Provided are a solder alloy and a solder joint which have high tensile strength, can suppress Ni leaching and can suppress generation of voids at a bonded interface. The solder alloy has an alloy composition consisting of, by mass %, Ag: 1.0 to 4.0%, Cu: 0.1 to 1.0%, Ni: 0.005 to 0.3%, Co: 0.003 to 0.1%, and Ge: 0.001 to 0.015% with the balance being Sn The alloy composition satisfies the following relation (1):

0.00030<(Ni/Co)×(1/Ag)×Ge<0.05   (1) Co, Ag, and Ge in the relation (1) each represent the contents (mass %) in the alloy composition.

A lead-free solder alloy comprising: from 2.5 to 5 wt. % silver; from 0.01 to 5 wt. % bismuth; from 1 to 7 wt. % antimony; from 0.01 to 2 wt. % copper; one or more of: up to 6 wt. % indium, up to 0.5 wt. % titanium, up to 0.5 wt. % germanium, up to 0.5 wt. % rare earths, up to 0.5 wt. % cobalt, up to 5.0 wt. % aluminium, up to 5.0 wt. % silicon, up to 0.5 wt. % manganese, up to 0.5 wt. % chromium, up to 0.5 wt. % iron, up to 0.5 wt. % phosphorus, up to 0.5 wt. % gold, up to 1 wt. % gallium, up to 0.5 wt. % tellurium, up to 0.5 wt. % selenium, up to 0.5 wt. % calcium, up to 0.5 wt. % vanadium, up to 0.5 wt. % molybdenum, up to 0.5 wt. % platinum, and up 0 to 0.5 wt. % magnesium; optionally up to 0.5 wt. % nickel; and the balance tin together with any unavoidable impurities.

Provided are a lead-free and antimony-free solder alloy, a solder ball, and a solder joint that have improved shear strength obtained by grain minuteness at a bonded interface and can suppress fusion failure. The lead-free and antimony-free solder alloy having an alloy composition consisting of, by mass%, 0.1 to 4.5% of Ag, 0.20 to 0.85% of Cu, 0.2 to 5.00% of Bi, 0.005 to 0.09% of Ni, and 0.0005 to 0.0090% of Ge with the balance being Sn, and the alloy composition satisfies the following relations (1) and (2): 0.013 ≤ (Ag + Cu + Ni + Bi) x Ge ≤ 0.027 (1), Sn x Cu x Ni ≤ 5.0 (2). Ag, Cu, Ni, Bi, Ge, and Sn in the relations (1) and (2) each represent the contents (mass%) in the alloy composition.

Provided are a lead-free and antimony-free solder alloy, a solder ball, and a solder joint that have improved shear strength obtained by grain minuteness at a bonded interface and can suppress fusion failure. The lead-free and antimony-free solder alloy having an alloy composition consisting of, by mass%, 0.1 to 4.5% of Ag, 0.20 to 0.85% of Cu, 0.2 to 5.00% of Bi, 0.005 to 0.09% of Ni, and 0.0005 to 0.0090% of Ge with the balance being Sn, and the alloy composition satisfies the following relations (1) and (2): 0.013 ≤ (Ag + Cu + Ni + Bi) x Ge ≤ 0.027 (1), Sn x Cu x Ni ≤ 5.0 (2). Ag, Cu, Ni, Bi, Ge, and Sn in the relations (1) and (2) each represent the contents (mass%) in the alloy composition.

Provided is a solder composition containing Sn. The composition comprises: 1.0% by mass or more and 5.0% by mass or less of Cu; 0.1% by mass or more and 0.5% by mass or less of Ni; and more than 0.01% by mass and 0.5% by mass or less of Ge.

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 μm.sup.2. Coarse Bi phases in the solder joint each have an area of greater than 0.5 μm.sup.2 and less than or equal to 5 μm.sup.2. A proportion of the fine Bi phases among the fine Bi phases and the coarse Bi phases is greater than or equal to 60%.

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 μm.sup.2. Coarse Bi phases in the solder joint each have an area of greater than 0.5 μm.sup.2 and less than or equal to 5 μm.sup.2. A proportion of the fine Bi phases among the fine Bi phases and the coarse Bi phases is greater than or equal to 60%.

A flux containing an organic acid, a water-soluble base agent, and a solvent, but not containing water is adopted. In this flux, the organic acid includes 1,2,3-propanetricarboxylic acid. The water-soluble base agent is one or more selected from the group consisting of a nonionic surfactant and a weak cationic surfactant. The content of the 1,2,3-propanetricarboxylic acid is 1% by mass or more and 15% by mass or less with respect to the total amount of the entire flux, the total content of the water-soluble base agent is 30% by mass or more and 65% by mass or less with respect to the total amount of the entire flux, and the total content of the solvent is 30% by mass or more and 65% 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 and ball missing after reflow and flux residue washing is suppressed.

A solder alloy that contains 0.005 mass % or more and 0.1 mass % or less of Mn, 0.001 mass % or more and 0.1 mass % or less of Ge, and a balance of Sn. A plurality of Ge oxides is distributed on an outermost surface side of an oxide film including Sn oxide, Mn oxide and Ge oxide by adding 0.005 mass % or more and 0.1 mass % or less of Mn, 0.001 mass % or more and 0.1 mass % or less of Ge to the solder alloy having a principal ingredient of Sn, so that it is possible to obtain the discolor-inhibiting effect even under the high-temperature and high-humidity environment.

A solder alloy that contains 0.005 mass % or more and 0.1 mass % or less of Mn, 0.001 mass % or more and 0.1 mass % or less of Ge, and a balance of Sn. A plurality of Ge oxides is distributed on an outermost surface side of an oxide film including Sn oxide, Mn oxide and Ge oxide by adding 0.005 mass % or more and 0.1 mass % or less of Mn, 0.001 mass % or more and 0.1 mass % or less of Ge to the solder alloy having a principal ingredient of Sn, so that it is possible to obtain the discolor-inhibiting effect even under the high-temperature and high-humidity environment.