Abstract: A flux and a solder paste capable of minimizing the time-dependent changes in viscosity when stored at 30° C. and minimizing the coloration of flux residues while having favorable reflow properties and favorable cleanability of flux residues are provided. As such a flux, a flux containing a rosin, a thixotropic agent, an activator, and a solvent is adopted. The rosin includes one or more selected from the group consisting of an acid-modified rosin, a hydrogenated rosin, and an acid-modified hydrogenated rosin, and the thixotropic agent includes a compound represented by General Formula (1). In General Formula (1), R11 and R12 each independently represent a hydrocarbon group which has 1 to 3 carbon atoms and may have a substituent, or a single bond. R21 and R22 each independently represent a hydrocarbon group which has 7 to 29 carbon atoms and may have a substituent. R13 represents a substituent. n represents an integer of 0 to 4.

Abstract: The present invention employs a flux containing a resin component, an activator, and a solvent. The resin component contains a copolymer (A) having an alkene-derived repeating unit (al), and an acrylic acid-derived repeating unit (a2) in which a hydrogen atom bonded to a carbon atom at an a-position may be substituted with a substituent, and contains a rosin (B). A mixing ratio of the copolymer (A) and the rosin (B) is 1 or more as a mass ratio represented by copolymer (A)/rosin (B).