Ceramic Green Tapes Research Articles

Low Loss LTCC Ag System for 5G Applications

Abstract Low dielectric constant/low loss LTCC materials have drawn much attention with the emergence of 5G wireless telecommunications. LTCC offers unique properties in the millimeter wave frequency range. The low dielectric constant and dielectric loss enable low latency devices with enhanced performance. To meet the market demands of higher performance and lower cost, Ferro has developed a new M7 LTCC/Ag cofireable system suitable for antenna in 5G and other high frequency applications. M7 LTCC ceramic green tape and cofireable Ag conductors have been developed and tested. Properties of the LTCC/Ag system are included herein including high frequency dielectric properties.

Application of composite binders in the fabrication of LTCC green tape based on the borosilicate glass/Al2O3 system with optimized Ca/Mg ratios

This study aimed at developing a high-performance low temperature co-fired ceramic (LTCC) green tape with good sintering characteristics and dielectric properties based on a borosilicate glass/Al2O3 system. First, the Ca/Mg ratio in the glass composition was optimized to modify the microstructure, sintering density, and dielectric properties. Subsequently, composite binders of various molecular weights were employed in the tape casting slurries, to improve the performance of the green tapes. Following a comprehensive analysis of the multiple necessary performance parameters, we concluded that the glass/Al2O3 composite with Ca/Mg = 4.30 sintered at 875 °C presented a dense microstructure with outstanding sintering characteristics and dielectric properties (density of 3.14 g/cm3, permittivity of 8.02 and dielectric loss of 11 × 10−4 (10 MHz)). The application of composite binders with 60% B20H and 40% B79 yielded a green tape with a high density (1.94 g/cm3), smooth surface (Ra = 213 nm), and good workability. In addition, the thermal and mechanical properties of the optimized composite were practical for electronic packaging applications. This positive assessment of the co-firing compatibility between the composite and Ag electrodes augments its application potential for LTCC technology.

3D-customized thin-walled ceramic mouldings produced by deep drawing of green tapes

Thin-walled 3D-customized ceramic components can be used, e.g. for inert and thermal resistant housings as well as special surface structured kiln furniture. For manufacturing such components, deep drawing of ceramic green tapes has been used. The technology has been almost not applied for processing of ceramic green tapes. A new approach was developed to realize a homogenous ceramic particle packing and hence uniform green density within a deep drawn green tape. After debinding and sintering, defect-free model structures with a dense microstructure (density > 99%) were achieved. Within this study, the deep drawing of ceramic green tapes by using a new approach was investigated. The developed approach brings several beneficial properties together, e.g. a reproducible form deviation and more importantly a homogeneous particle distribution allowing homogeneous and dense structures. With this results, the transformation of non-complex and cheap ceramic green tapes to 3D-customized and near-net-shape thin-walled mouldings becomes possible.

Tape casting of multilayer YAG-Nd:YAG transparent ceramics for laser applications: Study of green tapes properties

In this study, the mechanical properties of ceramic green tapes elaborated by tape casting were determined. The influence of slurry formulation (i.e. organic content and binder-to-plasticiser volume ratio) on these properties was studied. In the studied formulation domain with polyvinyl butyral (PVB) and benzyl butyl phthalate (BBP) as binder (B) and plasticiser (P) respectively, it was shown that maximum elongation, maximum stress and Young’s modulus are increased for higher organic content and B/P ratio. This work also shows the possibility to manufacture multi-layered transparent ceramics for waveguide applications by the tape casting process. In that case, a compromise has been identified between good mechanical properties and low organic content that can alter the transparency of the material.

Scanning electron microscopical observation of an osteoblast/osteoclast co-culture on micropatterned orthopaedic ceramics

Category: Basic Sciences/Biologics Introduction/Purpose: In biomaterial engineering, the surface of an implant can influence cell differentiation, adhesion and affinity towards the implant. On contact with an implant, bone marrow-derived mesenchymal stromal cells (BMSCs) demonstrate differentiation towards bone forming osteoblasts, which can improve osteointegration. The process of micropatterning has been shown to improve osteointegration in polymers, but there are few reports surrounding ceramics. Several implants in forefoot surgery like the Moje metatarsal phalangeal joint replacement were made from smoother ceramic zirconia toughened alumina (ZTA). The aim was to establish whether the pits were specifically bioactive towards osteogenesis or were generally bioactive and would also stimulate osteoclastogenesis that could potentially lead to osteolysis. Methods: We established a co-culture of bone marrow-derived mesenchymal stromal cells (BMSCs) with osteoclast progenitor cells and to observe the response to micropatterned ZTA ceramics with 30 µm diameter pits compared to smooth controls. Micropatterned masks were fabricated using a standard photolithography and electroplating technique. Micropatterned ceramic substrates were produced by embossing of visco-plastic green ceramic tapes at room temperature followed by sintering. After informed consent was obtained from healthy patients undergoing routine total hip arthroplasty, bone marrow was aspirated from the femoral medullary canal. At day 3, non-adherent cells were removed within the supernatant and cultured separately until a confluent BMSC layer was identified. The co-culture was maintained up to specific time points (days 3, 7, 14, 21 and 28) with thrice weekly media exchange. At each time point, duplicate samples were fixed and prepared for analysis by scanning electron microscopy (SEM) with immuofluorescence and histochemical staining, Results: SEM analysis of the patterned materials demonstrated successful micropatterning of the ZTA ceramic with approximately 30 µm diameter, 1.7 µm depth pits due to sintering shrinkage. At the longest time-point (day 28), osteoclast-like cells were visible across the planar surfaces and had strong interactions with the ceramic grains. Podosomes were notable on some of the osteoclast membranes. On the pitted surfaces, we observed significantly less osteoclast-like cells. Also, pit bridging by macrophage-like cells was regularly noted. Nodular clusters of osteoblast-like cells were noted statistically more often on the micropatterned ceramics. Conclusion: These results demonstrated specific bioactivity of micropatterned ZTA ceramics towards osteogenesis, with more bone nodule formation and less osteoclastogenesis compared to planar controls. In addition, we found that that macrophage and osteoclast-like cells did not interact with the pits and formed fewer full-size osteoclast-like cells on the pitted surfaces. This may have a role when designing ceramic orthopaedic foot implants. We are now using this co-culture for research on other micropatterned biomaterials used in foot and ankle surgery.

Tape casting and characterization of Li2.08TiO3-LiF glass free LTCC for microwave applications

Li2.08TiO3-LiF Glass-free Low temperature co-fired ceramic (LTCC) green tapes were prepared by tape casing technique. The rheology of the slurry was characterized using rheometer. The slurry exhibited pseudoplastic behavior. The sintering kinetics of the green tape was investigated using heating microscope. The sintering activation energy was determined to be ∼173kJ/mol. The green tape could be densified at 900°C/2h. Microwave dielectric properties of the sintered tape were characterized in a split-post dielectric resonator using a network analyzer. The ceramic sheet with thickness of 0.11mm demonstrated good microwave dielectric properties: εr=22.4 and Q×f=35,490GHz. The cross sectional microstructure of the cofired multilayer stack was observed by scanning electron microscopy (SEM). The green tape demonstrated good chemical and shrinkage compatibilities with Ag electrode during sintering process. The thermal expansion coefficient and thermal conductivity of the ceramic is 22.4ppm/∘C and 4.75Wm−1K −1, respectively.

The co-casting process: A new manufacturing process for ceramic multilayer devices

In this work we present a simplified process chain of the conventional multilayer ceramic technology and offer a comfortable method for precise multilayer manufacturing without complex equipment. To circumvent the usual stacking and laminating of single ceramic green tapes to get multilayer devices, a Magnetically Assisted Stencil Printing (MASP) technique was developed. It enables a subsequent casting of ceramic layers and printing of electrode layers. How the co-casting process can be performed either by the use of a modified tape caster at the lab scale or by use of a precision squeegee is described in this paper. Both variants are suited for manufacturing multilayer ceramics with layer thicknesses less than 25μm. We successfully manufactured pentalayers without cracks or de-laminations from a soft- and also a hard-PZT powder. In a previous work, we investigated sintering additives for PZT. By the use of a PZT-based low-temperature sintering powder composition, cost-effective silver inner electrodes could be realized inside the multilayer ceramics. Piezoelectric low-cost multilayer bending transducers are of particular interest for the use as generators in vibration energy harvesting systems. The proposed triplelayer beam harvests 20μW (3.2V) at 71Hz and an input acceleration of 17.8m/s2.

Multilayer capacitors with bismuth copper tantalate dielectric fabricated in LTCC technology

Purpose The work was aimed at preparation of green tapes based on a new material Bi2/3CuTa4O12, to achieve spontaneously formation of an internal barrier layer capacitor (IBLC), fabrication of multilayer elements using low temperature cofired ceramics (LTCC) technology and their characterization. Design/methodology/approach The study focused on tape casting, lamination and co-sintering procedures and dielectric properties of Bi2/3CuTa4O12 multilayer capacitors. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies of the ceramic elements were performed. Impedance spectroscopy was used for characterization of dielectric properties in the frequency range of 0.1 Hz to −2 MHz and in the temperature range from −55 to 400°C. DC conductivity was investigated in the temperature range 20 to 740°C. Findings SEM observations revealed a good compatibility of the applied commercial Pt paste with the ceramic layers. The EDS microanalysis showed a higher content of oxygen at grain boundaries. The dominant dielectric response, which was recorded in the low frequency range and at temperatures above 0°C, was attributed to grain boundaries. The dielectric response at low temperatures and/or high frequencies was related to grains. The fabricated multilayer capacitors based on Bi2/3CuTa4O12 exhibited a high specific capacitance. Originality/value A new material Bi2/3CuTa4O12 was applied for preparation of green ceramic tapes and utilized for fabrication of multilayer ceramic capacitors using the LTCC technology. This material belongs to the group of high permittivity nonferroelectric compounds with a complex perovskite structure of CaCu3Ti4O12, that causes the spontaneously formation of IBLCs.

Conceptual design and manufacture of spirally wound alumina tubes with improved thermal shock behavior for refractory applications

Rotationally symmetric refractory nozzles have been fabricated using the spiral winding technique with ceramic alumina green tapes. Different layer designs have been developed in order to obtain a homogeneous fired structure with locally delaminated interfaces, which are expected to improve the thermal shock behavior. In this regard, the microstructure of all fired structures has been investigated. Thermal shock tests have been conducted to evaluate the impact of the layer design on the formation of micro cracks and other damage. Subsequently, the corrosion behavior of these nozzle compositions has been investigated.

New Lightweight Kiln Furniture Made by Combination of Ceramic Green Tapes and Extrudates

Manufacturing technology for new kiln furniture with a significantly lower density and thermal capacity are presented. Extrusion and tape casting are used as two highly productive technologies to produce different green ceramic pre-products, which are combined and co-sintered to realize kiln furniture. Planar green tapes are laminated with an extruded supporting structure including macroscopic cavities to allow passage of the kiln atmosphere and additionally reduce the density and heat capacity of the structure. With such kiln furniture high heating and cooling rates up to 10 K/min can be realized without any defects resulting from thermal stresses. The improved temperature distribution achieved allows a reduction of necessary dwell times. Both make it possible to save energy and time.

A Novel Co-casting Process for Piezoelectric Multilayer Ceramics with Silver Inner Electrodes

The presented process offers a simplified method for manufacturing multilayer ceramics (MC) in comparison to the conventional multilayer ceramics technology (MCT). It combines the tape casting of ceramic green tapes and the subsequent screen printing of electrodes into one single co-casting process. Since the co-casting process circumvents also the stacking and laminating of single ceramic green tapes, MC with layer thicknesses as thin as 20μm could be manufactured by this technique. To create an easy contacting of the inner electrode in the MC, the generation of an interdigital electrode structures has been aspired. By means of the specific innovation, to fix a shadow mask by magnetic forces on top of the ceramic green tape, this was realized. With the intention to manufacture piezo generators for vibration energy harvesting, triple-layered bending transducers have been manufactured successfully from a hard-doped PZT powder and inner electrodes made of pure silver via this new co-casting process. The material compatibility for the co-firing step of PZT and the cost-effective base metal silver was achieved by means of the liquid phase sintering technology, using a combination of Li2CO3·Bi2O3·CuO (LBCu) as sintering additives.

Investigation of the storage and release of oxygen in a Cu-Pt element of a high-temperature microcombustor

A miniature combustor for converting organic samples into CO2 with application in carbon isotopic measurements has been manufactured and evaluated. The combustor was made of High-Temperature Co-fired Ceramic (HTCC) alumina green tapes. The device has a built-in screen printed heater and a temperature sensor made of platinum, co-sintered with the ceramic. A copper oxide oxygen supply was added to the combustor after sintering by in-situ electroplating of copper on the heater pattern followed by thermal oxidation. Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Thermal Gravimetric Analysis (TGA) were used to study electroplating, oxidation and the oxide reduction processes. The temperature sensor was calibrated by use of a thermocouple. It demonstrates a temperature coefficient resistance of 4.66×10−3/°C between 32 and 660 °C. The heat characterization was done up to 1000 °C by using IR thermography, and the results were compared with the data from the temperature sensor. Combustion of starch confirmed the feasibility of using copper oxide as the source of oxygen of combustion.

Lamination of Green Ceramic Tapes by Applying Pressures Directly at Ambient Temperature

The lamination of green ceramic tapes is the basis of the production of multilayer ceramic devices. In this paper, cordierite green ceramic tapes are laminated by applying pressures directly at ambient temperature. As a first attempt, the effect of pressure, layers, dwell time on lamination and the sintering temperature on laminates are investigated. It is shown that pressure makes the greatest effect on lamination and dwell time is not obvious. The effect of layers on lamination is mainly related to the pressure that is executed on tapes, and the sintering temperature is contributed to the dense of laminates. The pressure of lamination is not high, and the tapes do not need to be heated. Taking a pressure-assisted method, the deformation of laminates during sintering can be avoided, and a better lamination effect is acquired. The lamination and pressure-assisted methods are both of low cost and simple and feasible to work.

Thermomechanical stability and integrability of an embedded ceramic antenna with an integrated sensor element for wireless reading in harsh environments

This paper reports on the design, manufacturing and evaluation of a small, wirelessly powered and read resonating antenna circuit with an integrated pressure sensor. The work aims at developing miniature devices suitable for harsh environments, where high temperature prevents the use of conventional, silicon-based microdevices. Here, the device is made of alumina with platinum as conducting material. Ceramic green tapes were structured using high-precision milling, metallized using screen printing, and subsequently laminated to form stacks before they were sintered. The device's frequency shift as a function of temperature was studied up to 900°C. The contributions to the shift both from the thermomechanical deformation of the device at large, and from the integrated and, so far, self-pressurized sensor were sorted out. A total frequency shift of 3200 ppm was observed for the pressure sensor for heating over the whole range. Negligible levels of thermally induced radius of curvature were observed. With three-point bending, a frequency shift of 180 ppm was possible to induce with a curvature of radius of 220 m at a 10 N load. The results indicate that a robust pressure sensor node, which can register pressure changes of a few bars at 900°C and wirelessly transmit the signal, is viable.

Joining of Sintered Alumina Substrates and LTCC Green Tapes via Cold Low‐Pressure Lamination

Common technologies for the manufacture of ceramic‐based microelectronic devices are thick‐film hybrid technology and LTCC technology. The first one uses sintered ceramic substrates, mostly Al2O3, to provide very good heat conductivity, for example of 25 W/mK for alumina substrates; but there are only two sides to carry a metallization. An improved miniaturization can be accomplished by multilayer systems using the LTCC technology. A drawback of LTCCs is their low heat conductivity of typically 3 W/mK due to the high glass content. By combining hybrid and LTCC technology, the advantages of both methods can be joined. Because the failure rate is too high to laminate sintered substrates and ceramic green tapes via thermo compression, cold low‐pressure lamination (CLPL) has been used. CLPL is a lamination method, where the joining is performed at room temperature by application of very low pressure (<5 MPa) using a double‐sided adhesive tape. During heat treatment, the adhesive film keeps the tapes together until the adhesive is completely decomposed; during further temperature increase, the tapes are joined by sintering. The study describes the materials used and processing steps and discusses effects which occur during firing. These effects like edge curl and crack formation are mainly due to stresses which occur during constrained sintering.

Lamination of Green Ceramic Tapes with Adhesive at Ambient Temperature

In this paper, green ceramic tapes are joined together by adhesive based lamination technique. The effects of adhesive concentration, pressure on the lamination and sintering temperature on the laminate are mainly discussed. The parameters are also optimized. It was shown that the effect of adhesive concentration and pressure on the lamination is obvious and the effect of sintering temperature is not big. 10 layers of cordierite tapes can be laminated under 2MPa with a dwell time of 3min with PVA by adhesive based lamination. The adhesive based lamination can be used to be an alternative of thermo-compressive lamination.

Joining of Sintered Alumina Substrates and LTCC Green Tapes via Cold Low Pressure Lamination

In microelectronics there is a continuous trend for devices of higher integration and improved heat dissipation. For the manufacture of ceramic based microelectronic devices the following technologies can be applied. Thick-film hybrid technology uses sintered ceramic substrates, mostly Al2O3, which are screen printed with functional pastes, followed by firing at 850 °C. Alumina substrates provide very good heat conductivity (25 W/mK), but there are only two sides to carry a metallization. An improved miniaturization can be accomplished by multilayer systems using the LTCC technology. LTCC devices are manufactured by screen-printing, stacking and lamination of ceramic green tapes, followed by co-firing. A drawback of LTCCs is their low heat conductivity (3 W/mK) due to their high glass content. By combining hybrid and LTCC technology the advantages of both methods like good thermal conductivity and high multilayer integration, can be joined. Because the failure rate is too high to laminate green tapes on sintered ceramic substrates via thermo compression, Cold Low Pressure Lamination (CLPL) has been used as an alternative lamination process. CLPL is a lamination method, where the joining of the components is performed at room temperature by application of very low pressure (<5 MPa) by using a double sided adhesive tape. During heat treatment the adhesive film keeps the tapes together until the adhesive is completely decomposed; during further temperature increase the tapes are joined by sintering. The paper describes the materials used and processing steps to join the sintered material with the green tapes and discusses effects which occur during firing. These effects like edge curl and crack formation are mainly due to stresses which occur during constrained sintering. Their control can be influenced by changing process parameters.

Processing of preceramic paper and ceramic green tape derived multilayer structures

Multilayer laminates with gradients in material composition and porosity were fabricated by the combination of ZrO2, Al2O3–ZrO2 and Al2O3–MgAl2O4 preceramic papers with MgO–MgAl2O4, Al2O3 and MgAl2O4 ceramic green tapes. A ZrO2–loaded adhesive based on an aqueous dispersion of copolymerised polyvinyl acetate served as the interface adhesive. The shrinkage behaviour of the individual layers was adapted by combining coarse and fine grained ceramic powders in order to avoid crack formation and delamination during firing. Defect-free multilayer laminates were obtained after sintering at 1700°C for 5 h which offer a high potential for application in refractory functional components.

Embossing of micropatterned ceramics and their cellular response

The aim of this work is to investigate the use of microtopographies in providing physical cues to modulate the cellular response of human mesenchymal stem cells on ceramics. Two microgrooved patterns (100 μm/50 μm, 10 μm/10 μm groove/pitch) were transcribed reversely onto alumina green ceramic tapes via an embossing technique followed by sintering. Characterization of the micropatterned alumina surfaces and their cellular response was carried out. Spread and polygonal cell morphologies were observed on the wider groove (50 μm/100 μm) surface. Cells seeded onto the narrow groove (10 μm/10 μm) surface aligned themselves alongside the grooves, resulting in more elongated cell morphology. More osteoid matrix nodules shown by osteopontin and osteocalcin biomarkers were detected on the larger grooved surfaces after cell culture of 21 days, indicating a greater level of osteogenicity. This study has shown that micropatterned wider groove (50 μm) topographies are more suitable surfaces for improving osseointegration of ceramic implants.

Lamination of Green Ceramic Tapes in the Manufacturing of Multilayer Ceramic Devices

Lamination of green ceramic tapes is one of the most important technological processes in the manufacturing of multilayer ceramic devices and it has determined influence on the quality of the devices. Therefore, choosing proper lamination technique is very important to a designed structure. The development of lamination techniques of green ceramic tapes is of great significance for the electronic communication industry and it has become a hot spot in the research. In this paper, the main lamination techniques in the present research and practice are overviewed. As to the development prospect and direction of the lamination of green ceramic tapes, the own opinions are given on the basis of lamination study in recent years.