Abstract: A non-washing soldering flux which is capable of minimizing corrosion and insulation defects due to precipitation of metal salts and cracking of the base resin is disclosed. The flux includes an activator including a dibasic acid with a molecular weight of 250 or less, and a monobasic acid with a molecular weight of from 150 to 300 and/or a dibasic acid with a molecular weight of from 300 to 600. The dibasic acid of molecular weight 250 or less in the flux exhibits sufficient activity, thus ensuring satisfactory solderability. The monobasic acid of molecular weight from 150 to 300 and the dibasic acid of molecular weight from 300 to 600 which are combined therewith promote the activity while also uniformly dispersing the metal salt of the low molecular weight dibasic acid in the flux residue, allowing it to be enveloped by the hydrophobic base resin. For greater cracking resistance, the flux includes at least an acrylic resin of molecular weight 10,000 or less and an activator.

Abstract: A soldering flux composition comprising, as a flux base resin, a modified amine compound obtained by reacting (i) at least one member selected from the group consisting of vinyl group-containing compounds, carboxyl group-containing compounds and epoxy group-containing compounds (ii) with an amine compound having an active hydrogen.

Abstract: Disclosed is a soldering flux which prevents a release of an active ion contained in an activator when exposed to a high-temperature atmosphere maintaining at a temperature higher than 80.degree. C., for example, an atmosphere of an engine room of an automobile, and thus makes washing unnecessary. This soldering flux comprises, together with an activator, (1) a thermoplastic resin having a softening point not lower than 80.degree. C., and/or (2) an epoxy group-containing compound, a radical-polymerizable unsaturated double bond-containing compound or a blocked isocyanate group-containing compound, or (3) a thermosetting resin composed of a carboxyl group-containing resin and an epoxy resin and/or a thermosetting resin containing carboxy and epoxy groups.