Electroplating solution and method for electroplating article using same

Abstract

The purpose of the present invention is to provide an electric nickel plating solution in which a ceramic element body does not readily erode. An electroplating solution according to the present invention comprises: a nickel ion supply source; a sulfonic acid represented by formula 1: R-SO3H (R is an alkyl group or hydroxyalkyl group having 1-5 carbon atoms), or a salt thereof; sodium hydroxide; and a pH buffering agent.

Description

Electroplating solution and method for electroplating an article using the same

[0001] The present invention relates to an electroplating solution and a method for electroplating an article using the same, and in particular to a nickel electroplating solution that is resistant to corrosion of zinc-containing articles such as ceramic electronic components.

[0002] Nickel electroplating is used in the manufacture of ceramic electronic components such as varistors, thermistors, inductors, and capacitors. For example, nickel electroplating is used to form a base electrode of silver, copper, or the like on the surface of a ceramic electronic component having internal electrodes, and then form a terminal electrode consisting of a nickel plating layer and a tin plating layer on the surface of the base electrode. Conventional nickel electroplating solutions, as described in Patent Documents 1 and 2, for example, use nickel sulfate or nickel sulfamate as a nickel ion source. Patent Documents 3 and 4 also describe nickel electroplating solutions containing nickel alkanesulfonate, such as nickel methanesulfonate, as a nickel ion source. Patent Document 5 describes that using nickel chloride instead of nickel sulfate as a nickel ion source can more easily suppress corrosion of the element body.

[0003] On the other hand, Patent Document 2 describes that if nickel chloride is used to create a state in which a large amount of chloride ions are contained, this is undesirable as it can corrode transition metal oxide ceramics. Patent Document 5 also describes that alkali metal ions such as sodium hydroxide are unnecessary components in electroplating solutions because they can cause poor insulation and etching of the element body, and Patent Document 1 also describes that it is better not to include alkali metals (hydroxides of alkali metals) in the electroplating solution from the perspective of preventing corrosion of the element body.

[0004] JP 2012-77324 A JP 2008-285732 A JP 2006-213946 A JP 11-71695 A JP 2010-7172 A

[0005] Electroplating of ceramic elements using electroplating solutions containing nickel sulfate or nickel sulfamate is prone to erosion of the elements, which is a factor in reducing the quality of ceramic electronic components. Ceramic elements containing zinc oxide (zinc oxide varistors) are particularly prone to erosion than other ceramic elements. Therefore, an object of the present invention is to provide a nickel electroplating solution that is less prone to erosion of ceramic elements than conventional Watts baths or sulfamate baths (nickel electroplating solutions containing nickel sulfate or nickel sulfamate).

[0006] The present inventors conducted extensive research to solve the above-mentioned problems, and discovered that the combined use of a specific alkane sulfonic acid or hydroxyalkane sulfonic acid, or a salt thereof, with sodium hydroxide in an electroplating solution containing a nickel ion source can suppress corrosion of zinc-containing articles, such as ceramic electronic components, and thus completed the present invention. Specifically, the present invention provides the following electroplating solutions and methods for electroplating articles using the same. [1] An electroplating solution comprising a nickel ion source, a sulfonic acid or a salt thereof represented by Formula 1: R-SO3H (R is an alkyl or hydroxyalkyl group having 1 to 5 carbon atoms), sodium hydroxide, and a pH buffer. [2] The electroplating solution according to [1] above for electroplating zinc-containing articles. [3] The electroplating solution according to [1] above, wherein the sulfonic acid or a salt thereof includes methanesulfonic acid, 2-hydroxyethanesulfonic acid, and / or a salt thereof. [4] The electroplating solution according to any one of [1] to [3], which contains an inorganic halogen compound. [5] The electroplating solution according to [4], wherein the inorganic halogen compound contains chloride and / or bromide, and / or the concentration of halide ions is 0.03 mol / L or more and less than 1.7 mol / L. [6] The electroplating solution according to [4], wherein the nickel ion equivalent molar concentration (C Ni ) molar concentration of halide ions (C Halo ) to the ratio (C Ni / C Halo[7] The electroplating solution according to [4] or [5], wherein the molar concentration (C ) of the nickel ion source in terms of nickel ions is greater than 1 and not greater than 57. Ni ), the molar concentration of the sulfonic acid or its salt (C sulfo ), and the molar concentration of halide ions (C Halo ) satisfies the following relation: 0≦(C sulfo +C Halo -2 x C Ni )≦0.6. [8] The electroplating solution according to any one of [1] to [7], wherein the concentration of each component is: - 0.15 mol / L to 1.7 mol / L (in terms of nickel ions) for the nickel ion source, and / or - 0.3 mol / L to 4 mol / L for the sulfonic acid or a salt thereof. [9] The electroplating solution according to any one of [1] to [8], wherein the pH buffer contains boric acid or a salt thereof.

[10] The electroplating solution according to any one of [1] to [9], wherein the electroplating solution is substantially free of any or all of sulfate ions, sulfamic acid or a salt thereof, ammonia, and a chelating agent.

[11] The electroplating solution according to any one of [1] to

[10] , wherein the pH is 4.5 to 5.5.

[12] A method for electroplating an article, comprising a step of passing a current in a plating bath containing the electroplating solution according to any one of [1] to

[11] above.

[13] The method according to

[12] above, wherein the article contains zinc.

[14] The method according to

[12] or

[13] above, wherein the article is a ceramic electronic component.

[15] The method according to any one of

[12] to

[14] above, wherein the plating bath comprises a soluble electrode as an anode.

[0007] According to the present invention, by using a sulfonic acid or a salt thereof represented by the formula 1 in combination with sodium hydroxide in an electroplating solution containing a nickel ion source, corrosion of articles containing zinc, such as ceramic electronic components, can be suppressed, thereby improving the quality of ceramic electronic components produced by nickel electroplating.

[0008] The present invention is described in further detail below. The electroplating solution of the present invention contains: a nickel ion source; an alkane sulfonic acid or hydroxyalkane sulfonic acid or a salt thereof represented by Formula 1: R-SO3H (R is an alkyl group or hydroxyalkyl group having 1 to 5 carbon atoms); sodium hydroxide; and a pH buffer. The electroplating solution of the present invention is used for nickel electroplating and is particularly suitable for electroplating zinc-containing articles such as ceramic electronic components.

[0009] The "nickel ion source" described herein refers to a compound that supplies nickel ions used in nickel electroplating, and in the electroplating solution of the present invention, the nickel ion source is either ionized to generate nickel ions or forms a salt with a counter ion. The concentration of the nickel ion source is not particularly limited as long as nickel electroplating can be performed, but may be, for example, a concentration (concentration in terms of nickel ions) such that the concentration of nickel ions generated when the nickel ion source is completely ionized is about 0.15 mol / L to about 1.7 mol / L or about 0.3 mol / L to about 1.3 mol / L. Note that, when a numerical range is expressed in this specification with "to," the upper and lower limits are also included in the numerical range.

[0010] The nickel ion source is not particularly limited as long as it can supply nickel ions to the electroplating solution, but may include, for example, at least one selected from the group consisting of nickel sulfonate, basic nickel carbonate, anhydrous nickel carbonate, nickel chloride, nickel bromide, and nickel iodide, and may not include conventional nickel sulfate or nickel sulfamate. That is, in one embodiment, the electroplating solution is substantially free of sulfate ions and / or sulfamic acid or a salt thereof.

[0011] The nickel sulfonate as the nickel ion source is not particularly limited as long as it allows nickel electroplating to be carried out. For example, the nickel sulfonate may be represented by the following formula 2: R'(SO3H) n(R' is a hydrocarbon group which may have a hydroxy group, and n is an integer of 1 to 3). In one embodiment, R' may be a saturated chain hydrocarbon group having 1 to 15 carbon atoms (e.g., 1 to 7, 1 to 5, or 1 to 3 carbon atoms) which may have a hydroxy group, or a cyclic hydrocarbon group or heterocyclic hydrocarbon group having 4 to 16 carbon atoms (e.g., 6 to 14 carbon atoms) which may have a hydroxy group. More specifically, when n is 1, R' may be an alkyl group such as methyl, ethyl, propyl, isopropyl, butyl, t-butyl, isobutyl, pentyl, or isopentyl, or a linear or branched isomer thereof, or a hydroxyalkyl group in which the alkyl group is hydroxy-substituted, or a saturated or unsaturated alicyclic hydrocarbon group such as cyclobutyl, cyclobutenyl, cyclohexyl, cyclohexenyl, cyclohexadienyl, cyclooctanyl, or cyclooctadienyl, or an aromatic hydrocarbon group such as phenyl.

[0012] The alkane sulfonic acid or hydroxyalkane sulfonic acid, or salt thereof, contained as an essential component in the electroplating solution of the present invention functions as a conductivity-imparting substance in the electroplating solution and may be the same as or different from the nickel sulfonate serving as the nickel ion source. The alkane sulfonic acid and hydroxyalkane sulfonic acid contained as an essential component in the electroplating solution of the present invention are represented by Formula 1: R—SO H (R is an alkyl group having 1 to 5 carbon atoms or 1 to 3 carbon atoms, or a hydroxyalkyl group having 1 to 5 carbon atoms or 1 to 3 carbon atoms). The concentration of the sulfonic acid represented by Formula 1 or its salt is not particularly limited as long as nickel electroplating can be performed, but may be, for example, about 0.3 mol / L to about 4 mol / L or about 0.7 mol / L to about 2.6 mol / L. In one embodiment, the sulfonic acid or salt thereof represented by Formula 1 includes at least one selected from the group consisting of methanesulfonic acid, 2-hydroxyethanesulfonic acid (isethionic acid), and salts thereof.

[0013] The pH of the electroplating solution of the present invention is not particularly limited as long as it is adjusted with a pH adjuster containing sodium hydroxide, but may be, for example, about 4.5 to about 5.5. Surprisingly, when used in combination with the sulfonic acid or its salt, sodium hydroxide can suppress corrosion of articles to be plated in nickel electroplating, particularly articles containing zinc, such as ceramic electronic components. In one embodiment, the electroplating solution is substantially free of ammonia as a pH adjuster. In such an embodiment, corrosion of articles to be plated can be further suppressed.

[0014] The pH buffer is not particularly limited as long as it allows nickel electroplating to be carried out, but may include, for example, boric acid, metaboric acid, 2-morpholinoethanesulfonic acid, or a salt thereof. The concentration of the pH buffer is not particularly limited, but may be, for example, about 7 to about 20 g / L or about 10 to about 17 g / L of boric acid. In one embodiment, the pH buffer is substantially free of a chelating agent such as an organic carboxylic acid or a salt thereof. In such an embodiment, erosion of the article to be plated can be further suppressed. Examples of the organic carboxylic acid or a salt thereof include citric acid, glutamic acid, gluconic acid, and / or glycolic acid.

[0015] In one embodiment, the electroplating solution of the present invention may contain an inorganic halide compound. The inorganic halide compound provides halide ions in the electroplating solution and may be the same as or different from the nickel ion source. The inorganic halide compound is not particularly limited, but may include, for example, chlorides that generate chloride ions and / or bromides that generate bromide ions. The concentration of halide ions in the electroplating solution is not particularly limited as long as nickel electroplating can be performed, but may be, for example, from about 0.03 mol / L to less than about 1.7 mol / L, from about 0.1 mol / L to about 0.5 mol / L, or from about 0.1 to about 0.34 mol / L. In one embodiment, during the electroplating of the present invention, the molar concentration of the nickel ion source in terms of nickel ions (C Ni ) molar concentration of halide ions (C Halo ) to the ratio (CNi / C Halo ) is greater than 1 and not greater than about 57, greater than 1 and not greater than about 35, or greater than 1 and not greater than about 12. When the concentration of the inorganic halide ions is within this range, when electroplating is performed using a soluble electrode, ionization of the soluble electrode can be efficiently promoted while suppressing erosion of the ceramic body.

[0016] In one embodiment, the nickel ion equivalent molar concentration (C Ni ), the molar concentration of the sulfonic acid or its salt (C sulfo ), and the molar concentration of halide ions (C Halo ) satisfies the following relation: 0≦(C sulfo +C Halo -2 x C Ni )≦about 0.6, and the relationship satisfies: 0≦(C sulfo +C Halo -2 x C Ni )≦about 0.5 or about 0.4. The ions derived from the sulfonic acid or a salt thereof and the halide ions can serve as counter ions of the nickel ions. When the nickel ions and the counter ions satisfy this relationship, the nickel ions can be stably present while suppressing corrosion of the ceramic body.

[0017] The electroplating solution of the present invention may further contain any component commonly used in the art, as long as it does not impair the purpose of the electroplating solution. For example, the optional component may include an organic compound additive added to a plating bath for electroplating. The type of the organic compound additive is not particularly limited, and may be, for example, at least one selected from the group consisting of a brightener, a water conditioner, and an antifoaming agent.

[0018] In another aspect, the present invention relates to a method for electroplating an article, the method comprising the step of passing an electric current through a plating bath containing the electroplating solution described above as one aspect of the present invention. The article to which the method is applicable is not particularly limited, but the method is suitable for electroplating articles containing zinc, since the electroplating solution inhibits corrosion of articles containing zinc. Examples of such articles include ceramic electronic components such as varistors, thermistors, inductors, and capacitors.

[0019] The temperature of the plating bath is not particularly limited, but may be, for example, about 40°C to about 60°C, or about 45°C to about 55°C. Furthermore, as the anode used in the plating bath, a soluble electrode such as a nickel plate or an insoluble electrode such as a platinum plate may be used. The use of the soluble electrode allows nickel ions to be efficiently replenished to the electroplating bath.

[0020] The method of the present invention may further include any step commonly used in the art, as long as it does not impair the object of the method. For example, the method may include a step of washing the article before the energizing step, or a step of washing the article after the energizing step.

[0021] The present invention will be specifically described below with reference to examples, but the scope of the present invention is not limited to these examples.

[0022] [Production Example 1] The raw materials listed in Table 1 or Table 2 below were dissolved in water, and the pH was adjusted with a pH adjuster to prepare electroplating solutions for Examples 1 to 6 and Comparative Examples 1 to 3. Comparative Examples 2 and 3 correspond to conventional Watts baths and sulfamic acid baths, respectively.

[0023]

[0024] Test Example 1 2.5 g of zinc oxide powder was added to 100 mL of the electroplating solution of Examples 1 to 6 or Comparative Examples 1 to 3. The bath temperature of the electroplating solution was set to 50°C, and the electroplating bath was stirred at 600 rpm with a stirrer for 60 minutes. The concentration of zinc ions in the electroplating solution was measured by atomic absorption spectrometry, and the amount of dissolved zinc was evaluated according to the following criteria. The results are shown in Table 3. <Amount of dissolved zinc> ○: Less than 0.60 g / L △: 0.60 g / L or more but less than 0.70 g / L ×: 0.70 g / L or more

[0025]

[0026] The amount of dissolved zinc was smaller in electroplating solutions containing methanesulfonic acid or isethionic acid and sodium hydroxide than in electroplating solutions not containing either of these. Therefore, it is believed that electroplating solutions containing an alkane sulfonic acid or hydroxyalkane sulfonic acid such as methanesulfonic acid or isethionic acid and sodium hydroxide are particularly suitable for nickel electroplating of articles containing zinc oxide.

[0027] [Preparation Example 2] The raw materials shown in Table 4 below were dissolved in water, and the pH was adjusted with a pH adjuster to prepare electroplating solutions of Examples 7 and 8.

[0028] [Test Example 2] Ten zinc oxide varistors (chip element main component: zinc oxide) were immersed in 100 mL of the electroplating solution of Example 1, 2, or 8, and allowed to stand at a bath temperature of 50°C for 168 hours. The zinc oxide varistors were then removed and their appearance was visually evaluated according to the following criteria. The results are shown in Table 5. <Appearance Evaluation Criteria (Visual)> ○: Erosion of less than about 10% △: Erosion of about 10% or more but less than about 30% ×: Erosion of about 30% or more

[0029]

[0030] In the electroplating solution containing methanesulfonic acid or isethionic acid and sodium hydroxide, no corrosion of the zinc oxide varistor was observed. This test result is consistent with the results of Test Example 1. When the amount of zinc dissolved in the electroplating solution of Example 8 was tested using the same method as in Test Example 1, it was 0.55 g / L (evaluation: Good).

[0031] Test Example 3 500 mL of the electroplating solution of Examples 1 to 8 was placed in a long cell for Hull cell testing (anode plate: 65 x 65 x 0.5 mm, cathode copper plate: 65 x 200 x 0.3 mm), and a Hull cell test (Hull cell long type) was performed under plating test conditions of 0.5 A, 20 minutes, and a bath temperature of 50°C. A nickel plate (soluble anode) was used as the anode plate except for Example 2, and a platinum plate (insoluble anode) was used in Example 2. After plating, the cathode was removed and visually evaluated for high-voltage scorch and high-voltage gloss. The tensile stress was measured using a strip-type electrodeposition stress tester (manufactured by Fuji Kasei Co., Ltd.) and evaluated according to the following criteria. The evaluation results are shown in Table 6. <Tensile stress> ○: Less than 150 MPa ×: 150 MPa or more

[0032]

[0033] The electroplating solutions of Examples 1 to 8 were able to form plating films with good appearance and demonstrated plating performance equal to or better than that of conventional Watts baths and sulfamic acid baths. Furthermore, the tensile stress for each example was within an appropriate range that prevented the plating film from peeling. Therefore, taking into consideration the results of Test Examples 1 and 2, the electroplating solution of the present invention is considered to have an excellent effect of suppressing corrosion of articles containing zinc oxide, in particular, while maintaining plating performance.

[0034] Test Example 4 Barrel plating was performed on a zinc oxide varistor (chip element main component: zinc oxide) using the electroplating solution and nickel anode plate of Example 1, 2, or 8, or Comparative Example 2 or 3. The zinc oxide varistor after plating was observed with a digital microscope, and the length of the plating film (plating extension) formed on the element surface from one terminal electrode portion on the varistor, across the electrode line (the boundary between the terminal electrode portion and the ceramic portion) toward the other terminal electrode portion, was measured. If the length of the plating extension portion was less than 10 μm, it was evaluated as "none" plating extension. The results are shown in Table 7.

[0035]

[0036] In the production of terminal electrodes for zinc oxide varistors, it is necessary to form a plating film on the electrode layer at the terminal electrode portion, but plating elongation occurred in the conventional sulfamic acid bath (Comparative Example 3).In contrast, in electroplating using the electroplating solutions of Examples 1, 2, and 8, plating elongation was suppressed to the same extent as in the conventional Watts bath (Comparative Example 2).

[0037] From the above, it was found that the combined use of a sulfonic acid or its salt represented by Formula 1: R-SO3H (R is an alkyl or hydroxyalkyl group having 1 to 5 carbon atoms) and sodium hydroxide in an electroplating solution containing a nickel ion source can suppress corrosion of zinc-containing articles such as ceramic electronic components and form a good plating film. Therefore, the quality of ceramic electronic components manufactured by nickel electroplating can be improved.

Claims

1. An electroplating solution comprising a nickel ion source, a sulfonic acid represented by Formula 1: R-SO3H (wherein R is an alkyl group or hydroxyalkyl group having 1 to 5 carbon atoms) or a salt thereof, sodium hydroxide, and a pH buffer.

2. The electroplating solution according to claim 1, for electroplating an article containing zinc.

3. The electroplating solution according to claim 1 or 2, wherein the sulfonic acid or a salt thereof contains methanesulfonic acid, 2-hydroxyethanesulfonic acid, and / or a salt thereof.

4. The electroplating solution according to any one of claims 1 to 3, containing an inorganic halogen compound.

5. The electroplating solution according to claim 4, wherein the inorganic halogen compound contains chloride and / or bromide, and / or the concentration of halide ions is 0.03 mol / L or more and less than 1.7 mol / L.

6. The ratio (C Ni / C Halo ) of the molar concentration (C Ni ) of nickel ions in terms of nickel ions in the nickel ion source to the molar concentration (C Halo ) of halide ions is greater than 1 and 57 or less. The electroplating solution according to claim 4 or 5.

7. The nickel ion conversion molar concentration (C Ni ) of the nickel ion source, the molar concentration (C sulfo ) of the sulfonic acid or its salt, and the molar concentration (C Halo ) of the halide ion satisfy the following relational expression: 0 ≦ (C sulfo + C Halo - 2 × C Ni ) ≦ 0.

6. The electroplating solution according to any one of claims 4 to 6.

8. The concentration of each component is: - for the nickel ion source, 0.15 mol / L to 1.7 mol / L (in terms of nickel ions), and / or - for the sulfonic acid or a salt thereof, 0.3 mol / L to 4 mol / L. The electroplating solution according to any one of claims 1 to 7.

9. The electroplating solution according to any one of claims 1 to 8, wherein the pH buffer contains boric acid or a salt thereof.

10. The electroplating solution according to any one of claims 1 to 9, substantially free of any or all of sulfate ions, sulfamic acid or a salt thereof, ammonia, and a chelating agent.

11. The electroplating solution according to any one of claims 1 to 10, having a pH of 4.5 to 5.

5.

12. A method for electroplating an article, comprising the step of applying an electric current in a plating bath containing the electroplating solution according to any one of claims 1 to 11.

13. The method according to claim 12, wherein the article contains zinc.

14. The method according to claim 12 or 13, wherein the article is a ceramic electronic component.

15. The method according to any one of claims 12 to 14, wherein the plating bath is provided with a soluble electrode as an anode.