1997 Volume 15 Issue 4 Pages 623-630
Wettability of Cu and Cu-Sn intermetallic compound was investigated in terms of their surface oxidation by spreading and meniscograph tests, and their surface oxides were characterized by SEM, XRD, AES, XPS, TEM and galvanostatic coulometry analysis. In the case of Cu, surface oxidation influenced its wettability a little, although the crystalline Cu2O layer of about 55nm thick was formed on its surface during the heat treatment at 150°C for 2h in air. In the case of Cu-Sn intermetallic compound, surface oxidation appreciably lowered its wettability : spreading factor became smaller, wetting time longer, and wetting force smaller. The surface of the oxidized Cu-Sn intermetallic compound was covered with an amorphous layer of about 5nm thick, while the layer thickness was 55nm for Cu. This thin amorphous layer could not be identified by conventional surface analysis, but its existence was suggested by galvanostatic coulometry analysis. The amorphous layer was identified to be a Cu-Sn complex oxide, by the difference in cathodic potential from Cu2O or SnO. This Cu-Sn complex oxide is more difficult to reduce than Cu2O or SnO because of its lower cathodic potential, which cause the appreciable decrease in wettability of Cu-Sn intermetallic compound.
