional liquid phase provider at high sintering temperature, and it will suppress the formation of other crystalline phases so that the produced LBC/LaBO₃ composites exhibit unusual simple phase structures, which is beneficial to regulate the performance of composites. LBC/LaBO₃ composite with 50 wt% LaBO₃ sintered at 950 ºC for 2 h has a dielectric constant ε_r = 10.12, a dielectric loss tanδ = 1.82 × 10^―3, a Q × f = 9312 GHz (at 16.95 GHz), and shows good chemical compatibility while co-firing with Ag electrode. This indicates that LBC glass/LaBO₃ ceramic composites have a potential to meet the requirements of microwave LTCC applications.     

Development of low thermal expansion mono crystalline Sr-feldspar phase via Sr-cordierite ceramic/borosilicate glass composite

The present work focuses on fabrication of low thermal expansion monoclinic Sr-feldspar through sintering of Sr-cordierite ceramic/borosilicate glass composite. The prepared composites were sintered between 1200 and 1350?°C. Bulk density and apparent porosity of sintered composites were measured according to Archimedes technique. Phase composition and microstructure of sintered composites were tested by X-ray diffraction and scanning electron microscope attached with EDAX unit. Thermal expansion coefficient and dielectric constant of sintered composites were also determined. The results revealed that mono crystalline Sr-feldspar was formed after sintering up to 1350?°C especially in the composites that contain higher ceramic content. As indicated from the result of microanalysis conducted by EDAX, the obtained Sr-feldspar was deficient in SiO₂ and SrO. In the composites with higher glass content, little amounts of quartz or cristobalite were also formed, depending on the cooling conditions. The sinterability was increased with increasing sintering temperature and decreased with increasing ceramic content. The obtained sintered composites exhibited low thermal expansion coefficient and dielectric constant. The composite that contains 90% ceramic exhibited thermal expansion coefficient 2.533?×?10^?6 °C^?1 and dielectric constant value 8.42.     

Investigation on low-temperature sinterable behavior and tunable dielectric properties of BLMT glass-Li2ZnTi3O8 composite ceramics

The novel low-temperature sinterable ceramic composites were fabricated by mixing B₂O₃-La₂O₃-MgO-TiO₂ (BLMT) glass with Li₂ZnTi₃O₈ ceramic. All composites could be well sintered at 900?°C for 2?h through liquid-phase sintering and viscous sintering process. With BLMT glass increasing, the main phase of composites changed from Li₂ZnTi₃O₈ to LaBO₃ phase crystallized from glass. Nevertheless, the rutile phase was observed in composites with ≥10?wt% glass, which could adjust the temperature coefficient of resonant frequency (τ_f) to near-zero owing to the opposite τ_f value to other phases. Simultaneously relative permittivity (ε_r) and quality factor (Q$\times$f) could be controlled by varying the content of Li₂ZnTi₃O₈ ceramic and BLMT glass. The composite with 20?wt% glass exhibited excellent dielectric properties: ε_r?=?22.7, Q?×?f?=?19,900?GHz, and τ_f ?=?0.28?ppm/°C. In addition, the good chemical compatibility between the composite with 5?wt% glass and Ag electrode made it as a potential candidate for LTCC technology.     

Mechanical,thermal, and dielectric properties of glass mullite composites for low-temperature cofired ceramic and radome applications

SiO₂-Al₂O₃-CaO-based glass (10–60 wt%)/mullite composites were investigated for the LTCC and radome applications. The optimum densification temperatures decreased from 1550°C (10 wt% glass) to 1400°C (30 wt% glass) by means of liquid-phase sintering, and to 850°C–825°C (50–60 wt% glass) by means of viscous phase sintering. XRD analysis showed that mullite was the main phase as well as in situ crystallized anorthite after 825°C. The composite with 20 wt% glass was a suitable candidate for the radome applications (bulk density = 2.86 g/cm³ after sintering at 1450°C, dielectric constant (loss) = 7.12 (0.0025) at 5 MHz, thermal expansion coefficient = 4.27 ppm/°C between 25°C and 800°C, thermal shock resistance parameter = 162°C), and the composite with 50 wt% glass was a suitable candidate for the low-temperature cofired ceramic applications (bulk density = 2.64 g/cm³ after sintering at 850°C, dielectric constant (loss) = 6.79 (0.0043) at 5 MHz, thermal conductivity = 2.11 W/m⋅K at 25°C, and thermal expansion coefficient = 3.93 ppm/°C between 25°C and 300°C).     

Synthesis and characterization of low CTE value La2O3-B2O3-CaO-P2O5 glass/cordierite composites for LTCC application

Low-softening-point La₂O₃-B₂O₃-CaO-P₂O₅ (LBCP) glass-ceramic/cordierite composite systems have been prepared in this work. Influence of the ratio of La₂O₃ to B₂O₃ and the content of cordierite on the sintering behavior, microstructure, sintering quality, thermal properties and dielectric properties of composites are studied. The results show that high La₂O₃/B₂O₃ ratio improves the crystalline quality of LBCP glass-ceramic, but also narrows its process window. The increase of cordierite content reduces the coefficient of thermal expansion (CTE) value of composites obviously. However, excess cordierite is detrimental to the densification of the composite microstructure, and too low cordierite content causes serious foaming. Sample containing 30?wt% LBCP1 glass-ceramic and 70?wt% cordierite sintered at 850?°C shows excellent properties: relative density of 95.26%, CTE value of 4.12?ppm/°C, dielectric constant of 4.78 (1?MHz)/4.52 (12.8?GHz), dielectric loss of 2.3?×?10^?3 (1?MHz)/2.5?×?10^?3 (12.8?GHz) and the ability to co-fire with silver, which suggests that LBCP glass/cordierite composite system has potential to meet the requirements of LTCC substrate material.     

Co2O3 substitution effects on the structure and microwave dielectric properties of low-firing (Zn0.9Mg0.1)TiO3 ceramics

Low-firing (Zn_0.9Mg_0.1)_1?xCo_xTiO₃ (x = 0.02–0.10) (ZMC_xT) microwave dielectric ceramics with high temperature stability were synthesized via conventional solid-state reaction. The influences of Co₂O₃ substitution on the phase composition, microstructure and microwave dielectric properties of ZMC_xT ceramics were discussed. Rietveld refinement results show the coexistence of ZnTiO₃ and ZnB₂O₄ phases at x = 0.02–0.10. (Zn_0.9Mg_0.1)_1?xCo_xTiO₃ ceramic with x = 0.06 (ZMC_0.06T) obtains the best combination microwave dielectric properties of: ε_r = 21.58, Q × f = 53,948 GHz, τ_f = ? 54.38 ppm/°C. For expanding its application in LTCC field, 3 wt% ZnO-B₂O₃-SiO₂ (ZBS) and 9 wt% TiO₂ was added into ZMC_0.06T ceramic, great microwave dielectric properties were achieved at 900 °C for 4 h: ε_r = 26.03, Q × f = 34,830 GHz, τ_f = ? 4 ppm/°C, making the composite ceramic a promising candidate for LTCC industry.     

Low temperature cofirable Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ microwave dielectric ceramic with ZnO–B2O3–SiO2 frit

The sintering properties and microwave dielectric properties of Ca[(Li_1/3Nb_2/3)_1?xZr_3x]O_3+δ (x = 0.05, abbreviated as CLNZ) ceramic doped with ZBS frit are investigated for LTCC applications. XRD patterns and SEM photographs show that dense and single perovskite phase ceramics can be obtained with ZBS doping content of less than 10 wt%, before the Ca₂Nb₂O₇ pyrochlore phase begins to segregates. The results show that ZBS vitreous phase stays at the grain boundary in the final sintered ceramics, suggesting it acts as liquid phase lubrication during sintering, and has effectively lowered the sintering temperature of CLNZ ceramics from 1170 °C to 940 °C. The preferred orientation of CLNZ solid solution varies from (1 2 1) plane to (1 0 1) plane as ZBS content and sintering temperature increase. The optimal microwave dielectric properties of ?_r = 32.0, Q_f = 6.64 THz and τ_f = ?27.1 ppm/°C can be obtained in 15 wt% ZBS doped CLNZ ceramic when sintered at 940 °C for 4 h. The Ag-cofiring experiment clearly shows that no chemical reaction takes place between Ag and the ZBS-doped CLNZ ceramic, indicating its great potential applications in LTCC field.     

Effects of Li2O-B2O3-SiO2 glass on the low-temperature sintering of Zn0.15Nb0.3Ti0.55O2 ceramics

The influences of Li₂O-B₂O₃-SiO₂ glass (LBS) on the activation energy, phase composition, the stability of the structure and microwave dielectric properties of Zn_0.15Nb_0.3Ti_0.55O₂ ceramics have been systematically investigated. LBS glass acted as flux former and contributed to the reactive liquid-phase sintering mechanism, which remarkably lowed the sintering temperature from 1150?°C to 900?°C and enhanced the shrinkage and densification of ceramic at the low sintering temperatures. The ceramics with 1.5?wt% LBS glass sintered at 900?°C for 3?h show great properties: ε_r = 73.59, Q × f = 8024?GHz, τ_f = 270.54?ppm/°C.     

Densification,flexural strength and dielectric properties of CaO-MgO-ZnO-SiO2/Al2O3 glass ceramics for LTCC applications

Novel glass ceramics for LTCC applications with high flexural strength can be achieved by CaO-MgO-ZnO-SiO₂(CMSZ) glass cofiring with Al₂O₃. The sintering shrinkage behavior, crystalline phases, mechanical and dielectric properties, and thermal expansion of the CMZS/Al₂O₃ glass ceramic were determined. The X-ray diffraction results revealed that multiphases (CaMgSi₂O₆, Al₂Ca(SiO₄)₂ and ZnAl₂O₄) formed in the sintering process of the CMZS/Al₂O₃ glass ceramic. The flexural strength of CMZS/Al₂O₃ glass ceramics first increases and then decreases with increasing Al₂O₃ content. The CMZS/Al₂O₃ glass ceramic with 50 wt % Al₂O₃ sintered at 890 °C for 2 h achieved the best performance, with a maximum flexural strength of 256 MPa, dielectric constant (ε_r) of 7.89, dielectric loss (tan δ) of 3.41 × 10⁻³ (12 GHz), temperature coefficient of resonance frequency (τ_f) of −29 ppm/°C, and the CTE value of 7.93 × 10⁻⁶/°C.     

Effect of processing route on thermomechanical properties of low temperature firing ceramic for electronic packaging

Abstract

Mechanical properties and thermal expansivities of two compositionally identical ceramics intended for use in 'low temperature cofired ceramic' (LTCC) technology were investigated. Both were based on a commercial MgCaTiO₃ dielectric ceramic with the sintering temperature reduced by addition of ZnO-B₂O₃-SiO₂, either in the glassy state or as separate glass forming oxides. Although in each case the additions were accompanied by decreases in elastic modulus, flexural strength, hardness, fracture toughness, and linear thermal expansivity, the values remained close to those for commercial LTCC materials. The route which involved mixing the separate oxides produced a slightly tougher material, which also had a thermal expansivity closer to the optimum value. The study demonstrates that an acceptable LTCC ceramic can be produced starting from glass forming oxides as sintering aids, thus avoiding the need for glass melting and comminution steps.     

Microwave dielectric properties of glass-ceramic composites for low temperature co-firable ceramics

Ba–B–Si glass was added to Ba–Nd–Sm–Bi–Ti–O (BRT₁₁₄) microwave dielectric material for LTCC applications. Conventional one-step processing method for preparing glass-BRT₁₁₄ composite materials yields low dielectric constant, since the glass was easy to react with BRT₁₁₄ and forms a low dielectric constant phase, Ba₃B₆Si₂O₁₆. A large proportion of pores appeared. The nature of glass, whether it is sol-gel derived or fused, shows marked influence on the microstructure and microwave dielectric properties of the composites. A two-step process containing precoating the BRT₁₁₄ powders with a thin layer of glass, followed by conventional samples preparation process, tremendously improved the densification behaviour of the material. The formation of pores and interactions between glass and BRT₁₁₄ was greatly suppressed such that materials with high dielectric constant (ε_r=40) were achieved by sintering 9 wt.% glass-containing composite at 950 °C for 2.5 h.     

Low-dielectric-constant LiAlO2 ceramics combined with LBSCA glass for LTCC applications

This study used Li₂O–B₂O₃–SiO₂–CaO–Al₂O₃ (LBSCA) glass to reduce the sintering temperature of LiAlO₂ ceramics and to realise the low dielectric constants (ɛ_r<5) of low-temperature co-fired ceramic (LTCC) materials. LBSCA glass remarkably enhanced the densification of LiAlO₂ ceramics. X-ray diffraction patterns indicated that only the γ-LiAlO₂ phase occurred within the doping range of 1 wt% to 3.5 wt%. Scanning electron microscopy images showed dense and uniform grains in samples with 3.0 wt% LBSCA glass. These samples also exhibited low dielectric constants and low dielectric loss when sintered at 900 °C and 950 °C (i.e., ɛ_r=4.48, Qf=35,540 GHz and τ_f=−53 ppm/°C at 900 °C; ɛ_r=4.50, Qf=38,979 GHz and τ_f=−55 ppm/°C at 950 °C, respectively). The material prepared was chemically compatible with silver and showed potential in applications of high-frequency LTCC microwave substrates.     

Influences of Liquid‐Phase Sintering on Structure,Grain Growth,and Dielectric Behavior of PbZr0.52Ti0.48O3 Ceramics

In this work, to formulate piezoceramic systems such as PbZr_0.52Ti_0.48O₃ (PZT) for low‐temperature co‐fired ceramic (LTCC)‐based devices, liquid‐phase sintering approach is demonstrated. ZnO–B₂O₃ (ZB) binary glass system is used as sintering aid. X‐ray diffraction (XRD) study confirms the formation of morphotropic phase boundary (MPB; tetragonal + rhombohedral) in PZT prepared by hydrothermal route. ZB is found to induce change in tetragonal/rhombohedral ratio in MPB of PZT. 1%ZB in PZT is found to raise the tetragonality from 71% to 92% in MPB region of PZT. ZB addition in PZT has reduced the sintering temperature from 1250 to 825°C for relative density about 91% with sustaining MPB phase. 1% ZB content is optimal percentage to enhance sinterability and relative density. Uniform dispersion of glass in PZT matrix is confirmed by SEM images. ZB content in PZT is found to controlling grain growth during sintering. Highest dielectric constant and lowest dielectric loss with low sintering temperature (825°C) of 1%ZB among all glass added in PZT exhibit technical suitability of 1%ZB + PZT to use as LTCC‐based energy storage devices.     

Phase analysis and microwave dielectric properties of LTCC TiO2 with glass system

Glass–ceramic composites containing TiO₂ (anatase, rutile) and modified borosilicate glasses were prepared and their sintering behaviour, phase evolution, interface reactions, and microwave dielectric properties were investigated as new candidates for low-temperature cofired ceramic (LTCC) materials. It was found that the addition of small amounts of borosilicate glasses lowered the sintering temperature of TiO₂ from 1400 to 900 °C. X-ray diffraction results showed that second phases, including Zn₂SiO₄, were formed when TiO₂+zinc-borosilicate glass was used, while no crystalline phase except rutile could be found using unmodified borosilicate glass. High-density TiO₂+zinc borosilicate glass material showed promising microwave dielectric properties: relative dielectric constant (ε_r)=74, quality factor (Q×f)=8000 GHz, and temperature coefficient of resonant frequency (τ_f)=340 ppm/°C. The effect of borosilicate glasses on the anatase–rutile phase transition was also investigated.     

Low-fire processing and microwave dielectric properties of LB glass-doped Ba3.75Nd9.5Ti17.5(Cr0.5Nb0.5)0.5O54 ceramic

The effects of LB glass on the sintering behavior, structure, and dielectric properties for the Ba_3.75Nd_9.5Ti_17.5(Cr_0.5Nb_0.5)_0.5O₅₄ (BNTCN) ceramic were investigated. The results showed that the LB glass, as an effective sintering aid, successfully lowered the sintering temperature of BNTCN ceramic by formation of the liquid phase. Furthermore, the change of the structure and decrease in grain size had influences on the electrical conductivity, thermal stability, and microwave dielectric properties for the BNTCN ceramics doped LB glass. Finally, the excellent microwave dielectric properties with ε_r = 73.4, Q × f = 5277 GHz, and τ_f = +7.1 ppm/°C were obtained for samples sintered at 950°C when x = 5, indicating the BNTCN ceramic doped with 5 wt% LB glass is a promoting LTCC material.     

Design and preparation of a novel degradable low-temperature co-fired ceramic (LTCC) composites

New degradable low-temperature co-fired ceramic (LTCC) composites consisting of AlN ceramic and low-melting composition B₂O₃-2SiO₂ have been fabricated at sintering temperature of 850?°C. Boron exists in low-melting composition B₂O₃-2SiO₂ in the form of [BO₃] triangle, which can not form a uniform network structure with [SiO₄] tetrahedron, this cause relatively lower chemical stability, further leading to the reaction of amorphous phase with water, therefor, the material can disintegrate when exposed to water, while Ag as electrode can be easily separated and recycled with gentle agitation and centrifugation. This has a certain significance in reducing soil pollution and water pollution caused by the landfill of LTCC products. and also in reducing the recycling costs. When AlN content is 40?wt%, samples sintered at 850?°C have thermal conductivity of 1.632?W/(m?K), dielectric constant of 4.93, dielectric loss of 0.0064, and flexural strength of 60.26?MPa, results indicate that samples are potential for LTCC application.     

A lithium aluminium borate composite microwave dielectric ceramic with low permittivity,near-zero shrinkage,and low sintering temperature

A low temperature co-fired dielectric material with low shrinkage during the sintering process can enhance the circuit design of electronic devices. Lithium aluminium borate composite ceramic with a composition of Li₂O:Al₂O₃:B₂O₃ = 1:1:2 (abbreviated: LAB) was prepared by a traditional solid-state reaction method. These ceramics have a low sintering temperature (675–750 °C), low permittivity, and near-zero shrinkage. When the sintering temperature was 725 °C, the LAB ceramics exhibited a small shrinkage of ?2.4% and the best microwave dielectric properties with ε_r = 3.9, Q × f = 35 500 GHz, and τ_?= ?64 ppm/°C. The LAB ceramics sintered at 700 °C have near-zero shrinkage of ? 0.4% and good microwave dielectric properties. The ceramics transformed from (Li₂B₄O₇ and Al₂O₃) to (Li₂Al₂B₄O₁₀ and Li₄Al₄B₆O₁₇) phases with increasing the sintering temperature, which may be the reason why they show marginal shrinkage. In addition, the ceramics could be co-fired with Ag, indicating that this material is a good candidate for low-temperature co-fired ceramic devices.     

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.