JP2016166396A - Copper terminal material with silver platting and terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent scrape of a silver plating layer during withdrawal while suppressing recrystallization of the silver plating layer during heat load and suppress increase of contact resistance.SOLUTION: There is provided a terminal material where a silver plating layer is formed on a substrate consisting of copper or copper alloy, where the silver plating layer has carbon co-deposited with percentage content of 0.1 mass% or more and 0.6 mass% or less, average crystal particle diameter of the silver crystal structure of 2 μm or more and 25 μm or less and percentage of length occupied by a specific grain boundary to length of total crystal grain boundary of 60% or more and 85% or less.SELECTED DRAWING: None

Description

  The present invention relates to a copper terminal material with silver plating obtained by silver-plating a base material made of copper or a copper alloy, and a terminal subjected to such silver plating.

  Since a hybrid car or an electric vehicle uses a motor as power, the amount of current flowing through the high-voltage cable connecting the battery and the motor is dramatically increased as compared with that of conventional automobile electric wiring. Terminals for removal during assembly and maintenance may be attached to the end of the high voltage cable. This terminal is silver-plated at the contact part to suppress the heat generated at the contact part when a large current flows, and it is large and set at a very high contact pressure. High hardness is required to prevent scraping. In addition, since the energization current amount is large in this portion, the generation of Joule heat is inevitable, and it is required that there is no increase in contact resistance when a thermal load is applied.

  In Patent Literature 1, in a silver plating terminal for a connector in which a surface of a base material made of copper or a copper alloy is covered with a silver plating layer, the silver plating layer includes a first silver plating layer on the lower layer side, and the first A second silver plating layer on the upper layer side of one silver plating layer, the crystal grain size of the first silver plating layer is larger than the crystal grain size of the second silver plating layer, and the average grain size is 2 μm or more Is disclosed. In the terminal disclosed in Patent Document 1, the silver plating layer is divided into a lower layer and an upper layer, the crystal grains of the silver plating layer on the base material side are enlarged to prevent copper diffusion, and the crystal of the silver plating layer on the surface side It is trying to prevent the contact resistance from deteriorating while maintaining the wear resistance by making the grains fine.

  Patent Document 2 discloses the X-ray diffraction intensity of the {200} plane relative to the sum of the X-ray diffraction intensities of the {111} plane, {200} plane, {220} plane, and {311} plane on the material. Disclosed is a silver plating material in which a first silver plating layer having a ratio of 40% or more is formed, and a second silver plating layer having a Vickers hardness of Hv 140 or more and containing antimony is formed on the first silver plating layer. Has been. By forming the antimony-containing silver plating layer on the first silver plating layer whose crystal orientation is controlled, the wear resistance is improved while preventing the contact resistance from deteriorating.

  Further, in Patent Document 3, in the silver plating material in which the surface layer made of silver is formed on the surface of the material or the surface of the underlayer formed on the material, the area fraction of the surface layer in the {200} direction is 15% or more. In other words, it is disclosed that bending workability is good and an increase in contact resistance can be suppressed even when used in a high temperature environment.

JP 2008-169408 A JP 2013-189680 A JP 2014-198895 A

  However, in the configuration disclosed in Patent Document 1, there is a problem that silver is recrystallized when a thermal load is applied, and fine crystal grains on the surface side cannot be retained, and the silver plating layer on the surface side is scraped during insertion / extraction. . Further, in the silver plating material disclosed in Patent Document 2, although recrystallization of the antimony-containing silver plating layer is suppressed, an antimony oxide film is formed on the surface when a thermal load is applied, and the contact resistance increases. was there. Even in the silver plating material disclosed in Patent Document 3, the effect of suppressing recrystallization at the time of heat load was still insufficient.

  The present invention has been made in view of the above-described problems, and suppresses recrystallization of the silver plating layer at the time of thermal load, prevents the silver plating layer from being scraped at the time of insertion and removal, and increases the contact resistance. It aims at suppressing.

  The copper terminal material with silver plating of the present invention is a terminal material in which a silver plating layer is formed on a substrate made of copper or a copper alloy, and the silver plating layer has a carbon content of 0.1% by mass or more and 0.6%. While eutectoid with a content of not more than mass%, the average crystal grain size of the silver crystal structure is 2 μm or more and 25 μm or less, and the ratio of the length occupied by the special grain boundary to the total grain boundary length is It is 60% or more and 85% or less.

This silver-plated copper terminal material is recrystallized when a thermal load is applied due to the pinning effect of the carbon precipitates because carbon is co-deposited in the silver plating layer at the above mass ratio. Be blocked. Therefore, since fine crystal grains of the silver crystal structure are maintained, the silver plating layer can be prevented from being softened and prevented from being scraped during insertion and removal as a connector. In this case, if the carbon content is less than 0.1% by mass, there is no effect of maintaining the hardness, and if it exceeds 0.6% by mass, the silver plating layer becomes brittle and the workability deteriorates. On the other hand, when the average crystal grain size is less than 2 μm, the silver plating layer becomes brittle and the workability deteriorates. When it exceeds 25 μm, the hardness decreases and the wear resistance deteriorates.
Special grain boundaries have higher atomic consistency than general grain boundaries, and are therefore less likely to cause grain boundary diffusion. For this reason, from the viewpoint of grain boundary diffusion, the length ratio of the special grain boundary is preferably as high as possible, and at least 60% is required. On the other hand, if the length ratio of the special grain boundary exceeds 85%, the hardness cannot be maintained.

  In the silver-plated copper terminal material of the present invention, the silver plating layer preferably contains 30% or more of crystal grains having a Schmitt factor value of less than 0.45 in terms of surface area ratio. The Schmitt factor here is a value analyzed under a condition in which a compressive force parallel to the thickness direction of the terminal material is applied.

Since crystal grains having a small Schmid factor are difficult to deform, such a metal structure having many crystal grains is difficult to plastically deform and has high strength. For this reason, when the crystal grains having a Schmitt factor value of less than 0.45 occupy 30% or more in terms of area ratio, the strength of the silver plating layer is increased and the wear resistance is improved. If it is less than 30%, the effect of improving the wear resistance is poor.
In conventional antimony-added silver plating, the average crystal grain size has been reduced to 2 μm or less and high hardness has been obtained. However, the silver plating film obtained by this method is brittle and has poor bending workability. As a result, in the present invention, by controlling the Schmid factor optimally, a relatively high hardness can be maintained even when the average crystal grain size is 2 μm or more, and a silver plating film with good workability can be obtained. Can be obtained.

  The copper terminal material with silver plating of this invention WHEREIN: The thickness of the said silver plating layer is good in it being 1 micrometer or more and 70 micrometers or less. If the thickness of the silver plating layer is less than 1 μm, it is difficult to prevent copper from diffusing from the base material that is the base, and there is a risk of increasing contact resistance due to copper diffusion. On the other hand, when the thickness of the silver plating layer exceeds 70 μm, the workability may be deteriorated.

  In the copper terminal material with silver plating of the present invention, a nickel plating layer having a thickness of 0.3 μm or more and 2 μm or less is formed between the base material and the silver plating layer, and the silver plating layer is formed of the nickel plating layer. It is good to be laminated on top. The nickel plating layer as the base plating layer has an effect of further preventing the diffusion of copper from the base material, and is effective when the thickness is 0.3 μm or more. On the other hand, since this nickel plating layer is poor in toughness, if the thickness exceeds 2 μm, it tends to break and the workability may be deteriorated.

  In the copper terminal material with silver plating of the present invention, it is preferable that a copper tin alloy layer and a tin layer are laminated in order from the base material between the base material and the silver plating layer. By applying the present invention to a reflow tin-plated terminal material generally used as a terminal material, a terminal having excellent solderability can be obtained.

The copper terminal with silver plating of the present invention is a terminal in which a silver plating layer is formed on a base material made of copper or a copper alloy, and the silver plating layer has a carbon content of 0.1% by mass to 0.6% by mass. In addition to eutectoid, the average grain size of the silver crystal structure is 2 μm or more and 25 μm or less, and the ratio of the length occupied by the special grain boundary to the length of the total grain boundary is 60% or more and 85% or less. It is.
In this case, the silver plating layer may be formed on the base material and then molded into the terminal, or the silver plating layer may be formed after the terminal is molded with the base material. Moreover, when it divides into the part connected with an electric wire as a terminal, and the part inserted / extracted by another terminal etc., you may form a silver plating layer only in the part inserted / extracted.

  According to the terminal material with silver plating of the present invention, the pinning effect by carbon eutectoid prevents recrystallization when a thermal load is applied, and the silver plating layer does not soften. Generation | occurrence | production is prevented, and the grain-boundary diffusion of copper from a base material can be prevented, and low contact resistance can be maintained.

The copper terminal material with silver plating of embodiment of this invention is demonstrated.
In the copper terminal material with silver plating of this embodiment, a silver plating layer is formed on a base material made of copper or a copper alloy via a nickel plating layer.

  If a base material consists of copper or a copper alloy, the composition in particular will not be limited.

  The nickel plating layer is formed by electroplating nickel or a nickel alloy on the base material as a base layer before forming the silver plating layer on the base material. This nickel plating layer has an effect of preventing diffusion of copper from the base material, and is effective when the thickness is 0.3 μm or more. On the other hand, since this nickel plating layer is poor in toughness, if the thickness exceeds 2 μm, it tends to break and the workability may be deteriorated.

  In the silver plating layer, carbon is eutectoid with a content of 0.1% by mass or more and 0.6% by mass or less, and the average crystal grain size of the silver crystal structure is 2 μm or more and 25 μm or less. The ratio of the length occupied by the special grain boundary to the length is 60% or more and 85% or less.

  When the carbon is co-deposited in the above-described mass ratio in the silver plating layer, recrystallization when a thermal load is applied due to the pinning effect of the carbon precipitates is prevented. Therefore, since fine crystal grains of the silver crystal structure are maintained, it is possible to prevent scraping during insertion and removal as a connector without softening. In this case, if the carbon content is less than 0.1% by mass, there is no effect of maintaining the hardness, and if it exceeds 0.6% by mass, the silver plating layer becomes brittle and the workability deteriorates.

  If the average crystal grain size of the silver crystal structure is less than 2 μm, the silver plating layer becomes brittle and the workability deteriorates. If it exceeds 25 μm, the hardness decreases and the wear resistance deteriorates. The average crystal grain size can be measured from the surface of the silver plating layer by a backscattered electron diffraction (Electron Backscatter Diffraction Pattern: EBSD or EBSP) method using a scanning electron microscope (SEM).

  Special grain boundaries have higher atomic consistency than general grain boundaries, and are therefore less likely to cause grain boundary diffusion. For this reason, from the viewpoint of grain boundary diffusion, the length ratio of the special grain boundary is preferably as high as possible, and at least 60% is required. On the other hand, if the length ratio of the special grain boundary exceeds 85%, the hardness cannot be maintained.

Here, the special grain boundary is a corresponding grain boundary belonging to 3 ≦ Σ ≦ 29 with a Σ value defined based on “Trans.Met.Soc.AIME, 185,501 (1949)”, and “ Acta.Metallurica.Vol.14, p.1479, (1966) ”, the corresponding corresponding portion lattice orientation defect Dq in the corresponding grain boundary is a grain boundary satisfying Dq ≦ 15 ° / Σ1 / ^2. Is defined as being.

The length ratio of the special grain boundary is the unit total grain boundary length obtained by converting the total grain boundary length L of all crystal grains among the grain boundaries of the surface crystal grains measured by the EBSD method per unit area 1 mm ^2. is for _{L N,} the special grain boundaries of all the special grain boundary length Erushiguma the unit area 1 mm ² per in-converted units all special grain boundary length Erushiguma _N ratio of (Lσ _N / _{L N).}

“Kikuchi” obtained from the sample surface using an EBSD measuring device (HITACHI S4300-SE, EDAX / TSL OIM Data Collection) and analysis software (EDAX / TSL OIM Data Analysis ver. 5.2) By analyzing information on the diffraction pattern of the electron beam called “line”, the crystal grain boundary and the special grain boundary are specified, and the unit total grain boundary length L _N and the unit total special grain boundary length Lσ _N can be obtained. it can.

The silver plating layer preferably contains 30% or more of crystal grains having a Schmitt factor value of less than 0.45 in terms of the surface area ratio. For this Schmitt factor, as the silver plating bath, a specific organic additive is added to potassium cyanide and a potassium bath containing silver cyanide or potassium cyanide as a main component, thereby controlling the crystal growth direction and a desired value. Can be obtained.
In metallography, plastic deformation is caused by the fact that the crystal has a fine atomic density, that is, a so-called slip surface, and the crystal is deformed. The index of the slipperiness of the slip surface is the Schmitt factor (maximum is 0.5). It is determined by the angle (θ) between the tensile direction of the material and the normal direction of the crystal slip surface (θ), and the angle (φ) between the tensile direction and the crystal slip direction (Schmitt factor = cos (θ) cos (φ)) When each angle is 45 °, the Schmitt factor becomes the maximum value (0.5).

  This Schmitt factor can also be calculated by analyzing the data obtained by the EBSD method using the above software, and a predetermined Schmitt factor value for each crystal grain or a predetermined Schmitt factor value for the applied stress. The ratio of the crystal grains in the range to the measurement region can be calculated by the area ratio.

  Since the terminal material of the present invention is a polycrystal, a plurality of crystal grains exist in the silver plating layer, and the plurality of crystal grains have respective crystal orientations. Here, if the orientation of each crystal grain is different, the orientation of the slip plane is different, that is, crystal grains having various Schmid factors exist. A crystal grain having a small Schmid factor is difficult to be deformed by a stress in a direction defined when the Schmit factor is analyzed. Therefore, such a metal structure having many crystal grains is difficult to be plastically deformed and has high strength. For this reason, when the crystal grains having a Schmitt factor value of less than 0.45 occupy 30% or more in terms of area ratio, the strength of the silver plating layer is increased and the wear resistance is improved. If it is less than 30%, the effect of improving the wear resistance is poor.

  Furthermore, the thickness of the silver plating layer is preferably 1 μm or more and 70 μm or less. When the thickness is less than 1 μm, it is difficult to prevent copper from diffusing from the base material, which is the base, and there is a risk of increasing contact resistance due to copper diffusion. On the other hand, when the thickness of the silver plating layer exceeds 70 μm, the workability may be deteriorated.

  The copper terminal material with silver plating constituted in this way is subjected to nickel plating and silver plating in order after cleaning the surface by subjecting the substrate made of copper or copper alloy to degreasing, pickling, etc. It is manufactured by.

For nickel plating, a general nickel plating bath may be used. A watt bath mainly composed of nickel sulfate (NiSO ₄ ), boric acid (H ₃ BO ₃ ), nickel sulfamate (Ni (NH ₂ SO ₃ ) ₂ ), A sulfamic acid bath containing boric acid (H ₃ BO ₃ ) as a main component, or the like is used. In some cases, nickel chloride (NiCl ₂ ) or the like is added as a salt that easily causes an oxidation reaction. The bath temperature is 40 ° C. or more and 55 ° C. or less, and the current density is 1 A / dm ² or more and 40 A / dm ² or less.

In silver plating, an organic additive that is easily incorporated into a plating film may be added to a silver cyanide plating bath, which is a general silver plating bath, in order to obtain a desired film structure. As the organic additive, for example, thioalcohols such as 2,2thioethanol, azoles such as benzothiazole and benzotriazole, and imidazoles such as imidazole can be used. The addition concentration of the organic additive is preferably 0.1 g / L or more and 10 g / L or less. Conventionally, potassium cyanide, silver cyanide and potassium cyanide potassium bath, and sodium cyanide, silver cyanide and sodium cyanide sodium bath as main components are used as silver cyanide plating baths. However, it is desirable to use a potassium bath in the present invention. The preferential growth orientation of crystals differs between the potassium bath and the sodium bath, and the proportion of crystal grains having a small Schmid factor tends to decrease and the strength tends to be poor in the sodium bath. Temperature of the silver plating bath is 15 ℃ or 35 ° C. or less, the current density is set to 0.1 A / dm ² or more 10A / dm ² or less. In addition, before this silver plating, what is called silver strike plating may be given and the adhesiveness of a plating layer can be improved.

  By performing nickel plating and silver plating on the substrate in order using the above plating bath, a copper terminal material with silver plating can be obtained, and this terminal material is formed into a terminal by pressing. Even when heat generation or the like due to energization with a large current occurs, recrystallization of the silver plating layer is suppressed, so that the silver plating layer can be prevented from being scraped during insertion and removal, and an increase in contact resistance can be suppressed.

  In the embodiment, the silver plating layer is formed after the nickel plating is formed as a base. However, the nickel plating layer can be omitted. However, the diffusion of copper from the base material can be more effectively prevented by forming the nickel plating layer as a base.

  Moreover, although what formed the silver plating layer as a terminal material was shape | molded in the terminal, you may form a silver plating layer, after shape | molding the base material which has not formed the silver plating layer in the terminal. In that case, it is also possible to form a silver plating layer only in a necessary portion (for example, a contact portion) of the terminal.

  The present invention can also apply a reflow tin-plated terminal material that is generally used as a terminal material. For example, a terminal that can be manufactured by subjecting a base material to copper plating and tin plating in order, followed by reflow heat treatment, and then nickel plating to form a silver plating layer. Can be obtained. Also in this case, it is possible to partially form the silver plating layer of the present invention after forming the terminal against the reflow tin-plated terminal material. The reflow tin plating layer can be used, and the other portions can be silver plating layers.

  In addition, it is possible to apply tin plating and silver plating only to necessary portions after the base material is formed into terminals. However, if the silver plating layer is partially formed after the reflow tin plating terminal material is manufactured, The productivity is better than when partial tin plating and silver plating are performed twice.

The copper plate of the base material was degreased and pickled, and then subjected to nickel plating and silver plating.
The composition of the nickel plating bath was 400 g / L nickel sulfamate, 5 g / L nickel bromide, 35 g / L boric acid, a bath temperature of 45 ° C., and a current density of 5 A / dm ² .

The composition of the silver plating bath includes potassium cyanide 130 g / L, silver cyanide 50 g / L, potassium carbonate 15 g / L, nonionic surfactant 1 g / L, and the additives shown in Table 1 at the concentrations shown in Table 1. What was added was used. The bath temperature was 25 ° C. and the current density was as shown in Table 1. Prior to this silver plating, a silver strike plating treatment was carried out for 10 seconds at a current density of 2.5 A / dm ^{2 in a} silver strike plating bath composed of 3 g / L silver cyanide and 90 g / L potassium cyanide. .

In Table 1, samples 1 to 7 used oxygen-free copper as a base material, and sample 8 used a commercially available reflow tin plating terminal material.
Sample 9 used oxygen-free copper as a base material, and the composition of the silver plating bath was a sodium bath. As the bath composition, sodium cyanide 120 g / L, silver cyanide 40 g / L, potassium carbonate 15 g / L, nonionic surfactant 1 g / L, and the additives shown in Table 1 were added at the concentrations shown in Table 1. What was done was used. The bath temperature was 25 ° C. and the current density was as shown in Table 1. Prior to this silver plating, a silver strike plating treatment was carried out for 10 seconds at a current density of 2.5 A / dm ^{2 in a} silver strike plating bath composed of 3 g / L silver cyanide and 90 g / L potassium cyanide. .
Sample 10 was subjected to antimony-added silver plating, which is a known hard silver plating, instead of the above silver plating as a comparative example. In Sample 10, oxygen-free copper was used as the base material, and the silver plating bath was a sodium bath. As the bath composition, sodium cyanide 120 g / L, silver cyanide 40 g / L, potassium carbonate 15 g / L, nonionic surfactant 1 g / L, and antimony potassium tartrate shown in Table 1 as an antimony source are shown in Table 1. The one added at the concentration shown in FIG. The bath temperature was 25 ° C. and the current density was as shown in Table 1. Prior to this silver plating, a silver strike plating treatment was carried out for 10 seconds at a current density of 2.5 A / dm ^{2 in a} silver strike plating bath composed of 3 g / L silver cyanide and 90 g / L potassium cyanide. .

The carbon content in the silver plating layer of each sample produced as shown in Table 1, the average crystal grain size of the silver crystal structure, the special grain boundary length ratio, the area ratio occupied by crystal grains having a Schmid factor of less than 0.45, silver plating The thickness of each layer and the nickel plating layer was measured.
The carbon content was measured by quantitative analysis of the surface of the silver plating layer using EPMA ((Electron Probe Micro Analyzer).

The average crystal grain size was measured by area ratio (Area Fraction) by scanning the surface of the silver plating layer with an electron beam, specifying all crystal grain boundaries including special grain boundaries by orientation analysis of the EBSD method.
The special grain boundary length ratio is a crystal in which the cross section of the silver plating layer is analyzed by the EBSD method, the total grain boundary length of the crystal grain boundary in the measurement range is measured, and the interface between adjacent crystal grains constitutes the special grain boundary. The position of the grain boundary was specified, and the total grain boundary length L _N and the special grain boundary length Lσ _N per unit area 1 mm ² were calculated and obtained.
The area ratio occupied by crystal grains having a Schmid factor of less than 0.45 was determined by measuring the surface of the silver plating layer by the EBSD method.

  The thickness of the silver plating layer and the nickel plating layer was measured with a fluorescent X-ray film thickness meter. The nickel plating layer was measured before forming the silver plating layer.

The measurement conditions of the EBSD method and the observation conditions with the scanning electron microscope SEM were as follows. The sample surface was measured after adjusting the surface with an ion milling device at an acceleration voltage of 6 kV and an irradiation time of 2 hours.
<EBSD conditions>
Analysis range: 10.0 μm × 50.0 μm (Measurement range: 10.0 μm × 50.0 μm)
Measurement step: 0.1 μm
Acquisition time: 11msec / point
<SEM conditions>
Acceleration voltage: 15 kV
Beam current: about 3.5nA
WD: 15mm
These analysis results and measurement results are shown in Table 2.

  According to Table 2, since Samples 1 to 3 employ thioethanol as an additive, the carbon content, average particle size, special grain boundary ratio, and Schmitt factor are within the optimum value range. In Sample 9, since the silver plating bath is a sodium bath unlike Samples 1 to 8, the crystal orientation is changed and the Schmit factor is smaller than those of other samples. In sample 5, the thickness of the nickel plating layer is smaller than that of the other samples, and in contrast, sample 6 is larger. In Sample 7, the thickness of the silver plating layer is smaller than the others.

Subsequently, Vickers strength and contact resistance were measured for these samples, and bending workability was evaluated.
The Vickers hardness was measured from the surface of the silver plating layer with a load of 30 gf using a Mitutoyo micro Vickers hardness tester. Measurements were made immediately after sample preparation (initial Vickers hardness) and after the sample was left at 150 ° C. for 1000 hours.
The contact resistance was measured by a 4-terminal method using a contact simulator CRS-1 manufactured by Yamazaki Seiki for a sample left at 150 ° C. for 1000 hours under the conditions of a contact load of 50 g and a current of 200 mA.

Regarding the bending workability, the test piece was cut out so that the rolling direction was long, and using a W bending test jig defined in JISH3110, 9.8 × 10 ³ N so as to be perpendicular to the rolling direction. Bending was performed with a load of. Then, it observed with the stereomicroscope. Bending workability is evaluated as “good” when the copper alloy base material is not exposed due to cracks occurring in the bent part after the test, and the level where the copper alloy base material is exposed due to the generated cracks. Was evaluated as “bad”.
These measurement results and evaluation results are shown in Table 3.

As can be seen from Table 3, samples 1 to 3 have an initial Vickers hardness of 120 or more, hardly change after heating, and have a very good value of 1 mΩ or less in contact resistance. Although the contact resistance of Sample 4 is excellent, the Vickers hardness is slightly low because the Schmitt factor evaluation deviates from the optimum value. Since the sample 5 has a thin nickel plating layer, the contact resistance is high, but it is considered that there is no practical problem. In Sample 6, since the nickel plating layer was too thick, the base material was partially exposed, and the bending workability was slightly inferior to Sample 10. Sample 7 has a slightly high contact resistance due to the insufficient thickness of the silver plating layer, but it is considered that there is no practical problem. In Sample 8, a silver plating layer under optimum conditions was applied on the reflow tin plating terminal material, and it showed excellent characteristics. Sample 9 was inferior in hardness because a sodium bath was used as the silver plating bath. Regarding sample 10, the initial Vickers hardness was excellent because antimony was co-deposited, but the hardness decreased significantly after heating, and the contact resistance deteriorated because an antimony oxide film was formed on the surface. Moreover, since the silver plating layer was hard, bending workability was inferior.

Claims (6)

  A terminal material in which a silver plating layer is formed on a substrate made of copper or a copper alloy, and the silver plating layer is eutectoid with a content of carbon of 0.1% by mass or more and 0.6% by mass or less. In addition, the average crystal grain size of the silver crystal structure is 2 μm or more and 25 μm or less, and the ratio of the length occupied by the special grain boundary to the total grain boundary length is 60% or more and 85% or less. A copper terminal material with silver plating.   2. The copper terminal material with silver plating according to claim 1, wherein the silver plating layer contains 30% or more of crystal grains having a Schmitt factor value of less than 0.45 in terms of a surface area ratio.   The thickness of the said silver plating layer is 1 micrometer or more and 70 micrometers or less, The copper terminal material with silver plating of Claim 1 or 2 characterized by the above-mentioned.   A nickel plating layer having a thickness of 0.3 μm or more and 2 μm or less is formed between the base material and the silver plating layer, and the silver plating layer is laminated on the nickel plating layer. The copper terminal material with silver plating as described in any one of Claim 1 to 3.   The copper-tin alloy layer and the tin layer are laminated | stacked in an order from the said base material between the said base material and the said silver plating layer, The silver plating as described in any one of Claim 1 to 4 characterized by the above-mentioned. Copper terminal material.   A terminal in which a silver plating layer is formed on a base material made of copper or a copper alloy, and the silver plating layer has eutectoid of carbon in an amount of 0.1% by mass or more and 0.6% by mass or less, and a silver crystal A terminal characterized in that the average crystal grain size of the structure is 2 μm or more and 25 μm or less, and the ratio of the length occupied by the special grain boundary to the length of all crystal grain boundaries is 60% or more and 85% or less.