Sn-based lead-free solders such as Sn-Ag-Cu, Sn-Cu, and Sn-Bi have been used extensively for a long time in the electronic packaging field. Recently, low-temperature Sn-Bi solder alloys attract much attention from industries for flexible printed circuit board (FPCB) applications. Low melting temperatures of Sn-Bi solders avoid warpage wherein printed circuit board and electronic parts deform or deviate from the initial state due to their thermal mismatch during soldering. However, the addition of alloying elements and nanoparticles Sn-Bi solders improves the melting temperature, wettability, microstructure, and mechanical properties. Improving the brittleness of the eutectic Sn-58wt%Bi solder alloy by grain refinement of the Bi-phase becomes a hot topic. In this paper, literature studies about melting temperature, microstructure, inter-metallic thickness, and mechanical properties of Sn-Bi solder alloys upon alloying and nanoparticle addition are reviewed.

This study investigates the shear strength and aging characteristics of Sn-3.0Ag-0.5Cu (SAC 305)/Cu joints by the addition of ZrO₂ nanoparticles (NPs) having two different particle size: 5–15 nm (ZrO₂A) and 70–90 nm (ZrO₂B). Nanocomposite pastes were fabricated by mechanically mixing ZrO₂ NPs and the solder paste. ZrO₂ NPs decreased the β-Sn grain size and Ag₃Sn intermetallic compound (IMC) in the matrix and reduced the Cu₆Sn₅ IMC thickness at the interface of lap shear SAC 305/Cu joints. The effect is pronounced for ZrO₂A NPs added solder joint. The solder joints were isothermally aged at 175 °C for 24, 48, 144 and 256 h. NPs decreased the diffusion coefficient from 1.74 × 10^–16 m/s to 3.83 × 10^–17 m/s and 4.99 × 10^–17 m/s for ZrO₂A and ZrO₂B NPs added SAC 305/Cu joints respectively. The shear strength of the solder joints decreased with the aging time due to an increase in the thickness of interfacial IMC and coarsening of Ag₃Sn in the solder. However, higher shear strength exhibited by SAC 305-ZrO₂A/Cu joints was attributed to the fine Ag₃Sn IMC’s dispersed in the solder matrix. Fracture analysis of SAC 305-ZrO₂A/Cu joints displayed mixed solder/IMC mode upon 256 h of aging.

The study was designed to investigate the synergic effect of Ti and Sn in the active metal brazing of Al₂O₃ ceramic to copper brazed, using the multicomponent Ag-Cu-Zr filler alloy. Numerous fine and hexagonal-shaped rod-like ternary intermetallic (Zr, Ti)₅Sn₃ phase (L/D = 5.1 ± 0.8, measured in microns) were found dispersed in the Ag-Cu matrix of Ag-18Cu-6Sn-3Zr-1Ti alloy, along with the ternary CuZrSn intermetallic phases. An approximate 15° reduction in contact angle and 3.1 °C reduction in melting point are observed upon the incorporation of Ti and Sn in Ag-18Cu-3Zr filler. Interestingly, the interface microstructure of Al₂O₃/Cu joints brazed by using Ag-18Cu-6Sn-3Zr-1Ti filler shows a double reaction layer: a discontinuous Ti-rich layer consisting of (Cu, Al)₃(Ti, Zr)₃O, TiO, and in-situ Cu-(Ti, Zr) precipitates on the Al₂O₃ side and continuous Zr-rich layer consisting of ZrO₂ on the filler side. The shear strength achieved in Al₂O₃/Cu joints brazed with Ag-18Cu-6Sn-3Zr-1Ti filler is 31% higher, compared to the joints brazed with Ag-18Cu-6Sn-3Zr filler. Failure analysis reveals a composite fracture mode indicating a strong interface bonding in Al₂O₃/Ag-18Cu-6Sn-3Zr-1Ti filler/Cu joints. The findings will be helpful towards the development of high entropy brazing fillers in the future.

In this paper, a novel transient liquid phase bonding material was fabricated by consequent electroless plating of Cu and Sn on a multi-walled carbon nanotube (MWCNT). The resulting Sn-Cu-MWCNT composites were used to join the Cu interconnects at 260°C. After 8 min of reflow time, a complete transformation of Cu₃Sn intermetallic compound (IMC) occurred, leaving a Cu/MWCNT-Cu₃Sn /Cu joint capable of withstanding the high operating temperature. Due to flake-like morphology, the Sn-Cu-MWCNT composite particles were well packed with lesser voids. The shear strength of the Cu/Cu₃Sn-MWCNT/Cu joint was measured as 35.3 MPa, thus exhibiting the scope for replacing conventional transient liquid phase (TLP) powders in the future.

Dissimilar Al 3003 and Cu tubular components were successfully brazed without interface cracking using ZrO₂ nanomaterials reinforced with Al-19Cu-11Si-2Sn filler. The filler was initially cast using an induction furnace and processed into ring form for brazing. Al-19Cu-11Si-2Sn filler with coarse CuAl₂ and Si phases (43 and 20 μm) were refined to 8 and 4 μm, respectively, after the addition of 0.1 wt. % ZrO₂ and shows significant improvement in the mechanical properties. ZrO₂ nanomaterials’ induced diffusion controlled growth mechanism is found be the responsible for the refinement of CuAl₂ intermetallic and Si particles. The wettability of Al-19Cu-11Si-2Sn-0.1ZrO₂ increased to 78.17% on Cu side and 93.19% on the Al side compared from 74.8% and 89.9%, respectively. Increase in the yield strength, ultimate tensile strength, and percentage elongation were noted for the brazed joints. Microstructure of induction brazed joint with 40 kW for 6 seconds using Al-19Cu-11Si-2Sn-0.1ZrO₂ filler shows thin interfacial CuAl₂ intermetallic compound along the copper side and inter-diffusion region along the aluminum side and their respective mechanism is discussed. The tensile strength of the joints increased with increasing the nanomaterials addition and shows a base metal fracture. Analysis of fractured samples shows the effectiveness of ZrO₂ reinforced filler in crack propagation through the filler.