JP7119267B2 - Terminal materials for connectors - Google Patents

Description

TECHNICAL FIELD The present invention relates to a terminal material for a connector provided with a useful film, which is used for connecting electrical wiring in automobiles, consumer appliances, etc., to which large currents and high voltages are applied.

2. Description of the Related Art In-vehicle connectors used for connecting electrical wiring in automobiles and the like have been conventionally known. An in-vehicle connector (in-vehicle terminal) is designed to be electrically connected when a contact piece provided on a female terminal and a male terminal inserted into the female terminal come into contact with each other with a predetermined contact pressure. terminal pairs.

As such connectors (terminals), tin-plated terminals, which are obtained by plating a copper or copper alloy plate with tin and performing a reflow treatment, have generally been used. However, in recent years, with the increase in current and voltage in automobiles, the use of terminals plated with a precious metal such as silver, which allows a larger current to flow and is excellent in heat resistance and wear resistance, is increasing.

BACKGROUND ART For example, a silver-plated connector terminal described in Patent Literature 1 is known as an in-vehicle terminal that requires heat resistance and wear resistance. In the silver-plated connector terminal described in Patent Document 1, the surface of a base material made of copper or a copper alloy is coated with a silver-plated layer.

This silver plating layer has a first silver plating layer located on the lower layer side (base material side) and a second silver plating layer located on the upper layer side of the first silver plating layer. The crystal grain size of the plated layer is larger than the crystal grain size of the second silver plated layer. That is, in the configuration of Patent Document 1, by forming the crystal grain size of the first silver plating layer larger than the crystal grain size of the second silver plating layer, the copper from the base material becomes the second silver plating layer. It prevents the spread of

In Patent Document 2, a silver or silver alloy layer having an antimony concentration of 0.1% by mass or less is formed on at least part of the surface of a copper or copper alloy member as a base material, and a silver or silver alloy layer is formed on the silver or silver alloy layer. A copper or copper alloy member is disclosed in which a silver alloy layer having an antimony concentration of 0.5% by mass or more and a Vickers hardness of HV140 or more is formed as the outermost layer. That is, in the configuration of Patent Document 2, antimony is added to the silver or silver alloy layer to increase the hardness, thereby improving the wear resistance of the copper or copper alloy member.

Japanese Patent Application Laid-Open No. 2008-169408 Japanese Patent Application Laid-Open No. 2009-79250

In the structure of Patent Document 1, the hardness of the silver plating layer covering the surface of the base material decreases as the silver crystal grain size increases (coarsening) due to aging and use in a high-temperature environment. Abrasion resistance decreases with use of time and high temperature environment. In order to compensate for this decrease in wear resistance, it is conceivable to increase the film thickness of the silver plating layer, but there is a problem in terms of cost. In the structure of Patent Document 2, there is a problem that antimony diffuses to the outermost surface of the plating layer due to heating and is oxidized after concentrating, resulting in an increase in contact resistance.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a terminal material for connectors capable of improving wear resistance and heat resistance.

A terminal material for a connector of the present invention comprises a base material having at least a surface made of copper or a copper alloy, and a silver-nickel-potassium alloy plating layer formed on at least a part of the base material. The alloy plating layer has a film thickness of 0.5 μm or more and 20.0 μm or less, an average crystal grain size of 150 μm or less, a nickel content of 0.02 mass % or more and 0.60 mass % or less, and a potassium content is 0.03% by mass or more and 1.00% by mass or less.

In the present invention, since the silver-nickel-potassium alloy plating layer formed on the surface of the base material co-deposits nickel and potassium together with silver, the crystal grains of the silver-nickel-potassium alloy plating layer can be made finer. In addition, co-precipitation of nickel and potassium increases hardness and improves wear resistance. Furthermore, since nickel and potassium are difficult to thermally diffuse, coarsening of the crystal grains of the silver-nickel-potassium alloy plating layer in a high-temperature environment can be suppressed.
In this case, since the silver-nickel-potassium alloy plating layer contains nickel and potassium, coarsening of crystal grains is suppressed even when exposed to a high-temperature environment, and deterioration of wear resistance in a high-temperature environment is small. When the silver-nickel-potassium alloy plating layer is formed, the average grain size of the silver-nickel-potassium alloy plating layer may exceed 150 nm if nickel and potassium are not codeposited or the amount of codeposition is low. In this case, the amount of nickel and potassium eutectoid is small, and the plating layer has properties close to those of pure silver. Therefore, the crystal grains may become coarse in a high-temperature environment, and wear resistance may decrease.

In this case, if the nickel content is less than 0.02% by mass or the potassium content is less than 0.03% by mass, the average crystal grain size of the silver-nickel-potassium alloy plating layer increases, and the crystal grains coarsen. resulting in an associated increase in the coefficient of friction. If the nickel content exceeds 0.60% by mass or the potassium content exceeds 1.00% by mass, the deposition state of the silver-nickel-potassium alloy plating layer deteriorates, the smoothness is lost, and the friction coefficient increases. . Also, in this case, since the electrical conductivity of nickel and potassium themselves is poor, the electrical conductivity decreases and the contact resistance increases as the co-deposited amount of nickel and potassium increases. Moreover, the contact resistance further increases in a high temperature environment.

If the thickness of the silver-nickel-potassium alloy plating layer is less than 0.5 μm, the heat resistance and wear resistance cannot be improved. occur.

In this connector terminal material, the silver-nickel-potassium alloy plating layer preferably has an average crystal grain size of 10 nm or more .

It is preferable that the average crystal grain size of the silver-nickel-potassium alloy plating layer is small, but when measuring the crystal grain size of less than 10 nm, the reliability of the measurement result is low and not practical.

In another aspect of the connector terminal material, at least a portion of the silver-nickel-potassium alloy plating layer has a silver purity of 99% by mass excluding gas components C, H, S, O, and N. As described above, a silver plating layer having a film thickness of 0.1 μm or more and 5.0 μm or less may be further provided.

Since a relatively soft silver plating layer is formed on the surface, its lubricating effect improves wear resistance. If the thickness of the silver plating layer is less than 0.1 μm, the silver plating layer is too thin. A thickness exceeding 5.0 μm tends to increase the coefficient of friction because the soft silver plating layer is thick.

In still another aspect of the connector terminal material, a nickel plating made of nickel or a nickel alloy having a thickness of 0.2 μm or more and 5.0 μm or less is provided between the base material and the silver-nickel-potassium alloy plating layer. Layers are preferably formed.

The nickel plating layer prevents copper from diffusing from the substrate into the silver-nickel-potassium alloy plating layer. If the thickness of the nickel plating layer is less than 0.2 μm, copper may diffuse from the base material into the silver-nickel-potassium alloy plating layer in a high-temperature environment. If the copper diffused into the silver-nickel-potassium alloy plating layer diffuses to the surface of the plating film, the copper may be oxidized to increase the contact resistance and reduce the heat resistance. On the other hand, if the thickness of the nickel plating layer exceeds 5.0 μm, cracks may occur during bending or the like.

ADVANTAGE OF THE INVENTION According to this invention, the abrasion resistance and heat resistance of the terminal material for connectors can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically the terminal material for connectors which concerns on 1st Embodiment of this invention. It is sectional drawing which shows typically the terminal material for connectors which concerns on 2nd Embodiment of this invention. It is sectional drawing which shows typically the terminal material for connectors which concerns on 3rd Embodiment of this invention. It is sectional drawing which shows typically the terminal material for connectors which concerns on 4th Embodiment of this invention. 5 is a SIM (Scanning Ion Microscope) image of a cross section of the connector terminal material before heating in Sample 5. FIG.

An embodiment of the present invention will be described below with reference to the drawings.

[First embodiment]
As shown schematically in cross section in FIG. 1, the connector terminal material 1 of the first embodiment is formed on a plate-shaped base material 2 whose at least surface is made of copper or a copper alloy and on the base material 2. and a silver-nickel-potassium alloy plating layer 3.

The composition of the substrate 2 is not particularly limited as long as the surface is made of copper or a copper alloy. In this embodiment, as shown in FIG. 1, the base material 2 is made of a plate material made of copper or copper alloy such as oxygen-free copper (C10200) or Cu—Mg copper alloy (C18665). It may be composed of a plated material in which the surface of a base material that is not a copper alloy is plated with copper or a copper alloy. In this case, a metal plate other than copper can be applied as the base material.

The silver-nickel-potassium alloy plating layer 3 is formed by applying a silver-nickel-potassium alloy plating treatment after applying a silver strike plating treatment on the substrate 2 as described later. The silver-nickel-potassium alloy plating layer 3 is formed by co-deposition of nickel and potassium in silver of the mother phase.

This silver-nickel-potassium alloy plating layer co-deposits nickel and potassium together with silver, so that the crystal grains of the silver-nickel-potassium alloy plating layer can be made finer. In addition, co-precipitation of nickel and potassium increases hardness and improves wear resistance. Furthermore, since nickel and potassium are difficult to thermally diffuse, coarsening of the crystal grains of the silver-nickel-potassium alloy plating layer in a high-temperature environment can be suppressed.

The silver-nickel-potassium alloy plating layer 3 has a nickel content of 0.02% by mass or more and 0.60% by mass or less, and a potassium content of 0.03% by mass or more and 1.00% by mass or less. Since nickel and potassium are contained within these ranges, the contact resistance does not increase, the hardness of the surface increases, and the wear resistance improves.

When the nickel content is less than 0.02% by mass or the potassium content is less than 0.03% by mass, the average crystal grain size of the silver-nickel-potassium alloy plating layer 3 increases, resulting in coarsening of the crystal grains. result in an increase in the modulus.

If the nickel content exceeds 0.60% by mass or the potassium content exceeds 1.00% by mass, the deposition state of the silver-nickel-potassium alloy plating layer 3 deteriorates, losing smoothness and increasing the friction coefficient. do. Further, in this case, since the electrical conductivity of nickel and potassium themselves is poor, the electrical conductivity decreases and the contact resistance increases as the co-deposited amount of nickel and potassium increases. In addition, the impurities, nickel, and potassium in the plating solution caught in the silver-nickel-potassium alloy plating layer 3 in the plating process, which will be described later, are oxidized in a high-temperature environment, further increasing the contact resistance. In addition, since nickel and potassium have lower electrical conductivity than silver, if the nickel content exceeds 0.60% by mass or the potassium content exceeds 1.00% by mass, the silver-nickel-potassium alloy plating layer 3 Contact resistance increases.

Since nickel and potassium are difficult to thermally diffuse in the matrix of silver, they are difficult to concentrate on the outermost surface even in a high-temperature environment. Therefore, it is possible to suppress an increase in contact resistance in a high-temperature environment, keep the crystal grain size small, maintain a low coefficient of friction, and maintain wear resistance.

The nickel content is preferably 0.56% by mass or less, more preferably 0.30% by mass or less, and the potassium content is preferably 0.60% by mass or less.

The average crystal grain size of the silver-nickel-potassium alloy plating layer 3 is as fine as 10 nm or more and 150 nm or less. There is little decrease in wear resistance under the environment. When the silver-nickel-potassium alloy plating layer 3 is formed, the average crystal grain size of the silver-nickel-potassium alloy plating layer 3 may exceed 150 nm if nickel and potassium are not codeposited or the amount of codeposition is low. In this case, the amount of nickel and potassium eutectoid is small, and the plating layer has properties close to those of pure silver. Therefore, the crystal grains may become coarse in a high-temperature environment, and wear resistance may decrease. A smaller average crystal grain size is preferable, but when measuring a crystal grain size of less than 10 nm, the reliability of the measurement result is low and it is not practical.

The film thickness of the silver-nickel-potassium alloy plating layer 3 is set to 0.5 μm or more and 20.0 μm or less. If the thickness of the silver-nickel-potassium alloy plating layer 3 is less than 0.5 μm, the heat resistance and wear resistance cannot be improved. Cracking occurs due to processing or the like. A preferable film thickness of the silver-nickel-potassium alloy plating layer is 1.0 μm or more and 10.0 μm or less.

Next, a method for manufacturing the connector terminal material 1 will be described. A method for manufacturing the connector terminal material 1 includes a pretreatment step of washing a plate material whose surface is at least made of copper or a copper alloy, which serves as the base material 2, and a silver strike plating step of applying silver strike plating to the base material 2. and a silver-nickel-potassium alloy plating layer forming step of forming the silver-nickel-potassium alloy plating layer 3 by applying a silver-nickel-potassium alloy plating treatment after the silver strike plating treatment.

[Pretreatment process]
First, a plate made of at least a surface layer of copper or a copper alloy is prepared as the substrate 2, and pretreatment is performed to clean the surface of the plate by degreasing, pickling, or the like.

[Silver strike plating process]
After the base material 2 is subjected to activation treatment using a 5 to 10% by mass potassium cyanide aqueous solution, the base material 2 is subjected to silver strike plating treatment for a short period of time to form a thin silver plating layer.

The composition of the silver plating bath for performing this silver strike plating treatment is not particularly limited, but for example, it consists of silver cyanide (AgCN) of 1 g/L to 5 g/L and potassium cyanide (KCN) of 80 g/L to 120 g/L. . Using stainless steel (SUS316) as an anode for this silver plating bath, silver strike plating was performed for about 30 seconds under the conditions of a bath temperature of 25° C. and a current density of 1.5 A/dm ² . A layer is formed. Since the silver-nickel-potassium alloy plating layer 3 is subsequently formed on this silver strike plating layer, it becomes difficult to distinguish it as a layer.

[Silver-nickel-potassium alloy plating layer forming step]
After silver strike plating, silver-nickel-potassium alloy plating is applied to form a silver-nickel-potassium alloy plating layer 3 . The plating bath for forming the silver-nickel-potassium alloy plating layer 3 contains, for example, silver cyanide (AgCN) 30 g/L to 50 g/L, potassium cyanide (KCN) 120 g/L to ₂₀₀ g/L, potassium carbonate (K CO ₃ ) 15 g/L to 30 g/L, potassium tetracyanonickel(II) monohydrate (K ₂ [Ni(CN) ₄ ].H ₂ O) 120 g/L to 200 g/L, and silver nickel potassium A cyan bath having a composition containing additives for depositing the alloy plating layer 3 smoothly can be used. This additive may be a general additive as long as it does not contain antimony.

Using a pure silver plate as an anode for this plating bath, a silver-nickel-potassium alloy plating is applied at a bath temperature of 25°C and a current density of 4 A/dm ² to 12 A/dm ² to form a film thickness of 0.5 μm or more and 20 A silver-nickel-potassium alloy plating layer 3 of 0 μm or less is formed.

If the current density in the silver-nickel-potassium alloy plating treatment is less than 4 A/dm ² , codeposition of nickel and potassium is prevented, and if the current density exceeds 12 A/dm ² , the appearance of the silver-nickel-potassium alloy plating layer 3 becomes poor. undermined. The plating bath for forming the silver-nickel-potassium alloy plating layer 3 is not limited to the above composition, and the composition is not particularly limited as long as it is a potassium cyanide bath and does not contain antimony as an additive.

In this way, the connector terminal material 1 having the silver-nickel-potassium alloy plating layer 3 formed on the surface of the base material 2 is formed. Then, a connector terminal having a silver-nickel-potassium alloy plating layer 3 on its surface is formed by subjecting the connector terminal material 1 to press working or the like.

In the connector terminal material 1 of the present embodiment, since the silver-nickel-potassium alloy plating layer 3 formed on the outermost surface of the substrate 2 co-deposits nickel and potassium, the particles of the silver-nickel-potassium alloy plating layer 3 are It can be miniaturized, and even in a high-temperature environment, it is possible to suppress an increase in contact resistance compared to a hard silver-antimony plating layer. Moreover, the hardness of the outermost surface of the terminal material 1 can be increased, and the wear resistance can be improved.

[Second embodiment]
FIG. 2 shows a second embodiment of the invention. In the connector terminal material 11 of this embodiment, a nickel plating layer 4 made of nickel or a nickel alloy is formed between the substrate 2 and the silver-nickel-potassium alloy plating layer 3 .

The nickel plating layer 4 is formed by subjecting the base material 2 to a nickel plating process made of nickel or a nickel alloy, and covers the base material 2 . The nickel plating layer 4 has a function of suppressing diffusion of copper from the substrate 2 into the silver-nickel-potassium alloy plating layer 3 covering the nickel plating layer 4 .

The thickness (film thickness) of the nickel plating layer 4 is preferably 0.2 μm or more and 5.0 μm or less, more preferably 0.3 μm or more and 2.0 μm or less. If the thickness of the nickel plating layer 4 is less than 0.2 μm, copper may diffuse from the substrate 2 into the silver-nickel-potassium alloy plating layer 3 in a high-temperature environment. When the copper that has diffused into the silver-nickel-potassium alloy plating layer 3 diffuses to the surface of the plating film, the copper is oxidized and the contact resistance value of the silver-nickel-potassium alloy plating layer 3 increases, possibly reducing the heat resistance. .

On the other hand, if the thickness of the nickel plating layer 4 exceeds 5.0 μm, cracks may occur during bending. The composition of the nickel plating layer 4 is not particularly limited as long as it is made of nickel or a nickel alloy.

When manufacturing this connector terminal material 11, a pretreatment process, a nickel plating layer forming process, a silver strike plating process, and a silver-nickel-potassium alloy plating layer forming process are carried out in this order. Since the pretreatment process, the silver strike plating process, and the silver-nickel-potassium alloy plating process are the same as those in the first embodiment, description thereof is omitted.

[Nickel plating layer forming step]
A nickel plating process is performed on the surface of the pretreated base material 2 to form a nickel plating layer 4 on the base material 2 . Specifically, for example, using a nickel plating bath containing 350 g/L of nickel sulfamate, 10 g/L of nickel chloride hexahydrate, and 30 g/L of boric acid, the bath temperature is 45° C. and the current density is 5 A/dm ² . Nickel plating is applied under the following conditions. The nickel plating process for forming the nickel plating layer 4 is not particularly limited as long as a dense nickel-based film can be obtained, and may be an electroplating process using a known Watt bath.

In this connector terminal material 11, the surface of the base material 2 is covered with the nickel plating layer 4, so that the diffusion of copper from the base material 2 into the silver-nickel-potassium alloy plating layer 3 is prevented. The wear resistance and heat resistance of the alloy plating layer 3 can be maintained for a long period of time.

[Third Embodiment]
FIG. 3 shows a third embodiment of the invention. This connector terminal material 12 has a silver-plated layer 5 formed on the silver-nickel-potassium alloy-plated layer 3 . FIG. 3 shows an example in which a nickel plating layer 4 for preventing diffusion of copper from the substrate 2 is formed between the substrate 2 and the silver-nickel-potassium alloy plating layer 3 . However, the nickel plating layer 4 is not necessarily required in the present invention.

The surface of the silver plating layer 5 is not easily oxidized even in a high-temperature environment, and an increase in contact resistance can be suppressed. The silver plating layer 5 is made of pure silver with a purity of 99% by mass or more, preferably 99.9% by mass or more, excluding gas components such as C, H, S, O, and N. "Excluding gas components such as C, H, S, O, and N" means excluding elements of gas components. The reason why the purity is set to 99% by mass or more is that if the purity of silver in the silver plating layer 5 is less than 99% by mass, a large amount of impurities are contained, and the contact resistance tends to increase.

[Silver plating layer forming step]
The composition of the silver plating bath for forming the silver plating layer 5 is not particularly limited. Potassium carbonate (K ₂ CO ₃ ) 10 g/L to 20 g/L, and additives. Using a pure silver plate as an anode for this silver plating bath, plating is performed at a bath temperature of room temperature (25° C. to 30° C.) and a current density of 2 A/dm ² to 4 A/dm ² , A silver plating layer 5 is formed.

Although the silver plating layer 5 is relatively soft, it is supported by the underlying hard silver-nickel-potassium alloy plating layer 3, so that it has an excellent lubricating effect and improves wear resistance. The film thickness of the silver plating layer 5 is preferably 0.1 μm or more and 5.0 μm or less. If the film thickness of the silver plating layer 5 is less than 0.1 μm, it is too thin and is likely to be worn away early. If the film thickness exceeds 5.0 μm, the soft silver plating layer 5 becomes thick, which may increase the coefficient of friction. A preferable film thickness of the silver plating layer 5 is 0.25 μm or more and 3.0 μm or less.

In addition, detailed configurations are not limited to those of the embodiments, and various modifications can be made without departing from the scope of the present invention.

For example, in the above-described embodiment, the silver-nickel-potassium alloy plating layer 3 is formed on the entire upper surface of the substrate 2. However, the present invention is not limited to this. 3 may be formed. When forming the nickel plating layer 4, the nickel plating layer 4 may be formed on a part of the upper surface of the substrate 2, and the silver-nickel-potassium alloy plating layer 3 may be formed on the nickel plating layer 4. A silver-nickel-potassium alloy plating layer 3 may be formed on part of the upper surface of the nickel plating layer 4 formed on the entire upper surface of the substrate 2 . The silver-nickel-potassium alloy plated layer 3 may be formed on the surface of at least the portion that becomes the contact when the terminal is formed.

When the silver plating layer 5 is formed, in any of these forms, it may be formed on the entire upper surface of the silver-nickel-potassium alloy plating layer 3 or on a part of it, and it may be formed on the portion that will be the contact of the connector. Just do it. A connector terminal material 13 of the fourth embodiment shown in FIG. This is an example in which a silver plating layer 5 is formed on the silver-nickel-potassium alloy plating layer 3 .

A base material made of a copper alloy plate with a thickness of 0.25 mm was prepared, and the base material was subjected to pretreatment (pretreatment step) for cleaning the surface by degreasing, pickling, etc. After that, the surface of the base material was subjected to nickel plating treatment to form a nickel plating layer (nickel plating layer forming step).

Then, after performing activation treatment on the nickel plating surface using a 10% by mass potassium cyanide aqueous solution, the base material coated with the nickel plating layer was subjected to silver strike plating treatment (silver strike plating process).

A silver-nickel-potassium alloy plating process was applied thereon (silver-nickel-potassium alloy plating layer forming process), and a silver plating process was applied thereon (silver-plating layer forming process) to prepare samples shown in Tables 1 and 2. In Tables 1 and 2, a nickel plating layer is indicated as a Ni layer, a silver-nickel-potassium alloy plating layer is indicated as an AgNiK layer, and a silver plating layer is indicated as an Ag layer. The nickel content (expressed as Ni content) and potassium content (expressed as K content) in the silver-nickel-potassium alloy plating layer are determined by the amount of potassium tetracyanonickel(II) monohydrate in the plating process (Table 1) and current density during plating.
A silver-plated layer was formed on the nickel-plated layer without forming the silver-nickel-potassium alloy-plated layer (Comparative Example 14), and a silver-antimony alloy-plated layer was formed on the nickel-plated layer (Comparative Example 14). Example 15) was also made.

The conditions for each plating were as follows.
<Nickel plating conditions>
・Plating bath composition Nickel sulfamate: 350 g/L
Nickel chloride hexahydrate: 10g/L
Boric acid: 30g/L
・Bath temperature: 45℃
・Current density: 5 A/dm ²
・pH: 4

<Silver strike plating conditions>
・Plating bath composition silver cyanide: 2 g / L
Potassium cyanide: 100g/L
・Anode: SUS316
・Bath temperature: 25℃
・Current density: 1.5 A/dm ²

<Silver-nickel-potassium alloy plating conditions>
・Plating bath composition Silver cyanide: 45 g / L
Potassium cyanide: 180g/L
Potassium carbonate: 20g/L
Potassium tetracyanonickel(II) monohydrate: 120 g/L to 200 g/L
Additive: 5ml/L
・Anode: Pure silver plate ・Bath temperature: 25℃
・Current density: 4 A/dm ² to 14 A/dm ²

<Silver plating conditions>
・Plating bath composition Silver cyanide: 45 g / L
Potassium cyanide: 115g/L
Potassium carbonate: 15g/L
Brightener:
(manufactured by DDP Specialty Products Japan Co., Ltd.) SILVER GLO 3K: 15 ml / L
(same) SILVER GLO TY: 5ml/L
・Bath temperature: 25℃
・Current density: 4A/dm ²
・Anode: pure silver plate

For each sample, the film thickness of the silver-nickel-potassium alloy plating layer, the nickel content and potassium content in the silver-nickel-potassium alloy plating layer, the average grain size of the silver-nickel-potassium alloy plating layer, the silver plating layer and the nickel plating layer was measured.

[Measurement of film thickness of each plating layer]
The film thicknesses of the silver-nickel-potassium alloy plating layer, the silver plating layer and the nickel plating layer were measured as follows. A focused ion beam device manufactured by Seiko Instruments Inc.: FIB (model number: SMI3050TB) is used to perform cross-section processing on each sample, and the formed cross-section is observed with a scanning ion microscope (SIM: Scanning Ion Microscop), with an inclination angle of 60. The film thickness was measured at three arbitrary points in the cross-sectional SIM image of 10°, and after obtaining the average, it was converted into the actual length.

[Measurement of average grain size of silver-nickel-potassium alloy plating layer]
The plated material on which the silver-nickel-potassium alloy plated layer was formed was processed into a cross-sectional sample having a thickness of about 50 nm using FIB. A transmission electron microscope (TEM) equipped with an EBSD (Electron Back Scatter Diffraction) device was used to irradiate the silver-nickel-potassium alloy plating layer on the processed surface of the cross-sectional sample with an electron beam at an acceleration voltage of 200 kV. Meanwhile, the crystal orientation was measured twice with a measurement range of 200 nm × 400 nm and a measurement step of 2 nm.Then, the crystal orientation data was analyzed using analysis software, and the orientation difference between adjacent measurement points was 5° or more. The grain size (including twin crystals) of the silver-nickel-potassium alloy plated layer was measured by regarding the space between the measurement points as grain boundaries.

The equipment and analysis software used for the measurements are as follows.
EBSD device: OIM Data Collection manufactured by EDAX/TSL
Analysis software: EDAX/TSL OIM Data Analysis ver. 5.2

As for the sample (Comparative Example 10) in which the contents of nickel and potassium in the silver-nickel-potassium alloy plating layer were below the lower limits, the crystal grain size was expected to be large, so the measurement was performed by the following method.

A cross-section along the growth direction of electrodeposition of the silver-nickel-potassium alloy plating layer (thickness direction of the substrate) was processed by the ion milling method, and a field emission scanning electron microscope (FE-SEM: Field Emission-Scanning) equipped with an EBSD device was processed. Using an Electron Microscope (JSM-7001FA manufactured by JEOL Ltd.), the crystal orientation was measured at an acceleration voltage of 15 kV, a measurement range of 25 μm×3.0 μm, and a measurement step of 0.02 μm. The grain size (including twins) of the silver-nickel-potassium alloy plated layer was measured, considering the boundary of 5° or more as the grain boundary.
The apparatus and analysis software used for measurement are the same as those described above.

The obtained crystal grain size was approximated to an area circle, and the average crystal grain size was calculated by a weighted average weighted by the area.

[Measurement of nickel content (Ni content) and potassium content (K content)]
For each sample, the contents (% by mass) of nickel and potassium in the silver-nickel-potassium alloy plating layer were measured by GD-MS (Glow Discharge-Mass Spectrometry).

For the measurement, Astrum (trade name), which is a GD-MS apparatus manufactured by Nu Instruments, was used to detect the main component with a Faraday cup and the impurities with an IC multiplier. The detection conditions are as follows.
・Glow discharge: constant current mode ・Discharge current: 0.7mA
・Discharge voltage: 0.5 kV
・Discharge gas: Ar (>99.9999%)
・Depth direction resolution: 0.05 μm/scan

These measurement results are shown in Table 1. Since sample 11 had cracks during indentation for measuring contact resistance, the crystal grain size, contact resistance, and coefficient of friction of the silver-nickel-potassium alloy plating layer were not measured. "-" is shown in Table 1 for those for which these measurements were not performed.

[Measurement of contact resistance]
Each sample is cut into a test piece α of 60 mm × 30 mm and a test piece β of 60 mm × 10 mm, the flat plate test piece α is used as a substitute for the male terminal (male terminal test piece), and a hemispherical shape with a curvature radius of 5 mm is formed on the flat plate. A test piece β that was indented to form a convex portion was used as a substitute for the female terminal (female terminal test piece).

The contact resistance (mΩ) of these test pieces was measured before heating and after heating at 180° C. for 500 hours. For the measurement, a friction wear tester (UMT-Tribolab) manufactured by Bruker AXS Co., Ltd. was used, and the male terminal test piece placed horizontally was brought into contact with the convex surface of the female terminal test piece, and a load of 10 N was applied. The contact resistance value of the male terminal test piece when applied was measured by the four-probe method.

[Measurement of friction coefficient, wear resistance test (sliding test)]
In order to evaluate wear resistance, the coefficient of friction was measured as follows.
Test pieces α and β having the same shape as the test piece used for measuring the contact resistance were prepared. The convex surface of the convex portion of the test piece β and the test piece α were pressed against each other with a load of 5 N, and moved over a distance of 10 mm at a sliding speed of 1.33 mm/sec to measure changes in the coefficient of friction. An average value of the friction coefficients obtained over a moving distance of 5 mm to 10 mm was taken as the friction coefficient.

Note that the coefficient of friction depends on the film thickness of the plating. Therefore, when the total thickness of the silver plating layer and the silver-nickel-potassium alloy plating layer is large, it is not possible to compare the friction coefficient under the same conditions as the sample with a thin film thickness. A sliding test was carried out instead of the friction coefficient measurement for the samples whose total film thickness with the plating layer exceeded 8.0 μm.

In this sliding test, in a friction and wear tester (UMT-Tribolab) of Bruker AXS Co., Ltd., the convex surface of the convex part of the test piece β is brought into contact with the horizontally installed test piece α, and a load of 5 N is applied. In this state, the male terminal test piece was slid horizontally at a moving distance of 5 mm repeatedly 50 times. After the sliding test, the wear resistance was determined by whether or not the underlying nickel plating layer of the test piece was exposed. At this time, the case where the underlying nickel plating layer was not exposed after the sliding test was rated as good "A", and the case where the underlying nickel plating layer was exposed after the sliding test was rated as failing "B".

These results are shown in Table 2.

As can be seen from Tables 1 and 2, the film thickness of the silver-nickel-potassium alloy plating layer is 0.5 µm or more and 20.0 µm or less, the nickel content is 0.02 mass% or more and 0.60 mass% or less, and the potassium content is Samples 1 to 9 with a content of 0.03% by mass or more and 1.00% by mass or less exhibited low and stable contact resistance before and after heating, and a low coefficient of friction.

However, sample 1 exhibited a higher coefficient of friction than sample 2, although the silver-nickel-potassium alloy plating layer was thinner. This is because, unlike sample 2, sample 1 does not have a silver plating layer, so the silver plating layer does not have a lubricating effect.

Sample 6 had a low content of nickel and potassium in the silver-nickel-potassium alloy plating layer, so that the silver-nickel-potassium alloy plating layer was soft, and since the silver-plating layer was thick, the coefficient of friction was slightly high.

Sample 9 has a high content of nickel and potassium in the silver-nickel-potassium alloy plating layer, so the precipitation is somewhat rough. I didn't.

Among these, Samples 2, 4, 5, and 8 are good because the contact resistance is as low as 0.41 mΩ or less even after heating, and the friction coefficient is suppressed as low as 0.89 or less.

FIG. 5 is a cross-sectional SIM image of Sample 5, in which a silver-nickel-potassium alloy plating layer (denoted as AgNiK) and a silver plating layer (denoted as Ag) are formed on the nickel plating layer (denoted as Ni) on the substrate surface. are shown to be formed. It can be seen that the crystal grain size in the silver-nickel-potassium alloy plating layer is small.

Compared to the above samples, Sample 10 has a lower content of nickel and potassium in the silver-nickel-potassium alloy plating layer, so that the silver-nickel-potassium alloy plating layer has a larger average crystal grain size, resulting in a lower coefficient of friction. got higher Sample 12 has a thin silver-nickel-potassium alloy plated layer and a thick soft silver plated layer, so that the sum of these two film thicknesses has a higher coefficient of friction than sample 8, which has a similar film thickness. In addition, since the content of nickel and potassium in the silver-nickel-potassium alloy plating layer of sample 13 was large, the precipitation was rough and the coefficient of friction was high. Moreover, the contact resistance after heating is high, and the heat resistance is poor. Sample 14 did not form a silver-nickel-potassium alloy plating layer, but had only a silver plating layer. Therefore, the abrasion resistance was inferior, and the underlying nickel plating layer was exposed after the sliding test. In Sample 7, whose silver plating layer has a film thickness similar to that of Sample 14, the underlying nickel plating layer was not exposed after the sliding test. Sample 15 is a sample in which a silver-antimony alloy plating layer is formed instead of a silver-nickel-potassium alloy plating layer, and has a low coefficient of friction, but is inferior in heat resistance.

ADVANTAGE OF THE INVENTION According to this invention, the terminal material for connectors which improved abrasion resistance and heat resistance can be provided.

1, 11, 12, 13 Connector terminal material 2 Base material 3 Silver nickel potassium alloy plating layer 4 Nickel plating layer 5 Silver plating layer

Claims (4)

a base material at least the surface of which is made of copper or a copper alloy;
a silver-nickel-potassium alloy plating layer formed on at least a portion of the substrate;
with
The silver-nickel-potassium alloy plating layer has a film thickness of 0.5 µm or more and 20.0 µm or less, an average crystal grain size of 150 µm or less, and a nickel content of 0.02 mass% or more and 0.60 mass% or less. and a terminal material for a connector having a potassium content of 0.03% by mass or more and 1.00% by mass or less. 2. The connector terminal material according to claim 1, wherein the silver-nickel-potassium alloy plating layer has an average crystal grain size of 10 nm or more . At least part of the silver-nickel-potassium alloy plating layer has a silver purity of 99% by mass or more, excluding gas components C, H, S, O, and N, and a film thickness of 0.1 μm or more and 5.0 μm or less. 3. The connector terminal material according to claim 1, further comprising a silver plating layer. 2. A nickel plating layer made of nickel or a nickel alloy and having a thickness of 0.2 μm or more and 5.0 μm or less is formed between the base material and the silver-nickel-potassium alloy plating layer. 4. The connector terminal material according to any one of 3.

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