Microstructure and properties of Sn58Bi/Ni solder joint modified by Mg particles

In this study, the Sn58Bi-xMg (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) composite solders were synthesized to explore the impact of Mg particles. The study examined the wettability, thermal properties, mechanical properties, microstructure, and growth of interfacial IMC (intermetallic compound) of composite solder. Experimental results showed that adding Mg particles had no significant impact on the melting point of Sn58Bi solder. However, increasing the Mg content increased the undercooling of the solder. Moreover, the incorporation of Mg particles resulted in a consistent rise in the coefficient of thermal expansion (CTE) of the composite solder, ranging from 11.4×10-6/°C to 15.6×10-6/°C. It was worth noting that including Mg particles enhanced the wetting ability of Sn58Bi alloy on Cu substrates. With a 0.4% addition of Mg particles, the wetting area could be increased by 60.14%, and the lowest wetting angle was approximately 10.43 °. Adding Mg particles resulted in an amelioration in the brittleness of the Bi-rich phase within the solder matrix, coupled with a decrease in both the thickness of IMC and the grain size at the joint interface. Compared to the joints without mixed Mg particles, the shear strength of Sn58Bi-0.4Mg solder joints and the microhardness of the alloy increased by 30% and decreased by 10%, respectively. Also, the presence of dimples within the fracture indicated a rise in the ductility of the solder joints. Overall, adding 0.4 wt.% Mg particles in this experiment resulted in a more effective modification of the Sn58Bi solder comprehensive properties. 

Comprehensive analysis of Sn58Bi/Cu solder joints reinforced with Mg particles: wettability, thermal, mechanics, and microstructural characterization

In this study, Si3N4 nanowires (NWs) with ceramic properties were incorporated into Sn1.0Ag0.5Cu (SAC105) solder to enhance its overall performance. The thermal properties, spreading behavior, microstructure, interface, and mechanical properties of SAC105-xSi3N4 (x=0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) solders were systematically investigated. The research revealed that doping Si3N4 NWs into SAC105 solder could expand its melting range and decrease undercooling. Notably, the solder alloy containing 0.6 wt% Si3N4 NWs had the lowest thermal expansion coefficient (CTE), which improved the CTE matching of SAC105 solder with Cu substrate. Although the solder with 0.4 wt% Si3N4 NWs exhibited superior wetting properties, it was less effective in refining the microstructure and interfacial intermetallic compounds (IMC) than those containing 0.6 wt% Si3N4 NWs. Meanwhile, when the β-Sn phase in the matrix and the Cu6Sn5 IMC phase at the interface were analyzed by electron back scatter diffraction (EBSD), their grain orientation was found to be optimized by the doping of 0.6 wt% Si3N4 NWs. The <001> direction of the β-Sn grains of SAC105-0.6Si3N4 was perpendicular to the Cu substrate, showing a texture structure. The grain orientation of the interfacial Cu6Sn5 IMC made it well-adapted for three-dimensional (3D) packaging. Finally, the mechanical properties enhancement of the solder joints were analyzed in detail by combining the fracture morphology and the EBSD results of the Sn matrix. 

Microstructure and orientation evolution of β-Sn and interfacial Cu6Sn5 IMC grains in SAC105 solder joints modified by Si3N4 nanowires

Ultrasonic-assisted connection of Cu/Cu structure using Sn58Bi solder enhanced by B4C nanoparticles

PURPOSE
Transcutaneous auricular vagus nerve stimulation (taVNS) is an emerging non-invasive neuromodulation therapy. This study aimed to explore the therapeutic use of taVNS, optimal stimulation parameters, effective sham protocols, and safety.


METHODS
A scoping review was conducted. Five databases and grey literature were searched. The data extracted included stimulation parameters, adverse events (AEs), and therapeutic effects on clinical outcomes.


RESULTS
109 studies were included. taVNS was used across 21 different clinical populations, most commonly in psychiatric, cardiac, and neurological disorders. Overall, 2,214 adults received active taVNS and 1,017 received sham taVNS. Reporting of stimulation parameters was limited and inconsistent. taVNS appeared to have a favourable therapeutic effect across a wide range of clinical populations with varied parameters. Three sham protocols were reported but their effectiveness was documented in only two of the 54 sham-controlled studies. Most reported adverse events were localised to stimulation site.


CONCLUSION
There is growing evidence for taVNS therapeutic effect. taVNS appears safe and tolerable. Sham protocols need evaluation. Standardised and comprehensive reporting of both stimulation parameters and adverse events is required. Two different questionnaires have been proposed to evaluate adverse events and the effectiveness of sham methods in blinding participants.

Clinical application of transcutaneous auricular vagus nerve stimulation: a scoping review.

The mechanical mixed Sn58Bi solder reinforced by B4C nanoparticles for the interconnect of Cu/Cu same metal was studied. The hardness of solder alloy and shear strength of joints with Sn58Bi-xB4C (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) composite solder were tested. The feasibility of the solution was verified by the performance of melting characteristics, wettability, microstructure, and interfacial IMC structure. It is indicated that the proper amount of B4C nanoparticles can improve the mechanical properties of the solder joint, and the hardness of the solder alloy is decreased to 246.0 HV by 13.65% with the addition of 0.6 wt% B4C and the highest shear strength of the joint reaches 52.282 MPa, which is increased by 8.9%. The failure mode of fracture is mainly considered a brittle fracture. The preferred orientation of the β-Sn phase and Bi phase are (1 0 0) and (1 0 1), respectively, and the number of low-angle grain boundary and dislocation density are increased. The melting characteristics of the solder are less affected by B4C nanoparticles, which will not interfere with its normal use. When the amount of B4C is 0.6 wt%, the spreading area of the solder is increased by 35.44%. Besides, a moderate amount of B4C nanoparticles is able to refine the matrix structure of the solder and inhibit the growth of Cu6Sn5 IMC. 

Mechanical properties and microstructure evolution of Cu/Sn58Bi/Cu solder joint reinforced by B4C nanoparticles

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