C3F8 plasma fluorination of lead free solders for fluxless soldering

Fluorination of Sn–3.6 wt.% Ag lead free solder was achieved using a C3F8 and O plasma treatment. X-ray photoelectron spectroscopy (XPS) was used to analysis fluorinated surface before and after oxidation in air. Plasma treatment formed SnF2, Sn oxide, CO and CFX groups such as CF, CF2, CF3 and C-CFX on the surface. The CO and CFX groups only existed on the outermost surface. The native oxide layer was 56 nm thick. Plasma treatment reduced this oxide layer to the value between 16 nm and 31 m. Fluorine diffused to a depth of 427 nm. Increasing exposure time to air reduced the SnF2 peak in the top surface layer, in contrast, Sn oxide peak was increased. These results suggest that oxidation of the fluorinated surface took place by replacement of F with O atoms. Fluorine atoms diffused through the solder and reached a depth of 733 nm after 4 days. Wettability tests by reflow experiments in a nitrogen atmosphere showed that the affect of plasma treatment on fluxless solder bonding lasted at least 4 days in air. # 2003 Elsevier B.V. All rights reserved.