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Dependence of Wetting Temperature on Solder/Substrate Oxidation Under a Reduced Atmosphere
Keywords: solder, wetting, oxidation
Fluxless soldering is a desired process for high density solder joint and optical electronic interconnection. There are two species of oxides, one from the copper substrate, and the other from the tin-based solder.Utilizing hydrogen or forming gas can be a good candidate for the fluxless soldering. The effectiveness of the reduction processes on the wetting of solder on copper has to be evaluated. The roles of these oxides playing during the process have to be understood that is interesting to scientists and engineers. For these purpose, wetting behavior of SnPb solder on copper surface was investigated in a forming gas atmosphere (5% H2 and 95% Ar2) without flux, to determine how wetting temperature may be affected by oxidation of the copper surface. X-ray photoelectron spectroscopy (XPS) analysis indicated that Cu2O oxide layer, 2.0 ~ 4.2 nm thick, was formed after exposing the milled and polished copper surface in air from 5 min to 5 hours. The wetting temperature did not change much after copper was exposed to air for more than 3 hrs . When molten solder was in contact with reduced copper surfaces, wetting took place following with the reaction between copper and tin . The initial temperature of solder wetting on copper was close to the reduction temperature of Cu2O and increased with the thickness of the surface oxide layer.
Dr. Lei Zhang, Associate Professor
Chinese Academy of Sciences
Shenyang, Liaoning 110016,
P. R. China

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