Alloys or metallic compositions – Tin base – Copper containing
Reexamination Certificate
2000-01-27
2002-04-02
King, Roy (Department: 1742)
Alloys or metallic compositions
Tin base
Copper containing
C420S562000
Reexamination Certificate
active
06365097
ABSTRACT:
This application is based on Patent application No. 11-22403 filed on Jan. 29, 1999 in Japan, the content of which is incorporated herein to by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention primarily relates to a solder alloy mainly used in metal bonding of an electric device. In particular, the present invention relates to a lead free, eco-friendly solder alloy that does not cause pollution.
2. Description of Related Art
In an electric device, when solder bonding is performed, a solder alloy is required to have a desired bonding temperature, proper wettability during bonding, and superior thermal fatigue strength, ductility, and heat resistance. In addition, such a solder alloy is desired to be free of lead in consideration of environment conservation.
Conventional solder alloys include Sn—Pb, Sn—Ag, Sn—Sb, and Sn—Bi alloys.
A typical Sn—Pb alloy, 63Sn-37Pb (which means 63 wt.% Sn- 37 wt.% Pb, and has an eutectic point of 183° C.) contains lead. Thus, such Sn—Pb alloy may cause lead pollution, and is not eco-friendly. Lead-free solder alloys which may be substituted for 63Sn-37Pb include an Sn—Ag alloy (Sn-3.5 Ag, eutectic point of 221° C.) and an Sn—Sb alloy (Sn-9 Sb and peritectic temperature of 246° C.). These alloys have higher melting points than the 63Sn-37Pb eutectic solder, and have a problem with heat resistance during bonding for some electronic parts. Thus, a solder alloy having a melting point lower than these melting points is desired. A method for lowering a melting point includes an addition of Bi or In to Sn. A 42Sn-58Bi alloy has an eutectic point of 139° C., and a 52Sn-48In alloy has a eutectic point of 117° C.
As a lead-free alloy with a low melting point, a Sn—Bi based alloy having a composition of Sn-7.5 Bi-2.0 Ag-0.5 Cu has been disclosed in Japanese Patent Application Laid-Open No. 8-206874 and Scripta Materialia, Vol. 38, No. 9, pp. 1333-1340, 1998. However, lead-free Sn-based alloys have poorer wettability and bonding properties than Sn—Pb alloys, since Sn is prone to oxidation. Further, Bi and In that are additive elements for lowering the melting point of lead-free Sn-based solder alloys are more prone to be oxidized than Sn. Thus, there has been a problem that the above mentioned Sn—Bi based alloys and Sn—In alloys have unstable solderability. In addition, when Bi is added, it tends to become hard and brittle. Thus, there has been another problem that the above mentioned alloys have lower thermal fatigue strength.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above mentioned problems. It is an object of the present invention to provide a novel lead-free Sn—Bi based alloy having improved wettability and heat resistance as compared to conventional Sn—Bi based alloys, a lower melting point than the eutectic point of 221° C. of the Sn—Ag alloy, and proper solderability.
According to a first aspect of the present invention, the above mentioned object is achieved by providing a solder alloy containing tin, as a major component, and 21 wt.% or less bismuth, 4 wt.% or less silver, 2 wt.% or less (inclusive of zero) copper, and 0.2 wt.% or less nickel.
According to a second aspect of the present invention, the above object is achieved by providing a solder alloy containing tin, as a major component, and 21 wt.% or less bismuth, 4 wt.% or less silver, 2 wt.% or less (inclusive of zero) copper, and 0.1 wt.% or less germanium.
According to a third aspect of the present invention, the above object is achieved by providing a solder alloy containing tin, as a major component, and 21 wt.% or less bismuth, 4 wt.% or less silver, 2 wt.% or less (inclusive of zero) copper, 0.2 wt.% or less nickel, and 0.1 wt.% or less germanium.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5863493 (1999-01-01), Achari et al.
patent: 5980822 (1999-11-01), Moon et al.
patent: 19752215 (1998-09-01), None
patent: 8-206874 (1996-08-01), None
patent: 10-034376 (1998-02-01), None
patent: 10-230384 (1998-09-01), None
“Microstructural Features of Lift-Off Phenomenon in Through-Hole Circuit Soldered by Sn-Bi Alloy”Suganuma Scripta Materialia, vol. 38, No. 9, Apr. 3, 1998, pp. 1333-1340.
Binary Alloy Phase Diagrams Volumne 1, Massalaki et al, ed. 1986 p. 540.
Shiokawa Kunio
Tada Shinji
Yamashita Mitsuo
Frank Robert J.
Fuji Electric & Co., Ltd.
Haddaway Keith G.
King Roy
McGuthry-Banks Tima
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