JP3243195B2 - Reflow solder plating material and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plating member used for a lead portion of an electronic component, a connector for electrical connection, and the like, and more particularly to a reflow solder plating material having improved oxidation resistance and solderability, and a method of manufacturing the same. .

[0002]

2. Description of the Related Art A member in which the surface of a conductive substrate such as Cu or a Cu alloy is plated with Sn or a Sn alloy has the conductivity and mechanical strength of the conductive substrate, the corrosion resistance of the Sn or Sn alloy and the solder. It is a high-performance conductor that has a good combination of stickiness and is widely used for electric and electronic device parts such as terminals, connectors, lead wires, and electric cables.

Conventionally, a Sn or Sn alloy plating layer is formed of Sn-
It was formed by electroplating a Pb-based alloy. In general, electroplating materials have a problem that whiskers (needle-like single crystals) that cause short circuit accidents are easily generated. This problem is caused by the bright plating or the plating layer in the Sn—Pb alloy plating material. The problem has been solved by a reflow treatment for melting and solidifying the solid. Recently developed P harmful to human body
As for whisker countermeasures for Sn-Bi-based alloy plating materials that do not contain b, the method using bright plating has not been solved.
The reflow processing method is merely disclosed in JP-A-4-160196.

[0004]

However, in the reflow treatment method disclosed above, the base material component is diffused on the surface of the plating layer to deteriorate the solderability, or a flowing pattern is formed on the surface of the plating layer to cause poor appearance. And the solderability of the thin portion of the flow pattern is reduced. From these facts, the present inventors have conducted intensive research on the improvement of the solderability of the Sn—Bi alloy plating material, and performed the reflow treatment at a predetermined temperature to control the base material on the plating layer surface. It has been found that the diffusion of the compound can be prevented, and further research has been made to complete the present invention. The present invention relates to P which is harmful to the human body.
An object of the present invention is to provide a reflow solder plated material of an Sn-Bi-based alloy which does not contain b and has excellent solderability and appearance and a method for producing the same.

[0005]

According to the first aspect of the present invention,
In a solder plating material in which an Sn-Bi-based alloy plating layer is formed on a conductive base material, the Sn-Bi-based alloy plating layer is subjected to a reflow treatment, and a Bi-rich phase is formed at a crystal grain boundary on a surface of the plating layer. Consists of a continuously precipitated structure,
A reflow solder plating material, characterized in that the concentration of Bi in the Sn-Bi-based alloy plating layer gradually decreases from the surface of the plating layer toward the inside.

[0006] According to a second aspect of the invention, B on the electrically conductive substrate
An Sn—Bi-based alloy plating layer having an i-concentration equal to or less than the eutectic composition is electroplated, and then heated to the (L + β) forming temperature region of the Sn—Bi-based alloy two-phase phase diagram to rapidly reflow. 2. The method for producing a reflow solder plating material according to claim 1, wherein the reflow solder plating material is subjected to a low-temperature treatment.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Finishing of plating (before reflow treatment)
In the surface structure of the material, as shown in FIG. 1 (c), no Bi-rich phase or the like was precipitated. When this is subjected to a reflow treatment by a conventional method, the surface of the plating layer becomes Sn as shown in FIG.
A structure in which the Bi-rich phase 40 is randomly dispersed in the crystal grains composed of the rich phase is obtained. With such a structure, not only diffusion of the grain boundary of Cu or the like from the base material is not prevented, but also a flow pattern is generated on the surface of the plating phase, and the surface is not smooth. This is because the reflow temperature is too high. In the reflow solder plating material of the present invention, the surface of the plating layer is as shown in FIG.
As shown in FIG. 2A, the structure is such that the Bi-rich phase 30 is continuously precipitated at the boundary (crystal grain boundary) 20 of the crystal grain 10 composed of the Sn-rich phase. In addition, the surface is smooth and has excellent appearance and solderability. Bi-rich phase 30 continuously precipitated at the crystal grain boundaries
This prevents components such as Cu of the conductive base material from diffusing to the surface of the solder plating layer through the crystal grain boundaries 20 and oxidizing to deteriorate the solderability.

[0008] In the present invention, the concentration of Bi in the Sn-Bi alloy plating layer, a conductive substrate components to be reduced gradually toward the inside from the surface of the plating layer to Handa plating layer (e.g., Cu ) Is better prevented. This is B
This is because the i-rich phase precipitates at a high density at the crystal grain boundaries and efficiently suppresses diffusion to the surface of the substrate.

The invention according to claim 2 is a method for producing the reflow solder plating material. In the present invention, the reason why the reflow treatment temperature is performed by heating to the temperature range in which the (L + β) region of the phase diagram of the Sn—Bi alloy is formed as shown in FIG. This is because a structure in which a Bi-rich phase is continuously precipitated can be obtained. When the reflow treatment temperature is out of the temperature range on the low temperature side, the solder plating layer does not melt (reflow), and when the reflow treatment temperature is out of the temperature range on the high temperature side, the Bi-rich phase is randomly dispersed in the crystal grains, In addition, a flow pattern is formed on the surface, and the smoothness of the surface is reduced.

The reflow treatment may be performed by passing the conductive substrate through a furnace set at a high temperature at a high speed, or by passing the conductive substrate at a low speed through a furnace set at a low temperature. Since the cooling after the reflow treatment is performed more rapidly, the Bi concentration near the surface tends to be distributed at a higher concentration. In addition, a flow pattern is unlikely to occur on the plating layer surface.

[0011]

The present invention will be described below in detail with reference to examples. (Example 1) Cu was plated on a 0.5 mmφ brass wire to a thickness of 1 μm, then an Sn—Bi alloy was electroplated, and then passed through a furnace set at 800 ° C. to produce a reflow solder plating material. did. The equipment includes an electrolytic degreasing tank, a washing tank, an pickling tank, a washing tank, a base Cu plating tank, a washing tank, a solder (Cu
-Bi-based alloy) A plating apparatus was used in which a plating tank, a washing tank, a hot air dryer, and a reflow furnace (length: 1 m) were sequentially arranged. The Bi concentration of the solder plating layer was changed variously. The traveling speed of the brass wire is represented by (L +
β) The formation temperature range was variously changed without departing from the range.

Comparative Example 1 Example 1 was repeated except that the traveling speed of the brass wire was set to the speed at which the solder plating layer reached the L region in the state diagram shown in FIG.
A reflow solder plating material was manufactured in the same manner as in the above.

For each of the obtained reflow solder plating materials, the plating layer thickness, the concentration distribution of the alloy component of the plating layer,
The oxidation amount and solderability were examined. The oxidation amount and solderability were examined after heating and after humidification. The heating is performed at a temperature of 155 ° C. for 8 hours, and the humidification is performed at a temperature of 10 ° C.
Each test was carried out at 0 ° C. and 100% relative humidity for 8 hours. Also, the presence or absence of a flow pattern on the plating layer surface was observed. The results are shown in Table 1 and FIGS. The survey method is as follows. [Plating Layer Thickness] The thickness was measured with a fluorescent X-ray fine film thickness meter. Sample length 30cm
30 locations were measured per area. Table 1 shows the average value and the variation (standard deviation). [Concentration distribution of alloy component in plating layer] The concentration was measured by a fluorescent X-ray analyzer. 30 locations were measured per 30 cm of sample length. Table 1 shows the average value of the entire plating layer and the average value near the plating layer surface. [Concentration distribution] Bi, Sn, Cu in the plating layer, the underlayer, and the base material,
And Zn concentration distribution in the thickness direction were measured by an Auger electron spectrometer. [Oxidation amount] It was measured by a cathode reduction method. 0.1N K for electrolyte
The current density was 0.1 mA / cm ² using a Cl solution. [Solderability] Investigation was performed by the meniscograph method. That is, a sample coated with 25% rosin / methanol flux was heated at 230 ° C.
For 10 seconds in a eutectic solder bath held at a speed of 2 mm
/ Sec, immersion depth 2 mm), and evaluated by the wetting time (zero cross time). The shorter the wetting time, the better the solderability.

[0014]

[Table 1]

As is clear from Table 1, the examples of the present invention (No. 1)
In all of the cases ( 3) to ( 3) , the Bi-rich phase was continuously precipitated at the crystal grain boundaries of the plating layer, so that the oxidation amount was small and the solderability (solder wettability) was excellent. In addition, the plating layer had no flowing pattern and the appearance was good. Among them, the reflow processing speed was high and those cooled rapidly after reflow processing (Nos. 1 and 2)
As can be seen from the table, the Bi concentration rapidly decreased from the surface to the inside, and the Bi-rich phase was precipitated at a very high concentration at the crystal grain boundaries within a predetermined thickness near the surface of the plating layer. Diffusion was suppressed efficiently and solderability was particularly improved.
On the other hand, in Comparative Examples Nos. 4 and 5 , the reflow treatment temperature was too high due to the slow reflow treatment speed, and the surface of the plating layer became a structure in which Bi-rich phases were randomly dispersed in the crystal grains, and Bi-rich The effect of preventing the diffusion of the base component by the phase was not obtained, and the plating layer melted and flowed to form a thin portion in the plating layer, and a large amount of Cu was diffused into the thin portion to significantly oxidize the surface. Due to the large amount of oxidation, the solderability was also reduced. In addition, the plating layer surface had a flowing pattern, resulting in poor appearance. The Bi of the No. 5 plating layer of the comparative example
The concentration distributions of Sn and Sn are almost constant in the thickness direction except for the outermost surface which is relatively fast to cool.

Although the example in which the brass wire is used for the conductive substrate has been described above, the present invention can achieve the same effects even when other metal materials are used and the shape is a rod, a strip, a plate, or the like. can get.

[0017]

As described above, in the reflow solder plating material of the present invention, since the crystal structure of the solder plating layer is a structure in which the constituent elements of the base material hardly diffuse to the surface, surface oxidation is suppressed. Therefore, the solderability is excellent. Further, the reflow solder plating material of the present invention can be easily manufactured by performing the reflow treatment under appropriate temperature conditions. Therefore, an industrially remarkable effect is achieved.

[Brief description of the drawings]

1 (a) is a surface crystallographic structure of a material of the present invention after reflow treatment, (b) is a surface crystallographic structure of a conventional material after reflow treatment, and (c) is a material after plating (before reflow treatment). FIG. 3 is a surface crystal structure diagram.

FIG. 2 is a binary phase diagram of a Sn—Bi alloy.

FIG. 3 is a concentration distribution diagram of Sn, Bi, Cu, and Zn from the surface to the inside of a plating layer of a reflow solder plating material of the present invention.

FIG. 4 is a concentration distribution diagram of each element of Sn, Bi, Cu, and Zn from the surface to the inside of a plating layer of a conventional reflow solder plating material.

[Explanation of symbols]

 10 Crystal grains composed of Sn-rich phase 20 Boundaries (crystal grain boundaries) of crystal grains composed of Sn-rich phase 30 Bi-rich phase 40 Bi-rich phase randomly dispersed

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25D 5/50 B23K 35/26 H05K 3/34

Claims (2)

(57) [Claims] 1. A solder plating material in which a Sn—Bi-based alloy plating layer is formed on a conductive base material, wherein the Sn—Bi alloy
The alloy-based plating layer has been subjected to a reflow treatment, and has a structure in which a Bi-rich phase is continuously precipitated at a crystal grain boundary on the surface of the plated layer. A reflow solder plating material characterized by a gradual decrease from the surface to the inside. 2. The composition according to claim 1, wherein the Bi concentration on the conductive substrate is less than the eutectic composition.
The electroplating of the Sn-Bi-based alloy plating layer is performed, and then this is heated to the (L + β) forming temperature region of the two-phase phase diagram of the Sn-Bi-based alloy and reflowed at a high speed. 2. The method for producing a reflow solder plated material according to 1.