Microstructural, thermal and mechanical properties of Co added Sn–0.7Cu lead-free solder alloy

• Published in: Journal of materials science. Materials in electronics 2023-03, Vol.34 (7), p.590, Article 590
• Main Authors: El-Taher, A. M., Abd Elmoniem, H. M., Mosaad, S.
• Format: Article
• Language: English
• Subjects: Alloys; Characterization and Evaluation of Materials; Chemistry and Materials Science; Cobalt; Copper; Ductility; Eutectic alloys; Fibers; Grain refinement; Lead free; Materials Science; Mechanical properties; Microstructure; Modulus of elasticity; Optical and Electronic Materials; Precipitation hardening; Solders; Supercooling; Thermodynamic properties; Tin; Ultimate tensile strength
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-023-09967-7

This study investigated the effects of cobalt microalloying addition on the microstructural features, thermal characteristics and mechanical behavior of eutectic Sn–0.7wt%Cu lead-free solder alloys. The results show that minor cobalt addition of ~ 0.05 wt% causes significant grain refinement of β -Sn, facilitates the formation of fine fibers (Cu,Co) 6 Sn 5 phases and preventing the formation of η ′-Cu 6 Sn 5 phases, whereas a large amount of Co (~ 0.5 wt%) additions accumulated in the (Cu,Co) 6 Sn 5 IMCs and clearly changed into coarse fibers. The precipitation strengthening mechanisms of fine fibers (Cu,Co) 6 Sn 5 in the β -Sn matrix increased the ultimate tensile strength (UTS) and Young’s modulus (Y) of the alloy from 30.5 MPa and 15 GPa to 44.6 MPa and 22.3 GPa, respectively, but the ductility decreased from 60 to 45.7%. The coarse fibers (Cu,Co) 6 Sn 5 in eutectic alloys is of interest from not only increased UTS and Y to 38.7 MPa and 16.3 GPa but also maintaining the ductility at the same level, allowing for unique microstructure design. Furthermore, 0.05wt% of Co significantly reduce the onset, eutectic temperatures and undercooling, although pasty rang has been slightly raised, which may enhance the thermal characteristics. This presumably has important implications for the reliability of solders as well as their performance in electronic service.