Flux for soldering comprising inorganic ion-exchanger and activator containing halogen atom, solder composition the flux and solder particles, soldering method comprising coating the solder composition on a portion for soldering, soldering method comprising coating flux containing activator on a portion for soldering, applying inorganic ion-exchanger to the portion and applying solder to the portion, and soldering method comprising mixing inorganic ion-exchanger with creamy solder to give mixture, coating the mixture on a circuit pattern of a wiring plate and heating the wiring plate. The flux for soldering and the soldering composition are excellent in metal ion-migration resistance, corrosion resistance, soldering property and storage stability, and can be preferably used without cleaning and the soldering methods can be preferably used in practical no-clean soldering methods.