JP2002042548A - Lead wire for electronic parts and manufacturing process thereof, and electronic parts using this wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lead wire for electronic parts, with good solder wettability, good bending processability and good slidability and its manufacturing method. SOLUTION: In the lead wire for the electronic parts wherein a reflow- processed Sn-Bi alloy layer 2 is formed on a conductive substrate 1, the concentration gradient of Bi is formed in which Bi concentration is gradually reduced in a thickness area 2A ranging from the surface 2a of the Sn-Bi alloy layer 2 to the position of half depth. Bi concentration in the surface layer part 2C from the surface 2a to the depth of 0.5 μm of the Sn-Bi alloy layer 2 is 2 wt.% or more, and the Bi concentration in a thickness area 2B from the thickness area 2A to an interface 2b with the conductive substrate 1 is 0.01 wt.% or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead wire for an electronic component having a Sn-Bi alloy layer formed on its surface, a method for manufacturing the same, and an electronic component using the lead wire. Excellent and smooth surface,
The present invention relates to a lead wire for electronic parts having good slipperiness and excellent bending workability, and a method for producing the same.

[0002]

2. Description of the Related Art A wire rod in which the surface of a conductive substrate made of Cu or Cu alloy is plated with Sn or Sn alloy is
A high-performance conductor having excellent conductivity and mechanical strength provided by Cu or Cu alloy, and having both corrosion resistance and good solderability provided by Sn or Sn alloy. Are widely used in the field of electric and electronic devices such as connectors and leads, and in the field of power cables.

In the above-mentioned wire rod, when the plating layer covering the conductive substrate is formed only of Sn, the solderability is deteriorated due to the surface oxidation, and whiskers are easily generated. There is a problem that the cause of the accident is likely to occur. Therefore, it is widely practiced to form the plating layer with a Sn alloy so that the above problem does not occur. In this case, a typical example of the Sn alloy is an Sn-Pb alloy, which has been frequently used.

[0004] However, since the Pb component in the Sn-Pb alloy may adversely affect the human body,
Recently, the use of Sn-Pb alloys has been shunned despite its excellent properties. for that reason,
In recent years, Pb-free Sn-Bi alloys have begun to be used as an alternative to this Sn-Pb alloy. However, in the case of a lead wire covered with this Sn—Bi alloy plating layer, Sn
Since the diffusion rate of the components is high, a Sn—Cu layer is formed at the interface between the base and the plating layer when a high-temperature heat treatment is performed. Usually, in soldering, since the plating layer dissolves in the solder bath, active Cu on the surface of the base is exposed, thereby realizing solder wetting. However, Sn-C
When the u layer is formed, active Cu does not appear on the substrate surface. As a result, there arises a problem that the solder wettability deteriorates.

In order to solve such a problem, the present inventors first form an Sn plating layer on the surface of a conductive substrate, and further form a plating layer made of an Sn—Bi alloy on the Sn plating layer. As a result, a lead wire having a plating layer having a two-layer structure was developed (see Japanese Patent Application Laid-Open No. 10-229152). In the case of this lead wire, the diffusion rate of Sn in the Sn plating layer located in the lower layer is higher than that of Sn-
The diffusion rate of Sn in the Bi alloy layer is smaller than that of the Bi alloy layer, and the lower Sn plating layer functions as a so-called Sn diffusion barrier. Therefore, the above-described Sn-Cu layer is hardly formed, and is covered with the conventional Sn plating layer alone. It has almost the same solder wettability as the lead wire.

[0006]

However, when assembling an electronic component using the above-described lead wire covered with the plating layer having the two-layer structure, the following problem occurs, and the produced electronic component has a problem. This has caused a decrease in reliability and a decrease in productivity during manufacturing. For example, when the plating layer on the front side is formed by matte plating,
Since irregularities are generated on the surface of the plating layer, when the lead wire is soldered to the land of the electronic component, the solder is easily peeled off from the lead wire, so that a defective product is easily generated, and the product is manufactured. The reliability of electronic components tends to be low. For this reason, it is necessary to frequently stop the production line and perform an inspection of the production line, thereby lowering productivity during production.

Therefore, lead wires for electronic parts include:
It is important to note that the solder wettability is excellent, and that the surface smoothness is good. In that case, if matte plating is performed at the time of forming the plating layer on the surface side, the surface becomes relatively smooth, and thus it is considered to be effective in that the occurrence of the above problem can be suppressed.

However, on the other hand, when matte plating is applied, a new problem arises in that the heat resistance of the plating layer is reduced and the bending workability is also reduced. Further, in order to enhance the surface smoothness, it is effective to perform a heat treatment such as a reflow treatment after the formation of the plating layer, to once melt the plating layer and then to re-solidify,
This method has been widely used conventionally.

However, what should be noted in this reflow treatment is that if too much reflow treatment is performed, the thickness of a single layer formed after re-solidification varies greatly, and the smoothness of the surface is improved. This means that solder wetting is reduced. In particular, if excessive reflow treatment is performed on a lead wire having a Sn-Bi alloy layer on the surface side, Bi on the surface side is diffused to all layers, so that the effect of Bi is lost and the plating layer is thin. Since the problem that the component of the base material is easily diffused in a portion also occurs, in the case of the reflow treatment for the Sn—Bi alloy layer, in addition to the problem of minimizing the thickness variation in the re-solidified layer,
The problem of optimizing the Bi concentration becomes important.

The present invention is to solve the above-mentioned problem in a lead wire for an electronic component having a Sn—Bi alloy layer formed on the surface by a reflow treatment, and has a small thickness variation in a resolidified layer. It is obvious that the solder wettability is excellent, and the surface smoothness is excellent, so the slip property is good, and furthermore, the lead wire for electronic parts that is also excellent in bending workability and manufacture it The purpose is to provide a method.

[0011]

In order to achieve the above object, the present invention provides an electronic component lead wire having a reflow-processed Sn-Bi alloy layer formed on a conductive substrate. In the thickness region from the surface of the Sn—Bi alloy layer to a position at half the depth thereof, a Bi concentration gradient in which the Bi concentration gradually decreases is formed.
The Bi concentration in the surface layer portion from the surface of the Bi alloy layer to a depth of 0.5 μm is 2% by weight or more, and Bi in the thickness region from the thickness region to the conductive substrate side;
A lead wire for an electronic component having a concentration of 0.01% by weight or less is provided.

The lead wire for the electronic component is formed of the Sn-B
When the thickness of the thickest part of the i-alloy layer is a (μm) and the thickness of the thinnest part is b (μm), between a and b,
It is preferable that the following equation is satisfied: 0.8 ≦ b / a ≦ 1.0. Further, in the present invention, there is provided a method for manufacturing a lead wire for an electronic component, comprising sequentially forming a Sn layer and a Sn—Bi alloy layer on a conductive substrate, and then performing a reflow treatment.

Further, according to the present invention, there is provided an electronic component assembled using the electronic component lead wire.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a lead wire according to the present invention has a conductive substrate 1 and a Sn-Bi covering the same.
It is composed of an alloy layer 2. First, the conductive substrate 1 is preferably made of Cu or a Cu alloy such as brass or phosphor bronze. Further, for example, a steel material may be used as a core material, and the surface thereof may be coated with the above-described Cu or Cu alloy.

Next, the Sn—Bi alloy layer 2 of the present invention
Is characterized by having the following requirements. (1) First, a single S formed by the reflow process
This is an n-Bi alloy layer. That is, as described later, a Sn layer and a Sn—Bi alloy layer are sequentially formed on the base material 1 by a plating method to form a plating layer having a two-layer structure, and the Sn layer and the Sn layer are formed by performing a reflow process on the plating layer. Part or all of the Bi alloy layer is a single Sn-Bi alloy layer formed by melting and then re-solidifying.

(2) Since the Sn—Bi alloy layer 2 is formed by a reflow process, there are inevitably a thickest portion and a thinnest portion. And the thickness of the thickest part is a
(Μm), and the thickness of the thinnest portion is b (μm). In this Sn—Bi alloy layer 2, the relationship between a and b is as follows: 0.8 ≦ b / a ≦ 1.0 Is preferably satisfied. If the b / a value is less than 0.8, Sn
Since the thickness variation of the Bi alloy layer 2 is large, the solder wettability of the lead wire is reduced. Since b / a = 1 indicates a state in which there is no variation in thickness, the b / a value cannot be larger than 1.

(3) In this Sn—Bi alloy layer 2, FIG.
In the thickness direction from the surface 2a to the interface 2b with the conductive substrate 1, the thickness region 2A extending from the surface 2a to a position at half the depth has a Bi concentration gradient formed as shown by. . Specifically, the Bi concentration gradient is such that the Bi concentration is higher on the surface 2a side, and the Bi concentration is reduced on the interface 2b side.

The Bi concentration gradient is formed as follows. That is, the melting of the plating layer having the two-layer structure of the Sn layer and the Sn—Bi alloy layer formed by plating proceeds from the surface toward the core because heat during the reflow process is conducted from the surface side. In the process of resolidification, the temperature descends from the core, so it begins with the resolidification of Sn, which is the lower Sn layer and has a relatively high melting point, and the Bi-containing eutectic composition, which has a relatively low melting point Will re-solidify while moving to the surface side. As a result, the above-mentioned concentration gradient of Bi is formed.

In the case of the Sn—Bi alloy layer 2, the surface B
Since the Bi concentration gradient is formed in the state where the i concentration is the highest, first, the solder wettability is improved by the action of Bi existing at a high concentration on the surface. In addition, the higher the Bi concentration, the lower the melting point of the Sn-Bi alloy, so that the surface side is liable to become liquid at the time of the reflow treatment. As a result, the surface of the re-solidified Sn-Bi alloy layer 2 after the reflow treatment is smoothed. Properties are improved, and good solder wettability is exhibited.

However, a high Bi concentration means that cracks are likely to occur during bending. However, in the case of the Sn—Bi alloy layer 2, since the Bi concentration is lower on the conductive substrate 1 side and the bending workability thereof is better, cracks are generated on the surface having the highest Bi concentration. However, the propagation of the cracks stops at a relatively shallow position, so that the deterioration of the corrosion resistance of the lead wire is suppressed.

(4) In the case of the Sn—Bi alloy layer 2, as shown in FIG. 2, assuming that a Bi concentration gradient is formed in the thickness region 2A described in (3). Thickness region 2C from 2a to a depth of 0.5 μm
Is 2% by weight or more, and the Bi concentration in the thickness region 2B from the thickness region 2A to the interface 2b with the conductive substrate is 0.01% by weight or less.

In general, the surface of the Sn layer or the Sn—Bi alloy layer after the reflow treatment has a thickness of 1 mm.
A natural oxide film of about 2 nm is formed. And B
In the case of a Sn layer containing no i, for example, in the process of undergoing a heat treatment associated with component mounting, this oxide film grows to about 20 to 30 nm, causing a decrease in solder wettability.

However, in the case of the Sn—Bi alloy layer, the growth of the oxide film stops at a thickness of about 10 to 20 nm, and the decrease in solder wettability is suppressed. This effect of the Bi composition is exhibited when the Bi concentration is 2% by weight or more, preferably 3 to 5% by weight, and has little effect when the Bi concentration is less than 2% by weight. For this reason, in the Sn-Bi alloy layer 2, the Bi concentration in the thickness region 2C is set to 2% by weight or more. At this time, the reason why the upper limit of the thickness of the thickness region 2C is set to 0.5 μm is that if the high concentration region of Bi is made thicker than this, bending workability starts to decrease, which is inconvenient.

The thickness region 2B on the interface 2b side is made of Sn
By forming the region to be rich, it is formed for the purpose of functioning as a diffusion barrier for Sn diffused from the upper layer side to the conductive substrate 1 side. In order to exhibit such a function, the Bi concentration in the thickness region 2B needs to be 0.01% by weight or less.
If this condition is not satisfied, Sn-C
This is because the formation of a u-layer starts to cause a decrease in solder wettability.

(5) The Sn—Bi alloy layer 2 needs the above-mentioned conditions, but preferably satisfies the following conditions. That is, this Sn
-The average concentration of Bi in the Bi alloy layer 2 is 0.1 to 1.0;
Weight percent. This average density is 0.1
When the content is lower than the weight%, the surface oxidation and the generation of whiskers are likely to occur as in the case of the Sn single layer,
If the content is higher than 1.0% by weight, the above-mentioned Bi concentration on the surface side becomes too high, which causes a decrease in bending workability, and at the same time, the solder is peeled off at the time of soldering.
This is because so-called lift-off occurs.
The preferable average concentration of Bi is 0.2 to 1.0% by weight.

[0026] leads to the present invention, as shown in FIG. 3, the conductive substrate 1 of the surface, Sn layer 2 ₀ and Sn
The -Bi alloy layer 2 ₁ is formed by sequentially plating the plated layer of 2-layer structure, it can then be prepared by performing a reflow process to the whole. At this time, if the conditions of the reflow treatment, particularly the temperature conditions, are excessive, b / in the Sn—Bi alloy layer 2 when the Sn layer under the lower layer is melted and re-solidified.
The value a does not satisfy the above-mentioned range, the surface may have irregularities, and the Bi concentration on the surface may be lower than the above-mentioned value. Is set. Usually, it is preferable to employ a line speed of about 40 m / min at a temperature of 750 to 850 ° C.

[0027]

EXAMPLE 1-7, after performing a pretreatment of electrolytic degreasing and pickling of Cu coated steel wire of Comparative Example 1-5 wire diameter 0.5 mm, first, the Sn layer 2 ₀ and plating, further Figure 3 on the Sn-3% Bi alloy layer 2 ₁ is plated on the
Was manufactured.

At this time, by changing each plating condition, a wire having a thickness and a Bi concentration shown in Table 2 was obtained. Next, this wire was subjected to reflow treatment under the conditions shown in Table 1 to obtain a lead wire of FIG. 1 on which a single Sn—Bi alloy layer 2 was formed. The thickness of the Sn—Bi alloy layer 2, the concentration gradient of Bi,
The bending workability, slipperiness, and solder wettability were measured.

(1) Measurement of thickness: The thickness of a single Sn—Bi alloy layer 2 was measured at 40 points using a fluorescent X-ray film thickness meter having a collimator diameter of 0.1 mm, and the maximum thickness (a) and the minimum thickness were measured. (B) was determined. (2) Bi concentration gradient: Auger electron spectrometer, 0.5 μm in thickness direction from surface, １ ／ depth from alloy layer surface, の depth from alloy layer surface B at a depth of 3/4 from the surface of the alloy layer
The i concentration was measured. A part of the Sn—Bi alloy layer 2 was peeled off, its Bi concentration was analyzed, and the average Bi concentration was also measured.

(3) Bending workability: The lead wire is bent at a right angle of 90 °, and the bent portion is observed with an optical microscope.
The presence or absence of cracks was examined. ◎ indicates no crack, ○ indicates a small crack, and × indicates a large crack. (4) Slipperiness: A lead wire is fixed on a flat plate, and a stainless steel curved plate having a curvature of 1 mmR is pressed against the surface of the lead wire with a load of 5 gf, and slides once, and dynamic friction occurs. The coefficient was measured. After the measurement, observe the surface of the lead wire,
The peeled state of the n-Bi alloy layer 2 was visually observed.

(5) Solder wettability: A temperature of 1
After a heat treatment at 55 ° C. for 16 hours, it is cut to a desired length, and a flux of 25% rosin is put in a solder bath of Sn-2.5% Ag-0.5% Cu (bath temperature 250 ° C.). Immersion for 2 seconds, the wet area at that time was measured, and the value was divided by the immersion area to determine the ratio (%) of the wet area.
Those having a value of 95% or more are acceptable products. The above results are collectively shown in Tables 1 and 2.

[0032]

[Table 1]

[Table 2]

As is clear from Tables 1 and 2, Sn
-In the lead wires of the examples in which the Bi concentration gradient is formed in the Bi alloy layer, the variation in the thickness of the Sn-Bi alloy layer is small, and the solder wettability, slipperiness, and bending workability are all low. Are better. However, since the lead wire of Example 6 had a slightly higher Bi concentration, it had a small kinetic friction coefficient, but some large peeling was observed, and the bending workability was slightly inferior.

On the other hand, the lead wires of Comparative Examples 1 to 4 in which the Bi-gradient was not formed in the Sn—Bi alloy layer were inferior in bending workability, had large thickness variations, and were poor in solder wettability. Poor slipperiness. Here, FIGS. 4 and 5 show the results of measuring the concentration of each component in the thickness direction of the Sn—Bi alloy layer 2 for the lead wire of Example 3 and the lead wire of Comparative Example 1, respectively.

FIG. 4 shows the results of Example 3, and FIG. 5 shows the results of Comparative Example 1. As is clear from FIGS. 4 and 5, in the Sn—Bi alloy layer in the lead wire of Example 3, a Bi concentration gradient is formed in a thickness region of about 2 μm from the surface. However, the Bi concentration gradient as described above is not formed in the lead wire of Comparative Example 1. Therefore, the Bi concentration gradient defined by the present invention is expressed by S
The usefulness of forming an n-Bi alloy layer is clear.

[0036]

As is apparent from the above description, the lead wire of the present invention has a small variation in the thickness of the Sn-Bi alloy layer on the surface, has excellent solder wettability, and further has good slipperiness and bending workability. Is also excellent.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a sectional structure of a lead wire according to the present invention.

FIG. 2 shows B in a Sn—Bi alloy layer after a reflow treatment.
FIG. 7 is a cross-sectional view for explaining a concentration gradient of i.

FIG. 3 is a sectional view showing a sectional structure of a lead wire before a reflow process.

FIG. 4 is a graph showing the relationship between the composition and the depth from the surface of the Sn—Bi alloy layer of the lead wire of Example 3.

FIG. 5 is a graph showing the relationship between the composition and the depth from the surface of the Sn—Bi alloy layer of the lead wire of Comparative Example 1.

Sn-Bi alloy layer 2 ₀ Sn layer 2 ₁ Sn-Bi alloy layer 2a Sn-Bi surface 2b of the alloy layer 2 Sn-Bi alloy layer 2 and the conductive substrate after one conductive substrate 2 reflow process [Description of symbols] 2A Thick region from surface 2a to half depth position 2B Thick region from thickness region 2A to interface 2b with conductive substrate 2C Surface layer from surface 2a to 0.5 μm depth

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C23C 28/02 C23C 28/02 H05K 3/24 H05K 3/24 A 3/34 501 3/34 501F (72 ) Inventor Satoshi Suzuki 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Akira Matsuda 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72 ) Inventor Isao Segawa 2-5, Kusunekita-cho, Neyagawa-shi, Osaka Kyowa Electric Wire Co., Ltd. (72) Kinya Sugie Inventor 2-5, Kusune-Kitacho, Neyagawa-shi, Osaka F-term (reference) 4K044 AA06 AB04 BA01 BA10 BB03 BC02 BC05 BC08 CA04 CA11 CA18 CA53 CA62 5E319 BB01 CC33 GG03 5E343 AA02 AA11 BB09 BB16 BB22 BB24 BB34 BB52 BB71 ER33 GG18 5G301 AA20 AB05 AB12 AD10

Claims (5)

[Claims] 1. A reflow-processed Sn on a conductive substrate
-In the lead wire for an electronic component on which the Bi alloy layer is formed, a Bi concentration gradient in which the Bi concentration gradually decreases is provided in a thickness region extending from the surface of the Sn-Bi alloy layer to a position at a half depth thereof. And a Bi concentration of 2 μm in a surface layer portion having a depth of 0.5 μm from the surface of the Sn—Bi alloy layer.
A lead wire for an electronic component, wherein the Bi concentration is not less than 0.01% by weight and a Bi concentration in a thickness region from the thickness region to the conductive substrate side is not more than 0.01% by weight. 2. Assuming that the thickness of the thickest portion of the Sn—Bi alloy layer is a (μm) and the thickness of the thinnest portion is b (μm), the following equation is satisfied between a and b: 8 ≦ b / a ≦ 1.
2. The electronic component lead according to claim 1, wherein a relationship of 0 is established. 3. The lead wire for an electronic component according to claim 1, wherein the average concentration of Bi in the Sn—Bi alloy layer is 0.1 to 1.0% by weight. 4. The method for manufacturing a lead wire for an electronic component according to claim 1, wherein an Sn layer and an Sn—Bi alloy layer are sequentially formed on the conductive substrate, and then a reflow process is performed. . 5. An electronic component assembled using the electronic component lead wire according to claim 1.