JP2012049041A - Silver coating material for movable contact component and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silver coating material for a movable contact component and a manufacturing method therefor, in which a silver layer on a surface is not peeled and the contact resistance is not increased even after long-term use under an environment where switching is repeated.SOLUTION: The silver coating material for a movable contact component is constituted by sequentially laminating an underlayer 2 made of any one of nickel, a nickel alloy, cobalt, and a cobalt alloy, an intermediate layer 3 made of any one of copper, a copper alloy, tin, and a tin alloy, and an outermost layer 5 made of silver or a silver alloy, on a conductive base 1 made of copper, a copper alloy, iron, or an iron alloy. An intermediate oxide layer 4 as a second intermediate layer exists between the intermediate layer and the outermost layer.

Description

  TECHNICAL FIELD The present invention relates to a silver coating material for movable contact parts and a method for producing the same, and more particularly to a silver coating material for movable contact parts suitable as a disc spring material for connectors, switches, terminals and electronic contact parts, and a method for producing the same.

  Conventional push switches used in mobile phones, portable terminal devices, remote control switches, composite printers, etc. include phosphor bronze, beryllium copper, copper alloys such as Corson copper alloys, and iron-based materials such as stainless steel. A material obtained by applying silver plating to a conductive substrate excellent in springiness, such as an alloy, has been used. In this method, after a nickel underlayer is formed on a conductive substrate, a material in which a silver surface layer plating is directly formed on the surface of the nickel underlayer is used.

  On the other hand, in recent years, with the spread of functions such as e-mail and browsing on the mobile phone, the number of repeated switching operations has increased remarkably. It has been known that oxygen in the air permeates and oxidizes the underlying nickel, making it easier for the silver to peel off.

  In order to prevent such a phenomenon, it has been proposed to use a material in which a copper intermediate layer is provided between the silver layer and the nickel layer, for example, a material formed of silver / copper / nickel / stainless steel in order from the surface layer. (See Patent Documents 1 to 3). The copper intermediate layer is said to have an effect of capturing oxygen that has passed through the silver plating and preventing the oxidation of nickel in the underlayer.

For example, Patent Document 1 describes an invention of a metal plate having a copper plating layer of 0.1 to 0.5 μm on a Ni plating and a silver plating layer on the upper layer.
In Patent Document 2, a 0.2 to 0.4 μm Ni underlayer is provided on a stainless steel substrate, a 0.2 to 0.6 μm copper plating intermediate layer is provided on the upper layer, and a layer made of silver is provided on the outermost layer. Is done. The silver plating thickness is said to be 0.5 to 1.0 μm.
In Patent Document 3, it is recommended that the copper plating thickness of the intermediate layer be 0.05 to 2.0 μm, and that each layer be coated and then heat-treated in a non-oxidizing atmosphere.

Japanese Patent No. 3889718 Japanese Patent No. 3772240 JP 2005-133169 A

However, in the electrical contact materials described in the above patent documents, the copper forming the intermediate layer diffuses in the silver or silver alloy and appears on the outermost layer, which may oxidize and increase the contact resistance. . Even if the coating thickness described in Patent Documents 1 to 3 is controlled, the oxygen that the intermediate layer permeates cannot be sufficiently captured, and an oxide film is formed on the outermost layer, thereby increasing the contact resistance. I found out that Also, as shown in Patent Document 3, when heat treatment is performed in a non-oxidizing atmosphere, copper diffuses on the silver surface, which may oxidize and increase contact resistance. I understood.
Therefore, the present inventors have provided a silver coating for a movable contact component, in which even if it is used for a long time in an environment where switching is repeated, the surface silver layer does not peel off and no increase in contact resistance is observed. In order to provide a material and a manufacturing method thereof, intensive studies were conducted.

The present invention
(1) On a conductive substrate made of copper or copper alloy, or iron or iron alloy, any of an underlayer made of nickel, nickel alloy, cobalt, or cobalt alloy, copper or copper alloy, tin or tin alloy An intermediate layer composed of the above and an outermost layer composed of silver or a silver alloy in order, the intermediate oxide layer being present as a second intermediate layer between the intermediate layer and the outermost layer A silver coating material for movable contact parts, characterized in that:
(2) The silver coating material for movable contact parts according to claim 1, wherein the thickness of the copper or copper alloy intermediate layer or tin or tin alloy intermediate layer is 0.01 μm to 1.0 μm.
(3) The silver coating for movable contact parts according to (1) or (2), wherein the thickness of the intermediate oxide layer as the second intermediate layer is 0.001 μm to 0.01 μm Wood.
(4) The silver coating material for movable contact parts according to (1) to (3), wherein the outermost layer made of silver or a silver alloy has a thickness of 0.1 μm to 5.0 μm.
(5) The silver coating material for a movable contact part according to any one of (1) to (4), wherein the thickness of the base layer is 0.005 μm to 0.5 μm.
(6) A method for producing a silver coating material for movable contact parts, wherein at least one of the underlayer, the intermediate layer, and the outermost layer is formed by a plating method (1) to (5) The manufacturing method of the silver coating material for movable contact components of any one of (1).
(7) A method for producing a silver coating material for movable contact parts, wherein after forming the outermost layer, an intermediate oxide layer is formed by heating in an oxidizing atmosphere at a temperature of 200 ° C. or higher. The manufacturing method of the silver coating | covering material for movable contact parts of any one of (1)-(5).
In the present invention, the intermediate oxide layer is an intermediate layer made of an oxide formed on the second intermediate layer.

The silver coating material for a movable contact part of the present invention comprises an oxide layer as an upper layer of an intermediate layer between a copper or copper alloy or tin or tin alloy layer as an intermediate layer and a silver or silver alloy layer as an outermost layer. In the presence of the intermediate layer component, the intermediate layer component is prevented from diffusing to the surface and becoming an oxide in the surface layer, thereby preventing an increase in contact resistance. In addition, there is an effect of suppressing the peeling of the plating caused by the oxygen that has passed through the outermost silver from the surface being oxidized in the underlayer.
Moreover, according to the manufacturing method of the present invention, a high-quality silver coating material for a movable contact part having low contact resistance and excellent durability can be efficiently produced as described above.

It is a longitudinal cross-sectional view which shows one embodiment of this invention. It is a top view of the switch used for the keystroke test. FIG. 3 is a cross-sectional view taken along line AA in FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing one embodiment of the silver coating material for movable contact parts of the present invention. In FIG. 1, 1 is a conductive substrate made of copper or copper alloy, or iron or iron alloy, 2 is an underlayer made of nickel, nickel alloy, cobalt, or cobalt alloy, 3 is copper or copper alloy, tin or An intermediate layer made of any of tin alloys, 4 is a corresponding intermediate oxide layer containing a material corresponding to an oxide of the intermediate layer material, and 5 is an outermost layer made of silver or a silver alloy. The intermediate oxide layer 4 can be formed by heating the intermediate layer 2 in an oxidizing atmosphere as described later.

The conductive substrate 1 is a material having conductivity, spring characteristics, durability, etc. sufficient for use as a movable contact part. In the present invention, the conductive substrate 1 is made of copper or copper alloy, iron or iron alloy.
Examples of the copper alloy preferably used as the substrate 1 include bronze, phosphor bronze, brass, titanium copper, copper nickel silicon (Corson type) alloy, and beryllium copper. Examples of iron alloys that are preferably used include stainless steel (SUS) and 42 alloy. The thickness of the substrate 1 is preferably 0.03 to 0.5 mm, and more preferably 0.04 to 0.2 mm.

An underlayer made of nickel (Ni) or Ni alloy, cobalt (Co) or Co alloy having a thickness of preferably 0.005 to 0.5 μm, more preferably 0.01 to 0.1 μm on the surface of the substrate 1. 2 is coated. The lower limit of the thickness of the underlayer 2 is determined from the viewpoint of the adhesion between the substrate 1 and the intermediate layer 3, and the upper limit of the thickness of the underlayer 2 is determined when the electrical contact material is formed from the coating material by pressing or the like. However, it is determined from the viewpoint of preventing the workability from being deteriorated and the occurrence of cracks in the underlayer 2 or the like.
Ni alloy and Co alloy used for the underlayer 2 include Ni—P (phosphorus), Ni—Sn (tin), Ni—Co, Ni—Co—P, Ni—Cu, and Ni—Cr. (Chromium), Ni—Zn (Zinc), Ni—Fe (Iron), Co—P, Co—Sn, Co—Cu, Co—Cr, Co—Zn, Co—Fe An alloy such as is preferably used. Ni and Ni alloys, Co and Co alloys have good plating processability, are relatively inexpensive in price, and have a high melting point, and therefore have a barrier function (preventing diffusion of substrate components) in a high temperature environment. However, it is preferably used because it has little decay.

  On the underlayer 2, the thickness of copper (Cu) or Cu alloy, or tin (Sn) or Sn alloy is preferably 0.01 to 1.0 [mu] m, more preferably 0.05 to 0.2 [mu] m in the middle. Layer 3 is coated. The lower limit of the thickness of the intermediate layer 3 is determined from the viewpoint of maintaining the adhesion with the base layer 2, and the effect is insufficient when the thickness is less than 0.01 μm. Moreover, the upper limit of the thickness of the intermediate layer 3 is because when the electric contact material is formed from the covering material by press working or the like, the workability is lowered and the intermediate layer 3 and the underlayer 2 are not cracked. To decide.

Examples of the copper (Cu) or Cu alloy used for the intermediate layer 3 include Cu, Cu—Au (gold), Cu—Ag (silver), Cu—Sn, Cu—Ni, or Cu—In (indium). ) System. Similarly, tin (Sn) or Sn alloy is preferably an alloy of Sn, Sn—Au (gold), Sn—Ag (silver), Sn—Ni, or Sn—In (indium). .
On the intermediate layer 3, there is an intermediate oxide layer 4, which is a second intermediate layer made of an oxide layer that can be formed by the method described later. Here, when the oxide layer is too thick, an increase in contact resistance, cracking during bending, poor adhesion near the oxide layer interface, and the like occur. Therefore, the thickness of the intermediate oxide layer is 0.001 μm to 0.01 μm is preferable, and 0.001 μm to 0.005 μm is more preferable. The thickness of the layer can be measured by analyzing in the depth direction by Auger electron spectroscopy. In the present invention, Auger electron spectroscopy uses, for example, a MODEL-680 manufactured by ULVAC-PHI as a measuring instrument, and measures a sputtering rate of 5 nm / min and a surface area of a non-measurement of 25 μm square. The upper limit of the thickness of the intermediate oxide layer is determined in order to prevent peeling of the outermost layer, and the lower limit of the thickness is a necessary minimum thickness to prevent diffusion of the intermediate layer toward the outermost layer. To decide on the reason.

  The intermediate oxide layer can be formed by heating the intermediate layer 3 in an oxidizing atmosphere. For example, the formation of the oxide layer as the intermediate layer can be performed by heating at 200 ° C. or higher, preferably 200 to 350 ° C. in an oxygen atmosphere in a state after forming the outermost layer. Here, the oxygen atmosphere is preferably an oxygen concentration of 5 to 50%, more preferably 15 to 50%. For example, when heating in air having an oxygen concentration of about 20%, it is possible to easily form a desired intermediate oxide layer by appropriately adjusting the heating time and heating temperature as an alternative to heating in an oxygen atmosphere. It is possible. In the case of the air, the heating temperature is preferably 200 to 350 ° C., more preferably 250 to 300 ° C., and the heating time is preferably 1 to 60 minutes, more preferably 5 to 15 minutes. An intermediate oxide layer can be formed.

Oxide formation gradually proceeds even when a silver coating material is used as a product, but at that time, diffusion of the intermediate layer material to the surface also proceeds at the same time, which causes an increase in contact resistance due to oxidation of the diffusing element. I will. Therefore, an intermediate oxide layer is formed during manufacture. Since the oxide layer is formed in advance in this way, when the oxide layer is used as a product, the intermediate layer components do not diffuse toward the outermost surface, resulting in an increase in the contact resistance of the product. High stability because it does not.
The oxide of the oxide layer as the intermediate layer is mainly CuO, Cu ₂ O or a mixture thereof in the case of copper or copper alloy, or SnO, SnO ₂ , SnO ₃ or these in the case of tin or tin alloy It is mainly a mixture of

An outermost layer 5 made of silver (Ag) or a silver alloy is formed on the intermediate layer 4. The outermost layer 5 made of silver (Ag) or a silver alloy is a layer provided to improve conductivity as a contact member. Regarding the thickness, in the case of the present invention, the Ag thickness can be made thinner than the conventional product. Conventionally, unless the outermost layer silver coating thickness is increased, Cu and Sn, which are components of the intermediate layer, may propagate through the outermost silver layer and diffuse to the surface in long-term use. In the present invention, it is possible to prevent diffusion of the intermediate layer component to the surface. Thus, it is not essential to increase the outermost silver coating thickness. The thickness of the outermost layer is preferably 0.1 to 5.0 [mu] m, more preferably 0.5 to 1.0 [mu] m.
Examples of Ag or Ag alloy that can be preferably used as the outermost layer 5 include Ag, Ag—Sn alloy, Ag—Cu alloy, Ag—Sb alloy, Ag—Se alloy, Ag—Pd alloy, and Ag—In alloy. It has good contact characteristics and is preferably used.
When forming the outermost layer 5, a method of forming a thickening layer after providing a strike layer on the upper layer of the intermediate layer 4 for improving adhesion is also possible. At this time, the thickness of the outermost layer is such that the total thickness of the strike layer and the thickening layer is within the above range.

  The layer structure of the silver coating material for the movable contact part of the embodiment of FIG. 1 is as described above, and its production may be performed by sequentially laminating each layer by plating or the like, but after forming the outermost layer 5 Alternatively, the intermediate oxide layer 4 may be formed by heating in an oxidizing atmosphere.

  The method for producing the silver coating material for the movable contact part of the embodiment shown in FIG. 1 will be described. For example, the conductive substrate 1 is subjected to pretreatment such as electrolytic degreasing and pickling, and nickel or nickel alloy, or cobalt or cobalt alloy. Is coated with an intermediate layer 3 made of copper or a copper alloy, tin or a tin alloy, and an outermost layer 5 made of silver or a silver alloy, and then in an oxidizing atmosphere. It can form suitably by heating and forming 4.

  The underlayer 2, the intermediate layer 3, and the outermost layer 5 of the silver coating material for movable contact parts can be coated and formed by a plating method, a PVD method, or the like, but any one or more layers are formed by a wet plating method. It is desirable to be simple and low cost.

  The silver coating material for movable contact parts of the present invention can be suitably used as a disc spring material for connectors, switches, terminals and electronic contact materials, for example. In particular, the present invention is suitable for a tact switch used in a mobile phone, and can provide a contact material that can sufficiently satisfy the characteristics for hundreds of thousands of keystroke tests.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

  After pretreatment of SUS301 described in JIS G-4305 having a thickness of 0.05 mm and a width of 180 mm in order by degreasing and pickling treatment in the usual manner, in the plating bath having the following composition, an underlayer, an intermediate layer, A surface layer was formed, and an oxide layer was formed as a second intermediate layer on the upper surface of the intermediate layer by the following heat treatment. Thus, the silver coating materials shown in the invention examples and comparative examples having the layer constitution shown in Table 1 were obtained.

(Pretreatment conditions)
[Electrolytic degreasing]
Degreasing solution: NaOH 60 g / liter (water)
Degreasing conditions: 2.5 A / dm ² , temperature 60 ° C., degreasing time 60 seconds [pickling]
Pickling solution: H ₂ SO ₄ 10 wt. % Solution pickling conditions: room temperature immersion, immersion time 30 seconds

(Underlayer plating conditions)
[Ni plating]
Plating solution: HCl 120 g / liter (water), NiCl ₂ 30 g / liter (water)
Plating conditions: current density 1.5 A / dm ² , temperature 30 ° C.
[Co plating]
Plating solution: HCl 120 g / liter (water), CoCl ₂ 30 g / liter (water)
Plating conditions: current density 1.5 A / dm ² , temperature 30 ° C.

(Interlayer plating conditions)
[Cu plating]
Plating solution: CuSO ₄ · 5H ₂ O 250 g / liter (water), H ₂ SO ₄ 50 g / liter (water), NaCl 0.1 g / liter (water)
Plating conditions: current density 1-10 A / dm ² , temperature 40 ° C.
[Cu-Sn plating]
Plating _{solution: Na 2 SnO 3 · 3H 2} O 100 grams / liter, CuCN ₂ 12 grams / liter, NaCN 30 g / liter, NaOH 10 g / liter Plating conditions: current density 3A / dm ^2, temperature 65 ° C.
[Cu-Ag plating]
Plating solution: AgCN 2 g / liter (aqueous solution), Cu metal salt 90 g / liter (aqueous solution), KCN 2 g / liter (aqueous solution), KCO ₃ 18 g / liter (aqueous solution)
Plating conditions: current density 0.5 A / dm ² , temperature 50 ° C.
[Sn plating]
Plating solution: SnSO ₄ 40 g / liter (aqueous solution), H ₂ SO ₄ 100 g / liter (aqueous solution)
Plating conditions: current density 5 A / dm ² , temperature 13 ° C.

(Outermost layer plating conditions)
[Ag strike plating]
Plating solution: AgCN 5 g / liter (aqueous solution), KCN 60 g / liter (aqueous solution), K ₂ CO ₃ 30 g / liter (aqueous solution)
Plating conditions: current density 2 A / dm ² , temperature 30 ° C.
[Ag plating]
Plating solution: AgCN 50 g / liter (aqueous solution), KCN 100 g / liter (aqueous solution), K ₂ CO ₃ 30 g / liter (aqueous solution)
Plating conditions: current density 3 A / dm ² , temperature 30 ° C.
[Ag-Sn plating]
Plating solution: AgCN 5 g / liter (aqueous solution), NaCN 50 g / liter (aqueous solution), NaOH 50 g / liter (aqueous solution), K ₂ SnO ₃ .3H ₂ O 80 g / liter (aqueous solution)
Plating conditions: current density 1 A / dm ² , temperature 30 ° C.
[Ag-Se plating]
Plating solution: AgCN 50 g / liter (aqueous solution), KCN 100 g / liter (aqueous solution), K ₂ CO ₃ 30 g / liter (aqueous solution), K ₂ SeO ₃ 30 g / liter (aqueous solution)

(Heat treatment conditions)
Heat at 250 ° C. and O ₂ concentration of 21% (in air) for 5 minutes to 1 hour. However, in Comparative Example 1, no heat treatment was performed.

  Each of the silver coating materials of Examples and Comparative Examples obtained in Table 1 was cut to 50 mm × 100 mm, and then subjected to a peel test after heating at 400 ° C. for 5 to 15 minutes, and contact resistance measurement and plating adhesion were investigated. It was. The peel test was performed based on a tape test method defined in JIS H8504. A keystroke test was also conducted.

(Contact resistance measurement)
Using the four-terminal method, the contact resistance was measured initially and after heating in the atmosphere.
Measurement conditions: Ag probe R = 2 mm, load 0.1 N, resistance value at 10 mA energization was measured 10 times, and the average value was calculated.
(Adhesion evaluation)
After cutting the test piece after heating for 15 minutes in an air atmosphere at a temperature of 400 ° C. to 10 mm × 30 mm, a 2 mm square cross-cut is performed with a cutter, and then peeled off using # 631S tape manufactured by Teraoka Seisakusho. An adhesion test was performed.

(Pressability evaluation)
Furthermore, for pressability alternative evaluation, the top after the W-bending test was observed, and the presence or absence of a microscope (Keyence) crack was confirmed. After the test piece was cut into 10 mm × 30 mm, evaluation was performed by pressing with a load of 500 kg and a bending radius R = 0.2 mm.

(Keystroke test)
The obtained silver coating material of each of these Examples and Comparative Examples was processed into a dome-shaped movable contact part having a diameter of 4 mmφ, and a brass strip plated with silver in a thickness of 1 μm was used as the fixed contact. A keystroke test was performed with the switch having the structure shown in FIG. FIG. 2 is a plan view of the switch used for the key-stroke test. FIG. 3 shows a cross-sectional view of the switch used in the keystroke test and FIG. 2A-A cross section, and FIG. 3A, (a) before the switch operation, and (b) during the switch operation. In the figure, 6 is a silver-plated stainless steel dome-shaped movable contact, 7 is a silver-plated brass fixed contact, and these are incorporated in a resin case 9 with a resin filler 8.

In the keying test, contact resistance: 9.8 N / mm ² , keying speed: 5 Hz, a maximum of 1,000,000 times of keying was performed, and the change in contact resistance with time was measured. The results are shown in Table 2. The contact resistance was measured with a current of 10 mA, and the contact resistance value including variations was evaluated in four stages. Specifically, a contact resistance value of less than 15 mΩ is evaluated as “excellent” and the table is marked with “◎”, 15 mΩ or more and less than 30 mΩ is evaluated as “good”, and the table is marked with “O”. A value of 30 mΩ or more and less than 50 mΩ was evaluated as “possible”, and a “Δ” mark was attached to the table, and a value of 50 mΩ or more was evaluated as “impossible”, and an “x” mark was attached to the table. In addition, it was judged that the contact resistance value of less than 50 mΩ as a movable contact was ◎ to Δ having practicality as a contact.

  These evaluation results are summarized in Table 2.

From Table 1 and Table 2, when the oxide film layer was too thin (Comparative Example 2), a significant increase in contact resistance was observed. When there was no oxide film layer (Comparative Example 1), a marked increase in contact resistance and peeling of the plating were observed. On the contrary, when the oxide film layer was thick, peeling from the oxide film was observed in the peeling test, and cracking was observed in the press test (Comparative Examples 3 and 4).
On the other hand, it can be seen that the products of the present invention shown in Examples 1 to 11 have excellent contact resistance characteristics even after one million keystroke tests and can be used as excellent movable contacts. In addition, it can be seen that the contact resistance is very low even after heating in the atmosphere, and that the heat resistance, adhesion, and pressability are all very good.

DESCRIPTION OF SYMBOLS 1 Conductive substrate 2 Underlayer 3 Intermediate layer 4 Intermediate oxide layer 5 Outermost layer 6 Movable contact 7 Fixed contact 8 Filler 9 Resin case

Claims (7)

On a conductive base material made of copper or copper alloy, or iron or iron alloy, it is made of an underlayer made of nickel, nickel alloy, cobalt or cobalt alloy, or made of copper or copper alloy, tin or tin alloy. An intermediate layer and a material constituted by sequentially laminating an outermost layer made of silver or a silver alloy, wherein an intermediate oxide layer exists as a second intermediate layer between the intermediate layer and the outermost layer A silver coating for moving contact parts.   The silver coating material for a movable contact part according to claim 1, wherein the intermediate layer has a thickness of 0.01 µm to 1.0 µm.   The silver coating material for a movable contact part according to claim 1 or 2, wherein the intermediate oxide layer has a thickness of 0.001 to 0.01 µm.   The silver covering material for movable contact parts according to any one of claims 1 to 3, wherein the silver or silver alloy layer has a thickness of 0.1 µm to 5.0 µm.   The silver coating material for a movable contact part according to any one of claims 1 to 4, wherein a thickness of the underlayer is 0.005 µm to 0.5 µm.   6. A method for producing a silver coating material for a movable contact component, wherein one or more of the underlayer, the intermediate layer, and the outermost layer are formed by a plating method. The manufacturing method of the silver coating material for movable contact components of 1 item | term.   2. A method for producing a silver coating material for a movable contact part, wherein after forming the outermost layer, the intermediate oxide layer is formed by heating in an oxidizing atmosphere at a temperature of 200 ° C. or higher. The manufacturing method of the silver coating material for movable contact components in any one of -5.

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