Interfacial interaction of solid cobalt with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

• Published in: Journal of materials science Vol. 44; no. 22; pp. 5960 - 5979
• Main Authors: Dybkov, V. I., Khoruzha, V. G., Sidorko, V. R., Meleshevich, K. A., Samelyuk, A. V., Berry, D. C., Barmak, K.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-11-2009; Springer Nature B.V
• Subjects: Alloys; Antimony; Bismuth; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Cobalt base alloys; Crystallography and Scattering Methods; Dipping; Dissolution; Elongation; Interface Science; Intermetallics; Lead free; Liquids; Materials Science; Mathematical analysis; Melts; Polymer Sciences; Rate constants; Soldering; Solid Mechanics; Temperature dependence; Thickness; Tin; Zinc; Liquid Solder; Dissolution Rate Constant; Disc Rotational Speed; Intermetallic Layer; Cobalt
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-009-3717-z

Dissolution kinetics of cobalt in liquid 87.5%Sn–7.5%Bi–3%In–1%Zn–1%Sb and 80%Sn–15%Bi–3%In–1%Zn–1%Sb soldering alloys and phase formation at the cobalt–solder interface have been investigated in the temperature range of 250–450 °C. The temperature dependence of the cobalt solubility in soldering alloys was found to obey a relation of the Arrhenius type
c
s
 = 4.06 × 10
2
 exp (−46300/
RT
) mass% for the former alloy and
c
s
 = 5.46 × 10
2
 exp (−49200/
RT
) mass% for the latter, where
R
is in J mol
−1
 K
−1
and
T
in K. For tin, the appropriate equation is
c
s
 = 4.08 × 10
2
 exp (−45200/
RT
) mass%. The dissolution rate constants are rather close for these soldering alloys and vary in the range (1–9) × 10
−5
 m s
−1
at disc rotational speeds of 6.45–82.4 rad s
−1
. For both alloys, the CoSn
3
intermetallic layer is formed at the interface of cobalt and the saturated or undersaturated solder melt at 250 °C and dipping times up to 1800 s, whereas the CoSn
2
intermetallic layer occurs at higher temperatures of 300–450 °C. Formation of an additional intermetallic layer (around 1.5 μm thick) of the CoSn compound was only observed at 450 °C and a dipping time of 1800 s. A simple mathematical equation is proposed to evaluate the intermetallic-layer thickness in the case of undersaturated melts. The tensile strength of the cobalt-to-solder joints is 95–107 MPa, with the relative elongation being 2.0–2.6%.