NOVELTY - The method comprises supplying a solder wire (12) in a gap between a heating unit (16) and a sonotrode, and melting and flowing the solder wire on workpieces (10) through the gap. The gap between the sonotrode and the heating unit is adjusted to a width (B) with half the diameter of the solder wire. The sonotrode and the heating unit are heated to a temperature above each of the melting temperature of a solder. The temperature of the heating unit is adjusted independent of the temperature of the sonotrode. The heating unit is a block or cuboidal shape radiators (17).    USE - The method is useful for applying a molten solder wire on the workpieces of a semiconductor device such as solar cell using a sonotrode exposed to ultrasonic vibrations (claimed).    ADVANTAGE - The method is capable of effectively and economically applying a molten solder wire on the workpieces with improved thermal capacity.    DETAILED DESCRIPTION - The method comprises supplying a solder wire (12) in a gap between a heating unit (16) and a sonotrode, and melting and flowing the solder wire on workpieces (10) through the gap. The gap between the sonotrode and the heating unit is adjusted to a width (B) with half the diameter of the solder wire. The sonotrode and the heating unit are heated to a temperature above each of the melting temperature of a solder. The temperature of the heating unit is adjusted independent of the temperature of the sonotrode. The heating unit is a block or cuboidal shape radiators (17). A side of the sonotrodes includes gap-limiting projections that has a cylindrical geometry. The heating unit or the gap-limiting projection of the sonotrode is oriented so that the gap expands above its height and has same width in the direction of the workpieces. The gap is purified by pulsed flow of liquid or gases such as air, nitrogen, argon or other inert gases after soldering one workpiece and before soldering other workpiece. An INDEPENDENT CLAIM is included for a device for applying a solder to workpieces.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a device for applying a solder material to workpieces.    Workpieces (10)    Solder wire (12)    Heating zone (14)    Heating unit (16)    Radiators. (17)