Purpose: The purpose of this paper is to identify the solder joint with optimal mechanical properties among Cu/Sn/Cu, Ni/Sn/Ni and Cu/Sn/Ni solder joints.Design/methodology/approach: Solder joints with the same specimen shape were prepared by reflow. The microstructures were observed and analyzed by scanning electron microscopy and tensile testing was carried out to investigate the mechanical properties.Findings: The mechanical properties of solder joint correlate closely with the intermetallic compounds (IMC) layer structure and the dissociative IMC particles in the solder bulk. Under the influence of the opposite Cu bar, the Cu/Sn/Ni has a duplex IMC layer structure at the Ni side, involving a thin Ni‐Cu‐Sn IMC layer and a faceted (Cu,Ni)₆Sn₅ layer. The mechanical connection of the duplex IMC layers is weak due to the pores in the layers. The Cu/Sn/Ni fractures in the IMC layers in a brittle mode under tensile testing. Comparatively, the Ni/Sn/Ni also has duplex Ni₃Sn₄ layers, and they connect firmly with each other. The tensile fracture of the Ni/Sn/Ni occurs in the solder bulk in a ductile mode, as well as for the Cu/Sn/Cu. Compared with the Cu/Sn/Cu solder bulk, the solder bulk of the Ni/Sn/Ni and the Cu/Sn/Ni have higher ultimate tensile strengths, because the strengthening effect of the dissociative Ni₃Sn₄ and (Cu,Ni)₆Sn₅ particles on the solder bulk is stronger than that of the Cu₆Sn₅ particles. Among Cu/Sn/Cu, Ni/Sn/Ni and Cu/Sn/Ni, Ni/Sn/Ni has the optimal mechanical properties.Originality/value: The paper offers insights into the significant influence of base material matching on the microstructure and mechanical properties of solder joints.

This study employs density functional theory (DFT) to investigate three common free radical scavenging mechanisms (hydrogen atom transfer (HAT), single electron transfer proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET)) in UiO-66-(OH)₂ and UiO-66-NH₂ metal–organic framework (MOF) nanoparticles under gas, benzene and aqueous phase conditions. The reaction processes between UiO-66-(OH)₂/UiO-66-NH₂ and hydroxyl radicals (˙OH) were simulated to elucidate detailed radical capture pathways, and the computational results were validated by macroscopic DPPH radical scavenging experiments. The results indicate that: (1) among the three mechanisms, HAT consistently exhibits the lowest bond dissociation energy across all phases, suggesting MOF nanoparticles preferentially undergo hydrogen atom transfer over electron transfer during radical scavenging; (2) compared to gas phase and nonpolar solvent (benzene), polar solvent (water) significantly lowers the energy barriers for both electron transfer and hydrogen transfer, thus enhancing reactivity across all mechanisms; (3) UiO-66-(OH)₂ exhibits a radical scavenging rate constant of 1.0 × 10⁹ M⁻¹ s⁻¹, higher than 7.63 × 10⁸ M⁻¹ s⁻¹ for UiO-66-NH₂; (4) DPPH assays reveal that UiO-66-(OH)₂ exhibits an 8% greater radical scavenging efficiency than UiO-66-NH₂, in agreement with DFT predictions and confirming the antioxidative benefit of hydroxyl functionalization. This study proposes a combined DFT and experimental screening workflow for radical scavengers, offering an efficient and economical approach to rapidly identify novel MOF-based radioprotective radical scavengers.

The shear performance and fracture behavior of microscale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with increasing electric current density (from 1.0 × 10³ to 6.0 × 10³ A/cm²) at various test temperatures (25 °C, 55 °C, 85 °C, 115 °C, 145 °C, and 175 °C) were investigated systematically. Shear strength increases initially, then decreases with increasing current density at a test temperature of no more than 85 °C; the enhancement effect of current stressing on shear strength decreases and finally diminishes with increasing test temperatures. These changes are mainly due to the counteraction of the athermal effect of current stressing and Joule heating. After decoupling and quantifying the contribution of the athermal effect to the shear strength of solder joints, the results show that the influence of the athermal effect presents a transition from an enhancement state to a deterioration state with increasing current density, and the critical current density for the transition decreases with increasing test temperatures. Joule heating is always in a deterioration state on the shear strength of solder joints, which gradually becomes the dominant factor with increasing test temperatures and current density. In addition, the fracture location changes from the solder matrix to the interface between the solder matrix and the intermetallic compound (IMC) layer (the solder/IMC layer interface) with increasing current density, showing a ductile-to-brittle transition. The interfacial fracture is triggered by current crowding at the groove of the IMC layer and driven by mismatch strain at the solder/IMC layer interface, and the critical current density for the occurrence of interfacial fracture decreases with increasing test temperatures.

Intermetallic compounds (IMCs) are inevitable byproducts during the soldering of electronics. Cu₆Sn₅ is one of the main components of IMCs, and its mechanical properties considerably influence the reliability of solder joints. In this study, the effects of grain size (8–20 nm) on the mechanical properties (Young’s modulus, yield stress, ultimate tensile strength (UTS), and strain rate sensitivity) of polycrystalline Cu₆Sn₅ were investigated using molecular dynamics simulations at 300 K and at a strain rate of 0.0001–10 ps⁻¹. The results showed that at high strain rates, grain size only slightly influenced the mechanical properties. However, at low strain rates, Young’s modulus, yield stress, and UTS all increased with increasing grain size, which is the trend of an inverse Hall–Petch curve. This is largely attributed to the sliding and rotation of grain boundaries during the nanoscale stretching process, which weakens the interaction between grains. Strain rate sensitivity increased with a decrease in grain size.