Abstract: A flux containing 0.1 to 20 wt % of 2-hydroxyisobutyric acid as an activator, 10 to 60 wt % of a cationic surfactant and 5 to 60 wt % of a nonionic surfactant. A solder paste contains a flux containing 0.1 to 20 wt % of 2-hydroxyisobutyric acid as an activator, 10 to 60 wt % of a cationic surfactant, and 5 to 60 wt % of a nonionic surfactant and a metal powder.

Abstract: A flux containing 0.1 to 20 wt % of 2-hydroxyisobutyric acid as an activator, 10 to 60 wt % of a cationic surfactant and 5 to 60 wt % of a nonionic surfactant. A solder paste contains a flux containing 0.1 to 20 wt % of 2-hydroxyisobutyric acid as an activator, 10 to 60 wt % of a cationic surfactant, and 5 to 60 wt % of a nonionic surfactant and a metal powder.

Abstract: Using flux to suppress increase in the viscosity of solder paste during its storage and also to improve the fusibility of a solder alloy. The flux, which contains an activator and a solvent, forms solder paste by being mixed with a granular solder alloy. The flux contains a monoalkyl propylene glycol-based solvent. It is preferable that the monoalkyl propylene glycol-based solvent is butyl propylene triglycol or butyl propylene diglycol. It is also preferable that the amount of monoalkyl propylene glycol-based solvent is equal to or more than 75 percent by mass but less than 100 percent by mass of the amount of all the solvents.

Abstract: Provided is flux which is capable of suppressing increase in the viscosity of solder paste during its storage and is also capable of improving the fusibility of a solder alloy. In the flux which contains an activator and a solvent and forms solder paste by being mixed with a granular solder alloy, this flux contains a solvent of monoalkyl propylene glycol series. It is preferable that the solvent of monoalkyl propylene glycol series is butyl propylene triglycol or butyl propylene diglycol. It is also preferable that a contented amount of the solvent of monoalkyl propylene glycol series is equal to or more than 75% but equal to or less than 100% relative to a contented amount of all the solvents.