Conductive Adhesives Research Articles

A gel-free Ti3C2Tx-based electrode array for high-density, high-resolution surface electromyography.

Wearable sensors for surface electromyography (EMG) are composed of single- to few-channel large-area contacts, which exhibit high interfacial impedance and require conductive gels or adhesives to record high-fidelity signals. These devices are also limited in their ability to record activation across large muscle groups due to poor spatial coverage. To address these challenges, we have developed a novel high-density EMG array based on titanium carbide (Ti3C2Tx) MXene encapsulated in parylene-C. Ti3C2Tx is a two-dimensional nanomaterial with excellent electrical, electrochemical, and mechanical properties, which forms colloidally stable aqueous dispersions, enabling safe, scalable solutions-processing. Leveraging the excellent combination of metallic conductivity, high pseudocapacitance, and ease of processability of Ti3C2Tx MXene, we demonstrate the fabrication of gel-free, high-density EMG arrays which are ~8 μm thick, feature 16 recording channels, and are highly skin-conformable. The impedance of Ti3C2Tx electrodes in contact with human skin is 100-1000x lower than the impedance of commercially-available electrodes which require conductive gels to be effective. Furthermore, our arrays can record high-fidelity, low-noise EMG, and can resolve muscle activation with improved spatiotemporal resolution and sensitivity compared to conventional gelled electrodes. Overall, our results establish Ti3C2Tx-based bioelectronic interfaces as a powerful platform technology for high-resolution, non-invasive wearable sensing technologies.

Investigation of the impact on the radio frequency (RF) behaviour of electrically conductive adhesives (ECAs) used in wafer-level packaging (WLP) of RF-MEMS

In this work, an anisotropic conductive adhesive (ACA), belonging to the family of electrically conductive adhesives (ECAs), exploited for the wafer-level bonding phase in packaging of RF-MEMS (MEMS for radio frequency passives), is investigated in respect to its influence on the RF behaviour of packaged Microsystem structures and CPWs (coplanar waveguides). The explored encapsulation solution is based on the wafer-level packaging (WLP) approach, in which the capping substrate (high-resistivity silicon—HRS) provided of vertical through silicon vias (TSVs) is bonded to an RF-MEMS wafer using ACA as adhesion layer. After bonding of ACA, conductive metal particles within the epoxy-based matrix either contribute to the electrical path formation or, when uncompressed, remain isolated. Influence of such floating particles on the RF performance of adjacent structures is investigated by means of finite element method (FEM) electromagnetic simulations. The results show that the influence of floating ACA conductive particles on the S-parameters of the targeted planar structures is rather limited up to 60 GHz.

Stretchable conductive adhesives for connection of electronics in wearable devices based on metal-polymer conductors and carbon nanotubes

Stretchable wearable devices with various functions are being continuously developed. However, the problem of how to connect rigid electronics to stretchable circuits has not been properly solved. In this study, we use stretchable conductive adhesives to realize stretchable connections between electronics and circuits, so that the overall reliability of stretchable wearable devices can be strengthened. The adhesives are based on metal-polymer conductors where polydimethylsiloxane is used as an elastomer matrix, while liquid metals form electrically conductive networks collectively with carbon nanotubes. The composites show superior adaptability to stretchable wearable devices due to excellent stretchability (maximum tensile strain: 40%) and stability of electrical conductivity in deformation (ΔR/R < 16% at maximum tensile strain), which goes beyond existing conductive adhesives, and can satisfy the requirements of most applications. A stretchable light emitting diode screen is fabricated using the stretchable conductive adhesives and exhibits good performance under cyclic deformations.

Conducting polymer-based electrically conductive adhesive materials: design, fabrication, properties, and applications

In the past few decades, increasing demands for electrically conductive adhesives (ECAs) have led to growing interest in the design and development of innovative strategies to obtain materials with synergetic or complementary properties for various industrial as well as biomedical applications. In this context, the replacement of traditional tin/lead (Sn/Pb) solders due to their corrosion, low strength of joints, solder joint fatigue, stress-induced cracking within the interconnect, as well as environmental issues are attracted a great deal of interests, especially in industrial committees. The significant progress in polymer science as well as the advent of nanotechnology, have been led to design and development of alternative materials with higher performance over conventional adhesives. On the other hand, intrinsically conductive polymers (ICPs) offer promising materials for the replacement or reducing the content of metallic fillers (e.g., silver, gold, nickel, or copper) in ECAs due to some disadvantages of metallic fillers. For the first time, an overview of the recent progress in the design, fabrication, and applications of the ECAs based on ICPs is presented.

Synthesis of Ag-Cu based epoxy polymer composite for electrical conductivity

In this study bimetallic Ag-Cu alloy has been synthesized using chemical reduction method. Fabricated Ag-Cu nanoparticles were used as conductive filler and the epoxy resin as polymer to produce Ag-Cu epoxy composites. Conductive filler with different concentration (1 wt% 2 wt%, 3 wt%, 4 wt%, 5 wt% and 10 wt%) were added in epoxy resin to investigate the electrical properties of Ag-Cu based epoxy composites . XRD pattern of Ag-Cu alloy formed fcc phase with miller indices (0 0 2), (1 1 1) and (2 0 0). For surface morphology, scanning electron microscopy (SEM) was used to perceive structure of alloy based epoxy composites and EDX confirmed the Ag-Cu elements in samples. Surface and volume resistivity of epoxy-based composite was investigated by Mega Ohm Meter-1865. Electrical conductivity of the Ag-Cu based epoxy polymer composites was measured to enhance the flow of electron in dielectric property of epoxy resin with conductive material of Ag-Cu alloy for practical application and potential fabrication of numerous electronic devices such as electrical conductive adhesives as well as micro/nano electro-mechanical systems.

Convenient Design of Hollow Co3O4 Nanostructure on Carbon Cloth for Flexible Supercapacitors

We proposed a new approach to construct zeolitic imidazolate frameworks-67 (ZIF-67) powders directly on carbon cloth without any conductive agent and adhesion agent and the ZIF-67 nanoparticles on carbon cloth were successfully converted into hollow Co3O4 nanostructure via a facile calcination process. Compared with original ZIF-67 powders, the Co3O4@CC electrode materials had admirable specific capacitance of 1 164.8 F·g−1 at an area current density of 2.5 mA·cm−2. Furthermore, the rate performance remained 42.4% of initial value when the current density was increased to 30 mA·cm−2 and the specific capacitance maintained 93.4% of initial capacity after 5 000 cycles at an area current density of 10 mA·cm−2. This strategy may have potential prospect for the application of MOFs in the energy storage and conversion field.

Highly dispersed polypyrrole nanotubes for improving the conductivity of electrically conductive adhesives

It is imperative to fabricate electrically conductive adhesives (ECAs) with excellent electrical performance and mechanical properties. In this article, a kind of polypyrrole nanotubes (PPy nanotubes) having a high aspect ratio and excellent dispersibility in various kinds of organic solvents were prepared and added to conventional Ag-containing adhesives. Stable suspension characteristics of PPy nanotubes in common solvents provided homogeneous dispersion of the PPy nanotubes in the composites. A small amount of PPy nanotubes can remarkably change the structures of the conductive networks of conventional ECAs and significantly improve the ECAs’ conductivity. By only adding 3 wt% PPy nanotubes, the resistivity (5.8 × 10−5 Ω ‧ cm) of the ECAs containing 55 wt% silver decreased to 1/1000 of the comparative ECAs without PPy nanotubes. This resistivity is almost five to one-tenth of the ECAs materials reported by now. Furthermore, the resulted ECAs showed excellent mechanical properties. The electrical resistivity of the new PPy nanotube-containing ECAs remained stable after they were rolled at a 6 mm bending radius for over 5000 cycles or pressed under 1200 kPa. An elastic printed circuit was fabricated using the above-described ECA-containing PPy nanotube, which demonstrates its potential application in the field of flexible electronics.

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%.

Nickel Nanofibers Manufactured via Sol-Gel and Electrospinning Processes for Electrically Conductive Adhesive Applications

The electrospun fibers of poly(vinyl pyrrolidone) (PVP)-nickel acetate (Ni(CH3COO)2·4H2O) composite were successfully prepared by using sol-gel processing and electrospinning technique. Nickel oxide (NiO) nanofibers were obtained afterwards by high temperature calcinations of the precursor fibers, PVP/Ni acetate composite nanofibers, at 700 °C for 10 h. Following with the reduction of NiO nanofibers at 400 °C using hydrogen gas (H2) under inert atmosphere, the metallic nickel (Ni) nanofibers were subsequently produced. In addition, as-prepared Ni nanofibers were chemically coated with silver (Ag) nanoparticles to enhance their electrical property and prevent the surface oxidation. The characteristics of as-prepared fibers, such as surface morphology, fiber diameters, purity, the amount of NiO nanofibers, and metal crystallinity, were determined using a scanning electron microscope (SEM), a Fourier transform infrared spectrometer (FT-IR), a thermogravimetric analyzer (TGA), and a wide-angle x-ray diffractometer (WAXD). The volume resistivity of epoxy nanocomposite filled with Ag-coated short Ni nanofibers was lower than the one containing short Ni nanofibers with no coating due to the synergetic effect of Ag nanoparticles created during the coating process. We also demonstrated that the volume resistivity of epoxy nanocomposite filled with Ni nanofibers could be dramatically decreased by using Ni nanofibers in the non-woven mat form due to their small fiber diameter and high fiber aspect ratio, which yield a high specific surface area, and high interconnecting network.

Fabrication of lignin based renewable dynamic networks and its applications as self-healing, antifungal and conductive adhesives

The preparation of dynamic networks from lignin with multipurpose and multifunctional practical applications is highly desirable but still challenging. In this study, the combination of a “grafting from” reversible addition-fragmentation chain transfer (RAFT) polymerization and dynamic chemistry was utilized to synthesize lignin based dynamic networks. Vanillin, a derived chemical from lignin, was used as a building block to realize the structural reorganization of lignin via RAFT polymerization, together with fatty acid derivative as the comonomer. NMR analysis confirmed the expected structures. It was demonstrated that the physicochemical properties of grafted lignin were adjustable depending on polymerization reaction conditions. Due to the presence of aldehyde groups from vanillin moiety, a dynamic network was produced by using diamines as crosslinkers. The mechanical properties were also tunable via controlling the structure of crosslinkers. The crosslinked lignin-based dynamic networks exhibited various interesting properties, such as recyclability and UV-adsorption ability. In addition, it could be used as self-healing, antifungal and conductive adhesives. The shear strength after first time self-healing could reach 2.9 MPa, which was 83.1% of the pristine adhesion. This damage and repair process could be carried out at least four times under relatively low temperature (80 °C) and pressure (1.0 MPa). More importantly, antifungal activity was observed for the self-healing adhesive, which might enlarge its applications. Additionally, after the addition of carbon nanotubes, the generated conductive adhesive was weldable without compromising its conductivity. This study has demonstrated the potential of lignin to synthesize high value-added materials, which could be appealing to both biorefinery and materials society.

A review on epoxy-based electrically conductive adhesives

Electrically conductive adhesives (ECAs) are widely utilized in various electronic packaging applications including die fitting, solderless interconnections, component renovation, display interconnections, and heat dissipation, etc. ECAs seize attention of scientific researchers as green and sustainable lead-free interconnection material over conventional solders owing to their eco-friendliness, processing capability at low temperature, fewer processing steps, negligible stress on a substrate, flexibility and stretchability, and cost-effectiveness. Various researchers worked in the area of epoxy based conductive adhesives mainly focusing on the categories, conduction mechanisms, applications of conductive adhesives along with various types of conductive fillers, inherent conductive polymers and future prospective of epoxy resin in the field of conductive adhesives is presented.

Conductive acrylic pressure-sensitive adhesives

Conductive acrylic pressure-sensitive adhesives

Linear viscoelastic characterization of electrically conductive adhesives used as interconnect in photovoltaic modules

AbstractElectrically conductive adhesives (ECAs) are incorporated into recent designs of photovoltaic (PV) modules and replace the traditional metallic solders as interconnects. This transition depicts a significant material change, and a proper understanding of the interconnects' mechanical response has not yet been established. However, such an understanding is necessary to (a) identify the driving forces for module degradation and failure, (b) allow for module design optimization, and (c) enable accurate lifetime predictions. This study summarizes the framework for the mechanical materials characterization and modeling of ECAs for PV applications. Only high‐fidelity material models are able to capture the rate and temperature dependency of the ECA interconnect and allow for accurate modeling of the materials response. A linear viscoelastic representation is found to describe the mechanical response of the ECAs sufficiently well. The effects of curing conditions and environmental exposure are investigated, and material models for a variety of ECAs are reported and prepared for the use in numerical simulations. A finite element simulation of a generic submodel of a shingled cell module is used to highlight the need for high‐fidelity material models and demonstrates the error made in the predicted stress states by using less sophisticated models.

Electronic Component Mounting for Durable E-Textiles: Direct Soldering of Components onto Textile-Based Deeply Permeated Conductive Patterns.

For the improvement of the performance and function of electronic textiles (e-textiles), methods for electronic component mounting of textile circuits with electrical and mechanical durability are necessary. This manuscript presents a component mounting method for durable e-textiles, with a simpler implementation and increased compatibility with conventional electronics manufacturing processes. In this process, conductive patterns are directly formed on a textile by the printing of conductive ink with deep permeation and, then, components are directly soldered on the patterns. The stiffness of patterns is enhanced by the deep permeation, and the enhancement prevents electrical and mechanical breakages due to the stress concentration between the pattern and solder. This allows components to be directly mounting on textile circuits with electrical and mechanical durability. In this study, a chip resistor was soldered on printed patterns with different permeation depths, and the durability of the samples were evaluated by measuring the variation in resistance based on cyclic tensile tests and shear tests. The experiments confirmed that the durability was improved by the deep permeation, and that the samples with solder and deep permeation exhibited superior durability as compared with the samples based on commercially available elastic conductive adhesives for component mounting. In addition, a radio circuit was fabricated on a textile to demonstrate that various types of components can be mounted based on the proposed methods.

An investigation on shielding effectiveness of conductive adhesive

The use of metal shell is an effective method to solve electromagnetic interference caused by printed circuit board (PCB) of electronic equipment. Electromagnetic leakage mainly occurs at the junction of the upper metal shell and the lower metal shell. In order to reduce the electromagnetic interference caused by the electromagnetic leakage, the conductive adhesive is coated on the connection between the upper shell and the lower shell. In this paper, a simulation model of shielding effectiveness is established in CST STUDIO SUITE. It is mainly used to calculate the effects of conductivity and geometric size of conductive adhesives on shielding effectiveness. In the actual design process of electronic equipment, we can find a more economical combination of size and conductivity of conductive adhesives through the simulation of shielding effectiveness. The results can be used to guide the design of conductive adhesives to solve the electromagnetic compatibility problems of electronic equipment.

Sticky thermoelectric materials for flexible thermoelectric modules to capture low–temperature waste heat

ABSTRACTWe examined a working hypothesis of sticky thermoelectric (TE) materials, which is inversely designed to mass-produce flexible TE sheets with lamination or roll-to-roll processes without electric conductive adhesives. Herein, we prepared p-type and n-type sticky TE materials via mixing antimony and bismuth powders with low-volatilizable organic solvents to achieve a low thermal conductivity. Since the sticky TE materials are additionally injected into punched polymer sheets to contact with the upper and bottom electrodes in the fabrication process, the sticky TE modules of ca. 2.4 mm in thickness maintained temperature differences of ca. 10°C and 40°C on a hot plate of 40 °C and 120°C under a natural-air cooling condition with a fin. In the single-cell resistance analysis, we found that 75∼150-µm bismuth powder shows lower resistance than the smaller-sized one due to the fewer number of particle-particle interfaces in the electric pass between the upper and bottom electrodes. After adjusting the printed wiring pattern for the upper and bottom electrodes, we achieved 42 mV on a hot plate (120°C) with the 6 x 6 module having 212 Ω in the total resistance. In addition to the possibility of mass production at a reasonable cost, the sticky TE materials provide a low thermal conductivity for flexible TE modules to capture low-temperature waste heat under natural-air cooling conditions with fins for the purpose of energy harvesting.

A reversible and highly conductive adhesive: towards self-healing and recyclable flexible electronics

Flexible conductive adhesives are important materials for the next generation of flexible electronic devices.

Relationship Between Heterogeneous Materials Interface Region and Electrical Conductivity Development in Electrically Conductive Adhesives

Relationship Between Heterogeneous Materials Interface Region and Electrical Conductivity Development in Electrically Conductive Adhesives

Analysis of Hot Bar Soldering, Insulation Displacement Connections (IDC), and Anisotropic Conductive Adhesives (ACA), for the Automated Production of Smart Textiles.

Despite all the growth forecasts of the smart textiles market, there is no stable automated manufacturing process for attaching classic electronics to textiles. The great amount of manual production steps causes high prices, which slow down market growth. During the production process, the contacting step offers the greatest potential to reduce manual manufacturing steps. For this reason, we have analyzed various contacting methods for electronic parts on conductive yarns that have a high potential for automation. The chosen methods were thermode soldering, insulation–displacement connectors and anisotropic conductive adhesives. In order to ensure reliable mechanical contacting, the samples were tested in a peeling experiment. The examination of the contact resistances took place in the context of a resistance test using four-wire measuring technology.

An Injectable Conductive Three-Dimensional Elastic Network by Tangled Surgical-Suture Spring for Heart Repair.

Designing scaffolds with persistent elasticity and conductivity to mimic microenvironments becomes a feasible way to repair cardiac tissue. Injectable biomaterials for cardiac tissue engineering have demonstrated the ability to restore cardiac function by preventing ventricular dilation, enhancing angiogenesis, and improving conduction velocity. However, limitations are still among them, such as poor mechanical stability, low conductivity, and complicated procedure. Here, we developed thermal plastic poly(glycolic acid) surgical suture and mussel-inspired conductive particle's adhesion into a highly elastic, conductive spring-like coils. The polypyrrole (PPy)-coated biospring acted as an electrode and then was assembled into a solid-state supercapacitor. After being injected through a syringe needle (0.33 mm inner diameter), the tangled coils formed an elastically conductive three-dimensional (3-D) network to modulate cardiac function. We found that cardiomyocytes (CMs) grew along the spring coils' track with elongated morphologies and formed highly oriented sarcomeres. The biospring enhanced the CMs' maturation in synchronous contraction accompanied by high expressions of cardiac-specific proteins, α-actinin, and connexin 43 (cx43). After the elastic, conductive biosprings were injected into the myocardial infarction (MI) area, the left ventricular fractional shortening was improved by about 12.6% and the infarct size was decreased by about 34%. Interestingly, the spring can be utilized as a sensor to measure the CMs' contractile force, which was 1.57 × 10-3 ± 0.26 × 10-3 mN (∼4.1 × 106 cells). Accordingly, this study highlights an injectable biospring to form a tangled conductive 3-D network in vivo for MI repair.