Changes in the phase composition and structure of electrodeposited Sn-Co alloys in Sn-Co/Cu layer systems upon heating

Abstract

Changes in the phase composition and structure of electrodeposited tin-cobalt (Sn-Co) alloy layers (5-10 μm) containing a limited quantity of Co (0.24, 2.4, 11.0, 17.0 or 26.5. wt.%) were studied using X-ray diffraction (XRD) and optical microscopy.The phase composition and coating structures of Sn-Co alloys in Sn-Co/Cu layers underwent considerable changes upon heating at 170°C for 100-200h and at 170°C for 200h followed by 205°C for 20h. The changes were dependent on the Co content in the alloy and the heating temperature. When examining the sample containing 11.0wt.% cobalt, an unidentified phase containing a Sn-Co compound, CoSn2 and CoSn3 formed upon heating at 170°C for 100, 140 and 200h. The structure of the layer surface was composed of spherical crystallites. The formation of the unidentified phase possibly caused the formation of needle-shaped crystals in the structure consisting of spherical crystallites. When the Co content of the Sn-Co layer was increased to 17.0-26.5wt.% and the sample was heated to 170°C for 100-200h, phases of CoSn, CoSn2, Co3Sn2 and CoSn3 were formed. The coating maintained its structure and was composed of spherical crystallites.In the Sn-Co/Cu system of layers containing 11.0, 17.0 or 26.5wt.% Co, Sn-Cu intermetallic compounds (Cu6Sn5 and Cu3Sn) did not form after heating at 170°C for 200h followed by 205°C for 20h. © 2010.