A solder composition contains: a flux composition containing an (A) rosin resin, a (B) activator, a (C) thixotropic agent, and a (D) solvent; and (E) solder powder, in which the (B) component contains a (B1) dicarboxylic acid having 3 to 8 carbon atoms, the (C) component contains at least one selected from the group consisting of a (C1) amide thixotropic agent having a hydroxy group in one molecule and a (C2) glycerol thixotropic agent having a hydroxy group in one molecule, and the solder composition satisfies a condition represented by Numerical Formula (F1) below provided that a total of contents of the (C1) component and the (C2) component is defined as X and a content of the (B1) component is defined as Y,

[00001]$\text{X}\text{}/\text{}2\le \text{Y}\le 5\text{X}$

A connection structure including: a first circuit member having a plurality of first electrodes; a second circuit member having a plurality of second electrodes; and an intermediate layer having a plurality of bonding portions electrically connecting the first electrodes and the second electrodes, in which at least one of the first electrode and the second electrode that are connected by the bonding portion is a gold electrode, and 90% or more of the plurality of bonding portions include a first region containing a tin-gold alloy and connecting the first electrode and the second electrode and a second region containing bismuth and being in contact with the first region.

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, which 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 has an alloy composition consisting of, by mass %, 0.1 to 4.5% of Ag, 0.20 to 0.85% of Cu, 0.005 to 0.090% 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): 0.006≤(Ag+Cu+Ni)×Ge<0.023 (1), (Sn/Cu)×(Ni×Ge)/(Ni +Ge)<0.89 (2). Ag, Cu, Ni, Ge, and Sn in the relations (1) and (2) each represent the contents (mass %) in the alloy composition.

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 method of manufacturing an electronic module includes supplying paste to an electronic component and/or a wiring board. The paste includes solder powder and first resin. The method includes supplying second resin to the electronic component and/or the wiring board. The method includes placing one of the electronic component and the wiring board on another. The method includes curing the second resin to form a second resin portion. The method includes heating the paste to a temperature equal to or higher than a solder melting point after the second resin portion is formed. The method includes solidifying molten solder at a temperature lower than the solder melting point to form a solder portion that bonds the electronic component and the wiring board. The method includes curing the first resin after the solder portion is formed, to form a first resin portion.

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 resin flux solder paste includes a solder powder, and a flux, in which the flux contains at least an epoxy resin, a curing agent, a curing accelerator, and an activator, the epoxy resin contains 10% to 90% by weight of one or more of a biphenyl aralkyl type epoxy resin, a naphthalene type epoxy resin, and a dicyclopentadiene type epoxy resin, having an epoxy equivalent of 200 to 400, with respect to a total amount of the epoxy resin, and the curing agent contains 30% to 95% by weight of a biphenyl aralkyl phenol resin having a hydroxyl group equivalent of 150 to 350 with respect to a total amount of the curing agent, and 5% to 70% by weight of a phenol novolac resin having an allyl group having a hydroxyl group equivalent of 100 to 200 with respect to the total amount of the curing agent.

Aspects of the invention include receiving a printed circuit board (PCB) having one or more of mounting pads thereon, determining a stencil for applying a solder paste to the one or more mounting pads, the stencil having a smallest aperture for a component requiring a standoff, determining a maximum threshold size for standoff particles based on the smallest aperture, determining a first concentration of the standoff particles based on the smallest aperture, determining a minimum threshold size for standoff particles to create the standoff for the component, determining a second concentration of the standoff particles to create a three-standoff seating plane for the component, introducing the standoff particles to the solder paste, the standoff particles in the solder paste having a concentration between the first concentration and the second concentration, and a size between the maximum threshold size and the minimum threshold size.