Terminal material for connector and method for manufacturing same

Abstract

According to the present invention, a coating film is formed on the surface of a base material at least the outermost surface of which is formed of copper or a copper alloy, the coating film comprising: a nickel layer that is formed on the surface of the base material, and is formed of nickel or a nickel alloy; a silver layer that is formed on the nickel layer, and is formed of silver or a silver alloy; a copper-tin alloy layer that is formed on the silver layer, and is formed of an alloy of copper and tin; and a tin layer that is formed on the copper-tin alloy layer, and is formed of tin or a tin alloy. The average thickness of the nickel layer is 0.3 μm to 2.0 μm inclusive, the average maximum thickness of the silver layer is 0.02 μm to 0.50 μm inclusive, the average thickness of the copper-tin alloy layer is 0.35 μm to 1.00 μm inclusive, and the average thickness of the tin layer is 0.10 μm to 1.00 μm inclusive.

Description

Connector terminal material and method for manufacturing the same

[0001] The present invention relates to a terminal material for connectors that has heat resistance and low insertion force when mated with a mating terminal, and a method for manufacturing the same.

[0002] This application claims priority based on Japanese Patent Application No. 2025-056197, filed in Japan on March 28, 2025, and Japanese Patent Application No. 2026-049756, filed in Japan on March 24, 2026, the contents of which are incorporated herein by reference.

[0003] Traditionally, copper or copper alloys have been used in various electronic components, including connector terminals. However, since they oxidize easily, plating is a common practice.

[0004] In this case, the type of metal used for plating is optimized depending on the operating environment, location of use, and amount of current flowing, with tin plating being the most common. However, because the tin plating layer is soft, if it is formed as is and mated with the mating terminal, there is a problem of high insertion force.

[0005] Patent Document 1 describes a method of forming a hard copper-tin alloy layer beneath a tin layer, maintaining low friction and low contact resistance by retaining part of the tin layer on the outermost surface. Furthermore, inserting a nickel layer as a barrier layer on top of the base material prevents the diffusion of copper (Cu) components from the base material. However, under prolonged high-temperature conditions, the nickel layer fails to maintain its barrier properties, allowing copper components from the base material to pass through the nickel layer and diffuse into the tin layer, converting the tin into a copper-tin alloy and reducing its heat resistance. Additionally, tin itself does not have high heat resistance and oxidizes under high-temperature conditions, further reducing its heat resistance.

[0006] Furthermore, with the increasing electrification of automotive components in recent years, there are more areas where high currents flow, requiring higher heat resistance than before. However, tin layers lacked sufficient heat resistance. For this reason, silver plating is often used as a plating type with higher heat resistance than tin plating. This silver plating layer is resistant to oxidation, and if a nickel layer is formed as a barrier layer on the substrate, copper components hardly diffuse from the base material, resulting in high heat resistance.

[0007] However, silver is significantly more expensive than tin, and like tin, it is soft, which posed a problem when used as a connector, as it resulted in high insertion force. Therefore, techniques exist to deposit expensive silver only in the minimum necessary areas and tin elsewhere, or to form a silver-tin alloy layer on the surface, but these also had various problems.

[0008] For example, in Patent Document 2, silver and tin are layered sequentially and reflowed to form a silver-tin alloy layer. However, because silver-tin alloy is hard, the oxide film formed on the outermost surface in a high-temperature environment with a large amount of silver-tin alloy presents a problem. In the case of a tin layer, the contact resistance decreases as it is worn away during sliding, exposing a new surface. However, in the case of a silver-tin alloy layer, because it is hard, it is difficult for a new surface to be created at the sliding point, resulting in high contact resistance.

[0009] Furthermore, in Patent Documents 3 and 4, the silver plating layer and the tin plating layer are formed separately, and the tin plating layer is irradiated with infrared rays to form a reflow film, thereby preventing an increase in the contact resistance of the silver layer in high-temperature environments. However, this is time-consuming, and it does not achieve both low insertionability and high heat resistance with a single plating layer.

[0010] Japanese Patent Publication No. 2013-174006, Japanese Patent Publication No. 2021-075772, Japanese Patent Publication No. 2020-164909, Japanese Patent Publication No. 2022-174108

[0011] In these terminal materials, forming a silver layer across the entire surface to increase heat resistance is expensive and also increases insertion force. There was a need to improve heat resistance while maintaining the good low insertion properties of the tin layer.

[0012] This invention has been made in view of these circumstances, and aims to improve heat resistance while maintaining good low insertability of the tin layer.

[0013] The connector terminal material of the present invention has a coating formed on the surface of a substrate whose outermost surface is made of copper or a copper alloy, and the coating has a nickel layer made of nickel or a nickel alloy formed on the surface of the substrate, a silver layer made of silver or a silver alloy formed on the nickel layer, a copper-tin alloy layer made of a copper and tin alloy formed on the silver layer, and a tin layer made of tin or a tin alloy formed on the copper-tin alloy layer, wherein the average thickness of the nickel layer is 0.3 μm or more and 2.0 μm or less, the average maximum thickness of the silver layer is 0.02 μm or more and 0.50 μm or less, the average thickness of the copper-tin alloy layer is 0.35 μm or more and 1.00 μm or less, and the average thickness of the tin layer is 0.10 μm or more and 1.00 μm or less.

[0014] This connector terminal material has an outermost layer made of tin, with a copper-tin alloy layer underneath. This allows for low insertion resistance due to these layers, and the inclusion of a silver layer between the nickel layer and the copper-tin alloy layer suppresses the diffusion of copper (Cu) from the substrate in high-temperature environments, thereby improving heat resistance.

[0015] In this case, if the average thickness of the nickel layer is less than 0.3 μm, the effect of preventing copper diffusion from the substrate is weak, contact resistance tends to increase in high-temperature environments, and heat resistance decreases. If it exceeds 2.0 μm, the heat resistance does not increase any further, and as the hard nickel layer becomes thicker, the coating becomes more prone to cracking during shaping.

[0016] The average maximum thickness of the silver layer is less than 0.02 μm, resulting in a low heat resistance improvement effect. If it exceeds 0.50 μm, excessive silver-tin alloying occurs in high-temperature environments, increasing contact resistance and reducing heat resistance. The reason for using the average maximum thickness for this silver layer is that it is not necessarily formed as a layer extending across the entire surface, but may be formed partially or intermittently. Therefore, the average thickness of the maximum thickness of the parts where the silver layer exists was used.

[0017] When the average thickness of the copper-tin alloy layer is less than 0.35 μm, the coefficient of friction is high because there is less hard copper-tin alloy layer. When it exceeds 1.00 μm, the tin layer becomes thinner, which increases contact resistance in high-temperature environments, reduces heat resistance, and the lubrication provided by the tin layer is lost, resulting in a higher coefficient of friction.

[0018] If the average thickness of the tin layer is less than 0.10 μm, the contact resistance in high-temperature environments increases, reducing heat resistance. If it exceeds 1.00 μm, the soft tin layer becomes too thick, resulting in a high coefficient of friction.

[0019] The connector terminal material of the present invention further comprises a copper layer made of copper or a copper alloy formed on the silver layer, and the average maximum thickness of the copper layer may be 0.35 μm or less.

[0020] This copper layer is a residual layer formed in the copper-tin alloy layer, which is created by laminating a copper-plated layer and a tin-plated layer through plating and then reflowing the process. If the average maximum thickness of the copper layer exceeds 0.35 μm, excessive copper-tin alloying may occur in high-temperature environments, potentially increasing the coefficient of friction. Since this copper layer may be formed partially or intermittently, or may not remain as a layer, the average maximum thickness was used.

[0021] In the connector terminal material of the present invention, silver-tin alloy precipitates are contained in the surface of the copper-tin alloy layer and the tin layer, and it is preferable that the average area ratio of the silver-tin alloy precipitates to the tin layer, as measured from a cross-sectional image along the thickness direction, is 1% or more and 50% or less.

[0022] In this form, silver (Ag) in the silver layer diffuses into the tin layer during reflow, forming granular and rod-shaped silver-tin alloy precipitates on the surface of the copper-tin alloy layer and the tin layer. The presence of these hard silver-tin alloy precipitates reduces the coefficient of friction. Furthermore, in high-temperature environments, the diffusion of silver takes precedence over the diffusion of copper from the substrate, suppressing the formation of the copper-tin alloy. This allows for the preferential formation of a silver-tin alloy with higher conductivity, thereby suppressing increased contact resistance.

[0023] In this case, if the average area ratio of silver-tin alloy precipitates exceeds 50%, there is an excess of silver-tin alloy precipitates relative to the tin layer, which may reduce heat resistance. If the average area ratio is less than 1%, heat resistance will decrease, and the friction coefficient reduction effect will be diminished.

[0024] In the connector terminal material of the present invention, the tin layer contains rod-shaped silver-tin alloy precipitates connected to a portion of the surface of the copper-tin alloy layer, and the length of these rod-shaped silver-tin alloy precipitates, measured from a scanning electron microscope image taken at a magnification of 4000x of the surface after the tin layer has been peeled off, is 5 μm or more in the longitudinal direction and has an area of ​​650 μm. ２ Ideally, the average number should be between 1 and 35.

[0025] When rod-shaped silver-tin alloy precipitates form within the tin layer, the coefficient of friction decreases further. Heat resistance is also good.

[0026] In this case, the rod-shaped silver-tin alloy precipitates, which are 5 μm or larger, cover an area of ​​650 μm. ２ If the average number of strands exceeds 35, there may be an excess of silver-tin alloy precipitates relative to the tin layer, which could reduce heat resistance.

[0027] The present invention provides a method for manufacturing a connector terminal material, which involves a plating layer formation step to form a substrate with a plating layer by laminating a nickel plating layer made of nickel or a nickel alloy with an average thickness of 0.3 μm to 2.0 μm, a silver plating layer made of silver or a silver alloy with an average thickness of 0.02 μm to 0.53 μm, a copper plating layer made of copper or a copper alloy with an average thickness of 0.15 μm to 0.50 μm, and a tin plating layer made of tin or a tin alloy with an average thickness of 0.5 μm to 1.5 μm on the surface of the substrate; and a reflow step to heat the substrate with the plating layer to a temperature above the melting point of tin, thereby manufacturing the connector terminal material.

[0028] This method of manufacturing connector terminals allows for the production of connector terminals with reduced friction coefficient and excellent heat resistance by controlling the thickness of each plating layer and performing reflow processing.

[0029] In this case, if the average thickness of the nickel plating layer is less than 0.3 μm, the effect of preventing copper diffusion from the substrate is weak, contact resistance tends to increase in high-temperature environments, and heat resistance decreases. Even if it exceeds 2.0 μm, the heat resistance does not increase any further, and the thick, hard nickel layer makes the film prone to cracking during shaping.

[0030] If the average thickness of the silver plating layer is less than 0.02 µm, a silver layer of the required thickness cannot be formed after the reflow process. If it exceeds 0.53 µm, an excessive silver layer remains after the reflow process, leading to increased contact resistance in high-temperature environments and decreased heat resistance.

[0031] If the average thickness of the copper plating layer is less than 0.15 µm, a copper-tin alloy layer of the required thickness cannot be formed after the reflow process. In addition, when the copper plating layer is less than 0.15 µm, the silver layer is prone to excessive diffusion during reflow, and there is a risk that the average maximum thickness of the silver layer after reflow becomes less than 0.02 µm. If it exceeds 0.50 µm, a copper-tin alloy layer with excessive thickness is formed after the reflow process, leading to increased contact resistance in high-temperature environments, decreased heat resistance, and increased friction coefficient. In addition, since the average maximum thickness of the remaining copper layer becomes greater than 0.35 µm, there is also a risk that contact resistance increases in high-temperature environments.

[0032] If the average thickness of the tin plating layer is less than 0.5 µm, a tin layer of the required thickness cannot be formed after the reflow process. If it exceeds 1.5 µm, the tin layer remaining after the reflow process becomes excessively thick, leading to an increased friction coefficient.

[0033] It should be noted that by controlling the thicknesses of the copper plating layer and the silver plating layer, the shape and amount of silver-tin alloy precipitates can be controlled.

[0034] According to the present invention, heat resistance can be improved while maintaining good low insertion force property of the tin layer.

[0035] It is a cross-sectional view schematically showing a connector terminal material according to a first embodiment of the present invention. It is a cross-sectional view schematically showing a base material with a plating layer in the middle of manufacturing the connector terminal material of Fig. 1. It is a cross-sectional SEM image of the connector terminal material of Fig. 1. Regarding the connector terminal material of Example 13 (second embodiment), Fig. 4A is a cross-sectional SEM image, and Fig. 4B is a surface SEM image of the copper-tin alloy layer after removing the tin layer. Regarding the connector terminal material of Example 15 (third embodiment), Fig. 5A is a cross-sectional SEM image, and Fig. 5B is a surface SEM image after removing the tin layer. It is a cross-sectional SEM image obtained by cutting, along the length direction of the rod-shaped silver-tin alloy precipitate, a site where the rod-shaped silver-tin alloy precipitate is present in Fig. 5. It is a cross-sectional SEM image explaining the method for measuring the average thickness of the copper-tin alloy layer. It is a cross-sectional SEM image explaining the method for measuring the average maximum thickness of the silver layer and the copper layer.

[0036] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0037] [Configuration of Connector Terminal Material of First Embodiment] In the connector terminal material 1 of the present embodiment, as schematically shown in cross-section in Fig. 1, a coating 22 is formed on a base material 21 made of copper or a copper alloy. The coating 22 includes a nickel layer 23 made of nickel or a nickel alloy, a silver layer 24 made of silver or a silver alloy formed on the nickel layer 23, a copper layer 25 made of copper or a copper alloy formed on the silver layer 24, a copper-tin alloy layer 26 made of an alloy of copper and tin formed on the copper layer 25, and a tin layer 27 made of tin or a tin alloy formed on the copper-tin alloy layer 26, which are formed in this order.

[0038] The composition of the base material 21 is not particularly limited as long as at least the outermost surface thereof is made of copper or a copper alloy. For example, a plate material made of copper or a copper alloy such as oxygen-free copper (C10200), Cu-Mg based copper alloy (C18665), brass, or phosphor bronze can be applied. The base material 21 may also be constituted by a plated material obtained by performing copper plating or copper alloy plating on the surface of a base material not made of copper or a copper alloy, or a clad material obtained by bonding a copper or copper alloy plate (for example, a clad material of an aluminum plate and a copper plate). In this case, a metal plate other than copper can be applied as the base material.

[0039] The nickel layer 23 has the function of suppressing the diffusion of copper (Cu) from the substrate 21 to the layers from the silver layer 24 to the tin layer 27 formed thereon. The average thickness (film thickness) of the nickel layer 23 is 0.3 μm or more and 2.0 μm or less. If the average thickness of the nickel layer 23 is less than 0.3 μm, the effect of preventing copper diffusion from the substrate 21 is weak, contact resistance tends to increase in high-temperature environments, and heat resistance decreases. If it exceeds 2.0 μm, the heat resistance does not increase any further, and as the hard nickel layer 23 becomes thicker, the film 22 becomes more prone to cracking during shaping. The composition of the nickel layer 23 is not particularly limited as long as it is made of nickel or a nickel alloy. Preferably, the average thickness of the nickel layer 23 is 0.5 μm or more and 2.0 μm or less.

[0040] By interposing the silver layer 24 between the nickel layer 23 and the copper layer 25, the diffusion of copper (Cu) from the substrate 21 in a high-temperature environment can be suppressed, thereby improving heat resistance.

[0041] The average maximum thickness of this silver layer 24 is between 0.02 μm and 0.50 μm. If the average maximum thickness is less than 0.02 μm, the effect of improving heat resistance is low, and if it exceeds 0.50 μm, excessive silver-tin alloying occurs in high-temperature environments, increasing contact resistance and reducing heat resistance. The reason for using the average maximum thickness for this silver layer 24 is that it is not necessarily formed as a layer that extends across the entire surface, but may be formed partially or intermittently, so the average value of the maximum thickness of the parts where the silver layer 24 exists was used.

[0042] The composition of the silver layer 24 is not particularly limited, as long as it is made of silver or a silver alloy. The average maximum thickness of the silver layer 24 is preferably 0.029 μm or more and 0.345 μm or less.

[0043] The copper layer 25 and the copper-tin alloy layer 26 are layers obtained by sequentially forming a copper plating layer and a tin plating layer on a silver plating layer and then reflowing them. In the copper plating layer, the copper alloys with the tin in the tin plating layer to form the copper-tin alloy layer 26. However, a portion of the copper plating layer may remain as a layer, and this remaining layer is the copper layer 25 in the product. Therefore, there are cases where no copper plating layer remains, and in such cases, the copper layer 25 does not exist in the product.

[0044] The average maximum thickness of this copper layer 25 is 0.35 μm or less. Since there may be no residual layer, it includes "0" μm. If the average maximum thickness of the copper layer 25 exceeds 0.35 μm, excessive copper-tin alloying may occur in high-temperature environments, potentially increasing the coefficient of friction.

[0045] If the copper layer 25 is not formed, a copper-tin alloy layer 26 is formed on the surface of the silver layer 24.

[0046] The copper-tin alloy layer 26 is a layer obtained by sequentially forming a copper plating layer and a tin plating layer on top of the silver plating layer and then performing a reflow treatment, as described above. ６ Sn ５ Alloy only, or most of Cu ６ Sn ５ The alloy and a small amount of Cu placed beneath it ３ It is formed by a composite structure with a tin alloy. The surface of this copper-tin alloy layer 26, that is, the interface with the tin layer 27 above it, is formed with an uneven shape.

[0047] The average thickness of the copper-tin alloy layer 26 is between 0.35 μm and 1.00 μm. If the average thickness of the copper-tin alloy layer 26 is less than 0.35 μm, the coefficient of friction will be high because there is less hard copper-tin alloy layer. If it exceeds 1.00 μm, the tin layer 27 becomes thin, which increases contact resistance in high-temperature environments, reduces heat resistance, and also reduces the lubricity provided by the tin layer 27, resulting in a higher coefficient of friction. It is preferable that the average thickness of the copper-tin alloy layer 26 be between 0.50 μm and 0.79 μm.

[0048] The tin layer 27 is a layer made of tin or a tin alloy remaining after the reflow treatment of the copper plating layer and the tin plating layer, and is formed to have an average thickness of 0.10 µm or more and 1.00 µm or less. If the average thickness of this tin layer 27 is less than 0.10 µm, the contact resistance in a high-temperature environment increases and heat resistance decreases; if it exceeds 1.00 µm, the soft tin layer 27 becomes excessively thick, resulting in an increased friction coefficient. The average thickness of this tin layer 27 is preferably 0.25 µm or more and 0.73 µm or less.

[0049] [Method for Producing Connector Terminal Material] Next, a method for producing this connector terminal material 1 will be described.

[0050] This method for producing the connector terminal material 1 includes: a pretreatment step of cleaning the surface of a base material 21 in which at least the outermost surface is a plate material made of copper or a copper alloy; a plating layer forming step of sequentially forming a nickel plating layer 31, a silver plating layer 32, a copper plating layer 33, and a tin plating layer 34 on the surface of the base material 21; and a reflow treatment step of heating the base material 35 with plating layers, on which the four plating layers 31 to 34 have been formed, to perform reflow treatment. The following is a description in order of steps. (Pretreatment Step) A pretreatment for cleaning the surface is performed by subjecting the base material 21 to electrolytic degreasing, pickling, or the like.

[0051] (Plating Layer Forming Step) On the base material 21 after pretreatment, a nickel plating layer 31 made of nickel or a nickel alloy, a silver plating layer 32 made of silver or a silver alloy, a copper plating layer 33 made of copper or a copper alloy, and a tin plating layer 34 made of tin or a tin alloy are formed in this order as described below (see Figure 2).

[0052] - Nickel Plating Layer - A nickel plating treatment for forming the nickel plating layer 31 made of nickel or a nickel alloy is performed on the surface of the pretreated base material 21. A general nickel plating bath may be used as the plating bath; for example, a sulfamic acid bath containing nickel sulfamate and boric acid as main components can be used. The temperature of the plating bath is 40°C or higher and 60°C or lower, and the current density is 1 A / dm ２ or more and 10 A / dm ２ or less.

[0053] In this case, the average thickness of the nickel plating layer 31 is set to 0.3 μm or more and 2.0 μm or less. If the average thickness of the nickel plating layer 31 is less than 0.3 μm, the effect of preventing copper diffusion from the substrate is weak, contact resistance tends to increase in high-temperature environments, and heat resistance decreases. If it exceeds 2.0 μm, the heat resistance does not increase any further, and the thick hard nickel layer 31 makes the film 22 prone to cracking during shaping. It is preferable that the average thickness of the nickel plating layer 31 be 0.5 μm or more and 2.0 μm or less.

[0054] -Silver Plating Layer- A silver plating treatment is performed on the nickel plating layer 31 to form a silver plating layer 32 made of silver or a silver alloy. The silver plating can be done using a strike bath or a general silver plating bath. For example, if the average maximum thickness of the silver plating layer 32 is thin, such as 0.1 μm or less, a strike bath mainly composed of silver cyanide and potassium silver cyanide can be used. The temperature of the plating bath is room temperature, and the current density is 0.5 A / dm². ２ 2A / dm or more ２ The following applies: If the average maximum thickness of the silver plating layer 32 exceeds 0.1 μm, after applying the above-mentioned strike silver plating, a silver plating consisting of silver cyanide, potassium cyanide, and additives is used. The bath temperature is 20°C to 30°C, and the current density is 2 A / dm². ２ 4A / dm or more ２ The reason for applying strike silver plating first when the average maximum thickness of the silver plating layer 32 exceeds 0.1 μm is to improve the adhesion of the entire silver plating layer.

[0055] The average thickness of the silver plating layer 32 is set to be between 0.02 μm and 0.53 μm. If the average thickness of the silver plating layer 32 is less than 0.02 μm, the silver layer cannot be formed to the required thickness after the reflow process. If it exceeds 0.53 μm, an excess silver layer 24 remains after the reflow process, increasing contact resistance in high-temperature environments and reducing heat resistance.

[0056] The average thickness of this silver plating layer 32 is preferably 0.029 μm or more and 0.352 μm or less.

[0057] - Copper Plating Layer - A copper plating treatment is performed to form a copper plating layer 33 made of copper or a copper alloy on the silver plating layer 32. A general copper plating bath can be used for copper plating; for example, a copper sulfate bath mainly composed of copper sulfate and sulfuric acid can be used. The temperature of the plating bath is 35°C to 55°C, and the current density is 1 A / dm ２ 10A / dm or more ２ The following is considered to be the case.

[0058] The average thickness of this copper plating layer 33 is set to 0.15 μm or more and 0.50 μm or less. If the average thickness of the copper plating layer 33 is less than 0.15 μm, the copper-tin alloy layer 26 cannot be formed to the required thickness after the reflow process. Also, if the copper plating layer 33 is less than 0.15 μm, the silver layer 24 tends to diffuse excessively during reflow, and there is a risk that the silver layer 24 after reflow will be less than 0.02 μm. If it exceeds 0.50 μm, an excessively thick copper-tin alloy layer 26 will be formed after the reflow process, resulting in increased contact resistance in high-temperature environments, reduced heat resistance, and a higher coefficient of friction. In addition, since the remaining copper layer 25 will be thicker than 0.35 μm, there is a risk that contact resistance will be high in high-temperature environments. It is preferable that the average thickness of this copper plating layer 33 be 0.2 μm or more and 0.3 μm or less.

[0059] -Tin Plating Layer- A tin plating treatment is performed on the copper plating layer 33 to form a tin plating layer 34 made of tin or a tin alloy. A general tin plating bath can be used as the plating bath for forming the tin plating layer 34. For example, a methanesulfonic acid bath mainly composed of methanesulfonic acid, tin methanesulfonate, and organic additives can be used. The temperature of the plating bath is 20°C to 40°C, and the current density is 3 A / dm ２ 15A / dm or more ２ The following is considered to be the case.

[0060] The average thickness of this tin plating layer 34 is set to be between 0.5 μm and 1.5 μm. If the average thickness of the tin plating layer 34 is less than 0.5 μm, the tin layer 27 cannot be formed to the required thickness after the reflow process. If it exceeds 1.5 μm, the tin layer 27 remaining after the reflow process becomes too thick, resulting in a high coefficient of friction. It is preferable that the average thickness of this tin plating layer 34 be between 0.6 μm and 1.0 μm.

[0061] In this manner, a nickel plating layer 31, a silver plating layer 32, a copper plating layer 33, and a tin plating layer 34 are sequentially formed on the surface of the substrate 21, thereby obtaining a plated substrate 35 with four layers of plating 31 to 34 stacked on top of each other. Surface activation treatment using sulfuric acid or the like is performed between each plating process.

[0062] (Reflow Processing Process) The plated substrate 35, on which the plating layers 31 to 34 have been formed as described above, is subjected to a reflow process. This reflow process is carried out by heating the plated substrate 35 to a temperature above the melting point of tin in the tin plating layer 34 (for example, 232°C), melting the tin plating layer 34, and then cooling it.

[0063] This reflow process causes the copper in the copper plating layer 33 and the tin in the tin plating layer 34 to alloy, forming a copper-tin alloy layer 26 with an uneven surface. At the same time, parts of the copper plating layer 33 and the tin plating layer 34 remain partially unreacted as a copper layer 25 and a tin layer 27, and a film 22 is formed on the substrate 21, having a nickel layer 23, a silver layer 24, a copper layer 25, a copper-tin alloy layer 26, and a tin layer 27 in that order.

[0064] The connector terminal material 1 manufactured in this manner has a coating 22 formed on both its front and back surfaces. The outermost layer of the coating 22 is made of a tin layer 27, and beneath that is a copper-tin alloy layer 26 with an uneven surface. This creates a composite structure in which the relatively soft tin layer 27 on the surface is supported by the hard copper-tin alloy layer 26. These layers reduce the coefficient of friction, thus maintaining low insertability. Furthermore, the formation of a nickel layer 23 and a silver layer 24 acts as a barrier layer, suppressing the diffusion of copper (Cu) from the substrate 21 in high-temperature environments and improving heat resistance.

[0065] In the first embodiment, if the connector terminal material having the layered structure described above is used, silver may diffuse into the copper-tin alloy layer and the tin layer, and silver-tin alloy precipitates may be formed on or within the copper-tin alloy layer.

[0066] The precipitates of this silver-tin alloy include granular and flake-like precipitates (referred to as granular silver-tin alloy precipitates) and rod-shaped precipitates (rod-shaped silver-tin alloy precipitates). There are two forms: one in which granular silver-tin precipitates are scattered (referred to as the second embodiment), and another in which rod-shaped silver-tin alloy precipitates are formed in addition to granular silver-tin alloy precipitates (referred to as the third embodiment).

[0067] In other words, the first embodiment described above is a form that does not have these silver-tin alloy precipitates. The connector terminal materials of the second and third embodiments will be described in order below.

[0068] [Configuration of the Second Embodiment] In the connector terminal material of the second embodiment, the overall layer structure is the same as in the first embodiment, with a nickel layer 23, a silver layer 24, a copper layer 25, a copper-tin alloy layer 26, and a tin layer 27 formed in this order on a base material 21. The average thickness of the nickel layer 23 is 0.3 μm or more and 2.0 μm or less, the average maximum thickness of the silver layer 24 is 0.02 μm or more and 0.50 μm or less, the average maximum thickness of the copper layer 25 is 0.35 μm or less, the average thickness of the copper-tin alloy layer 26 is 0.35 μm or more and 1.00 μm or less, and the average thickness of the tin layer 27 is 0.10 μm or more and 1.00 μm or less. For this reason, in this second embodiment, components common to the first embodiment are denoted by the same reference numerals to simplify the explanation.

[0069] Furthermore, granular silver-tin alloy precipitates 41 are formed on the surface of the copper-tin alloy layer 26 and the tin layer 27 (see Figure 4, which is an SEM image of Example 13 described later). Specifically, the granular silver-tin alloy precipitates 41 are formed by contact with the copper-tin alloy layer 26 so as to adhere to the uneven surface of the copper-tin alloy layer 26, and are also scattered within the tin layer 27.

[0070] In this case, the silver layer 24 is not formed as a uniform, even layer, but rather partially or intermittently, because some of the silver diffuses to form granular silver-tin alloy precipitates 41. Similarly, the copper layer 25 on top of the silver layer 24 is not formed as a uniform layer, but rather partially or intermittently, in order to form diffusion pathways for the silver. As described in the first embodiment, there are also cases where the copper layer 25 is absent and a copper-tin alloy layer 26 is formed on the surface of the silver layer 24.

[0071] The method for manufacturing this connector terminal material is the same as the method described as the method for manufacturing the connector terminal material 1 in the first embodiment.

[0072] In this manufacturing method, the amount of granular silver-tin alloy precipitate 41 can be controlled by controlling the thickness of the copper plating layer 33 and the silver plating layer 32.

[0073] In this second embodiment of the connector terminal material, the silver (Ag) in the silver layer 24 diffuses to form hard granular silver-tin alloy precipitates 41 in the copper-tin alloy layer 26 and the tin layer 27, thereby reducing the coefficient of friction. Furthermore, in a high-temperature environment, the diffusion of silver takes precedence over the diffusion of copper from the substrate 21, suppressing the formation of the copper-tin alloy and allowing for the preferential formation of a silver-tin alloy with higher conductivity, thereby suppressing an increase in contact resistance.

[0074] In this case, the average area ratio of the granular silver-tin alloy precipitates 41 to the tin layer 27, calculated from a cross-sectional image taken along the thickness direction parallel to the rolling direction of the terminal material, is between 1% and 50%. This area ratio is calculated by (area of ​​silver-tin alloy precipitates / area of ​​tin layer) × 100. If the average area ratio of the granular silver-tin alloy precipitates 41 exceeds 50%, there is an excess of silver-tin alloy precipitates relative to the tin layer 27, which may reduce heat resistance. It is preferable that the average area ratio of the granular silver-tin alloy precipitates 41 be between 5% and 22%.

[0075] [Configuration of the Third Embodiment] In the connector terminal material of the third embodiment, a portion of the silver-tin alloy precipitate 41, which was formed in granular form in the second embodiment, is formed in a rod shape, as shown in Figures 5 and 6, which are SEM images of Example 15 described later. In other words, in this third embodiment, the silver-tin alloy precipitate includes both granular silver-tin alloy precipitate 41 and rod-shaped silver-tin alloy precipitate 45.

[0076] The overall layer structure is the same as in the first embodiment, with a nickel layer 23, a silver layer 24, a copper layer 25, a copper-tin alloy layer 26, and a tin layer 27 formed in this order on a substrate 21. The average thickness of the nickel layer 23 is 0.3 μm or more and 2.0 μm or less, the average maximum thickness of the silver layer 24 is 0.02 μm or more and 0.50 μm or less, the average maximum thickness of the copper layer 25 is 0.35 μm or less, the average thickness of the copper-tin alloy layer 26 is 0.35 μm or more and 1.00 μm or less, and the average thickness of the tin layer 27 is 0.10 μm or more and 1.00 μm or less.

[0077] Furthermore, the average area ratio of silver-tin alloy precipitates (granular silver-tin alloy precipitates 41 and rod-shaped silver-tin alloy precipitates 45) to the tin layer 27, determined from a cross-sectional image taken along the thickness direction parallel to the rolling direction of the terminal material, is calculated by {(area of ​​silver-tin alloy precipitates / area of ​​tin layer) × 100}, which is 1% or more and 50% or less, preferably 5% or more and 39% or less.

[0078] In this third embodiment of the connector terminal material, the rod-shaped silver-tin alloy precipitate 45 is formed within the tin layer 27, connected to the surface of the copper-tin alloy layer 26 (see Figure 6). As shown in Figure 6, the rod-shaped silver-tin alloy precipitate 45 is formed connected to the surface of the copper-tin alloy layer 26, which makes it difficult for the silver-tin alloy precipitate 45 to separate when sliding with the mating terminal when used as a connector, thus reducing the coefficient of friction.

[0079] The number of rod-shaped silver-tin alloy precipitates 45 with a longitudinal length of 5 μm or more, measured from the image obtained by scanning electron microscopy at a magnification of 4000x after the tin layer 27 of the film has been removed, is 650 μm in area. ２ The average is said to be between 1 and 35.

[0080] When rod-shaped silver-tin alloy precipitates 45 precipitate within the tin layer 27, the coefficient of friction decreases more significantly compared to the first and second embodiments. Heat resistance is also good, but the area of ​​the rod-shaped silver-tin alloy precipitates 45, which are 5 μm or larger, is 650 μm. ２ If the average number of strands exceeds 35, there may be an excess of silver-tin alloy precipitates relative to the tin layer 27, which could reduce heat resistance.

[0081] These rod-shaped silver-tin alloy precipitates 45, which are 5 μm or larger, cover an area of ​​650 μm. ２ It is preferable to have 21 or fewer.

[0082] Furthermore, the detailed configuration is not limited to that of the embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0083] As the base material, 0.25 mm thick sheet metal of alloy symbols C18665 and C26000 from the CDA (Copper Development Association) was used. Pretreatment included electrolytic degreasing and pickling, followed by nickel plating, silver plating, copper plating, and tin plating on the surface in sequence. Table 1 shows that Silver Plating 1 is the condition for strike plating when the average maximum thickness of the silver layer is 0.1 μm or less, and Silver Plating 2 is the condition for additional silver plating performed after Silver Plating 1 when the average maximum thickness of the silver layer exceeds 0.1 μm. In the table, 3K and TY are DuPont additives, with 3K being SILVER GLO 3K bright silver and TY being SILVER GLO TY.

[0084] Furthermore, pickling or alkaline washing was performed between each plating stage. The conditions for electrolytic degreasing, pickling or alkaline washing, and plating are shown in Table 1 in order of the process. In the table, "RT" indicates room temperature.

[0085]

[0086] Plating layers were formed on substrates for the examples and comparative examples under the above conditions. The thickness of each plating layer was controlled by adjusting the plating time within the following range.

[0087] Nickel plating: 30 to 200 seconds Silver plating: 5 to 100 seconds (If silver plating 2 is performed, this is the sum of silver plating 1 and silver plating 2) Copper plating: 10 to 40 seconds Tin plating: 15 to 60 seconds

[0088] In addition, samples without a silver plating layer (Comparative Example 1) and samples without copper and tin plating layers (Comparative Example 2) were also prepared. Comparative Example 3 had a different plating order, with nickel plating, copper plating, tin plating, and silver plating in that order.

[0089] The average thickness of each plating layer was measured for the obtained substrates with plating layers as follows.

[0090] The average thickness of the nickel plating layer, silver plating layer, and tin plating layer was determined by measuring five arbitrary points using the Fundamental Parameter Method (FP) with an X-ray fluorescence thickness gauge and averaging the values.

[0091] The average thickness of the copper plating layer was determined by copper plating a stainless steel (SUS316) plate, measuring five arbitrary points on the copper plating material using a fluorescence X-ray film thickness gauge, and averaging the results. From the film deposition rate obtained from these results, the plating time required for a given plating thickness was calculated. The values ​​listed in the table are not actual measured values, but rather thicknesses calculated from the copper plating time used when preparing the substrate with the plated layer.

[0092] These results are shown in Table 2. The type of plating layer is indicated by its elemental symbol.

[0093]

[0094] Next, the plated substrate was reflow-treated in an atmospheric environment, and the average thickness of each layer of the coating, the area ratio of silver-tin alloy precipitates, the number of rod-shaped silver-tin alloy precipitates, the coefficient of friction, and the contact resistance after heating were measured for the terminal material after reflow treatment.

[0095] (Average thickness of each layer) The average thickness of the nickel layer was determined by measuring five arbitrary points using the FP method (Fundamental parameter method) with an X-ray fluorescence film thickness gauge and averaging the values.

[0096] The average maximum thickness of the silver layer was determined by taking five images of arbitrary cross-sections of the plated substrate using a scanning electron microscope (SEM) at a magnification of 10,000x and projecting them onto an ESB detector (Energy and Angle Selective Backscattered Electron Detector). As shown in Figure 7, the maximum thickness of the silver layer within one copper-tin alloy particle (Ag1 in Figure 7) was measured and averaged. One copper-tin alloy particle refers to a single particle demarcated by the boundary (valley) of a copper-tin alloy layer having an uneven shape, as shown by X1 and X2 in Figure 7.

[0097] The average maximum thickness of the copper layer was determined by measuring the maximum thickness of the copper layer (Cu1 in Figure 7) within a single particle of the copper-tin alloy from five images projected onto an ESB detector (Energy and Angle Selective Backscattered Electron Detector) by scanning electron microscope (SEM) at a magnification of 10,000x, and then averaging the results.

[0098] The average thickness of the copper-tin alloy layer was calculated by taking five images of the cross-section using a scanning electron microscope (SEM) at a magnification of 10,000x and projecting them onto an ESB detector (Energy and Angle Selective Backscattered Electron Detector). As shown in Figure 8, the average thickness was calculated by taking (A + B) / 2 for the height A of the apex (convex part) and the height B of the grain boundary (valley part) of all copper-tin alloy particles, and then determining the average value.

[0099] The average thickness of the tin layer was determined by measuring the thickness of the tin-containing layer in the material before stripping and after stripping the tin layer using a stripping solution that removes only tin, using a calibration curve method with an X-ray fluorescence film thickness gauge. The average thickness of the tin layer was calculated from the difference between the thickness before and after stripping. Five arbitrary points were measured and averaged.

[0100] (Area ratio of silver-tin alloy precipitates) The area ratio of silver-tin alloy precipitates was calculated by freehand drawing of the tin layer and silver-tin alloy layer using the image processing software ImageJ1.54g from cross-sectional images taken at 15,000x magnification using a scanning electron microscope (SEM) equipped with a focused ion beam (FIB). The area ratios calculated from three cross-sectional images were averaged. Values ​​less than 1% were treated as 0.

[0101] Note that this area ratio indicates the area ratio of granular silver-tin alloy precipitates if only granular silver-tin alloy precipitates are present, but if rod-shaped silver-tin alloy precipitates are also present, it indicates the ratio of the total alloy area of ​​granular silver-tin alloy precipitates and rod-shaped silver-tin precipitates.

[0102] (Number of rod-shaped silver-tin alloy precipitates) The number of rod-shaped silver-tin alloy precipitates was determined by removing everything except the silver-tin alloy precipitates from the tin layer using a tin stripping solution, and then imaging the surface at 4000x magnification using a scanning electron microscope (SEM) over an area of ​​650 μm. ２ From a total of five field-of-view images, rods with a length of 5 μm or more were counted and averaged.

[0103] (Coefficient of friction) From each sample, test pieces measuring 60 mm parallel to the rolling direction and 30 mm perpendicular were cut out and used as substitutes for male terminals (male terminal test pieces). All female terminal samples were the same, and the base material was plated with nickel, copper, and tin, and then reflowed to form a nickel layer with an average thickness of 0.3 μm, a copper-tin alloy layer with an average thickness of 0.58 μm, and a tin layer with an average thickness of 0.35 μm in that order. Using this reflow material, test pieces were cut to 60 mm parallel to the rolling direction and 10 mm perpendicular, and an embossed pattern with a radius of curvature of 1.5 mm was applied to the center of the test piece.

[0104] Using this test specimen sample, a friction and wear tester (UMT-Tribolab) from Bruker AXS Corporation was used to bring the convex surfaces of a horizontally positioned male terminal test specimen and a female terminal test specimen into contact. A load of 5N was applied to the male terminal test specimen, and it was slid over a distance of 10 mm. The average value of the friction coefficient obtained from a distance of 0.1 mm to 10 mm was calculated, and the values ​​obtained from three measurements were averaged to obtain the measured value of the friction coefficient.

[0105] (Contact Resistance) Similar to the friction coefficient, male and female terminal test pieces were prepared. The male test piece was heated at 150°C for 500 hours, and then the contact resistance (mΩ) was measured. For the measurement, a friction and wear tester (UMT-Tribolab) from Bruker AXS Co., Ltd. was used. The convex surface of the female terminal test piece was brought into contact with the heated male terminal test piece, which was placed horizontally, and the contact resistance value was measured three times using the four-terminal method when a load of 1N was applied. The average value was taken as the contact resistance value.

[0106] These measurement results are shown in Tables 3 and 4. The type of layer and precipitates for each layer are indicated by elemental symbols, with copper-tin alloys being indicated as "CuSn" and silver-tin alloys as "AgSn". A "-" is used to indicate that measurements were not taken.

[0107]

[0108]

[0109] As can be seen from Tables 3 and 4, the example in which the nickel layer had an average thickness of 0.3 μm to 2.0 μm, the silver layer had an average maximum thickness of 0.02 μm to 0.50 μm, the copper layer had an average maximum thickness of 0.35 μm or less, the copper-tin alloy layer had an average thickness of 0.35 μm to 1.00 μm, and the tin layer had an average thickness of 0.10 μm to 1.00 μm exhibited low contact resistance after heating, excellent heat resistance, a low coefficient of friction, and maintained low insertability.

[0110] In contrast, Comparative Example 1 had high contact resistance because it did not form a silver layer. Comparative Example 2 had low contact resistance because the outermost layer of the film was a silver layer, but the coefficient of friction was high because silver is soft. Since no silver-tin alloy was formed in Comparative Examples 1 and 2, the area ratio and number of silver-tin alloy precipitates were not measured. Comparative Example 3 had a low coefficient of friction but high contact resistance because silver-tin alloy precipitates were concentrated on the surface of the film. Also, because silver-tin alloy precipitates were present on the surface, it was not possible to peel off anything other than the silver-tin alloy precipitates from the tin layer, so the area ratio and number of silver-tin alloy precipitates could not be measured. Comparative Example 4 had high contact resistance because the nickel layer was thin, resulting in insufficient barrier effect against copper diffusion from the substrate.

[0111] In Comparative Example 5, the silver plating layer was too thin, resulting in a small average maximum thickness of the silver layer. Under high-temperature conditions, tin preferentially formed a copper-tin alloy over silver, leading to high contact resistance. Conversely, in Comparative Example 6, the silver plating layer was too thick, resulting in an excessively large average maximum thickness of the silver layer. Under high-temperature conditions, tin was quickly lost through silver-tin alloying, also leading to high contact resistance.

[0112] In Comparative Example 7, the copper plating layer was too thin, resulting in a small average thickness of the copper-tin alloy layer after reflow treatment. Furthermore, the silver plating layer was completely converted into a silver-tin alloy during reflow treatment and did not remain as a silver layer. In this case, although the copper-tin alloy layer can also act as a barrier layer against copper diffusion from the substrate, this layer was also thin, and the absence of a silver layer contributed to poor heat resistance and high contact resistance. The fact that the coefficient of friction was not particularly high despite the thinness of the copper-tin alloy layer suggests that the presence of the silver-tin alloy layer suppressed the increase in the coefficient of friction, even with a thin copper-tin alloy layer. Conversely, in Comparative Example 8, the copper plating layer was too thick, resulting in a large average thickness of the copper-tin alloy layer and a high average maximum thickness of the copper layer. Consequently, excessive copper-tin alloy was generated in a high-temperature environment, resulting in high contact resistance and a high coefficient of friction.

[0113] Comparative Example 9 had a small average thickness of the tin plating layer, resulting in no tin layer remaining after reflow treatment. It also had a small average maximum thickness of the silver layer, leading to high contact resistance in high-temperature environments. Comparative Example 10 had an excessively thick tin plating layer, resulting in a thick tin layer remaining after reflow treatment. While this resulted in low contact resistance, the thick, soft tin layer increased the coefficient of friction.

[0114] The present invention can be suitably used in terminal materials for connectors that have heat resistance and low insertion force.

[0115] 1 Connector terminal material 21 Base material 22 Coating 23 Nickel layer 24 Silver layer 25 Copper layer 26 Copper-tin alloy layer 27 Tin layer 31 Nickel plating layer 32 Silver plating layer 33 Copper plating layer 34 Tin plating layer 35 Plating layered base material 41 Granular silver-tin alloy precipitate 45 Rod-shaped silver-tin alloy precipitate

Claims

1. A terminal material for a connector characterized in that a film is formed on the surface of a substrate whose outermost surface is made of copper or a copper alloy, and the film comprises a nickel layer made of nickel or a nickel alloy formed on the surface of the substrate, a silver layer made of silver or a silver alloy formed on the nickel layer, a copper-tin alloy layer made of a copper-tin alloy formed on the silver layer, and a tin layer made of tin or a tin alloy formed on the copper-tin alloy layer, wherein the average thickness of the nickel layer is 0.3 μm or more and 2.0 μm or less, the average maximum thickness of the silver layer is 0.02 μm or more and 0.50 μm or less, the average thickness of the copper-tin alloy layer is 0.35 μm or more and 1.00 μm or less, and the average thickness of the tin layer is 0.10 μm or more and 1.00 μm or less.

2. The connector terminal material according to claim 1, further comprising a copper layer made of copper or a copper alloy formed on the silver layer, wherein the average maximum thickness of the copper layer is 0.35 μm or less.

3. The connector terminal material according to claim 1 or 2, characterized in that the copper-tin alloy layer surface and the tin layer contain silver-tin alloy precipitates, and the average area ratio of the silver-tin alloy precipitates to the tin layer, as measured from a cross-sectional image along the thickness direction, is 1% or more and 50% or less.

4. The tin layer contains rod-shaped silver-tin alloy precipitates connected to a portion of the surface of the copper-tin alloy layer, and the length of these rod-shaped silver-tin alloy precipitates, measured from a scanning electron microscope image taken at 4000x magnification of the surface after the tin layer has been peeled off, is 5 μm or more in the longitudinal direction and has an area of ​​650 μm. ２ The connector terminal material according to claim 3, characterized in that it has an average of 1 to 35 strands.

5. A method for manufacturing a connector terminal material according to claim 1, characterized in that a plating layer formation step is performed to form a substrate with a plating layer by laminating a nickel plating layer made of nickel or a nickel alloy with an average thickness of 0.3 μm or more and 2.0 μm or less, a silver plating layer made of silver or a silver alloy with an average thickness of 0.02 μm or more and 0.53 μm or less, a copper plating layer made of copper or a copper alloy with an average thickness of 0.15 μm or more and 0.50 μm or less, and a tin plating layer made of tin or a tin alloy with an average thickness of 0.5 μm or more and 1.5 μm or less on the surface of the substrate; and a reflow step is performed to heat the substrate with the plating layer to a temperature above the melting point of tin, thereby manufacturing the connector terminal material.

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