Method for refining and homogeneously distributing alloying partners and for removing undesirable reaction products and slags in or from soft solder during the production of fine solder powder

Method for producing fine solder powder from lead-free soft solder alloys, comprising:

• melting a lead-free soft solder alloy in an oil in a first container to form a melt, wherein said oil acts as a separating medium to separate said soft solder and reaction products and/or slag by a release of said reaction products and/or slag from said melt into said oil when said soft solder is melted into a melt, and wherein said reaction products and/or slag build up in said oil away from said melt due to differences in density between said melt and said reaction products and/or slag;
• separating said oil with said reaction products and/or slag from said melt by transferring said melt to a second container to obtain a transferred melt, said second container having a second oil with a temperature of at least 20° C. greater than a liquidus temperature of said transferred melt;
• withdrawing of said oil with said reaction products and/or slag from said first container;
• shearing said transferred melt with rotors and stators with a peripheral rotor speed of 15 to 25 m/s while retaining a melt-to-oil volume ratio of 1:20 to 1:50 for forming a dispersion comprising solder balls and said second oil, said shear treatments enlarging a surface area of said transferred melt and driving out reaction products and/or slag from said transferred melt, wherein said reaction products and/or slag build up in said second oil away from said transferred melt due to differences in density between said transferred melt and said reaction products and/or slag and wherein said transferred melt and said second oil are circulated through a shearing device for 10 to 30 minutes for performing said shearing multiple times until the desired diameter distribution of the solder balls is obtained and wherein the shearing causes the alloy partners in the transferred melt to be homogeneously distributed in the transferred melt;
• separating the solder from said dispersion by sedimentation;
• and
• separating said second oil with said built-up reaction products and/or slag from said solder balls after said solder balls have settled, wherein
• said solder balls have a diameter of 2.5 to 45 μm.