JP2008150690A - Metal strip, connector, and method of manufacturing metal strip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal strip which is good in solderability to a substrate, generates no whisker when it is stored, subjected to reflow, or fitted to FPC (flexible print cable) or FFC (flexible flat cable), and is required for a lead-free connector. <P>SOLUTION: Ni plating is applied onto a parent metal of the metal strip; Cu plating is applied onto it; furthermore, Sn plating is applied onto it. The thickness of the Cu plating layer is made such that the ratio of the Cu plating with respect to Cu plating plus Sn plating is 3-7 mass%. At least one king of metal selected from the group consisting of Zn, Al, Si, Mg and Ti is made to be contained in the Sn plating layer in an amount of 1 mass% or less. A Cu-Sn compound layer is formed between the Ni plating layer and the Sn plating layer by heat-treating the connector having the characteristics at a temperature of the melting point of Sn or higher. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a connector terminal to be mated for electrical connection with a terminal constituting an electrical connector, in particular, another member such as a flexible printed circuit board, a metal strip constituting the terminal, and a method for manufacturing the same. In particular, the present invention relates to a lead-free plated connector terminal subjected to lead-free plating and a metal strip constituting the lead-free plated connector terminal.

  Since the terminals constituting the connector are soldered when attached to the substrate, the entire surface of the metal strip constituting the terminals is generally plated. As a lead-free plating process, it is known that an Sn-based solder layer is formed on a Ni underlayer from the viewpoint of solderability. Further, in the case of a narrow pitch connector, it is necessary to simultaneously prevent the occurrence of whiskers that come into contact with adjacent connector terminals and may cause a short circuit.

  There has been proposed a method for ensuring solder wettability by applying Ni plating on a base metal and then applying Sn-Cu plating thereon (Patent Document 1). In addition, a method has been proposed in which whisker is prevented from being generated from a contact portion at the time of connection by performing Ni or Cu base plating on a base metal and then Sn-Bi plating thereon (Patent Document). 2). Furthermore, by forming a plating layer having a Ni layer, a Ni-Sn intermetallic compound layer, a Ni-Sn intermetallic compound and Sn mixed layer, and an oxidized Sn layer in order on the base metal, whisker generation can be prevented. A method for achieving both solder wettability has also been proposed (Patent Document 3).

JP 2002-164106 A JP 2005-56605 A JP 2006-49083 A

  However, in the metal strip provided by simply Sn-Cu plating on the Ni base plating, solder wettability is ensured, but it is difficult to completely prevent whisker generation. Cu-Sn compound is not formed at the interface between Ni base plating and Sn-Cu plating only by two-layer plating, and the Sn-Cu plating Sn and Ni compound formation reaction is sufficiently suppressed in the subsequent reflow treatment. However, a large amount of Ni—Sn compound is formed at the interface, thereby generating a large internal compressive stress inside the plating, and thus whisker.

  In addition, it is difficult to completely prevent whisker generation by simply performing Sn-Bi plating on the Ni or Cu base plating of the metal strip. Ni or Cu and Sn of Sn—Bi plating react at the time of reflow, Ni—Sn compound or Cu—Sn compound is formed at the interface, and there is no reaction barrier layer, so the amount of these reaction layers formed is large. As a result, a large internal compressive stress is generated inside the plating, and as a result, whisker is generated although the frequency of occurrence is lower than that of the Ni base plating / Sn—Cu plating.

  Furthermore, in the method of forming a plating layer having a Ni layer, a Ni—Sn intermetallic compound layer, a mixed layer of Ni—Sn intermetallic compound and Sn, and an oxidized Sn layer in this order, the Ni—Sn compound is oxidized on the surface by It grows as it reaches the material layer, and a large amount of Ni-Sn compound is generated, so that a large internal compressive stress is generated inside the plating, and whisker is generated even with the support column effect of Ni-Sn compound. End up. In addition, since a part of the Ni—Sn compound reaches the Sn oxide layer on the surface, the solder wettability is also inferior compared to the case where it is not.

  In any of the above examples, there is a problem that no means capable of suppressing the generation of internal compression stress due to the lid effect of the outermost oxidized Sn layer, that is, the generation of whiskers, is provided.

  Therefore, the present invention provides a metal strip satisfying ensuring solder wettability, suppression of whisker generation by mass growth of intermetallic compounds inside the plating film, and suppression of whisker generation by the lid effect of the Sn oxide film on the solder surface, and The connector formed by this is provided.

The following is a brief description of an outline of typical inventions disclosed in the present application.
(1) a base metal, a Ni layer formed on the base metal, a layer of eutectic composition of Sn and the first metal formed on the Ni layer, the Ni layer and the co A metal strip comprising a compound layer of Sn and the first metal formed between layers having a crystal composition.
(2) Base metal, Ni layer formed on the base metal, Sn-Cu eutectic composition layer formed on the Ni layer, Ni layer and Sn-Cu eutectic composition And a Cu—Sn compound layer formed between the two layers.
(3) Base metal, Ni layer formed on the base metal, Sn layer formed on the Ni layer, and Cu-Sn formed between the Ni layer and the Sn layer And a metal layer.
(4) A connector formed by processing the metal strip according to any one of (1) to (3).
(5) A method for producing a metal strip, comprising a step of sequentially laminating a Ni layer, a Cu layer, and a Sn layer on a base metal, and the stacked base metal is more than a solidus line of Sn-Cu alloy. Heat treatment at a temperature, and forming a Cu-Sn compound layer on the Ni layer and a Sn-Cu eutectic composition layer on the Cu-Sn compound layer, Method.

  According to the present invention, a metal strip that can satisfy solder wettability, suppression of whisker generation by mass growth of intermetallic compounds inside the plating film, and suppression of whisker generation by the lid effect of the Sn oxide film on the solder surface, And a connector formed thereby.

  First, 1st Embodiment of the metal strip which concerns on this invention is described using FIG.

FIG. 1 shows a cross section of the layer structure of a metal strip 1 according to the present invention. On a base metal 2, a Ni layer 3 and a Cu—Sn compound layer 4 formed on the Ni layer 3 are shown. In addition, a laminated structure is formed by the Sn-0.7Cu layer 5 having a Sn-Cu eutectic composition formed on the Cu-Sn compound layer 4.
In this structure, it is important that a double reaction barrier layer is formed between the base metal 2 and the Sn-0.7Cu layer 5. That is, according to this, the reaction between the Ni layer 3 and the Sn-0.7Cu layer 5 can be suppressed by the Cu—Sn compound layer 6, and the base metal 2 and the Cu—Sn compound layer can be prevented by the Ni layer 3. 4. Since the reaction between the Sn-0.7Cu layer 5 can be suppressed, whisker suppression can be achieved. In general, as the base metal 2, a Cu alloy such as phosphor bronze is often used, and the promotion of compounding by the Cu supply from this Cu alloy may cause whiskers. Since the Cu supply from the metal is cut off and the reaction between the base metal and the Cu-Sn compound layer 6 is inhibited, the base metal is made a special material according to the metal strip having the layer structure of the present invention. Ordinary phosphor bronze can be used.
Furthermore, according to the present invention, since the outermost surface is the Sn-0.7Cu layer 5 with relatively little Sn oxide, it is possible to provide a metal strip with good solder wettability at the time of subsequent connection.

In this embodiment, the Ni layer is used as the first layer, the Cu—Sn compound layer is used as the second layer, and the Sn—Cu eutectic composition layer is used as the third layer. However, the present invention is not limited to this. As described above, various modifications can be made within the range of combinations of materials that can form a double reaction-preventing barrier layer to prevent the progress of compounding.
Specifically, a Zn—Sn compound layer may be used as the second layer, and a layer having a eutectic composition of Sn and Zn may be used as the third layer. Further, the first layer may be a Co layer, an Fe layer, or the like.

Next, the manufacturing method of the metal strip which concerns on this invention is demonstrated.
FIG. 2 is a cross-sectional view of the first laminated structure used for manufacturing the metal strip according to the present invention, which is formed by sequentially plating a Ni layer 3, a Cu layer 6, and a Sn layer 7 on the base metal 2. The metal strip before heat treatment is shown. The thickness of the Ni layer 3 is preferably in the range of 1 to 5 μm. If the thickness of the Ni layer 3 is less than 1 μm, the reaction suppression function between the base metal 2 and the Cu layer 6 and the Sn layer 7 does not function sufficiently, and if it exceeds 5 μm, the elasticity of the metal strip is impaired. Because it is.

The reason why the Cu layer 6 and the Sn layer 7 are formed on the Ni layer 3 is that the Cu—Sn compound layer 6 is formed immediately above the Ni layer 3 by a subsequent heat treatment. The reason why the Sn layer 7 is the outermost surface is to ensure solder wettability.
The total thickness of the Cu layer 6 and the Sn layer 7 is preferably in the range of 1 to 5 μm. This is because if the thickness is less than 1 μm, the solder wettability decreases, and if it exceeds 5 μm, no further improvement in solder wettability is observed.
Moreover, it is preferable that the thickness of the Cu layer 6 is such that the ratio of the Cu layer 6 to (Cu layer 6 + Sn layer 7) is 3 to 7 mass%. When the ratio of the Cu layer 6 is less than 3 mass%, when the heat treatment is performed later, the formation of the Cu—Sn compound layer 4 immediately above the Ni layer 3 becomes insufficient in some places, and the Ni layer 3 formed by the Cu—Sn compound layer 4 The reaction suppression effect between the Sn-0.7Cu layers 5 becomes insufficient. If the ratio of the Cu layer 6 exceeds 7 mass%, it takes time to completely react the Cu layer 6 with the Sn layer 7 during the subsequent heat treatment.

  Furthermore, the Sn layer 7 preferably contains 1 mass% or less of one or more metals selected from Zn, Al, Si, Mg, and Ti. By containing a small amount of these easily oxidizable metals, these metals are selectively oxidized during the subsequent heat treatment or reflow. As a result, the oxidation of the outermost Sn layer 7 can be minimized, and the occurrence of internal compressive stress in the plating film due to the lid effect of the outermost oxidized Sn layer can be suppressed, thereby preventing the generation of whiskers. When the content of these metals in the Sn layer 5 exceeds 1 mass%, solder wettability is deteriorated.

After the above layer formation treatment (mainly plating treatment), the metal strip 1 is heat-treated at a temperature equal to or higher than the melting point of Sn and at least equal to or higher than the solidus of the Sn—Cu alloy to completely react the Cu layer 6 and the Sn layer 7. By doing so, the Cu—Sn compound 4 is formed immediately above the Ni layer 3, and the eutectic composition layer of Cu and Sn is formed on the surface layer.
According to this manufacturing method, Cu of the Cu—Sn compound layer 4 to be formed is supplied only from the first Cu layer 6, and Cu from the base metal 2 such as phosphor bronze is not supplied. That is, since the thickness of the Cu—Sn compound layer 4 depends only on the thickness of the first Cu layer 6, the Cu—Sn compound layer 4 is formed so as not to be insufficient in some cases. The Cu—Sn compound 4 immediately above the Ni layer 3 does not become too thick, and the generation of compressive stress inside the plating film due to this can be suppressed, and the generation of whiskers can be suppressed.

  Next, as a cross-sectional view of the second laminated structure used for manufacturing the metal strip according to the present invention, FIG. 3 shows a Sn layer 3 in which a Ni layer 3 and a Cu—Sn compound exist in a floating island shape on a base metal 2. The metal strip before heat treatment formed by sequentially plating the Cu alloy layer 8 is shown. The thickness of the Ni layer 3 is preferably in the range of 1 to 5 μm. When the thickness of the Ni layer 3 is less than 1 μm, the reaction suppression function between the base metal 2 and the Sn—Cu alloy layer 8 does not sufficiently function, and when it exceeds 5 μm, the elasticity of the metal strip 1 is impaired. Because it is.

  Here, the reason why the Sn—Cu alloy layer 8 in which the Cu—Sn compound exists in a floating island shape is formed on the Ni layer 3 is that the Cu—Sn compound layer 4 is formed immediately above the Ni layer 3 by the subsequent heat treatment. Because. Therefore, it is preferable that the ratio of Cu in the Sn—Cu alloy layer 8 is 3 to 7 mass%. When the proportion of Cu is less than 3 mass%, when heat treatment is performed later, the formation of the Cu—Sn compound layer 4 immediately above the Ni layer 3 becomes insufficient in some places, and the Ni layer 3 and the Sn— This is because the reaction inhibiting effect with the layer 5 having a Cu eutectic composition becomes insufficient. Further, if the Cu ratio exceeds 7 mass%, the melting point of the Sn—Cu alloy layer 8 becomes high, and when heat treatment and reflow treatment are performed later, the heat resistance of other members, the heat resistance of the substrate, and the post-process From the allowable temperature, heat treatment and reflow treatment must be performed at a temperature lower than the liquidus temperature. In this case, the Cu—Sn compound existing in the floating island shape in the Sn—Cu alloy layer 8 before the heat treatment Is not completely melted, and the formation of the Cu—Sn compound layer 6 immediately above the Ni layer 3 is inadequate in some places, and between the Ni layer 3 formed by the Cu—Sn compound layer 6 and the layer 5 of Sn—Cu eutectic composition. This is because the reaction inhibition effect is insufficient.

  Note that the thickness of the Sn—Cu alloy layer 8 is preferably in the range of 1 to 5 μm. This is because if the thickness is less than 1 μm, the solder wettability decreases, and if it exceeds 5 μm, no further improvement in solder wettability is observed.

  Further, the Sn—Cu alloy layer 8 preferably contains 1 mass% or less of one or more kinds of metals of Zn, Al, Si, Mg, and Ti. By containing a small amount of these easily oxidizable metals, these metals are selectively oxidized during the subsequent heat treatment or reflow. This makes it possible to minimize the oxidation of the outermost surface Sn—Cu alloy layer 8 and to suppress the generation of internal compressive stress in the plating film due to the lid effect of the outermost surface oxidized Sn layer. Can be suppressed. When the content of these metals in the Sn-Cu alloy layer 8 exceeds 1 mass%, solder wettability is deteriorated.

After the above layer formation treatment (mainly plating treatment), the metal strip 1 was heat-treated at a temperature equal to or higher than the melting point of the Sn—Cu alloy layer 8 so as to exist in a floating island shape in the Sn—Cu alloy layer 8. The Cu—Sn compound is once melted and reprecipitated immediately above the Ni layer 3 to form the Cu—Sn compound layer 4, and the surface layer is a layer having a eutectic composition of Cu and Sn.
According to this manufacturing method, Cu of the Cu—Sn compound layer 4 to be formed is supplied only from the first Sn—Cu compound layer 8, and Cu from the base metal 2 such as phosphor bronze is not supplied. That is, since the thickness of the Cu—Sn compound layer 4 depends only on the amount of Cu in the first Sn—Cu alloy layer 8, the thickness is so small that the formation of the Cu—Sn compound layer 4 does not become insufficient in some places. By setting the content, the Cu—Sn compound layer 4 immediately above the Ni layer 3 does not become too thick, and the generation of compressive stress inside the plating film due to this can be suppressed, and the generation of whiskers can be suppressed.

  As described above, in each of the embodiments, the manufacturing method of the layer structure in which the Ni layer is the first layer, the Cu—Sn compound layer is the second layer, and the Sn—Cu eutectic composition layer is the third layer is described. This is not the only case, and the same applies to the manufacturing method of the layer structure in which the Zn—Sn compound is used as the second layer and the eutectic composition of Sn and Zn is used as the third layer, and Zn is used instead of Cu. Just do it.

  In any of the above-described embodiments, an example in which the surface layer is the most stable Sn-Cu eutectic composition layer has been shown. However, when the surface layer is extremely thin, for example, about 2 μm or less. In this case, the surface layer may be an Sn layer. When the layer thickness is 2 μm or less, all Cu components are used on the Cu-Sn compound layer side below the surface layer rather than existing as a layer of Sn—Cu eutectic composition, and the surface layer is This is because the Sn layer becomes stable.

  Here, a connector is mainly used as a usage form of the metal strip. A flexible printed circuit board (FPC) or a flexible flat cable (FFC) may be used to connect the boards together. It is necessary to provide connectors on both boards and connect both connectors via FPC or FFC. However, among these connectors, the metal strip of the present invention can be used especially for lead-free connectors with a narrow terminal pitch of 0.5 mm or less.

The results of specific experiments are shown below.
[Experimental example]
FIG. 4 shows the results of confirming the solder wettability and the presence or absence of whisker generation for the metal strip samples before the heat treatment of the present invention (Experimental Examples 1 to 10) and the conventional metal strip samples (Comparative Examples 1 to 3). . For the sample, a phosphor bronze base metal was used, and a plating layer was sequentially formed on the surface by a normal electroplating method. Thereafter, heat treatment was performed in N 2 at 250 ° C. for 10 seconds.

  In the solder wettability test, Sn-3Ag-0.5Cu lead-free solder containing 11 mass% of rosin flux was applied on the outermost metallized layer of each of the above samples. evaluated. The lead-free solder bath temperature was 250 ° C. In FIG. 4, a sample with good solder wettability was indicated by “◯”, a sample with slightly poor wettability was indicated by “Δ”, and a sample with poor wettability was indicated by “X”.

  The presence or absence of whisker generation was confirmed as follows. The connector was mated with an FPC, and was allowed to stand for 1000 hours at room temperature and 50% relative humidity, followed by observation with an optical microscope and a scanning electron microscope. Samples with no whisker generation or whisker generation were observed. The sample with the maximum length of 50 μm or less was marked with “◯”, and the sample with whisker generation with a maximum length of 50 μm or more was marked with “X”.

In Experimental Examples 1 to 10, good solder wettability was obtained, and no whisker generation was observed. In any of these samples, the plating layer after heat treatment is composed of the Ni layer / Cu—Sn alloy compound layer / Sn—Cu eutectic composition (a trace amount of Zn, Al, Si, Mg, Ti oxide contained).
Moreover, in Comparative Examples 1-3 which are background art, the problem was seen in either solder wettability or whisker generation | occurrence | production.

  From the above experimental results, it was found that the metal strips according to the present invention are all good in solder wettability and whisker resistance.

It is typical sectional drawing of the layer structure of 1st Embodiment of the metal strip which concerns on this invention. It is a typical sectional view of the 1st layer structure before heat treatment of the metal strip concerning the present invention. It is typical sectional drawing of the 2nd layer structure before heat processing of the metal strip which concerns on this invention. It is a figure which shows the solder wettability and whisker generation | occurrence | production situation of the metal strip of this invention and the conventional metal strip.

Explanation of symbols

1 Metal strip 2 Base metal 3 Ni layer 4 Cu-Sn compound layer 5 Sn-Cu eutectic layer 6 Cu layer 7 Sn layer 8 Sn-Cu alloy layer

Claims (23)

With base metal,
Ni layer formed on the base metal,
A layer of eutectic composition of Sn and the first metal formed on the Ni layer;
A compound layer of Sn and the first metal formed between the Ni layer and the layer of the eutectic composition;
Metal strip characterized by having. With base metal,
Ni layer formed on the base metal,
A layer of Sn-Cu eutectic composition formed on the Ni layer;
A Cu-Sn compound layer formed between the Ni layer and the Sn-Cu eutectic composition layer;
Metal strip characterized by having. The metal strip according to claim 2,
The metal strip, wherein the Ni layer and the Sn-Cu eutectic composition layer are not in contact with each other by the Cu-Sn compound layer formed therebetween. The metal strip according to claim 2 or 3,
The Cu-Sn compound layer is formed in contact with the Ni layer,
The metal strip, wherein the Sn—Cu eutectic composition layer is formed in contact with the Cu—Sn compound layer without contacting the Ni layer. A metal strip according to any one of claims 2 to 4,
The Sn-Cu eutectic composition layer and the Cu-Sn compound layer are:
A metal strip formed by heat-treating a Cu layer and an Sn layer sequentially laminated on the Ni layer. With base metal,
Ni layer formed on the base metal,
A layer of Sn-Zn eutectic composition formed on the Ni layer;
A Zn-Sn compound layer formed between the Ni layer and the Sn-Zn eutectic composition layer;
Metal strip characterized by having. A metal strip according to claim 6,
The metal sheet, wherein the Ni layer and the Sn-Zn eutectic composition layer are not in contact with each other by the Zn-Sn compound layer formed therebetween. A metal strip according to claim 6 or 7,
The Zn-Sn compound layer is formed in contact with the Ni layer,
The layer of Sn-Zn eutectic composition is formed in contact with the Zn-Sn compound without being in contact with the Ni layer. A metal strip according to any one of claims 6 to 8,
The Sn-Zn eutectic composition layer and the Zn-Sn compound layer are:
A metal strip formed by heat-treating a Zn layer and a Sn layer sequentially stacked on the Ni layer. With base metal,
Ni layer formed on the base metal,
A Sn layer formed on the Ni layer;
A Cu-Sn compound layer formed between the Ni layer and the Sn layer;
Metal strip characterized by having. The metal strip according to claim 10,
The metal strip, wherein the Ni layer and the Sn layer are not in contact with each other by the Cu-Sn compound layer formed therebetween. The metal strip according to claim 10 or 11,
The metal strip, wherein the Sn layer has a thickness of 2 μm or less. The metal strip according to any one of claims 1 to 12,
A metal strip, wherein a Co layer or an Fe layer is formed instead of the Ni layer. A metal strip according to any one of claims 1 to 13,
The metal strip is characterized in that the base metal is a Cu alloy. The metal strip according to claim 14, wherein
The metal strip is characterized in that the base metal is phosphor bronze. A connector formed by processing the metal strip according to any one of claims 1 to 15. A method of manufacturing a metal strip,
A step of sequentially stacking a Ni layer, a Cu layer, and a Sn layer on the base metal;
The laminated base metal is heat-treated at a temperature equal to or higher than the solidus of the Sn—Cu alloy, a Cu—Sn compound layer on the Ni layer, and a Sn—Cu eutectic layer on the Cu—Sn compound layer Forming a
A method for producing a metal strip characterized by comprising: It is a manufacturing method of the metal strip according to claim 17,
The said heat processing is processed at the temperature more than the liquidus of Sn-Cu alloy, The manufacturing method of the metal strip characterized by the above-mentioned. A method for producing a metal strip according to claim 17 or 18,
The ratio of the said Cu layer with respect to the total mass of the said Sn layer and the said Cu layer is 3-7 mass%, The manufacturing method of the metal strip characterized by the above-mentioned. A method for producing a metal strip according to any one of claims 17 to 19,
1. The metal strip manufacturing method according to claim 1, wherein the Sn layer contains 1 mass% or less of at least one metal selected from Zn, Al, Si, Mg, and Ti. A method of manufacturing a metal strip,
A step of sequentially laminating a Ni layer and a Sn-Cu alloy layer on the base metal,
The laminated base metal is heat-treated at a temperature equal to or higher than the solidus of the Sn—Cu alloy, a Cu—Sn compound layer on the Ni layer, and a Sn—Cu eutectic layer on the Cu—Sn compound layer Forming a
A method for producing a metal strip characterized by comprising: It is a manufacturing method of the metal strip according to claim 21,
The ratio of Cu in the said Sn-Cu alloy layer is 3-7 mass%, The manufacturing method of the metal strip characterized by the above-mentioned. It is a manufacturing method of the metal strip according to claim 21 or 22,
1. The metal strip manufacturing method according to claim 1, wherein the Sn—Cu alloy layer contains 1 mass% or less of at least one metal selected from Zn, Al, Si, Mg, and Ti.

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