Ceramic Green Tapes Research Articles

Lamination based embossing technique for LTCC

This article describes a LTCC embossing technique performed during the isostatic lamination process. The technique allows for the reduction of manufacturing steps by patterning simultaneously the top and bottom faces of a green ceramic tape using structured metal sheets. The experiments detail the manufacture of raised and recessed patterns on the self constrained HL2000 ceramic system, including bump arrays, raised wall structures and recessed channels.

Fatigue strength testing of LTCC and alumina ceramics bonds

In this paper the results of fatigue strength tests of ceramic joints are presented. These tests have been performed on the samples subjected to thermal and vibration fatigue as well as on the reference samples without any additional loads. The main goal of the investigation was to determine the strength of hybrid ceramics joints using tensile testing machine. The experiment enabled evaluation of fatigue effects in the mentioned joints. Geometry of test samples has been designed according to FEM simulations, performed in ANSYS FEM environment. Thermal stress as well as the stress induced by vibrations have been analyzed in the designed model. In the experiments two types of ceramics have been used — LTCC green tape DP951 (DuPont) and alumina ceramic tape. The samples have been prepared by joining two sintered ceramic beams made of different types of material. The bonds have been realized utilizing low temperature glass or a layer of LTCC green tape.

Cold Embossing of Ceramic Green Tapes

The development of alumina green tapes, made of water based binder systems, allows the structuring by so-called cold embossing. The cold embossing disclaims time expensive heating and cooling phases as needed for hot embossing. That allows a reduction of process time. The structuring by embossing becomes more practicable for high throughput manufacturing. For investigating the influence of powder amount and with or without plasticizer inside ceramic green tapes on deformation behaviour, tensile tests have been carried out. Furthermore, cold embossing tests with uniaxial compression tools were carried out. Channel structures allow investigations concerning stability against elastic recovery. In a first series of tests various green tape compositions have been investigated. As results inferences to the elastic and plastic material behaviour can be obtained. The characterisation of structured tapes in green state has been carried out by using SEM and scanning surface area by confocal white light microscopy.

Combined 3D Micro Structuring of Ceramic Green Tape Using Punching, Embossing and Laser Processing

Multilayer ceramics technology, as LTCC, offers several advantages for the fabrication of miniaturized three-dimensional structures, e.g. for microsystem applications, where electrical, mechanical and fluidic functions can be combined in robust and compact packages. 3D features, required by those applications, are e.g. vias for electrical and thermal interconnection, cavities for chip integration and channels for fluidic functions. They can be realized, in principle, in the sintered, as well as in the green state, but structuring in the green state dominates due to the then far better machinability of the material. Ceramic green tape structuring is usually accomplished by mechanical or laser machining. Punching is the standard process for realizing vias or cavities in LTCC. By nature, only through tape features can be realized, but 3D features can be realized by stacking of several layers. Embossing can be used for the realization of quite complex 3D structures with high resolution. It can be carried out either at elevated temperature, at which the binder of the tape is softened (hot embossing) or at room temperature (cold embossing). Laser structuring is a quite flexible method, which allows both through-cutting and engraving without any specific tool. However, a certain roughness of ablated areas cannot be avoided, and depth control and uniformity of laser engraved features remain challenging. In the present paper, the different techniques will be compared regarding their appropriateness for different structuring tasks. A combined use of punching, embossing and laser processing is described, which has been made possible by a novel machine and tool concept.

Realisation of Large Cavities in Multilayer Ceramics by Cold Low Pressure Lamination and Their Characterisation by μCT

In microelectronics the ceramic multilayer technology is frequently used as it allows a precise and yet flexible production of MEMS, microelectronic devices, micro reactors or devices for micro fluidics. During production of those multilayer structures the single layers are typically laminated by thermo-compression. However, large cavities cannot be realised using thermo-compression without adding sacrificial fillings. In contrast, the cold low pressure lamination (CLPL) technique allows lamination at room temperature without applying a high pressure. As in this lamination technique no mass flow occurs, internal cavities are not destroyed during the lamination step. In this study, commercially available LTCC green tapes were structured using a milling plotter with a high frequency spindle. Different process parameters (milling speed, spindle frequency) were evaluated regarding the accuracy of shape and quality of the channel edge. Channels with various dimensions (2.5 - 15 mm width and 30 mm length) were milled into the green tapes. Subsequently, the green tapes were laminated using the CLPL technique. With CLPL adjacent ceramic green tapes are joined by a double sided adhesive tape, which is applied by a soft roller. By alternately applying green (structured or unstructured) and adhesive tapes multilayer structures with internal cavities are formed. For characterisation of the sintered LTCC structures μCT (computed tomography) was used to analyse the internal structure without destroying the sample. Influence of sintering regime on deformation was evaluated. It was shown that milling of green tapes in combination with CLPL is a suitable method to fabricate internal cavities in LTCC multilayer structures.

Cold Embossing of Ceramic Green Tapes

Hot embossing of ceramic green tape allows high throughput manufacturing. Tensile tests were carried out to investigate the embossing ability of alumina green tape at room temperature. The deformation behavior was analyzed based on powder content and the use or absence of plasticizer within the ceramic green tape. Furthermore, cold embossing tests with uniaxial compression tools were carried out. A channel structure was used as a test vehicle to allow investigations into stability against elastic recovery. In the first series of tests, various green tape compositions were investigated. Inferences were made, based on the elastic and plastic material behavior. The characterisation of structured tapes in the green state was carried out by using SEM and by scanning the surface area by confocal white light microscopy.

Fabrication and properties of radially 〈001〉C textured PMN-PT cylinders for transducer applications

〈001〉C Textured PMN-PT ceramics have electromechanical properties (d33 = 850–1050 pm/V, k33 = 0.79–0.83) between those of conventional PZT ceramics and relaxor PMN-PT crystals. In this work, we tailor crystallographic orientation in textured PMN-PT ceramics for transducer designs with non-planar poling surfaces. Specifically, omni-directional cylindrical transducer elements were fabricated using monolithic, radially 〈001〉C textured and poled PMN-PT ceramic. Texture was produced by templated grain growth using NBT-PT templates, which were oriented radially by wrapping green ceramic tapes around a cylindrical mandrel. Finished transducer elements measure ∼5 cm in diameter by ∼2.5 cm in height and demonstrate scalability of textured ceramic fabrication techniques. The fabricated cylinders are ∼50 vol. % textured and show high 31-mode electromechanical properties compared to PZT ceramics (d31 = −259 pm/V, k31 = 0.43, ɛT33 = 3000, and Qm = 350). Frequency bandwidth is related to the square of the hoop mode coupling coefficient kh2, which is ∼60% higher in textured PMN-PT cylinders compared to PZT 5H. Finite element simulations show that this parameter may be further increased by improving texture quality to ≥90 vol. %. Radially textured PMN-PT may thus improve performance in omni-directional cylindrical transducers while avoiding the need for segmented single crystal designs.

Formulation and screen printing of water based conductive flake silver pastes onto green ceramic tapes for electronic applications

Abstract Environmentally friendly, water-based silver pastes, adapted for screen printing, were formulated with different silver contents (67–75%). These pastes allowed screen printing onto low temperature co-fired ceramic (LTCC) of narrow conductive tracks with a 60 μm line width and a 3 × 10−8 Ω m electrical resistivity. Inks were formulated with a mixture of spherical and flake shape silver particles with 2–4 μm mean diameter. Rheological behaviour of pastes was studied in order to determine its effect on printed lines properties. Prepared inks were then screen printed and sintered under normal atmosphere at 875 °C. As expected, electrical properties depended on silver content. Resistivity values varying from 1.6 × 10−8 to 3.3 × 10−8 Ω m were calculated over 36.3 cm line length. These values are very close to bulk silver resistivity (1.6 × 10−8 Ω m). Compared to previous research and commercial pastes, the newly formulated pastes reached equivalent or even better conductivities with lower silver content (70% by weight).

Combinatorial Study of Ceramic Tape-Casting Slurries

Ceramic tape-casting slurries are complex systems composed of ceramic powder, solvent, and a number of organic components. Conventionally, the development of ceramic tape-casting slurries is time-consuming and of low efficiency. In this work, combinatorial approaches were applied to screen the ethanol and ethyl-acetate binary solvent based slurry for ceramic green tape-casting. The combinatorial libraries were designed considering the variation of the amount of PVB (Poly vinyl-butyral) binder, polyethylene-400, and butyl-benzyl-phthalate plasticizers, and glyceryl triacetate dispersant. A parallel magnetic stirring process was used to make the combinatorial slurry library. The properties mapping of the slurry library was obtained by investigating the sedimentation and rheological characteristics of the slurries. The slurry composition was refined by scaling up the experiments and comparing the microstructure, mechanical property, and sintering behavior of green tapes made from the selected slurries. Finally, a kind of ethanol-ethyl acetate binary solvent based slurry system suitable for making X7R dielectric ceramic green tapes was achieved.

Low-pressure, thermo-compressive lamination

Lamination of green ceramic tapes is one of the most important technological processes in multilayer ceramic technology. Lamination affects the quality of all 3D structures (e.g., channels, chambers, membranes, etc.). Novel chemical methods of lamination reduce the deformation of 3D structures. However, these methods are useless in the fabrication of thin membranes and structures with thick-film electronic components or electric vias. Therefore, thermo-compressive lamination is still the best solution for the lamination of green ceramic tapes. Low-pressure thermo-compressive lamination with an insert material is presented in this paper. The influence of pressure and Low Temperature Cofired Ceramics (LTCC) material on the compressibility and shrinkage of LTCC, as well as the influence of the insert material on deflection and distortion of the membranes are presented and discussed in this paper.

Continuous Manufacture of Submicron Thick Ceramic Green Tapes and Coatings Demonstrated for TCO Nano Particles

This presentation introduces a new technique to manufacture continuously submicron thick ceramic green tapes and coatings from nano particulate suspensions. A profiled steel rod is used to coat large areas with a very low film thickness of down to 250 nm. This technique can easily be scaled up and is therefore suitable for mass production at high throughput and low cost. The profile rod technique could be a method to overcome the limit of the tape casting process and therefore this technique exhibits an enormous economical potential. The technique is demonstrated at the example of nano particulate indium tin oxide (ITO) and zinc oxide (ZnO) particles, which are both transparent conductive oxides (TCOs) and therefore interesting materials for printed displays etc. Nano particles from Evonik Degussa GmbH were first dispersed and stabilized in organic solvents. Subsequently, dispersions as well as slurries were prepared. Their rheological and wetting behavior were studied and the effect on the microstructure of the resulting layer was evaluated. Furthermore, the influence of the processing parameters during coating on the layer quality was analyzed. Finally, the functionality of the printed layers was proven by electrical measurements as well as the assembly of electron devices.

Profile Rod Technique: Continuous Manufacture of Submicrometer-Thick Ceramic Green Tapes and Coatings Demonstrated for Nanoparticulate Zinc Oxide Powders

There is a fast-growing market for printable electronics, which requires new techniques for micro- and nanofabrication suitable for mass production of functional electronic products. This makes the evaluation and comparison of different printing techniques highly important. In this work, a coating process, referred to as “profile rod technique,” is presented as an alternative to the spin-coating process for the production of nanoparticulate zinc oxide (ZnO) layers with thicknesses of several hundred nanometers. Such layers could be used, e.g., as semiconducting layers for printed thin film transistors. The profile rod technique, in contrast to spin-coating, is a continuous process, which allows for easier mass production and reduction in manufacturing costs. To compare the spin-coating and the profile rod process, submicrometer-thick layers of ZnO nanoparticle dispersions in ethanol were prepared. Different dispersion techniques were studied concerning their applicability for the manufacture of nanosized particle dispersions because well-dispersed suspensions are the basic requirement for the manufacture of submicrometer-thick layers with high morphological quality. The quality of the deposited layers was evaluated concerning their microstructure. Moreover, the profile rod technique could be successfully used for the manufacture of submicrometer ceramic green tapes.

Properties of tape-cast Y-substituted strontium titanate for planar anode substrates in SOFC applications

This work evaluates the use of fine-grained yttrium-substituted strontium titanate powders for the preparation of planar anode supported solid oxide fuel cells. Starting from a submicron-sized powder of Y-substituted strontium titanate Sr0.895Y0.07TiO3 (SYT), which was synthesised via spray pyrolysis followed by a grinding process, suspensions of high solid concentration were prepared by steric stabilisation. From these suspensions, tape casting slurries of up to 25 vol% were produced and further processed to ceramic green tapes using the doctor blade technique. The rheological behaviour of the slurries was investigated in dependence on the content of solids and organic additives. Furthermore, the binder burnout and sintering behaviour of the green sheets were characterised. After firing, crack-free substrates of high planarity were obtained. The achieved properties of the sintered tapes such as density, porosity, warping, mechanical strength, and electrical conductivity were determined in dependence on sintering temperature.

Wideband Bandstop Filter Based on Capacitively Coupled λ/4 Short-Circuited Lines

A new wideband bandstop filter(BSF) with a sharp roll-off characteristic is introduced in a stripline structure in this paper. The BSF consists of two sections: the first is two capacitively coupled λ/4 short-circuited lines with opposite ground positions, while the second is a capacitively coupled λ/4 short-circuited line. The BSF provides three transmission zeros within the stopband and better than 22 ㏈ rejection over the whole wireless local area network (WLAN) band from 5.15 to 5.825 ㎓. The BSF, cascaded to an U.S. ultra-wideband(UWB: 3.1~10.6 ㎓) bandpass filter(BPF), is simulated with HFSS and realized with low-temperature co-fired ceramic(LTCC) green tape with a dielectric constant of 7.8. The measurement results agree well with the HFSS simulation results. The size of the UWB BPF including the BSF is 3×6.3×0.45 ㎣.

Development of a micro-heat exchanger with stacked plates using LTCC technology

A green ceramic tape micro-heat exchanger was developed using Low Temperature Co-fired Ceramics technology (LTCC). The device was designed by using Computational Aided Design software and simulations were made using a Computational Fluid Dynamics package (COMSOL Multiphysics) to evaluate the homogeneity of fluid distribution in the microchannels. Four geometries were proposed and simulated in two and three dimensions to show that geometric details directly affect the distribution of velocity in the micro-heat exchanger channels. The simulation results were quite useful for the design of the microfluidic device. The micro-heat exchanger was then constructed using the LTCC technology and is composed of five thermal exchange plates in cross-flow arrangement and two connecting plates, with all plates stacked to form a device with external dimensions of 26 x 26 x 6 mm³.

Steeply Sloped UWB Bandpass Filter Based on Stub-Loaded Resonator

This letter introduces an ultrawideband (UWB) bandpass filter (BPF) with very sharp roll-off characteristics in stripline structure for the U.S. band (3.1-10.6 GHz). The UWB characteristic is basically obtained from capacitive coupling between a main line and a λ/2-length stub-loaded resonator. The stub-loaded resonator consists of λ/8 short-circuited and open-circuited stubs at the center of the λ/2 line. The two stubs provide two attenuation poles at lower and upper cutoff frequencies. For input and output lines, two λ/4 identical capacitively coupled lines have been installed to suppress the unwanted signals in the lower and upper stopbands. The filter has been designed with two transmission zeros at 2.4 and 11.1 GHz to provide 81- and 86-dB/GHz slopes in the lower and upper transition bands, respectively, and realized with low-temperature co-fired ceramic (LTCC) green tape that has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results. Insertion loss less than 1.1 dB and return loss better than 14 dB in the whole passband have been measured. The group delay at the center frequency is 0.26 ns, and the group delay variation within the passband is less than 0.5 ns. The size of the filter is 6 × 18 × 0.6 mm3.

"+"자 공진기와 용량성 결합을 이용한 초광대역 대역 통과 여파기

본 논문에서는 급격한 감쇄율 특성을 갖는 독창적인 초광대역(UWB: Ultra Wideband) 스트립라인 대역 통과 여파기(BPF)를 소개한다. 초광대역의 특성은 기본적으로 "+"자 공진기와 주 전송 선로간의 용량성 결합으로부터 얻어진다. "+" 자 공진기는 <TEX>${\lambda}/2$</TEX>의 전송 선로의 중심에 두 개의 스터브를 병렬 연결된 구조를 가진다. 하나는 <TEX>${\lambda}/8$</TEX> 단락 회로 스터브로 <TEX>${\lambda}/2$</TEX> 전송 선로의 상측에 연결되고, 다른 하나는 <TEX>${\lambda}/8$</TEX> 개방 회로 스터브로 <TEX>${\lambda}/2$</TEX> 전송 선로의 하측에 연결된다. 이 두 개의 스터브들은 통과 대역의 하단과 상단의 차단주파수에서 두 개의 감쇄극을 제공한다. "+" 자 공진기 상측에 위치하여 용량성 결합을 이루는 주 전송 선로는 입력과 출력 선로에 또 한 번의 <TEX>${\lambda}/4$</TEX> 길이의 용량성 결합을 하여 통과 대역 하부과 상부의 저지 대역에서 원하지 않는 신호를 억압하기 위해 구성하였다. 본 여파기는 미국에서 허가한 초광대역(3.1~10.6 GHz)의 대역에서 선택도가 우수한 대역 통과 특성을 얻기 위해 2.4 GHz와 11.1 GHz에서 81 dB/GHz와 86 dB/GHz의 기울기를 제공하는 두 개의 전송 영점(감쇄극)을 갖도록 설계되었다. 본 여파기는 유전상수 7.8을 갖는 저온 동시 소성 세라믹(LTCC) 그린테이프로 제작되었다. 측정 결과는 HFSS 해석 결과와 거의 일치하였다. 통과 대역에서 0.7 dB 이하의 삽입 손실과 14 dB 이상의 반사 손실이 측정되었다. 중심 주파수 군 위상 지연은 0.27 ns이고, 통과 대역에서 군 위상 지연의 변화량은 0.5 ns 이하이다. 본 여파기의 크기는 <TEX>$6{\times}18{\times}0.6\;mm^3$</TEX>이다. This article introduces a novel ultra wideband(UWB) bandpass filter(BPF) with sharp roll-off characteristics in stripline structure. The UWB characteristic is basically obtained from capacitive coupled cross resonator. The resonator has <TEX>${\lambda}/2$</TEX> length. And at the center of the resonator, two stubs are loaded, one is a <TEX>${\lambda}/8$</TEX> short-circuited stub and the other is a <TEX>${\lambda}/8$</TEX> open-circuited stub. The two stubs provide two attenuation poles at lower and upper cutoff frequencies. For input and output lines, two identical capacitively coupled lines have been installed to suppress the unwanted signals in the lower and upper stopbands. The filter has been designed for the U.S. UWB band(3.1~10.6 GHz) with two transmission zeros at 2.4 and 11.1 GHz. The filter has been realized with Low Temperature Core-fired Ceramic(LTCC) green tape which has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results. Insertion loss less than 0.7 dB and return loss better than 14 dB in the pass band have been measured. The group delay in the center frequency is 0.27 ns and the group delay variation within pass band is less than 0.5 ns. The size of the filter is <TEX>$6{\times}18{\times}0.6\;mm^3$</TEX>.

New UWB 1:2 Power Divider with Flat In-Band Splitting and Bandpass Filtering Functions

This paper introduces a new U.S. ultra-wideband(UWB: 3.1~10.6 GHz) 1:2 power divider based on a single section Wilkinson type configuration. The divider provides very flat in-band power splitting, high isolation, low insertion loss, sharp roll-off bandpass filtering, and DC blocking characteristics. The circuit consists of a <TEX>$\lambda$</TEX>/4 Y resonator, three capacitively coupled <TEX>$\lambda$</TEX>/2 short-circuited lines, and a resistor between the two output ports. The circuit structure was simulated with ADS and HFSS, and realized with low-temperature co-fired ceramic(LTCC) green tape, which has a dielectric constant of 7.8. <TEX>$|S_{11}|$</TEX> better than 10 dB, <TEX>$|S_{21}|$</TEX> and <TEX>$|S_{31}|$</TEX> less than 3.2 dB, with both <TEX>$|S_{22}|$</TEX> and <TEX>$|S_{32}|$</TEX> measured as better than 12 dB for the whole UWB band. Measurement results agree closely with HFSS simulation results. The power divider has a compact size of <TEX>$4\times9\times0.6mm^3$</TEX>.

Solvent-assisted low pressure room temperature lamination of low temperature cofirable ceramic green tapes for formation of embedded micro channels

Low temperature cofired ceramic substrates are becoming increasingly attractive for high density electric circuits and microsystems. Embedded micro patterns such as channels and cavities in ceramic substrates are indispensable for circuit cooling and media transportation. One of process challenges is how to make these embedded micro channels and cavities, which would be collapsed or deformed under conventional lamination. This paper reports on a novel solvent-assisted lamination that could provide low pressure and room temperature lamination of ceramic green tapes. The solvent used in this study was turpentine oil, which demonstrated a proper capability of dissolving polymeric additives on surface of green tapes without obviously changing the distribution of ceramic particles. Procedures for forming embedded micro channels in ceramic green substrates include micro embossing to create open channels, coating of turpentine solvent, followed by low pressure and room temperature lamination. Embedded micro channels with channel width ranging from 25 to 1,000 μm were obtained in ceramic green substrates; Depths of embedded channels shrank by 3–12% versus embossed depths due to turpentine-assisted lamination. The ceramic green substrates with embedded channels were then sintered under a standard cofiring process.

Active Optical Fiber Alignment with a Piezoelectric Ultrasonic Motor Integrated Into Low Temperature Cofired Ceramics

The major goal of this research was to integrate an ultrasonic motor into a ceramic package for an active optical fiber alignment. Two degrees of freedom ultrasonic motor was successfully cofired with commercial low temperature cofired ceramic green tapes as well as with silver electrodes without encountering serious delamination, camber, and inter diffusion issues. High-power piezoelectric ceramics that can be sintered at 900°C was used for the ultrasonic motor. The motor successfully achieved fiber-to-laser optical alignment. Once alignment was achieved, a pre-stressed structure maintained the position of the fiber without any external electrical field or adhesive material. This package design provided a unique ability to adjust and realign an optical fiber.