Low Temperature Co-fired Ceramics Tapes Research Articles

Design and Fabrication of a Complex LTCC-Based Reactor for the Production of Hydrogen for Portable PEM Fuel Cells

The development process for complex 3D ceramic structures in the integrated evaporator, mixer, reformer and combustor (EMRC) system for the production of hydrogen needed in portable polymer-electrolyte membrane (PEM) fuel cells is presented. Low-temperature co-fired ceramic (LTCC) technology was used to fabricate the ceramic structures of the system. The process started with the design and fabrication of each separate (stand-alone) component, which was developed and tested, and then optimized to fulfill the requirements for the integrated EMRC system. The final 3D ceramic structure consists of 45 LTCC tapes (Du Pont 951PX). The dimensions of the structure are 75 × 41 × 9 mm3 and the weight is about 73 g.

LTCC ultra wide band filter

This article presents the analysis of ultra wide band (UWB) filter designed using a symmetrical three parallel coupled line resonator in low temperature co-fired ceramic (LTCC) medium. The ground plane with an aperture incorporated in it improves the coupling. Based on circuit models, the designed UWB filter has been analyzed, and the results have been confirmed by experiments. The filter has been realized with Dupont LTCC tape DuPont 951 (that has dielectric constant of 7.8). Maximum insertion loss of the experimental filter is 1.5 dB. The group variation over the pass band of the filter is within 0.2 ns. Dimensions of the experimental LTCC filter are 20 × 10 × 0.72 mm. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2580–2583, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26311

Thick‐film photoimageable and laser‐shaped arms for thermoelectric microgenerators

PurposeThe purpose of this paper is to investigate the possible application of thick‐film, metal‐based thermocouples to microsystems power supply. The subject of matter was development of the procedure of thick‐film thermopile miniaturisation.Design/methodology/approachThe aptitude of four photoimageable inks (based on silver or silver‐palladium) to fabrication of miniaturised thermocouples' arms was investigated. The object of interest was their compatibility with different kinds of low temperature cofired ceramic (LTCC) substrates, maximum resolution, shrinkage and electrical resistivity. Usage of the laser shaping technique to fabrication of narrow thermocouples' arms was also subject of matter. After tests and processes optimization both techniques were combined to fabricate the thick‐film Ag/Ni microthermopile.FindingsMost of investigated inks were compatible with all tested LTCC tapes – fired as well as unfired (green tapes). Photoimageable inks technique can be successfully used for thermocouples' arms miniaturization. 40 μm/40 μm line/spaces resolution can be easily achieved. Combining this technique with laser shaping enabled microthermopile fabrication. It consisted of 42 Ag (photoimageable)/Ni (laser shaped) thermocouples. Arms width was 40 μm and 225 μm (Ag‐ and Ni‐arm, respectively), spaces between them – 65 μm. Overall, width of single thermocouple was smaller than 0.4 mm.Practical implicationsFabrication of microthermopile consisting of several hundreds of thick‐film thermocouples will be possible if described procedure is applied. Such microgenerator will generate output power sufficient to supply some microsystems or microelectronic circuits.Originality/valueThe properties of four photoimageable inks were investigated as well as their compatibility with five different LTCC substrates (fired and unfired). Procedure of thick‐film microthermopile fabrication using photoimageable inks technique combined with laser shaping was proposed for the first time.

Influence of lamination parameters on mechanical properties of low temperature co-fired ceramic tapes

For the development of force sensors, manufactured in LTCC (low temperature co-fired ceramics) technology for musical wind instruments, the mechanical properties of laminated LTCC tapes were characterized. Since one layer of LTCC tape is not always fulfilling the requirements of the force sensor’s loading capacity, the influence of lamination parameters for different number of layers were investigated. The measurements were carried out with miniaturized (2 × 1 mm 2) beam samples of four different LTCC tape materials, namely Heraeus AHT01-005, AHT08-047, CT707; and CeramTec GC. The results of the measurements can be used to determine the proper LTCC tape material, the lamination pressure and the number of layers to allow the development of customized force sensors, not only for musical wind instruments.

Bulk and In-Circuit Dielectric Characterization of LTCC Tape Systems Through Millimeter Wave Frequency Range

Low Temperature Co-fired Ceramic (LTCC) material systems offer a highly versatile microwave and millimeter wave packaging platform. Extremely low microwave loss, excellent control of dielectric constant, uniform dielectric thickness, non-existent water absorption leading to very high hermeticity, ability to support multilayer structure leading to 3-dimensional packaging, ability to embed passive functions within the tape layers, availability of a wide range of metallizations, etc. are some of the key advantages of LTCC for microwave packaging. One of the important parameters which needs to be determined at the very early stages of circuit designs are the dielectric properties - dielectric constant and loss tangent, both of which are functions of frequency. These properties need to be known accurately over the entire frequency range of operation for the circuit. For LTCC based designs, the use of dielectric constant of bulk material can lead to deviations between the performance expected at the design stage and for the fabricated circuit. Such deviations are a significant concern for broadband circuits as well as for circuits with sharp resonant behavior such as filters. One of the significant sources of deviation between bulk LTCC and “in-circuit” dielectric constant is the nature of the thick film metallizations used in LTCC technology. Work described here is a comprehensive characterization of three DuPont™ GreenTape™ LTCC systems 951, 943, and 9K7 - in the frequency range 10 to 70 GHz. Both bulk and “in-circuit” dielectric properties with silver and gold metallizations are studied to quantify the deviations in dielectric properties. A Fabry-Perot open resonator technique is used for the bulk characterization while printed ring resonators are used for the in-circuit characterization. This comprehensive characterization will provide key design data for LTCC designers in the 10 – 70 GHz frequency range.

Determination of Electric and Magnetic Properties of Commercial LTCC Soft Ferrite Material

This paper offers an effective, accurate, and simple method for permittivity and permeability determination of an LTCC (low temperature cofired ceramic) ferrite sample. The presented research can be of importance in the fields of ferrite component design and application, as well as for RF and microwave engineering. The characterization sample is a stack of LTCC tapes forming a toroid. Commercially available ferrite tape ESL 40012 was used and standard LTCC processing was applied for the sample fabrication. For the first time, the electrical properties of a ferrite toroid sample of ESL 40012 LTCC ferrite tape is presented at various frequencies. The electrical properties of LTCC ferrite materials, permittivity and specific resistivity, are shown in a frequency range from 10 kHz to 1 MHz using the capacitive method. The hysteresis properties of this material are also determined. B-H hysteresis loops were measured applying a maximum excitation of 2 kA/m and frequencies of 50 Hz, 500 Hz, and 1000 Hz. Permeability is determined in the frequency range from 10 kHz to 1 GHz and a characterization procedure is divided in two segments, for low and high frequencies. Low frequency measurements (from 10 kHz to 1 MHz) are performed using LCZ meter and discrete turns of wire, while a short coaxial sample holder and vector network analyzer were used for the higher frequency range (from 300 kHz to 1 GHz). In addition, another important factor required for the practical design of devices is presented, the temperature variation of the permeability dispersion parameters.

Permittivity of LTCC substrates porousified with a wet chemical etching process

In this work, the permittivity of porous LTCC (low temperature co-fired ceramics) DP 951 is measured and evaluated. The dielectric constant is locally lowered to improve the performance of e.g. radar sensors operated in the GHz range. Porousification is done at originally dense LTCC substrates in the fired state by a wet chemical etching procedure using hot phosphoric acid. Choosing this approach, areas with tailored permittivity can be generated in one single LTCC layer. The etch time and the bath temperature precisely control the penetration and hence, the porosification depth. Therefore, the decrease in dielectric constant of the LTCC substrate can be correlated to the thickness of the porous layer. The dielectric constant is measured using a ring resonator in microstrip configuration. From the resonances occurring in the transmission S-parameter |S21| spectrum between 1 to 10 GHz, the relative dielectric constant can be determined. Using 820 μm thick substrates a relatively low reduction from ϵr=7.8 to 6.45 is achieved when a porosification depth of about 35 μm is reached. Based on numerical simulations, the effective dielectric constant for a 100 μm thick glass-ceramic layer which is porousified to a depth of 35 μm is calculated to 5.2, whereas the thickness represents a lower limit for tapes being typically implemented into the fabrication process of monolithic LTCC systems with integrated metallization planes. This value is lower compared to those of commercially available low-k LTCC tape systems.

A Wireless Embedded Resonant Pressure Sensor Fabricated in the Standard LTCC Technology

This paper proposes a fully embedded resonant pressure sensor operating in the MHz range and realized in the standard low-temperature co-fired ceramics (LTCC) technology. Buried sensor design and usage of LTCC materials enable application of this sensor in high-temperature and chemically aggressive environments. Upgraded sensor and sensor-antenna models residing on an analytical concept are used for prediction of the system performance. Also, simulation results show that an increase of Young's modulus for the LTCC tape diminishes the sensor sensitivity. An experimental setup for wireless data retrieval is designed enabling precise measurement of the influence of pressure variation on the sensors resonant frequency. Experimentally attained results are compared with electrical characteristics determined by analytical calculations as well as those derived from electrical simulations.

UC-EBG on LTCC for 60-GHz Frequency Band Antenna Applications

The relatively high dielectric constant of the low-temperature cofired ceramic (LTCC) substrate materials can reduce the antenna gain and increase the mutual coupling in antenna arrays due to the increased surface-wave power. We present a design of a uniplanar-compact electromagnetic band-gap (UC-EBG) structure on the Ferro A6-S LTCC tape system operating in the 60-GHz frequency band. The UC-EBG design is used with an aperture-coupled microstrip-line-fed patch antenna (ACMPA) and with a 16-element array to increase the antenna gain. The UC-EBG is also used to reduce the mutual coupling between antennas in the E- and H-planes. The performance of the antennas with and without UC-EBG are evaluated with the probe-station and radiation-pattern measurements. In addition, the reflection from the UC-EBG surface is measured using a WR-15 waveguide excitation. Good agreement is achieved between the simulations and the measurements. An increase of up to 4.5 and 2.3 dBi is achieved in the gain for a single element and for a 16-element array, respectively. A reduction of up to 11.8 dB is observed in the E-plane coupling between two patches. The presented design is suitable for electromagnetic shielding, reduction of coupling in integrated LTCC modules, and providing high gain antennas for low-cost millimeter-wave applications.

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).

Development and analysis of a LTCC micro stagnation-point flow combustor

A micro stagnation-point flow burner was fabricated using low-temperature co-fired ceramic (LTCC) tapes. Methane/oxygen counterflow micro diffusion flames with luminous zones of less than 1 mm in length and 250 µm in width were stabilized in the reaction channel of the burner and analyzed using microscopic imaging spectroscopy. The burner was built with 25 layers of LTCC tapes which were pre-laminated into seven blocks. Integrated sapphire windows and sub-millimeter sized internal channels provide optical accessibility and reactant feeds, respectively. Spatial distributions of CH* and C*2 species were measured and compared with those obtained from multi-dimensional reacting flow calculations. Results show that the location and size of the diffusion flame may be controlled by flow velocity, or strain rate, just as in larger centimeter scale flames, and that the chemical structure of the micro flames was in agreement with those predicted by the numerical simulations. In this paper, we show that LTCC tape technology may be used to fabricate microburners for continuous flow steady-state homogeneous gaseous combustion and that integrated optical windows may be incorporated into the fabrication process for in situ optical diagnostics. The understanding and analysis of the present reacting flowfield, because of its simplicity, is important to the development of more complicated microreactors and microburners, in which mixing and variable strain rates exist.

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.

Particle Shape and Size Effects on Anisotropic Shrinkage in Tape‐Cast Ceramic Layers

The particle shape of a commercial low‐temperature cofired ceramic (LTCC) composite powder was determined quantitatively in the as‐received and milled state using a new particle image analyzer. All grades of the milled powder with average particle sizes of 3.0, 2.4, and 1.8 μm, respectively, exhibit a considerable stretched particle shape, because 40% of their particles have circularity values below 0.95. On the basis of the fast particle image analyzer, the influence of the raw materials on particle alignment during tape casting was investigated using “design of experiments” (DOE). In the cast LTCC green tapes, the degree of particle orientation was measured and correlated with the information from the particle shape analyses and with other material and process factors from the DOE. The results showed that the degree of particle alignment correlates significantly with the measured particle shape and size; more than 80% of the particles were oriented in the casting direction if their shape factor was below 0.5. The particle orientation causes shrinkage anisotropy. The use of a coarser LTCC powder with an average particle size d50 of 3.0 μm instead of 1.8 μm increased the sintering anisotropy factor of LTCC tapes and laminates significantly from 1.0% to 1.85% and from 3.6% to 7.6%, respectively. The use of more binder or less solvent led to higher shrinkage anisotropies too. The casting velocity showed only a minor effect on the degree of particle orientation and sintering anisotropy, which is due to the shorter shearing period in which particle rotation can take place.

Photoimageable Thick-Film Components for a Ceramic Analytical Microsystem

This paper presents ceramic microfluidic components—a meander capillary column and a flame ionization detector—which have been designed and fabricated using photoimageable thick-film dielectric Fodel QM44F combined with low-temperature cofired ceramic tape. The components are integrated on a single piece of alumina substrate of dimensions 65 × 50 mm and have incorporated thick-film platinum heaters to ensure their temperature control. Details of the technological process as well as the application set-up for the tested components are presented. The samples of analyte were detected by a flame ionization detector after passage through a capillary column.

Influence of Low‐Temperature Co‐Fired Ceramics Green Tape Characteristics on Shrinkage Behavior

To establish a better understanding of the complex densification and shrinkage processes of low‐temperature co‐fired ceramics (LTCC) and to improve the dimensional control in the manufacture of LTCC multilayer devices, the influence of glass, composite, and microstructural green tape characteristics on the densification and shrinkage behavior of LTCC materials, with special focus on the development of anisotropy, was investigated. To study the influence of these factors, a commercial LTCC system was analyzed regarding chemical and microstructural composition as well as sintering behavior. The results of the analysis showed that the commercial LTCC system is composed of alumina as a ceramic filler and a CaO–SiO2–B2O3–Al2O3 glass. Based on these results, a similar glass was produced. To understand the mechanisms of densification, its wetting behavior and viscosity as a function of temperature were investigated. As developed glass was mixed with an alumina powder and milled down to average grain sizes of 1, 2, and 3 μm, respectively. From these composite powders, slurries were prepared and tape cast. The sintering kinetics including onset temperature, development of viscous flow as well as phase development of both commercial and internally developed LTCC tapes LTCC tapes in relation to their modified composition and green tape structures were analyzed in situ by means of optical dilatometry, thermo‐mechanical analysis (TMA), and high‐temperature‐X‐ray diffraction. The viscous behavior of the glass‐filler composites was determined by means of cyclic dilatometry in a TMA device.

In-house development of co-fireable thick film silver conductor for LTCC applications

The rapidly growing wireless industry needs new high performance materials to build low loss, high density, and thermally stable integrated packages. Applications include automotive safety, control, global positioning system (GPS) mapping and entertainment, multifunctional portable phones, video and data transmission through wireless local area network (WLAN) etc. Recently, low temperature co-fired ceramics (LTCC) technology is referred as a key approach for smart packaging. Although its use has been initiated in the telecommunication field due to the excellent dielectric properties of the LTCC tapes, its application areas have been diversified recently. In the present work, the attempt has been made towards the development of thick film silver conductor composition compatible with available LTCC tapes (DuPont DP-951AX). The physical, microstructural, and electrical properties of the pastes prepared with different compositions are presented in this paper.

Modification of Thick-Film Conductors Used in IP Technology for Reduction of Warpage during Co-Firing of LTCC (Low Temperature Co-Fired Ceramic) Modules

LTCC technology offers low temperature firing (<900 °C) of a materials system, which is based on LTCC sheets/tapes and (ideally) compatible thick-film components. Screen-printed materials on LTCC tapes, such as conductor, resistor, inductor thick-films are co-fired (simultaneously fired), providing a highly-functional package. This comes along with additional benefits such as ease of LTCC tape structuring, fabrication of hermetic and complex 3-D structures, etc. The major difficulty encountered arises from the differential shrinkage rate of LTCC tape and thick-film components, which has to be avoided for fabrication of warpage-free, flat surfaces that is vital for membranes, beams, etc. Therefore the goal of this study is the reduction of deformation, by matching the shrinkage rate of conductor with that of LTCC, which is achieved by mixing the commercially-available paste with selected additives.

Factors Influencing the Green Body Properties and Shrinkage Tolerance of LTCC Green Tapes

Low‐temperature co‐fired ceramics (LTCC) is a powerful technology for the manufacture of integrated electronic devices. To fulfill the needs of miniaturization, the applied materials must be of constant quality and the manufacturing processes must be well controlled. The reproducibility in shrinkage is one of the most important quality issues of LTCC tapes. To guarantee the customer a narrow shrinkage tolerance, the tape producer must know the important influencing factors of tape manufacturing on shrinkage. In this work, the effects of slurry composition, tape‐casting parameters like casting speed and opening of the blades, and tape handling on the sintering shrinkage behavior were investigated by using design of experiments. The investigation showed that the green density and therefore the shrinkage values of tapes depend considerably on the variation of the solvent mixture. Furthermore, significant interactions were quantified between the tape‐casting velocity as well as the particle size and the shrinkage behavior. The shrinkage values were also influenced by mechanical deformations of the tapes before firing.

Influences of the Glass Phase on Densification, Microstructure, and Properties of Low‐Temperature Co‐Fired Ceramics

Multilayer ceramic devices based on low‐temperature co‐fired ceramics (LTCC) materials provide a very promising technology. Most LTCC tapes available today contain considerable fractions of glass powders to lower the sintering temperature. However, the glassy phases offer more possibilities to set a proper sintering behavior, on the one hand, and to tailor the desired properties of the final LTCC substrate, on the other. The exploitation of demixing and subsequent crystallizing glass compositions was shown on an example of a low‐permittivity (4.4)—low‐loss (1.5 × 10−3) LTCC with a high quartz content. In another LTCC material, undesired demixing could be restricted and the crystal phase anorthite could be triggered by partial dissolution of alumina in the liquid phase during sintering. To estimate the effect of silver diffusion in the latter material, the surroundings of a pure silver via were studied. A silver‐contaminated range of 50 μm was detected. Using model glasses containing silver oxide, a strong influence of dissolved silver on viscosity and crystallization behavior of the liquid phase was demonstrated. The dielectric properties of the sintered substrates were not degraded.

Thick‐film strain and temperature sensors on LTCC substrates

PurposeAims to evaluate different thick‐film materials for use in strain sensors and temperature sensors on low‐temperature co‐fired ceramic (LTCC) substrates.Design/methodology/approachLTCC materials are sintered at the low temperatures typically used for thick‐film processing, i.e. around 850°C, The thick‐film resistor materials for use as strain and temperature sensors on LTCC tapes are studied. Thick‐film piezo‐resistors in the form of strain‐gauges are realised with 10 kΩ/sq. 2041 (Du Pont)and 3414‐B (ESL), resistor materials; thick‐film temperature‐dependent resistors were made from PTC 5093 (Du Pont), and NTC‐4993 (EMCA Remex) resistor materials.FindingsThe X‐ray spectra of the 2041 and 3414‐Bb low TCR resistors after drying at 150°C and after firing display more or less the same peaks. The electrical characteristics of 2041 resistors fired on alumina and LTCC substrates are similar indicating that the resistors are compatible with the LTCC material. After firing on LTCC substrates the sheet resistivities and TCRs of the 3414‐B resistors increased. Also, there is a significant increase in the GFs from 13 to over 25.Originality/valueInvestigates the compatibility of thick‐film materials and the characteristics of the force and temperature sensors.