STUDY OF THE INTERACTION OF PB-SN SOLDER WITH O2,H2O, AND NO2 BY X-RAY PHOTOELECTRON (ESCA) AND AUGER (AES) SPECTROSCOPY

An ESCA and AES study of the corrosion of 1:1 Pb-Sn solder is reported. The solder was reacted at room temperature with O//2 (1 Torr), H//2O (10 Torr), 100 ppm of NO//2 in N//2 (1 atm), and the latter at 50% relative humidity. Pb and Sn foils were examined under similar conditions. The Pb/Sn ratios observed by ESCA and AES for unmelted solder are close to those expected from bulk composition. After melting, a 50% decrease in Pb/Sn was obtained by ESCA; no AES signal for Pb was observed. Before melting, 90% of the Pb and 100% of the Sn were oxidized; after melting, 18% Pb and 70% Sn were oxidized. Exposure of solder to O//2 (1 Torr) resulted in a Pb/Sn ratio which decreased as a function of time to a minimum value, rapidly increased through a maximum around 60 min and then decreased to an equilibrium value.