Ceramic Green Tapes Research Articles

New Elliptic Function Type UWB BPF Based on Capacitively Coupled $\lambda/4$ Open T Resonator

This paper introduces two new circuit structures for European and U.S. ultra-wideband (UWB) bandpass filters (BPFs) with sharp roll-off characteristics. The circuit structures consist of capacitively coupled three parts in stripline structure, a λ/4 open T resonator, a λ/4 short-circuited line, and input and output lines. We show first that ultra wide bandpass property is basically obtained from the T resonator with a capacitively coupled λ/4 short-circuited line, which provides two attenuation poles at lower and upper cutoff frequencies. Two identical capacitively coupled input/output lines, which can be λ/4 length open ends or λ/2 length short ends, with the T resonator are adopted to suppress lower and higher frequency components outside of the passband. There is coupling between the input and output lines providing two additional transmission zeros in the lower and upper transition bands of the filter. Since the coupling between the T resonator with the λ/4 short-circuited line and the input/output lines limits the bandwidth of the filter to the European UWB band, both the λ/4 short-circuited line and the input/output lines are inserted between the two stacked T resonators for the U.S. UWB band. The filter structures are simulated with ADS and HFSS and realized with low-temperature co-fired ceramic (LTCC) green tape which has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results.

Effect of lamination conditions for green ceramic tapes on adhesion strength, gas permeability, and yield during binder removal

The trade-off between adhesion strength and gas permeability of green ceramic tapes was examined for tapes laminated at times of 120–600 s, pressures of 1·8–7 MPa, and temperatures of 50–85°C. The dielectric in the green tapes was barium titanate, and the main components in the binder were poly(vinyl butyral) and dioctyl phthalate. The adhesion strength increased with increasing lamination time, pressure and temperature whereas the permeability decreased. The trade-off between permeability and adhesion strength with lamination conditions also influenced the component yield and cycle time for the thermal removal of binder from multilayer green ceramic bodies.

New UWB BPF with Steep Selectivity Based on T-Resonator and Capacitively Coupled λ/4 and λ/2 Line Sections

In this paper, two new circuit structures for European and U.S. ultra-wide band(UWB) bandpass filters(BPFs) with sharp roll-off characteristics are introduced. We show first that the ultra-wide bandpass property is obtained from a λ/4 open T resonator with a capacitively coupled λ/4 short-circuited line, which provides two attenuation poles at lower and upper cutoff frequencies. Then, two identical capacitively coupled input/output lines, which can be λ/4-length open ends or λ/2-length short ends, with the T-resonator, are adopted to suppress lower and higher frequency components outside of the pass band. There is coupling between the input and output lines providing two additional transmission zeros in the lower and upper transition bands of the filter. Since the coupling between the T-resonator with the λ/4 short-circuited line and the input/output lines limits the bandwidth of the filter to the European UWB band, both the λ/4 short-circuited line and the input/output lines are inserted between the two stacked T-resonators for the U.S. UWB band. The filter structures are simulated with ADS and HFSS and realized with low-temperature co-fired ceramic(LTCC) green tape which has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results.

Comparison of solvent and sacrificial volume-material-based lamination processes of low-temperature co-fired ceramics tapes

The lamination process determines the quality of low temperature co-fired ceramics (LTCC) based spatial structures. This paper compares two methods of the microchannel fabrication process in zero-shrinkage LTCC substrates. The first one is based on a two-step lamination process and uses various sacrificial volume materials (SVM). The second one is based on the cold chemical lamination (CCL) process. On the one hand, the SVM gives the possibility of decreasing the deformation of the three-dimensional (3D) structures during the lamination process. The channel volume is filled with a special fugitive material. It protects the spatial structure from deformation during lamination, and evaporates completely during the co-firing process. The bonding quality and strength depend strongly on the fugitive phase type. On the other hand, the CCL is a solvent-based method. It is another alternative for bonding of green ceramic tapes. A special liquid agent is screen printed on the green tape, which melts the tape surface. Then the tapes are stacked and compressed at room temperature by a printing roll. The influence of each method on the microchannel geometry is analyzed in this paper. The resulting structures' bonding quality and mechanical properties are examined by a scanning electron microscope (SEM).

Processing procedures for the realization of fine structured channel arrays and bridging elements by LTCC-Technology

This report deals with technological procedures to provide channel partition walls of minimum width inside of Low Temperature Co-fired Ceramics (LTCC) micro fluidic devices demonstrated by means of the fabrication of parallel closely-spaced channels which may act as a specific functional part of a fluidic heat exchanger. Furthermore, the realization of single layer bridging elements inside of channels is discussed. Such an element may be introduced as a delicate sensor substrate providing adequate thermal insulation and low thermal mass as well. The technological processing steps under consideration start with laser micromachining of green ceramic tapes using Nd-YAG-laser equipment and are followed by a modified low-pressure lamination step comprising the application of appropriate adhesives and the incorporation of polymer sacrificial volume materials (SVMs). Consequently, the increased fraction of involved organics requires an adequate adaptation of the firing process to provide a residue-free burnout. Great attention is paid to the prevention of channel cross-section distortion and to the integrity of structures, verified by optical inspection of microsectioned samples. The optimized processing procedures enable the fabrication of channel arrays with a partition wall thickness as small as 100 μm, while single layer bridging elements may span a channel width of 4 mm.

Experimental study of influential process parameters in hot embossing for micropattern formation on low temperature cofirable ceramic green substrates

Micropunching and laser drilling are conventional techniques for patterning microcavities as well as microvias on low temperature cofirable ceramic (LTCC) green tapes. Micro-hot-embossing is, however, an emerging and promising method for fabricating microstructures on prefired ceramic green tapes. This article presents experimental studies of influential process parameters in hot embossing for micropattern formation on LTCC green substrates. By means of dynamic mechanical thermal analysis, the impacts of process temperature and holding time on embossed profiles were studied and their correlation was discussed. When the temperature exceeds a certain range, the organic additives in the LTCC green substrates start to decompose at the isothermal condition, and this loss of organic additives increases the difficulty in embossing. Micropatterns with various dimensional scales, including microchannels, were formed on green ceramic substrates under optimal process parameters, and the patterned ceramic substrates were obtained via sintering.

Manufacture of 3D structures by cold low pressure lamination of ceramic green tapes

3D multilayer devices were generated by Laminated Object Manufacturing (LOM), a well-known rapid-prototyping technology. Divergent from this method, commercial ceramic green tapes were used which were laminated by Cold Low Pressure Lamination (CLPL). In contrast to thermo-compression, which works at pressures and elevated temperatures, CLPL allows to join particularly fine, complex structures with cavities or undercuts, because no mass flow occurs. This technique is based on gluing the adjacent tapes by means of an adhesive film at room temperature under a low pressure. After binder burnout and sintering the ceramic laminate has a homogenous and dense microstructure free of interfaces. This modified LOM technique is particularly suitable for the production of Micro Electro Mechanical Systems (MEMS). In the given paper commercial Low Temperature Co-fired Ceramic (LTCC) green tapes were used, which were structured by means of a high-frequency milling plotter and laminated by using CLPL. Various 3D devices of different shape with inlying cavities were manufactured. The quality of the fired and unfired structures of the devices were characterised by different methods and show a high quality surface of the multilayer structures. Process aspects of the CLPL technique are discussed. The results demonstrate the advantages of this method for the fabrication of MEMS.

Thermal analysis and microstructural characterization of ceramic green tapes prepared by aqueous tape casting

In this study, aqueous lead magnesium niobate (PMN) slurry formulations were developed for tape casting using a poly(acrylic acid) - poly(ethylene) oxide comb polymer as the dispersant, nonionic acrylic latex as the binder phase and hydroxypropyl methylcellulose as the wetting agent. Concentrated suspensions were cast onto a silicone-coated mylar film, and the effect of acrylic latex on deposition was investigated.Thermal analyses were performed to investigate the mass loss of the green tapes as a function of calcination temperature. Differential scanning calorimetric analyses were made under air and nitrogen atmospheres to investigate the binder distribution through the green tapes. Results showed that it is possible to prepare flexible, crack free PMN thick films using a proper slurry composition in the presence of acrylic latex binder, without using any plasticizer. Additionally, decomposing mechanisms of the acrylic based binder were essentially different in the two atmospheres.

Study of mechanical response in micro-indentation of laminated ceramic green substrates

Micro-indentation at elevated temperature is an effective method for studying the mechanical response of a material used in micro embossing. In this study, micro-indentation was performed on co-firable green ceramic substrates for the purpose of simulating micro embossing process and investigating the mechanical response at certain temperature. The laminated low temperature co-firable ceramic (LTCC) green tapes were used as the testing materials, the correlations of indentation depth versus applied force at various temperatures ranging from 25 to 75°C were studied. The results showed that permanent indentation cavities could be formed and retained at the temperatures ranging from 25 to 75°C; the depth of cavities created was applied force, temperature and holding time dependent. Creep during holding period occurred and made a significant contribution to the plastic deformation at elevated temperatures. There were instantaneous recoveries during the unloading and cooling processes, and retarded recovery in the first day after indentation as well. No significant pile-up around the indented cavities at the temperatures up to 75°C was observed, suggesting that there was little material flow during indentation at this temperature range. The indented cavities on green ceramic substrates were formed mainly due to the plastic deformation under compression. The findings could be used as a guideline for micro embossing of ceramic green substrates.

A micro roller embossing process for structuring large-area substrates of laminated ceramic green tapes

This paper presents a micro roller embossing process for patterning large-area substrates of laminated green ceramic tapes. The aim of this research is to develop a large-area microstructure formation technique for green ceramic substrates using a thermal roller laminator, which is compatible with screen printing apparatus. A thin film nickel mold was developed via photolithographic patterning and nickel electroplating on a 75-μm-thick nickel film. The mold had an effective panel size of 150 mm × 150 mm with the height of plated protrusive patterns being about 38 μm. Formation of micro patterns was successfully demonstrated over the whole panel area on laminated green ceramic tapes using roller embossing. Micro patterns for inductors, heaters as well as interconnection with 50 μm line-width were embossed on green ceramic substrates. By means of tuning process parameters including roller temperature, applied pressure and feeding speed, we have demonstrated that micro roller embossing is a promising method for patterning large-area green ceramic substrates.

Study on micro hot embossing of low temperature co-firable ceramic green substrates

Multi-layered ceramic substrates with embedded micro patterns are becoming increasingly important, for example, in harsh environment electronics, enabling microsystems and microfluidic devices. Fabrication of these embedded micro patterns, such as micro channels, cavities and vias, is a challenge. This study focuses on the process aspects of patterning micro features on low temperature co-firable ceramic (LTCC) green substrates using micro hot embossing. Green ceramic tapes that possessed near-zero shrinkage in the x–y plane were used, six layers of which were stacked and laminated as a substrate. The process parameters that impact on the embossing fidelity were investigated and optimized in this study. Micro features with channel-width as small as several micrometers were formed on green ceramic substrates. The dynamic thermo-mechanical analysis indicated that extending the holding time at a certain temperature range would harden the substrates with little effect on improving the embossing fidelity. Ceramic substrates with embossed micro patterns were obtained after co-firing; the shrinkage ratios of the embossed depth and channel-width were 8–15 and 12–17%, respectively. The changes of pitches between two embossed channels were within ±1.0% due to the interlocking effect of the ceramic tapes.

Cold chemical lamination of ceramic green tapes

The cold chemical lamination (CCL) is a new technique of bonding ceramic green tapes into one 3D structure. Instead of a standard thermo-compression method, new solvent-based lamination is presented. A film of a special chemical agent is put on the green tape surface. The solvent melts the surface. Then the tapes are stacked. The bonding of the green tapes is made at a room temperature. The new method is used for joining green tapes of the low temperature co-fired ceramics (LTCC). A quality of the bonding depends on the solvent type. The cold chemical lamination is examined on two types of the LTCC tapes: DuPont 943 and DuPont 951. Six types of the solvents are analyzed in the paper. The bonding quality and geometry of the test structures are examined. The lamination quality is investigated by the scanning electron microscope.

Permeability of Laminated Green Ceramic Tapes as a Function of Binder Loading

The gas permeability of laminated green ceramic tapes was determined versus organic loading for samples subjected to air oxidation. The dielectric in the tapes was barium titanate, and the binder consisted primarily of poly(vinyl butyral) and dioctyl phthalate. Both the normalized gas flux and the gas permeability were seen to approach constant values for five or more tapes laminated together. Because the characteristic pore size was 0.5–1 μm, Poiseuille flow was the dominant flow mechanism, and thus Darcy's law was valid. The permeability of five laminated tapes was a factor of five smaller than for unlaminated tapes. Values were also obtained for the permeability versus binder loading in terms of the microstructural features of specific surface, porosity, and a parameter to account for tortuosity and constrictions.

Electrochemical oxygen separation and compression using planar, cosintered ceramics

Cosintered, planar electrochemical devices were used to separate and compress oxygen at pressures as high as 2 MPa. Thin samaria-doped ceria electrolytes (CSO) were mechanically supported by porous electrodes and dense microchannel layers. Composite electrodes, comprised of CSO and La 1 − x Sr x Co 0.2Fe 0.8O 3 − δ (LSCF) particles, were used for cathodic and anodic reactions. The incoming air and the separated oxygen were manifolded through microchannel layers composed of La 1 − y Ca y MnO 3 (LCM), a dense electrically conductive ceramic. Multiple green ceramic tape layers were featured by laser cutting before lamination. The laminated structure was cosintered to produce a functional microchanneled electrochemical device or couple suitable for electrically driven oxygen separation at temperatures > 600 °C. Multiple couples were assembled into stacks and connected electrically in series to generate the oxygen flow desired. The high chemical expansion of the electrodes resulted in microcracking, which facilitated the operation of this planar device without damage to the electrolyte. The thermal expansion of the LCM can be tailored to eliminate residual tensile stress in the electrolyte. Fabrication challenges include the different initial sintering temperatures and varying sintering rates of the materials. Good bonding between layers during cosintering enables the device to withstand internal oxygen pressures high enough to be used for many applications requiring pressurized high-purity oxygen; without the aid of an auxiliary mechanical endload.

An X-Ray Imaging-Based Layer Alignment and Tape Deformation Inspection System for Multilayer Ceramic Circuit Boards

Advances in conductor patterning and via preparation techniques have facilitated a continuous increase in the circuit packaging density of ceramic multilayer substrates. A decrease in feature size combined with the trend toward constantly increasing the processed panel size is placing extremely high demands for layer-to-layer alignment as well as ceramic green tape stability. This paper describes the main mechanisms contributing to layer-to-layer alignment errors in the ceramic tape alignment and stacking process and introduces a simple, nondestructive, X-ray imaging-based method for measuring alignment error in a ceramic multilayer substrate. A low-temperature cofired ceramic (LTCC) test panel was manufactured and analyzed using the introduced X-ray inspection method. In order to define the error caused by tape alignment and stacking as well as tape deformation, the alignment error between the layers was calculated over the whole panel area. The specific area of an LTCC panel that meets the required alignment tolerances can be identified from the calculated results.

Laminated Ceramic Structures within Alumina / YTZP System Obtained by Low Pressure Joining

The production of multilayer ceramics by laminating stacked green ceramic tapes is one of the most attractive methods to fabricate layered materials. In this work, a new lamination technique was employed to obtain laminated ceramic structures in the aluminazirconia system with residual stress compression at the outer layers. This reinforcement mechanism would lead to ceramics with changed material properties and R-curve behaviour. The optimization of processing parameters for fabrication of defect free monolithic and laminated structures is described. The residual stresses developed in the laminated structures are discussed in terms of the results obtained from piezo-spectroscopic technique measurements and finite element method calculations.

Fabrication and Properties of the Tape-Cast Si<sub>3</sub>N<sub>4</sub> with Rod-Like Si<sub>3</sub>N<sub>4</sub> Seed Addition

Silicon nitride ceramics with and without β-Si3N4 seed addition were prepared via tape casting nonaqueous ceramic slurries, laminating the green ceramic tapes, and gas pressure sintering the green bodies in nitrogen atmosphere. Lu2O3 and SiO2 were used as sintering additives. The results showed that the rod-like β-Si3N4 seed was helpful to enhance β-Si3N4 grain growth unidirectionally. The elongated grains grown from seeds were preferentially oriented parallel to the casting direction, resulting in anisotropic microstructure. When a stress was applied with along the grain alignment, the bending strength of the tape-cast Si3N4 with 3 wt% β-Si3N4 seed addition measured at 1500oC was 738 MPa, which was almost the same as the room temperature bending strength 739 MPa, and the fracture energy can be improved from 301 J/m2 at room temperature to 781 J/m2 at 1500oC. The large fracture energy and bending strength at 1500oC were attributable primarily to the unidirectional alignment fibrous grains and a high melting point grain boundary phase.

Permeability of Green Ceramic Tapes as a Function of Binder Loading

The permeability of green ceramic tapes was determined as a function of binder content for binder removed by air oxidation. The tapes were comprised of barium titanate as the dielectric, and polyvinyl butyral and dioctyl phthalate were the main components of the binder mixture. The flow in porous media through the tapes was analyzed in terms of models for describing Knudsen, slip, and Poiseuille flow mechanisms. The characteristic pore size was determined to be 1–2 μm, and thus Poiseuille flow was the dominant transport mechanism contributing to the flux. The permeability was then determined from Darcy's law for flow in porous media. The permeability was also determined from microstructural attributes in terms of the specific surface, the pore fraction, and a term to account for tortuosity and constrictions.

Optimization of accumulating sequence for solid freeform fabrication system

Solid freeform fabrication system has recently been used in many practical areas for fast manufacturing of a concept model. Prototype model can easily be made using a solid freeform fabrication system at the product-developing step for checking and correcting the probable design error. The system considered for this paper basically consists of laser cutting apparatus and material handling equipment. The basic principle of the process is such that 3D CAD data is sliced into thin 2D layers, each slice is cut by laser source along the profile of the 2D layer information and the slices are stacked for sintering in a furnace. Material for the process initially was raw ceramic green tape and becomes hard enough for practical use

Alumina–zirconia layered ceramics fabricated by stacking water processed green ceramic tapes

Lamination of stacked green ceramic tapes is one of the most attractive methods for the production of multilayer ceramics with strong interfaces. In this work the fabrication of high density layered ceramics by joining ceramic green tapes processed from aqueous ceramic slurries is described. Layers with different thickness and compositions in the alumina–zirconia system were combined to obtain layered ceramics with R-curve behaviour. The optimization of the sintering schedule to obtain crack free structures is described. The mechanical behaviour of the laminates, characterized by the indentation strength method, is discussed in terms of that of the constituent layers and the residual stresses developed.