JPH10109187A - Solder alloy for fitting electronic parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drastically improve a heat fatigue resistance and to improve the reliability to the heat fatigue after fitting electronic parts while reducing defective ratio at the time of fitting the electronic parts by adding specific elements in specific wt. ratios in a solder alloy for fitting the electronic parts. SOLUTION: To 100wt. parts Sn-Pb-Bi base solder alloy containing by wt.% of 40-70% Sn, 2.5-15% Bi and the balance Pb, 0.3-2.0wt. parts Cu, 0.1-2.0wt. parts Sb and further, 0.5-3.5wt. parts Ag are added. Further, as necessary requires, restraining action to Manhattan phenomenon of the Sn-Pb-Bi base solder alloy is sufficiently maintained by adding <=0.5wt. parts P or Ga. Furthermore, the powdery solder used as a cream solder is made to 65-20μm grain diameter, and the composition of flux is made to 20-60wt.% resin, 0.2-5wt.% activator, 3-20wt.% thixo agent and the balance solvent. The composition of the cream solder is ordinarily made to 85-93wt.% powdery solder and the balance flux.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder alloy used for mounting an electronic component, and more particularly, to a solder alloy suitably used for mounting an electronic component by a reflow method.

[0002]

2. Description of the Related Art When electronic parts are mounted on a circuit board, a reflow method is used, that is, the electronic parts are cream soldered at a predetermined position on the circuit board (a mixture of solder powder and flux).
In some cases, the solder paste is melted by passing it through a heating furnace to melt the cream solder, and then the solder is cooled and solidified to electrically and mechanically join the electronic component to the circuit board. Traditionally, solder powder for cream solder has a P
b-Sn eutectic solder has been used. This Pb-Sn
In eutectic, the solidus temperature and liquidus temperature match, so
When the melting point is reached, there is an immediate transition from the solid phase to the liquid phase. In the above-mentioned reflow mounting, uneven heating of the electronic component is unavoidable, and the cream solder on one side electrode of the electronic component first reaches the melting point and is liquefied. The state where the cream solder of the side electrode remains in a solid phase occurs, the electronic component is raised by the surface tension due to the liquid phase of the cream solder of the one side electrode, and the other side electrode is lifted up (the so-called Manhattan phenomenon). ), Defective soldering may occur.

[0003] If a solder alloy having a difference between the solidus temperature and the liquidus temperature is used by setting the temperature difference in accordance with the above-mentioned non-uniform temperature difference, the use of a solder alloy can be improved. The above-mentioned one side electrode side is at an intermediate temperature between the solidus temperature and the liquidus temperature, so that the cream solder is in a semi-molten state (a mixed phase state of the solid phase and the liquid phase), and the other side electrode is a clear solder. Even if the solder is still in the solid state, the surface tension in the semi-molten state is small, so it is possible to prevent the electronic components from standing up. Thus, even if the cream solder on the other side electrode side is still in a semi-molten state, the difference in surface tension between the liquid phase state and the semi-molten state is small, so that it is possible to prevent the electronic component from rising. Become.

[0004] In view of the above, in order to prevent the Manhattan phenomenon by giving a difference between the liquidus temperature and the solidus temperature,
According to JIS Z 3282-1986, Sn43PbBi14
(43% by weight of Sn, 14% by weight of Bi, the balance Pb,
The solidus temperature is 135 ° C, the liquidus temperature is 165 ° C), and Sn46PbBi8 (solidus temperature 175 ° C,
Liquidus temperature 190 ° C) and Sn57PbBi3 (solidus temperature 175 ° C, liquidus temperature 185 ° C) are also known.

[0005]

In recent years, electronic components have become more complex, more sophisticated, and surface-mounting has been accelerated, the amount of heat generated by the electronic circuit board has been increased, and soldering has been performed based on the current heat cycle. The repetitive thermal stress applied to the attachment portion is becoming increasingly severe, and there is a demand for better thermal fatigue resistance. However, in the above-mentioned Sn-Pb-Bi-based solder alloy, voids are easily formed when the molten liquid phase is cooled and passes through a semi-molten state, and Bi is formed in Sn or Pb.
Dissolves easily to form a solid solution, so that Pb-Sn
The mechanical strength is lower than that of eutectic solder, and it is difficult to expect the above-mentioned improvement in thermal fatigue resistance. 2. Description of the Related Art Conventionally, there has been known a solder alloy for electronic components in which Cu is added in an amount of 0.2% by weight or less based on a Sn-Pb-Bi-based solder alloy (Japanese Patent Publication No. 24-5999).

However, the inventor of the present invention has made intensive studies to achieve the improvement of the thermal fatigue resistance while maintaining the Manhattan phenomenon suppressing action. By adding Cu and Sb at a specific ratio, the above-mentioned Cu alone is removed. It has been found that a remarkable improvement in thermal fatigue resistance, which cannot be achieved by addition, can be obtained. An object of the present invention is to achieve a dramatic improvement in thermal fatigue resistance while sufficiently maintaining the Manhattan phenomenon suppressing effect of a Sn-Pb-Bi-based solder alloy based on the above-mentioned unexpected experimental results.

[0007]

The solder alloy for mounting electronic parts according to the present invention comprises 40 to 70% by weight of Sn and Bi2.5.
0.3 to 2.0 parts by weight of Cu and 100 parts by weight of Sn-Pb-Bi based solder alloy of Pb
b 0.1 to 2.0 parts by weight and further 0.5 to 3.5 parts by weight of Ag are added, and further 0.5 parts by weight or less of P or Ga is added. Can be added. In the present invention, Sn is 40 to 70% by weight, Bi
2.5-15.0% by weight, the balance being Sn-Pb-B with Pb
By adding a specific amount of Cu and Sb, further Ag and, if necessary, P or Ga to the base of the i-based solder alloy, the action of suppressing the Manhattan phenomenon of the Sn-Pb-Bi-based solder alloy is sufficiently maintained. It is possible to dramatically improve the thermal fatigue resistance while performing the same.

In the present invention, Sn is contained in an amount of 40 to 70% by weight.
The reason is that if the content is less than 40% by weight, not only the workability of soldering is deteriorated, but also the alloy strength and the joining strength are remarkably reduced, the joining reliability is impaired, and the liquidus temperature is increased. The thermal shock to the substrate and the surface-mounted components during mounting becomes severe. On the other hand, if it exceeds 70% by weight, not only does the cost increase, but also the liquidus temperature increases as described above. This is because the thermal shock to the substrate and the surface mount component in the above becomes severe. In the present invention, B
The addition of i is for giving a difference between the solidus temperature and the liquidus temperature to suppress the Manhattan phenomenon, and the reason for adding 2.5 to 15.0% by weight is that 2.5% by weight is used. %, It is difficult to satisfactorily suppress the Manhattan phenomenon.
If the content exceeds 5.0% by weight, the elongation is reduced, the material becomes brittle, the mechanical strength is reduced, and it becomes difficult to guarantee the joining reliability.

In the present invention, the addition of Cu and Sb is intended to dramatically improve the thermal fatigue resistance while sufficiently maintaining the Manhattan phenomenon-suppressing action. Cu or Sb alone is not suitable for use alone. The added amount is Cu 0.3-2.
The reason for setting 0 parts by weight and 0.1 to 2.0 parts by weight of Sb is that within these ranges, a dramatic improvement in thermal fatigue resistance can be achieved,
In addition, if the Cu content is 2.0 parts by weight or more or the Sb content is 2.0 parts by weight or more, the liquidus temperature becomes high, and the thermal shock to the substrate and the surface-mounted electronic components during soldering becomes considerably severe. In the present invention, the addition of Ag causes the member to be joined to be A
In the case of g, there is a concern about poor bonding due to Ag erosion (Ag diffuses into the solder, also referred to as erosion). The reason for setting the addition amount to 0.5 to 3.5 parts by weight is that if it is less than 0.5 parts by weight, it is difficult to satisfactorily suppress Ag erosion, while if it exceeds 3.5 parts by weight, the cost increases. Alternatively, the liquidus temperature increases, and the thermal shock to the substrate and the surface-mounted electronic components during soldering becomes severe.

In the present invention, the addition of P or Ga is
This is to compensate for the decrease in the wettability of the solder alloy due to the added Cu or Sb and to suppress the oxidation under the melting of the solder alloy to prevent the strength of the solder joint portion from being reduced by the inclusion of the oxide. The reason for setting the content to 0.5 part by weight or less is that if the content exceeds 0.5 part by weight, the solder alloy will become brittle.

[0011] Solder alloys usually contain components other than additive elements as impurities.
According to the class A chemical composition specified in Table 3, the solder alloy according to the present invention also has a Z content.
n: 0.003% by weight or less, Fe: 0.03% by weight or less, Al: 0.005% by weight or less, As: 0.03% by weight or less, Cd: 0.005% by weight or less Is acceptable.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the base Sn-
Examples of the Pb-Bi-based solder alloy include Sn 43% by weight, Bi 14% by weight, and
The balance Pb (solidus temperature 135 ° C, liquidus temperature 165
° C) or known Sn 46% by weight, Bi8, balance Pb (solidus temperature 175 ° C, liquidus temperature 190 ° C)
n57, Bi3, and the balance Pb (solidus temperature 175 ° C., liquidus temperature 185 ° C.) and the like can be used.

The solder alloy for mounting electronic parts according to the present invention is suitably used as a cream solder in a reflow method. In this case, the powder solder can be obtained by, for example, a centrifugal spray method, and the particle diameter thereof is usually 65 to 20.
The composition of the flux is 20 to 60% by weight of rosin, 0.2 to 5% by weight of an activator, 3 to 20% by weight of a thixotropic agent, and the remainder is a solvent. The solder is 85 to 93% by weight, and the balance is flux.
In order to perform surface mounting by the reflow method, a cream solder is printed on a place where electronic components are to be mounted on a circuit board, and the electronic components are temporarily fixed by the adhesive strength of the cream solder. Through a heating furnace having a temperature several tens of degrees higher than the liquidus temperature, for example, an infrared heating furnace, to melt the cream solder, then cool and solidify the solder, and finally wash the flux residue. Done, and this ends the implementation.

In the solder alloy according to the present invention, Cu
And the amount of Sb added is within a range that can sufficiently maintain the Manhattan phenomenon suppressing action of the Sn-Pb-Bi-based solder alloy. Due to the uneven heating, the one-side electrode side of the electronic component has a solidus temperature and a solidus temperature. When the temperature reaches an intermediate temperature from the liquidus temperature, the cream solder is in a semi-molten state (a mixed phase state of a solid phase and a liquid phase), and the cream solder on the other side electrode side is still in a solid phase state. However, since the surface tension in the semi-molten state is small, it is possible to prevent the electronic component from standing up well.In addition, one side electrode side exceeds the liquidus temperature and becomes in a liquid state, and the other side electrode side has cream solder. Even though is still in a semi-molten state, since the difference in surface tension between the liquid phase state and the semi-molten state is small, the electronic component can be prevented from standing up.

The mechanism of the destruction (cracks and wrinkles) caused by the heat cycle of the soldered portion of the electronic component mounted by the reflow method is complicated,
It is based on the fact that thermal stress is generated based on the difference in thermal expansion / contraction coefficient between the solder and the board or electronic component, the difference in Young's modulus, the change in environmental temperature, etc. It is difficult to accurately grasp the thermal fatigue properties only by evaluating the tensile strength and elongation percentage of the solder alloy, and it is difficult to accurately grasp the wettability of the solder and the interface between the electrode and conductor and the solder. It is appropriate to reflect changes in the mechanical properties (structure strength, Young's modulus, elongation, thermal expansion / shrinkage coefficient, etc.) due to the formation of the alloy layer in (1). However, the bonding strength described below can sufficiently evaluate the thermal fatigue resistance by sufficiently reflecting the change in mechanical properties due to the wet state of the solder and the formation of the alloy layer at the interface, and the bonding strength is as follows. Required.

That is, two copper foils each having a width of 10 mm and a thickness of 0.5 mm are stacked with a gap therebetween, and a spacer is sandwiched at one end to set the gap to 0.5 mm. After applying the flux to the end, the molten solder is immersed in a molten solder bath to penetrate the molten solder to a depth of 10 mm between the gaps by capillary action, and after cooling and solidifying the solder,
After removing the spacer, the copper foil is bent outward at a right angle at the solder entry end, and the bent copper foils are used as tension terminals using a load cell universal testing machine at a pulling speed of 5 mm / mi.
n, tensile stress when breaking at a temperature of 20 ° C. (kgf /
mm ² ). According to this joint strength, unlike the tensile strength and elongation of the solder alloy, it is possible to reflect the change in mechanical strength and wettability due to the metallurgical reaction at the interface between the copper and the solder, and Thermal fatigue resistance can be evaluated accurately. Thus, in the implementation according to the present invention, C
Since u is added in an amount of 0.3 to 2.0 parts by weight and Sb in an amount of 0.1 to 2.0 parts by weight, excellent bonding strength is exhibited, and extremely excellent thermal fatigue resistance can be guaranteed.

[0017] The assurance of the thermal fatigue resistance is such that the formation of a mechanically fragile solid solution can be suppressed, the generation of voids can be eliminated, the wettability is excellent, and the alloy layer at the interface between the electrode or conductor and the solder can be prevented. This is presumed to be a result of preventing abnormal changes in mechanical properties (tissue strength, Young's modulus, elongation, thermal expansion / shrinkage coefficient, etc.) due to formation. Although the solder alloy for electronic parts according to the present invention is suitably used in the reflow method, it can also be used as a flow method and as a flux solder.

[0018]

EXAMPLES In the following Examples and Comparative Examples, the solder powder of the cream solder had a grain diameter of 63 to 63 by a centrifugal spray method.
Use a 38μm one, and use rosin 5
0.0% by weight, activator (cyclohexylamine hydrobromide) 1.0% by weight, thixotropic agent (hydrogenated castor oil)
5.0% by weight, the balance solvent (butyl carbitol) was used, and the mixture of cream solder was 90% by weight of solder powder,
The remaining flux was used. The Manhattan phenomenon occurrence rate was determined from 1000 samples in which a chip resistor having a chip size of 32 mm × 16 mm × 0.5 mm was mounted on a glass epoxy circuit board by a reflow method using a cream solder. Further, a heat cycle test was performed on the sample manufactured in the same manner as above, and the sample was heated at 125 ° C. for 1 hour.
One cycle of cooling at 55 ° C. for 1 hour was applied, and 500 cycles were applied. A solder joint having cracks, wrinkles, peeling, etc. was regarded as defective, and the number of samples was 100.

[Examples 1 to 8 and Comparative Examples 1 to 4] A Sn—Pb—Bi-based solder alloy based on
Bi 3% by weight and the balance Pb (solidus temperature 175 ° C., liquidus temperature 185 ° C.) are used, and the blending of the used solder alloy is as shown in Table 1 (the blending unit is part by weight).
Each bonding strength (the bonding strength of Example 1 is shown as 1. The bonding strength of Example 1 is 6.18 kgf / m.
m ² ) and the results of the heat cycle test are shown in Table 1.

[0020]

[Table 1]

As is clear from Table 1, in the examples, the failure occurrence rate in the heat cycle test was 0%, and this effect was due to the synergistic effect of Cu and Sb from the comparison with Comparative Examples 1 and 2. Can be presumed. Also, Cu0.3
If the amount is less than 0.1 parts by weight and Sb is less than 0.1 part by weight, the failure rate of the heat cycle test cannot be made zero. It is evident from Comparative Examples 3 and 4 that it cannot be set to 0, and the significance of limiting the added amounts of Cu and Sb in the present invention can be confirmed. The excellent thermal fatigue resistance of the example means that the failure rate of the heat cycle test was 0%.
And excellent bonding strength. The Manhattan phenomenon occurrence rate of the Sn-Pb eutectic solder alloy is 15% to 20%, and according to the present invention, the Manhattan phenomenon suppression effect of the base Sn-Pb-Bi-based solder alloy is sufficiently improved. It can be confirmed from Table 1 that it can be maintained.

Embodiments 9 to 16: Base Sn-Pb-
46% by weight of Sn, 8% by weight of Bi,
Remainder Pb (solidus temperature 175 ° C, liquidus temperature 190 ° C)
Table 2 shows the composition of the solder alloy used.
(The unit of blending is parts by weight). Table 2 shows the bonding strength (the bonding strength of Example 1 is shown as 1) and the results of the heat cycle test.

[0023]

[Table 2]

[Embodiments 17 to 24] Base Sn-Pb
In the Bi-based solder alloy, 43% by weight of Sn, 14% by weight of Bi, and the balance Pb (solidus temperature 135 ° C, liquidus temperature 165)
° C), and the composition of the used solder alloy is as shown in Table 3 (the unit of the composition is parts by weight). Each bonding strength (the bonding strength of Example 1 is shown as 1)
The results of the heat cycle test are as shown in Table 3.

[0025]

[Table 3]

[0026]

According to the solder alloy for electronic parts according to the present invention, the effect of suppressing the Manhattan phenomenon of the Sn-Pb-Bi solder alloy can be sufficiently maintained, and the thermal fatigue of the Sn-Pb-Bi solder alloy can be maintained. It is possible to remarkably improve disadvantages in heat resistance by resolving disadvantageous inferiority, and to remarkably improve reliability against heat fatigue after mounting while reducing the failure rate at the time of mounting electronic components.

Claims (3)

[Claims] 1. 40 to 70% by weight of Sn, 2.5 to 1% of Bi
5.0% by weight, the balance being 0.3 to 2.0 parts by weight of Cu and 100 parts by weight of Sn-Pb-Bi-based solder alloy of Pb
A solder alloy for mounting electronic components, wherein 0.1 to 2.0 parts by weight is added. 2. Sn 40 to 70% by weight, Bi 2.5 to 1
5.0% by weight, the balance being 0.3 to 2.0 parts by weight of Cu and 100 parts by weight of Sn-Pb-Bi-based solder alloy of Pb
A solder alloy for mounting electronic components, wherein 0.1 to 2.0 parts by weight and 0.5 to 3.5 parts by weight of Ag are added. 3. The solder alloy according to claim 1, wherein P or Ga is added in an amount of 0.5 part by weight or less.