JP5498710B2 - Conductive member and manufacturing method thereof - Google Patents

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 conductive members include those described in Patent Document 1 to Patent Document 4. The conductive members described in Patent Document 1 to Patent Document 3 are subjected to a reflow treatment by heating after forming Ni, Cu, Sn on the surface of a substrate made of Cu or Cu alloy in order to form a three-layered plating layer. Thus, an Sn layer is formed on the outermost 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. Further, the one described in Patent Document 4 is a technique in which a base plating layer is made of, for example, Ni—Fe, Fe, or the like, and Cu and Sn are sequentially plated thereon to perform a reflow process.

Japanese Patent No. 3880877 Japanese Patent No. 4090488 JP 2004-68026 A JP 2003-171790 A

By the way, when such a connector or terminal is used in a high temperature environment such as around an automobile engine, the conductive members described in Patent Document 1 to Patent Document 3 are exposed to the high temperature for a long time. Cu and each other are thermally diffused and the surface state tends to change with time, and the contact resistance tends to increase. Further, for example, when the temperature is higher than 170 ° C., the diffusion rate of Ni atoms increases, Ni diffuses into Cu ₆ Sn ₅ , and as a result, defects occur in the Ni layer and Cu diffusion cannot be blocked. There is a problem that contact resistance deteriorates. 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, the thing of patent document 4 has the problem that the adhesiveness of the base plating layer of Fe-Ni or Fe, and Cu is bad, and it peels easily.
In addition, when used for connectors, as the circuit density increases, the connectors also become multipolar, and the insertion force at the time of assembling the automobile wiring is increasing. Therefore, a conductive member that can reduce the insertion / extraction force is required. ing.

  The present invention has been made in view of such circumstances, and has a stable contact resistance, is difficult to peel off, and has a small and stable insertion / extraction force when used as a connector, and a manufacturing method thereof I will provide a

Conductive member of the present invention, the surface of the Cu-based substrate, through a Fe-based base layer, Ni-based thin film layer, Cu-Sn intermetallic compound layer, with Sn-based surface layer are formed in this order, the Fe The system base layer has a thickness of 0.1 to 1.0 μm, and the Cu—Sn intermetallic compound layer further includes a Cu ₃ Sn layer disposed on the Ni-based thin film layer, and the Cu ₃ Sn. consists of a _Cu 6 Sn ₅ layer disposed on the layer, the thickness of the recess of the Cu-Sn intermetallic compound layer together, _Cu 3 Sn layer and _Cu 6 Sn ₅ layer is 0.05. 5 μm, 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 average thickness of the Cu ₃ Sn layer is 0.01 to 0.5 μm. There, and area coverage of the _Cu 3 Sn layer with respect to the Ni-based thin film layer 60 It characterized in that it is 00%.

In this conductive member, Fe has a slower diffusion rate into Cu ₆ Sn ₅ than Ni. Therefore, the Fe-based underlayer functions effectively as a highly heat-resistant barrier layer at high temperatures, and the surface contact resistance is stably reduced. Can be maintained. In addition, since Fe is hard, high wear resistance is exhibited in the use of connector terminals and the like. Further, the Ni-based thin film layer is interposed between the Fe-based underlayer and the Cu-Sn intermetallic compound layer, thereby maintaining good adhesion between the Fe-based underlayer and the Cu-Sn intermetallic compound layer. it can. That is, since Fe and Cu do not form a solid solution and do not form an intermetallic compound, mutual interdiffusion of atoms does not occur at the interface of the layers, and it is not possible to obtain adhesion between them. By interposing an Ni element that can be dissolved in both Cu and these, the adhesion can be improved.
Moreover, the effect of preventing Fe from moving from the Sn plating defect portion to the surface and forming Fe oxide by coating the Ni thin film layer on Fe that is easily corroded by the external environment to form oxide. There is. The thickness of the Ni thin film layer is preferably 0.05 to 0.3 μm.

In this conductive member, the Cu—Sn intermetallic compound layer between the Ni-based thin film layer and the Sn-based surface layer has a two-layer structure of a Cu ₃ Sn layer and a Cu ₆ Sn ₅ layer. 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 the thickness is less than 0.05 μm, Sn may diffuse from the concave portion to the Ni-based thin film layer at a high temperature, and the Ni-based thin film layer may be damaged. Is easily peeled off. 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 surface layer in this way, the flexible Sn base is hardened and used in a multipolar connector or the like. Reduction of insertion / extraction force and suppression of variation thereof can be achieved.

In the conductive member of the present invention, the Fe-based underlayer has a thickness of 0 . The reason why the thickness is 1 to 1.0 μm is that when the Fe base layer is less than 0.1 μm, the Cu diffusion preventing function in the Cu base 1 is not sufficient, and 1.0 μm This is because it is not preferable because cracks are likely to occur in the Fe-based underlayer during bending.

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 thin film layer is less than 0.01 μm, the effect of suppressing the diffusion of the Ni-based thin film layer 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 surface 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.

And the manufacturing method of the electrically-conductive member of this invention has plated each plating layer by plating Fe or Fe alloy, Ni or Ni alloy, Cu or Cu alloy, Sn or Sn alloy in this order on the surface of Cu-type base material. After forming, a conductive member in which an Fe-based underlayer, a Ni-based thin film layer, a Cu-Sn intermetallic compound layer, and a Sn-based surface layer are sequentially formed on the Cu-based substrate by heating and reflow treatment. The plating layer made of Fe or Fe alloy is formed by electrolytic plating with a current density of 5 to 25 A / dm ² , and the plating layer made of Ni or Ni alloy has a current density of 20 to 50 A / dm 2. formed by ^two of the electrolytic plating, the Cu or current density plating layer of Cu alloy is formed by electroplating of 20~60A / dm ^2, current plating layer by the Sn or Sn alloy Degrees is formed by electrolytic plating 10~30A / dm ^2, the reflow treatment is carried out after a lapse of 15 minutes after forming the plating layer, heating rate of the plated layer 20 to 75 ° C. / sec A heating step of heating to a peak temperature of 240 to 300 ° C., 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 a temperature of 100 to 250 ° C. after the primary cooling. And a secondary cooling step of cooling at a cooling rate of / sec .

Cu plating at a high current density increases the grain boundary density and helps to form a uniform alloy layer. 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.

Further, when the current density of Fe plating is less than 5 A / dm ² , Fe plating particles are enlarged and the effect of suppressing the diffusion of Sn is poor. On the other hand, when the current density exceeds 25 A / dm ² , pinholes due to hydrogen generation occur. It tends to occur and is not preferable.

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 the crystal grains are refined and reflowed or commercialized. When the 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 adhesion of bubbles, which makes it easy to peel off from this. 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.
Cu or Fe alloy, Ni or Ni alloy, Cu or Cu alloy, Sn or Sn alloy is plated at a higher current density than the prior art, and the reflow treatment is performed immediately after plating, so that Cu can be used during reflow. Sn reacts actively, and a large amount of Ni-based thin film layer is covered with the Cu ₃ Sn layer, and a uniform Cu ₆ Sn ₅ layer is generated.

When the heating rate in the heating process is less than 20 ° C./second, Cu atoms preferentially diffuse in the Sn grain boundary until Sn plating melts, and the intermetallic compound grows abnormally in the vicinity of the grain boundary. Therefore, 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 stable Cu—Sn intermetallic compound layer having a two-layer structure with few irregularities can be obtained.

  According to the present invention, the Fe-based underlayer formed on the surface of the Cu-based substrate has high heat resistance as a barrier layer, and can effectively prevent Cu diffusion at high temperatures. Since the formation of the Cu-Sn intermetallic compound layer is formed on the Ni-based thin film layer on the underlayer, these adhesions are also good, so that the surface state is well maintained and the increase in contact resistance is suppressed. In addition, it is possible to prevent peeling of the plating film, and to reduce wear and insertion / extraction force when using the connector and to suppress variations.

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. It is a graph which shows the time-dependent change of the contact resistance in each electrically-conductive member of a present Example and a comparative example.

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, and as shown in FIG. 1, Ni is interposed on the surface of a Cu-based substrate 1 via an Fe-based underlayer 2. The Cu-Sn intermetallic compound layer 4, the Cu-Sn intermetallic compound layer 4, and the Sn-based surface layer 5 are formed in this order, and the Cu-Sn intermetallic compound layer 4 is further formed of a Cu ₃ Sn layer 6 and a Cu ₆ Sn ₅ layer 7. It consists of and.
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 Fe-based underlayer 2 is formed by electrolytic plating of Fe or an Fe alloy, and is formed on the surface of the Cu-based substrate 1 with a thickness of 0.1 to 1.0 μm. If the Fe base layer 2 is less than 0.1 μm, the Cu base substrate 1 does not have sufficient Cu diffusion preventing function. If it exceeds 1.0 μm, the Fe base layer 2 cracks during bending. Is likely to occur. For example, an Fe—Ni alloy is used as the Fe alloy.
The Ni-based thin film layer 3 is formed by electrolytic plating of Ni or a Ni alloy, and is formed on the surface of the Fe-based underlayer 2 with a thickness of, for example, 0.05 to 0.3 μm. If this Ni-based thin film layer 3 is as small as less than 0.05 μm, there is a risk of peeling due to Ni diffusion at high temperatures, and if it exceeds 0.3 μm, the strain becomes large and it is easy to peel off. Cracks are likely to occur during bending.

The Cu-Sn intermetallic compound layer 4 is an alloy layer formed by diffusing Cu plated on the Ni-based thin film layer 3 and Sn on the surface by reflow treatment, as will be described later. The Cu—Sn intermetallic compound layer 4 further includes a Cu ₃ Sn layer 6 disposed on the Ni-based thin film layer 3, 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 4 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.
When the thickness X of the recess 8 is less than 0.05 μm, Sn diffuses from the recess 8 to the Ni-based thin film layer 3 at a high temperature, and the Ni-based thin film layer 3 may be damaged. When defects occur in the Ni-based thin film layer 3, the adhesion at the interface between the Fe-based underlayer 2 and the Cu—Sn intermetallic compound layer 4 is reduced, causing peeling. 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, when 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 4 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 4 is set to 1.2-5. If this ratio is reduced and the unevenness of the Cu—Sn intermetallic compound layer 4 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 4 is reduced. The Cu—Sn intermetallic compound layer 4 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 protruding portion 9 to the recessed portion 8 exceeds 5, the unevenness of the Cu-Sn intermetallic compound layer 4 becomes a resistance during insertion / extraction when used as a connector, so that the insertion / extraction force The effect of reducing is poor.
For example, when the thickness X of the concave portion 8 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 4 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 4 covers the Ni-based thin film layer 3, the area coverage is 60 to 100%. If the area coverage is less than 60%, diffusion of Ni atoms in the Ni-based thin film layer 3 from the uncoated portion to the Cu ₆ Sn ₅ layer 7 at a high temperature is promoted, and the Ni-based thin film layer 3 There is a risk of loss. 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 on the Ni-based thin film layer 3 is 60% or more means that the Cu ₃ Sn layer 6 is not locally present on the surface of the Ni-based thin film layer 3 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 4 is 0.05 to 1.5 μm. Therefore, the Cu ₆ Sn ₅ layer 7 covers the Ni-based thin film layer 3 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 4, 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 thin film layer 3, when the average thickness is as small as less than 0.01 μm, the effect of suppressing the diffusion of the Ni-based thin film layer 3 becomes poor. . On the other hand, if it exceeds 0.5 μm, the Cu ₃ Sn layer 6 is changed to the Sn-rich Cu ₆ Sn ₅ layer 7 at a high temperature, and the Sn-based surface layer 5 is reduced correspondingly, 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.
The Cu—Sn intermetallic compound layer 4 is alloyed by diffusion of Cu plated on the Ni-based thin film layer 3 and Sn on the surface. In some cases, the entire Cu plating layer is diffused to form the Cu—Sn intermetallic compound layer 4, 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.
Further, since Ni in the Ni-based thin film layer 3 slightly diffuses into the Cu—Sn intermetallic compound layer 4, Ni is slightly mixed in the Cu ₆ Sn ₅ layer 7.

  The outermost Sn-based surface layer 5 is formed by performing reflow treatment after electrolytic plating of Sn or an Sn alloy, and is formed to a thickness of, for example, 0.05 to 2.5 μm. If the thickness of the Sn-based surface layer 5 is less than 0.05 μm, Cu diffuses at high temperatures and Cu oxide is easily formed on the surface, so that the 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 4 existing in the lower layer of the flexible Sn-based surface layer 5 is weakened, and the insertion / extraction force during use as a connector is increased. However, it is difficult to reduce the insertion / extraction force associated with the increase in the number of pins of the connector.

Next, a method for manufacturing such a conductive member will be described.
First, as a Cu-based substrate, a Cu or Cu alloy plate material is prepared, and after cleaning the surface by degreasing, pickling, etc., Fe plating, 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 conditions for Fe plating, a sulfuric acid bath mainly composed of ferrous sulfate (FeSO ₄ ) and ammonium chloride (NH ₄ Cl) is used as a plating bath. When the Fe—Ni plating is used, a plating bath mainly composed of nickel sulfate (NiSO ₄ ), ferrous sulfate (FeSO ₄ ), and boric acid (H ₃ BO ₃ ) is used. The plating temperature is 45 to 55 ° C., and the current density is 5 to 25 A / dm ² .

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 5 below. Table 1 shows the conditions for Fe plating, and Table 2 shows the conditions for Fe-Ni plating.

And after performing the four types of plating processing of the plating processing of the conditions of either Table 1 or Table 2, and the plating processing of the conditions of Table 3-Table 5, it heats and performs reflow processing. 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 four-layer plating is performed on the surface of the Cu-based substrate 1 according to the plating conditions in combination of Table 1 or Table 2 and Tables 3 to 5, reflow is performed under the temperature profile conditions shown in FIG. by processing as shown in FIG. 1, the surface of the Cu Keimotozai 1 is covered by the Fe-based base layer 2, Cu 3 _Sn layer 6 through the Ni-based thin film layer 3 formed thereon, further thereon Cu ₆ Sn ₅ layer 7 is formed, and Sn-based surface layer 5 is formed on the outermost surface.

Next, examples of the present invention will be described.
As a 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 each of the plating treatments of Fe, Ni, Cu, and Sn was sequentially performed. In this case, as shown in Table 6, 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 Fe plating layer is 0.5 μm, the thickness of the Ni plating layer is 0.3 μm, the thickness of the Cu plating layer is 0.3 μm, and the thickness of the Sn plating layer is The thickness 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 four 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 four 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.

The cross section of the treatment material of this example is the result of energy dispersive X-ray spectroscopic analysis (TEM-EDS analysis) using a transmission electron microscope. As a result, a Cu-based substrate, an Fe-based underlayer, a Ni-based thin film layer, a Cu ₃ Sn layer. Cu ₆ Sn ₅ layer and Sn-based surface layer have a five-layer structure, and 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 thin film layer has a 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 thin film layer was 60% or more.

For the samples prepared as shown in Table 6, the contact resistance after 175 ° C. × 1000 hours, the presence or absence of peeling, the wear resistance, and the corrosion resistance were measured. The dynamic friction coefficient was also measured.
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.
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.
The abrasion resistance was determined by a reciprocating wear test specified in JIS H 8503, with a test load of 9.8 N and abrasive paper no. 400, the number of times until the substrate (Cu-based substrate) was exposed was measured, a sample in which plating remained even after 50 times of testing, and a sample in which the substrate was exposed within 50 times were evaluated as x. .
As for corrosion resistance, a neutral salt spray test specified in JIS H8502 was used for 24 hours. The case where no red rust was observed was evaluated as ◯, and the case where red rust was observed was evaluated as x.
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. 3, the male test piece 22 is fixed on the horizontal base 21, the hemispherical convex surface of the 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.
These results are shown in Table 7.

  As is apparent from Table 7, the conductive member of this example had low contact resistance at high temperatures, no peeling, and excellent wear resistance and solderability. Further, since the dynamic friction coefficient is small, it can be determined that the insertion / extraction force when using the connector is small and good.

Regarding the contact resistance, Sample 6 and Sample 31 were also measured for changes over time during heating at 175 ° C. × 1000 hours. The result is shown in FIG.
As shown in FIG. 4, in the sample 6 of the present invention, the increase in contact resistance is slight even when exposed to a long time at high temperature, whereas in the case of the sample 31 of the prior art, the contact resistance increases after 1000 hours. Increased to 10 mΩ or more. The sample 6 of the present invention has a five-layer structure in which the Sn-based surface layer remains due to the heat resistance of the Fe-based underlayer, whereas in the sample 31 of the prior art, the Fe-based underlayer is thin and has a barrier. Since the function as a layer is not sufficient, it is considered that the contact resistance increased due to the Cu oxide covering the surface.

  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. The results are shown in Table 8.

As can be seen from Table 8, peeling occurs when the standing time after plating becomes longer. 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.

As a result of the above research, by providing the Fe-based underlayer, the heat resistance is improved, and due to the ductility of Fe, it is possible to prevent plating peeling and cracking during bending. Furthermore, since the Fe-based underlayer having high hardness and high toughness is provided, the wear resistance is good and sliding wear as a connector terminal can be prevented. Furthermore, the solderability is also improved, and soldering is easier than the conductive member by the conventional three-layer plating. Further, the Cu ₆ Sn ₅ layer and the Cu ₃ Sn layer have an effect of preventing the reaction between the Ni-based thin film layer and the Sn-based surface layer, and among these, the Cu ₃ Sn alloy layer is more effective. Further, since Sn atoms diffuse into Ni from the recesses of the Cu ₆ Sn ₅ layer and Sn and Ni react with each other, the Cu ₆ Sn ₅ layer has relatively few irregularities, and the Cu ₃ Sn layer is more surface of the Ni-based thin film layer. It was found that the coating of a large amount prevents contact resistance deterioration during heating, prevents the occurrence of peeling, and further reduces the insertion / extraction force when using the connector.
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.

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

Claims (3)

On the surface of the Cu-based substrate, a Ni-based thin film layer, a Cu-Sn intermetallic compound layer, and a Sn-based surface layer are formed in this order via an Fe-based underlayer.
The Fe-based underlayer has a thickness of 0.1 to 1.0 μm,
The Cu—Sn intermetallic compound layer further comprises a Cu ₃ Sn layer disposed on the Ni-based thin film layer and a Cu ₆ Sn ₅ layer disposed on the Cu ₃ Sn layer. The thickness of the concave portion of the Cu-Sn intermetallic compound layer including the ₃ Sn layer and the Cu ₆ Sn ₅ layer is 0.05 to 1.5 μm ,
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,
An average thickness of the Cu ₃ Sn layer is 0.01 to 0.5 μm, and an area coverage of the Cu ₃ Sn layer with respect to the Ni-based thin film layer is 60 to 100%. Element. By plating the surface of the Cu-based substrate with Fe or Fe alloy, Ni or Ni alloy, Cu or Cu alloy, Sn or Sn alloy in this order to form each plating layer, and then heating and reflowing A method for producing a conductive member in which an Fe-based underlayer, a Ni-based thin film layer, a Cu-Sn intermetallic compound layer, and a Sn-based surface layer are sequentially formed on the Cu-based substrate,
The plating layer made of Fe or Fe alloy is formed by electrolytic plating with a current density of 5 to 25 A / dm ² ,
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 after 1 to 15 minutes have elapsed since the formation of the plating layer, and a 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; 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. The manufacturing method of the electrically-conductive member characterized by the above-mentioned. The electrically-conductive member manufactured by the manufacturing method of Claim 2 .

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