C/sub 3/F/sub 8//O plasma treatment of lead free solders for fluxless soldering

Fluorination of Sn-3.6 wt%Ag lead free solder was achieved using a C/sub 3/F/sub 8/ and O plasma treatment. X-ray photoelectron spectroscopy (XPS) was used to analysis fluorinated surface before and after oxidation in air. Three layers were existed perpendicular to the surface after plasma irradiation. The top surface layer was a complex mixture of absorptions (CF/sub x/ groups such as CF, CF/sub 2/, CF/sub 3/ and C-CF/sub x/ and CO), Sn oxide, SnF/sub 2/ and Sn-Ag. The second layer was a complex mix of Sn oxide, SnF/sub 2/ and Sn-Ag. The thickness of this layer was 16-31 nm. The third layer consisted of diffused fluorine to a depth of 427nm. Increasing exposure time to air reduced the SnF/sub 2/ 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 four days. Wettability tests by reflow experiments in a nitrogen atmosphere showed that the affect of plasma treatment on fluxless solder bonding lasted at least four days in air.