Abstract: A solder joint, for bonding an electrode of a circuit board to an electrode of an electronic component, that includes: an Sn—Bi-based solder deposited on the electrode of the circuit board; and a solder alloy deposited on the electrode of the electronic component. The Sn—Bi-based solder alloy has a lower melting point than the solder alloy deposited on the electrode of the electronic component. Fine Bi phases in the solder joint each have an area of less than or equal to 0.5 ?m2. Coarse Bi phases in the solder joint each have an area of greater than 0.5 ?m2 and less than or equal to 5 ?m2. A proportion of the fine Bi phases among the fine Bi phases and the coarse Bi phases is greater than or equal to 60%.

Abstract: A solder joint, for bonding an electrode of a circuit board to an electrode of an electronic component, that includes: an Sn—Bi-based solder deposited on the electrode of the circuit board; and a solder alloy deposited on the electrode of the electronic component. The Sn—Bi-based solder alloy has a lower melting point than the solder alloy deposited on the electrode of the electronic component. Fine Bi phases in the solder joint each have an area of less than or equal to 0.5 ?m2. Coarse Bi phases in the solder joint each have an area of greater than 0.5 ?m2 and less than or equal to 5 ?m2. A proportion of the fine Bi phases among the fine Bi phases and the coarse Bi phases is greater than or equal to 60%.

Abstract: A solder bonding method that bonds, using a solder joint, an electrode of a circuit board to an electrode of an electronic component includes: depositing, on the electrode of the circuit board, an Sn—Bi-based solder alloy with a lower melting point than a solder alloy deposited on the electrode of the electronic component; mounting the electronic component on the circuit board such that the Sn—Bi-based solder alloy contacts the solder alloy on the electrode of the electronic component; heating the circuit board to a peak temperature of heating of 150° C. to 180° C.; holding the peak temperature of heating at a holding time of greater than 60 seconds and less than or equal to 150 seconds; and cooling, after the heating and to form the solder joint, the circuit board at a cooling rate greater than or equal to 3° C./sec.

Abstract: It is an object of the present invention to provide a flux containing flux components homogeneously dispersed without precipitation of aggregates in addition to having an appropriate balance between fluidity and shape retention property, and a solder paste. A flux comprising 0.5 to 3.5 mass % of a sorbitol-type thixotropic agent selected from the group consisting of dibenzylidene sorbitol, bis(4-methylbenzylidene)sorbitol and a combination thereof, and 2 to 350 mass ppm of a sorbitol-type additive selected from the group consisting of sorbitol, monobenzylidene sorbitol, mono(4-methylbenzylidene)sorbitol and a combination thereof, and a glycol ether-type solvent.

Abstract: It is an object of the present invention to provide a flux containing flux components homogeneously dispersed without precipitation of aggregates in addition to having an appropriate balance between fluidity and shape retention property, and a solder paste. A flux comprising 0.5 to 3.5 mass % of a sorbitol-type thixotropic agent selected from the group consisting of dibenzylidene sorbitol, bis(4-methylbenzylidene)sorbitol and a combination thereof, and 2 to 350 mass ppm of a sorbitol-type additive selected from the group consisting of sorbitol, monobenzylidene sorbitol, mono(4-methylbenzylidene)sorbitol and a combination thereof, and a glycol ether-type solvent.

Abstract: A solder bonding method that bonds, using a solder joint, an electrode of a circuit board to an electrode of an electronic component includes: depositing, on the electrode of the circuit board, an Sn—Bi-based solder alloy with a lower melting point than a solder alloy deposited on the electrode of the electronic component; mounting the electronic component on the circuit board such that the Sn—Bi-based solder alloy contacts the solder alloy on the electrode of the electronic component; heating the circuit board to a peak temperature of heating of 150° C. to 180° C.; holding the peak temperature of heating at a holding time of greater than 60 seconds and less than or equal to 150 seconds; and cooling, after the heating and to form the solder joint, the circuit board at a cooling rate greater than or equal to 3° C./sec.

Abstract: Provided is a flux for a solder paste that can prevent peeling from electrode, which is seen in a component, a thickness of which is reduced, such a semiconductor package like BGA. Rosin, a glycol-ether-based solvent, an organic acid, a thixotropic agent, a halogen compound, and an imidazole compound are contained and the halogen compound is either an amine hydrohalide or an organohalogen compound or a combination of them. Their addition amounts stay within a range satisfying a formula of 2.5-X-0.625Y?0 in which the addition amount of the amine hydrohalide is indicated by X (weight %) and the addition amount of the organohalogen compound is indicated by Y (weight %). However, the addition amount X of the amine hydrohalide and the addition amount Y of the organohalogen compound are such that 0?X?2.5 and 0?Y?4, excluding a range of 0?X<0.02 and 0?Y<0.1.

Abstract: A solder paste comprising a solder alloy powder and a flux. The volumetric expansion at the time of melting of the solder alloy is at most 0.5%. The flux contains a bisphenol A epoxy resin and a curing agent selected from a carboxylic anhydride and a dicarboxylic acid. The solder paste can be used in applications suitable for high-temperature solders. The solder alloy has an alloy composition comprising, in mass percent, 70-98% of Bi, a total of 0-0.5% of at least one substance selected from Ag, Cu, Sb, In, Zn, Ni, Cr, Fe, Mo, P, Ge, and Ga, and a remainder of Sn.

Abstract: A solder paste comprising a solder alloy powder and a flux. The volumetric expansion at the time of melting of the solder alloy is at most 0.5%. The flux contains a bisphenol A epoxy resin and a curing agent selected from a carboxylic anhydride and a dicarboxylic acid. The solder paste can be used in applications suitable for high-temperature solders. The solder alloy has an alloy composition comprising, in mass percent, 70-98% of Bi, a total of 0-0.5% of at least one substance selected from Ag, Cu, Sb, In, Zn, Ni, Cr, Fe, Mo, P, Ge, and Ga, and a remainder of Sn.

Abstract: As BGA's and CSP's become widespread, the number of steps in soldering module boards to rigid printed wiring boards increases. A printed circuit board warps due to heating during reflow, so even if mounting is carried out at a temperature sufficiently exceeding the melting point of a solder alloy, there was a problem of the phenomenon of fusion defects in which the solder bumps of a module board of a CSP, a BGA, or the like and the mounting paste do not fuse or parts having leads and solder paste do not fuse, resulting in conduction defects. Means for Solving the Problem When soldering a module board to a rigid printed wiring board, a post-flux is applied to a module board before mounting, a solder paste is then applied to the rigid printed wiring board, and the module board is soldered.