With the widespread application of lead-free solder, solder represented by the SAC series has been widely used. However, with the miniaturization and multifunctionalization of electronic devices, the distance between solder joints is becoming increasingly smaller, and the problem of electrochemical migration caused by Ag in the SAC series is gradually emerging. Therefore, it becomes imperative to develop a solder that has a melting point, mechanical properties, and other properties similar to those of the SAC series but does not contain silver. In this study, 1–3% of Bi and 1–3% of In were added to the Sn-0.7Cu solder to investigate the effects of these elements on the melting characteristics, microstructure, mechanical properties, wettability, and electrical conductivity of the Sn-0.7Cu solder. Due to the addition of Bi and In elements, the melting point of the Sn-0.7Cu solder was lowered, the shear strength was improved, and the solderability was enhanced, but the electrical conductivity was reduced. This article obtained the mechanism of the influence of Bi and In elements on the properties of the Sn-0.7Cu solder through experiments and theoretical analysis, providing a certain degree of theoretical support for the development of silver-free solder.

The development of Ag-free Sn solders has attracted significant attention due to the requirement of high-density electronic packaging. In this study, we investigate the Ni element on the microstructures and mechanical properties of Ag-free Sn-Cu-Bi-In solders. This paper details the microstructures and phases of the as-prepared Sn-Cu-Bi-In-Ni solders, as well as its mechanical properties. Specifically, the intermetallic compound (IMC) Cu₆Sn₅ is observed to be distributed in the Sn matrix, forming near-eutectic structures. The incorporation of Ni into Sn-Cu-Bi-In enhances the mechanical properties of the solder joints, including the shear strength and vibrational stability. In the joint obtained using the as-prepared Sn-Cu-Bi-In-Ni solders, a (Cu,Ni)₆Sn₅ IMC layer forms at the interface between Sn ball and Cu pad. The beneficial effects of Ni can be primarily attributed to its ability to adjust the mechanical properties and thermal expansion, enhancing the stability of solder joints. A TEM analysis reveals the closely packed atomic interface of Cu/(Cu,Ni)₆Sn₅ and (Cu,Ni)₆Sn₅/Sn, elucidating the joining mechanism involved.

Integrating nanocrystalline diamond (NCD) films on silicon chips has great practical significance and many potential applications, including high-power electronic devices, microelectromechanical systems, optoelectronic devices, and biosensors. In this study, we provide a solution for ensuring heterogeneous interface integration between silicon (Si) chips and NCD films using low-temperature bonding technology. This paper details the design and implementation of a magnetron sputtering layer on an NCD surface, as well as the materials and process for the connection layer of the integrated interface. The obtained NCD/Ti/Cu composite layer shows uniform island-like Cu nanostructures with 100~200 nm diameters, which could promote bonding between NCD and Si chips. Ultimately, a heterogeneous interface preparation of Si/Ag/Cu/Ti/NCD was achieved, with the integration temperature not exceeding 250 °C. The TEM analysis shows the closely packed atomic interface of the Cu NPs and deposited Ti/Cu layers, revealing the bonding mechanism.

The formulation of robust Welding Procedure Specifications (WPS) is paramount in aviation manufacturing, where quality directly impacts structural integrity and flight safety. Current practices, however, often rely on experiential knowledge and lack a systematic methodology for balancing performance, reliability, and economy, leading to unstable product quality and limited forward-design capability. This study addresses these gaps by proposing a novel, three-layer structural model for aviation WPS based on trade-off design principles. The model integrates a comprehensive correlation matrix linking product requirements to process elements, a modular architecture for enhanced reusability, and a knowledge-driven validation workflow. A key feature of the validation method is the use of a scientifically designed process test matrix and Statistical Process Control (SPC) to quantitatively determine process margins and capability indices (Cv, Cpk), moving beyond traditional pass/fail criteria. The application of this methodology is demonstrated and validated through a case study on electron beam welding. The results indicate that the proposed framework provides a systematic approach for developing stable, economical, and digitally ready welding process specifications, thereby significantly improving the forward-design capability in aviation welding.

Aviation products demand exceptionally high safety standards, where welding quality directly impacts structural integrity and flight safety. Welded joints must possess high strength and fatigue resistance. Since the welding process cannot be fully inspected and is classified as a special process, its manufacturing and production procedures require strict control, making the completeness of process specifications particularly crucial. Currently, the formulation of welding process specifications primarily relies on the production experience of process designers, with excessive focus on equipment processing parameters. This often leads to unstable product quality during production and fails to provide valuable references for aircraft structural designers. To enhance the performance, stability, and cost-effectiveness of Aviation welded products, this paper thoroughly considers the design requirements for welded products. It analyzes the full spectrum of elements within process specifications based on trade-off design. A structural model for welding process specifications is proposed, and a knowledge-driven methodology for standard verification and determining critical indicators is investigated. Using a laser welding production process as a case study, the structural model for Aviation product welding process specifications is validated.