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This paper aims to report on fabrication procedure and presents microstructure and dielectric behaviour of LiZn_0.92Cu_0.08PO₄ ceramic material with Li₂CO₃ as a sintering aid.

Substrates based on LiZn_0.92Cu_0.08PO₄ with Li₂CO₃ addition were prepared via solid-state synthesis, doping, milling, pressing and sintering. Characterization of the composition, microstructure and dielectric properties was performed using X-ray diffractometry, energy dispersive spectroscopy, scanning electron microscopy, impedance spectroscopy in the 100 Hz to 2 MHz range and time-domain spectroscopy in the 0.1–3 THz range.

Doped LiZnPO₄ ceramic, which exhibits a low dielectric constant of 5.9 at 1 THz and low sintering temperature of 800 °C, suitable for low temperature co-fired ceramics (LTCC) technology, was successfully prepared. However, further studies are needed to lower dielectric losses by optimising the doping level, synthesis and sintering conditions.

Search for new low dielectric constant materials applicable in LTCC technology and optimization of processing are essential tasks for developing modern microwave circuits. The dielectric characterization of doped LiZnPO₄ ceramic in the terahertz range, which was performed for the first time, is crucial for potential millimetre-wave applications of this substrate material.

The paper aims to report on fabrication procedure and present microstructure and dielectric behavior of multilayer porous low-temperature cofired ceramic (LTCC) structures based on glass-cordierite and glass-alumina.

The LTCC structures were created as multi-layered composites with dense external layers and inner layers with intentionally introduced porosity. Two preparation methods were applied – subsequent casting of both kinds of slurries and conventional isostatic lamination of dried green tapes arranged in the designed order. Optical microscope observations were carried out to analyze the microstructure of green and fired multilayer structures and pore concentration. To evaluate the adhesion strength of the composite layers, pull test was performed. Dielectric behavior of the composites was studied in the frequency range 50 kHz-2 MHz.

The fabricated porous LTCC structures showed dielectric constant of 3-5.6. The lowest dielectric constant was attained for glass-cordierite composite made by the conventional tape casting/lamination/firing method from slurry with 50 per cent graphite content. The samples prepared using multiple casting were of worse quality than those fabricated in conventional process, contained irregular porosity, showed tendency for deformation and delamination and exhibited a higher dielectric constant.

Search for new low dielectric constant materials applicable in LTCC technology and new methods of their fabrication is an important task for development of modern microwave circuits.

The purpose of this paper is to report on fabrication procedure and present microstructure and dielectric behavior of willemite ceramic material with addition of 5% Li₂CO₃ as a sintering aid.

The samples were fabricated by ball milling of the ceramic powders, preparation of granulate and pressing and co-firing using temperature profile based on heating microscope observation. The dielectric properties of the material were measured by impedance spectroscopy (Hz-MHz), transmission method (GHz) and time domain spectroscopy (THz). The composition and microstructure of the material were investigated using X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy analysis. Ceramic powder was used to fabricate a green tape and low temperature co-fired ceramics (LTCC) multilayer structures, which in the next steps of the research were examined at the angle of cooperation with conductive pastes, strength and geometric repeatability.

The fabricated material showed low sintering temperature (920°C–960°C), low dielectric constant 6.2–6.34 and low dissipation factor at the level of 0.004–0.007. As LTCC material, willemite with 5% Li₂CO₃ addition showed good compatibility with AgPd conductive paste.

Search for new materials with low dielectric constant, applicable in LTCC technology, and development of their fabrication procedure are important tasks for the progress in modern microwave circuits.

This paper aims to investigate the quality and reliability of solder joints prepared from Pb-free alloys on direct bounded Cu (DBC) substrates. Two types of solder alloys were studied: Sn90.95Ag3.8Cu0.7Sb1.4Ni0.15Bi3.0, with a high melting point of 225°C, and Sn42Bi58, with low a melting point of 138°C.

Capacitor components of size 1806 were soldered on DBC substrates by using convection reflow soldering and vacuum vapor-phase soldering technologies. A part of the samples was subjected to the thermal shock test. The structure of the solder joints and the content of the voids were investigated using three-dimensional X-ray tomography. The mechanical strength of the joints was evaluated using the shear force test, and the microstructure of the joints was studied on metallographic cross sections by using scanning electron microscopy.

It was found that the number of voids is not related directly to the mechanical strength of the solder joints. The mechanical strength of the solder joints depends more on the amount of Ag₃Sn precipitation, Au precipitation and the intermetallic layer in the solder joints. In some cases, the thermal shock test caused micro-cracks around the Au precipitation because of a mismatch of Au, AuSn₄ and Sn in terms of coefficients of thermal expansion.

DBC substrates are usually used for power electronics, where the quality of the solder joints is even more important than in the case of commercial electronics.

The work was aimed at preparation of green tapes based on a new material Bi_2/3CuTa₄O₁₂, 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.

The study focused on tape casting, lamination and co-sintering procedures and dielectric properties of Bi_2/3CuTa₄O₁₂ 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.

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 Bi_2/3CuTa₄O₁₂ exhibited a high specific capacitance.

A new material Bi_2/3CuTa₄O₁₂ 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.

This paper aims to present a method for the reduction of dielectric constant of low-temperature co-fired ceramics (LTCC) substrates with the use of controlled internal porosity.

A glass-ceramic green tape with addition of graphite as a pore former was developed. The green tapes were laminated and then sintered into multilayer structures with porous interior and thin external dense layers. Microstructure of green and fired structures was studied using optical and scanning microscopy. The behavior of the samples during heating was examined in a heating microscope. Impedance spectroscopy was applied for investigation of dielectric properties of the fabricated substrates.

Microstructure and dielectric properties of the fabricated LTCC structures were compared with the characteristics for non-porous samples with the similar composition. Introduction of 50 Wt.% admixture of graphite in the internal layers of the LTCC substrate was found to result in decrease in dielectric constant value down to about 3. Application of non-porous outer layers improved mechanical strength of the structure and smoothness of its surface, allowing screen printing of conductive pastes on both sides of the substrate.

The rapid growth of the wireless communication industry has created a great demand for the development of new and improved materials and devices operating properly at high frequencies. The fabricated materials can be useful for substrates of microwave devices.

The paper presents an innovative method of dielectric constant decrease of substrate materials. Getting insight into the phenomena responsible for formation of pores is crucial for designing materials for microwave electronics.

The purpose of this paper is to assess the reliability of thermoelectric generators after ageing at elevated temperature and to determine the influence of the technology used (i.e. type of thermoelectric material, type of substrate and soldering technology) for thermogenerator (TGE) assembly.

In this paper, the Seebeck coefficient and the current voltage were measured for lead telluride doped with either manganese (PMT), germanium (PGT) or sulfur (PST) TGEs. The Seebeck coefficient measurements were taken at temperatures between 230 and 630 K.

The Seebeck coefficient determined for PMT, PGT and PST TGEs increases approximately linearly with increasing temperature and is greater by about 40 per cent for PST and about 30 per cent for PMT than in commercially available PbTe TGEs. The best outcome in terms of stability after long-term ageing was that of PMT material.

The choice of proper technology (i.e. thermoelectric materials, type of substrate and soldering technology) for the TGE assembly is essential for their functioning overtime and reliability.

This paper aims to present certain issues in direct bonded copper (DBC) technology towards the manufacture of Al2O3 or AlN ceramic substrates with one or both sides clad with a copper (Cu) layer.

As part of the experimental work, attempts were made to produce patterns printed onto DBC substrates based on four substantially different technologies: precise cutting with a diamond saw, photolithography, the use of a milling cutter (LPKF ProtoMat 93s) and laser ablation with differential chemical etching of the Cu layer.

The use of photolithography and etching technology in the case of boards clad with a 0.2-mm-thick Cu layer, can produce conductive paths with a width of 0.4 mm while maintaining a distance of 0.4 mm between the paths, and in the case of boards clad with a 0.3-mm-thick copper layer, conductive paths with a width of 0.5 mm while maintaining a distance of 0.5 mm between paths. The application of laser ablation at the final step of removing the unnecessary copper layer, can radically increase the resolution of printed pattern even to 0.1/0.1 mm. The quality of the printed pattern is also much better.

Etching process optimization and the development of the fundamentals of technology and design of power electronic systems based on DBC substrates should be done in the future. A limiting factor for further research and its implementation may be the relatively high price of DBC substrates in comparison with typical PCB printed circuits.

Several examples of practical implementations using DBC technology are presented, such as full- and half-bridge connections, full-wave rectifier with an output voltage of 48 V and an output current of 50 A, and part of a battery discharger controller and light-emitting diode illuminator soldered to a copper heat sink.

The paper presents a comparison of different technologies used for the realization of precise patterns on DBC substrates. The combination of etching and laser ablation technologies radically improves the quality of DBC-printed patterns.

This paper aims to fabricate and characterize ZnO-based multilayer varistors.

Tape casting technique was utilized for preparation of multilayer varistors based on ZnO doped with Pr, Bi, Sb, Co, Cr, Mn and Si oxides. Scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) methods were used to study the microstructure, elemental and phase compositions, respectively, of the varistors. Dielectric properties were investigated by impedance spectroscopy. Current–voltage (I–U) dependences were measured to characterize nonlinear behavior of the fabricated varistors.

XRD, SEM and EDS studies revealed dense microstructure of ceramic layers with ZnO grains sized 1-4 μm surrounded by nanometric Bi-rich films, submicrometer Zn₇Sb₂O₁₂ spinel grains and needle-shaped Pr₃SbO₇ crystallites. Praseodymium oxide was found to be very effective as an additive restricting the ZnO grain growth. I–U characteristics of the fabricated multilayer varistors were nonlinear, with the nonlinearity coefficients of 23-27 and 19-51 for the lower and higher Pr₂O₃ content, respectively. The breakdown voltages were 60-150 V, decreasing with increasing sintering temperature.

Low-temperature cofired ceramics technology enables attaining a significant progress in miniaturization of electronic passive components. Literature concerning application of this technology for multilayer varistors fabrication is limited. In the present work, the results of XRD, SEM and EDS studies along with the I–U and complex impedance dependences are analyzed to elucidate the origin of the observed varistor effect. The influence of sintering temperature and Pr₂O₃-doping level was investigated.

The main advantages of vapour phase soldering are a non-oxygen environment, the elimination of overheating and the possibility of the vacuum application, which can guarantee undeniably higher quality of solder joints, especially as regards void formation. These features are less affected by the alloy composition. The paper aims to discuss these issues.

The quality of solder joints made in two VPS options (with and without vacuum) was investigated in terms of voids formation. Solder alloys of 37%Pb63%Sn (PbSn) and 96%Sn3.5%Ag0.5%Cu (SAC 305) were applied to an etched Cu layer on a glass-epoxy substrate using the screen-printing method. 1206 SMD resistors were placed on the solder pads with a Quadra pick-and place machine. For the inspection of joint structure and void identification, 3D X-ray images of samples were taken using a computed tomography system with a 180 kV/15 W nanofocus. For comparison, traditional cross-sections of the samples were performed using a metallographic polisher. The cross-section analysis was done in a scanning electron microscope (SEM). To confirm the relevance of these data, a statistical analysis was carried out.

The paper shows that alloy composition has less impact on the quality of joints as regards void formation. The tendency for a different arrangement of voids in a junction depending on the distance SMD element and the thickness of the solder layer was investigated using X-ray computed tomography.

The use of 3D computed tomography for void investigation gives full information about the internal structure of the joint and allows for precise void identification. Vacuum application during the soldering allows significant voids elimination.