Microstructure evolution and mechanical properties of Sn0.7Cu0.7Bi lead-free solders produced by directional solidification

• Published in: Journal of alloys and compounds Vol. 566; pp. 239 - 245
• Main Authors: Hu, Xiaowu, Li, Ke, Min, Zhixian
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01-07-2013; Elsevier
• Subjects: Alloys; Applied sciences; Brazing. Soldering; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Directional solidification; Electroluminescence; Exact sciences and technology; Fatigue, brittleness, fracture, and cracks; Fibers; Growth from melts; zone melting and refining; Joining, thermal cutting: metallurgical aspects; Lead free; Lead-free solder; Materials science; Mechanical and acoustical properties of condensed matter; Mechanical properties; Mechanical properties of solids; Metals. Metallurgy; Methods of crystal growth; physics of crystal growth; Microstructure; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Other luminescence and radiative recombination; Physics; Sn0.7Cu0.7Bi alloy; Solders; Temperature gradient; Yield strength; Mechanical properties; Sn0.7Cu0.7Bi alloy; Lead-free solder; Directional solidification; Microstructure; Ultimate strength method; Ruptures; Intermetallic compounds; Growth rate; Temperature gradients; Electroluminescence; Tensile strength; Fibers; Experimental result; Fractures; Growth mechanism; Lead free solder; Yield strength; Property structure relationship; Soldered joints; Fractography; Elongation (mechanics); Crystal growth from melts
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2013.03.034

•The Sn0.7Cu0.7Bi solder alloy was directionally solidified.•Both inter-fiber spacing and fiber diameter decrease with increasing growth rate.•The UTS and YS first increased with increase growth rate, then decrease.
Sn–0.7wt.%Cu–0.7wt.%Bi (Sn0.7Cu0.7Bi) lead-free solder alloy was directionally solidified undergoing temperature gradient of 12K/mm and growth rate (V) varying from 5 to 100μm/s. The microstructure was characterized along the growth direction and the present experimental results included the inter-fiber spacing (λ), fiber diameter (d), ultimate tensile strength (UTS), yield tensile strength (YS) and elongation to fracture (EL) at room temperature. The aim is to examine the effects of growth rate on both microstructure and mechanical properties. The microstructure observation shows that the microstructure consists of β-Sn matrix and rod-like Cu6Sn5 intermetallics compounds (IMCs). For a constant temperature gradient (12K/mm), it is found that the inter-Cu6Sn5 fiber spacing and fiber diameter are mainly controlled by the growth rate (V), and both of them decrease with increased growth rate. The tensile results show that the UTS and YS initially increase with increased growth rate which ranges from 5 to 60μm/s, then decrease with further increased growth rate, such as 100μm/s. In addition, the EL is between 25% and 32.5% as the growth rate is ranging from 5 to 60μm/s, and achieves to the highest value (41%) with the growth rate of 100μm/s. That is due to the formation of finer Cu6Sn5 in the solders. Finally, the fracture surfaces of the solders are examined.