Lenovo (singapore) Pte. Ltd.

Senju Metal Industry Co., Ltd.

Murata Manufacturing Co., Ltd.

Lenovo Limited

Ko Inaba

Tadashi Kosuga

Tetsu Takemasa

Hiroyoshi Kawasaki

Hidekiyo Takaoka

Kosuke Nakano

Shizuharu Watanabe

Masato Shiratori

Hiroaki Kawamata

Kazuhiro Minegishi

Masafumi Seino

A solder joint, for bonding an electrode of a circuit board to an electrode of an electronic component, that includes: an Sn&#x2014;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&#x2014;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 &#x3bc;m. Coarse Bi phases in the solder joint each have an area of greater than 0.5 &#x3bc;mand less than or equal to 5 &#x3bc;m. A proportion of the fine Bi phases among the fine Bi phases and the coarse Bi phases is greater than or equal to 60%.

Solder joint

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&#x2014;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&#x2014;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&#xb0; C. to 180&#xb0; 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&#xb0; C./sec.

Solder bonding method and solder joint

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.

Flux and solder paste

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.

Lead-free solder paste and its use

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Tokyo, Japan

Ko Inaba