JP3423387B2 - Solder alloy for electronic components - 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 having excellent thermal fatigue resistance, and is used, for example, when an electronic circuit part is soldered to a printed circuit board by a flow method.

[0002]

2. Description of the Related Art A reflow method or a flow method is used for mounting electronic circuit parts such as semiconductor elements on a printed circuit board. In the reflow method, cream solder (kneaded product of low melting point solder powder, flux and solvent)
The chip-type circuit component is temporarily fixed at a predetermined position by the adhesive force of the cream solder, and then introduced into a heating furnace to melt the solder for soldering.

Further, in the flow method, a lead of a discreet component is inserted into a spool of a printed circuit board, and molten solder is attached to the insertion portion by a dipping method, a jet method or the like to solder. I am adding.

In the electronic circuit component mounted as described above, a heat cycle is caused by the heat of the electronic circuit component itself and ambient conditions, and the solder at the joint expands.
Since it contracts and thermal stress is repeatedly generated, the solder joint is required to have durability against such repeated stress, that is, thermal fatigue resistance.

Conventionally, in order to improve the thermal fatigue resistance of the low melting point solder used in the above reflow method, for example, Sn is used.
-Adding a small amount of Cu to the Bi-Pb alloy (S
n: 20 to 47% by weight, Bi: 2 to 12% by weight, Cu:
0.03-0.5% by weight and the balance Pb) have been proposed (Japanese Patent Publication No. 1-24599).

[0006]

In the above flow method, Sn-Pb type eutectic solder is usually used, and this solder has a higher melting point than the low melting point solder and is excellent in mechanical properties. It also excels in heat fatigue resistance. However, with the recent improvement in the performance of electronic devices, even in this Sn-Pb-based solder, further improvement in heat resistance fatigue resistance of the solder joint is required.
.About.90% by weight, Cu: 0.5 to 3.0% by weight, Ag: 0.5 to 4.0% by weight, and a balance of Sn: solder alloy is proposed (JP-A-51-54056). Gazette).
However, since Ag is an additive component, the cost is high.

To improve the thermal fatigue resistance of solder joints,
Mechanical properties such as tensile strength, elongation and creep of solder,
It is effective to improve the interfacial bonding strength. However, suitable solidus and liquidus of solder (small difference, solidification from liquid to solid and dissolution from solid to liquid occur instantly), fluidity or wettability of molten solder, etc. It is important in terms of soldering workability.

An object of the present invention is to use Sn-- when soldering electronic circuit parts to a printed circuit board by the flow method.
An object of the present invention is to provide a solder alloy capable of improving the thermal fatigue resistance while guaranteeing the workability of soldering by adding a low-priced metal such as Bi, Cu, Sb to the Pb-based solder in a specific range.

[0009]

The solder alloy for electronic parts according to the present invention has a Sn content of 50 to 70 wt% and a Bi content of 0.1.
.About.2.0 wt%, Cu 0.03 to 0.3 wt% ( 0.
(Excluding 03% by weight) , Sb is 0.1 to 2.0% by weight, and the balance is Pb. 0.002 to 0.5 parts by weight of P is added to 100 parts by weight of this composition. It can also be added.

In the alloy of the present invention, the additive element (B
i, Cu, Sb) is usually contained as an impurity, and 0.003% by weight of Zn is added in accordance with the Class A chemical components defined in JIS-Z-3282-Table 3.
Hereinafter, Fe is 0.03 wt% or less, Al is 0.005 wt% or less, As is 0.03 wt% or less, and Cd is 0.00.
It is allowed to be contained in the range of 5% by weight or less.

In the solder alloy of the present invention, the Sn-Pb system is used as a base for mounting electronic circuit components on a printed circuit board by using the existing flow equipment as it is, and the Sn content is 50 to 70 weight. %, The workability of soldering is considerably deteriorated as compared with the Sn-Pb eutectic alloy, and the liquidus line becomes high, so that the thermal shock of the printed circuit board or the electronic circuit parts is caused when the content is 50% by weight or less. This is because the heat shock becomes severe and the thermal shock becomes severe even at 70% by weight or more, and the cost becomes high.

The addition of Bi, Cu, and Sb is to enhance the mechanical strength of the solder.
More than 1 wt%, the addition amount of Cu exceeds 0.03% by weight,
The reason why the amount of Sb added is 0.1% by weight or more is that it is difficult to satisfactorily increase the mechanical strength if the amount is less than 0.1%. Cu
Addition amount 0.03% by weight is specified in JIS-Z-3282A class
The upper limit of the Cu content as an impurity was excluded. B
The reason why the amount of i added is 2.0% by weight or less is that addition of more than this not only leads to coarsening of the solder structure, but also reduces the viscosity of the solder itself, reduces elongation, and avoids brittleness. Because I can't. The reason why the amount of Cu added is 0.3% by weight or less is that the liquidus temperature rises and the thermal shock of the printed circuit board and electronic circuit components becomes severe, and the fluidity of the solder decreases, if Cu is added more than this amount. Is. S
The reason why the addition amount of b is 2.0% by weight or less is that if it is added more than this, the solder becomes a hard and brittle structure, the elongation is lowered, the interfacial bonding strength is lowered, and the fluidity is further deteriorated. This is because the attaching workability is reduced.

Thus, the specified amount of Bi, Cu, Sb
The addition of Al enhances mechanical properties such as mechanical strength, extensibility, and creep of the solder itself by these synergistic effects. In this case, the solidus line and the liquidus line are well brought close to each other and the semi-molten state is obtained. To prevent coarsening of the solder structure, effectively promote the improvement of its mechanical properties, and further form an alloy layer with a robust structure at the soldering interface to increase the bonding strength and heat fatigue resistance. The characteristics are improved.

In the invention described in claim 2, the reason why P is added is that oxidation under melting is suppressed, deterioration of mechanical strength of the joint due to inclusion of the oxide is prevented, and Cu and Sb are added. This is to compensate for the decrease in wettability due to the addition, and the reason why the amount of P added is 0.002 to 0.5 parts by weight is that it is difficult to achieve the effect satisfactorily with 0.002 parts by weight or less. This is because if the amount is 5 parts by weight or more, the solder becomes brittle. The solder alloy according to the present invention can be used not only in the solder bath by the flow method but also in the form of rod-shaped or linear, slightly-cored solder or powder.

[0015]

The liquidus temperature can be suppressed to about 185 ° C. to 200 ° C., and the soldering by the flow method can be performed safely without fear of thermal damage to the printed circuit board or electronic circuit parts. Further, the temperature difference between the liquidus line and the solidus line is small, the period of the semi-molten state until the flow solder is solidified can be sufficiently shortened, the coarsening of the structure of the solder at the joint can be well prevented, and the uniform Can be a fine organization. Furthermore, the flowability or wettability of the flow solder is excellent.

Therefore, it is possible to perform soldering by the flow method with good workability while eliminating soldering defects.

In the solder alloy of the present invention, the mechanical strength and elongation of the solder itself are excellent, and since the adhesive strength at the solder joint interface can be increased, the durability of the solder joint portion against repeated stress, that is, Excellent in heat fatigue resistance. Therefore, according to the present invention, it is possible to perform soldering by the flow method with excellent thermal fatigue resistance while ensuring good workability.

[0018]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. The tensile strength and elongation in the following examples and comparative examples are JIS-Z-22 for each alloy composition.
Prepare 20 test pieces according to the regulations of No. 01-4, and
Tensile speed of 5 mm / mi using a docel type universal testing machine
n is an average value of measurement values measured at a temperature of 20 ° C.

Further, the defect occurrence rate in the heat cycle test is 125 ° C. for 20 samples soldered by a flow method using a jet bath with discrete components on a paper phenol printed circuit board. The heat cycle test was carried out for 200 cycles with heating for 1 hour and cooling at -55 ° C for 1 hour as one cycle, and the presence or absence of defects such as wrinkles, cracks, and peeling at the solder joints was observed and determined.

Impurities other than the additive element in each of the Examples and Comparative Examples are as specified in JIS-Z-3282-Table 3 above.

Example 1 Sn: 63% by weight, Bi: 0.6% by weight, Cu: 0.0
The alloy composition is 9% by weight, Sb: 0.6% by weight, and the balance is Pb. The tensile strength is 6.767 kg / mm 2 and the elongation is 34.2.
The rate of occurrence of defects in the heat cycle test was 0%. The liquidus temperature is approximately 190 ° C.

Comparative Example 1 Sn: 63% by weight, the balance of Pb is an alloy composition close to the eutectic, tensile strength is 4.750 kg / mm, elongation is 32.32.
%, And the failure occurrence rate in the heat cycle test was 40%. The liquidus temperature is approximately 185 ° C. Example 1
The soldering workability was about the same as in Comparative Example 1.
Therefore, according to Example 1, it is clear that the thermal fatigue resistance can be sufficiently improved as compared with the conventional Sn-Pb-based eutectic solder without impairing the soldering workability.

Comparative Example 2 The same composition as in Example 1 except that the addition of Bi and Cu was omitted (Sn: 63% by weight,
Sb: 0.6% by weight, balance Pb). Tensile strength is 5.0
It was 31 kg / mm 2, the elongation was 30.98%, and the failure rate in the heat cycle test was 50%.

Comparative Example 3 Example 1 is the same as Example 1 except that the addition of Bi is omitted.
(Sn: 63% by weight, Cu: 0.0
9% by weight, Sb: 0.6% by weight, balance Pb). The tensile strength was 5.995 kg / mm 2, the elongation was 30.89%, and the failure rate in the heat cycle test was 40%.

Comparative Example 4 Example 1 is the same as Example 1 except that the addition of Cu is omitted.
(Sn: 63% by weight, Bi: 0.6
% By weight, Sb: 0.6% by weight, balance Pb). The tensile strength is 6.185 kg / mm, the elongation is 32.71%,
The failure occurrence rate in the cycle test was 10%.

Comparative Example 5 Example 1 is the same as Example 1 except that the addition of Sb is omitted.
(Sn: 63% by weight, Bi: 0.6
% By weight, Cu: 0.09% by weight, balance Pb). The tensile strength was 6.274 kg / mm 2, the elongation was 31.69%, and the failure rate in the heat cycle test was 15%. From the comparison between Comparative Examples 2 to 5 and Example 1, in the present invention, B
It is clear that the thermal fatigue resistance is improved by the synergistic action of i, Cu and Sb.

Examples 2 to 4 The same composition as in Example 1 except that 0.01 parts by weight, 0.1 parts by weight, and 0.5 parts by weight of P were added to 100 parts by weight of the composition of Example 1. . Tensile strength is 6.5-6.8
kg / mm, the elongation was 33 to 34.5%, the failure rate in the heat cycle test was 0, and the thermal fatigue resistance was substantially the same as in Example 1, but in the solder bath. The generation of oxides could be suppressed to a very low level. Therefore, it is advantageous in managing the solder bath.

Example 5 Sn: 63% by weight, Bi: 0.1% by weight, Cu: 0.0
The alloy composition is 3% by weight, Sb: 0.1% by weight, and the balance is Pb. The tensile strength is 6.20 kg / mm 2 and the elongation is 32.75.
%, And the failure occurrence rate in the heat cycle test was 0%. The liquidus temperature is approximately 185 ° C.

Example 6 Sn: 63% by weight, Bi: 2.0% by weight, Cu: 0.3
% By weight, Sb: 2.0% by weight, the balance is Pb, and the alloy composition is 6.53 kg / mm in tensile strength and 33.75% in elongation.
The failure rate in the heat cycle test was 0%. The liquidus temperature is approximately 200 ° C.

From the test results of Examples 5 and 6, it was confirmed that Bi
It can be presumed that in the range of 0.1 to 2.0% by weight, Cu in the range of 0.03 to 0.3% by weight, and Sb in the range of 0.1 to 2.0% by weight, they contribute to the improvement of the thermal fatigue resistance.

Example 7 The same composition as in Example 1 was used except that Sn was 70% by weight. The mechanical properties were slightly better than those of Example 1, and the failure rate in the heat cycle test was 0%. However, if the addition amount of Sn exceeds 70% by weight, the liquidus temperature becomes high, which causes a problem of thermal damage to the printed circuit board and electronic circuit components.

Example 8 The same composition as in Example 1 was used except that Sn was 50% by weight. The mechanical properties were slightly inferior to those of Example 1, but the failure rate in the heat cycle test was 0%. When the addition amount of Sn is 50% by weight or less, the liquidus temperature becomes high, which causes a problem of thermal damage to the printed circuit board and electronic circuit parts.

From the test results of Example 1 and Examples 7 and 8, it can be estimated that the improvement of the above-mentioned thermal fatigue resistance is effectively achieved in the range of 50 to 70 wt% Sn.

[0034]

According to the present invention, the liquidus temperature, solidus temperature, fluidity or wettability is approximated to that of the conventional Sn-Pb type solder, while the tensile strength, elongation and interfacial bonding strength are improved. As a result, the existing flow soldering equipment can be used to perform soldering excellent in thermal fatigue resistance, and the continuity reliability and stability of the electronic circuit component mounting board can be guaranteed for a long time.

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Claims (2)

(57) [Claims] 1. Sn is 50 to 70% by weight and Bi is 0.1 to 0.1%.
2.0 wt%, Cu 0.03-0.3 wt% ( however
0.03 excluding wt%), Sb 0.1 to 2.0 wt%, the electronic component'm <br/> alloy, characterized in that the balance of Pb. 2. A solder alloy for electronic parts, wherein 0.002 to 0.5 part by weight of P is added to 100 parts by weight of the composition according to claim 1.