阅读说明：本技术 镀锡铜端子材及其制造方法 (Tin-plated copper terminal material and method for producing same ) 是由 马渡芙弓 牧一诚 船木真一 井上雄基 中矢清隆 于 2019-03-29 设计创作，主要内容包括：一种镀锡铜端子材,在由铜或铜合金构成的基材上依次层叠镍或镍合金层、铜锡合金层及锡层而成,锡层的平均厚度为0.2μm以上且1.2μm以下,铜锡合金层是以Cu<Sub>6</Sub>Sn<Sub>5</Sub>为主成分且所述Cu<Sub>6</Sub>Sn<Sub>5</Sub>的一部分铜取代为镍的化合物合金层,并且平均结晶粒径为0.2μm以上且1.5μm以下,在锡层表面露出有铜锡合金层的一部分,并且锡凝固部以岛状存在,所述锡凝固部的沿锡层表面的方向的平均直径为10μm以上且1000μm以下,所述锡凝固部相对于锡层表面的面积率为1％以上且90％以下。(A tin-plated copper terminal material comprising a base material made of copper or a copper alloy and, laminated thereon in this order, a nickel or nickel alloy layer, a copper-tin alloy layer and a tin layer, wherein the tin layer has an average thickness of 0.2 to 1.2 [ mu ] m, and the copper-tin alloy layer is made of Cu 6 Sn 5 As a main component and the Cu 6 Sn 5 Has an average crystal grain diameter of 0.2 to 1.5 [ mu ] m, and one of the copper-tin alloy layers is exposed on the surface of the tin layerAnd a tin solidified portion having an island shape, an average diameter of the tin solidified portion in a direction along a surface of the tin layer being 10 μm or more and 1000 μm or less, and an area ratio of the tin solidified portion to the surface of the tin layer being 1% or more and 90% or less.)

1. A tin-plated copper terminal material comprising a base material made of copper or a copper alloy and, laminated thereon in this order, a nickel or nickel alloy layer, a copper-tin alloy layer and a tin layer,

the average thickness of the tin layer is 0.2-1.2 μm,

the copper-tin alloy layer is made of Cu₆Sn₅As a main component and the Cu₆Sn₅Wherein a part of copper is substituted with nickel, and the average crystal grain size is 0.2 to 1.5 μm,

a part of the copper-tin alloy layer is exposed on the surface of the tin layer, and a tin solidified portion is present in an island shape,

the average diameter of the tin solidified portion in the direction along the surface of the tin layer is 10 [ mu ] m or more and 1000 [ mu ] m or less, and the area ratio of the tin solidified portion to the surface of the tin layer is 1% or more and 90% or less.

2. The tin-plated copper terminal material according to claim 1,

the thickness of the tin solidified part is more than 0.1 μm and less than 10 μm.

3. The tin-plated copper terminal material according to claim 1 or 2,

the exposed area ratio of the copper-tin alloy layer to the surface of the tin layer excluding the tin solidified portion is 1% or more and 60% or less.

4. A method for producing a tin-plated copper terminal material, which comprises forming a nickel-plated or nickel-plated alloy layer, a copper-plated layer and a tin-plated layer in this order on a base material made of copper or a copper alloy, and then forming a tin-plated copper terminal material by reflow soldering, wherein the nickel-plated or nickel-plated alloy layer, the copper-tin alloy layer and the tin layer are laminated in this order on the base material,

the thickness of the nickel plating or the nickel alloy plating layer is set to be more than 0.05 μm and less than 1.0 μm,

the thickness of the copper plating layer is set to be 0.05 μm or more and 0.40 μm or less,

the thickness of the tin-plated layer is set to be more than 0.5 μm and less than 1.5 μm,

the reflow soldering process includes: a heat treatment step of performing a primary heat treatment in which the substrate is heated to 240 ℃ or higher at a temperature rise rate of 20 ℃/sec or more and 75 ℃/sec or less, and then performing a secondary heat treatment in which the substrate is heated at a temperature of 240 ℃ or more and 300 ℃ or less for a time of 1 second or more and 15 seconds or less; a primary cooling step of cooling the substrate at a cooling rate of 30 ℃/sec or less for 2 seconds to 15 seconds after the heat treatment step; and a secondary cooling step of cooling at a cooling rate of 100 ℃/sec or more and 300 ℃/sec or less after the primary cooling.

5. The method for producing a tin-plated copper terminal material according to claim 4,

in the reflow process, the substrate on which the nickel or nickel alloy plating layer, the copper plating layer, and the tin plating layer are applied is moved in a surface direction of the substrate, and hot air is blown to the surface of the substrate in the moving direction to heat the surface of the substrate.

Technical Field

The present invention relates to a terminal for a connector used for connecting an electric wire of an automobile, a daily use device, or the like, and more particularly to a tin-plated copper terminal material useful as a terminal for a multi-pin connector, and a method for producing the same. The present application claims priority based on japanese patent application No. 2018-067620, filed on 30/3/2018, and the contents of which are incorporated herein by reference.

Background

In the automobile industry in recent years, electrification has been rapidly carried out, and with the increase in functionality and integration of electrical equipment, the miniaturization and increase in the number of pins of connectors used have become remarkable. If the number of pins of the connector is increased, a large force is required for the entire connector when the connector is mounted even if the insertion force per one pin is small, and the productivity may be lowered. Therefore, attempts have been made to reduce the friction coefficient of the tin-plated terminal material and to reduce the insertion force per one pin.

As a measure to respond to these requirements, for example, a terminal material of patent document 1 is proposed. The terminal material can reduce the coefficient of dynamic friction and the insertion force by growing a copper-tin intermetallic compound in a columnar shape under the tin layer on the surface and uniformly and finely exposing the copper-tin intermetallic compound on the surface of the tin layer.

Further, patent document 2 disclosesBy coating the surface of the tin layer at a rate of 35mm per minute²There is a radial tin solidification structure, and the surface roughness Ra of the outermost surface in the direction perpendicular to rolling is set to be 0.05 [ mu ] m or less. The radial tin solidification structure is formed by reflow-soldering a base material plated with tin or the like, heating the base material to a specific temperature, and spraying cooling water in the form of mist, thereby reducing the surface roughness. In patent document 2, the copper-tin alloy layer is also exposed on the surface of the tin layer at an area ratio of 40% or less.

Patent document 1: japanese patent laid-open No. 2014-240520

Patent document 2: japanese patent laid-open publication No. 2016-156051

Further, the increased amount of electric current due to the increased number of pins of connectors and the miniaturization of electric devices, and the increased use in high temperature environments such as the vicinity of an engine room, require high heat resistance of terminals. In this regard, in the above-described conventional technique, when the copper-tin alloy is placed at a high temperature for a long time, the copper-tin alloy exposed on the surface is oxidized to increase the contact resistance, and thus it is difficult to say that the copper-tin alloy is suitable for long-term use at a high temperature. Therefore, a material with less increase in contact resistance even when used at high temperatures for a long time is required.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object of the present invention is to improve high-temperature reliability by suppressing an increase in contact resistance at high temperatures while maintaining good electrical connection characteristics and insertion/removal properties of terminals.

As a result of active studies, the present inventors have found that by intentionally providing tin aggregation portions on the surface, an increase in contact resistance can be suppressed even after long-term use at high temperatures.

That is, the tin-plated copper terminal material of the present invention is obtained by laminating a nickel or nickel alloy layer, a copper-tin alloy layer and a tin layer in this order on a base material made of copper or a copper alloy, wherein the average thickness of the tin layer is 0.2 μm or more and 1.2 μm or less, and the copper-tin alloy layer is made of Cu₆Sn₅As a main component and the Cu₆Sn₅A part of copper is substituted with a nickel compound alloy layer, and the average crystal grainThe tin layer has a diameter of 0.2 [ mu ] m or more and 1.5 [ mu ] m or less, a part of the copper-tin alloy layer is exposed on the surface of the tin layer, and tin solidified portions protruding from the surface of the tin layer are present in island shapes, the average diameter of the tin solidified portions in the direction along the surface of the tin layer is 10 [ mu ] m or more and 1000 [ mu ] m or less, and the area ratio of the tin solidified portions to the surface of the tin layer is 1% or more and 90% or less.

Herein, the "nickel layer or nickel alloy layer" is referred to as the "nickel or nickel alloy layer".

The reason why the average thickness of the tin layer is set to 0.2 μm or more and 1.2 μm or less is that if it is less than 0.2 μm, the electrical connection reliability is lowered, and if it exceeds 1.2 μm, the surface layer cannot be a composite structure of tin and copper-tin alloy and is occupied only by tin, and thus the kinetic friction coefficient is increased. The upper limit thickness of the tin layer is preferably 1.1 μm or less, and more preferably 1.0 μm or less.

Since the copper-tin alloy layer is made of Cu₆Sn₅As a main component, the Cu is present₆Sn₅A part of copper is substituted by nickel (Cu, Ni)₆Sn₅The alloy can form a steep uneven shape at the interface with the tin layer. The reason why the average crystal grain size of the copper-tin alloy layer is set to 0.2 μm or more and 1.5 μm or less is that if it is less than 0.2 μm, the copper-tin alloy layer becomes too fine and cannot grow sufficiently in the longitudinal direction (surface normal direction) as it is exposed to the surface, the coefficient of kinetic friction of the terminal material surface cannot be set to 0.3 or less, and if it exceeds 1.5 μm, it grows largely in the transverse direction (direction orthogonal to the surface normal direction) and cannot be made into a steep uneven shape, and the coefficient of kinetic friction cannot be set to 0.3 or less.

The lower limit of the average crystal grain size of the copper-tin alloy layer is preferably 0.3 μm or more, more preferably 0.4 μm or more, and still more preferably 0.5 μm or more. The upper limit of the average crystal grain size of the copper-tin alloy layer is preferably 1.4 μm or less, more preferably 1.3 μm or less, and still more preferably 1.2 μm or less.

In addition, since a part of the copper-tin alloy layer is exposed on the surface of the tin layer and a tin solidified portion is present in an island shape independently of this, and tin remains in the portion where the tin solidified portion is present even when used at high temperature, the copper-tin alloy in this portion can be inhibited from being oxidized and expanded, and the increase in contact resistance can be inhibited. In this case, if the average diameter of the tin solidified portion is less than 10 μm or the area ratio of the tin solidified portion is less than 1%, the effect of suppressing the increase in contact resistance is poor, and if the average diameter exceeds 1000 μm or the area ratio of the tin solidified portion exceeds 90%, the friction coefficient of the surface becomes large and the insertion/extraction property is impaired.

In a preferred embodiment of the tin-plated copper terminal material according to the present invention, the maximum thickness of the tin solidified portion is preferably 0.1 μm or more and 10 μm or less.

When the maximum thickness of the tin solidified portion is less than 0.1 μm, the effect of suppressing the increase of the contact resistance at high temperature is poor, and when it exceeds 10 μm, the coefficient of dynamic friction tends to increase. The maximum thickness of the tin solidified portion is preferably 0.3 μm or more and less than 8.0 μm. More preferably 0.5 μm or more and 7.0 μm or less.

In a preferred embodiment of the tin-plated copper terminal material according to the present invention, the exposed area ratio of the copper-tin alloy layer to the surface of the tin layer excluding the tin solidified portion is preferably 1% or more and 60% or less.

When the exposed area ratio of the copper-tin alloy layer on the tin layer surface is less than 1%, the coefficient of dynamic friction is hardly 0.3 or less, and when it exceeds 60%, there is a possibility that the electrical connection characteristics are deteriorated. The lower limit of the area ratio is preferably 1.5% or more, and the upper limit is 50% or less. The lower limit is more preferably 2% or more and the upper limit is more preferably 40% or less.

The method for producing a tin-plated copper terminal material according to the present invention is a method for producing a tin-plated copper terminal material in which a nickel or nickel-plated alloy layer, a copper plated layer, and a tin plated layer are sequentially formed on a base material made of copper or a copper alloy, and then the nickel or nickel alloy layer, the copper-tin alloy layer, and the tin layer are sequentially stacked on the base material by a reflow soldering process, wherein the thickness of the nickel or nickel-plated alloy layer is 0.05 μm or more and 1.0 μm or less, the thickness of the copper plated layer is 0.05 μm or more and 0.40 μm or less, and the thickness of the tin plated layer is 0.5 μm or more and 1.5 μm or less, the reflow soldering process including: a heat treatment step of performing a primary heat treatment in which the substrate is heated to 240 ℃ or higher at a temperature rise rate of 20 ℃/sec or more and 75 ℃/sec or less, and then performing a secondary heat treatment in which the substrate is heated at a temperature of 240 ℃ or more and 300 ℃ or less for a time of 1 second or more and 15 seconds or less; a primary cooling step of cooling the substrate at a cooling rate of 30 ℃/sec or less for 2 seconds to 15 seconds after the heat treatment step; and a secondary cooling step of cooling at a cooling rate of 100 ℃/sec or more and 300 ℃/sec or less after the primary cooling.

Herein, the "nickel layer or nickel alloy layer" is referred to as the "nickel or nickel alloy layer". Also, the "nickel plating layer or nickel alloy plating layer" is referred to as the "nickel plating or nickel alloy plating layer".

Formed by plating nickel or a nickel alloy on a substrate after a reflow process (Cu, Ni)₆Sn₅The alloy can thereby steepen the irregularities of the copper-tin alloy layer and make the kinetic friction coefficient 0.3 or less.

When the thickness of the nickel-plated layer or the nickel-plated alloy layer is less than 0.05 μm, (Cu, Ni)₆Sn₅The content of nickel contained in the alloy is small, and a copper-tin alloy having a steep uneven shape cannot be formed, and if it exceeds 1.0 μm, bending and the like are difficult.

When the nickel or nickel alloy layer is made to have a function as a barrier layer for preventing diffusion of copper from the base material to improve heat resistance or when wear resistance is improved, the thickness of the nickel plating or nickel alloy layer is preferably 0.1 μm or more. The plating layer is not limited to pure nickel, and may be a nickel alloy such as nickel-cobalt (Ni — Co) or nickel-tungsten (Ni — W).

When the thickness of the copper plating layer is less than 0.05 mu m, (Cu, Ni)₆Sn₅The higher the nickel content in the alloy, the more minute the shape of the copper-tin alloy becomes, and the more exposed the alloy becomes to the surface, the less the alloy can grow sufficiently in the longitudinal direction (normal direction of the surface), so that the coefficient of kinetic friction cannot be 0.3 or less, and if it exceeds 0.40 μm, (Cu, Ni)₆Sn₅The amount of nickel contained in the alloy is small, and the alloy grows largely in the lateral direction (direction orthogonal to the surface normal direction), and a copper-tin alloy layer having a steep uneven shape cannot be formed.

If the thickness of the tin plating layer is less than 0.5 μm, the tin layer after reflow soldering becomes thin and the electrical connection characteristics are impaired, and if it exceeds 1.5 μm, the exposure of the copper-tin alloy layer on the surface becomes small, and it is difficult to make the kinetic friction coefficient 0.3 or less.

In the reflow process, the tin solidified portion is easily generated by performing the heat treatment in the heating step under two different conditions. The surface tin layer is rapidly heated in the primary heat treatment to a high temperature of 240 ℃ or higher in an early stage, and then the surface tin layer is secondarily heat-treated at 240 ℃ or higher and 300 ℃ or lower, thereby ensuring a long melting time of the surface tin layer.

As a result, a part of the copper-tin alloy layer having sharp irregularities at the interface with the tin layer is exposed to the surface, and the tin in a molten state is repelled and aggregated in the copper-tin alloy layer. In this case, if the temperature increase rate of one temperature increase is less than 20 ℃/sec, copper atoms preferentially diffuse in the tin grain boundaries until the tin plating melts, and the intermetallic compound abnormally grows in the vicinity of the grain boundaries, so that a copper-tin alloy layer having a steep uneven shape cannot be formed. On the other hand, if the temperature increase rate exceeds 75 ℃/sec, the growth of the intermetallic compound becomes insufficient, and a desired intermetallic compound layer cannot be obtained in the subsequent cooling.

When the temperature reached by the primary heat treatment is less than 240 ℃, the tin is insufficiently melted, and a desired tin solidified portion cannot be obtained. If the secondary heat treatment is carried out in the range of 240 ℃ to 300 ℃, the temperature may be appropriately raised or lowered, or may be maintained at a specific temperature, but if the heat treatment time exceeds 15 seconds, the tin solidified portion becomes excessively large and the dynamic friction coefficient becomes large. If the time is less than 1 second, the tin is insufficiently melted, and a desired tin solidified portion cannot be formed. The time of the secondary heat treatment includes a time when the temperature is raised or lowered from the temperature reached by the primary heat treatment. The peak temperature of the secondary heat treatment is more preferably 250 ℃ or higher.

Further, if the peak temperature in the heat treatment step is less than 240 ℃, tin does not melt uniformly, and if the peak temperature exceeds 300 ℃, the tin solidified portion becomes excessively large, which is not preferable.

In the cooling step, primary cooling at a relatively low cooling rate is providedAnd a step of stably diffusing copper atoms in the tin particles to grow a desired intermetallic compound structure. If the cooling rate in the primary cooling step exceeds 30 ℃/sec, the intermetallic compound cannot be sufficiently grown due to the influence of rapid cooling, and the copper-tin alloy layer cannot be sufficiently exposed to the surface. In the case where the cooling time is less than 2 seconds, the intermetallic compound also does not grow sufficiently. If the cooling time exceeds 15 seconds, Cu₆Sn₅The alloy grows excessively and coarsens, and a nickel-tin compound layer is formed under the copper-tin alloy layer depending on the thickness of the copper plating layer, and the barrier property of the nickel or nickel alloy layer is lowered.

The primary cooling process is suitable for air cooling. Therefore, after the primary cooling step, rapid cooling is performed by the secondary cooling step, and the growth of the intermetallic compound layer is completed in a desired structure. If the cooling rate in the secondary cooling step is less than 100 ℃/sec, the growth of the intermetallic compound further progresses, and a desired shape of the intermetallic compound cannot be obtained.

In a preferred embodiment of the method for producing a tin-plated copper terminal material according to the present invention, the reflow soldering process preferably advances the base material on which the nickel-plated or nickel-plated alloy layer, the copper-plated layer, and the tin-plated layer are applied in a surface direction of the base material, and blows hot air in the advancing direction on the surface of the base material to heat the surface of the base material.

According to the present invention, it is possible to improve high-temperature reliability by suppressing an increase in contact resistance at high temperatures while maintaining good electrical connection characteristics and insertion/removal properties of the terminal.

Drawings

Fig. 1 is a cross-sectional view schematically showing a tin-plated copper terminal material according to an embodiment.

FIG. 2 is a photomicrograph of the surface of example 4.

Fig. 3 is a front view generally showing an apparatus for measuring a dynamic friction coefficient.

Fig. 4 is a cross-sectional view generally showing a test piece for measuring a contact resistance value.

Detailed Description

A tin-plated copper terminal material according to an embodiment of the present invention will be described. Hereinafter, the "nickel layer or nickel alloy layer" is referred to as "nickel or nickel alloy layer". The "nickel plating layer or nickel alloy plating layer" is referred to as "nickel plating or nickel alloy plating layer".

The tin-plated copper terminal material 1 of the present embodiment is formed by stacking a nickel or nickel alloy layer 3, a copper-tin alloy layer 4, and a tin layer 5 in this order on a base material 2 made of copper or a copper alloy layer.

The composition of the base material 1 is not particularly limited as long as it is made of copper or a copper alloy.

The nickel or nickel alloy layer 3 is a layer made of a nickel alloy such as pure nickel, nickel cobalt (Ni — Co), or nickel tungsten (Ni — W).

The nickel or nickel alloy layer 3 is not necessarily limited, but the average thickness of the nickel or nickel alloy layer 3 is 0.05 μm or more and 1.0 μm or less, the average crystal grain size is 0.01 μm or more and 0.5 μm or less, the standard deviation of the crystal grain size/the average crystal grain size is 1.0 or less, and the arithmetic average roughness Ra of the surface in contact with the copper-tin alloy layer is 0.005 μm or more and 0.5 μm or less.

When the average thickness of the nickel or nickel alloy layer 3 is less than 0.05. mu.m, (Cu, Ni)₆Sn₅The content of Ni contained in the alloy is small, and it is difficult to form a copper-tin alloy layer having a steep uneven shape, and if it exceeds 1.0 μm, bending and the like are difficult. The average thickness of the nickel or nickel alloy layer 3 is preferably 0.075 μm or more, and more preferably 0.1 μm or more. When the nickel or nickel alloy layer 3 is made to have a function as a barrier layer for preventing diffusion of Cu from the substrate 1 to improve heat resistance, the thickness of the nickel or nickel alloy layer 3 is preferably 0.1 μm or more.

This is because, when the average crystal grain size of the nickel or nickel alloy layer 3 is less than 0.01 μm, bending workability and heat resistance are deteriorated, and when it exceeds 0.5 μm, it is difficult to introduce nickel of the nickel or nickel alloy layer 2 at the time of forming the copper-tin alloy layer 4 during reflow treatment, and Cu₆Sn₅It is difficult to contain nickel. Further, when the crystal grains of the nickel or nickel alloy layer 3 are coarse, abrasion is liable to occur, and the number of times until the base material is exposed in a sliding test may not be 30 or more times, for example. The upper limit of the average crystal grain size of the nickel or nickel alloy layer 3 is preferably 0.4 μm or less, more preferably 0.3 μm or less, and still more preferably 0.2 μm or less.

The standard deviation/average crystal grain diameter of the nickel or nickel alloy layer 3 represents an index of the deviation of the crystal grain diameter. If the value is 1.0 or less, the thickness of the copper plating layer is increased, and the thickness of the copper plating layer is increased to (Cu, Ni)₆Sn₅The Ni content in the alloy is also increased, and the interface with the tin layer can be formed into a steep uneven shape. The standard deviation of the crystal grain size of the nickel or nickel alloy layer 3/the average crystal grain size is preferably 0.95 or less, and more preferably 0.9 or less.

If the arithmetic mean roughness Ra of the surface of the nickel or nickel alloy layer 3 in contact with the copper-tin alloy layer 4 exceeds 0.5 μm, a projecting portion is formed in the nickel or nickel alloy layer 3, and when the wear progresses to the nickel or nickel alloy layer 3, the wear powder generated by the projecting portion being worn first may exert a grinding effect to accelerate the wear rate, and it is difficult to set the number of times until the base material is exposed in the sliding test to 30 or more. The lower limit of the arithmetic mean roughness Ra of the surface of the nickel or nickel alloy layer 3 in contact with the copper-tin alloy layer 4 is preferably 0.01 μm or more, more preferably 0.02 μm or more, and the upper limit is preferably 0.4 μm or less, more preferably 0.3 μm or less.

The copper-tin alloy layer 4 is Cu₆Sn₅As a main component and the Cu₆Sn₅A compound alloy layer in which a part of copper is replaced with nickel is formed by forming a nickel-plated or nickel-plated alloy layer, a copper-plated layer, and a tin-plated layer in this order on the base material 2 and performing reflow soldering. The average crystal grain size of the copper-tin alloy layer 4 is preferably 0.2 μm or more and 1.5 μm or less, and a part thereof is exposed on the surface of the tin layer 5. And, preferably, the Cu₆Sn₅The alloy layer 4a contains nickel in an amount of 1 atomic% to 25 atomic%.

Cu₆Sn₅When the nickel content in the alloy layer 4a is less than 1 atomic%, Cu cannot be formed₆Sn₅A compound alloy layer in which a part of copper is replaced with nickel is difficult to form a steep uneven shape. When the content exceeds 25 atomic%, the shape of the copper-tin alloy layer 4 tends to be too fine, and when the content exceeds 25 atomic%, the copper-tin alloy layer tends to be too fineIf the alloy layer 4 is too fine, the kinetic friction coefficient may not be 0.3 or less. Cu₆Sn₅The lower limit of the nickel content in the alloy layer 4a is preferably 2 atomic% or more, and the upper limit is 20 atomic% or less.

Then, in the Cu₆Sn₅Cu is partially present between the alloy layer 4a and the nickel or nickel alloy layer 3₃And a Sn alloy layer 4 b. Thus, Cu₆Sn₅Cu with alloy layer 4a formed on nickel or nickel alloy layer 3₃Sn alloy layer 4b or Cu is not present₃The Sn alloy layer 4b is formed on any one of the nickel and nickel alloy layers 3, or formed so as to straddle them. In this case, Cu₃Sn alloy layer 4b with respect to Cu₆Sn₅The volume ratio of the alloy layer 4a is preferably 20% or less.

By forming Cu on the nickel or nickel alloy layer 3₆Sn₅Alloy layer 4a, or Cu formed on at least a part of nickel or nickel alloy layer 3₃Cu is formed on the Sn alloy layer 4b₆Sn₅The alloy layer 4a is advantageous in that the surface of the copper-tin alloy layer 4 has a steep uneven shape. In this case, if Cu₃Sn alloy layer 4b with respect to Cu₆Sn₅When the volume ratio of the alloy layer 4a exceeds 20%, Cu₆Sn₅The alloy layer 4a is difficult to grow in the longitudinal direction, Cu₆Sn₅The alloy layer 4a is difficult to have a steep uneven shape. Cu₃Sn alloy layer 4b with respect to Cu₆Sn₅The volume ratio of the alloy layer 4a is preferably 15% or less, and more preferably 10% or less.

Further, it is preferable that the interface between the copper-tin alloy layer 4 and the tin layer 5 is formed into a steep concave-convex shape as described above, a part of the copper-tin alloy layer 4 is exposed on the surface of the tin layer 5, and the average height Rc of the copper-tin alloy layer 4 ÷ the average thickness of the copper-tin alloy layer 4 (hereinafter referred to as the average height Rc of the copper-tin alloy layer 4/the average thickness of the copper-tin alloy layer 4) measured when the tin layer 5 is dissolved and removed to allow the copper-tin alloy layer 4 to appear on the surface is 0.7 or more.

When the average height Rc of the copper-tin alloy layer 4/the average thickness of the copper-tin alloy layer 4 is less than 0.7, Cu₆Sn₅The alloy layer 4a is hard to form a steep concave-convex shapeIn this case, the coefficient of dynamic friction is hardly 0.3 or less. In addition, the number of times until the base material 2 is exposed in the sliding test is reduced, and the number of times cannot be 30 or more in some cases. The average height Rc of the copper-tin alloy layer 4/the average thickness of the copper-tin alloy layer 4 is preferably 0.75 or more, and more preferably 0.8 or more.

The tin layer 5 has an average thickness of 0.2 μm or more and 1.2 μm or less, and has a region on the surface of the tin layer 5, in which tin solidified portions 5a protruding from the surface exist in island shapes, and a region composed of a tin layer 5b (hereinafter referred to as "base tin layer") in which the tin solidified portions 5a do not exist (see fig. 2). The average diameter of the tin solidified portions 5a is 10 μm or more and 1000 μm or less, and the area ratio of the tin solidified portions 5a to the surface of the tin layer 5 is 1% or more and 90% or less. In this case, the average thickness of the tin layer 5 including the tin solidified portion 5a is measured.

The tin solidified portion 5a is circular in plan view, but may have a directional shape such as a linear shape or an elliptical shape. Therefore, the average diameter of the tin solidified portions 5a is an average value of a major diameter (a length of the longest straight line drawn in the tin solidified portion without being in contact with the outer edge in the middle) and a minor diameter (a length of the longest straight line drawn in the grain without being in contact with the outer edge in the middle in a direction perpendicular to the major diameter) at the outer edge of the tin solidified portions 5a in the direction of the surface of the tin layer 5. The island-like tin solidified portions 5a mean that a plurality of circular, linear, elliptical or other tin solidified portions 5a are present on the surface of the tin layer 5 at intervals in a plan view.

The thickness of the tin solidified portion 5a is 0.1 μm or more and 10 μm or less. The thickness in this case is the projection height of the tin solidified portion 5a with respect to the surface of the underlying tin layer 5b at a portion other than the tin solidified portion 5 a.

As described above, the exposed area ratio of the portion of the tin layer 5 other than the tin solidified portion 5a, on which the copper-tin alloy layer 4 is exposed, is 1% to 60%. The exposed area ratio of the copper-tin alloy layer 4 is a ratio to the area of the surface of the underlying tin layer 5 b.

In the terminal material 1 having these structures, the interface between the copper-tin alloy layer 4 and the tin layer 5 has a steep uneven shape, and the hard copper-tin alloy layer 4 and the tin layer 5 have a composite structure in a range of several hundred nanometers deep from the surface of the tin layer 5, and a part of the hard copper-tin alloy layer 4 is in a state of being slightly exposed to the tin layer 5, and the softened tin existing around the hard copper-tin alloy layer functions as a lubricant, thereby realizing a low coefficient of dynamic friction of 0.3 or less. Since the exposed area ratio of the copper-tin alloy layer 4 is within the limited range of 1% or more and 60% or less, the excellent electrical connection characteristics of the tin layer 5 are not impaired.

Further, since the tin solidified portion 5a exists in an island shape on the surface and tin remains even in a portion where the tin solidified portion 5a exists even when used at high temperature, the oxidation spread of the copper-tin alloy 4 in the portion is suppressed, and an increase in contact resistance can be suppressed.

In the tin-plated copper terminal material 1, the number of times until the base material is exposed can be set to 30 or more by performing a sliding test in which the sliding distance is 1.0mm, the sliding speed is 80mm/min, and the contact load is 5N, and the sliding test is performed on the surface of the same material. The surface glossiness can be set to 500GU or more. The upper limit of the dynamic friction coefficient is preferably 0.29 or less, and more preferably 0.28 or less.

The glossiness is also increased when the average crystal grain size of the copper-tin alloy layer 4 is 0.2 μm or more and 1.5 μm or less and the exposed area ratio of the copper-tin alloy layer 4 on the surface of the underlying tin layer 5b is 1% or more and 60% or less.

Next, a method for manufacturing the tin-plated copper terminal material 1 will be described.

As the substrate 2, a plate material made of pure copper or a copper alloy such as Cu — Mg — P alloy is prepared. The plate is degreased and pickled to clean the surface, and then nickel plating, copper plating, and tin plating are performed in this order.

The nickel plating may be performed by using a general nickel plating bath, and for example, sulfuric acid (H) may be used₂SO₄) With nickel sulfate (NiSO)₄) A sulfuric acid bath as a main component.

The temperature of the plating bath is set to 20 ℃ to 60 ℃, and the current density is set to 5 to 60A/dm²The following. This is because it is less than 5A/dm²In this case, the average crystal grain size of the nickel or nickel alloy layer is not changedThe surface roughness Ra of the surface of the fine copper-tin alloy layer in contact with the copper-tin alloy layer is increased, (Cu, Ni)₆Sn₅The content of nickel contained in the alloy is reduced, and a copper-tin alloy layer having a steep uneven shape cannot be formed.

The thickness of the nickel-plated layer is set to 0.05 μm or more and 1.0 μm or less. This is because when the thickness is less than 0.05. mu.m, (Cu, Ni)₆Sn₅The content of nickel contained in the alloy is small and a copper-tin alloy layer having a steep uneven shape cannot be formed, and when it exceeds 1.0 μm, bending or the like is difficult.

Copper plating may be performed using a general copper plating bath, and for example, copper sulfate (CuSO) may be used₄) And sulfuric acid (H)₂SO₄) Copper sulfate bath as a main component, and the like. The temperature of the plating bath is set to 20 to 50 ℃, and the current density is set to 1 to 30A/dm²。

The thickness of the copper plating layer formed by this copper plating is set to 0.05 μm or more and 0.40 μm or less. This is because when the thickness is less than 0.05. mu.m, (Cu, Ni)₆Sn₅The Ni content in the alloy becomes large, and the shape of the copper-tin alloy becomes too fine, and if it exceeds 0.40. mu.m, (Cu, Ni)₆Sn₅The content of nickel contained in the alloy is reduced, and a copper-tin alloy layer having a steep uneven shape cannot be formed.

The plating bath for forming the tin plating layer may be a general tin plating bath, and for example, sulfuric acid (H) may be used₂SO₄) And stannous sulfate (SnSO)₄) A sulfuric acid bath as a main component. The temperature of the plating bath is set to 15 to 35 ℃, and the current density is set to 1 to 30A/dm²。

The tin-plated layer has a thickness of 0.5 to 1.5 μm. If the thickness of the tin plating layer is less than 0.5 μm, the tin layer after reflow soldering becomes thin, which impairs the electrical connection characteristics, and the tin solidification cannot grow to a sufficient size, whereas if it exceeds 1.5 μm, the tin on the surface becomes too much, the tin solidification becomes too coarse, the copper-tin alloy layer is less exposed on the surface, and it is difficult to set the kinetic friction coefficient to 0.3 or less.

After the plating treatment, the solder is heated to perform a reflow treatment.

That is, the reflow process is a process including the steps of: a heat treatment step of performing a primary heat treatment in which the plated treatment material is heated to 240 ℃ or higher at a temperature rise rate of 20 to 75 ℃/sec in a heating furnace in a CO reducing environment, and then performing a secondary heat treatment in which the treatment material is heated at 240 to 300 ℃; primary cooling treatment, after the heat treatment process, cooling at a cooling rate of less than 30 ℃/second for 2-15 seconds; and a secondary cooling step of cooling the steel sheet at a cooling rate of 100 to 300 ℃/sec for 0.5 to 5 seconds after the primary cooling. The primary cooling step is performed by air cooling, and the secondary cooling step is performed by water cooling using water at 10 to 90 ℃.

The base material 2 is formed into a strip-like material, and the above-described respective plating is performed while the base material 2 is moved in the longitudinal direction, followed by performing a reflow process. In the reflow process, the base material (strip) subjected to the plating is heated by blowing hot air to the surface thereof while traveling in the longitudinal direction in the reflow furnace. When the hot air is blown along the traveling direction (from the upstream side to the downstream side) of the base material (strip) at a speed substantially equal to the traveling speed of the base material, a circular tin aggregation portion is formed.

By performing this reflow treatment in a reducing atmosphere, it is possible to prevent a tin oxide film having a high melting temperature from being formed on the tin plating surface, and it is possible to perform the reflow treatment at a lower temperature and in a shorter time, thereby facilitating the production of a desired intermetallic compound structure.

In this case, the tin solidified portion is easily generated by setting the heat treatment step to two stages. After the rapid heating is performed in the primary heat treatment and the surface tin layer is set to a high temperature state of 240 ℃ or higher at an early stage, the secondary heat treatment ensures a long aggregation time of the surface tin layer, and thus a part of the copper-tin alloy layer whose interface with the tin layer is in a sharp uneven shape is exposed to the surface, whereby tin in a molten state is flicked off and aggregated in the copper-tin alloy layer.

In this case, the shape of the tin solidified portion may be changed to an ellipse or a line, in addition to a circle, by blowing hot air to the surface of the base material in the traveling direction and changing the relative air speed (hot air speed — base material traveling speed).

Further, the primary heat treatment is a temperature raising treatment, but if the secondary heat treatment is in the range of 240 ℃ to 300 ℃, the temperature may be raised or lowered as appropriate, or may be maintained at a specific temperature, and for example, various methods such as: a case where the temperature is raised to a peak temperature at an appropriate rate after the primary heat treatment, and the process is immediately shifted to a primary cooling step; heating and maintaining after the temperature is raised to the peak temperature; a case where the temperature is not raised from the reaching temperature of the primary heat treatment and the heating is maintained; the temperature to be reached in the primary heat treatment is set to be higher than 240 c, for example, 250 c, and then the temperature is lowered to a specific temperature within the above temperature range, for example, 240 c.

Further, by providing the primary cooling step with a relatively low cooling rate in two stages, copper atoms are stably diffused in tin particles and grow in a desired intermetallic compound structure. Further, by preventing the growth of the intermetallic compound by the subsequent rapid cooling, the structure can be fixed as desired.

However, copper and tin electrodeposited at a high current density have low stability, and are alloyed or enlarged in crystal grain size even at room temperature, and it is difficult to produce a desired intermetallic compound structure by a reflow soldering process. Therefore, it is preferable to perform the reflow process promptly after the plating process. Specifically, it is necessary to perform reflow in 15 minutes or less, preferably 5 minutes or less. The short standing time after the plating is not a problem, but is about 1 minute in a general processing line in view of the structure.