Abstract: The present invention uses a flux which contains a rosin, a rosin amine; one or more types of organic sulfonic acid selected from the group consisting of an alkane sulfonic acid, an alkanol sulfonic acid, and an aromatic sulfonic acid, a thixotropic agent, and a solvent, wherein: the rosin content is 5-50 mass %, inclusive, of the total amount (100 mass %) of the flux, the rosin content is 5-30 mass %, inclusive, of the total amount (100 mass %) of the flux, the organic sulfonic acid content is 0.2-10 mass %, inclusive, of the total amount (100 mass %) of the flux, and the proportion (mass ratio) of the rosin amine content to the organic sulfonic acid content is 3.33-10, inclusive.

Abstract: A flux containing: a rosin; a solvent (S); a thixotropic agent; and an activator is disclosed. The rosin contains a rosin amine. The solvent (S) contains a first solvent (S1) having a boiling point of 250° C. or less, and the amount of the first solvent (S1) relative to the total amount of the solvent (S) is 50% by mass or more and 100% by mass or less.