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%.

Provided is a preform solder including a first metal containing Sn and a second metal formed of an alloy containing Ni and Fe. Alternatively, provided is a preform solder (1) having a metal structure including a first phase (10) that is a continuous phase and a second phase (20) dispersed in the first phase (10), the first phase (10) contains Sn, the second phase (20) is formed of an alloy containing Ni and Fe, and a grain boundary (15) of a metal is present in the first phase (10).

Provided is a preform solder including a first metal containing Sn and a second metal formed of an alloy containing Ni and Fe. Alternatively, provided is a preform solder (1) having a metal structure including a first phase (10) that is a continuous phase and a second phase (20) dispersed in the first phase (10), the first phase (10) contains Sn, the second phase (20) is formed of an alloy containing Ni and Fe, and a grain boundary (15) of a metal is present in the first phase (10).

An objective of the present invention is to provide a flux that suppresses occurrence of flux drying up during soldering and occurrence of precipitation during storing.

The flux comprising, based on the whole flux, 3.5 to 11% by mass of a rosin ester, more than 0% by mass and 18% by mass or less of a rosin resin other than a rosin ester, and 70% by mass or more and less than 96.5% by mass of a solvent.

A Magnetic-field melting preform solder that melts by action of an AC magnetic field, wherein the preform solder includes a laminated structure made up of two or more layers, at least two layers constituting the laminated structure is made up of solder material, the at least two layers do not contain ferromagnetic material, each of the at least two layers includes a surface facing with each other, and the surfaces facing with each other are in contact with each other. A bonding method using the preform solder includes a providing the preform solder between an electrode on a substrate and an electrode of an electronic component, and bonding together the electrode on the substrate and the electrode of the electronic component by generating an AC magnetic field around the substrate and thereby melting the preform solder.

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.

Embodiments of the present invention provide a method (1000) of assembling an electrical circuit comprising one or more copper electrical conductors, the method comprising plating (1010) a surface of the one or more conductors with a layer comprising tin; annealing the plating; applying (1020) solder to at least a portion of the one or more electrical conductors, wherein said solder comprises tin and copper; and annealing the electrical circuit.

A lead-free solder alloy includes bismuth (Bi), content of which is equal to or greater than 56 wt % and equal to or less than 57.5 wt %, indium (In), content of which is equal to or greater than 0.05 wt % and equal to or less than 1.0 wt %, and the balance of tin (Sn) and another unavoidable impurity. The lead-free solder alloy of the disclosure may enable bonding with improved ductility and thermal shock reliability while not having a large melting point change compared to an Sn-58Bi alloy.