Rheologically Assisted Design of Conductive Adhesives for Stencil Printing on PCB

Driven by the need to deliver new, lead-free, eco-friendly solder pastes for soldering electronic components to Printed Circuit Boards (PCB), electrically conductive adhesives (ECAs) based on epoxy, carbon nanotubes (CNT), and exfoliated graphite (EG) were designed. The rheology of the adhesives prepared is paramount for the success of the deposition process, which is based on stencil printing. Thus, a rheological analysis of the process was first performed. Then, an experimental protocol was defined to assess the relevant viscoelastic characteristics of the adhesives for stencil printing application. Different composite formulations of epoxy/CNT/EG were produced. Their rheological characteristics were established following the designed protocol and benchmarked with a commercial solder paste. The thermal and electrical properties of the composite formulations were also characterized. As a result, a new, electrically conductive adhesive was delivered with potential to be an eco-friendly alternative to the solder paste currently used in stencil printing of PCB.

Fabrication of an Electrically Conductive Adhesive for Skin Mounted Bioelectronic Devices

Background: Skin mounted bioelectronics are difficult to integrate with the skin since biocompatible adhesives are not conductive or unsuitable for long-term use. Skin conformability is essential but strong adhesives can damage soft tissue in younger and frail individuals as well as the device during removal. Developing a noninvasive long-lasting biocompatible conductive adhesive for skin that can be used with bioelectronics allows for better treatment options and the improvement of patient outcomes. Methods: This study creates a soft hydrogel using graphene oxide flakes (GO) and polyvinyl alcohol. Networked GO is reduced in a solution of sodium dithionite and sodium hydroxide to form a conductive network within the hydrogel. Adhesive properties are achieved by incorporating a polyacrylic acid polymer into the hydrogel with the addition of N-hydroxysulfosuccinimide (NHS) groups to the polymer. NHS reacts with amine groups found on tissue to form covalent bonds that can be released with a biocompatible trigger solution of sodium bicarbonate and glutathione. Results: Hydration of the hydrogel at 65°C demonstrated that the hydrogel swelled anistropically with swelling ratios of 1.05/1.06/5.5 (length/width/thickness). This showed that the hydrogel can integrate into various surfaces without deformation. The hydrogel demonstrated an impedance of 106.1~164.6 Ω⋅m (20~500 Hz), which is comparable to conventional devices. The hydrogel was chemically bound to amine functionalized polydimethylsiloxane (PDMS) and glass. Peel test showed peak adhesion forces of 100.5 N⋅m-1(Force⋅Width-1) when bound to PDMS or glass. Signal quality of the hydrogel showed that the hydrogels demonstrated ECG and EMG signals comparable to commercially available materials. Conclusions: The importance of this study is to create a soft material that bonds between electrodes and skin. The results demonstrate that the hydrogel has electrical characteristics comparable to conventional electrodes for use in ECG and EMG. In addition, it can create adhesion via chemical bonds that can be released on demand.

Preparation of Silver Nanopowders and Its Application in Low Temperature Electrically Conductive Adhesive

Printable electrically conductive adhesive with high electrical conductivity and good mechanical properties has wide application prospect in electronic device. In order to explore new conductive fillers of interconnecting materials in electronic circuit and electronic packaging industries, silver nanopowders were prepared by DC arc plasma method with high pure. The silver nanopowders present a spherical structure, the particle’s diameter range from 15 to 220 nm. In this paper, a high performance electrically conductive adhesive (ECA) was prepared. This ECA was fabricated by mixing silver nanopowders with epoxy resin and was screen-printed to a required shape. It was found that the ECA can be solidified through a low temperature sintering method in the air at 150 ℃ for 10 min. The electrical and mechanical of above ECA were investigated and characterized. The ECA filled with 75% silver nanopowders exhibits excellent performances, including high electrical conductivity (9.5×10-4 Ω·cm), high bonding strength ( 8.3 MPa). Based on the performance characteristics, the ECA applications in flexible printed electrodes and interconnecting materials are demonstrated.

Development of Multi-Layer Circuitry Using Electrically Conductive Adhesive and Low-Temperature Solder Material for Surface-Mount Component Attachment

The increased versatility in the design and manufacturing of components in low volumes, as well as the shorter time between design and prototype, has increased interest in the field of additively printed electronics. The ability to directly print on a variety of substrates, whether rigid, flexible, or conformable, provides several benefits over conventional electronics fabrication methods. Furthermore, the growing complexity of flexible electronics necessitates the development of multilayered circuits similar to traditional PCBs to decrease the volumetric and gravimetric effect of the underlying electronics. Using z-axis interconnections with dielectric materials, which may allow or prevent the connection between two layers, is one method of reaching several layers of circuits. In this paper, a working multilayer circuitry test vehicle is designed and additively printed using the direct-write method. The circuit model involves conductive and dielectric ink printing, as well as passive and active component attachments using an electrically conductive adhesive (ECA) and low-temperature solder (LTS). The study also shows details about the process of developing dielectric printing parameters for microvias for multilayer z-axis interconnections.

Printed Flexible LC Filter Using Additive Micro-Dispensing With Silver Conductive Paste and ECA for Component Attachment

Filters are used in a variety of signal processing applications in commercial and defense electronics. The use of additively printed electronics in high-frequency applications requires an understanding of the process-performance interactions versus frequency of operation. Assembly of filters for integration into existing circuits requires additively printed metallization traces in addition to component attachment methods. Comparison of frequency response of the additively-printed filtering circuits vs conventional filters subtractively-fabricated on rigid substrates is needed to determine the performance parity of additive fabrication methods. In this paper, a micro-dispensing device is used to print conductive traces and electrically conductive adhesive (ECA) pads for the attachment of components. The effect of different print parameters on the width and height of the trace has been studied. Mechanical and electrical properties also play an important role in the study of different sintering conditions. Optimized parameters from the printing process and sintering analysis are used to print and compare commercially available LC filter circuitry using the Bode plot.

INFLUENCE OF THE COMPOSITION AND CONDITIONS OF HEAT TREATMENT OF THE CONDUCTIVE PROPERTIES OF SILVER-CONTAINING ELECTRICALLY CONDUCTIVE ADHESIVE COMPOSITIONS (review). Part 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.