The work aims to investigate the effect law and action mechanism of self-developed special Sn-Zn flux, rosin-based flux, water-soluble flux, and ZnCl2-NH4Cl flux on the wettability, interfacial microstructure, joint mechanical properties, and high-temperature aging stability of Sn-Zn solder micro-joints, providing a theoretical basis for the performance optimization of Sn-Zn solder and the development of dedicated matching fluxes. The optimal formulation of self-prepared flux, namely LF-8, was screened through orthogonal tests. Based on the wetting balance method, joint mechanical property tests, mechanical performance tests of micro-joints after 150 ℃ high-temperature aging, as well as interfacial and fracture morphology observation, the wetting behavior, mechanical property evolution, and microscopic morphological characteristics of Sn-Zn/Cu soldering systems with different fluxes were comparatively analyzed. When LF-8 flux was applied to Sn-Zn/Cu solder, the maximum wetting force reached 4.67 mN, the minimum wetting time was 0.8 s, and the maximum spreading area was 116.8 mm2, which could significantly refine the interfacial microstructure. The maximum shear strength and tensile strength of the solder joints were 39.06 MPa and 25.65 MPa, respectively. Compared with joints prepared with rosin-based, water-soluble and ZnCl2-NH4Cl fluxes, the tensile strength increased by 111.11%, 53.96% and 27.49%, and the shear strength increased by 99.69%, 76.18% and 9.26%, with finer and more uniform dimples observed on the joint fracture surface. The maximum shear force and tensile force of micro-joints reached 86.46 N and 26.16 N, which increased by 61.15%, 41.71%, 6.74% and 47.88%, 30.93%, 12.42% respectively compared with the other three control fluxes, and the micro-joints exhibited the slowest attenuation during the aging process, remarkably improving the mechanical properties and service stability of micro-joints. In conclusion, the self-developed LF-8 special flux can effectively improve the wetting and spreading ability of Sn-Zn solder, optimize the interfacial structure, and significantly enhance the mechanical properties and high-temperature aging stability of solder joints, which is suitable for electronic welding applications of Sn-Zn lead-free solder.
Key words
Sn-Zn /
flux /
wetting ability /
mechanical properties /
intermetallic compounds
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Funding
State Key Laboratory of Advanced Brazing Materials and Technology Open Project (SKLABFMT-2023-02)
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