A solder composition contains: a flux composition containing an (A) rosin resin, a (B) activator, a (C) thixotropic agent, and a (D) solvent; and (E) solder powder, in which the (B) component contains a (B1) dicarboxylic acid having 3 to 8 carbon atoms, the (C) component contains at least one selected from the group consisting of a (C1) amide thixotropic agent having a hydroxy group in one molecule and a (C2) glycerol thixotropic agent having a hydroxy group in one molecule, and the solder composition satisfies a condition represented by Numerical Formula (F1) below provided that a total of contents of the (C1) component and the (C2) component is defined as X and a content of the (B1) component is defined as Y,

[00001]$\text{X}\text{}/\text{}2\le \text{Y}\le 5\text{X}$

A solder composition contains: a flux composition containing an (A) rosin resin, a (B) activator, a (C) thixotropic agent, and a (D) solvent; and (E) solder powder, in which the (B) component contains a (B1) dicarboxylic acid having 3 to 8 carbon atoms, the (C) component contains at least one selected from the group consisting of a (C1) amide thixotropic agent having a hydroxy group in one molecule and a (C2) glycerol thixotropic agent having a hydroxy group in one molecule, and the solder composition satisfies a condition represented by Numerical Formula (F1) below provided that a total of contents of the (C1) component and the (C2) component is defined as X and a content of the (B1) component is defined as Y,

[00001]$\text{X}\text{}/\text{}2\le \text{Y}\le 5\text{X}$

A flux containing an organic acid, an acrylic resin, a rosin, a thixotropic agent, and a solvent, but not containing water is adopted. In this flux, the organic acid includes 1,2,3-propanetricarboxylic acid, and the content of the 1,2,3-propanetricarboxylic acid is 0.1% by mass or more and 15% by mass or less with respect to the total amount of the entire flux. According to this flux, the wettability of solder can be enhanced, temperature cycle reliability is excellent, and scattering due to heating during reflow can be suppressed.

A solder paste is adopted, the solder paste containing: a solder alloy powder in which a content of solder alloy particles having a particle size of 8 μm or less is 99% by mass or more with respect to a total mass of the solder alloy powder; and a flux. This flux contains an acid-modified rosin, a solvent, an activator, and a thixotropic agent, in which the activator contains a halogenated aliphatic compound, and a dicarboxylic acid represented by General Formula (2).

##STR00001##

[in the formula, R represents an alkylene group having 1 to 7 carbon atoms, or a single bond, provided that a methylene group constituting the alkylene group may be substituted with an oxygen atom]

A solder paste is adopted, the solder paste containing: a solder alloy powder in which a content of solder alloy particles having a particle size of 8 μm or less is 99% by mass or more with respect to a total mass of the solder alloy powder; and a flux. This flux contains an acid-modified rosin, a solvent, an activator, and a thixotropic agent, in which the activator contains a halogenated aliphatic compound, and a dicarboxylic acid represented by General Formula (2).

##STR00001##

[in the formula, R represents an alkylene group having 1 to 7 carbon atoms, or a single bond, provided that a methylene group constituting the alkylene group may be substituted with an oxygen atom]

A flux according to the present invention is a flux for soldering, the flux including: an unsaturated aliphatic alcohol having one unsaturated bond, a thixotropic agent, and a solvent, in which the unsaturated aliphatic alcohol includes oleyl alcohol, and a content of the oleyl alcohol is 2.0 mass % or more and 12.0 mass % or less based on the entire flux.

A flux according to the present invention is a flux for soldering, the flux including: an unsaturated aliphatic alcohol having one unsaturated bond, a thixotropic agent, and a solvent, in which the unsaturated aliphatic alcohol includes oleyl alcohol, and a content of the oleyl alcohol is 2.0 mass % or more and 12.0 mass % or less based on the entire flux.

A flux composition includes an aromatic resin including one benzene ring and one or two hydroxyl (—OH) groups, an activator selected from a group consisting of a dicarboxylic acid and a dicarboxylic anhydride, and a solvent.

A flux composition includes an aromatic resin including one benzene ring and one or two hydroxyl (—OH) groups, an activator selected from a group consisting of a dicarboxylic acid and a dicarboxylic anhydride, and a solvent.

A solder paste includes a solder powder and a flux. The flux includes a rosin, an activator, a solvent, and a thixotropic agent containing a polyethylene glycol. A content of the polyethylene glycol is 10 mass % to 20 mass % with respect to a total mass of the flux, a content of the thixotropic agent excluding the polyethylene glycol is 5 mass % or less with respect to the total mass of the flux, and a content of the rosin is more than 15 mass % and 50 mass % or less with respect to the total mass of the flux.