JP2010090433A - Method of manufacturing metal strip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a metal strip required for connector that satisfies both of low insertion force and high heat resistance. <P>SOLUTION: The method of manufacturing a metal strip includes: a first process of laminating a Ni layer and a Sn-Cu alloy layer in the order on a metal base material; and a second process of thermally treating the metal base material having the laminated layers thereon at a melting point of Sn-Cu eutectic crystal or more to form a compound layer in which a Cu-Ni-Sn compound and a Cu-Sn compound are mixed and a Sn layer or Sn-based alloy layer in the order on the Ni layer on the metal base material, wherein, in the first process, an Sn-Cu alloy layer having a Cu content of 5 mass% or more is obtained as the Sn-Cu alloy layer and, therefore, the metal strip that satisfies both of low insertion force and high heat resistance can be easily manufactured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a connector having mating terminals used for connecting electrical wiring of automobiles / consumer equipment and the like, and a method for producing a surface-treated metal strip as a connector material. In particular, the present invention relates to a method for manufacturing a metal strip for a connector that requires high heat resistance and low insertion force in addition to low contact resistance, corrosion resistance, and solderability.

  Except in the case of important electrical circuits that require high electrical connection reliability for low-level signal voltages and currents, etc., for connector terminals used to connect electrical wiring of automobiles and consumer devices, etc. Cu or Cu alloy subjected to Sn plating (including Sn alloy plating such as solder plating) is used.

Sn plating is less expensive than Au plating and other surface treatments. In addition, Sn is soft (Vickers hardness H _v ≒ 30) and has a thin and stable oxide film on the surface. This is destroyed by a little force, and when it slides, it has a low contact resistance value (less than 5mΩ) ). Because of these characteristics, Sn plating is often used. Among them, Sn-free plating that responds to recent regulations on environmentally hazardous substances, especially reflow Sn plating that has almost no reports of short circuit failure due to whisker generation. It has become mainstream.

  However, Sn has a gas tight (airtight) structure that adheres male and female at the contact point of the connector due to its softness, so the insertion force required to insert the connector is higher than a connector made of gold plating or the like . In recent years, due to the increase in the number of circuits of electric / electronic components, the number of connectors for supplying electric signals to the circuits has been increased, and the accompanying increase in connector insertion force has become a problem. For example, in an automobile assembly line, the work of fitting a connector is currently almost done manually. If the insertion force of the connector is increased, a burden is placed on the worker on the assembly line, which directly leads to a decrease in work efficiency. For this reason, it is strongly desired to reduce the insertion force of the Sn plating material.

  Here, since the compound layer (for example, Cu—Sn compound) formed inside the plating layer by reflow is hard, the insertion force can be reduced by the presence of this compound layer. From the viewpoint of reducing insertion force, the compound layer may be exposed on the surface or directly below the outermost Sn layer, but in the former case, the Cu-Sn compound exposed on the surface when left at high temperature Since Cu is oxidized to form Cu oxide, the contact resistance is greatly increased and the solderability is greatly deteriorated. That is, it does not have high heat resistance.

  On the other hand, in the automobile, the electrification is rapidly progressing from the pursuit of safety, environment and comfort. Along with this, the number of circuits increases, so that connection parts such as connector terminals are required to have high heat resistance that can be mounted in an engine room in order to save space. Therefore, in order to achieve both low insertion force and high heat resistance, it is necessary to control the thickness of the Sn layer on the Cu-Sn compound to be thin without exposing the Cu-Sn compound to the surface as in the latter case. is there. If the Sn layer on the Cu-Sn compound is thick, Sn is soft and the insertion force becomes high.

  A method has been proposed in which the electroplating is performed in the order of Ni plating, Cu plating, and Sn plating on the base metal, and then reflow is performed, so that both the insertability and heat resistance of the Cu alloy Sn plating strip are compatible (Patent Literature). 1). Also, after roughening the surface of the base metal, a Cu plating layer and an Sn plating layer are formed in this order on top of each other, and by reflow treatment, both low insertion force and low contact resistance after holding at high temperature for a long time are achieved. A method to do this has been proposed (Patent Document 2).

JP 2007-63624 A JP 2007-100220 A

  However, Patent Document 1 tries to control the thickness of the outermost Sn layer by reducing the surface roughness of the compound layer. However, in the method of reflowing Ni / Cu / Sn three-layer plating, each layer is formed by reflowing. It is difficult to control sufficiently thinly with high accuracy. As a result, the average thickness of the outermost Sn layer after reflowing is 0.02 μm at the minimum, and considering the surface roughness of the compound layer, a part of the compound layer is exposed on the surface. Even if a low insertion force can be realized with this, high heat resistance cannot be achieved as described above.

  In Patent Document 2, it is assumed that a part of the compound is exposed from the surface. By controlling the exposure rate, both low insertion force and high heat resistance are achieved. However, as in Patent Document 1, even though a low insertion force can be realized, high heat resistance cannot be achieved at the same time.

  The present invention provides a method for producing a metal strip for a connector that has no compound layer surface exposure after reflow treatment and has a small insertion force (small coefficient of dynamic friction).

The following is a brief description of an outline of typical inventions disclosed in the present application.
(1) A method for producing a metal strip, in which a Ni layer and a Sn—Cu alloy layer are sequentially laminated on a base metal, and the laminated base metal is at least the melting point of the Sn—Cu eutectic. To form a structure in which a compound layer in which a Cu-Ni-Sn compound and a Cu-Sn compound are mixed, a Sn layer or a Sn-based alloy layer are sequentially laminated on the Ni layer on the base metal. A metal strip manufacturing method characterized in that, in the first step, a Sn-Cu alloy layer having a Cu content of 5 mass% or more is used as the Sn-Cu alloy layer. .
(2) A method for producing a metal strip, in which a Ni layer and a Sn—Cu alloy layer are sequentially laminated on a base metal, and the laminated base metal is at least the melting point of the Sn—Cu eutectic. A second step of forming a structure in which a Cu-Ni-Sn compound layer, a Cu-Sn compound layer, a Sn layer or a Sn-based alloy layer is sequentially laminated on the Ni layer on the base metal In the first step, a Sn-Cu alloy layer having a Cu content of 5 mass% or more is used as the Sn-Cu alloy layer.

  Since the metal strip manufactured by the manufacturing method of the present invention and the connector using the same are not exposed to the Cu-Ni-Sn compound or Cu-Sn compound, they can be stored for a long time or at a high temperature for a long time. Even when used, since no Cu oxide is formed on the outermost surface, contact resistance is not significantly increased and solderability is not significantly deteriorated. That is, it has high heat resistance. In addition, the surface roughness of the Cu-Ni-Sn compound layer or Cu-Sn compound layer formed immediately above the Ni layer after reflow can be reduced, so these compounds are not exposed to the surface, and the outermost Sn layer or Sn- Since the thickness of the Cu alloy layer can be controlled thinly, the coefficient of dynamic friction can be reduced, and the insertion force of the connector can be reduced.

  FIG. 2 shows a cross section of the layer structure of the metal strip before heat treatment used for producing the metal strip according to the present invention. On the base metal, a laminated structure is formed by a Ni layer and a Sn—Cu alloy layer formed on the Ni layer. In general, a Cu alloy is used as a base metal. As the Cu alloy, phosphor bronze, spring Corson alloy or the like is applicable as the metal strip for the connector of the present invention. The Ni layer is usually formed by electro Ni plating, but may be formed by other methods. The Ni layer needs to be formed thick enough so that it does not dissolve in the compound layer during reflow and disappears after reflow. For this purpose, the Ni layer should have a thickness of 0.7 μm or more, preferably at least 0.4 μm, if possible. The Sn—Cu alloy layer is also usually formed by electroplating, but may be formed by other methods (dipping or the like). The thickness of the Sn—Cu alloy layer is preferably in the range of 1 to 5 μm. This is because if the thickness is less than 1 μm, the solderability decreases, and if it exceeds 5 μm, the moldability of the metal strip decreases. The total thickness of the surface layers (Ni layer and Sn—Cu alloy layer) is preferably in the range of 1 to 10 μm. This is because if the thickness is less than 1 μm, the solderability decreases, and if it exceeds 10 μm, the moldability of the metal strip decreases.

Next, the Sn—Cu alloy layer is partially melted by raising the metal strip before the heat treatment to a temperature equal to or higher than the melting point 227 ° C. (solidus temperature) of the Sn—Cu alloy layer. Thereby, a part of Cu-Sn compound which existed in the floating island shape in the Sn-Cu alloy layer melts. Furthermore, when the temperature is raised to a temperature above the liquidus, the Sn—Cu alloy layer and the Cu—Sn compound are completely melted. At this time, a part of Ni is melted from the Ni layer, and then the Cu—Ni—Sn compound is reprecipitated when cooled. At this time, the Ni layer serves as a nucleus for reprecipitation, and the Cu—Ni—Sn compound precipitates on the Ni layer, resulting in any one of the laminated structures shown in FIGS. In addition to the Cu—Ni—Sn compound, a Cu—Sn compound may also precipitate. Here, it is desirable that the heat treatment be performed at a low temperature of 300 ° C. or less and in a short time of about 0 to 60 seconds as much as possible from the viewpoint of securing solderability and suppressing the increase in surface hardness. The atmosphere is preferably in an inert gas having an oxygen concentration of 10 ppm or less, for example, in N ₂ . When the hardness of the surface is high, when the male terminal and female terminal of the connector are mated and stress is applied from the outside, compressive stress is generated in the mating part, causing whiskers that cause electrical shorting. It becomes easy to grow. Further, when heat treatment is performed at a high temperature, the degree of oxidation of the surface is increased, and the solder wettability is remarkably deteriorated.

  Here, in the present invention, by using a Sn-Cu alloy layer having a Cu content of 5 mass% or more, the Cu-Ni-Sn compound precipitated on the Ni layer becomes a small lump, as will be described in detail later. As in the laminated structure shown in FIG. 4, the surface roughness of the compound layer can be reduced. Furthermore, the layer structure before reflow is only two layers of Ni layer and Sn-Cu alloy layer, and thickness control is easy, so the surface roughness of the outermost Sn layer after reflow is based on the surface roughness after reflow. It becomes easy to adjust in advance to reduce the thickness.

Hereinafter, the compound layer interface after reflow which is different from the case where the Cu content of the Sn—Cu alloy layer before reflow is less than 5 mass% and the case where it is 5 mass% or more will be described.
When the Cu content of the Sn—Cu alloy layer formed on the Ni layer is less than 5 mass%, it was found that a rod-like Cu—Ni—Sn compound as shown as an example in FIG. 9 is precipitated. When this compound was analyzed by EDX, it was found to be a Cu—Ni—Sn compound having a high Ni / Cu ratio and a relatively high Ni content (FIG. 10). When such a compound is generated, as can be seen from the cross-sectional SEM image of FIG. 9, the degree of unevenness (surface roughness) of the compound layer increases. When the surface roughness Rmax of the compound layer of various samples with a Cu content of the Sn-Cu alloy layer of less than 5 mass% was measured, it was 1.2 μm or more for a sample with a large plating layer thickness, and 0.8 for a sample with a small plating layer total thickness. It was as large as μm or more.

  These results are summarized in FIG. 3 as a comparative example. These samples in which the surface roughness of the compound layer was large are two of the sample in which the compound is exposed on the surface (FIG. 5) and the sample in which the compound is large but the compound is not exposed on the surface (FIG. 6). Divided into types. The former sample has a low coefficient of dynamic friction of around 0.4 and a low insertion force level, but the contact resistance after leaving at 150 ° C. for 1000 hours after exposure to the compound is significantly high at 13.5 to 14.0 mΩ. As described above, this is considered to be because Cu of the Cu—Ni—Sn compound partially exposed on the surface is oxidized by leaving it at a high temperature for a long time to form Cu oxide. Since the latter sample was not exposed to the compound, there was almost no decrease in contact resistance even after standing at high temperature for a long time. However, the average thickness of the outermost Sn or Sn alloy layer is as large as 0.65 to 0.75 μm, and the Sn or Sn alloy layer on the compound layer recess is very thick (FIG. 6). All were large, 0.52 to 0.68, and the insertion force was at a high level.

  Next, when the Cu content of the Sn-Cu alloy layer formed on the Ni layer is 5 mass% or more, it was found that a small block of Cu-Ni-Sn compound as shown as an example in FIG. 7 is precipitated. . When this compound was analyzed by EDX, it was found to be a Cu-Ni-Sn compound having a low Ni / Cu ratio and a relatively low Ni content (FIG. 8). When such a compound is produced, as can be seen from the cross-sectional SEM image of FIG. 7, the degree of unevenness (surface roughness) of the compound layer becomes small. When the surface roughness Rmax of the compound layer of various samples having a Cu content of 5 mass% or more in the Sn—Cu alloy layer was measured, all samples were as small as 0.5 to 0.6 μm.

  These results are summarized as an example in FIG. These samples, which had a small surface roughness of the compound layer, had no surface exposure of the compound (Fig. 4), had a low coefficient of dynamic friction of around 0.4, a low insertion force level, and reduced contact resistance even after standing at high temperature for a long time. Was hardly seen. The reason why the contact resistance did not deteriorate is as described above. The reason why the coefficient of dynamic friction was low was that the surface roughness of the compound layer was small, so the average thickness of the outermost Sn or Sn alloy layer was as small as 0.30 to 0.35 μm, and the Sn or Sn alloy above the compound layer recess This is because the layer thickness is also relatively thin (FIG. 4).

  In FIG. 4, the final final adjustment of the thickness of the outermost Sn or Sn alloy layer is that the Sn content of the Sn—Cu alloy layer formed on the Ni layer in the initial stage is set to 5 mass% or more. This is done by controlling the thickness of the Cu alloy layer. The thinner the Sn—Cu alloy layer, the thinner the outermost Sn or Sn alloy layer after reflow.

Since the outermost layer after reflowing becomes a residual phase after reprecipitation of the Cu—Ni—Sn compound, it usually has a eutectic composition of Sn—0.7Cu. However, since this phase is very thin, the Cu-Sn compound (Cu ₆ Sn ₅ ) phase that is normally dispersed in the Sn-0.7Cu eutectic phase is integrated with the Cu-Ni-Sn compound layer, It is also assumed that the outermost surface is pure Sn. This is because when the Sn-0.7Cu layer is very thin, the Cu-Sn compound is integrated with the Cu-Ni-Sn compound layer rather than existing as a phase of the Sn-Cu eutectic composition, and the outermost surface becomes the Sn layer. This is because the direction becomes stable.

The results of specific experiments are shown below.
[Experimental example]
About the metal strip samples (Examples 1 to 3) of the present invention and the conventional metal strip samples (Comparative Examples 1 to 6), the compound layer surface roughness (a), the average of the outermost Sn or Sn-based alloy layer FIG. 3 shows the results of examining the thickness (b), presence / absence of surface exposure of the compound, cross-sectional state, dynamic friction coefficient, contact resistance after leaving at 150 ° C. for 1000 hours. For the sample, a phosphor bronze base metal (32 mm x 15 mm x 0.25 mm thickness) was used. After the electrolytic degreasing treatment and acid activation treatment were performed as plating pretreatment, the plating layer was applied to the surface of a normal electric layer. It formed one by one by the plating method. A fluorescent X-ray film thickness meter was used to measure the plating film thickness. Then, it heat-processed by hold | maintaining for 10 second at 260 degreeC in N2.

  The compound layer surface roughness (a) (maximum height Rmax) and the average thickness (b) of the Sn or Sn alloy layer on the outermost surface are FIB processed in the depth direction to obtain a cross-section, and the cross-section SIM image It was determined by observing. The presence or absence of the surface exposure of the compound and the cross-sectional state were confirmed by observing and analyzing the sample with SEM / EDX after cross-sectional polishing.

The dynamic friction coefficient was obtained from the average value of the maximum frictional force when both the plate specimen and the contact specimen were made of metal strip samples and they were slid 15 mm at a load of 4.9 N and a feed rate of 50 mm / min. The contact sample R was 3.5 mm.
Contact resistance was measured by the four probe method. The open-circuit voltage was 20mV, the current was 10mA, the sliding load was 0.49N, the speed was 1mm / min, and the distance was 1mm.

  In Examples 1 to 3, the surface roughness Rmax (a) of the compound layer was as small as 0.5 to 0.6 μm. Further, the surface of the compound was not exposed, and the average thickness (b) of the outermost Sn or Sn-based alloy layer was as small as 0.30 to 0.32 mm. That is, the cross-sectional state was as shown in FIG. The coefficient of dynamic friction was as low as around 0.4, and it was at a low insertion force level, and contact resistance was hardly reduced even after standing at high temperature for a long time. An example of the SEM image of the cross section after actual reflow is shown in FIG. The Cu—Ni—Sn compound was in a small lump shape and had a low degree of unevenness. The Cu—Ni—Sn compound was found to be a Cu—Ni—Sn compound having a relatively low Ni / Cu ratio and a low Ni content from the EDX analysis results shown in FIG.

  In Comparative Examples 1 to 6 using conventional metal strip samples, the surface roughness Rmax (a) of the compound layer was as large as 0.8 to 1.4 μm. The sample with a larger total plating layer thickness was 1.2 μm or more, and the sample with a smaller total plating layer thickness was 0.8 μm or more. In Comparative Examples 1 and 5, there was exposure of the surface of the compound, whereby the contact resistance after holding at high temperature for a long time was remarkably high at 13.5 to 14.0. The coefficient of dynamic friction was as low as 0.4 or less. From the average thickness (b) of the outermost Sn or Sn-based alloy layer and the cross-sectional observation results, the cross-sectional state was as shown in FIG.

  On the other hand, in Comparative Examples 2 to 4 and 6, there was no surface exposure of the compound. Accordingly, the contact resistance after holding at high temperature for a long time was as low as 2.2 to 2.5. The coefficient of dynamic friction was as high as 0.52 to 0.68. From the average thickness (b) of the outermost Sn or Sn-based alloy layer and the cross-sectional observation results, the cross-sectional state was as shown in FIG.

  The relationship between the Cu content of the initial Sn—Cu alloy layer and the surface roughness of the compound layer formed on Ni after reflow is summarized in FIG. The composition of the compound formed on Ni after reflow differs depending on whether the Cu content of the Sn-Cu alloy layer is 5 mass% or more, and a large difference was caused in the surface roughness of the compound layer.

  From the above experimental results, if the method for producing a metal strip according to the present invention is used, it is possible to easily produce a metal strip constituting a connector that achieves both low insertion force and high heat resistance.

  The main use form of the metal strip of the present invention is a connector. In order to simplify the assembly of electrical and electronic equipment, the connector is a connector that is a pair of females and males used when connecting cables, cables and boards, and boards, and has mating terminals. Typical required characteristics are low contact resistance, corrosion resistance, and solderability. The metal strip of the present invention can be used particularly for connectors that require high heat resistance and low insertion force in addition to these required characteristics.

It is the figure which showed the relationship between Cu content of the Sn-Cu plating of embodiment of the metal strip which concerns on this invention, and the surface roughness of a compound layer. It is typical sectional drawing of the layer structure of the metal strip before heat processing used in order to manufacture the metal strip which concerns on this invention. It is a figure which shows the various characteristics after heat processing of the metal strip of this invention, and the conventional metal strip. It is typical sectional drawing of the surface layer structure after the heat processing of the metal strip of this invention. It is an example of typical sectional drawing of the surface layer structure after the heat processing of the conventional metal strip. It is another example of typical sectional drawing of the surface layer structure after the heat processing of the conventional metal strip. It is a figure which shows an example of the cross-sectional SEM image of the surface layer after the heat processing of the metal strip of this invention. It is a figure which shows an example of the EDX analysis result of the Cu-Ni-Sn compound layer after heat processing of the metal strip of this invention. It is a figure which shows an example of the cross-sectional SEM image of the surface layer after the heat processing of the conventional metal strip. It is a figure which shows an example of the EDX analysis result of the Cu-Ni-Sn compound layer after the heat processing of the conventional metal strip.

Claims (5)

A method of manufacturing a metal strip,
A first step of sequentially laminating a Ni layer and a Sn-Cu alloy layer on the base metal,
A compound layer in which a Cu—Ni—Sn compound and a Cu—Sn compound are mixed on the Ni layer on the base metal by heat-treating the laminated base metal above the melting point of the Sn—Cu eutectic. A second step of forming a structure in which Sn layers or Sn-based alloy layers are sequentially laminated;
Have
In the first step, a Sn-Cu alloy layer having a Cu content of 5 mass% or more is used as the Sn-Cu alloy layer. A method of manufacturing a metal strip,
A first step of sequentially laminating a Ni layer and a Sn-Cu alloy layer on the base metal,
The laminated base metal is heat-treated to a melting point of Sn-Cu eutectic or higher, and a Cu-Ni-Sn compound layer, a Cu-Sn compound layer, a Sn layer, or a Sn layer is formed on the Ni layer on the base metal. A second step of forming a structure in which Sn-based alloy layers are sequentially laminated;
Have
In the first step, a Sn-Cu alloy layer having a Cu content of 5 mass% or more is used as the Sn-Cu alloy layer. It is a manufacturing method of the metal strip according to claim 1 or 2,
In the first step, the thickness of the Ni layer is 0.4 μm or more. It is a manufacturing method of the metal strip according to claim 3,
In the first step, the thickness of the Sn—Cu alloy layer is set to 1 μm to 5 μm. A method for producing a metal strip according to any one of claims 1 to 4,
A method for producing a metal strip, wherein a Cu alloy is used as the base metal.

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