PURPOSE: To provide a soldering paste free of an activator and a soldering method without need for flux cleaning by removing the metal oxide film such as a non-globular solder powder produced by the atomization method.
CONSTITUTION: A metal 1 is dipped in a heating medium 3 consisting of rosin or its derivative and an org. solvent having a higher b.p. than the metal and heated above the b.p. of the metal 1. The diameter of a globular grain 4 is not increased by adding hardened castor oil or high-softening-point rosin or its derivative to the medium 3 as a thickener. Meanwhile, an oxide film 2 is removed by heating the metal grain 1 below its m.p. without spheroidizing the grain. The solder freed from the oxide film is used to obtain a soldering paste free of an activator. The surface oxide film is removed after a solder bump is formed, an org. solvent having a higher b.p. than the m.p. of solder is applied, then thermal soldering is applied, and cleaning is not needed in this case.
HASHIMOTO KAORU
KAWAHARA TOSHISANE
OSUMI MAYUMI
