Silver-plated product

Abstract

There is provided a silver-plated product which has good thermal resistance, bendability and wear resistance. In a silver-plated product wherein a surface layer of silver having a thickness of 10 m or less is formed on a base material of copper or a copper alloy, the full-width at half maximum of a rocking curve on a preferred orientation plane (preferably {200} or {111} plane) of the surface layer is caused to be 2 to 8, preferably 3 to 7, to improve the out-of-plane orientation of the surface layer to improve the thermal resistance, bendability and wear resistance of the silver-plated product.

Claims

1. A silver-plated product comprising: a base material of copper or a copper alloy; and a surface layer of silver which is formed on the base material, wherein the full-width at half maximum of a rocking curve on a preferred orientation plane of the surface layer is 6 to 8, and the preferred orientation plane of the surface layer is {200} plane.

2. A silver-plated product as set forth in claim 1, wherein said full-width at half maximum of the rocking curve on the preferred orientation plane of the surface layer is 6 to 7.

3. A silver-plated product as set forth in claim 1, wherein said surface layer has a thickness of 10 m or less.

4. A contact or terminal part which is made of a silver-plated product as set forth in any one of claims 1, 2 and 3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph showing a rocking curve on a preferred orientation plane of a silver plating film of a silver-plated product in each of Example 3 and Comparative Example 3, and a full-width at half maximum thereof.

BEST MODE FOR CARRYING OUT THE INVENTION

(2) In the preferred embodiment of a silver-plated product according to the present invention, the full-width at half maximum of a rocking curve on a preferred orientation plane of a surface layer of a silver-plated product, wherein the surface layer of silver is formed on a base material, is 2 to 8, preferably 3 to 7.

(3) If the full-width at half maximum of the rocking curve on the preferred orientation plane of the surface layer of silver is thus 2 to 8 preferably 3 to 7, the out-of-plane orientation of the surface layer is improved, so that it is possible to improve the thermal resistance, bendability and wear resistance of the silver-plated product.

(4) In this silver-plated product, the preferred orientation plane of the surface layer is preferably {200} or {111} plane. The base material is preferably made of copper or a copper alloy, and the surface layer preferably has a thickness of 10 m or less.

(5) The surface layer of silver of the silver-plated product can be formed by electroplating at a current density of 3 to 10 A/dm.sup.2 and a liquid temperature of 10 to 40 C. (preferably 15 to 30 C.) in a silver plating solution which comprises silver potassium cyanide (KAg(CN).sub.2), potassium cyanide (KCN), and 3 to 30 mg/L of potassium selenocyanate (KSeCN) and wherein the concentration of selenium in the silver plating solution is 5 to 15 mg/L, the mass ratio of silver to free cyanogen being in the range of from 0.9 to 1.8.

(6) Examples of a silver-plated product according to the present invention will be described below in detail.

Example 1

(7) First, a pure copper plate having a size of 67 mm50 mm0.3 mm was prepared as a base material (a material to be plated). The material to be plated and a SUS plate were put in an alkali degreasing solution to be used as a cathode and an anode, respectively, to carry out electrolytic degreasing at 5 V for 30 seconds. The material thus electrolytic-degreased was washed, and then, pickled for 15 seconds in a 3% sulfuric acid.

(8) Then, the material to be plated and a titanium electrode plate coated with platinum were used as a cathode and an anode, respectively, to electroplate (silver-strike-plate) the material at a current density of 2.5 A/dm.sup.2 for 10 seconds in a silver strike plating bath comprising 3 g/L of silver potassium cyanide and 90 g/L of potassium cyanide while stirring the solution at 400 rpm by a stirrer.

(9) Then, the material to be plated and a silver electrode plate were used as a cathode and an anode, respectively, to electroplate (silver-plate) the material at a current density of 5 A/dm.sup.2 and a liquid temperature of 18 C. in a silver plating bath comprising 148 g/L of silver potassium cyanide (KAg(CN).sub.2), 140 g/L of potassium cyanide and 18 mg/L of potassium selenocyanate (KSeCN) while stirring the solution at 400 rpm by a stirrer, until a silver plating film having a thickness of 3 micrometers was formed. Furthermore, in the used silver plating bath, the concentration of Se was 10 mg/L, and the concentration of Ag was 80 g/L, the concentration of free CN being 56 g/L, and the mass ratio of Ag to free CN being 1.44.

(10) With respect to a silver-plated product thus produced, the crystal orientation, thermal resistance, bendability and wear resistance of a silver plating film were evaluated.

(11) In order to evaluate the crystal orientation of the silver plating film of the silver-plated product, an X-ray diffractometer (XRD) (Full-Automatic Multi-Purpose Horizontal X-ray diffractometer, Smart Lab produced by RIGAKU Corporation) was used for obtaining an X-ray diffraction pattern by carrying out the 2/ scan using an X-ray tube of Cu and the K filter method. Then, from the X-ray diffraction pattern thus obtained, each of X-ray diffraction peak intensities (intensities of X-ray diffraction peaks) on {111}, {200}, {220} and {311} planes of the silver plating film was corrected by relative intensity ratios (relative intensity ratios in the measurement of powder) described on JCPD card No. 40783. Then, the plane orientation of an X-ray diffraction peak, at which each of values (corrected intensities) obtained by the above-described correction was highest, was evaluated as the direction of the crystal orientation (the preferred orientation plane) of the silver plating film to obtain a diffraction angle 2 of the X-ray diffraction peak on the preferred orientation plane in the scanning range of 2/ to obtain a rocking curve (intensity curve) by scanning an angle of incidence at a fixed diffraction angle 2 to obtain a full-width at half maximum of the rocking curve. Furthermore, it is possible to determine the strength of the out-of-plane orientation by the full-width at half maximum of the rocking curve, and the out-of-plane orientation is stronger as the full-width at half maximum of the rocking curve is sharper (i.e., the full-width at half maximum is smaller). As a result, in the silver-plated product in this example, the crystals of the silver plating film were orientated to {200} plane (orientated so that {200} plane was directed to the surface (plate surface) of the silver-plated product), i.e., the preferred orientation plane of the silver plating film was {200} plane. The full-width at half maximum of the rocking curve was a small value of 3.8, so that the out-of-plane orientation was strong.

(12) The thermal resistance of the silver-plated product was evaluated by measuring a contact resistance thereof at a load of 50 gf by means of an electrical contact simulator (CRS-1 produced by Yamasaki-Seiki Co., Ltd.) before and after a heat-proof test in which the silver-plated product was heated at 200 C. for 144 hours by means of a dryer (OF450 produced by AS ONE Corporation). As a result, the contact resistance of the silver-plated product was 0.9 m before the heat-proof test and 2.4 m after the heat-proof test. Thus, the contact resistance after the heat-proof test was a good value which was not higher than 5 m, so that the rise of the contact resistance was restrained after the heat-proof test.

(13) The bendability of the silver-plated product was evaluated on the basis of the presence of cracks in a bent portion of the silver-plated product by observing the bent portion at a power of 1000 by means of a microscope (Digital Microscope VHX-1000 produced by KEYENCE CORPORATION) after the silver-plated product was bent by 90 degrees at R=0.1 in a direction perpendicular to the direction of rolling of the base material in accordance with the V-block method described in Japanese Industrial Standard (JIS) Z2248. As a result, cracks were not observed, so that the bendability of the silver-plated product was good.

(14) The wear resistance of the silver plating film of the silver-plated product was evaluated as follows. First, about 30 mg of a grease (MULTEMP D No. 2 produced by Kyodo Yushi Co., Ltd.) per an area of 8 cm.sup.2 was applied on the plate surface of the silver-plated product to be uniformly extended. Then, a sliding tester was used for causing a silver rivet containing 89.7 wt % of Ag and 0.3 wt % of Mg and having a curvature radius of 8 mm to slide as a reciprocation sliding motion on the plate surface of the silver-plated product, to which a current of 500 mA was applied, while the silver rivet was pressed against to the plate surface thereof at a load of 100 gf. After such a reciprocation sliding motion (sliding distance of 5 mm, sliding speed of 12 mm/sec) was continued 300,000 times, the abrasion loss of the silver plating film was measured for evaluating the wear resistance. As a result, the abrasion loss of the silver plating film was 0.6 m, so that the wear resistance of the silver-plated product was good.

Example 2

(15) A silver-plated product was produced by the same method as that in Example 1, except that the material to be plated was electroplated (silver-plated) in a silver plating bath comprising 148 g/L of silver potassium cyanide, 140 g/L of potassium cyanide and 11 mg/L of potassium selenocyanate. Furthermore, in the used silver plating bath, the concentration of Se was 6 mg/L, and the concentration of Ag was 80 g/L, the concentration of free CN being 56 g/L, and the mass ratio of Ag to free CN being 1.44.

(16) With respect to a silver-plated product thus produced, the crystal orientation, thermal resistance, bendability and wear resistance of the silver plating film were evaluated by the same methods in those in Example 1.

(17) As a result, in the evaluation of the crystal orientation of the silver plating film, the crystals of the silver plating film were orientated to {200} plane, i.e., the preferred orientation plane of the silver plating film was {200} plane. The full-width at half maximum of the rocking curve was a small value of 5.2, so that the out-of-plane orientation was strong. In the evaluation of the thermal resistance of the silver-plated product, the contact resistance of the silver-plated product was 1.0 m before the heat-proof test and 2.4 m after the heat-proof test. Thus, the contact resistance after the heat-proof test was a good value which was not higher than 5 m, so that the rise of the contact resistance was restrained after the heat-proof test. In the evaluation of the bendability of the silver-plated product, cracks were not observed, so that the bendability of the silver-plated product was good. In the evaluation of the wear resistance of the silver-plated product, the abrasion loss of the silver plating film was 0.6 m, so that the wear resistance of the silver-plated product was good.

Example 3

(18) A silver-plated product was produced by the same method as that in Example 1, except that the material to be plated was electroplated (silver-plated) in a silver plating bath comprising 148 g/L of silver potassium cyanide, 140 g/L of potassium cyanide and 6 mg/L of potassium selenocyanate. Furthermore, in the used silver plating bath, the concentration of Se was 3 mg/L, and the concentration of Ag was 80 g/L, the concentration of free CN being 56 g/L, and the mass ratio of Ag to free CN being 1.44.

(19) With respect to a silver-plated product thus produced, the crystal orientation, thermal resistance, bendability and wear resistance of the silver plating film were evaluated by the same methods in those in Example 1.

(20) As a result, in the evaluation of the crystal orientation of the silver plating film, the crystals of the silver plating film were orientated to {200} plane, i.e., the preferred orientation plane of the silver plating film was {200} plane. The full-width at half maximum of the rocking curve was a small value of 6.0, so that the out-of-plane orientation was strong. In the evaluation of the thermal resistance of the silver-plated product, the contact resistance of the silver-plated product was 1.0 m before the heat-proof test and 1.9 m after the heat-proof test. Thus, the contact resistance after the heat-proof test was a good value which was not higher than 5 m, so that the rise of the contact resistance was restrained after the heat-proof test. In the evaluation of the bendability of the silver-plated product, cracks were not observed, so that the bendability of the silver-plated product was good. In the evaluation of the wear resistance of the silver-plated product, the abrasion loss of the silver plating film was 0.4 m, so that the wear resistance of the silver-plated product was good.

Example 4

(21) A silver-plated product was produced by the same method as that in Example 1, except that the material to be plated was electroplated (silver-plated) at a liquid temperature of 25 C. in a silver plating bath comprising 111 g/L of silver potassium cyanide, 120 g/L of potassium cyanide and 18 mg/L of potassium selenocyanate. Furthermore, in the used silver plating bath, the concentration of Se was 10 mg/L, and the concentration of Ag was 60 g/L, the concentration of free CN being 48 g/L, and the mass ratio of Ag to free CN being 1.26.

(22) With respect to a silver-plated product thus produced, the crystal orientation, thermal resistance, bendability and wear resistance of the silver plating film were evaluated by the same methods in those in Example 1.

(23) As a result, in the evaluation of the crystal orientation of the silver plating film, the crystals of the silver plating film were orientated to {111} plane, i.e., the preferred orientation plane of the silver plating film was {111} plane. The full-width at half maximum of the rocking curve was a small value of 6.3, so that the out-of-plane orientation was strong. In the evaluation of the thermal resistance of the silver-plated product, the contact resistance of the silver-plated product was 0.8 m before the heat-proof test and 1.7 m after the heat-proof test. Thus, the contact resistance after the heat-proof test was a good value which was not higher than 5 m, so that the rise of the contact resistance was restrained after the heat-proof test. In the evaluation of the bendability of the silver-plated product, cracks were not observed, so that the bendability of the silver-plated product was good. In the evaluation of the wear resistance of the silver-plated product, the abrasion loss of the silver plating film was 0.4 m, so that the wear resistance of the silver-plated product was good.

Comparative Example 1

(24) A silver-plated product was produced by the same method as that in Example 1, except that the material to be plated was electroplated (silver-plated) in a silver plating bath comprising 148 g/L of silver potassium cyanide, 140 g/L of potassium cyanide and 73 mg/L of potassium selenocyanate. Furthermore, in the used silver plating bath, the concentration of Se was 40 mg/L, and the concentration of Ag was 80 g/L, the concentration of free CN being 56 g/L, and the mass ratio of Ag to free CN being 1.44.

(25) With respect to a silver-plated product thus produced, the crystal orientation, thermal resistance, bendability and wear resistance of the silver plating film were evaluated by the same methods in those in Example 1.

(26) As a result, in the evaluation of the crystal orientation of the silver plating film, the crystals of the silver plating film were orientated to {111} plane, i.e., the preferred orientation plane of the silver plating film was {111} plane. The full-width at half maximum of the rocking curve was a large value of 13.3, so that the out-of-plane orientation was weak. In the evaluation of the thermal resistance of the silver-plated product, the contact resistance of the silver-plated product was 0.7 m before the heat-proof test and 574.5 m after the heat-proof test. Thus, the contact resistance after the heat-proof test was very high, so that the rise of the contact resistance was not restrained after the heat-proof test. In the evaluation of the bendability of the silver-plated product, cracks were observed, so that the bendability of the silver-plated product was not good. In the evaluation of the wear resistance of the silver-plated product, the abrasion loss of the silver plating film was 1.5 m, so that the wear resistance of the silver-plated product was not good.

Comparative Example 2

(27) A silver-plated product was produced by the same method as that in Example 1, except that the material to be plated was electroplated (silver-plated) in a silver plating bath comprising 148 g/L of silver potassium cyanide, 140 g/L of potassium cyanide and 2 mg/L of potassium selenocyanate. Furthermore, in the used silver plating bath, the concentration of Se was 1 mg/L, and the concentration of Ag was 80 g/L, the concentration of free CN being 56 g/L, and the mass ratio of Ag to free CN being 1.44.

(28) With respect to a silver-plated product thus produced, the crystal orientation, thermal resistance, bendability and wear resistance of the silver plating film were evaluated by the same methods in those in Example 1.

(29) As a result, in the evaluation of the crystal orientation of the silver plating film, the crystals of the silver plating film were orientated to {111} plane, i.e., the preferred orientation plane of the silver plating film was {111} plane. The full-width at half maximum of the rocking curve was a large value of 8.1, so that the out-of-plane orientation was weak. In the evaluation of the thermal resistance of the silver-plated product, the contact resistance of the silver-plated product was 1.0 m before the heat-proof test and 6.5 m after the heat-proof test. Thus, the contact resistance after the heat-proof test was higher than 5 m, so that the rise of the contact resistance was not restrained after the heat-proof test. In the evaluation of the bendability of the silver-plated product, cracks were observed, so that the bendability of the silver-plated product was not good. In the evaluation of the wear resistance of the silver-plated product, the abrasion loss of the silver plating film was 1.5 m, so that the wear resistance of the silver-plated product was not good.

Comparative Example 3

(30) A silver-plated product was produced by the same method as that in Example 1, except that the material to be plated was electroplated (silver-plated) at a current density of 1.2 A/dm.sup.2 and a liquid temperature of 47 C. in a silver plating bath comprising 150 g/L of silver potassium cyanide and 90 g/L of potassium cyanide. Furthermore, in the used silver plating bath, the concentration of Se was 0 mg/L, and the concentration of Ag was 81 g/L, the concentration of free CN being 36 g/L, and the mass ratio of Ag to free CN being 2.25.

(31) With respect to a silver-plated product thus produced, the crystal orientation, thermal resistance, bendability and wear resistance of the silver plating film were evaluated by the same methods in those in Example 1.

(32) As a result, in the evaluation of the crystal orientation of the silver plating film, the crystals of the silver plating film were orientated to {111} plane, i.e., the preferred orientation plane of the silver plating film was {111} plane. The full-width at half maximum of the rocking curve was a large value of 10.8, so that the out-of-plane orientation was weak. In the evaluation of the thermal resistance of the silver-plated product, the contact resistance of the silver-plated product was 0.9 m before the heat-proof test and 2.0 m after the heat-proof test. Thus, the contact resistance after the heat-proof test was a good value which was not higher than 5 m, so that the rise of the contact resistance was restrained after the heat-proof test. In the evaluation of the bendability of the silver-plated product, cracks were observed, so that the bendability of the silver-plated product was not good. In the evaluation of the wear resistance of the silver-plated product, the abrasion loss of the silver plating film was 2.0 m, so that the wear resistance of the silver-plated product was not good.

Comparative Example 4

(33) A silver-plated product was produced by the same method as that in Example 1, except that the material to be plated was electroplated (silver-plated) at a current density of 2 A/dm.sup.2 and a liquid temperature of 25 C. in a silver plating bath comprising 111 g/L of silver potassium cyanide, 120 g/L of potassium cyanide and 18 mg/L of potassium selenocyanate. Furthermore, in the used silver plating bath, the concentration of Se was 10 mg/L, and the concentration of Ag was 60 g/L, the concentration of free CN being 48 g/L, and the mass ratio of Ag to free CN being 1.26.

(34) With respect to a silver-plated product thus produced, the crystal orientation, thermal resistance, bendability and wear resistance of the silver plating film were evaluated by the same methods in those in Example 1.

(35) As a result, in the evaluation of the crystal orientation of the silver plating film, the crystals of the silver plating film were orientated to {220} plane, i.e., the preferred orientation plane of the silver plating film was {220} plane. The full-width at half maximum of the rocking curve was a large value of 13.0, so that the out-of-plane orientation was weak. In the evaluation of the thermal resistance of the silver-plated product, the contact resistance of the silver-plated product was 1.0 m before the heat-proof test and 11.1 m after the heat-proof test. Thus, the contact resistance after the heat-proof test was higher than 5 m, so that the rise of the contact resistance was not restrained after the heat-proof test. In the evaluation of the bendability of the silver-plated product, cracks were observed, so that the bendability of the silver-plated product was not good. In the evaluation of the wear resistance of the silver-plated product, the abrasion loss of the silver plating film was 1.9 m, so that the wear resistance of the silver-plated product was not good.

(36) The producing conditions and characteristics of the silver-plated product in each of these examples and comparative examples are shown in Tables 1 and 2, respectively. In order to explain the rocking curve and the full-width at half maximum thereof, FIG. 1 shows the rocking curve on the preferred orientation plane of the silver plating film of the silver-plated product in each of Example 3 and Comparative Example 3 and the full-width at half maximum thereof.

(37) TABLE-US-00001 TABLE 1 Silver Plating Composition of Silver Conditions Plating Bath Current Plating K[Ag(CN).sub.2] KCN KSeCN Density Temp. (g/L) (g/L) (mg/L) (A/dm.sup.2) ( C.) Example 1 148 140 18 5 18 Example 2 148 140 11 5 18 Example 3 148 140 6 5 18 Example 4 111 120 18 5 25 Comp. 1 148 140 73 5 18 Comp. 2 148 140 2 5 18 Comp. 3 150 90 0 1.2 47 Comp. 4 111 120 18 2 25

(38) TABLE-US-00002 TABLE 2 Full-Width at Half Maximum of Contact Contact Rocking Resistance Resistance Curve before after on Preferred Heat Heat Bendability Abrasion Preferred Orientation Proof Proof (Presence Loss Orientation Plane Test Test of of Ag Plane (deg) (m) (m) Cracks) (m) Ex. 1 {200} 3.8 0.9 2.4 None 0.6 Ex. 2 {200} 5.2 1.0 2.4 None 0.6 Ex. 3 {200} 6.0 1.0 1.9 None 0.4 Ex. 4 {111} 6.3 0.8 1.7 None 0.4 Comp. 1 {111} 13.3 0.7 574.5 Presence 1.5 Comp. 2 {111} 8.1 1.0 6.5 Presence 1.0 Comp. 3 {111} 10.8 0.9 2.0 Presence 2.0 Comp. 4 {220} 13.0 1.0 11.1 Presence 1.9

(39) As can be seen from Tables 1 and 2, the silver-plated product in each of Examples 1 through 4, wherein the full-width at half maximum of the rocking curve on the preferred orientation plane of the silver plating film was 3 to 7, has good thermal resistance, bendability and wear resistance.