JP3262113B2 - Solder alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder alloy mainly used for metal joining of electronic equipment, and more particularly to a solder alloy which does not contain lead and has no pollution and is environmentally friendly.

[0002]

2. Description of the Related Art When performing solder bonding in electronic equipment, a solder alloy has a desired bonding temperature, good wettability at the time of bonding, and excellent thermal fatigue strength, ductility, and heat resistance. Is required. Also, it is desired that the solder alloy does not contain lead from environmental considerations. Conventional solder alloys include Sn-Pb alloy, Sn-Ag alloy, Sn-Sb alloy and Sn-Bi alloy.

[0003]

A typical Sn-Pb alloy, 63Sn-37Pb (63wt% Sn-37wt% Pb), has a eutectic temperature of 18%.
(Having 3 ° C) contains lead, so it causes lead pollution and is not environmentally friendly. As lead-free solder alloys replacing 63Sn-37Pb solder, there are Sn-Ag alloy (Sn-3.5Ag, eutectic temperature 221 ° C) and Sn-Sb alloy (Sn-9Sb, peritectic temperature 246 ° C). Since these alloys have a higher melting point than 63Sn-37Pb eutectic solder and have a problem of heat resistance at the time of joining depending on electronic components, solder alloys lower than these melting points are desired. As a method of lowering the melting point, Bi or In is added to Sn. The 42Sn-58Bi alloy has a eutectic temperature of 139 ° C and the 52Sn-48In alloy has a eutectic temperature of 117 ° C.

As a lead-free alloy having a low melting point, Sn
Sn-Bi alloy having a composition of -7.5Bi-2.0Ag-0.5Cu is disclosed in JP-A-8-206874 and Scripta Materialia, Vol. 38, No. 9,
pp1333-1340, 1998. However, lead-free Sn-based alloys have poor wettability and poor bonding properties compared to Sn-Pb alloys because Sn is easily oxidized. In addition, Bi and In, which are additive elements that lower the melting point of lead-free Sn-based solder alloys, are more easily oxidized than Sn,
The above-mentioned Sn-Bi alloy and Sn-In alloy have a problem that the bonding property is unstable. In addition, when Bi is added, it tends to be hard and brittle, so that the thermal fatigue strength is reduced.

The present invention has been made in view of the above points, and has as its object to improve the wettability of a conventional Sn-Bi alloy so that the melting point of the Sn-Ag alloy is lower than the eutectic point of 221 ° C. It is an object of the present invention to provide a new lead-free Sn-Bi-based alloy having a good performance.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide a composition containing tin as a main component, bismuth not more than 21 wt%, silver not more than 4 wt%, and copper
This is achieved by containing 2 wt% or less (including 0) and nickel of 0.2 wt% or less.

In addition, tin is a main component, and bismuth is 21 wt.
%, Not more than 4 wt% of silver, not more than 2 wt% of copper (including 0), and not more than 0.1 wt% of germanium.

According to the present invention, as a most preferable composition, tin is a main component, bismuth is 21 wt% or less, silver is 4 wt% or less, copper is 2 wt% or less (including 0), nickel is 0.2 wt% or less.
It is achieved by containing not more than 0.1 wt% of germanium.

The addition of Ag to Sn improves the heat resistance, fatigue strength and wettability of the alloy. Ag is present at a high concentration at the grain boundaries, and the movement of the grain boundaries is suppressed, thereby improving the thermal fatigue strength of the alloy. Since the Sn-Ag alloy has a eutectic point of 221 ° C when the amount of Ag added is 3.5 wt%, if the amount of Ag exceeds 3.5 wt%, the liquidus temperature will increase, and the joining temperature will be secured. Need to be higher. The strength is almost the same level even if the amount of Ag exceeds 3.5 wt%. Therefore, an appropriate amount of Ag added is 4 wt% or less.

[0010] The addition of Cu improves the strength and heat resistance of the alloy without impairing the wettability. When the joining metal is Cu, there is an effect of suppressing the elution of Cu from the joining metal into the solder alloy. When Cu is added at 3 wt% or more, the liquidus temperature rises sharply. In the present invention, the CuSn intermetallic compound is also formed in order to prevent the fatigue strength from being reduced due to excessive formation.
Was added at 2 wt% or less.

[0011] The addition of Bi lowers the melting point of the Sn-based alloy. As described above, the Sn-Bi system has a eutectic point of 139 ° C. when the Bi content is 58 wt% and the eutectic composition is 58 wt%. As shown in the phase diagram of the Sn-Bi binary system, the Sn-Bi alloy begins to melt at a temperature of 139 ° C. when the Bi content is 21 wt% or more. In the composition range where the amount of Bi added is 21 wt% or less, both the liquidus temperature and the solidus temperature decrease.

FIG. 1 is a phase diagram of the Sn-Bi binary system. The addition of Ni increases the thermal stability of the alloy due to the higher melting temperature of Ni. Also, in the case where Ni was added to the Sn-Ag-based alloy, the inventors' experiments revealed that the thermal fatigue strength was improved. Therefore, improvement of thermal fatigue strength is expected even when Ni is added to the Sn-Bi-Ag alloy. Further, as will be described later, it is clear from the experimental results of the present inventors that the wettability is improved.

When Ge is added, a thin oxide film of Ge is formed in preference to Sn when the solder is melted, and the oxidation of solder components such as Sn is suppressed. If the addition amount is too large, the oxide film of Ge becomes too thick, which adversely affects the bondability. Further, as described later, by adding both Ni and Ge, the wettability is further improved by the synergistic effect. Further, it has been clarified that the addition of both increases the creep deformation resistance and further improves the heat resistance.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Solder alloys are Sn, Bi, Ag, Cu, Ni, G
e was prepared by melting each raw material in an electric furnace. Each raw material used had a purity of 99.99% or more. Sn as the main component, Bi
21 wt% or less, Ag 4 wt% or less, Cu 2 wt% or less, Ni 0.2 w
Sn-Bi alloy containing t% or less, or
21 wt% or less, Ag 4 wt% or less, Cu 2 wt% or less, Ni 0.2 w
An alloy containing t% or less and Ge of 0.1 wt% or less is produced.

[0015] A tensile test of the obtained Sn-Bi-based solder alloy was carried out at room temperature using a test piece having a diameter of 3 mm.
The wettability was measured by a meniscograph method at 270 ° C. for an alloy containing 2 wt% of Bi and at 250 ° C. for an alloy containing 7.5 to 21 wt% of Bi.

[0016]

[Example] As an example, Bi was added to the solder composition Sn-2.0Ag.
~ 21wt% added alloy (7.5wt% added alloy has melting point of 2
The melting point of the alloy added at 12 ° C and 21 wt% is 185 ° C).
Add 0.5wt%, and further add Ni and Ge respectively 0.1wt%, 0.05w
Addition of t%, Sn-2.0Bi-2.0Ag-0.5Cu-0.1Ni alloy, Sn-2.0
Bi-2.0Ag-0.5Cu-0.1Ni-0.05Ge alloy, Sn-7.5Bi-2.0Ag-0.
5Cu-0.1Ni alloy, Sn-7.5Bi-2.0Ag-0.5Cu-0.05Ge alloy, or Sn-7.5Bi-2.0Ag-0.5Cu-0.1Ni-0.05Ge alloy, Sn-21Bi
-2.0Ag-0.5Cu-0.1Ni alloy, Sn-21Bi-2.0Ag-0.5Cu-0.1Ni-
A 0.05Ge alloy was produced. Tensile strength, elongation (ductility) and wetting force of the obtained Sn-Bi alloy were measured. In order to compare and better understand the effect of Ni addition, Sn-2.0Bi-2.0Ag alloy, Sn
-2.0Bi-2.0Ag-0.07Ni alloy, Sn-2.0Bi-2.0Ag-0.1Ni alloy,
Sn-7.5Bi-2.0Ag alloy, Sn-7.5Bi-2.0Ag-0.5Cu alloy, Sn-
7.5Bi-2.0Ag-0.1Ni alloy, Sn-21Bi-2.0Ag alloy, Sn-21Bi-2.
A 0Ag-0.5Cu alloy was prepared, and the characteristics were evaluated in the same manner.

The results are shown in Table 1.

【table 1 】 When Ni, Cu and further Ge are added to Sn-2.0Bi-2.0Ag alloy,
Wettability is better than Sn-2.0Bi-2.0Ag alloy. Sn-7.5Bi-
Addition of Cu or Ni to 2.0Ag alloy makes Sn-7.5Bi-
Better than 2.0Ag alloy. Sn-7.5Bi-2.0Ag-0.5Cu alloy with N
Addition of i or Ge further improves the wettability. Ni
When both Ge and Ge are added, the wettability increases with Ni and
It is further improved than when Ge is added alone.

Further, Sn-21Bi-2.0Ag-0.5Cu-0.1Ni alloy,
Or Sn-21Bi-2.0Ag-0.5Cu-0.1Ni-0.05Ge alloy is Sn-21B
Improved wettability compared to i-2.0Ag alloy or Sn-21Bi-2.0Ag-0.5Cu alloy.

In the Sn-7.5Bi-2.0Ag alloy system, Sn-2.0Bi-2.0
Elongation is lower than Ag alloy system and Sn-21Bi-2.0Ag alloy system. Sn-7.5Bi with 0.5wt% of Cu added to Sn-7.5Bi-2.0Ag alloy
-2.0Ag-0.5Cu alloy increases both tensile strength and elongation. Sn-7.5Bi with 0.1wt% Ni added to Sn-7.5Bi-2.0Ag alloy
The -2.0Ag-0.1Ni alloy decreases both tensile strength and elongation. However, the elongation of the Sn-7.5Bi-2.0Ag-0.5Cu-0.1Ni alloy with both Cu and Ni added at 0.5 wt% and 0.1 wt%, respectively, was Sn-7.5
It is larger than Bi-2.0Ag-0.1Ni alloy, and the decrease in elongation decreases. Ni tends to form an intermetallic compound with Bi, causing a decrease in elongation.However, when Cu is added together with Ni, Cu and Ni form a solid solution, preventing the formation of intermetallic compounds and reducing the decrease in elongation. It is presumed to have been done. Therefore Sn
-7.5Bi-2.0Ag-0.5Cu-0.1Ni alloy has tensile strength, elongation,
It is a Sn-Bi alloy with good wettability.

Ge suppresses the oxidation of Sn, but consumes less by oxidation on the molten surface than phosphorus, which has a similar effect,
Has a stable Sn oxidation inhibiting action. When a solder alloy powder is used for cream solder, Ge forms a thin oxide film on the surface, and is effective in producing spherical particles due to surface tension and in the oxidation resistance of the particles. In addition, 0.1 wt% Ni was added to Sn-2Bi-2Ag.
And further, 0.5 wt% Cu and 0.05 wt% Ge were added, and the creep deformation characteristics in each case were examined at 125 ° C. and 1 kg / mm 2 using a 3 mmφ test piece. Table 2 shows the results organized by the creep strain rate.

[Table 2] It can be seen that the creep strain rate becomes smaller and the creep deformation resistance becomes larger and the heat resistance becomes more excellent with each addition.

The eutectic composition of the SnAgCu-based alloy is Sn 4.7 wt%
Ag1.7wt% Cu, Sn3.5wt% Ag0.7wt% Cu and the like are known.
The above-mentioned Sn-7.5Bi-2.0Ag-0.5Cu-0.1Ni-0.05Ge alloy has a Cu content of 0.5 wt%, but considering the composition of the ternary eutectic alloy described above, the Cu content is Sn- even if increased to 2.0 wt%
The effect of the 7.5Bi-2.0Ag-0.5Cu-0.1Ni-0.05Ge alloy is maintained. Although the solid solution limit of Ni to Sn is not clear, the eutectic point of Sn-Ni is 0.15wt% Ni (231.2 ° C), 0.1
8wt% Ni (232 ℃) has been reported (Constitution of Bin
ary Alloys, Second Edition, Max Hansen and Kurt A
nderko, McGRAW-HILL Book Company), and Ni C
Considering the solid solution for u, the effect of the Sn-7.5Bi-2.0Ag-0.5Cu-0.1Ni-0.05Ge alloy is maintained even when the Ni content is increased to 0.2 wt%. If the amount of Bi added is 21 wt% or less, the Sn-Bi-based alloy crystallizes with Sn as the primary crystal during solidification.
The effects of Bi-2.0Ag-0.5Cu-0.1Ni-0.05Ge alloy are maintained.

[0022]

According to the present invention, tin is a main component, bismuth is 21 wt% or less, silver is 4 wt% or less, copper is 2 wt% or less, nickel is 0.2 wt% or less, and germanium is 0.1 wt% or less. Thus, a novel lead-free Sn-Bi-based alloy having a lower melting point than eutectic point 221 of Sn-Ag alloy, good wettability, and excellent heat resistance can be obtained.

[Brief description of the drawings]

Fig. 1 Sn-Bi binary phase diagram 1

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-34376 (JP, A) JP-A-10-230384 (JP, A) JP-A-11-77366 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B23K 35/26 310 C22C 13/02 H05K 3/34 512

Claims (1)

(57) [Claims] (1) It contains tin as a main component, bismuth at 21 wt% or less, silver at 4 wt% or less, copper at 2 wt% or less (including 0), nickel at 0.2 wt% or less, and germanium at 0.1 wt% or less. A solder alloy.