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Cu6Sn5-xAg alloys (x = 0, 3, 6; %, mass fraction) were synthesized using Ag as a dopant through a high-temperature melting technique. The microstructure of the alloy was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and other equipment, while the hardness of the alloy was measured to investigate the impact of Ag addition on the structure and microstructure of the Cu6Sn5 intermetallic compound. This study explored the influence of varying Ag contents on the properties of Cu6Sn5 intermetallic compounds, with calculations based on first principles revealing the mechanical properties and density of states of η′-Cu6Sn5 and its Ag-doped systems. The results indicated that Cu6Sn5-xAg alloys predominantly existed in three distinct forms, all exhibiting large masses without any impurities or precipitates. First-principle calculations demonstrated that Ag substitution in certain sites suppressed the anisotropy of the Young's modulus of Cu6Sn5, particularly in the Cu1, Cu3, Sn1, and Sn3 positions, while the effect was less significant at the Cu2, Cu4, and Sn2 sites. The introduction of Ag through doping enhanced the covalent bonding within the η′-Cu6Sn5 structure, promoting the formation of a stable (Cu, Ag)6Sn5 structure. [ABSTRACT FROM AUTHOR]

In this study, the interfacial structure and abnormal long-term increase of tensile strength in the interfacial intermetallic compounds (IMCs) between SnAg3Cu0.5 solder and Cu substrates during isothermal aging were investigated. After reflow soldering, the IMC layer at the interface was thin and scallop-type. The interfacial layer became thicker with the increase in aging time. After 200 h of aging at 150 °C, the thickness of the interface gradually increased to 3.93 μm and the interface became smooth. Compared with the unaged Cu-Sn interface, the aged joint interface contained more Cu3Sn. The top of the IMC being reflown was relatively smooth, but became denser and prismatic in shape after 200 h of aging at 150 °C. The tensile strength of the joint, immediately after the reflow, reached 81.93 MPa. The tensile properties of the solder joints weakened and then strengthened as they aged. After 200 h of aging at 150 °C, the tensile strength was 83.86 MPa, which exceeded that of the unaged solder joint interface, because the fracture mode of the solder joints changed during aging. [ABSTRACT FROM AUTHOR]

In this study, Bi, Sb, and Ni were incorporated into Sn3.0Ag0.5Cu (SAC305) solder to enhance its properties. The composite solders SAC305- x Bi-2.0Sb-0.1Ni (x = 2.5, 3.0, 3.5 wt%) were systematically investigated for their microstructure, thermal characteristics, wettability, thermal aging behavior, intermetallic compound (IMC) formation at interfaces, and mechanical properties of solder joints. The results demonstrated that the combined addition of Bi, Sb, and Ni effectively suppressed IMC growth within the solder matrix, leading to microstructure refinement. Increasing Bi content expanded the spreading area, thereby enhancing wettability. During thermal aging, the growth rate of solder joint interfaces decreased as the Bi content increased up to 3.5 wt%. Electron backscatter diffraction (EBSD) analysis indicated that these alloying elements reduce slip and deformation in the Sn matrix of SAC305-3.5Bi-2.0Sb-0.1Ni solder. Moreover, the tensile strength of solder joints consistently increased with the incorporation of these elements. • Adding Bi, Sb, and Ni to SAC305 solder refines microstructure and improves overall properties, including wettability and thermal properties. • Increased Bi content in the solder alloy enhances spreading area and wettability, while broadening the melting range and reducing subcooling. • Higher Bi content decreases the growth coefficient of the solder joint interface during heat aging, forming a "Bi barrier layer. • The alloying elements increase the tensile strength of solder joints, with improved resistance to slip and deformation, transitioning to a mixed fracture mechanism. [ABSTRACT FROM AUTHOR]

The majority of studies on high-reliability solder alloys have focused on the six-element system of Sn, Ag, Cu, Bi, Sb, and Ni. However, there is limited research on the influence of Co element within this system. In this study, a Sn 3.0Ag 0.5Cu Bi Sb Ni xCo (x = 0 wt%, 0.02 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%) alloy (referred to as SACBSN-xCo alloy) was prepared using a melting method. The mechanical properties of SACBSN-xCo alloy solder joints were evaluated through ultimate shear strength testing. The composition analysis of the alloy, phase composition examination, intermetallic compound (IMC) investigation and interfacial layer morphology analysis were conducted using ICP, XRD, SEM and EDS techniques respectively. Furthermore, the evolution process of solder structure and solder joint interface layer under different aging times was observed in detail. Results indicate that with the addition of Co element in the alloy solder system two heat release peaks appear during the solidification process; specifically when adding 0.05 wt% Co element content to the mixture it reduces supercooling degree by 15.17 °C to only 1.03 °C; Moreover wettability improvement can be achieved to some extent when adding either 0.02 wt% or 0.05 wt% Co content. The addition of trace Co can inhibit the excessive growth of IMC in the solder alloy matrix and refine the alloy structure. It can promote the growth of Cu 6 Sn 5 -based IMCs and inhibit the growth of Cu 3 Sn layer in intermetallic compound layer (IMCs). In addition, the mechanical properties and thermal fatigue stability of the solder joints are steadily improved by Co element. After adding Co element, the shear strength of the alloy solder joint is increased by about 14.84 %. After aging at 150 °C for 25 days, the shear strength of SACBSN-xCo alloy solder joints is increased by about 20.4 %, which significantly improves the thermal fatigue stability of the solder joints after high temperature aging treatment. The results show that when Co content is 0.05 wt%, the alloy solder has better comprehensive properties. • The addition of Co element can increase the nucleation point in the solder matrix, refine the structure, reduce the formation of large size intermetallic compounds and inhibit their overgrowth during high temperature treatment. • The addition of Co element can increase the nucleation density of IMC, and promote the growth of Cu6Sn5-based IMCs. Thicker Cu6Sn5-based IMCs act as a good diffusion barrier, preventing the mutual diffusion of Sn and Cu atoms. Thus impeding the growth of the Cu3Sn layer. • The addition of Co can effectively improve the shear resistance of the solder joint, and make the shear resistance of the solder joint show excellent stability in the process of high temperature aging treatment. [ABSTRACT FROM AUTHOR]

η′-Cu 6 Sn 5 is one of the main components of intermetallic compounds in the solder joint of electronic components. The research on improving its performance will help to solve the problem of increasing mechanical properties, electrical conductivity and thermal conductivity of solder joints of electronic devices. In this paper, we use the first-principles method to calculate the effects of 0.57 at.% and 1.14 at.% Zn doped on the Cu1, Cu2, Cu3 and Cu4 positions of η′-Cu 6 Sn 5 on the mechanical and electronic properties of the structure. And we draw a 3D model to express the mechanical anisotropy of the doping system. The calculated results show that doping Zn makes η′-Cu 6 Sn 5 more stable. However, the addition of Zn also reduces the fracture toughness of η′-Cu 6 Sn 5 , increases the anisotropy of η′-Cu 6 Sn 5 , and weakens the shear resistance of the solder joint of electronic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A model of nucleation and growth of intermetallic compounds during welding was proposed. • The diffusion coefficient decreases exponentially during the nucleation and growth of intermetallic compounds until thin layers are formed. • The diffusion patterns between matrix and different intermetallic compounds are different. In this study, the formation and growth of intermetallic compounds (IMC) at Sn/Cu interface were studied by using the molecular dynamics method of modified embedded atom method (MEAM) potential combined with practical experiments. The formation and growth process models of IMC layer at the initial stage of soldering were improved, and the growth trend and mechanism of IMC layer were analyzed. Further analysis of diffusivity shows that the diffusivity changes exponentially during welding and is related to the nucleation and growth of intermetallic compounds. Thus, this study provides valuable insights for the subsequent study on the initial stage of Sn/Cu interface and Sn/Cu solder joint reliability. [ABSTRACT FROM AUTHOR]