JP5280957B2 - Conductive member and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive member which has stable contact resistance and is hardly peeled off, wherein the inserting/removing force is made small when it is used as a connector. <P>SOLUTION: In the conductor member, a Cu-Sn intermetallic compound layer 3 and a Sn-based plating layer 4 are formed on the surface of a Cu-based base material 1 in this order through a Ni-based ground layer 2. Further, the Cu-Sn intermetallic compound layer 3 comprises a Cu<SB>3</SB>Sn layer 6 arranged on the Ni-based ground layer 2 and a Cu<SB>6</SB>Sn<SB>5</SB>layer 7 arranged on the Cu<SB>3</SB>Sn layer 6. The thickness X of each recessed part 8 of the Cu-Sn intermetallic compound layer 3, obtained by summing up the thicknesses of the Cu<SB>3</SB>Sn layer 6 and the Cu<SB>6</SB>Sn<SB>5</SB>alloy layer 7, is 0.05-1.5 &mu;m, the surface coverage of the Cu<SB>3</SB>Sn layer 6 to the Ni-based ground layer 2 is &ge;60% and a Ag<SB>3</SB>Sn alloy layer 5 having 0.01-0.5 &mu;m thickness is formed on the Sn based plating layer 4. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a conductive member used for an electrical connection connector or the like, in which a plurality of plating layers are formed on the surface of a base material made of Cu or Cu alloy, and a method for manufacturing the same.

As a conductive member used for automobile electrical connectors and printed circuit board connection terminals, Sn-based metal plating is applied to the surface of a Cu-based substrate made of Cu or a Cu alloy for the purpose of improving electrical connection characteristics. Many of them have been used.
Examples of such a conductive member include those described in Patent Document 1 or Patent Document 2. The conductive members described in these patent documents are formed by plating Ni, Cu, Sn on the surface of a base material made of Cu or Cu alloy in order to form a three-layered plating layer, and then heating and performing a reflow treatment. An Sn layer is formed on the surface layer, and a Cu—Sn intermetallic compound layer (for example, Cu ₆ Sn ₅ ) is formed between the Ni layer and the Sn layer.

Japanese Patent No. 3880877 Japanese Patent No. 4090488

By the way, when such a connector or terminal is used in a high temperature environment such as around an automobile engine, for example, reaching about 150 ° C., Sn and Cu are thermally diffused by being exposed to the high temperature for a long time. Thus, the surface state tends to change with time, and the contact resistance tends to increase. Further, Kirkendall voids are generated on the surface of the Cu-based substrate due to the diffusion of Cu, and peeling may occur. These solutions are desired.
On the other hand, when used for a connector, as the circuit density increases, the connector also becomes multipolar, and the insertion force at the time of assembling the automobile wiring has increased. Therefore, a conductive member that can reduce the insertion / extraction force is required. ing.

In order to solve such problems, the present applicant has previously filed Japanese Patent Application No. 2009-9752, having a stable contact resistance, being difficult to peel off, and making the insertion / extraction force small and stable when used as a connector. An electrically conductive member that can be manufactured and a method for manufacturing the same are provided.
The present invention is an improvement of the invention according to this application, and aims to further increase heat resistance.

The present inventor analyzed the conventional plating surface, and the cross section of the conventional plating material has a three-layer structure of a base copper alloy, a Ni layer, a Cu ₆ Sn ₅ layer, and a Sn-based plating layer. It was confirmed that a Cu ₃ Sn layer was present in a very small part on the layer. The Cu ₆ Sn ₅ layer and the Cu ₃ Sn layer are mixed in a predetermined state on the Ni layer, so that contact resistance at high temperatures, generation of Kirkendall voids, insertion / removal when used in connectors I found that it affects power.
Moreover, for further improving heat resistance, to form the Ag 3 _Sn alloy layer on the Sn-based plating layer it has been found to be suitable.

That is, in the conductive member of the present invention, a Cu-Sn intermetallic compound layer and an Sn-based plating layer are formed in this order on the surface of a Cu-based substrate via a Ni-based underlayer, and between the Cu-Sn intermetallic layers. compound layer further wherein the _Cu 3 Sn layer disposed on the Ni-based base layer composed of a _Cu 6 Sn ₅ layer disposed on the said _Cu 3 Sn layer, these _Cu 3 Sn layer and Cu ₆ The Cu-Sn intermetallic compound layer combined with the Sn ₅ layer has irregularities on the surface in contact with the Sn-based plating layer, the thickness of the concave portion is 0.05 to 1.5 μm, and The area coverage of the Cu ₃ Sn layer with respect to the Ni-based underlayer is 60% or more, the ratio of the thickness of the convex portion to the concave portion of the Cu—Sn intermetallic compound layer is 1.2 to 5, and the Cu ₃ Sn The average thickness of the layer is 0.01 ~ 0.5μm Further characterized in _{that Ag} 3 Sn alloy layer having a thickness of 0.01~0.5μm the Sn-based plating layer is formed.

In this conductive member, the Cu—Sn intermetallic compound layer between the Ni-based underlayer and the Sn-based plating layer has a two-layer structure of a Cu ₃ Sn layer and a Cu ₆ Sn ₅ layer, and the lower Cu ₃ layer. The Cu ₆ Sn ₅ layer is present so that the Sn layer covers the Ni-based underlayer and covers it. The Cu—Sn intermetallic compound layer formed by combining the Cu ₃ Sn alloy layer and the Cu ₆ Sn ₅ layer is not necessarily uniform in film thickness and has irregularities, but the thickness of the recesses is 0. It is important that the thickness is 0.05 to 1.5 μm. If it is less than 0.05 μm, Sn diffuses from the recesses to the Ni-based underlayer at high temperatures, and there is a risk of defects occurring in the Ni-based underlayer. Due to the defects, Cu of the base material diffuses to form Cu ₆ Sn _5. When the layer reaches the surface and Cu oxide is formed on the surface, the contact resistance is increased. Further, at this time, Kirkendall voids are likely to be generated due to diffusion of Cu from the defect portion of the Ni-based underlayer. On the other hand, when the thickness of the recess exceeds 1.5 μm, the Cu—Sn alloy layer becomes brittle, and the plating film is easily peeled off during bending. Therefore, the thickness of the concave portion of the Cu—Sn intermetallic compound layer is desirably 0.05 to 1.5 μm.
And when the Cu—Sn intermetallic compound layer having a predetermined thickness is arranged in the lower layer of the Sn-based plating layer in this way, the flexible Sn base is hardened and used when used in a multipolar connector or the like. Reduction of insertion / extraction force and suppression of variation thereof can be achieved.

The reason why the area coverage of the Cu ₃ Sn layer with respect to the Ni-based underlayer is 60% or more is that when the coverage is low, the Ni atoms in the Ni-based underlayer are Cu ₆ Sn at high temperatures from the uncoated portion. _{This is} because the Ni-based underlayer is deficient in _five layers and the Cu of the base material diffuses from the deficient portion, resulting in increased contact resistance and generation of Kirkendall voids as in the above case. is there. In order to prevent this increase in contact resistance at high temperatures and the generation of Kirkendall voids and to achieve heat resistance higher than that of the prior art, it is necessary that the Ni-based underlayer is coated at least 60% or more. Further, it is desirable that the area coverage is 80% or more.

  Moreover, when the ratio of the thickness of the convex portion to the concave portion of the Cu-Sn intermetallic compound layer is reduced and the unevenness of the Cu-Sn intermetallic compound layer is reduced, the insertion / extraction force during use of the connector is reduced, which is preferable. When the ratio is less than 1.2, the unevenness of the Cu—Sn intermetallic compound layer is almost eliminated, the Cu—Sn intermetallic compound layer becomes extremely brittle, and peeling of the film easily occurs during bending, which is not preferable. Moreover, when the unevenness of the Cu—Sn intermetallic compound layer exceeds 5, and the unevenness of the Cu—Sn intermetallic compound layer becomes resistance during insertion / extraction when used as a connector, the effect of reducing the insertion / extraction force is poor. .

Further, if the average thickness of the Cu ₃ Sn layer covering the Ni-based underlayer is less than 0.01 μm, the effect of suppressing the diffusion of the Ni-based underlayer is poor. On the other hand, if the thickness of the Cu ₃ Sn layer exceeds 0.5 μm, the Cu ₃ Sn layer changes to a Cu ₆ Sn ₅ layer at a high temperature, which decreases the Sn-based plating layer and increases the contact resistance.
This average thickness is an average value when the thickness of the Cu ₃ Sn layer portion is measured at a plurality of locations.

In addition, since an Sn ₃ Sn alloy layer having a thickness of 0.01 to 0.5 μm is formed on the Sn-based plating layer, an oxide film is not formed even at a high temperature, so that the contact resistance is more stable and excellent. Heat resistance can be exhibited. Further, since Ag is hard, the surface hardness is high, and the insertion / extraction property when used as a connector is improved.
In this case, if the thickness of the Ag ₃ Sn alloy layer is less than 0.01 μm, the effect cannot be obtained, and if it exceeds 0.5 μm, expensive silver is wasted and insertion / removability is also achieved. since reduced, preferably 0.01~0.5μm as the thickness of the _Ag 3 Sn alloy layer.

In the conductive member of the present invention, the Ag ₃ Sn alloy layer has an area coverage of 50% or more with respect to the Sn-based plating layer, and the surface roughness is 0.005 to 0.5 μm in terms of arithmetic average roughness Ra. There should be.
When the area coverage with respect to the Sn-based plating layer is 50% or more, the effect of improving heat resistance and insertion / removability by the Ag ₃ Sn alloy layer is sufficiently exerted, and when it is less than 50%, the effect is reduced. In this case, it is preferable that an uncoated portion is not concentrated on a specific location but is dispersed and mixed with the coated portion. Further, even if the surface roughness of the Ag ₃ Sn alloy layer is less than 0.005 μm, further improvement in the effect cannot be expected, and it is difficult to manufacture. When the surface roughness is within 0.5 μm, the insertion / extraction properties when using the connector are further improved.

And the manufacturing method of the electrically-conductive member of this invention heats, after plating the surface of Cu base material, Ni or Ni alloy, Cu or Cu alloy, Sn or Sn alloy in this order, and forming each plating layer Then, a Ni-based underlayer, a Cu-Sn intermetallic compound layer, and a Sn-based plating layer are formed in order on the Cu-based substrate by reflow treatment, and an Ag ₃ Sn alloy is further formed on the Sn-based plating layer. A method for producing a conductive member having a layer, wherein the plating layer made of Ni or Ni alloy is formed by electrolytic plating with a current density of 20 to 50 A / dm ² , and the plating layer made of Cu or Cu alloy is formed by current density. There was formed by electrolytic plating 20~60A / dm ^2, current density plating layer by the Sn or Sn alloy is formed by electroplating 10~30A / dm ^2, the reflow treatment 1 to 15 minutes after the formation of the plating layer, the heating step of heating the plating layer to a peak temperature of 240 to 300 ° C. at a temperature rising rate of 20 to 75 ° C./second, and the peak temperature A primary cooling step of cooling for 2 to 10 seconds at a cooling rate of 30 ° C./second or less, and a secondary cooling step of cooling at a cooling rate of 100 to 250 ° C./second after the primary cooling. After removing the oxide film on the surface of the Sn-based plating layer after the treatment by an electrochemical reduction method, Ag plating is applied to the surface by a silver strike plating method using a cyanide compound in an amount of 0.01 to 0.5 μm. After that, alloying and discoloration prevention treatment are performed in an aqueous solution containing a benzothiazole compound.

Cu plating at a high current density increases the grain boundary density, helps to form a uniform alloy layer, and at the same time forms a Cu ₃ Sn layer with a high coverage.
The reason why the current density of Cu plating is set to 20 to 60 A / dm ² is that when the current density is less than 20 A / dm ² , the reaction activity of the Cu plating crystal is poor, and thus the effect of forming a smooth intermetallic compound when alloying is performed. On the other hand, when the current density exceeds 60 A / dm ² , the smoothness of the Cu plating layer is lowered, and therefore, a smooth Cu—Sn intermetallic compound layer cannot be formed.
Also, to that the current density of the Sn-plated with 10~30A / dm ^2, taken low grain boundary density of Sn is the current density is less than 10A / dm ^2, between smooth Cu-Sn metal when alloyed This is because the effect of forming the compound layer is poor, and on the other hand, if the current density exceeds 30 A / dm ² , the current efficiency is remarkably lowered, which is undesirable.

In addition, by setting the current density of Ni plating to 20 A / dm ² or more, Ni atoms are difficult to diffuse into Sn and intermetallic compounds during heating after refining and commercializing crystal grains, and Ni plating defects Can be reduced and the occurrence of Kirkendall void can be prevented. On the other hand, when the current density exceeds 50 A / dm ² , hydrogen generation on the plating surface during electrolysis becomes intense, and pinholes are generated in the film due to air bubbles adhering, and the underlying Cu-based substrate diffuses starting from this. Kirkendall void is likely to occur. For this reason, it is desirable that the current density of Ni plating be 20 to 50 A / dm ² .

Further, Cu and Sn electrodeposited at a high current density are low in stability, and alloying and grain enlargement occur even at room temperature, making it difficult to form a desired intermetallic compound structure by reflow treatment. For this reason, it is desirable to perform the reflow process immediately after the plating process. Specifically, the reflow process may be performed within 15 minutes, preferably within 5 minutes.
When Cu or Cu alloy is plated with Sn or Sn alloy at a higher current density than in the prior art, and reflow treatment is performed immediately after plating, Cu and Sn react actively during reflow, and Cu ₃ A large amount of the Ni-based underlayer is covered with the Sn layer, and a uniform Cu ₆ Sn ₅ layer is generated.

Further, in the reflow process, if the rate of temperature increase in the heating step is less than 20 ° C./second, Cu atoms preferentially diffuse in the Sn grain boundary until Sn plating melts, and in the vicinity of the grain boundary. Since the intermetallic compound grows abnormally, it is difficult to form a Cu ₃ Sn layer having a high coverage. On the other hand, if the rate of temperature rise exceeds 75 ° C./second, the growth of the intermetallic compound is insufficient and the Cu plating remains excessively, and a desired intermetallic compound layer cannot be obtained in the subsequent cooling.
In addition, when the peak temperature in the heating process is less than 240 ° C., Sn does not melt uniformly, and when the peak temperature exceeds 300 ° C., the intermetallic compound grows rapidly and the unevenness of the Cu—Sn intermetallic compound layer Is unfavorable because of the increase.
Further, in the cooling step, by providing a primary cooling step with a low cooling rate, Cu atoms diffuse gently in the Sn grains and grow with a desired intermetallic compound structure. When the cooling rate in the primary cooling step exceeds 30 ° C./second, the intermetallic compound cannot grow into a smooth shape due to the effect of rapid cooling, and unevenness increases. Similarly, even when the cooling time is less than 2 seconds, the intermetallic compound cannot grow into a smooth shape. When the cooling time exceeds 10 seconds, the growth of the Cu ₆ Sn ₅ layer proceeds excessively and the coverage of the Cu ₃ Sn layer decreases. Air cooling is appropriate for this primary cooling step.
Then, after the primary cooling step, the secondary cooling step is rapidly cooled to complete the growth of the intermetallic compound layer with a desired structure. When the cooling rate in the secondary cooling step is less than 100 ° C./second, the intermetallic compound further proceeds, and a desired intermetallic compound shape cannot be obtained.
Thus, by precisely controlling the electrodeposition conditions and the reflow conditions for plating, a Cu—Sn intermetallic compound layer having a two-layer structure with less unevenness and a high coverage with the Cu ₃ Sn layer can be obtained.

Then, after removing the oxide film on the Sn-based plating layer after the reflow treatment, an Ag plating is formed with a thickness of 0.01 to 0.5 μm, and then subjected to alloying and anti-discoloration treatment. Then, an Ag ₃ Sn alloy layer having a thickness of 0.01 to 0.5 μm is formed on the Sn-based plating layer.
Moreover, in the manufacturing method of this invention, you may make it perform a reflow process after performing the said alloying and discoloration prevention process.

According to the present invention, among the Cu-Sn intermetallic compound layers having a two-layer structure, the Cu ₃ Sn layer constituting the lower layer appropriately covers the Ni-based underlayer, and a Cu ₆ Sn ₅ layer is further formed thereon. By being formed, Cu can be prevented from diffusing at high temperatures, the surface state can be maintained well and contact resistance can be prevented from increasing, and plating film peeling and generation of Kirkendall void can be prevented. Furthermore, the insertion / extraction force when using the connector can be reduced, and variations thereof can be suppressed. Moreover, it has still higher heat resistance by forming an Ag ₃ Sn alloy layer having a thickness of 0.01 to 0.5 μm on the Sn-based plating layer.

It is sectional drawing which modeled and showed the surface layer part of one Embodiment of the electrically-conductive member which concerns on this invention. It is the temperature profile which made the relationship between the temperature of reflow conditions and time concerning the manufacturing method of this invention a graph. It is a front view which shows notionally the apparatus for measuring the dynamic friction coefficient of an electrically-conductive member.

Embodiments of the present invention will be described below.
The conductive member 10 of this embodiment is used for, for example, a terminal of an in-vehicle connector of an automobile. As shown in FIG. 1, a Cu base material 1 is provided with a Ni base layer 2 on the surface of a Cu base material 1. -Sn intermetallic compound layer 3, Sn-based plating layer 4, _Ag 3 with Sn alloy layer 5 are formed in this order, Cu-Sn intermetallic compound layer 3 further, _Cu 3 Sn layer 6 and the _Cu 6 Sn ₅ layer 7.
The Cu-based substrate 1 is, for example, a plate-like one made of Cu or a Cu alloy. The material of the Cu alloy is not necessarily limited, but Cu—Zn alloy, Cu—Ni—Si (Corson) alloy, Cu—Cr—Zr alloy, Cu—Mg—P alloy, Cu—Fe -P-based alloy and Cu-Sn-P-based alloy are suitable, and for example, MSP1, MZC1, MAX251C, MAX375, MAX126 manufactured by Mitsubishi Shindoh Co., Ltd. are preferably used.
The Ni-based underlayer 2 is formed by electrolytic plating of Ni or a Ni alloy, and is formed on the surface of the Cu-based substrate 1 to a thickness of, for example, 0.1 to 0.5 μm. If this Ni-based underlayer 2 is less than 0.1 μm, the Cu diffusion prevention function of the Cu-based substrate 1 is not sufficient, and if it exceeds 0.5 μm, the strain becomes large and is easy to peel off. Cracks are likely to occur during bending.

The Cu-Sn intermetallic compound layer 3 is an alloy layer formed by diffusing Cu plated on the Ni-based underlayer 2 and Sn on the surface by a reflow process, as will be described later. The Cu—Sn intermetallic compound layer 3 further includes a Cu ₃ Sn layer 6 disposed on the Ni-based underlayer 2, and a Cu ₆ Sn ₅ layer 7 disposed on the Cu ₃ Sn layer 6. It is composed of In this case, the Cu—Sn intermetallic compound layer 3 as a whole has irregularities, and the combined thickness X of the Cu ₃ Sn layer 6 and the Cu ₆ Sn ₅ layer 7 in the recess 8 is 0.05 to 1.5 μm.
If the thickness X of the concave portion 8 is less than 0.05 μm, Sn diffuses from the concave portion 8 to the Ni-based underlayer 2 at a high temperature, and the Ni-based underlayer 2 may be damaged. The Sn-based plating layer 4 maintains the contact resistance of the terminal low, but if a defect occurs in the Ni-based underlayer 2, Cu of the Cu-based substrate 1 diffuses and the Cu-Sn alloy layer 3 grows. Then, the Cu ₆ Sn ₅ layer 7 reaches the surface of the conductive member 10, thereby forming Cu oxide on the surface and increasing the contact resistance. At this time, Kirkendall voids are also likely to be generated at these interfaces due to the diffusion of Cu from the defect portion of the Ni-based underlayer 2. Therefore, the thickness X of the recess 8 needs to be at least 0.05 μm, and more preferably 0.1 μm.
On the other hand, if the combined thickness X of the Cu ₃ Sn layer 6 and the Cu ₆ Sn ₅ alloy layer 7 in the recess 8 exceeds 1.5 μm, the Cu—Sn intermetallic compound layer 3 becomes brittle, and a plating film is formed during bending. Peeling easily occurs.

Moreover, the ratio of the thickness of the convex part 9 with respect to the concave part 8 of this Cu-Sn intermetallic compound layer 3 is set to 1.2-5. If this ratio is reduced and the unevenness of the Cu—Sn intermetallic compound layer 3 is reduced, the insertion / extraction force during use of the connector is preferably reduced, but if this is less than 1.2, the Cu—Sn intermetallic compound layer 3 The Cu—Sn intermetallic compound layer 3 becomes extremely fragile, and the film is easily peeled off during bending. In addition, when the unevenness becomes so large that the ratio of the thickness of the protrusion 8 to the recess 7 exceeds 5, the unevenness of the Cu-Sn intermetallic compound layer 3 becomes a resistance during insertion / extraction when used as a connector. The effect of reducing is poor.
For example, when the thickness X of the concave portion 7 is 0.3 μm and the thickness Y of the convex portion 9 is 0.5 μm, the ratio (Y / X) is 1 .67. In this case, the thickness of the Cu—Sn intermetallic compound layer 3 including the Cu ₃ Sn layer 6 and the Cu ₆ Sn ₅ layer 7 is desirably 2 μm at the maximum.

Further, _Cu 3 Sn layer 6 is arranged under one of the Cu-Sn intermetallic compound layer 3 covers the Ni-based base layer 2, the area coverage is 60 to 100%. When the area coverage is less than 60%, Ni atoms in the Ni-based underlayer 2 diffuse into the Cu ₆ Sn ₅ layer 7 at a high temperature from the uncovered portion, and the Ni-based underlayer 2 has defects. May occur. Then, Cu of the Cu-based substrate 1 diffuses from the defect portion, so that the Cu—Sn intermetallic compound layer 3 grows to reach the surface of the conductive member 10, thereby forming Cu oxide on the surface. , Contact resistance increases. Further, Kirkendall voids are also likely to occur due to the diffusion of Cu from the defect portion of the Ni-based underlayer 2.
By covering at least 60% or more of the Ni-based underlayer 2 with the Cu ₃ Sn layer 6, it is possible to prevent an increase in contact resistance at high temperatures and generation of Kirkendall voids. More preferably, 80% or more is covered.
This area coverage can be confirmed from a surface scanning ion image (SIM image) obtained by observing a cross-section of the film with a focused ion beam (FIB) and observing with a scanning ion microscope (SIM). it can.
The area coverage with respect to the Ni-based underlayer 2 is 60% or more means that the Cu ₃ Sn layer 6 is not locally present on the surface of the Ni-based underlayer 2 when the area coverage is less than 100%. Even in this case, the combined thickness of the Cu ₃ Sn layer 6 and the Cu ₆ Sn ₅ layer 7 in the recess 8 of the Cu—Sn intermetallic compound layer 3 is 0.05 to 1.5 μm. Therefore, the Cu ₆ Sn ₅ layer 7 covers the Ni-based underlayer 2 with a thickness of 0.05 to 1.5 μm.

In the _Cu 3 Sn layer 6 constituting the lower layer of Cu-Sn intermetallic compound layer 3, the average thickness is set to 0.01 to 0.5 [mu] m. Since this Cu ₃ Sn layer 6 is a layer covering the Ni-based underlayer 2, when the average thickness is as small as less than 0.01 μm, the effect of suppressing the diffusion of the Ni-based underlayer 2 becomes poor. . On the other hand, if it exceeds 0.5 μm, the Cu ₃ Sn layer 6 changes to a Sn-rich Cu ₆ Sn ₅ layer 6 at a high temperature, and accordingly, the Sn-based plating layer 4 is reduced and the contact resistance is increased. . This average thickness is a portion where the Cu ₃ Sn layer 6 exists and is an average value when the thickness is measured at a plurality of locations.
In addition, since this Cu-Sn intermetallic compound layer 3 is alloyed by diffusion of Cu plated on the Ni-based underlayer 2 and Sn on the surface, depending on conditions such as reflow processing, In some cases, the entire Cu plating layer is diffused to form the Cu—Sn intermetallic compound layer 3, but the Cu plating layer may remain. When this Cu plating layer remains, the Cu plating layer has a thickness of 0.01 to 0.1 μm, for example.

  The Sn-based plating layer 4 is formed by performing reflow treatment after electrolytic plating of Sn or an Sn alloy, and is formed to a thickness of 0.05 to 2.5 μm, for example. If the thickness of the Sn-based plating layer 4 is less than 0.05 μm, Cu diffuses at high temperatures and Cu oxide is easily formed on the surface, so that contact resistance increases, and solderability and Corrosion resistance also decreases. On the other hand, when the thickness exceeds 2.5 μm, the effect of hardening the surface base by the Cu—Sn intermetallic compound layer 3 existing in the lower layer of the flexible Sn-based plating layer 4 is diminished, and the insertion / extraction force during use as a connector increases. However, it is difficult to reduce the insertion / extraction force associated with the increase in the number of pins of the connector.

The outermost Ag ₃ Sn alloy layer 5 has a thickness of 0.01 to 0.5 μm, covers the Sn-based plating layer 4 thereunder, and has an area coverage of 50% or more. This Ag ₃ Sn alloy layer is a layer having a high hardness, and by covering the flexible Sn-based plating layer 4, it is possible to improve the insertion / extraction properties when the connector is used. Moreover, since an oxide film is not formed at high temperature, the contact resistance at high temperature is also stable. In this case, if the thickness of the Ag ₃ Sn alloy layer 5 is less than 0.01 μm, the effect cannot be expected, and if it exceeds 0.5 μm, the effect is saturated, and it is uneconomical to make it thicker. If it is too much, the insertability / removability is reduced. Further, the Ag ₃ Sn alloy layer 5 does not necessarily completely cover the entire Sn-based plating layer 4, but the effect can be sufficiently exhibited by setting the area coverage to 50% or more. Can do.
The surface roughness of the surface of the Ag ₃ Sn alloy layer 5 is 0.005 to 0.5 μm in terms of arithmetic average roughness Ra. In order to maintain good insertability when using the connector, Ra should be as small as 0.5 μm or less. However, even if Ra is less than 0.005 μm, there is no meaning and manufacture is difficult.

Next, a method for manufacturing such a conductive member will be described.
First, a Cu or Cu alloy plate material is prepared as a Cu-based substrate, and the surface is cleaned by degreasing, pickling, etc., and then Ni plating, Cu plating, and Sn plating are sequentially performed in this order. In addition, pickling or rinsing is performed between the plating processes.
As the conditions for Ni plating, the plating bath is a watt bath mainly composed of nickel sulfate (NiSO ₄ ), boric acid (H ₃ BO ₃ ), nickel sulfamate (Ni (NH ₂ SO ₃ ) ₂ ) and boric acid. A sulfamic acid bath or the like mainly composed of (H ₃ BO ₃ ) is used. In some cases, nickel chloride (NiCl ₂ ) or the like is added as a salt that easily causes an oxidation reaction. The plating temperature is 45 to 55 ° C., and the current density is 20 to 50 A / dm ² .
As the conditions for Cu plating, a copper sulfate bath containing copper sulfate (CuSO ₄ ) and sulfuric acid (H ₂ SO ₄ ) as main components is used in the plating bath, and chlorine ions (Cl ⁻ ) are added for leveling. . The plating temperature is 35 to 55 ° C., and the current density is 20 to 60 A / dm ² .
As the conditions for Sn plating, a sulfuric acid bath mainly composed of sulfuric acid (H ₂ SO ₄ ) and stannous sulfate (SnSO ₄ ) is used as a plating bath, the plating temperature is 15 to 35 ° C., and the current density is 10 to 10. 30 A / dm ² .

All the plating processes are performed at a higher current density than a general plating technique. In this case, the plating solution agitation technology is important. However, by using a method of spraying the plating solution at a high speed toward the processing plate or a method of flowing the plating solution in parallel with the processing plate, A fresh plating solution can be supplied quickly, and a uniform plating layer can be formed in a short time with a high current density. The flow rate of the plating solution is desirably 0.5 m / second or more on the surface of the treatment plate. In addition, in order to enable the plating process at a current density that is an order of magnitude higher than that of the prior art, an insoluble anode such as a Ti plate coated with iridium oxide (IrO ₂ ) having a high anode limit current density is used as the anode. It is desirable.
These plating conditions are summarized as shown in Tables 1 to 3 below.

And after giving these three types of plating processes, it heats and performs a reflow process. As the reflow process, the temperature profile shown in FIG. 2 is desirable.
In other words, the reflow treatment is a heating step in which the treated material after plating is heated to a peak temperature of 240 to 300 ° C. for 2.9 to 11 seconds at a temperature rising rate of 20 to 75 ° C. in a heating furnace having a CO reducing atmosphere. And a primary cooling step of cooling for 2 to 10 seconds at a cooling rate of 30 ° C./second or less after reaching the peak temperature, and cooling for 0.5 to 5 seconds at a cooling rate of 100 to 250 ° C./second after the primary cooling. And a secondary cooling step. The primary cooling step is performed by air cooling, and the secondary cooling step is performed by water cooling using 10 to 90 ° C. water.
By performing this reflow treatment in a reducing atmosphere, it is possible to prevent the formation of a tin oxide film having a high melting temperature on the surface of the Sn plating, and to perform the reflow treatment at a lower temperature and in a shorter time. It becomes easy to produce an intermetallic compound structure. Further, by providing a cooling process in two stages and providing a primary cooling process with a low cooling rate, Cu atoms diffuse gently in the Sn grains and grow with a desired intermetallic compound structure. Then, by performing rapid cooling after that, the growth of the intermetallic compound layer can be stopped and fixed in a desired structure.
By the way, Cu and Sn electrodeposited at a high current density are low in stability, and alloying and crystal grain enlargement occur at room temperature, making it difficult to produce a desired intermetallic compound structure by reflow treatment. For this reason, it is desirable to perform the reflow process immediately after the plating process. Specifically, it is necessary to perform reflow within 15 minutes, preferably within 5 minutes. A short standing time after plating does not cause a problem, but in a normal processing line, it is about one minute after construction.

As described above, after three-layer plating is performed on the surface of the Cu-based substrate 1 under the plating conditions shown in Tables 1 to 3, reflow treatment is performed under the temperature profile conditions shown in FIG. Thus, the Ni-based underlayer 2 formed on the surface of the Cu-based substrate 1 is covered with the Cu ₃ Sn layer 6, and the Cu ₆ Sn ₅ layer 7 is further formed thereon, and the Sn-based plating layer 4 is formed on the outermost surface. Is formed.

After this reflow treatment, the surface oxide film is removed from the Sn plating layer 4 by an electrochemical reduction method, and then Ag plating is formed on the surface by a silver strike plating method using a cyan compound. To do.
The Sn metal surface of the Sn-based plating layer 4 is exposed by reducing and completely removing the oxide film of the Sn-based plating layer 4 in the electrolytic solution by an electrochemical reduction method, and the next silver plating is adhered. Thereby, mutual diffusion of Ag and Sn can be ensured in the alloying process. A weak alkaline electrolytic degreasing solution is used as the electrolytic treatment solution.
The conditions for silver strike plating are as shown in Table 4 below.

Here, if the concentration of silver cyanide is less than 1 g / L, a desired area coverage cannot be obtained for the Sn-based plating layer 4, and if it exceeds 8 g / L, the Ag plating surface becomes rough. 1-8 g / L is preferable. And the thickness of Ag plating formed by this silver strike plating shall be 0.01-0.5 micrometer. With Ag plating layer in this range, the final Ag 3 _Sn alloy layer can be set to a desired thickness.
Next, this Ag-plated treatment material is subjected to alloying and discoloration prevention treatment in an aqueous solution containing a benzothiazole compound. The alloying and discoloration prevention treatment conditions are shown in Table 5 below.

By immersing the Ag-plated treatment material in this treatment solution, Ag on the surface and Sn underneath are mutually diffused and alloyed, and an Ag ₃ Sn alloy layer 5 is formed on the surface. Furthermore, the benzothiazole treatment solution by being immersed in the hydrophobic protective film is formed on the surface of the Ag 3 _Sn alloy layer 5, oxidation and discoloration are prevented.
The conductive member 10 thus obtained has improved heat resistance due to the Ag ₃ Sn alloy layer 5 on the surface, is stable with low contact resistance even at high temperatures, and is hard due to the hard Ag ₃ Sn alloy layer 5. Also, the insertion / extraction force when using the connector is reduced.

Next, examples of the present invention will be described.
As the Cu alloy plate (Cu-based substrate), a MAX251C material manufactured by Mitsubishi Shindoh Co., Ltd. having a thickness of 0.25 mm was used, and Ni, Cu, and Sn plating treatments were sequentially performed thereon. In this case, as shown in Table 4, a plurality of samples were prepared by changing the current density of each plating treatment. Regarding the target thickness of each plating layer, the thickness of the Ni plating layer was 0.3 μm, the thickness of the Cu plating layer was 0.3 μm, and the thickness of the Sn plating layer was 1.5 μm. Further, a water washing step for washing the plating solution from the surface of the treatment material was inserted between these three types of plating steps.
In the plating treatment in this example, an insoluble anode of a Ti plate coated with iridium oxide was sprayed on the Cu alloy plate at a high speed.
After performing the above three types of plating treatments, a reflow treatment was performed on the treated material. This reflow process was performed 1 minute after the last Sn plating process, and the heating process, the primary cooling process, and the secondary cooling process were performed under various conditions.
The above test conditions are summarized in Table 6.

As a result of energy dispersive X-ray spectroscopic analysis (TEM-EDS analysis) using a transmission electron microscope, the cross section of the treatment material of this example is based on Cu-based substrate, Ni-based underlayer, Cu ₃ Sn layer, and Cu ₆ Sn _5. The surface of the Cu ₆ Sn ₅ layer was uneven, and the thickness of the recess was 0.05 μm or more. The _Cu 6 at the interface Sn ₅ layer and the Ni-based base layer has discontinuous _Cu 3 Sn layer, Ni of _Cu 3 Sn layer observed from a scanning ion microscope of a cross section by focused ion beam (FIB-SIM image) The surface coverage with respect to the system underlayer was 60% or more.
Table 7 shows the cross-sectional observation results for each sample in Table 6.

Moreover, the presence or absence of peeling and the presence or absence of Kirkendall void were measured for the samples prepared as shown in Table 6.
In the peel test, 90 ° bending (curvature radius R: 0.7 mm) was performed with a load of 9.8 kN, then held in the atmosphere at 160 ° C. for 250 hours, bent back, and the peeled state of the bent portion was confirmed. Went. In addition, cross-sectional observation confirmed the presence or absence of Kirkendall voids at the Ni-based underlayer that causes peeling and the Cu-based substrate interface therebelow.
The results are shown in Table 8.

  As apparent from Table 8, in Samples 1 to 6, there was no peeling or generation of Kirkendall voids, but in Samples 7 to 11, peeling or Kirkendall voids were observed.

  Next, an experiment was conducted on the plating peelability depending on the standing time between the plating treatment and the reflow treatment. As described above, the peel test was performed by bending 90 ° with a load of 9.8 kN (curvature radius R: 0.7 mm), holding in the atmosphere at 160 ° C. for 250 hours, bending back, The peeling state of was confirmed. In addition, cross-sectional observation confirmed the presence or absence of Kirkendall voids at the Ni-based underlayer that causes peeling and the Cu-based substrate interface therebelow. The results are shown in Table 9.

As can be seen from Table 9, peeling and Kirkendall voids occur when the standing time after plating becomes long. This is because Cu crystal grains precipitated at a high current density are enlarged due to a long standing time, and Cu and Sn react spontaneously to form Cu ₆ Sn _5, and smooth Cu ₆ Sn during reflowing. _This is thought to be because the alloying between ₅ and Cu ₃ Sn is hindered. If a smooth Cu—Sn intermetallic compound layer does not exist, defects occur in the Ni-based underlayer during heating, and Cu atoms in the base material flow out from the Ni base layer, thereby making it easy to generate Kirkendall voids.

As a result of the above research, the Cu ₆ Sn ₅ layer and the Cu ₃ Sn layer have an effect of preventing the reaction between the Ni-based underlayer and the Sn-based plating layer, and among these, the Cu ₃ Sn alloy layer is more effective. taller than. In addition, Sn atoms diffuse into Ni from the concave portion of the Cu ₆ Sn ₅ layer and Sn and Ni react with each other. Therefore, the Cu ₆ Sn ₅ layer has relatively few irregularities, and the Cu ₃ Sn layer has a surface of the Ni-based underlayer. It was found that peeling and generation of Kirkendall voids can be prevented by coating a large amount of.

Next, the treated material after the reflow treatment was immersed in a weak alkaline electrolytic degreasing solution to remove the surface oxide film, and then the Sn-based plating layer was subjected to Ag plating. A plurality of types of silver cyanide concentrations in the plating solution and the thickness of the Ag plating layer were prepared. Then, as a result of alloying and anti-discoloration treatment on these Ag-plated treatment materials, an Ag ₃ Sn alloy layer was formed on the surface as shown in Table 10. As a result of measuring the contact resistance and the dynamic friction coefficient of these, they were as shown in the same table.
The contact resistance was measured under the condition of sliding with a load of 0.49 N (50 gf) using an electrical contact simulator manufactured by Yamazaki Seiki Co., Ltd. after the sample was left at 175 ° C. for 1000 hours.
As for the dynamic friction coefficient, a plate-shaped male test piece and a hemispherical female test piece having an inner diameter of 1.5 mm are prepared for each sample so as to simulate the contact portion of the male terminal and female terminal of the fitting type connector. Then, using a horizontal load measuring device (Model-2152NRE) manufactured by Aiko Engineering Co., Ltd., the frictional force between the two test pieces was measured to obtain the dynamic friction coefficient. Referring to FIG. 4, a male test piece 22 is fixed on a horizontal base 21, a hemispherical convex surface of a female test piece 23 is placed on the male test piece 22, and the plating surfaces are brought into contact with each other. The load P of 9N (500 gf) is applied and the male test piece 22 is pressed. With the load P applied, the frictional force F when the male test piece 22 was pulled 10 mm in the horizontal direction indicated by the arrow at a sliding speed of 80 mm / min was measured by the load cell 25. A dynamic friction coefficient (= Fav / P) was obtained from the average value Fav of the friction force F and the load P.

From the results shown in Table 10, an Ag ₃ Sn alloy layer having an appropriate thickness is formed on the outermost surface, and the Sn-based plating layer is covered to prevent deterioration of contact resistance during heating, and insertion / removal when using the connector It has been found that the force can be reduced.

In addition, according to the above-mentioned TEM-EDS analysis, 0.76 to 5.32% by weight of Ni was recognized in the Cu ₆ Sn ₅ layer. In the present invention, in the Cu—Sn intermetallic compound layer. It shall also include those in which a slight amount of Ni is mixed.
It may also be reflow process after forming the Ag 3 _Sn layer on the outermost surface as described above. By performing this reflow process, the Ag ₃ Sn alloy particles are dispersed, which is advantageous for heat resistance and insertion / extraction when using the connector. However, by performing this reflow treatment, the area coverage of the Cu ₃ Sn layer in the Cu—Sn intermetallic compound layer with respect to the Ni-based underlayer is slightly reduced.

DESCRIPTION OF SYMBOLS 1 Cu-type base material 2 Ni-type base layer 3 Cu-Sn intermetallic compound layer 4 Sn-type plating layer 5 Ag ₃ Sn layer 6 Cu ₃ Sn layer 7 Cu ₆ Sn ₅ layer 8 Concave part 9 Convex part 10 Conductive member

Claims (5)

A Cu-Sn intermetallic compound layer and a Sn-based plating layer are formed in this order on the surface of the Cu-based substrate via a Ni-based underlayer, and the Cu-Sn intermetallic compound layer further includes the Ni-based underlayer. and _Cu 3 Sn layer disposed over the formation consists of a _Cu 6 Sn ₅ layer disposed on the said _Cu 3 Sn layer, the the combined these _Cu 3 Sn layer and _Cu 6 Sn ₅ layer Cu- The surface of the Sn intermetallic compound layer in contact with the Sn-based plating layer has irregularities, the thickness of the concave portion is 0.05 to 1.5 μm, and the Cu ₃ Sn layer with respect to the Ni-based underlayer The area coverage is 60% or more,
The ratio of the thickness of the convex portion to the concave portion of the Cu-Sn intermetallic compound layer is 1.2 to 5,
The Cu ₃ Sn layer has an average thickness of 0.01 to 0.5 μm,
Furthermore, an Ag ₃ Sn alloy layer having a thickness of 0.01 to 0.5 μm is formed on the Sn-based plating layer. 2. The Ag ₃ Sn alloy layer has an area coverage of 50% or more with respect to the Sn-based plating layer and an arithmetic average roughness Ra of 0.005 to 0.5 μm. The conductive member as described. The surface of the Cu-based substrate is plated with Ni or Ni alloy, Cu or Cu alloy, Sn or Sn alloy in this order to form each plating layer, and then heated and reflowed, whereby the Cu-based substrate is obtained. In this method, a Ni-based underlayer, a Cu—Sn intermetallic compound layer, and a Sn-based plating layer are formed in this order on a material, and an Ag ₃ Sn alloy layer is further formed on the Sn-based plating layer. And
Forming a plating layer of the Ni or Ni alloy by electrolytic plating with a current density of 20 to 50 A / dm ² ;
Forming a plated layer of Cu or Cu alloy by electrolytic plating with a current density of 20 to 60 A / dm ² ; forming a plated layer of Sn or Sn alloy by electrolytic plating with a current density of 10 to 30 A / dm ² ; The reflow treatment is performed by heating the plating layer to a peak temperature of 240 to 300 ° C. at a temperature rising rate of 20 to 75 ° C./second after 1 to 15 minutes have elapsed since the formation of the plating layer, After reaching the peak temperature, it has a primary cooling step of cooling at a cooling rate of 30 ° C./second or less for 2 to 10 seconds, and a secondary cooling step of cooling at a cooling rate of 100 to 250 ° C./second after the primary cooling. ,
After removing the oxide film on the surface of the Sn-based plating layer after the reflow treatment by an electrochemical reduction method, 0.01 to 0 Ag plating is performed on the surface by a silver strike plating method using a cyan compound. A method for producing a conductive member, characterized in that the conductive member is formed with a thickness of 5 μm, and thereafter subjected to alloying and discoloration prevention treatment in an aqueous solution containing a benzothiazole compound.   The method for manufacturing a conductive member according to claim 3, wherein a reflow treatment is performed after the alloying and discoloration prevention treatment. The electrically-conductive member manufactured by the manufacturing method of Claim 3 or 4.

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