JP2014122403A - Tin-plated electroconductive material and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tin-plated electroconductive material in which the barrier properties of an underlying base material comprising Cu or a Cu alloy are enhanced, and diffusion of Cu is surely prevented to improve the heat resistance thereof and which can keep stabilized contact resistance even under a high-temperature environment and to provide a production method of the tin-plated electroconductive material.SOLUTION: The tin-plated electroconductive material is obtained by forming a Ni layer, an intermediate layer comprising a Cu-Sn alloy layer, a surface layer comprising Sn or a Sn alloy in this order on the surface of the base material which has no work-affected layer and comprises Cu or the Cu alloy. The Ni layer is grown epitaxially on the base material. The average diameter of crystal grains of the Ni layer is 1 μm or larger. The thickness of the Ni layer is 0.1-1.0 μm, that of the intermediate layer is 0.2-1.0 μm, and that of the surface layer is 0.5-2.0 μm.

Description

  The present invention relates to a conductive material with Sn plating used as a material for semiconductor devices and electronic / electrical components, and a method for manufacturing the same.

As a conductive material such as a terminal, a connector, or a lead frame, a material obtained by applying Sn plating to the surface of a Cu or Cu alloy base material is often used. In addition, with the recent development of electronics, there are increasing opportunities for electronic components to be used in a high temperature environment such as in the vicinity of an automobile engine room.
For this reason, the conductive material is also required to have heat resistance that can be used in a severe temperature environment. For example, even after being placed in a high temperature environment such as 160 ° C. for 1000 hours, the contact resistance increases. There is an increasing demand for a plating material that is small, does not peel off, and does not show discoloration and has high heat resistance.

Therefore, a conductive material as described in Patent Document 1 or Patent Document 2 has been developed.
In the conductive material described in Patent Document 1, a Ni or Ni alloy layer is formed on the surface of a substrate made of Cu or Cu alloy, an Sn or Sn alloy layer is formed on the outermost surface side, and the Ni or Ni alloy layer and Sn are formed. Alternatively, one or more intermediate layers containing Cu and Sn are formed between the Sn alloy layers. In this case, the thickness of the Ni or Ni alloy layer is 0.05 to 1.0 μm, and the thickness of the intermediate layer in contact with the Sn or Sn alloy layer is 0.2 to 2.0 μm, Sn or Sn. The thickness of the alloy layer is 0.25 to 1.5 μm.

Also, the conductive material described in Patent Document 2 is similar to that of Patent Document 1 in that a surface plating layer composed of a Ni layer, a Cu-Sn alloy layer, and a Sn layer is formed in this order on the surface of a substrate composed of Cu or Cu alloy. The Ni layer has a thickness of 0.1 to 1.0 μm, the Cu—Sn alloy layer has a thickness of 0.1 to 1.0 μm, and the Sn layer has a thickness of 0.1 to 0.5 μm. Has been.
In either case, Ni plating, Cu plating, and Sn plating are performed in this order on a substrate made of Cu or a Cu alloy, and then reflow treatment is performed.

Japanese Patent No. 3880877 Japanese Patent No. 4090302

In the conductive materials described in these patent documents, the Ni layer prevents Cu diffusion from the base substrate made of Cu or Cu alloy, and the Cu-Sn alloy layer on the Ni layer plays a role of preventing Ni diffusion. This ensures the desired heat resistance.
However, the Ni film deposited from the conventional Ni plating bath does not have a sufficient diffusion preventing effect on the underlying Cu under a high temperature environment of about 175 ° C., for example, and Ni in the Ni plating layer is not retained when held at a high temperature. There is a problem that contact resistance increases because Cu diffused to the base material and Cu diffused from the base reacts with the Sn layer to consume Sn and disappear.

  The present invention has been made in view of such circumstances, and enhances the barrier property to the base substrate made of Cu or Cu alloy, more reliably prevents the diffusion of Cu, improves the heat resistance, and in a high temperature environment. However, it aims at providing the electrically conductive material with Sn plating which can maintain the stable contact resistance, and its manufacturing method.

  As a result of diligent research, the present inventors have found that in a Ni layer formed by a conventional plating method, Cu diffuses from the underlying layer through the grain boundaries of the fine Ni layer. It has been found that by controlling the crystal to be coarse and free of crystal, the performance as a barrier layer is improved and the above-mentioned problems can be solved.

  That is, the conductive material with Sn plating according to the present invention has a Ni layer, an intermediate layer composed of a Cu-Sn alloy layer, a surface layer composed of Sn or Sn alloy on the surface of a substrate composed of Cu or Cu alloy without a work-affected layer. Are formed in this order, the Ni layer is epitaxially grown on the substrate, the average crystal grain size of the Ni layer is 1 μm or more, the thickness of the Ni layer is 0.1 to 1.0 μm, and the intermediate layer The thickness is 0.2 to 1.0 μm, and the thickness of the surface layer is 0.5 to 2.0 μm.

The Ni layer is epitaxially grown on the surface of the base material without the work-affected layer, and the barrier layer is a Ni layer having a uniform film thickness and no defects such as voids and having a crystal grain size controlled to 1 μm or more. The barrier property against diffusion of Cu is improved, and even when used at high temperatures, Sn in the surface layer does not disappear and stable contact resistance can be maintained. When the crystal grain size is less than 1 μm, the barrier effect is insufficient and diffusion occurs at a high temperature.
In this case, if the thickness of the Ni layer is less than 0.1 μm, the anti-diffusion effect is not sufficient, and if it exceeds 1.0 μm, bending or the like becomes difficult.
Further, if the thickness of the intermediate layer made of Cu or Cu—Sn alloy is less than 0.2 μm, Ni may be diffused from the underlying Ni layer, whereas if it exceeds 1.0 μm, The intermediate layer becomes brittle and easily causes peeling.
Further, if the surface layer made of Sn or Sn alloy has a thickness of less than 0.5 μm, Cu diffuses at high temperatures and Cu oxide is easily formed on the surface, so that the contact resistance increases. When the thickness exceeds 2.0 μm, the surface layer made of flexible Sn becomes too thick, so that the support effect by the intermediate layer below it is weakened, and the insertion / extraction force during use of a connector or the like tends to increase.

In the method for producing a conductive material with Sn plating according to the present invention, after removing the work-affected layer on the substrate surface made of Cu or Cu alloy, Ni plating, Cu plating, and Sn plating are performed in this order, and then reflow treatment is performed. It is characterized by.
The work-affected layer of the substrate is formed with a fine crystal structure, and by removing this, a Ni layer having a large crystal grain size and a high barrier property can be formed by epitaxial growth of Ni plating.
In the method for producing a conductive material with Sn plating according to the present invention, the Ni plating is performed using a Ni plating solution mainly composed of a nickel salt and an acid and not added with additives such as a brightener, a smoothing agent, and a hardness improver. Electroplating is recommended.
Since these additives have the effect of refining the crystal grain size of Ni, it is preferable to perform Ni plating with a plating solution that does not contain them.

  According to the conductive material with Sn plating of the present invention, by using a Ni layer having a uniform film thickness and a crystal grain size controlled to 1 μm or more as a barrier layer, the barrier property against diffusion of Cu from the base is improved, and high temperature Even if it is used below, Sn in the surface layer does not disappear and stable contact resistance can be maintained.

It is the cross-sectional photograph after the reflow process of Example 2. It is a cross-sectional photograph after the reflow process of Comparative Example 1. 6 is a surface photograph of Example 2. 2 is a surface photograph of Comparative Example 1. 2 is a cross-sectional photograph of Example 2 after heating at 175 ° C. for 500 hours. It is a cross-sectional photograph after heating at 175 degreeC of the comparative example 1 for 500 hours. 3 is a crystal orientation map of the surface of the base material of Example 2. It is a reverse pole figure of the base material of FIG. 6 is a crystal orientation map of the Ni layer surface of Example 2. FIG. It is a reverse pole figure of the Ni layer of FIG.

Hereinafter, an embodiment of the present invention will be described.
In the Sn-plated conductive material of the present embodiment, a Ni layer, an intermediate layer made of a Cu-Sn alloy, and a surface layer made of Sn or Sn alloy are arranged in this order on the surface of a base material made of Cu or Cu alloy without a work-affected layer. The overall configuration is formed.
A base material is a plate-shaped thing comprised from Cu or Cu alloy, and what is generally used as a electrically conductive material is applicable.

The Ni layer is a diffusion preventing layer for preventing Cu from diffusing from the base material and making it difficult to peel off. As described later, by plating after removing the work-affected layer of the base material, Ni is epitaxially grown on the base material, and a Ni layer having a uniform film thickness without defects such as voids is formed. Will improve. The average crystal grain size in this Ni layer is 1 μm or more. By making the crystal grain size a large crystal of 1 μm or more, the grain boundary is reduced and the barrier property is improved.
Moreover, the thickness of this Ni layer shall be 0.1-1.0 micrometer. If the thickness is less than 0.1 μm, the anti-diffusion effect is not sufficient, and if it exceeds 1.0 μm, bending or the like becomes difficult, and a thickness of 0.1 to 1.0 μm is desirable.

The intermediate layer made of a Cu—Sn alloy is an alloy layer formed by diffusing Cu and Sn by performing reflow treatment after applying Cu plating and Sn plating on the Ni layer, and Cu ₃ Sn and Cu ₆ Sn ₅ is contained. The Cu layer may remain.
The intermediate layer made of this Cu—Sn alloy layer has a thickness of 0.2 to 1.0 μm. If the thickness is less than 0.2 μm, Ni may be diffused from the underlying Ni layer. On the other hand, if it exceeds 1.0 μm, the intermediate layer becomes brittle and may cause peeling. Yes, a thickness of 0.1 to 1.0 μm is desirable.

  The surface layer made of Sn or Sn alloy is formed by reflow treatment after plating Sn or Sn alloy on the Cu plating layer, and constitutes the outermost surface layer as a conductive material. The surface layer has a thickness of 0.5 to 2.0 μm. When the thickness is less than 0.5 μm, Cu diffuses at high temperature and Cu oxide is easily formed on the surface, so that the contact resistance increases. On the other hand, when the thickness exceeds 2.0 μm, the Sn is flexible. Since the surface layer becomes too thick, the support effect by the lower intermediate layer is weakened, and the insertion / extraction force during use of the connector or the like tends to increase. For this reason, the thickness of the surface layer 4 is preferably 0.5 to 2.0 μm.

Next, a method for producing a conductive material with Sn plating having such a layer structure will be described.
A plate material of Cu or Cu alloy base material is prepared. In general, since a Cu or Cu alloy base material is subjected to various processes such as rolling and polishing in the production process, a work-affected layer having a finer crystal structure than the inside is formed on the surface portion. Therefore, the surface of the Cu or Cu alloy base material is cleaned by degreasing, pickling, etc., and then chemically polished with a polishing liquid containing hydrogen peroxide as a main component, or phosphoric acid as a main component. After removing the work-affected layer by electrolytic polishing with the electrolytic polishing solution or the like, Ni plating, Cu plating, and Sn plating are performed in this order.

As a plating bath for forming the Ni plating layer, if nickel sulfate is used as the nickel salt, sulfuric acid is used as the acid, sulfamic acid is used in the case of nickel sulfamate, and plating bath using hydrochloric acid is used in the case of nickel chloride. Good. The temperature of the plating bath is 20 ° C. to 50 ° C., and the current density is 1 A / dm ² or more to 30 A / dm ² . The film thickness of the Ni plating layer formed by this Ni plating is 0.1 to 1.0 μm.
In addition, it is desirable that this Ni plating bath does not contain additives such as brighteners, smoothing agents and hardness improvers (for example, saccharin and butanediol). This is because these additives make the crystal grains finer, making it difficult to obtain a Ni layer having a crystal grain size of 1 μm or more. A pH buffer such as boric acid or citric acid may be contained.

For Cu plating, a general Cu plating bath may be used. For example, a copper sulfate bath mainly composed of copper sulfate (CuSO ₄ ) and sulfuric acid (H ₂ SO ₄ ) may be used. The temperature of the plating bath is 20 to 50 ° C., and the current density is 1 to 30 A / dm ² . The film thickness of the Cu plating layer formed by this Cu plating is 0.1 to 0.5 μm.

As a plating bath for forming the Sn plating layer, a general Sn plating bath may be used. For example, a sulfuric acid bath mainly composed of sulfuric acid (H ₂ SO ₄ ) and stannous sulfate (SnSO ₄ ) is used. Can do. The temperature of the plating bath is 15 to 35 ° C., and the current density is 1 to 20 A / dm ² . The film thickness of this Sn plating layer shall be 1-3 micrometers.

Using such a plating bath, a Ni plating layer, a Cu plating layer, and a Sn plating layer are sequentially applied to a Cu or Cu alloy substrate, and then reflow treatment is performed. Although it does not specifically limit as reflow process conditions, For example, it is preferable to carry out rapid cooling, after heating up until the surface temperature of a base material will be 240-360 degreeC in nitrogen atmosphere, hold | maintaining at the said temperature for 1 to 12 seconds.
By this reflow process, Cu of the Cu plating layer on the Ni plating layer and Sn of the Sn plating layer are alloyed to form a Cu—Sn alloy layer. The Cu-Sn alloy layer has a _Cu 3 Sn and _Cu 6 Sn _5, the surface is formed in an uneven shape.

  The conductive material with Sn plating thus formed is formed as a barrier layer by epitaxially growing a Ni layer having a uniform film thickness and no defects such as voids and having a crystal grain size controlled to 1 μm or more. The base substrate exhibits high barrier properties against Cu diffusion, and even when used at high temperatures, Sn in the surface layer does not disappear and stable contact resistance can be maintained.

Next, the results of experiments conducted to confirm the effectiveness of the present invention will be described.
A copper alloy having a thickness of 0.25 mm with different crystal grain sizes was used as a base material, and after degreasing and pickling, electrolytic polishing, Ni plating, Cu plating, and Sn plating were performed in this order. The conditions are shown in Tables 1 and 2. As a comparative example, an electropolished substrate on which a damaged layer remained was plated.

After this plating treatment, both the examples and comparative examples were heated in a nitrogen atmosphere until the surface temperature of the substrate reached 270 ° C., held at that temperature for 3 to 9 seconds, and then cooled with water.
And about the sample obtained by doing in this way, the thickness of Ni layer, Cu-Sn alloy layer, and Sn layer was measured with the SII nanotechnology Co., Ltd. fluorescence X-ray film thickness meter (SF9400). In this case, for the Cu-Sn alloy layer and the Sn layer, first, after measuring the total Sn thickness of the sample after reflowing, pure Sn such as L80 manufactured by Reybold Co., Ltd. is etched to not corrode the Cu-Sn alloy. The Sn-based surface layer was removed by immersing in an etching solution for removing the plating film made of the components for 5 minutes, the underlying Cu-Sn intermetallic compound layer was exposed, and the Cu-Sn thickness was measured. (Thickness−CuSn thickness) was defined as the Sn surface layer thickness.
Further, the crystal grain sizes of the substrate and the Ni layer were measured by observing with an electron microscope (SEM).

And in order to evaluate heat resistance, each sample was heated in air | atmosphere 175 degreeC x 1000 hours, and the time-dependent change of contact resistance was measured. The measuring method is based on JIS-C-5402, 4 terminal contact resistance tester (manufactured by Yamazaki Seiki Laboratories: CRS-113-AU), sliding type (1mm) load change from 0 to 50g-contact resistance Was measured. In addition, all resistance values of 20 mΩ or more are indicated as 20 mΩ because of the performance of the testing machine. The change in contact resistance value when the load was 50 g was as shown in Table 3.
In Table 3, “None” was obtained by removing the work-affected layer of the base material, and “Yes” was obtained by leaving the work-affected layer.

  As is apparent from Table 3, all the examples show a low contact resistance value of 5 mΩ or less even after heating at 175 ° C. for 1000 hours. In particular, the Ni layer having a thickness of 0.3 μm or more can maintain a very low value of 2 mΩ or less. In the case where Ni is plated on the base material on which the work-affected layer remains without being electropolished (Comparative Example 1), or when the crystal grain size of the base material is epitaxially grown and the crystal grain size of Ni is less than 1 μm ( Comparative Example 2), Cu—Sn intermediate layer is less than 0.2 μm thin and Ni layer is damaged (Comparative Example 3), and Ni layer is less than 0.1 μm thin (Comparative Example 4) In the initial state where the heating is not performed, the contact resistance is low, but the contact resistance is remarkably increased by heating for a long time. In the table, the intermediate layer is described as a CuSn layer for the sake of convenience, but includes a multilayer structure of Cu / CuSn.

FIG. 1 is a cross-sectional photograph of Example 2 and FIG. In the example, since electropolishing is performed, there is no work-affected layer, and it can be seen that Ni is epitaxially grown. On the other hand, since the comparative example has a work-affected layer, Ni does not grow epitaxially and has a fine structure.
3 is a surface photograph of Example 2 and FIG. 4 is a surface photograph of Comparative Example 1. In both cases, the average crystal grain size of the base material is 4 μm, but when the work-affected layer is removed, it grows epitaxially, so the average grain diameter is as large as 4 μm. It turns out that it is a crystal.
5 is a cross-sectional photograph of Example 2 and FIG. 6 is a cross-sectional photograph of Comparative Example 1 after heating at 175 ° C. for 500 hours. In the example, there is no Cu layer, and all are Cu ₆ Sn ₅ layers, but since the diffusion of Cu from the substrate is suppressed, the Sn layer remains firmly. On the other hand, it can be seen that the comparative example cannot suppress the diffusion of Cu from the substrate because the Ni layer has insufficient barrier properties, the Cu ₆ Sn ₅ layer grows thick, and the Sn layer hardly remains. In addition, a lot of Kirkendall voids caused by the diffusion of Cu, which causes peeling, can be seen directly under the Ni layer.

  7 and 8 are crystal orientation maps and reverse pole figures obtained by measuring the substrate surface after electropolishing in Example 2 by the EBSD method, and FIGS. 9 and 10 are diagrams after Ni plating in Example 2. It is a crystal orientation map and a reverse pole figure. Although these figures do not measure the same location, the average crystal grain size is the same for the substrate and the Ni layer (both 4 μm as shown in Table 3), and the preferred orientation is both (101). Therefore, it is recognized that the Ni layer is epitaxially grown on the surface of the base material and has a surface structure that inherits the characteristics of the structure of the base material surface as it is.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.

Claims (3)

  An Ni layer, an intermediate layer made of Cu-Sn alloy layer, and a surface layer made of Sn or Sn alloy are formed in this order on the surface of the base material made of Cu or Cu alloy without the work-affected layer. Epitaxially grown on the material, the Ni layer has an average crystal grain size of 1 μm or more, the Ni layer has a thickness of 0.1 to 1.0 μm, and the intermediate layer has a thickness of 0.2 to 1.0 μm, A conductive material with Sn plating, wherein the surface layer has a thickness of 0.5 to 2.0 μm.   After removing the work-affected layer on the surface of the base material made of Cu or Cu alloy, Ni plating, Cu plating, Sn plating are performed in this order, and then reflow treatment is performed. Production method.   3. The Ni plating according to claim 2, wherein the Ni plating is electroplated using a Ni plating solution mainly composed of a nickel salt and an acid and not added with additives such as a brightener, a smoothing agent and a hardness improver. The manufacturing method of the electrically conductive material with Sn plating.