Methods for making metal particle spherical and removing oxide film solder paste and soldering method

摘要

Metal such as solder is immersed in a heating medium containing a rosin or derivative thereof and an organic solvent and heated to a temperature above the melting point of the metal, to remove the oxide film of the metal and make the metal spherical. If a hardened caster oil or high softening point rosin or derivative thereof is further added as a thickener to the heating medium, the size increase of the metal particle can be prevented. By heating at a temperature lower than the melting point of the metal, the oxide film can be removed without making the particles spherical. Using thus obtained solder particles, fluxless soldering can be done. Also, a fluxless soldering method is provided.