PURPOSE: To prevent the decrease of electrical insulation resistance and to provide good solderability with the decreased influence on a solder-resist film by incorporating ≥2 kinds of oxycarboxylic acids into a water washable flux compsn. for soldering.

CONSTITUTION: The more preferable compsn. of the water washable flux compsn. for soldering contains at least one kind of the oxycarboxylic acid selected from an oxysuccinic acid, tartaric acid and citric acid. The compsn. contg. 2 among 3 kinds of these oxycarboxylic acids or all of the three kinds is most preferable. The oxycarboxylic acids are usable at ≥5wt% at the temp. below the saturation. temp. and is more preferably adjusted to 10W50wt%. The washing with water is thus possible and the deterioration of electrical characteristics is obviated. The generation of the blister or whitening of the solder resist film is prevented.