Mitsui Minings & Melting Co., Ltd.

Junichi Matsunaga

Ryuji Ninomiya

Yuunosuke Nakahara

The present invention provides a lead-free tin-silver-based soldering alloy which has a low melting point equal to alloy H without containing harmful lead, expensive In or the like, and has excellent mechanical characteristics, that is, a tensile strength, an elongation value and heat fatigue characteristic as compared with alloy H, and thus, is applicable to soldering work at a low temperature and can make products which have a high reliability and long useful life or durability. The lead-free tin-silver-based soldering alloy consists essentially of Ag: 2 to 4% by weight, Zn: 0.5 to 2% by weight, Bi: 2 to 6% by weight, and the balance being substantially Sn.

Lead-free tin-silver-based soldering alloy

The present invention provides a soldering alloy which does not include harmful Pb or Cd and which has an excellent tensile strength, elongation value, and melting point property. The soldering alloy according to the present invention can thus solve the conventional environmental problems, set the soldering temperature at a low level to thereby restrict the thermal damage to a soldered portion, and prevent breaking of the soldering alloy due to a heat cycle, with an excellent tensile strength and elongation value. A tin-silver-based soldering alloy according to the present invention consist essentially of 3 to 4% by weight of Ag, 2 to 6% by weight of Bi, 2 to 6% by weight of In, and the balance being Sn.

Tin-silver-based soldering alloy

Described is a lead-free tin-zinc-based soldering alloy made up of 7 to 9 wt. % of Zn and 0.1 to 0.5 wt. % of Cu or which further contains not more than 3 wt. % of Bi and, in either case, the balance being Sn except for inevitable impurities. The present invention has made it possible to provide a lead-free soldering alloy which has mechanical properties, such as tensile strength and elongation, comparable with those of conventional Pb--Sn soldering alloys without adding thereto lead which causes environmental pollution, has a melting point not higher than 200.degree. C., which is lower than the heat-resistant temperature of an IC package, and has a low cost.

Lead-free tin-zinc-based soldering alloy

A lead-free solder consisting of 1 to 4 wt % of Ag, at least one of Bi and In in respective amounts meeting the conditions that the value of expression (1), A, is equal to or greater than 5.00 and that the value of expression (2), B, is equal to or less than 6.90, and Sn for the balance:

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Ageo, Japan

Junichi Matsunaga