JP2007169706A - Electroplating solution and electroplating method for forming amorphous gold-nickel based alloy plated film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroplating solution and an electroplating method which achieve formation of a high hardness low contact resistant amorphous gold-nickel based alloy plated film useful as a contact material for an electric/electronic part such as relay. <P>SOLUTION: The electroplating solution contains 0.01-0.1 mol/dm<SP>3</SP>gold cyanide in terms of gold , 0.017-0.67 mol/dm<SP>3</SP>water soluble nickel salt in terms of nickel and citric acid or the salt thereof, wherein the concentration ratio (Au/Ni) of gold to nickel by mol is 0.15-0.6, the concentration ratio (Cit/Ni) of citric acid or the salt thereof to nickel is 1-3 and the pH of the plating solution is 3-11. The amorphous gold-nickel based alloy plated film having a ratio (Au:Ni) by atom of (31:69)-(60:40) is formed using the electroplating solution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electroplating solution and an electroplating method capable of depositing and forming an amorphous gold-nickel alloy plating film.

A so-called hard gold plating film is currently widely used as a highly reliable electrical contact material such as a connector, a small relay, and a printed wiring board as a part of an electronic component. The hard gold plating film is composed of extremely small gold crystallites (20 to 30 nm), and the hardness reaches 170 to 200 kgmm ⁻² (Knoop hardness). Such a high hardness necessary for obtaining good wear resistance of the contact material is obtained by bonding a large amount of crystal grains having a small grain size.
On the other hand, with the recent miniaturization of electronic components, the size of electrical contacts is also becoming smaller, and in the near future, the size of contacts will be compared with the size of hard gold crystal grains. . The gold plating film on such a fine contact is presumed to be unable to maintain the hardness obtained with a large contact because the total number of crystal grains constituting it is small. As a fine structure whose physical properties are not affected even when such a nanometer level size is reached, an amorphous structure is ideal instead of crystallinity.
Also, in order to be useful as a contact material, the electrical resistance when the contacts come into contact with each other must be low. Moreover, considering that the stability of the contact material under the usage environment is necessary, gold or a gold alloy having an amorphous structure is desirable.

The prior art document information related to the present invention includes the following.
JP-A-60-33382 Japanese Patent Laid-Open No. 62-290893 Satoshi Kawai, “Study on deposition structure of gold-nickel alloy plating”, Metal Surface Technology, 1968, Vol. 19, no. 12, p. 487-491 Yasuo Shimizu et al., "Electron microscopic study on microstructure and phase of electrodeposited Au-Ni alloy", Metal Surface Technology, 1976, Vol. 27, no. 1, p. 20-24 Toru Watanabe, “Fine plating plating structure control technology and its analysis method”, Technical Information Association, February 2002, p256-262 Toru Watanabe, “Mechanism of Amorphous Alloy Formation by Plating”, Surface Technology, 1989, Vol. 40, no. 3, p. 21-26

  The present invention has been made in view of the above circumstances, and provides an amorphous gold-nickel alloy electroplating solution and an electroplating method capable of forming an amorphous gold-nickel alloy plating film having high hardness and low contact resistance. The purpose is to do.

  As a result of intensive studies to achieve the above object, the present inventors have used a specific cathode using an electroplating solution containing a gold cyanide salt, a water-soluble nickel salt, citric acid or a salt thereof in a specific ratio. It has been found that by performing electroplating at a current density, an amorphous gold-nickel alloy plating film is formed in a range where the composition in the metal component is Au 31 at%, Ni 69 at% to Au 60 at%, Ni 40 at%.

That is, the present inventors previously proposed an electroplating solution capable of obtaining a gold-nickel-based amorphous alloy plating film formed of a homogeneous amorphous phase having no fine crystals (Japanese Patent Application No. 2005-28523). ). This electroplating solution has a gold cyanide salt concentration of 0.01 to 0.1 mol / dm ^{3 on} a gold basis, a nickel salt concentration of 0.02 to 0.2 mol / dm ^{3 on} a nickel basis, and a tungstate salt. Is contained at a concentration of 0.1 to 0.5 mol / dm ^{3 on} the basis of tungsten, thereby containing metal components including gold and nickel at 97.5% by mass or more and carbon at 2.5% by mass or less. In addition, a gold-nickel amorphous alloy in which the composition of gold and nickel in the metal component is 98% by mass or more as a total amount of gold and nickel and gold / nickel = 2.2 to 5.0 (mass ratio) A plating film can be obtained, but the plating solution requires the addition of tungstate.

  On the other hand, as a result of further investigation, the present inventors have selected a specific cathode current density by selecting a specific ratio of a gold cyanide salt, a water-soluble nickel salt, a citric acid as a complexing agent or a salt thereof. By performing electroplating, it was found that an amorphous gold-nickel alloy plating film was deposited and formed without adding tungstate, and an amorphous gold-nickel alloy obtained from this electroplating solution It was confirmed that the hardness of the plating film was high and the contact resistance was as low as the value of normal hard gold plating, and the present invention was made.

Accordingly, the present invention relates to a gold cyanide salt of 0.01 to 0.1 mol / dm ³ on a gold basis, a water-soluble nickel salt of 0.017 to 0.67 mol / dm ³ on a nickel basis, and citric acid or It contains the salt, gold to nickel concentration ratio (Au / Ni) as a molar ratio of 0.15-0.6, citric acid or its salt to nickel concentration ratio (Cit / Ni) as a molar ratio of 1 to 1 3. An electroplating solution for forming an amorphous gold-nickel alloy plating film with an Au: Ni ratio of 31:69 to 60:40 as the atomic ratio is 3 and has a pH of 3 to 11 To do. Furthermore, the present invention is immersed in the electroplating solution to be plated as a cathode, the temperature 20 to 90 ° C., cathode current density 3mA / cm ² or more 10 mA / cm ² or less than 20 mA / cm ^2, greater 200 mA / cm ² An electroplating method for forming an amorphous gold-nickel alloy plating film having an atomic ratio of Au: Ni of 31:69 to 60:40 is provided.

  According to the present invention, an amorphous gold-nickel alloy plating film having high hardness and low contact resistance can be formed, which is useful as a contact material for electrical / electronic parts such as relays.

  The amorphous gold-nickel alloy electroplating solution of the present invention contains a gold cyanide salt, a water-soluble nickel salt, citric acid or a salt thereof.

In this case, examples of the gold cyanide salt include potassium gold cyanide, sodium gold cyanide, lithium gold cyanide and the like, and the concentration thereof is 0.01 to 0.1 mol / dm ³ on a gold basis. When KAu (CN) ₂ is used, it can be 2.9 to 29 g / dm ³ .

Examples of the water-soluble nickel salt include nickel sulfate and nickel nitrate, and the concentration thereof is 0.017 to 0.67 mol / dm ³ on the basis of nickel. For example, when NiSO ₄ .6H ₂ O is used, 4 0.5 to 176 g / dm ³ .

  In this case, the ratio of gold and nickel concentration is preferably Au / Ni = 0.15 to 0.6 as a molar ratio, and it is difficult to obtain an amorphous structure outside this range.

  The plating solution of the present invention contains citric acid or a water-soluble salt such as a sodium salt, potassium salt or ammonium salt as a complexing agent. The concentration is such that the ratio of citric acid concentration (Cit) to nickel is in the range of Cit / Ni = 1-3, especially 1.2-2.0, as a molar ratio. If the citric acid concentration is too low, the plating solution may be decomposed. If the citric acid concentration is too high, an amorphous structure cannot be obtained.

  If necessary, the plating solution may contain other complexing agents such as tartaric acid, malic acid and the like, and buffering agents such as boric acid as long as the effects of the present invention are not impaired.

  Moreover, pH of a plating solution is 3-11, Preferably it is 5-9.

In the plating method of the present invention, electroplating is performed by immersing an object to be plated in the above plating solution as a cathode. In this case, the temperature of the plating solution is preferably 20 to 90 ° C., particularly preferably 50 to 70 ° C., and the cathode current density (D _k ) is 3 mA / cm ² or more and less than 10 mA / cm ² , or 20 mA / cm ^2. Exceeding 200 mA / cm ² . Preferably it is 30-150 mA / cm < ² >. When D _{k is} 50 mA / cm ² or more, gold / nickel in the plating film is proportional to the ratio of the bath composition. When the current density is lowered, a large amount of nickel is precipitated, and at D _{k of} 10 to 20 mA / cm ² , the composition becomes amorphous. Furthermore, when the current density becomes low, the deposition rate of gold increases and enters the amorphous region again.

  As the anode, an insoluble anode such as platinum or platinum-coated titanium or a soluble anode such as nickel can be used. Further, although stirring is not particularly required, gentle stirring such as cathode locking may be performed.

  The plating film obtained by using the plating solution of the present invention is an amorphous gold-nickel alloy. In this case, the ratio is Au: Ni = 31: 69 to 60:40 as an atomic ratio (atomic%). As the mass ratio, Au / Ni is 1.5 to 5.0, the total content of gold and nickel is 97 mass% or more, particularly 98 mass% or more, and may contain carbon and nitrogen as non-metallic components, Its content is C2.5 mass% or less and N 0.5 mass% or less.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In the following examples, the methods and conditions for each analysis and measurement are as follows. Moreover, mass% is described as wt%.

XRD
RINT-TTR manufactured by Rigaku Corporation: CuKα (50 kV / 200 mA)
Metal composition Rigaku Denki Kogyo RIX2100: X-ray fluorescence method
Knoop hardness Measured according to JIS Z 2251: Load 49.0 mN (HK0.005) Load holding time 5 seconds
Contact resistance Using electrical contact simulator CRS-112-AL manufactured by Yamazaki Seiki: Measured under the conditions of a load of 1 N and an applied current of 10 mA by the four-terminal method.

[Example 1]
KAu (CN) ₂ and _{^{0.035mol / dm 3, NiSO 4 ·}} 6H 2 O and 0.076 mol / dm ^3, citric acid 0.076 mol / dm ³ and containing, electroplating was adjusted to pH 6 with aqueous ammonia Using the solution, a gold-nickel amorphous alloy plating film (film thickness: 5 μm) was formed on a copper plate having a temperature of 70 ° C. and a current density of 150 mA / cm ² and a purity of 99.96%. A platinum plate was used as the anode, and the plating bath was not stirred during plating.
The structure of the obtained alloy plating film was analyzed by XRD, and the composition was analyzed by fluorescent X-rays. It can be seen that the XRD pattern has a broad and amorphous structure as shown in FIG. The metal component analysis results of the coating are as shown in Table 1, and were 73 wt% gold and 27 wt% nickel.

[Example 2]
Plating was performed under the same conditions as in Example 1 except that the citric acid concentration was 0.143 mol / dm ³ . The XRD pattern of the obtained plating film was broad as shown in FIG. 1 and had an amorphous structure. The metal component analysis results of the coating are as shown in Table 1 and were 75 wt% gold and 25 wt% nickel. Furthermore, when the Knoop hardness and contact resistance of the plating film were measured, the Knoop hardness was 460 kg / mm ² and the contact resistance was 1.9 mΩ. The Knoop hardness was measured with a plating thickness of 30 μm.

[Example 3]
Plating was performed under the same conditions as in Example 2 except that the current density was 50 mA / cm ² . The XRD pattern of the obtained plating film was broad as shown in FIG. 1 and had an amorphous structure. The metal component analysis results of the coating are as shown in Table 1, and were gold 72 wt% and nickel 28 wt%.

[Example 4]
Plating was performed under the same conditions as in Example 1 except that NiSO ₄ .6H ₂ O was 0.057 mol / dm ³ , the citric acid concentration was 0.143 mol / dm ³ , and the current density was 100 mA / cm ² . The XRD pattern of the obtained plating film was broad as shown in FIG. 1 and had an amorphous structure. The metal component analysis results of the film are as shown in Table 1, and were 79 wt% gold and 21 wt% nickel.

[Example 5]
Plating was performed under the same conditions as in Example 1 except that the current density was 5 A / cm ² . The obtained plating film had a broad XRD pattern and an amorphous structure. The metal component analysis results of the coating are as shown in Table 1, and were 64 wt% gold and 36 wt% nickel.

[Comparative Example 1]
Plating was performed under the same conditions as in Example 1 except that the citric acid concentration was 0.357 mol / dm ³ . The metal component analysis results of the obtained film were 75 wt% gold and 25 wt% nickel as shown in Table 1, but the XRD pattern was Au (111) or Au-- around 2θ = 38 ° as shown in FIG. A minute peak derived from the Ni solid solution was observed, and it was found that it was out of the amorphous structure.

[Comparative Example 2]
Plating was performed under the same conditions as in Example 1 except that the citric acid concentration was 0.257 mol / dm ³ . The metal component analysis results of the obtained film were 76 wt% gold and 24 wt% nickel as shown in Table 1, but the XRD pattern showed a relatively sharp peak as shown in Fig. 2 and deviated from the amorphous structure. It was judged that.

[Comparative Example 3]
Plating was performed under the same conditions as in Example 3 except that the current density was 10 mA / cm ² . The metal component analysis results of the obtained plating film are 49 wt% gold and 51 wt% nickel as shown in Table 1, and the XRD pattern shows Ni (111) or Au− around 2θ = 45 ° as shown in FIG. A peak derived from the Ni solid solution was observed. Further, a peak derived from Au (111) or Au—Ni solid solution was observed in the vicinity of 2θ = 39 °, and it was found that an amorphous structure was not taken.

[Comparative Example 4]
Plating was performed under the same conditions as in Example 4 except that the current density was 10 mA / cm ² . The metal component analysis results of the obtained plating film are 87 wt% gold and 13 wt% nickel as shown in Table 1. As shown in FIG. 2, the XRD pattern shows Au (111) or Au− around 2θ = 38 °. A peak derived from the Ni solid solution was observed, and it was found that an amorphous structure was not taken.

  Tables 1 and 2 show the above plating solution composition, current density, and metal component composition in the obtained plating film.

It is a figure which shows the XRD pattern of the gold- nickel alloy plating film obtained in the Example. It is a figure which shows the XRD pattern of the gold- nickel alloy plating film obtained by the comparative example.

Claims (2)

Containing 0.01 to 0.1 mol / dm ³ of gold cyanide salt based on gold, 0.017 to 0.67 mol / dm ^{3 of} water-soluble nickel salt based on nickel, and citric acid or a salt thereof, The ratio of gold to nickel concentration (Au / Ni) is 0.15 to 0.6 as the molar ratio, the ratio of citric acid or its salt to nickel concentration (Cit / Ni) is 1 to 3 as the molar ratio, and the pH is An electroplating solution for forming an amorphous gold-nickel alloy plating film having an Au: Ni ratio of 31:69 to 60:40 as an atomic ratio, which is 3 to 11. Immersed in an electroplating solution of claim 1, wherein the object to be plated as a cathode, the temperature 20 to 90 ° C., the cathode current density 3mA / cm ² or more 10 mA / cm ² or less than 20 mA / cm ^2, greater 200 mA / cm ² range An electroplating method for forming an amorphous gold-nickel alloy plating film having an Au: Ni atomic ratio of 31:69 to 60:40, characterized in that electroplating is performed.

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