PURPOSE: To improve a soldering in reliability by a method wherein a printed wiring board is dipped into the liquid or vapor of a second fluorocarbon whose boiling point is lower than that of a first fluorocarbon liquid, and the second fluorocarbon is removed through evaporation using a flux cleaning solvent.

CONSTITUTION: When a VPS(Vapor phase soldering) method is employed, the residue of a first fluorocarbon is diffused and substituted with a second fluorocarbon by dipping a printed wiring board into the second fluorocarbon whose boiling point is lower than that of the first fluorocarbon. Next, the board is dipped into a flux cleaning solvent whose boiling point is higher than that of the second fluorocarbon, which is heated at a temperature higher than the boiling point of the second fluorocarbon to remove the second fluorocarbon. That is, the first fluorocarbon is substituted with the second fluorocarbon whose boiling point is lower than that of the first fluorocarbon, and then the second fluorocarbon is brought into contact with the flux cleaning solvent whose boiling point is higher than that of the second fluorocarbon, and the printed board is heated at a temperature higher than the boiling point of the second fluorocarbon to remove the second fluorocarbon and the flux is completely dissolved to be removed.