During the wave-soldering process, the dross problem originated by oxidation of solder-metal tin is serious. The formation of big amount of oxide dross not only causes great economic loss, but also threatens the quality of soldering junction. And with the lead-free trend and development in electronic packaging, lead-free solders are widely used. In comparison with traditional tin-lead solder, majority of lead-free solders has a much higher proportion of tin, and a much higher melting point. It needs a higher temperature to complete the soldering process. This aggravates the oxidation issue of tin in liquid solder alloy, which causes huge economic loss every year. So to decrease the oxidation of molten tin becomes an urgent issue in packaging industry. Therefore, in present work the structure of oxide formed on liquid tin surface is studied, the oxidation of liquid tin is improved successfully by doping trace elements, and the working mechanism of trace dopant is discussed simply.
In present work X-ray Diffraction(XRD), Laser-Raman and X-ray Photoelectron Spectrum(XPS) is employed to determine the structure and chemical composition of the oxide formed on surface of liquid tin. Trace doping elements Ge and P is alloyed with tin, the influence of trace dopant on tin oxidation process is studied, and the distribution of trace doping elements and the working mechanism is analyzed also.
The experimental results show that: strong (001)-textured tetragonal SnO formed on liquid tin firstly, and when the temperature became higher, partial SnO transformed to Sn3O4 or (101)-textured SnO2 with one-step and two-step transitions respectively. Trace doping Ge and P affected the oxidation behavior dramatically, and there existed a best alloying concentration of dopant. A much higher doping decreased or even deteriorated the oxidation resistance of the alloy. There was a strong segregation of doping elements in oxide film, which destroyed the layered tetragonal SnO on surface of liquid tin, and helped to build a dense composite oxide film.
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