Effects of organic binder on rheological behaviors and screen-printing performance of silver pastes for LTCC applications

Journal of Materials Science: Materials in Electronics - Ethyl celluloses (ECs) organic binder with different molecular weights and contents was applied to silver pastes for LTCC applications. The...     

Silver content effect on rheological and electrical properties of silver pastes

The novelty of this work is laboratory formulation of environmentally friendly, water-based silver inks adapted for screen printing. The challenge was also to elaborate inks that can withstand temperatures as high as 900 °C. Indeed, when printed on ceramic substrate, they were sintered at these high temperatures. These inks can replace conductive silver pastes present in the market, today, and containing irritant solvents such as terpineol and other aromatic solvents. Besides, screen printing is considered as an additive technique, thus allowing reducing wastes. Furthermore, only with 72.5% silver, considered as low content compared to commercial inks (≥75%), prepared inks presented good electrical resistivity, 23 nΩ m, close to that of bulk silver resistivity, 16 nΩ m. Formulation of silver inks with spherical particles, 2–3 μm mean diameter, was performed. The aim of the study was to determine silver content effect on pastes rheological behaviour, lines properties (width, thickness and roughness) and electrical properties. Therefore, rheological behaviour of inks was studied; in particular, Casson and Bingham models were applied in order to determine the yield stress. Viscosity evolution as a function of shear rate was also determined. Besides, the thixotropic behaviour of inks was highlighted. Inks were then screen printed on alumina sintered substrates and cured at different temperatures during 15 min. Topography measurements were performed. Line resistivity as small as 35 nΩ m was measured on cured lines. These inks, printed on ceramic tapes, can be used to print microwave transmission lines, for which resistivities lower than 1 mΩ m are requested.     

Synthesis and electrical properties of uniform silver nanoparticles for electronic applications

Silver nanoparticles are considered to apply a silver paste for electrode because of their high conductivity. However, the dispersion of silver nanoparticles in electronically conductive adhesives (ECAs) restricts them used as conductive fillers. A simple method had enabled the synthesis of silver nanoparticles by reducing silver nitrate with ethanol in the presence of poly(N-vinylpyrrolidone) (PVP). Reaction conditions, such as silver nitrate concentration, PVP concentration, reaction time, and reaction temperature, had been studied. Fine dispersion and narrow size distribution of silver nanoparticles were obtained. They were added to ECAs by re-dispersing them in ethanol while it was used as the diluent to adjust the volatility of ECAs, preventing them from the aggregation and increasing the chance to fill the gaps between silver flakes. This proposed process offers the possibility to effectively use these synthesized silver nanoparticles for improving the conductivity of ECAs.     

Preparation and rheological behavior of lead free silver conducting paste

The lead free silver conducting pastes were prepared by using silver powder, lead free low-melting glass and terpineol ethyl cellulose solution. By analyzing the sheet resistance, Vickers hardness as well as the adhesion strength of the fired film by the pastes formulated with different content of the glass, the desired glass weight percentage was determined as 4–6 wt%. The films, prepared by the pastes using the lead free glass with a glass transition temperature of 488 °C, were perfectly flat and compact after fired at a peak temperature within the range from 540 °C to 590 °C. The sheet resistance of the fired film with glass content of 5 wt% was 2.3 × 10⁻³ Ω mm⁻² at the thickness of 15 ± 3 μm, while the Vickers hardness was 61 MPa, and the adhesion strength was 28.5 MPa. In addition, the rheological, thixotropic, and viscoelasticity behaviors of the typical paste characterized by using an ARES (RFS-III) rheometer, were similar to that of the screen printing paste with high solid filler. The pastes are applicable for manufacturing electrical components on glass substrate.     

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.     

Improving the microstructural and physical properties of alumina electrical porcelain with Cr2O3, MnO2 and ZnO additives

The optimum concentrations of Cr₂O₃, MnO₂ and ZnO were added separately and combined to the basic composition of the alumina electrical porcelain body. The samples were prepared from wet and plastic porcelain bodies according to IEC standard methods. After drying and firing under appropriate conditions, the effects of added oxides on the microstructural and physical properties of sintered porcelain were studied. It was found that the microstructure of this material was remarkably improved compared to one without additives. The sintering temperature was decreased by 60 °C, and at the same time closed porosity decreased considerably resulting in a density increase. The mullite content increased slightly, but both the size and shape of its acicular crystals were limited to values providing formation of a very strong network connecting other crystalline phases in the glassy matrix without any significant internal microcracks. It was concluded that these oxides acted as densification catalysts, partly as mineralizers, and as crystal growth inhibitors causing significant improvement of mechanical, electrical and thermal properties of the alumina electrical porcelain investigated.     

Monitoring the effects of storage on the rheological properties of solder paste

Solder paste is widely used as a bonding medium for surface mount assemblies in the electronics industry. The stencil printing of solder paste is a potentially low cost method of depositing solder paste onto printed circuit boards. It is very important to use the right paste, as a high proportion of all surface mount assemblies defects are related to the printing process. This is likely to continue with the drive to further miniaturization and the implementation of die-size devices. One of the key factors affecting solder paste print quality is its rheology. The rheological properties such as viscosity of solder paste are dependent on its history (i.e. paste storage). Key factors that influence solder paste viscosity have been identified over the years. In this paper, we examine the effects that storing solder paste at two different temperature and humidity conditions has on its rheological properties. Viscosity measurements at different storage intervals reveal about 60% increase for samples kept at room temperature conditions after 5 months. A model of the change in viscosity at both storage conditions is also presented. From this model, the shelf life of the solder paste can be determined. This model can also be used during quality control.     

Structural,electrical, and rheological properties of palladium/silver bimetallic nanoparticles prepared by conventional and ultrasonic-assisted reduction methods

Polyvinylpyrrolidone stabilized Pd/Ag bimetallic nanoparticles (NPs) with average particle sizes of 9 and 6 nm were synthesized by simultaneous reduction in the presence and absence of ultrasound waves, respectively. The prepared NPs were characterized by six methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution-TEM (HRTEM), UV–vis spectroscopy, scanning tunneling microscopy (STM), and energy dispersive X-ray (EDX) analysis. The rheological properties of Pd/Ag NPs in ethylene glycol as a base fluid with various mass fractions of NPs from 2% to 5% at different temperatures were studied experimentally and theoretically. The experimental results showed that viscosity of Pd/Ag NPs in ethylene glycol increases with increasing particle mass fraction and decreases with increasing temperature. A maximum of 31.58% increase in viscosity of ethylene glycol at 20 °C was observed when 5% Pd/Ag NPs was added. Measurement of the electrical conductivity of nanofluids of Pd/Ag bimetallic NPs in distilled water at different mass fractions and temperatures was performed. A 3841% increase in electrical conductivity of distilled water at 25 °C was observed when 1% Pd/Ag NPs was added. Both the rheological and electrical properties of Pd/Ag bimetallic NPs were measured in ethylene glycol and distilled water, respectively for the first time.     

Substitution of Nb doping on the structural, microstructural and electrical properties in PZT films

Undoped and niobium (Nb) doped Pb_1−y(Zr_0.54Ti_0.46)_1−yNb_yO₃ have been deposited by sputtering on Pt metallized silicon substrates. The niobium concentration, y, was varied from 1 to 7 at.% by 1 at.%. The Zr/Ti ratio was fixed to 54/46 corresponding to the Morphotropic Phase Boundary. Structural, microstructural, and electrical properties were evaluated depending on Nb content. The films (doped and undoped) present a (1 1 1)-preferred orientation. The Nb doping induces an increase of the grain size and as it was observed in bulk materials the dielectric constant (ε_r) and the piezoelectric coefficients (e₃₁ and d₃₃) reach their maximum for low Nb concentration (2 at.%). The remnant and the maximum polarizations increase as the coercive field decreased slightly with the Nb concentration. The internal electric field increases with Nb content; as a result, the ‘self-polarization’ of the films (polarization measured without poling treatment) is enhanced with niobium substitution. In term of fatigue behavior, it was found that switching endurance characteristics are maximum for low Nb doping level.     

Effects of filler shape and size on the properties of silver filled epoxy composite for electronic applications

Epoxy composites filled with nano- and micro-sized silver (Ag) particulate fillers were prepared and characterized based on flexural properties, coefficient of thermal expansion, dynamic mechanical analysis, electrical conductivity, and morphological properties. The influences of these two types of Ag fillers, especially in terms of their sizes and shapes, were investigated. Silver nanoparticles were nano-sized and spherical, while silver flakes were micron-sized and flaky. It was found that the flexural strength of the epoxy composite filled with silver flakes decreased, while the flexural strength of the epoxy composite filled with silver nanoparticles showed an optimum value at 4 vol.% before it subsequently dropped. Both silver composites showed improvement in flexural modulus with increasing filler loads. CTE value indicated significant decrements in filled samples compared to neat epoxy. Results on the electrical conductivity of both systems showed a transition from insulation to conduction at 6 vol.%.     

银粉性质对太阳能电池浆料的影响

作为传统化石能源的有效替代品,太阳能电池引起了学者们的广泛关注.导电银浆作为太阳能电池的重要原料,影响着太阳能电池的光电转换率和度电成本.银粉作为银浆中的导电相,其性能对银浆的电性能、流动性、粘附性等性质起着关键作用.近年来针对银粉的形态、尺寸、分散度、粒度分布和振实密度对导电银浆电性能的影响有较多研究.研究表明银粉的...     

Structural, electrical and optical properties of ZnO:Al films deposited on flexible organic substrates for solar cell applications

Aluminum doped ZnO thin films (ZnO:Al) were deposited on glass and poly carbonate (PC) substrate by r.f. magnetron sputtering. In addition, the electrical, optical properties of the films prepared at various sputtering powers were investigated. The XRD measurements revealed that all of the obtained films were polycrystalline with the hexagonal structure and had a preferred orientation with the c-axis perpendicular to the substrate. The ZnO:Al films were increasingly dark gray colored as the sputter power increased, resulting in the loss of transmittance. High quality films with the resistivity as low as 9.7 × 10^− 4 Ω-cm and transmittance over 90% have been obtained by suitably controlling the r.f. power.     

Investigation of the structural,microstructural, and dielectric properties of Ho-doped PbTiO3 for piezoelectric applications

Journal of Materials Science: Materials in Electronics - In this work, sol–gel-processed Ho-doped PbTiO3 powder samples with the compositions Pb1?XHoxTiO3 (x?=?0; 1; 3; 6;...     

Study of microstructural, optical and electrical properties of Mg dopped SnO thin films

Mg doped SnO thin films were fabricated via electron beam evaporator on the glass substrate. The XRD analysis showed that reference and Mg doped SnO thin films were consisted of tetragonal α-SnO phase with preferred directions along (101) and (002) orientations. It was observed that the intensity of the diffraction pattern peaks increased and crystallite size decreased with the Mg doping. Scanning electron microscopy showed that the needle-like particles having length in the range of 0.4–0.6 μm with a diameter of 0.1–0.2 μm are sintered together to form a compact structure of Sn_1?xMg_xO layer. In the Raman spectrum, two active mode (A _2u and E _u ) were observed for Sn_1?xMg_xO thin films. The complex plot (Nyquist plot) showed the data point laying on a single semicircle and the dc resistance increases with the increase of Mg doping concentration.     

Tunable plasmonic properties of silver nanorods for nanosensing applications

Localized surface plasmon resonance (LSPR) sensitivity to the surrounding medium refractive index has been studied for silver nanorods using Gans theory including the effect of retardation and surface scattering. The simulation results show the refractive index sensitivity (eV/RIU) maxima positions at width of 9, 6, and 4 nm for aspect ratios of 2, 3, and 4, respectively. Based on the sensing figure of merit (FOM), 9 nm is found to be a significant nanorod width, where the FOM dependence on width with respect to aspect ratio inverts. However, the optimal nanorod width for both the FOM and the modified figure of merit (MFOM) is about 6 nm for aspect ratios of 2, 3, and 4. A comparison with gold shows that silver nanorods exhibit relatively higher FOM and MFOM and thus, making them potential candidates for biochemical nanosensing applications.     

硅烷浓度对微晶硅薄膜微结构及电学性质的影响

采用RF-PECVD技术,在玻璃衬底上低温沉积了优质微晶硅薄膜,并深入研究了硅烷浓度对微晶硅薄膜微结构及电学性质的影响.研究结果表明,微晶硅薄膜的沉积速率、平均晶粒尺寸、晶化率和电导率均呈现相似的变化规律,而谱中出现的拐点由硅烷浓度决定.该变化规律可通过相应的薄膜生长的微观理论得到合理的解释.     

Structural and electrical properties of perovskite ruthenate-based lead-free thick film resistors on alumina and LTCC

CaRuO₃ perovskite-based lead-free thick-film resistors (TFRs) were prepared on 96%-alumina and Low Temperature Co-fired Ceramic (LTCC) substrates. The microstructure evolution, possible interactions, and electrical properties of resistors were investigated. The hot and cold TCR values of all the resistors were measured in the temperature range (+20 to +120 ^∘C) and (+20 to −120 ^∘C), respectively. TFRs with 25% by vol. of CaRuO₃ on alumina exhibit a sheet resistance R_s = 5kΩ/sq. with hot and cold TCR of 225 and 470 ppm/^∘C respectively, whereas the same composition gives 1.2 kΩ/sq., 16.5 kΩ/sq. and 0.7 kΩ/sq. for co-fired, post-fired resistors on LTCC and buried resistors, respectively. The hot (HTCR) and cold (CTCR) values were evaluated; HTCR = 190 ppm/^∘C and CTCR = 314 ppm/^∘C were found for co-fired structures; HTCR = 216 ppm/^∘C and CTCR = 205 ppm/^∘C for post-fired samples and HTCR = 520 ppm/^∘C and CTCR = 350 ppm/^∘C for buried in LTCC structures.