Intermetallic compounds (IMCs) are essential in the soldering of electronic products and are composed mainly of Cu₆Sn₅ and Cu₃Sn. They must maintain reliable mechanical and electrical connections. As they are usually only a few microns thick, and it is difficult to study their mechanical properties by traditional methods. In this study, a 100 Å × 100 Å × 100 Å polycrystal with 10 grains was created by Atomsk through Voronoi tessellation based on a Cu₆Sn₅ unit cell. The effects of the temperature and strain rate on the tensile properties of the polycrystalline Cu₆Sn₅ were analyzed based on MEAM potential function using a molecular dynamics (MD) method. The results show that Young’s modulus and ultimate tensile strength (UTS) of the polycrystalline Cu₆Sn₅ decrease approximately linearly with an increase in temperature. At high strain rates (0.001–100 ps⁻¹), Young’s modulus and UTS of the Cu₆Sn₅ are logarithmic with respect to the strain rate, and both increase with an increase in strain rate. In addition, at low strain rates (0.00001–0.0005 ps⁻¹), the UTS has a quadratic increase as the strain rate increases.

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.

Liquid gallium (Ga) enables low-temperature transient liquid phase bonding (TLPB), but optimizing microstructure and joint performance remains challenging. Here, we developed a copper (Cu)-powder/liquid-Ga composite paste for Cu/Cu interconnects and systematically studied the effects on the interconnect joint performance of Cu powder particle size (Cu_PS, 10–20, 20–30 and 30–40 μm) and Cu mass fraction (Cu_MF, 10–30 wt%). The microstructure, electrical conductivity, and shear strength of the joint were evaluated, followed by an assessment of bonding temperature, pressure, and time. Under bonding conditions of 220 °C, 5 MPa and 720 min, a dense intermetallic compound (IMC) microstructure predominantly composed of Cu₉Ga₄ and CuGa₂ was formed, yielding an electrical conductivity of approximately 1.1 × 10⁷ S·m⁻¹ and a shear strength of 52.2 MPa, thereby achieving a synergistic optimization of electrical and mechanical properties; even under rapid bonding conditions of 220 °C, 5 MPa and 1 min, the joint still attained a shear strength of 39.2 MPa, demonstrating the potential of this process for high-efficiency, short-time interconnection applications. These results show that adjusting the composite paste formulation and dosage enables Cu–Ga TLPB joints that combine high conductivity with robust mechanical integrity for advanced packaging.

Characterized by its low melting temperature of 138 °C, the eutectic Sn-58Bi solder expands the melting temperature range of interconnect joints in electronic packaging, making it widely used in multi-level packaging processes. However, its reliability at higher current densities poses a challenge. This paper employs a hybrid process combining laser soldering and hot-air reflow to fabricate Cu/Sn-58Bi/Cu solder joints in ball grid array (BGA) structures. Through mechanical testing under current loading, the effects of increasing current density (0 A/cm², 0.85 × 10³ A/cm², 1.70 × 10³ A/cm², 2.55 × 10³ A/cm², 3.40 × 10³ A/cm², 4.25 × 10³ A/cm²) were studied systematically. Results indicate that the shear strength decreases markedly with increasing current density, exhibiting a reduction of approximately 5.63% to 95.75%. This degradation is initiated by the overall temperature increase and material softening due to Joule heating. It is further exacerbated by the loss of the non-thermal electron wind’s strengthening contribution, which weakens as the dominant thermal impact escalates with current density. Fracture mode transitions from ductile failure within the solder matrix to a ductile-brittle mixture at the solder/IMC interface, with the transition initiating at 3.40 × 10³ A/cm². Finite element simulations reveal that current crowding in Sn-rich regions and at the solder/IMC interface induces localized Joule heating and thermomechanical strain, which jointly drive the degradation in shear strength and the shift in fracture path.

With the ongoing miniaturization of solder joints in three-dimensional integrated electronic packaging, electromigration reliability has become a pressing concern. This study systematically examines the interfacial intermetallic compound (IMC) growth behavior of Cu/Sn-58Bi/Cu joint under electromigration (EM) with a symmetrical square-wave alternating current (AC). Electron backscatter diffraction (EBSD) was employed to perform statistical spatial analysis of Sn grain orientations within the joints to reveal the growth mechanism of interfacial IMC. Results demonstrate that the AC field markedly enhances the anisotropy of IMC growth in Cu/Sn-58Bi/Cu joints, exhibiting two phenomena: uniform growth on both sides and rapid growth (polar growth) on one side of the interfacial IMC. Among them, the IMC thickness difference characterization quantity Δ_IMC reached as high as 45.56% for the latter. This is attributed to the directional regulation of atomic migration rate by Sn grain orientation (the angle θ between the c-axis and the electron flow) and is further amplified by the altered atomic diffusion pathways imposed by the Bi phase distribution. Specifically, the Sn grains exhibit a pronounced preferential orientation mode along the current path (horizontal direction), with an orientation gradient of 0.915 μm⁻¹. The arrangement of Bi-rich phases alters the distribution of Sn grains in Cu/Sn-58Bi/Cu joints, thereby reshaping the internal electron transport pathways and significantly intensifying the orientation-dependent effect of IMC growth. Moreover, Sn grains adjacent to the Bi-rich phase boundaries (phase boundary grains) display a stronger tendency for c-axis orientation parallel to the current direction, exhibiting an average effective orientation parameter 1.948 times greater than that of bulk grains, which establishes a well-defined spatial orientation gradient.