Silver Fillers Research Articles

Selected Mechanical Properties of Dental Hybrid Composite with Fluorine, Hydroxyapatite and Silver Fillers

Selected Mechanical Properties of Dental Hybrid Composite with Fluorine, Hydroxyapatite and Silver Fillers

Construction of silver-epoxy adhesive with suppressed silver migration rate based on thiol-silver interaction

The silver migration limits the application of silver based conductive adhesives in wet environment. The existing methods for inhibiting silver migration in epoxy conductive silver adhesives involve one or more issues such as cost, complexity, and inhibition of conductivity. Moreover, there is currently a lack of strategies that can suppress the silver migration effect while ensuring good dispersion of silver fillers in the matrix and constructing a good filler matrix interface. Herein, a facile method was reported suppressing the silver migration in silver-epoxy conductive adhesive. Tetrafunctional thiopentaerythritol tetramercaptoacetate (PERTMA) was introduced into 1,4-cyclohexanedimethanol diglycidyl ether (CHDMGE) epoxy resin as the curing agent. This method utilized the strong interaction between silver and thiols, including coordination and covalent bonding, to achieve good compatibility between filler and matrix. By tightly combining silver with the resin system, the content of free silver atoms was reduced, capturing and inhibiting the hydrolysis of silver atoms and their migration with current, and the conductivity of the conductive silver adhesive was not greatly degraded due to the silver-thiol interaction. At the same time, the introducing of PERTMA was able to reduce the surface hydrophilicity of epoxy resin, which also helped suppressing the silver migration effect under humid circumstances. The interaction between silver and thiol was characterized, and the influence of silver content on the curing behavior, material mechanical performance, conductivity, resistivity on silver migration and flexibility was explored. The CHDMGE/PERTMA/Ag conductive adhesive based on strong thiol-silver interaction had excellent resistance to silver migration, which occurred after 3500s, which was 10.67 times longer than the control group. In addition, the silver filler enhanced the tensile strength of the matrix resin by this thiol-silver interaction. This study will provide new ideas for the design and development of silver migration resistant conductive adhesives based on matrix filler interaction.

The effects of increasing filler loading on the contact resistivity of interconnects based on silver–epoxied conductive adhesives and silver metallization pastes

AbstractOur previous work highlighted how microscopic structural effects influence the sheet and contact resistance of electrically conductive adhesives (ECAs). Herein, we delve further by investigating how the contact and bulk resistivity of several ECAs that are based on the same formulation, but with different filler content, are correlated with the filler content. Additionally, two different filler geometries — high and low surface area (HSA and LSA) fillers — are combined in different ratios to maintain a similar viscosity and therefore processability. Hence, contact and bulk resistivities are also correlated with the different geometry ratios of these two fillers. As expected, it was found that the contact and bulk resistivities decreased when the filler content was increased. However, the magnitude of the decrease was found to depend strongly on the filler geometry ratio. At extreme filler geometry ratios, when the bulk is either mostly loaded with HSA‐fillers or mostly with LSA‐fillers, the impact of changes in the filler content on the bulk and contact resistivities is markedly different. The measured data is interpreted within the context of percolation theory and it is determined that the optimum ratio of the LSA and HSA Ag‐fillers investigated in this study is approximately 60:40 (for an epoxy‐based adhesive). This work has important ramifications for the design of ECAs, where cost considerations and the need to reduce silver resource usage demand the lowest (silver) filler content, but the demands of product performance point to higher filler content.

Influence of microalloying with B on the microstructure and properties of brazed joints with Ag–Cu–Zn–Sn filler metal

Abstract Processing and formation of Ag–Cu–Zn–Sn filler metals with high Sn content are difficult owing to their high brittleness. A composite flux-cored silver (Ag) filler metal of a CuSn + XB alloy powder was designed using the principle of in situ synthesis. Copper–Copper (Cu–Cu) joints were obtained using a novel Ag-based filler metal (at B contents of 0, 2, and 3%). The microstructure and evolution of the mechanical properties of the Cu–Cu brazed joints were studied by field emission scanning electron microscopy, electron probe microscope, electron backscattering diffraction, tensile testing, and nanoindentation tester. The brazed joints mainly consisted of Ag-based solid solution (Ag(s.s)) and Cu-based solid solution (Cu(s.s)). Due to the addition of 3% B, (Ag + Cu) eutectic network structures were formed in the brazing seam. At the same time, the grain size, texture strength, misorientation distribution, and deformation of Ag(s.s) and Cu(s.s) in the brazing seam changed significantly. The overall microhardness of the brazing seam significantly increased as the B content increased in the filler metals. The tensile strength of the joints followed a parabola. At the B content of 2%, the ultimate tensile strength of the Cu–Cu joints was 248.0 MPa. The brazed joints featured intergranular, dimple, and cleavage fractures.

Effect of B on microstructure and properties of joints brazed by In-situ Ag-Cu-Zn-Sn filler metal with high Sn content

The copper brazed joints were obtained by induction brazing using in situ synthetic high Sn content silver filler metals with different B contents and the effect of element B on the wettability of filler metals and microstructure and mechanical properties of the joints were studied. With the addition of element B, the spreading area of the filler metals on the copper increases. The microstructure of the joints mainly consists of silver-based solid solution and copper-based solid solution, and the distribution of silver-based solid solution in the brazing seam becomes dispersed with the addition of B. The width of the brazing seam increases significantly with the increase in B content. Meanwhile, the B element was mainly distributed in the Ag-based solid solution. The tensile strength firstly increased and then sharply decreased with B added. The maximum average tensile strength of 206.83 MPa was obtained with a 2% addition of B and the joint fracture pattern is a brittle fracture.

Effects of silver nano-particles and nano-wires on properties of electrically conductive adhesives

The morphology and content of the silver fillers, resin matrix composition and curing process could significantly affect performance properties of electrically conductive adhesives (ECAs). In this study, the effects of silver nano-particles (NPs) and nano-wires (NWs) were studied on the properties of ECAs, which are under the same curing and aging conditions varied with three kinds of fillers: the mixture of silver micro flakes and NPs at a mass ratio of 17:3, the mixture of silver micro flakes and NWs at a mass ratio of 19:1, and the pure silver micro flakes as the reference sample. Results show that silver NPs might cause the deterioration of electrical conductivity and thermal conductivity in ECAs with the filler weight fraction of 70 wt%, because segregation of silver NPs might increase the average distance between silver micro flakes; but silver NPs could improve the performance properties of ECAs at a filler loading of 85 wt% especially after 200 °C aging. Silver NWs could reduce bulk resistivity of ECAs with the filler weight fraction of 70 wt% from 2.5 × 10−3 Ω·cm to 1.8 × 10−4 Ω·cm. In addition, thermal conductivity and shear strength of ECAs seemed irrelevant to the filler morphology but only correlated positively and negatively with filler loading ratio respectively.

Structure formation and conductive properties of epoxy/in situ polymerized methacrylate polymer/silver filler composites

The structure formation and electrical conductivity of poly[diglycidyl ethers of bisphenol-F (DGEBF)]/poly[dicyclopentenyloxyethyl methacrylate (DPOMA)]/silver (Ag) filler composites were investigated. DGEBF/40 wt% DPOMA blends showed low viscosity and formed co-continuous phase structures at the micrometer scale via in situ radical polymerization of DPOMA followed by anionic polymerization of DGEBF. Scanning electron microscopy and nano-infrared spectroscopy revealed that the Ag fillers, surface-treated with myristic acid, were selectively localized in the methacrylate polymer-rich phases. Consequently, the Ag fillers were present in the self-assembled narrow area, which formed a conductive channel. The DGEBF/DPOMA/Ag composites thus achieved electrical conductivity with a reduction of the 30% Ag fillers, compared to the DGEBF/Ag composites. The mechanism for the selective placement of the Ag fillers was clarified in terms of the affinity among the epoxy-rich phase, the DPOMA polymer-rich phase, and the surface-treated Ag fillers by measurement of their Hansen solubility parameters (HSPs).

Enhancing Thermal Transport in Silicone Composites via Bridging Liquid Metal Fillers with Reactive Metal Co-Fillers and Matrix Viscosity Tuning.

Polymer matrix composites containing room temperature liquid metal (LM) microdroplets offer a unique set of thermo-mechanical characteristics that makes them attractive candidates for high performance thermal interface materials. However, to achieve the desired level of the composite thermal conductivity, effective bridging of such fillers into interconnected percolation networks needs to be induced. Thermal percolation of the LM microdroplets requires two physical barriers to be overcome. First, the LM microdroplets must directly contact each other through the polymer matrix. Second, the native oxide shell on the LM microdroplet must also be ruptured. In this work, we demonstrate that both physical barriers can be penetrated to induce ample bridging of the LM microdroplets and thereby achieve higher thermal conductivity composites. We accomplish this through a synergistic combination of solid silver and LM fillers, tuning of the silicone oil "matrix" viscosity, and sample compression. We selected silver as the solid additive because it rapidly alloys with gallium to form microscale needles that could act as additional paths that aid in connecting the LM droplets. We systematically explore the impact of the composition (filler type, volume fraction, and matrix oil viscosity) and applied pressure on the thermal conductivity and multiscale structure of these composites. We reveal the microscopic mechanism underlying the macroscopic experimental trends and also identify an optimal composition of the multiphase Ag-LM-Silicone oil composite for thermal applications. The identified design knobs offer path for developing tunable LM-based polymer composites for microelectronics cooling, biomedical applications, and flexible electronics.

Hybrid silver pastes with synergistic effect of multi-scale silver fillers and the application in flexible circuits

Silver circuits prepared by new hybrid pastes exhibit high electrical conductivity and mechanical properties, which are ideal for modern flexible electronics. Herein, the hybrid silver pastes composed of different silver nanoparticle content (0, 10, 20, 30 wt%), micron-sized silver flakes and epoxy-based binders were prepared. The corresponding electrical conductivity and bending resistance of the screen-printed silver circuits were studied. The experimental results demonstrated that the synergistic effect of micro-size silver flakes and nanoparticles can greatly improve the electrical conductivity and bending resistance of flexible circuits. Specifically, the silver circuits with 46 wt% micro-size silver flakes and 20 wt% silver nanoparticles incorporation exhibit a lower electrical resistivity of 8.1 × 10−5 Ω·cm. Moreover, 10 wt% silver nanoparticles can be applied to significantly reduce the resistance change of flexible circuit, indicting a superior bending property. Our designed hybrid silver pastes with excellent performance might enable valuable applications in advanced electronic devices.

Nanojoining with Ni Nanoparticles for Turbine Applications.

Thermal joining can lead to high thermal stresses, undesired structural changes, and the associated loss of properties. In the turbine industry, monocrystalline materials are often used to take advantage of their high creep resistance and heat resistance. For process-related reasons, components are mechanically machined, and the contours usually have slightly work-hardened areas due to the mechanical processing. Downstream thermal processes at temperatures above 1100 °C can lead to recrystallization (Rx) at these areas, so that the properties are negatively affected. Usually, the joining temperatures for high-temperature brazing are in the range of 1200 °C, both in new installations and in the case of repairs. It is therefore desirable to reduce the joining temperature without changing the choice of filler material, which can lead to susceptibility to corrosion and oxidation. According to investigations of the last years, nanojoining with nanoparticles offers great potential. The joining temperature can be lowered due to the “surface effect.” A considerable reduction in the size of the particles leads to a significant increase in surface atoms and thus in the specific surface area. The connection of the materials occurs predominantly due to sintering processes. After the joining process, the properties of a bulk material are available again. Mechanical properties comparable to those of brazing have already been achieved with silver nanoparticles (Hausner in WWA 56, 2015). Up to now, publications on the topic of nanojoining have largely referred to silver nanoparticles/silver sintering. Due to the temperature application range, silver filler material cannot be used in gas turbines. Therefore, the first results of nickel nanoparticles for joining of the nickel-based superalloy PWA 1483 using induction heating are described in this paper. During joining, the parameters brazing temperature, holding time and the surface treatment of the base materials were varied. It becomes clear that the microstructure of the joint is dependent on temperature and holding time. Moreover, if the temperature is too low and holding time too short, only insufficiently sintering occurs, which leads to sample failure during the metallographic preparation. On the other hand, samples with a tensile shear strength of up to 165 MPa can be achieved with convenient joining conditions.

Synergistic effect of phase structures and in situ sintering of silver fillers on thermal conductivity of epoxy/polyethersulphone/silver filler composites

The thermal conductivity of the diglycidyl ethers of bisphenol-A (DGEBA)/4,4′-diaminodiphenylmethane (DDM)/polyethersulphone (PES)/silver (Ag) filler composites has been investigated. The DGEBA/DDM/PES blend as the matrix for the polymer composites formed co-continuous phase structures at the micrometer scale via reaction-induced phase separation during the curing process. The Ag fillers were selectively localized in the epoxy-rich phases, and consequently the fillers experienced more opportunities for contact within the narrow self-assembled templates. As the result, sintering of the Ag fillers occurred at the surface during curing, especially in the post-curing process at 180 °C. Curve-fitting of the thermal conductivity data for the composites using an extended Bruggemann's equation clarified the differences in the in situ sintering at the two curing temperatures. The synergistic effect of the phase structures of the polymer blend matrices and the in situ sintering of Ag fillers accounted for the enhanced thermal conductivities of the polymer composites.

Lutowanie wiązką elektronów na przykładzie stali austenitycznej odpornej na korozję – AISI 304

Electron beam brazing is a joining technology combining the advantages of a precisely controlled heat source and those of vacuum brazing process. The oxide layer decomposes in high-temperature vacuum conditions, which improves the wetting process and, consequently, leads to the obtainment of more favourable properties of the brazed joint. In comparison with brazing in vacuum furnaces, the electron beam brazing process enables the precise heating of selected areas without the necessity of heating the entire element, which, in turn, results in smaller structural changes in the brazed material and the lower consumption of energy. During tests discussed in this article, sheets made of stainless steel AISI 304 were brazed using various copper and silver filler metals. Brazed joints were subjected to microstructural tests and shear strength tests. The results revealed the high efficiency of the electron beam brazing of corrosion-resistant steel sheets using filler metals.

ВЛИЯНИЕ СОСТАВА И УСЛОВИЙ ТЕРМООБРАБОТКИ НА ПРОВОДЯЩИЕ СВОЙСТВА СЕРЕБРОСОДЕРЖАЩИХ ТОКОПРОВОДЯЩИХ КЛЕЕВЫХ КОМПОЗИЦИЙ (обзор). Часть 1

Data on the use of various types of silver filler in electrically conductive adhesive compositions are presented. The influence of form and size particles of silver filler on the conductive properties of adhesive bondline. The effect of surface treatment of conductive particles with surfactants, the component composition of the resin part and the curing conditions of conductive adhesive compositions on their microstructure and conductive properties is shown. An overview of the results of studies of the microstructure of conductive silver-containing adhesive compositions is given.

Mechanical properties of joints of stainless steel and titanium brazed with silver filler material

Mechanical properties of joints of stainless steel and titanium brazed with silver filler material

Simultaneous improvement of the electrical conductivity and mechanical properties via double-bond introduction in the electrically conductive adhesives

For electrically conductive adhesives (ECAs), high electrical conductivity generally conflicts with excellent mechanical properties because electrical conductivity increases while desirable mechanical properties decrease with the increase in loading of conductive fillers or removal of lubricants on the silver filler surface. In this work, a method was developed to improve both the electrical conductivity and mechanical properties of the ECAs by introducing double bonds. Itaconic acid (IA) was used to replace the lubricant on the silver flake (Ag-F) surface, and acrylic acid (AA) was used as part of the ECA resin matrix. IA can replace the lubricant on the Ag-F surface, similar to other short-chain dibasic acids, to improve the ECA electrical conductivity. Furthermore, IA can be polymerized with AA to form covalent bonds between the silver flakes and the resin matrix, enhancing the mechanical properties of ECA. Compared with ECA filled with commercial silver flakes, the electrical conductivity of ECA filled with IA-treated silver flakes increased by ~ 21%, and the lap shear strength increased by ~ 29%.

Ecofriendly Catechol Lipid Bioresin for Low-Temperature Processed Electrode Patterns with Strong Durability.

We demonstrated catechol lipid-based bioresin, which is collected from lacquer trees, to produce conductive pastes that can be processed at low temperatures, which are highly adhesive and multidurable. Our conductive paste, which consists of catechol lipid-based urushiol resin and a multimodal mixture of silver fillers, exhibited stable dispersion with shear thinning properties. The urushiol lacquer induced spontaneous reduction of silver salt at the surface of the silver fillers, thereby contributing to lower the contact resistance between conductive fillers in the electrical conduction. Furthermore, the directional volume shrinkage of the urushiol lacquer matrix in a cross-linking reaction resulted in a highly ordered microstructure of the silver fillers with layer-by-layer stacking of the silver flakes. This structure contributed to the improvement of the electrical contact between fillers as well as excellent mechanical hardness, anti-scratch capability, and the long-term environmental stability of the conductive films. Conductive films based on the silver paste with urushiol lacquer exhibited low electrical resistivity below 4.4 × 10-5 Ω cm, 5B-class strong adhesion strength, and high hardness exceeding 200 MPa. Finally, we demonstrated the facile room-temperature processability and screen printability of the UL-Ag paste by fabricating a printed antenna and three-dimensional (3D) electrode assembly based on a plastic 3D block.

From Silver Nanoflakes to Silver Nanonets: An Effective Trade-Off between Conductivity and Stretchability of Flexible Electrodes.

Flexible and stretchable conductive materials have received significant attention due to their numerous potential applications in flexible printed electronics. In this paper, we describe a new type of conductive filler for flexible electrodes—silver nanonets prepared through the “dissolution–recrystallization” solvothermal route from porous silver nanoflakes. These new silver fillers show characteristics of both nanoflakes and nanoparticles with propensity to form interpenetrating polymer–silver networks. This effectively minimizes trade-off between composite electrode conductivity and stretchability and enables fabrication of the flexible electrodes simultaneously exhibiting high conductivity and mechanical durability. For example, an electrode with uniform, networked silver structure from the flakiest silver particles showed the lowest increase of resistivity upon extension (3500%), compared to that of the electrode filled with less flaky (3D) particles (>50,000%).

Fabrication of Novel Printable Electrically Conductive Adhesives (ECAs) with Excellent Conductivity and Stability Enhanced by the Addition of Polyaniline Nanoparticles.

Electrically conductive adhesives (ECAs) are one of the low temperature bonding materials. It can be used to replace toxic Sn-Pb solder. The key issue for the application of ECAs is how to improve their electrical properties. In the present study, we develop an effective method to promote the electrical properties of ECAs by addition of polyaniline (PANI) nanoparticles. PANIs were synthesized via a facile one-step chemical oxidative polymerization method. After adding 0.5 wt% PANI nanoparticles, the conductivity of ECAs increased dramatically by an order of magnitude. The bulk resistivity of 8.8 × 10−5 Ω·cm is achieved for 65 wt% silver fillers with 0.5 wt% PANIs loaded ECAs. Besides, this improvement has no negative effect on the shear strength and the aging life of ECAs. Moreover, the use of PANIs not only lowers the percolation threshold of ECAs, but also reduces the cost and improves the bonding reliability. Finally, PANIs enhanced ECAs patterns were successfully printed by a stencil printing method, which proved their potential applications in replacing conventional solder pastes and printing functional circuits.

Glass transition temperature of nanoparticle-enhanced and environmentally stressed conductive adhesive materials for electronics assembly

In our paper, the characterization of glass transition temperature (Tg) was performed for one- and two-component electrically conductive adhesive used in electronic joining technologies. Both adhesives were of the epoxy type with the silver filler. Dynamic mechanical analysis (DMA) was used to measure the Tg. The adhesives were modified with nanoparticles, namely, carbon nanotubes (concentration of 0.5 and 0.8% by weight) and silver nanoballs (2.5% by weight). The values of Tg were determined from the plot of the Tg δ parameter. Two types of environmental stresses were used for climatic aging: 125 °C/56% RH and 85 °C/85% RH. The aging of the samples at 125 °C and 56% RH caused increase Tg for all formulations. The cause of these changes is additional curing of adhesive. Aging in the combined climate 85 °C/85% RH caused a shift in Tg toward lower values for formulations based on the one-component adhesive modified by CNT and toward higher values for all other formulations. The major cause of the decrease in Tg was that CNT inhered the curing reactions and banned them from completion. In cases where Tg grew, glue hardening take place. DMA was performed to examine Tg of the samples. The DMA measurements were carried out up to 200 °C. Repeated DMA measurement confirmed that this measurement caused additional hardening and increase Tg for all samples. The results will contribute to the use of conductive adhesives with better quality and reliability in electronics manufacturing.

Joint Gap and Joint Strength of Cemented Carbide Brazed with Silver Filler Metal

Joint Gap and Joint Strength of Cemented Carbide Brazed with Silver Filler Metal