JP6162817B2 - Silver coating material and method for producing the same - Google Patents

Description

  The present invention relates to a silver coating material and a method for producing the same, and more particularly to a silver coating material suitable as a connector, a switch, a terminal, and an electronic component contact part.

  For connectors and switches that are connection parts for electronic devices, a material is often used in which a base plate of copper or nickel is applied to the surface of brass or phosphor bronze, and further, silver is applied thereon. Since silver is a good conductor of electricity and heat, silver is used as a plating for connectors, switches or lead frames as described above.

In recent years, switches used in mobile phones and remote controls have a large number of repeated switching operations, and it is known that silver plating is scraped and contact resistance increases by repeating many switching operations in a short time. .
In order to prevent such a phenomenon, the conventional method has been to increase the film thickness of silver plating, but the demand for cost reduction of electronic parts has become stricter year by year. Product specifications are increasing. Thus, there is an urgent need to examine the improvement in wear resistance of silver plating.
In general, increasing the hardness of the coating is effective for improving the wear resistance, and attempts have been made to increase the coating hardness by adding a curing agent such as Sb to silver. However, the coating is brittle. As a result, the wear resistance deteriorates.

  Patent Document 1 discloses that a conductive base material made of copper or copper alloy, or iron or iron alloy, an underlayer made of nickel, nickel alloy, cobalt, or cobalt alloy, copper or copper alloy, tin Alternatively, a movable contact in which an intermediate layer made of either tin alloy and an outermost layer made of silver or a silver alloy are sequentially laminated, and an intermediate oxide layer exists as a second intermediate layer between the intermediate layer and the outermost layer. A silver coating for parts is disclosed. The intermediate oxide layer is a metal oxide layer of the intermediate layer. By the presence of the intermediate oxide layer between the intermediate layer and the outermost layer, the intermediate layer component diffuses to the surface and becomes an oxide in the surface layer. It is said that it has the effect of preventing the increase in contact resistance and the increase in contact resistance, and further has the effect of suppressing the peeling of the silver layer on the surface. The intermediate oxide layer is formed by heating in the atmosphere at a temperature of 250 ° C. for 5 to 60 minutes after forming the outermost layer.

JP 2012-49041 A

  Even if the present invention is used, for example, as a movable contact and / or a fixed contact of a switch that is used for a long time under a condition where switching is repeatedly performed, the surface silver or silver alloy layer is not scraped and the contact resistance is further reduced It aims at providing the silver coating material excellent in abrasion resistance which does not rise.

  As a result of intensive studies, the present inventors have solved the above problem by forming a layer made of at least silver or a silver alloy on the conductive substrate by plating as the outermost layer and performing heat treatment under specific heating conditions. As a result, the present invention has been achieved.

That is, the present invention is as follows.
(1) On a conductive substrate, a silver coating layer is provided with or without an underlying layer, and the silver coating layer is a silver coating material that is the outermost layer made of silver or a silver alloy, The layer made of a silver alloy contains columnar structure crystals having an average crystal grain size of 0.2 μm or more and 0.5 μm or less made of silver or a silver alloy, and the amount of film scraping in the wear resistance test is less than 40 mg, and the initial A silver coating material characterized by having a contact resistance and a contact resistance of less than 10 mΩ after a sliding wear test under the following conditions.
Sliding wear test conditions:
[Load] 1.6N
[Sliding range] 0.2mm
[Sliding speed] 1mm / s
[Number of times] 50,000 times (2) The silver coating material as described in (1) above, wherein the amount of film abrasion in the abrasion resistance test is less than 30 mg.
(3) The wear resistance test was performed in accordance with JIS H 8682, under the conditions of a load of 500 gf (scraped area 12 mm × 31 mm), # 1500 emery abrasive paper, and 200 reciprocating conditions. Silver covering material as described in 2).
( 4 ) A switch using the silver coating material according to any one of (1) to ( 3 ) as a movable contact and / or a fixed contact of the switch.
( 5 ) The conductive coating according to any one of (1) to ( 3 ) above has a silver coating layer on or without a base layer, and the silver coating layer is silver or silver. A method for producing a silver coating material which is an outermost layer made of an alloy, the method comprising the step of forming the layer made of silver or a silver alloy by plating and heat-treating at 200 to 500 ° C. for 1 to 299 seconds A method for producing a silver coating material.
( 6 ) The method for producing a silver coating material according to ( 5 ), wherein the heat treatment is performed at 250 to 450 ° C. for 1 to 59 seconds.
( 7 ) The method for producing a silver coating material according to ( 5 ), wherein the heat treatment is performed at 270 to 450 ° C for 1 to 30 seconds.
( 8 ) The method for producing a silver coating material according to ( 5 ), wherein the heat treatment is performed at 300 to 450 ° C for 1 to 10 seconds.

  According to the present invention, for example, even when used as a movable contact and / or a fixed contact of a switch that is used for a long time under a condition in which switching is repeatedly performed, the surface silver or silver alloy layer is not scraped, and contact resistance is further improved. It is possible to provide a silver coating material excellent in wear resistance, in which no increase occurs.

2 is a cross-sectional SIM image photograph of the silver coating material of Example 1. FIG. 3 is a cross-sectional SIM image of the silver coating material of Comparative Example 1. It is a cross-sectional SIM image photograph of the silver coating material of the comparative example 3.

The silver coating material of the present invention is a silver coating material having, as an outermost layer, a layer made of at least silver or a silver alloy on a conductive substrate, and the amount of film abrasion in an abrasion resistance test is less than 40 mg, and the initial value And a contact resistance after a sliding wear test under the following conditions is less than 10 mΩ.
Sliding wear test conditions:
[Load] 1.6N
[Sliding range] 0.2mm
[Sliding speed] 1mm / s
[Number of times] 50,000 times In addition, the silver coating material of the present invention is a silver coating material having a layer made of at least silver or a silver alloy as an outermost layer on a conductive substrate, and made of the silver or silver alloy The layer is formed by plating and heat-treated at 200 to 500 ° C. for 1 to 299 seconds.

  The conductive substrate is a material having conductivity, spring characteristics, durability, and the like, and in the present invention, it is preferably made of copper or a copper alloy, iron or an iron alloy. Preferred copper alloys include bronze, phosphor bronze, brass, titanium copper, copper nickel silicon (Corson) alloy, and beryllium copper. Examples of iron alloys that are preferably used include stainless steel (SUS) and 42 alloy.

As the silver alloy in the outermost layer made of silver or a silver alloy, an Ag—Sn alloy, an Ag—Cu alloy, an Ag—In alloy, an Ag—Se alloy, or the like has good contact characteristics and can be suitably used. The silver alloy preferably has a silver content exceeding 50% by mass.
The outermost layer made of silver or a silver alloy is formed by plating using a known silver plating solution or silver alloy plating solution. The plating solution is not particularly limited, but a plating solution containing cyan as a complex is preferable. Silver strike plating may be performed before plating using the plating solution containing cyan as a complex. By forming the outermost layer made of silver or a silver alloy by plating, it can be easily formed at low cost.
The thickness of the outermost layer is preferably 0.05 to 5 μm, more preferably 0.1 to 2 μm, and still more preferably 0.2 to 2 μm.

The silver coating material of this invention may have a base layer between a base material and the outermost layer which consists of silver or a silver alloy. Examples of the base layer include a Ni plating layer, a copper plating layer, and a cobalt plating layer. These can be formed by a known plating solution and plating conditions.
As a plating solution for forming the underlying Ni plating layer, a sulfamine bath is preferable.
As a plating solution for forming the base copper plating layer, a cyan copper bath is preferable.
The silver coating material of the present invention has an undercoat layer between the conductive base material and the outermost layer made of silver or a silver alloy. It is preferable to have a copper plating layer or a Ni plating layer.

  The silver coating material of the present invention is heat-treated at 200 to 500 ° C. for 1 to 299 seconds after the outermost layer is formed. It is preferable to lengthen the treatment time at a low temperature in the above temperature range and shorten the treatment time at a high temperature. From the viewpoint of productivity, heat treatment is preferably performed at 250 to 450 ° C. for 1 to 59 seconds, more preferably heat treatment at 270 to 450 ° C. for 1 to 30 seconds, and heat treatment at 300 to 450 ° C. for 1 to 10 seconds. It is particularly preferred that

  When heat treatment is performed within this range of conditions, the outermost spherical silver or silver alloy crystal grains grow to have an average crystal grain size of 0.2 μm or more and become columnar in the plating thickness direction. The surface layer includes columnar structure crystals made of silver or a silver alloy. As a result, it was found that the wear resistance of the surface was greatly improved. More preferably, the outermost layer has an average crystal grain size of 0.2 μm or more and 0.5 μm or less and includes a columnar structure crystal. Under these conditions, when the temperature was low and / or when the time was short, crystals did not grow and no improvement in wear resistance was observed. On the contrary, if the temperature is higher and / or the time is longer than this condition, the crystal grows, so that the wear resistance is improved, but the average crystal grain size exceeds 0.5 μm, and the plating thickness direction On the other hand, when the film was horizontally long and formed into a layer, the wear resistance was not significantly improved as compared with the case where the columnar structure crystals were included in the plating thickness direction. The shape of the crystal particles was observed by a cross-sectional SIM image in the plating thickness direction after the heat-treated plated substrate was subjected to FIB (focused ion beam) processing.

Further, since silver is difficult to oxidize, the contact resistance does not increase in the heat treatment in this condition range. However, if the heat treatment temperature is higher and / or the heat treatment time is longer than this condition, the initial oxidation is caused by surface oxidation. Contact resistance increases.
The heat treatment is intended to grow the outermost silver crystal grains into a columnar shape and is not intended to form an oxide layer. Therefore, the heat treatment may be performed in an inert gas atmosphere. . However, heat treatment in the atmosphere is easy and preferable.
The heating method for the heat treatment is not particularly limited, and can be performed using, for example, a hot plate or a hot air circulation oven.

Therefore, the silver coating material having the layer made of silver or a silver alloy as the outermost layer has a film abrasion amount of less than 40 mg in the wear resistance test by the heat treatment, and an initial contact resistance and sliding wear under the following conditions. The contact resistance after the test is less than 10 mΩ.
Sliding wear test conditions:
[Load] 1.6N
[Sliding range] 0.2mm
[Sliding speed] 1mm / s
[Number of times] 50,000 times It is more preferable that the film scraping amount in the abrasion resistance test is less than 30 mg. The film scraping amount can be less than 30 mg depending on heat treatment conditions.
The abrasion resistance test was performed in accordance with JIS H 8682, under the conditions of a load of 500 gf (scraped area 12 mm × 31 mm), # 1500 emery abrasive paper, and 200 reciprocations.

  Since the silver coating material of the present invention is excellent in peel resistance and wear resistance as described above and does not increase contact resistance, it can be suitably used for connectors and switches that are connecting parts for electronic devices. In particular, it can be suitably used as a movable contact and / or a fixed contact of a switch used in a mobile phone or a remote control switch, for example, as a tactile switch. The silver or silver alloy layer is not scraped and the contact resistance is not increased.

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

Example 1
A plated substrate in which phosphor bronze (C5210, 25 mm × 20 mm × 0.2 mmt) was subjected to 0.05 μm silver strike plating and 0.4 μm silver plating using a high cyan silver bath was used as a test material.
The plated substrate was heat-treated in the atmosphere using a hot plate under the conditions of Example 1 in Table 1. The heat treatment temperature is a temperature obtained by measuring the temperature of the plating substrate placed on the hot plate with a thermocouple.

Example 2 and Example 3
A phosphor bronze (C5210, 25 mm × 20 mm × 0.2 mmt) is provided with a plated substrate in which copper plating using a cyan copper bath is performed 3 μm, silver strike plating is 0.05 μm, and silver plating using a high cyan silver bath is performed in order of 0.4 μm. Samples were used.
The plated substrate was heat-treated in the atmosphere using a hot plate under the conditions of Example 2 and Example 3 in Table 1.

Example 4
A plated substrate in which phosphor bronze (C5210, 25 mm × 20 mm × 0.2 mmt) is subjected to nickel plating with a sulfamic acid bath at 3 μm, silver strike plating at 0.05 μm, and silver plating at a high cyan silver bath in order of 0.4 μm is provided. Samples were used.
The plated substrate was heat-treated in the atmosphere using a hot plate under the conditions of Example 4 in Table 1.

Example 5
In Example 2, the heat treatment conditions were changed to the conditions shown in Table 1, and a heat-treated plated substrate was obtained in the same manner as in Example 2 except that heating was performed in a nitrogen atmosphere (oxygen concentration <1%).

Example 6
In Example 4, except that the heat treatment conditions were changed to the conditions shown in Table 1, a plated substrate that was heat treated in the same manner as in Example 4 was obtained.

Example 7
In Example 2, a heat treated plated substrate was obtained in the same manner as in Example 2 except that the heat treatment conditions were changed to those shown in Table 1.

Example 8
In Example 4, except that the heat treatment conditions were changed to the conditions shown in Table 1, a plated substrate that was heat treated in the same manner as in Example 4 was obtained.

Comparative Example 1
In Example 4, a plated substrate was obtained in the same manner as in Example 4 except that the heat treatment was not performed.

Comparative Example 2
In Example 2, a heat treated plated substrate was obtained in the same manner as in Example 2 except that the heat treatment conditions were changed to those shown in Table 1.

Comparative Example 3
A heat-treated plated substrate was obtained in the same manner as in Example 1 except that the heat treatment conditions in Example 1 were changed to those shown in Table 1.

Comparative Example 4 to Comparative Example 6
In Example 4, except that the heat treatment conditions were changed to the conditions shown in Table 1, a plated substrate that was heat treated in the same manner as in Example 4 was obtained.

A wear resistance test was performed on the heat-treated plated substrate. The abrasion resistance test was performed according to the method described in JIS H 8682, using a Suga abrasion tester (NUS-IS03) under a load of 500 gf (scraped area 12 mm × 31 mm), # 1500 emery abrasive paper, 200 reciprocating conditions.
Evaluation criteria:
○: Film abrasion amount in the abrasion resistance test is less than 30 mg. Δ: Film abrasion amount in the abrasion resistance test is 30 mg or more and less than 40 mg. X: Film abrasion amount in the abrasion resistance test is 40 mg or more.

After subjecting the heat-treated plated substrate to FIB processing, the average crystal grain size and the crystal shape were confirmed by a cross-sectional SIM image (using SMI3050SE manufactured by SII Nanotechnologies).
Measurement of the average crystal grain size was calculated by the cutting method from the cross-sectional SIM image according to JIS H 0501.
Evaluation criteria:
Small: Average grain size <0.2μm
Medium: 0.2 μm ≦ average grain size ≦ 0.5 μm
Large: Average crystal grain size> 0.5μm
Cross-sectional SIM images of the plated substrates of Example 1, Comparative Example 1, and Comparative Example 3 are shown in FIGS.
As shown in FIG. 1, in the plated substrate of Example 1, the silver plating layer includes silver columnar structure crystals. Such a shape was defined as “columnar”. In the plated substrate of Comparative Example 1, the silver particles of the silver plating layer are round as shown in FIG. Such a shape was defined as “circle”. Further, in the plated substrate of Comparative Example 3, the silver crystals are horizontally long as shown in FIG. Such a shape was defined as “landscape”.

The initial contact resistance and the contact resistance after performing a sliding wear test under the following conditions were measured on the heat-treated plated substrate.
Contact resistance measurement conditions:
Equipment: Yamazaki contact simulator CRS-1
Conditions: Contact load 10g (Au probe), sliding distance 1mm
Sliding wear test conditions:
Equipment: CRS-G2050-JNS manufactured by Yamazaki Seiki Laboratory
Condition: [Load] 1.6N
[Sliding range] 0.2mm
[Sliding speed] 1mm / s
[Number of times] 50,000 times

Claims (8)

On a conductive substrate, a silver coating layer is provided with or without an underlying layer, and the silver coating layer is a silver coating material that is an outermost layer made of silver or a silver alloy, and is made of the silver or silver alloy. The layer comprises a columnar structure crystal having an average crystal grain size of 0.2 μm or more and 0.5 μm or less made of silver or a silver alloy, and the amount of film abrasion in the abrasion resistance test is less than 40 mg, and the initial contact resistance, And a silver coating material having a contact resistance of less than 10 mΩ after a sliding wear test under the following conditions.
Sliding wear test conditions:
[Load] 1.6N
[Sliding range] 0.2mm
[Sliding speed] 1mm / s
[Number of times] 50,000 times   2. The silver coating material according to claim 1, wherein a film scraping amount in the abrasion resistance test is less than 30 mg.   3. The silver according to claim 1, wherein the abrasion resistance test is performed in accordance with JIS H 8682, under the conditions of a load of 500 gf (a scraped area of 12 mm × 31 mm), # 1500 emery polished paper, and 200 reciprocating conditions. Coating material. As the movable contact and / or fixed contacts of the switch, the switch characterized by using the silver-coated material according to any one of claims 1-3. It has a silver coating layer on the electroconductive base material as described in any one of Claims 1-3 through or without a base layer, and this silver coating layer is the outermost layer which consists of silver or a silver alloy. A method for producing a silver coating material, comprising the step of forming the silver or silver alloy layer by plating and heat-treating at 200 to 500 ° C. for 1 to 299 seconds. . The method for producing a silver coating material according to claim 5 , wherein the heat treatment is performed at 250 to 450 ° C. for 1 to 59 seconds. The method for producing a silver coating material according to claim 5 , wherein the heat treatment is performed at 270 to 450 ° C. for 1 to 30 seconds. The method for producing a silver coating material according to claim 5 , wherein the heat treatment is performed at 300 to 450 ° C. for 1 to 10 seconds.