PROBLEM TO BE SOLVED: To provide a flux for soldering, which flux can sufficiently suppress the generation of cracks on a residue of the flux after soldering, and also has high reliability and excellent soldering performance, and is equivalent to a conventional flux in a manufacturing cost and an effect on environments, and further to provide a solder paste composite.
SOLUTION: The flux for soldering contains low softening point rosin having a softening point of 60°C or low as a base resin. It is preferable that the low softening point rosin contains secodehydroabietic acid and/or thermolysis components of rosin, and the content of the secodehydroabietic acid and/or the thermolysis components is 5 wt.% or more of the low softening point rosin. Further, it is preferable that the content of the low softening point rosin is 0.5 to 80 wt.% of the total amount of the flux. The solder paste composite contains the flux and powder of a solder alloy.
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