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.     

Effects of Pb–B–Si–O glass on the microstructures and electrical properties of silver electrode for LTCC application

The co-firing compatibility between green tape and the Ag electrode is a crucial characteristic in low-temperature co-fired ceramic (LTCC) technology and plays a vital role in improving the performance and application status of LTCC device modules. In this work, we studied the effects of lead content on the glass viscosity, the microstructure, and co-firing compatibility of silver electrode film. It was found that the softening point and viscosity of the glass were decreased, and the wettability between the glass and silver was improved with the increase of the lead content, which promoted the co-firing densification and interfacial bonding between the silver electrode film and the ceramic layer. The film presented the best electrical properties co-firing at 875 °C for 15 min, with the resistivity of 1.21 mΩ/sq. And the film was densified. The sintering interface was clear and well bonded. The results showed that an appropriate lead content in glass could effectively improve the interfacial bonding and the electrical properties during co-fired process, providing a new control methodology for realizing co-fired matching of the silver electrode film with low-temperature co-fired ceramics.

     

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.     

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.     

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.     

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.%.     

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.     

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...     

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;...     

Effects of NaOH concentrations on physical and electrical properties of high calcium fly ash geopolymer paste

The effects of sodium hydroxide (NaOH) concentration on setting time, compressive strength and electrical properties at the frequencies of 100 Hz–10 MHz of high calcium fly ash geopolymer pastes were investigated. Five NaOH concentrations (8, 10, 12, 15 and 18 molar) were studied. The liquid to ash ratio of 0.4, sodium silicate to sodium hydroxide ratio of 0.67 and low temperature curing at 40 °C were selected in making geopolymer pastes. The results showed that NaOH concentration had significant influence on the physical and electrical properties of geopolymer paste. The pastes with high NaOH concentrations showed increased setting time and compressive strength due to a high degree of geopolymerization as a result of the increased leaching of silica and alumina from fly ash. The dielectric constant and conductivity increased with NaOH concentration while tan δ decreased due to an increase in geopolymerization. At the frequency of 10³ Hz, the dielectric constants of all pastes were approximately 10⁴ S/cm and decreased with increased frequency. The relaxation peaks of tan δ reduced with an increase in NaOH concentration and ranged between 2.5 and 4.5. The AC conductivity behavior followed the universal power law and the values were in the range of 3.7 × 10⁻³–1.5 × 10⁻² at 10⁵–10⁶ Hz.     

掺(Ga,Si)银铝浆对n型TOPCon太阳能电池电性能的影响

银铝浆是新一代太阳能电池(n型TOPCon)的关键材料,但其金属化后在Si发射极表面形成很大且很深的“银铝尖钉”,尖钉易击穿p-n结造成短路,成为限制其应用的瓶颈。引入Si、Ga元素对银铝浆进行优化,分别制备了掺Si和掺Ga, Si的银铝浆,研究其对金属化区域暗态饱和电流密度J_0.metal、欧姆接触电阻R_c的影响机制。结果表明：掺入少量Si后,金属化区域未见明显“银铝尖钉”,说明掺Si后抑制了在浆料金属化时出现“银铝尖钉”的现象,对p-n结损伤较小,J_0.metal下降,开路电压V_oc上升,但是R_c增大。再掺入Ga组分后“银铝尖钉”明显变浅,数量变多,R_c下降,弥补了掺Si银铝浆欧姆接触差的弊端,有较高的电池转换效率;用扩散浓度测试仪(ECV)对发射极表层进行元素浓度分析,发现Ga分布于表层0～50 nm处,有利于改善欧姆接触。研究了Ga、Si的掺入量对银铝浆电性能的影响,电池转换效率最高达到24.68%,太阳能电池效率提升0.55%。     

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.