A forming method of solder bumps, comprising: preparing a substrate that has a copper electrode; whereby on the copper electrode only portions for mounting electronic components are exposed, whereas other portions of the substrate are covered with an insulation layer or an insulation film; preparing a mask from a layer of heat-resistant material, the layer being provided with an opening portion, the mask having a thickness in the range of from 20 to 500 μm; and subsequently overlapping the mask and the substrate by matching and superimposing the position of the opening portion in the mask with the position of the copper electrode; piling up a molten solder by spraying a jet stream of the molten solder at a temperature of not less than 150 °C and not more than 300 °C, wherein the substrate is held in a horizontal position during spraying and the jet stream of the molten solder is sprayed from above until a thickness of the molten solder is greater than a thickness of the mask, wherein the molten solder is purified by a refining process; forming the solder bumps having the predetermined thickness by removing an excess of the molten solder that is piled up beyond the thickness of the mask; and removing the mask from the overlapped substrate, wherein an atmosphere temperature during processing in both the step of piling up the molten solder and the step of forming the solder bumps by removing the excess of the molten solder is maintained at a temperature that can keep the molten state of molten solder as it is; the refining process is performed by stirring and mixing the molten solder with a solution including 5 % to 25 % by mass of organic fatty acid and having 12 to 20 carbon atoms and being heated to a temperature of from 180 °C to 350 °C; the molten solder is molten lead-free solder that includes tin as a main component and at least nickel as an accessory component, and further includes one or more components selected from among silver, copper, zinc, bismuth, antimony and germanium as an optional accessory component, and removing the excess of the molten solder piled up beyond the thickness of the mask is performed by a removal unit, selected from a group consisting of a blade, an air cutter, and a removal unit spraying organic fatty acid-containing solution having 12 to 20 carbon atoms. preparing a substrate that has a copper electrode; whereby on the copper electrode only portions for mounting electronic components are exposed, whereas other portions of the substrate are covered with an insulation layer or an insulation film; preparing a mask from a layer of heat-resistant material, the layer being provided with an opening portion, the mask having a thickness in the range of from 20 to 500 μm; and subsequently overlapping the mask and the substrate by matching and superimposing the position of the opening portion in the mask with the position of the copper electrode; piling up a molten solder by spraying a jet stream of the molten solder at a temperature of not less than 150 °C and not more than 300 °C, wherein the substrate is held in a horizontal position during spraying and the jet stream of the molten solder is sprayed from above until a thickness of the molten solder is greater than a thickness of the mask, wherein the molten solder is purified by a refining process; forming the solder bumps having the predetermined thickness by removing an excess of the molten solder that is piled up beyond the thickness of the mask; and removing the mask from the overlapped substrate, wherein an atmosphere temperature during processing in both the step of piling up the molten solder and the step of forming the solder bumps by removing the excess of the molten solder is maintained at a temperature that can keep the molten state of molten solder as it is; the refining process is performed by stirring and mixing the molten solder with a solution including 5 % to 25 % by mass of organic fatty acid and having 12 to 20 carbon atoms and being heated to a temperature of from 180 °C to 350 °C; the molten solder is molten lead-free solder that includes tin as a main component and at least nickel as an accessory component, and further includes one or more components selected from among silver, copper, zinc, bismuth, antimony and germanium as an optional accessory component, and removing the excess of the molten solder piled up beyond the thickness of the mask is performed by a removal unit, selected from a group consisting of a blade, an air cutter, and a removal unit spraying organic fatty acid-containing solution having 12 to 20 carbon atoms.