Electrical characteristics of printed Ag nanopaste on polyimide substrate

We investigated the effects of sintering temperature on the microstructural evolution and electrical characteristics of screen-printed Ag patterns. A conducting paste containing 20 nm Ag nanoparticles (73 wt%) was screen printed onto a polyimide (PI) substrate and sintered at a temperature of 150, 200, 250 and 300 degrees C for 30 min. The microstructures of the sintered patterns were examined using field emission scanning electron microscopy (FESEM). The resistivity under the application of a DC signal decreased with increasing temperature. In the frequency range from 10 MHz to 20 GHz, the S-parameters of the sintered Ag conducting patterns were measured. The S-parameters indicated that the insertion losses at high frequency decreased with increasing sintering temperature due to the formation of interparticle necking after sintering.     

Electrochemical migration characteristics of screen-printed silver patterns on FR-4 substrate

We evaluated the electrical reliability of screen-printed silver (Ag) patterns sintered at various temperatures under variable bias voltages. Comb-type patterns were screen-printed onto a flame resistance-4 substrate using a commercial Ag nanopaste (24 nm in diameter, 73 wt% of Ag nanoparticles). The printed patterns were then sintered for 30 min in air at various temperatures ranging from 100 degrees C to 200 degrees C. The microstructures and thickness profiles of the sintered conductive patterns were identified with a field emission scanning electron microscope and a 3-D surface profiler, respectively. In this study, the phenomenon of electrochemical migration was investigated with a water drop test with deionized water. These results showed that the time required by dendrites to bridge from a cathode to an anode was affected by the sintering temperature and applied voltage; when the sintering temperature was 200 degrees C, the time to achieve a short circuit was nearly four times that of the sample sintered at 100 degrees C, and while the applied voltage increased from 3 V to 9 V, the time to reach a short circuit decreased, on average, by 11%.     

High frequency characteristics of printed Cu conductive circuit

The effects of sintering temperature on microstructural evolution and electrical characteristics of screen printed Cu patterns were observed. A commercial conducting paste containing Cu nanoparticles was screen printed onto a sodalime wafer sintered under a sintering temperature range of 300 degrees C to 450 degrees C. A network analyzer and Cascade's probe system in the frequency range of 10 MHz to 20 GHz were employed to measure the S-parameters of the sintered Cu conducting patterns. From the measured S-parameters, the insertion losses in high frequencies decreased with increasing sintering temperature due to the formation of an interparticle necking after heat treatment at high temperatures. However, oxidation of Cu nanoparticles during the sintering deteriorated the RF performance of the circuits, resulting large deviation of the S-parameters from the simulated curves.     

Crack formation and substrate effects on electrical resistivity of inkjet-printed Ag lines

We investigated electrical properties of inkjet-printed Ag lines by varying the substrate, dimension of lines and sintering temperature. The effect of cracks developed in the lines during drying and sintering was also examined. The results show clear evidence of a strong crack and substrate effect on electrical properties of printed Ag lines. The crack formation is clearly dependent on the dimension of lines. Crack network occurs and becomes more pronounced for wider and thicker lines. Even without the crack formation, the resistance and resistivity of lines on glass are higher than those on polyimide due to residual thermal stresses.     

Inkjet printing of conductive Ag lines and their electrical and mechanical characterization

This paper aims to investigate the effects of the substrate, the printed line thickness and the sintering temperature on the electrical resistivity, Young's modulus and hardness of inkjet-printed Ag thin films. Electrical resistivity was determined from the four-point method and Young's modulus and hardness were evaluated from nanoindentation test. Several models for evaluating Young's modulus and hardness were used and compared to account for the influence of substrates. It is noted that Ag lines on glass have higher resistance and resistivity than those on polyimide (PI) since Ag lines on glass and PI have tensile and compressive residual thermal stresses, respectively, due to the difference of coefficient of thermal expansion between Ag lines and substrates. Young's modulus of Ag films on glass can be predicted by the modified King and Bec models considering the substrate effect, but these models offer unstable results for Ag films on PI. Young's modulus and hardness of Ag films increase with the sintering temperature, and they are little affected by the film thickness when fully sintered.     

Evaluation of the flexibility of silver circuits screen-printed on polyimide with an environmental reliability test

The flexibility of screen-printed silver (Ag) circuits on a polyimide (PI) substrate was investigated under a high temperature and relative humidity (RH). The conductive circuits were constructed on a PI film with a commercial Ag nanopaste via screen printing. The printed patterns were sintered at 200 degrees C for 30 min in a box-type furnace, after which they were placed in a chamber at 85 degrees C/85% RH for various durations: 100, 300, 500, and 1000 h. The Institute for Interconnecting and Packaging Electronic Circuits (IPC) flexural resistance endurance test was conducted to measure the flexibility of the conductive circuits, and the flexibility of the printed patterns was evaluated by detecting the variation of the electrical resistance. The flexibility of the screen-printed conductive circuits decreased as the duration of the 85 degrees C/85% RH test increased. After the 1000 h run of the 85 degrees C/85% RH test, the flexibility of the printed circuits was almost halved compared to that after the 100 h test. To demonstrate the decreased flexibility, the microstructural evolution and partial volume were investigated with a field emission scanning electron microscope (FE-SEM) and a 3D surface profiler, respectively.     

Flexibility of silver conductive circuits screen-printed on a polyimide substrate

The microstructural evolution and mechanical characteristics, especially folding endurance, of screen-printed Ag circuits under various sintering conditions were investigated. The circuits were constructed on a polyimide (PI) film by a screen printing technique using a commercial Ag nanopaste. The sintering temperature and time were raised from 150 to 300 degrees C and from 15 min to 1 hour while the sintering time and temperature were fixed at 30 min and 200 degrees C, respectively. The Massachusetts Institute of Technology (MIT)-type folding endurance tester was used to measure the flexibility of the screen-printed Ag circuits. We observed the change of electrical resistance while the printed Ag patterns were being folded. The folding endurance was better at lower sintering temperature and time, which was explained by the microstructural evolution and macrostructural change of the screen-printed Ag circuits; however, the electrical characteristics were generally poor. Further research is therefore required to improve the electrical and mechanical properties of patterns using direct printing technologies simultaneously.     

镍基Ni-Ag复合纳米粒子直流电弧等离子体法制备及其烧结电学性能

采用直流电弧等离子体法,在氢/氩气氛下蒸发高Ni含量的Ni-Ag块体靶材,获得以Ni为主相的复合纳米粉体产物,Ni和Ag元素之间形成各自固溶体相,其中Ni含量为70.54%(质量分数),纳米粒子产物平均尺寸在30~70 nm范围。将纳米粉体压制成片,其室温电学性能测试结果表明:25 MPa压力下的样品电阻率为5.36×10^-5Ω·cm。利用纳米粉体作为导电组分,配制成液态导电墨水,在聚酰亚胺薄膜基体上绘制导电线路,在Ar气氛下完成烧结处理。烧结样品电学性能测试结果表明:在300℃以上温度,烧结体结构致密,导电性能良好。随温度提高,烧结样品的电阻率逐渐下降,450℃时烧结体的电阻率达1.83×10^-3Ω·cm,明显优于纯Ni纳米粉体墨水的烧结体电阻率。     

Preparation of nickel–silver core–shell nanoparticles by liquid-phase reduction for use in conductive paste

Nickel–silver (Ni–Ag) core–shell nanoparticles (NPs) were prepared by depositing Ag on Ni nanocores using the liquid-phase reduction technique in aqueous solution, and their properties were characterised using various experimental techniques. The core–shell NPs had good crystallinity, and the thicknesses of the Ag nanoshells could be tuned effectively. The oxidation resistance of the Ag surface and the electroconductive properties of the Ni core allowed these Ni–Ag core–shell NPs to be used in a conductive paste. Thick films composed of Ni–Ag core–shell NPs were screen-printed on a polycrystalline silicon substrate then sintered at temperatures ranging from 500 °C to 800 °C. Stable resistivity was obtained when the sintering temperature was higher than 650 °C, and the electrical properties of the Ni–Ag core–shell paste were close to those of pure Ag paste. Thus, the Ni–Ag NPs can partly replace pure Ag NPs in conductive pastes.     

Submicron Cu@glass core-shell powders for the preparation of conductive thick films on ceramic substrates

Coating Cu powders with glasses to form a core-shell structure provides an important route to achieve uniform distribution of glass components in Cu pastes for the fabrication of various electronic devices. In this study, submicron Cu powders are synthesized via a chemical solution method at first, and then coated with Bi-Si-B-Zn-Al glass by a sol-gel method to form submicron Cu@glass core-shell powders which are then prepared into Cu pastes with different glass contents. The Cu@glass pastes are printed on alumina ceramic substrates and sintered at temperatures ranging from 600 to 800 °C to form conductive thick films. Enhanced anti-oxidation properties are observed for the Cu@glass core-shell powders. The Cu pastes can be sintered into conductive films with a good electric conductivity and adhesion strength on alumina substrate at a relatively low temperature of 600 °C. A low resistivity of 3.0 µΩ cm is achieved for the sintered Cu film with a glass content of 6 wt%. The glass shells are observed to transform into uniformly distributed glass phases which provide advantages for the formation of Cu-grain conductive pathway at a low sintering temperature.     

Study on the characteristics of building bricks produced from reservoir sediment

This research investigates the feasibility of building bricks produced from reservoir sediment sintering using various sintering temperatures and clay additions. The experimental results indicate that sintered specimen densification occurred at sintering temperatures of 1050-1100 degrees C. Increasing the sintering temperature decreases the water absorption and increases the shrinkage, density and compressive strength of sintered specimens. The experiments were conducted at a temperature ranged from 1050 to 1150 degrees C with clay addition contents varying from 0% to 20%. All sintered specimens made from reservoir sediment were in compliance with Taiwan building bricks criteria. This means that raw materials for producing building bricks can be replaced with reservoir sediment. The metals concentrations of the leachate from the toxicity characteristics leaching procedure (TCLP) test are all complying with the current regulatory limits. These results confirm the feasibility of using reservoir sediment to produce sintered construction brick.     

Effect of the different shapes of silver particles in conductive ink on electrical performance and microstructure of the conductive tracks

The electrical performance of the ink-jet printed conductive tracks composed of silver particles was investigated. Three different shapes silver particles were synthesized via chemical reduction method in the presence of poly vinyl pyrrolidone, and then they were used to study the shape influence on the electrical property and thermal stability of the conductive tracks. The resistivity variation and microstructure of the silver conductive tracks was monitored as a function of fillers content using a four-point probe and scanning electron microscopy as well as thermal analysis. In addition, we proposed the possible formation mechanism of conductive tracks with different fillers. It demonstrated that the conductive tracks filled with silver nanorods and nanoparticles could achieve the volume electrical resistivity of ~3.2?×?10^?5?Ω?cm after sintering at 160?°C for 15?min. Finally, we fabricated highly conductive silver patterns on a glass substrate by ink-jet printing.     

Low-temperature sintering properties of the screen-printed silver paste for a-Si:H/c-Si heterojunction solar cells

For a-Si:H/c-Si heterojunction (SHJ) solar cells, low-temperature sintered silver paste is necessary to fabricate the metal electrodes on transparent conductive oxide layer. Here, the thermal characteristic, the conductivity, the adhesion strength on indium tin oxide substrate and the microstructure evolution of the screen-printed low-temperature sintered silver grid were investigated by varying the sintering temperature and the sintering time. The results show that the grid performance is closely related to its microstructure. A relatively high sintering temperature and a long sintering time are beneficial to make the organics in the Ag paste burn out and the adjacent Ag particles coalesce together to be larger ones. As a result, the Ag grid can get a dense microstructure and tightly adhere onto the substrate surface. Thus, low line and contact resistance is achieved. What is more, the evolution of the preferential orientation of Ag particles has some contributions to the improved grid conductivity. Specifically, for the SHJ solar cell fabrication, in order to be compatible with the low-temperature deposition of a-Si:H, a long sintering time larger than 60 min with the sintering temperature in the range of 200–230 °C is preferred to realize high performance Ag electrical contacts.     

Preparation and sintering properties in air of silver-coated copper powders and pastes

In this paper, uniform and well dispersed silver-coated copper powders were prepared by replacing reaction at first. The structure and properties of the bimetallic powders were investigated by XRD, SEM and TGA. It was found that anti-oxidization of the silver-coated copper powders increased with the increase of the silver content slightly and a dense coating surface was observed at Ag content of 53.9 wt%. Furthermore, the pastes with relatively low silver content which were prepared from silver-coated copper powders, displayed high conductivity similar to pure silver even after sintering in air. And their sintering properties were also investigated at different temperature in air atmosphere. The film exhibits good electrical properties at sintering temperature between 800 and 900 °C. When the paste from silver-coated copper powder with Ag content of 53.9 wt% was printed on Al₂O₃ substrate and sintered at 800 °C in air, the sheet resistance of the film is 0.036 Ω/□ only.     

Inkjet-printing of antimony-doped tin oxide (ATO) films for transparent conducting electrodes

Antimony-doped Tin oxide (ATO) films have been prepared by inkjet-printing method using ATO nanoparticle inks. The electrical and optical properties of the ATO films were investigated in order to understand the effects of rapid thermal annealing (RTA) temperatures. The decrease in the sheet resistance and resistivity of the inkjet-printed ATO films was observed as the annealing temperature increased. The film annealed at 700 degrees C showed the sheet resistance of 1.7 x 10(3) Omega/sq with the film thickness of 350 nm. The optical transmittance of the films remained constant regardless of their annealing temperatures. In order to further reduce the sheet resistance of the films as well as the annealing temperature, Ag-grid was printed in between two layers of inkjet-printed ATO. With 1.5 mm Ag line spacing, the Ag-grid embedded ATO film showed the sheet resistance of 25.6 Omega/sq after RTA at 300 degrees C.     

A low sintering temperature and electrical performance of nanoparticle copper ink for use in ink-jet printing

Copper nanoparticles were successfully synthesized from copper chloride with various capping agents. The formation of copper nanoparticles was controlled by varying the species and concentration of the capping agents. The Cu nanoparticles were easily re-dispersed into n-tetradecane, and Cu films were prepared by solution deposition. The thin Cu films form a highly conducting film at low temperature via sintering due to the high surface area to volume ratio. The films were thermally treated at a range of temperatures and then their morphology and resistivity were analyzed. When the Cu films were sintered at 200 degrees C, their electrical resistivity was about 40 microomega. cm.     

Sintering temperature, microstructure and resistivity of polycrystalline Sm0.2Ce0.8O1.9 as SOFC's electrolyte

In this work, near-completely soft-agglomerated Sm_0.2Ce_0.8O_1.9 powders have been prepared. The pellets were formed and sintered at various sintering conditions of temperature and time. It was found that the sintering conditions have significant effects on the pellet resistivity. By the measurements with the DC four-probe method, it was found that the overall resistivity of the polycrystalline Sm_0.2Ce_0.8O_1.9 material sintered at 1500°C increases linearly with the reciprocal of the average grain size. The AC impedance spectroscopy has been used to distinguish the grain resistivity and the apparent grain boundary resistivity. The brick layer microstructural model has been used to provide an estimate of the apparent grain boundary resistivity and to relate the electrical properties to the microstructural parameters. By lowering the sintering temperature to 1100–1200°C, the true grain boundary resistivity was nearly two orders lower than that sintered at 1500°C, and thus the overall resistivity decreases to about 31 ohm-cm at 700°C measurement. This makes the Sm_0.2Ce_0.8O_1.9 material capable of working as SOFC's electrolyte at temperatures lower than 700°C.     

Effect of submicron grains on ionic conductivity of nanocrystalline doped ceria

Doped ceria has been considered for high oxygen ion conductivity for solid oxide fuel cells. In the present study, 20 mole% samarium doped nano ceria powder was prepared by wet chemical synthesis and sintered at different temperatures to retain submicron grains (> 92-96% density). ionic conductivity of the sintered pellets was measured using impedance spectroscopy as a function of temperature (200-800 degrees C). The total maximum conductivity was 1.0 x 10(-2)S.cm(-1) (at 600 degrees C) for samples sintered at 1200 degrees C. The activation energy at higher test temperature decreases with the decrease in the sintering temperature (by 25%). The grain boundary, grain interior conductivity and activation energy of the electrolyte were correlated to the resulting microstructure. It has been demonstrated that use of doped nano ceria powder as precursor not only reduced the sintering temperature but also provided segregation free grain boundary for engineering higher conductivity dense electrolytes.     

Synthesis and Thermophysical Studies of Nanoferrites

Soft ferrites are very useful for a wide variety of technological applications especially in high frequency devices due to high resistivity and low eddy current losses. Co nanoferrite particles were synthesized by co-precipitation method and characterized to understand the microstructure and electrical transport properties. The composition was varied by changing the ??A?? concentration in Co_1?x A _x Fe₂O₄ (A= Zn, Ni) nanoparticles with stoichiometric proportion (x) varying from 0.0 to 1.0. X-ray diffraction was used for structural analysis. Then samples were sintered at 550?°C and 750?°C for 2 hours, characterized by X-ray diffraction at room temperature and DC electrical resistivity measurements were done as a function of temperature. The effects of sintering on structure were investigated. Activation energy was calculated from DC electrical resistivity data as a function of temperature.     

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.