Effects of Co and Ni addition on reactive diffusion between Sn–3.5Ag solder and Cu during soldering and annealing

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 420; no. 1-2; pp. 39 - 46
• Main Authors: Gao, F., Takemoto, T., Nishikawa, H.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25.03.2006; Elsevier
• Subjects: Additive; Applied sciences; Brazing. Soldering; Diffusion; Exact sciences and technology; Intermetallic compounds; Joining, thermal cutting: metallurgical aspects; Lead-free solder; Metals. Metallurgy; Thermodynamic; Additive; Lead-free solder; Intermetallic compounds; Diffusion; Thermodynamic; Intermetallic compound; Tin alloy; Isothermal annealing; Cobalt addition; Transition metal; Diffusion pair; Thermodynamic model; Nickel addition; Lead free solder; Interface reaction; Copper; Soldering; Interface
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2006.01.032

The reactive diffusion between Sn–Ag solders and Cu was experimentally examined during soldering and isothermal annealing. Three sorts of solders with compositions of Sn–3.5Ag, Sn–3.5Ag–0.1Ni and Sn–3.5Ag–0.1Co were used for the experiment. Each solder was soldered on a Cu plate at 523K (250°C) for 1–60s in a pure nitrogen gas, and then the solder/Cu diffusion couple was isothermally annealed at 423K (150°C) for 168–1008h. Due to soldering, only Cu6Sn5 is formed at the interface in each diffusion couple. On the other hand, Cu3Sn is produced between Cu6Sn5 and Cu owing to the isothermal annealing. The composition of Cu6Sn5 is (Cu0.8Ni0.2)6Sn5 and (Cu0.93Ni0.07)6Sn5 on the solder and Cu3Sn sides, respectively, in the (Sn–3.5Ag–0.1Ni)/Cu diffusion couple, and it is (Cu0.9Co0.1)6Sn5 and (Cu0.99Co0.01)6Sn5 on the solder and Cu3Sn sides, respectively, in the (Sn–3.5Ag–0.1Co)/Cu diffusion couple. Different rate-controlling processes were suggested for the (Sn–3.5Ag)/Cu, (Sn–3.5Ag–0.1Ni)/Cu and (Sn–3.5Ag–0.1Co)/Cu diffusion couples. Finally, thermodynamic models were herein adopted to explore influences of the additives on the thermodynamic interaction of the component elements and the driving force for the growth of intermetallics.