Flexible wearable devices and solar flexible units often use thermally sensitive organic materials as substrates, which are prone to thermal damage during the bonding process in 3D packaging, leading to chip deformation or failure. Multicomponent solders, with well-designed multicomponent metallic elements, exhibit unique low-melting-point characteristics. The application of low-temperature multicomponent solders in electronic packaging can significantly reduce bonding temperatures and minimize thermal damage to chips. This paper reviews the wettability and preparation methods of low-temperature multicomponent solders, and concludes the effect of different metallic elements on the solders. Additionally, this paper discusses the research on interfacial reactions, mechanical properties of low-temperature multicomponent solder joints, providing valuable insights for future research and development in this field.

To meet the requirements of hierarchical packaging, this paper investigated a low-melting-point high-entropy alloy (HEA) solder. The solder was synthesized by melting pure metal blocks of In, Zn, Sn, and Bi in equimolar proportions to form HEA ingots, which were then deformed into solder foils with a thickness of 100 μm. The solder consists of Zn-rich, Bi-In, Sn-rich, and Bi-rich phases, with a melting point of approximately 82 ℃. Using this solder, Cu/HEA solder/Cu joints were fabricated. The reflow parameters were: temperature of 90–160 ℃, pressure of 0–0.08 MPa, and time of 1–80 min. Microstructural observation and elemental analyses revealed the formation of a dual-layer interface comprising pure Cu₅Zn₈ and mixed-Cu₅Zn₈ intermetallic compounds (IMC) at the solder/Cu interface, with an IMC reaction activation energy of 35.67 ± 3.4 kJ/mol. Effective bonding was achieved even at 90 ℃, with a shear strength of up to 19.6 MPa. Cracks initiated at the IMC/solder interface and propagated along grain boundaries within the solder. Moreover, significant lattice distortion was observed at the IMC/solder interface, which inhibited IMC growth and enhanced interface stability. This low-temperature HEA solder provides promising potential for applications in three-dimensional hierarchical packaging.

Using two fencing swords manufactured in Europe and China, we investigated the typical materials used for fencing blades and compared the experimental results with the nominal compositions of a variety of steels. We found that spring steels and maraging steels were the primary metals used in fencing blades. The review then provides an overview of the chemical compositions, heat treatment processes, microstructures and associated mechanical properties of these materials. By combining the requirements for the safety of athletes, mechanical behaviors of different steels, and production costs for industry, we introduced possible directions for the heat treatments and processing methods that have the potential to enhance performance and overcome the limitations of previous materials. In addition, an ultra-strong steel, Fe-9.95Mn-0.44C-1.87Al-0.67V which could be a promising new candidate in this area, was recommended. Finally, we suggested that successful cooperation between manufacturers and researchers is necessary to reach the various requirements of fencing blades to meet the growing popularity of fencing in China.

This study systematically investigates the In30Sn30Bi30ZnxCu(10–x) (x = 9, 7, 5, 3, 1) multicomponent alloy solders and their ultra-low-temperature bonding behavior in Cu/solder/Cu structures. The melting characteristics, interfacial intermetallic compound (IMC) formation, thermal aging microstructural evolution, and shear performance were analyzed. The results shows that solders in this series exhibit low-melting-point characteristics, with melting temperatures ranging between 80–82 °C. With increasing Cu/Zn ratio, the interfacial IMCs evolved sequentially from Cu₅Zn₈ to Cu₅(Sn,Zn)₈ and subsequently to Cu₃Sn. Mechanical testing revealed that the shear strength of the joints followed a ”rise-then-fall” trend with compositional variation, reaching a maximum of 28.7 MPa at x = 3. This enhancement was attributed to the favorable metallurgical connect between the rod-shaped Cu₃Sn and the solder layer. However, when the Cu content became excessive, aggregation of Cu3Sn and the formation of cracks within the solder joint occurred, thereby weakening the overall strength. In the joint after thermal aging at 65°C, the thickness of the IMC layer remained at approximately 4.5-5.0 μm after 144 hours. Meanwhile, this process was accompanied by the precipitation and growth of the brittle Bi phase, which increased the brittleness of the solder layer. As a result, the shear performance of the joint decreased by 40.4% after 720 hours. These findings elucidate the synergistic effects of the Cu/Zn ratio on microstructure, interfacial reactions, and joint mechanical performance, providing important insights for the design and optimization of low-temperature electronic interconnection materials.