A Novel Highly Durable Carbon/Silver/Silver Chloride Composite Electrode for High-Definition Transcranial Direct Current Stimulation

High-definition transcranial direct current stimulation (HD-tDCS) is a promising non-invasive neuromodulation technique, which has been widely used in the clinical intervention and treatment of neurological or psychiatric disorders. Sintered Ag/AgCl electrode has become a preferred candidate for HD-tDCS, but its service life is very short, especially for long-term anodal stimulation. To address this issue, a novel highly durable conductive carbon/silver/silver chloride composite (C/Ag/AgCl) electrode was fabricated by a facile cold rolling method. The important parameters were systematically optimized, including the conductive enhancer, the particle size of Ag powder, the C:Ag:PTFE ratio, the saline concentration, and the active substance loading. The CNT/Ag/AgCl-721 electrode demonstrated excellent specific capacity and cycling performance. Both constant current anodal polarization and simulated tDCS measurement demonstrated that the service life of the CNT/Ag/AgCl-721 electrodes was 15-16 times of that of sintered Ag/AgCl electrodes. The much longer service life can be attributed to the formation of the three-dimensional interpenetrating conductive network with CNT doping, which can maintain a good conductivity and cycling performance even if excessive non-conductive AgCl is accumulated on the surface during long-term anodal stimulation. Considering their low cost, long service life, and good skin tolerance, the proposed CNT/Ag/AgCl electrodes have shown promising application prospects in HD-tDCS, especially for daily life scenarios.

Fatigue Testing of Copper Nanoparticle Based Joints and Bonds

Fused or sintered Cu nanoparticle structures are potential alternatives to solder for ultra-fine pitch flip chip assembly and to sintered Ag for heat sink attach in high temperature microelectronics. Meaningful testing and interpretation of test results in terms of what to expect under realistic use conditions do, however, require a mechanistic picture of degradation and damage mechanisms. As far as fatigue goes, such a picture is starting to emerge. The porosity of sintered nano-particle structures significantly affects their behavior in cycling. The very different sensitivities to parameters, compared to solder, means new protocols will be required for the assessment of reliability. The present study focused on fatigue in both isothermal and thermal cycling. During the latter, all damage occurs at the low temperature extreme, so life is particularly sensitive to the minimum temperature and any dwell there. Variations in the maximum temperature up to 125 °C did not affect, but a maximum temperature of 200 °C led to much faster damage. Depending on particle size and sintering conditions deformation and damage properties may also degrade rapidly over time. Our picture allows for recommendations as to more relevant test protocols for vibration, thermal cycling, and combinations of these, including effects of aging, as well as for generalization of test results and comparisons in terms of anticipated behavior under realistic long-term use conditions. Also, the fatigue life seems to vary with the ultimate strength, meaning that simple strength testing becomes a convenient reference in materials and process optimization.

Effect of CU Foam and Ag-Coated Layer on the Microstructure and Mechanical Behavior of Nano-Ag Sintered Joint

Cu foam (Cu-F) and Ag-coated Cu-F were added into nano-Ag paste to obtain Cu-F@nano-Ag composite sintered joint. The microstructure, hardness, and shear behavior of the sintered joints were investigated. Experimental results indicated that the addition of Cu-F and Ag-coated Cu-F suppressed the generation and propagation of cracks at the interface of the sintered joint. As the thickness of the Cu-F increased from 0.1mm to 0.2mm, the deformation ratio of the Cu-F sheet raised from 12 % to 50 %. Thereby, the hardness and bonding strength of the sintered joint was improved due to the microstructural densification. The bonding quality between Cu-F and sintered Ag is enhanced by the Ag-coating treatment. Therefore, the Ag-coated composite joints show higher shear strength than the others.