Electroplating solution and method for electroplating an article using the same

Abstract

Provided is a nickel plating solution in which a ceramic substrate is less likely to be eroded. The plating solution of the present invention contains a nickel ion supply source, a sulfonic acid represented by formula 1: R-SO3H (R is an alkyl group or a hydroxyalkyl group having 1 to 5 carbon atoms) or a salt thereof, sodium hydroxide, and a pH buffer.

Description

Technical Field

[0001] This invention relates to electroplating solutions and methods for electroplating articles using the same solution, and particularly to nickel plating solutions that prevent zinc-containing articles, such as ceramic electronic components, from being corroded. Background Technology

[0002] Nickel plating is used in the manufacture of ceramic electronic components such as varistors, thermistors, inductors, and capacitors. For example, nickel plating is used when forming a base electrode (such as a silver or copper base electrode) on the surface of a ceramic electronic component with internal electrodes, and then forming a terminal electrode consisting of a nickel plating layer and a tin plating layer on the surface of that base electrode. In conventional nickel plating solutions, such as those described in Patent Documents 1 and 2, nickel sulfate or nickel sulfamate is used as the nickel ion supply source. Furthermore, Patent Documents 3 and 4 describe nickel plating solutions containing alkyl sulfonates such as nickel methanesulfonate as the nickel ion supply source. Patent Document 5 describes the principle that using nickel chloride instead of nickel sulfate as the nickel ion supply source easily suppresses substrate corrosion.

[0003] On the other hand, Patent Document 2 describes that if nickel chloride is used, resulting in a state containing a large amount of chloride ions, the transition metal oxide ceramic may be corroded, which is not preferable. In addition, Patent Document 5 describes alkali metal ions such as sodium hydroxide as unwanted components in the electroplating solution because they can cause poor insulation or substrate etching; Patent Document 1 also describes that, from the viewpoint of preventing substrate corrosion, the electroplating solution preferably does not contain alkali metals (alkali metal hydroxides).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2012-77324

[0007] Patent Document 2: Japanese Patent Application Publication No. 2008-285732

[0008] Patent Document 3: Japanese Patent Application Publication No. 2006-213946

[0009] Patent Document 4: Japanese Patent Application Publication No. 11-71695

[0010] Patent Document 5: Japanese Patent Application Publication No. 2010-7172 Summary of the Invention

[0011] When electroplating ceramic substrates using electroplating solutions containing nickel sulfate or nickel sulfamate, the substrates are easily corroded, which contributes to the degradation of the quality of ceramic electronic components. In particular, ceramic substrates containing zinc oxide (zinc oxide varistors) are more easily corroded than other ceramic substrates. Therefore, the object of the present invention is to provide an electroplating solution that is less prone to corrosion of ceramic substrates compared to conventional watt baths or sulfamate baths (nickel plating solutions containing nickel sulfate or nickel sulfamate).

[0012] In order to solve the above-mentioned problems, the inventors conducted in-depth research and discovered that by using a specific alkyl sulfonic acid or hydroxyalkyl sulfonic acid or their salts with sodium hydroxide in an electroplating solution containing a nickel ion supply source, the corrosion of zinc-containing articles such as ceramic electronic components can be suppressed, thus completing the present invention. Specifically, the present invention provides the electroplating solution shown below and a method for electroplating articles using the electroplating solution.

[0013] [1] An electroplating solution comprising:

[0014] Nickel ion supply source

[0015] Sulfonic acids or their salts represented by Formula 1: R-SO3H (R is an alkyl or hydroxyalkyl group having 1 to 5 carbon atoms),

[0016] Sodium hydroxide, and

[0017] pH buffer.

[0018] [2] The electroplating solution described in [1] above is used for electroplating articles containing zinc.

[0019] [3] The electroplating solution according to [1] or [2] above, wherein the sulfonic acid or its salt comprises methanesulfonic acid, 2-hydroxyethanesulfonic acid and / or their salts.

[0020] [4] The electroplating solution according to any one of [1] to [3] above, wherein it contains an inorganic halogen compound.

[0021] [5] According to the electroplating solution described in [4] above, wherein the inorganic halogen compound comprises chloride and / or bromide, and / or,

[0022] The concentration of halide ions is above 0.03 mol / L and less than 1.7 mol / L.

[0023] [6] According to the electroplating solution described in [4] or [5] above, wherein the nickel ion molar concentration (C) of the nickel ion supply source is... Ni ) and molar concentration of halide ions (C Halo The ratio of (C) Ni / C Halo () Greater than 1 and less than 57.

[0024] [7] The electroplating solution according to any one of [4] to [6] above, wherein the nickel ion molar concentration (C) of the nickel ion supply source is... Ni The molar concentration (C) of the above sulfonic acid or its salt sulfo ) and the molar concentration of halide ions (C Halo The following relationship must be satisfied:

[0025] 0≤(C sulfo +C Halo -2×C Ni ≤0.6

[0026] [8] The electroplating solution according to any one of [1] to [7] above, wherein the concentrations of each component are as follows:

[0027] For the aforementioned nickel ion supply source, the concentration is 0.15 mol / L to 1.7 mol / L (converted from nickel ion concentration); and / or

[0028] For the above sulfonic acids or their salts, the concentration is 0.3 mol / L to 4 mol / L.

[0029] [9] The electroplating solution according to any one of [1] to [8] above, wherein the pH buffer comprises boric acid or a salt thereof.

[0030]

[10] The electroplating solution according to any one of [1] to [9] above, wherein it substantially does not contain any or all of sulfate ions, aminosulfonic acid or its salts, ammonia and chelating agents.

[0031]

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

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

[0032]

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

[11] above.

[0033]

[13] According to the method described in

[12] above, the article contains zinc.

[0034]

[14] The method described in

[12] or

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

[0035]

[15] The method according to any one of

[12] to

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

[0036] According to the present invention, in an electroplating solution containing a nickel ion supply source, corrosion of zinc-containing articles such as ceramic electronic components can be suppressed by using sulfonic acid or its salt represented by Formula 1 above with sodium hydroxide. Therefore, the quality of ceramic electronic components manufactured by nickel electroplating can be improved. Detailed Implementation

[0037] The present invention will now be described in further detail. The electroplating solution of the present invention comprises: a nickel ion supply source, an alkyl sulfonic acid or hydroxyalkyl sulfonic acid or a salt thereof represented by Formula 1: R-SO3H (R being an alkyl 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.

[0038] The term "nickel ion supply source" as used in this specification refers to a compound that provides nickel ions for nickel plating. In the plating solution of this invention, it ionizes to generate nickel ions or forms a salt with counter ions. The concentration of the nickel ion supply source is not particularly limited as long as nickel plating can be performed. For example, the concentration of nickel ions generated when the nickel ion supply source is fully ionized can be approximately 0.15 mol / L to approximately 1.7 mol / L or approximately 0.3 mol / L to approximately 1.3 mol / L (converted nickel ion concentration). It should be noted that when "~" is used to indicate a numerical range in this specification, the upper and lower limits are also included within that range.

[0039] The nickel ion supply source is not particularly limited as long as it can provide nickel ions in the electroplating solution. For example, it may contain at least one of nickel sulfonate, basic nickel carbonate, anhydrous nickel carbonate, nickel chloride, nickel bromide, and nickel iodide, and may not contain conventional nickel sulfate or nickel sulfamate. That is, in some manner, the electroplating solution substantially does not contain sulfate ions and / or sulfamate or its salts.

[0040] The nickel sulfonate used as the nickel ion supply source is not particularly limited as long as nickel electroplating can be performed. For example, it can also be made from formula 2: R'(SO3H). _n(R' is a hydrocarbon group that may have a hydroxyl group, and n is an integer from 1 to 3) represents a nickel salt of a sulfonic acid. In some cases, R' can be a saturated chain hydrocarbon group with hydroxyl groups having 1 to 15 carbon atoms (e.g., 1 to 7, 1 to 5, or 1 to 3 carbon atoms), or it can be a cyclic hydrocarbon group or a heterocyclic hydrocarbon group with hydroxyl groups having 4 to 16 carbon atoms (e.g., 6 to 14 carbon atoms). More specifically, when n is 1, R' can be an alkyl group such as methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, isobutyl, pentyl, or isopentyl, and their straight-chain or branched isomers, or it can be a hydroxyalkyl group formed by substituting the alkyl group with a hydroxyl group, or it can be a saturated or unsaturated alicyclic hydrocarbon group such as cyclobutyl, cyclobutenyl, cyclohexyl, cyclohexenedenyl, cyclohexadienyl, cyclooctyl, and cyclooctadienyl, or it can be an aromatic hydrocarbon group such as phenyl.

[0041] The alkyl sulfonic acid or hydroxyalkyl sulfonic acid or its salt, which are essential components in the electroplating solution of the present invention, function as a conductive agent in the electroplating solution. They may be the same as or different from nickel sulfonate, which serves as the nickel ion supply source. The alkyl sulfonic acid and hydroxyalkyl sulfonic acid, which are essential components in the electroplating solution of the present invention, are represented by Formula 1: R-SO3H (where 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 or its salt represented by Formula 1 is not particularly limited as long as nickel electroplating can be performed; for example, it may be from about 0.3 mol / L to about 4 mol / L, or from about 0.7 mol / L to about 2.6 mol / L. In some embodiments, the sulfonic acid or its salt represented by Formula 1 includes at least one selected from methanesulfonic acid, 2-hydroxyethanesulfonic acid (hydroxyethanesulfonic acid), and their salts.

[0042] The pH of the electroplating solution of the present invention is not particularly limited as long as it is adjusted by a pH adjuster containing sodium hydroxide; for example, it can be about 4.5 to about 5.5. Surprisingly, if the sodium hydroxide is used in combination with the aforementioned sulfonic acid or its salt, it can inhibit the corrosion of the nickel-plated items, especially zinc-containing items such as ceramic electronic components. In one embodiment, the electroplating solution, acting as a pH adjuster, is substantially free of ammonia. In such an embodiment, corrosion of the plated items can be further inhibited.

[0043] The pH buffer described above is not particularly limited as long as nickel electroplating can be performed; for example, it may contain boric acid, metaboric acid, or 2-morpholinoethanesulfonic acid or their salts. The concentration of the pH buffer is not particularly limited; for example, if boric acid is used, it may be about 7 to about 20 g / L or about 10 to about 17 g / L. In some embodiments, the pH buffer substantially does not contain chelating agents such as organic carboxylic acids or their salts. In such embodiments, corrosion of the plated object can be further inhibited. Examples of organic carboxylic acids or their salts include citric acid, glutamic acid, gluconic acid, and / or glycolic acid.

[0044] In one embodiment, the electroplating solution of the present invention may contain an inorganic halogen compound. This inorganic halogen compound is a component that provides halide ions in the electroplating solution, and may be the same as or different from the nickel ion supply source. The inorganic halogen compound is not particularly limited; for example, it may include 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; for example, it may be more than about 0.03 mol / L and less than about 1.7 mol / L, about 0.1 mol / L to about 0.5 mol / L, or about 0.1 to about 0.34 mol / L. In one embodiment, in the electroplating of the present invention, the nickel ion molar concentration (C) of the nickel ion supply source is... Ni ) and molar concentration of halide ions (C Halo The ratio of (C) Ni / C Halo The concentrations of inorganic halide ions are greater than 1 and less than about 57, greater than 1 and less than about 35, or greater than 1 and less than about 12. If the concentration of inorganic halide ions is within such a range, when electroplating is performed using a soluble electrode, the ionization of the soluble electrode can be effectively promoted while suppressing the erosion of the ceramic substrate.

[0045] In one manner, the nickel ion molar concentration (C) of the aforementioned nickel ion supply source is... Ni The molar concentration (C) of the above sulfonic acid or its salt sulfo ) and the molar concentration of halide ions (C Halo The following relationship must be satisfied:

[0046] 0≤(C sulfo +C Halo -2×C Ni ≤ Approximately 0.6

[0047] Furthermore, the above relation can also be expressed as:

[0048] 0≤(C sulfo +C Halo -2×C Ni ) ≤ Approximately 0.5 or approximately 0.4.

[0049] Ions from the aforementioned sulfonic acids or their salts, as well as the aforementioned halide ions, can serve as counterions to nickel ions. When the aforementioned nickel ions and the aforementioned counterions satisfy the following relationship, the aforementioned nickel ions can be stably maintained while suppressing the corrosion of the ceramic matrix.

[0050] The electroplating solution of the present invention may further contain any components commonly used in the art, provided that their purpose is not compromised. For example, such components may include organic compound additives added to the plating bath for electroplating. The types of such organic compound additives are not particularly limited; for example, they may be at least one selected from brighteners, water conditioners, and defoamers.

[0051] In another aspect, the present invention also relates to a method for electroplating articles, the method comprising a step of energizing a plating bath in the electroplating solution described above as an aspect of the present invention. The articles to which the above method is applied are not particularly limited, but since the corrosion of articles containing zinc is suppressed in the electroplating solution, the above method is applicable to the electroplating of zinc-containing articles. Examples of such articles include ceramic electronic components such as varistors, thermistors, inductors, and capacitors.

[0052] The temperature of the plating bath described above is not particularly limited; for example, it can be approximately 40°C to approximately 60°C, or approximately 45°C to approximately 55°C. Furthermore, the anode used in the above plating bath can be a soluble electrode such as a nickel plate, or an insoluble electrode such as a platinum plate. If a soluble electrode is used, nickel ions can be effectively added to the electroplating bath.

[0053] The method of the present invention may further include any steps commonly used in the art, provided that it does not impair its purpose. For example, any of the above methods may include a step of cleaning the article before the above-mentioned energizing step, or a step of cleaning the article after the above-mentioned energizing step, etc.

[0054] The present invention will be specifically described below through embodiments, but the scope of the present invention is not limited to these embodiments.

[0055] Example

[0056] [Manufacturing Example 1]

[0057] 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 the electroplating solutions for Examples 1-6 and Comparative Examples 1-3. It should be noted that Comparative Examples 2 and 3 correspond to the conventional Watt's bath and aminosulfonic acid bath, respectively.

[0058]

[0059]

[0060] [Experimental Example 1]

[0061] 2.5 g of zinc oxide powder was added to 100 mL of the electroplating solution used in Examples 1-6 or Comparative Examples 1-3. The bath temperature was set to 50°C, and the electroplating bath was stirred at 600 rpm for 60 minutes. The concentration of zinc ions in the electroplating solution was determined by atomic absorption spectrometry, and the zinc dissolution was evaluated according to the following criteria. The results are shown in Table 3.

[0062] <Zinc solubility>

[0063] ○: Less than 0.60 g / L

[0064] △: Above 0.60g / L and less than 0.70g / L

[0065] ×: Above 0.70g / L

[0066]

[0067] In electroplating solutions containing methanesulfonic acid or hydroxyethanesulfonic acid and sodium hydroxide, less zinc is dissolved compared to electroplating solutions that do not contain either of these. Therefore, electroplating solutions containing alkyl sulfonic acids such as methanesulfonic acid or hydroxyalkyl sulfonic acid and sodium hydroxide are considered particularly suitable for nickel plating of articles containing zinc oxide.

[0068] [Manufacturing Example 2]

[0069] The raw materials listed in Table 4 below were dissolved in water, and the pH was adjusted with a pH adjuster to prepare the electroplating solutions of Examples 7 and 8.

[0070]

[0071] [Experimental Example 2]

[0072] Ten zinc oxide varistors (main component of the chip substrate: zinc oxide) were immersed in 100 mL of the electroplating solution of Examples 1, 2, or 8, and left 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.

[0073] <Appearance Evaluation Criteria (Visual Inspection)>

[0074] ○: Erosion less than approximately 10%

[0075] △: Erosion of approximately 10% to less than approximately 30%

[0076] ×: Erosion of approximately 30% or more

[0077]

[0078] No corrosion of the zinc oxide varistor was observed in the electroplating solution containing methanesulfonic acid or hydroxyethanesulfonic acid and sodium hydroxide. This result is consistent with that of Test Example 1. It should be noted that the zinc dissolution in the electroplating solution of Example 8 was tested using the same method as in Test Example 1, and the result was 0.55 g / L (judgment: ○).

[0079] [Experimental Example 3]

[0080] 500 mL of the electroplating solutions from Examples 1 to 8 were added to a long Hull cell (anode plate: 65×65×0.5 mm, cathode copper plate: 65×200×0.3 mm) used for the Hull cell test. The Hull cell test (long Hull cell type) was conducted under plating test conditions of 0.5A for 20 minutes and a bath temperature of 50°C. As the anode plate, a nickel plate (soluble anode) was used except in Example 2, while a platinum plate (insoluble anode) was used in Example 2. The plated cathode was then removed, and the charring and gloss in the high current density area were visually evaluated. Tensile stress was measured using a peel-type electrodeposition stress testing machine (manufactured by Fujikasei Co., Ltd.), and evaluated according to the following criteria. The evaluation results are shown in Table 6.

[0081] <Tensile Stress>

[0082] ○: Less than 150MPa

[0083] ×: Above 150MPa

[0084]

[0085] Even when the electroplating solutions of Examples 1-8 are used for electroplating, a plating film with a good appearance can be formed, exhibiting plating performance equivalent to or better than that of conventional Watt baths or sulfamic acid baths. Furthermore, the tensile stress in each example is within a suitable range where the plating film is not easily peeled off. Therefore, considering the results of Test Examples 1 and 2, it can be concluded that the electroplating solution of the present invention achieves an excellent effect of inhibiting corrosion, especially of articles containing zinc oxide, while maintaining plating performance.

[0086] [Experimental Example 4]

[0087] Zinc oxide varistors (main component of the chip substrate: zinc oxide) were barrel-plated using the plating solutions and nickel anode plates of Examples 1, 2, or 8, or Comparative Examples 2 or 3. The plated zinc oxide varistors were observed using a digital microscope, and the length of the plating film (plating extension) formed on the substrate surface from one terminal electrode location across the electrode line (the boundary between the terminal electrode location and the ceramic location) towards the other terminal electrode location was measured. When the length of the plating extension was less than 10 μm, it was evaluated as "no" plating extension. The results are shown in Table 7.

[0088]

[0089] In the fabrication of the terminal electrodes of the zinc oxide varistor, although it is required to form a plating film on the electrode layer at the terminal electrode location, plating extension occurred in the conventional aminosulfonic acid bath (Comparative Example 3). In contrast, in electroplating using the plating solutions of Examples 1, 2, or 8, plating extension was suppressed to the same extent as in the conventional Watt's bath (Comparative Example 2).

[0090] As shown above, in an electroplating solution containing a nickel ion supply source, the corrosion of zinc-containing materials such as ceramic electronic components can be inhibited and a good plating film can be formed by using sulfonic acid or its salt, represented by Formula 1: R-SO3H (R is an alkyl or hydroxyalkyl group with 1 to 5 carbon atoms), and sodium hydroxide. Therefore, the quality of ceramic electronic components manufactured by nickel electroplating can be improved.

Claims

1. An electroplating solution, comprising: Nickel ion supply source Sulfonic acid or its salt represented by formula 1: R-SO3H, wherein, R is an alkyl or hydroxyalkyl group having 1 to 5 carbon atoms. Sodium hydroxide, and pH buffer.

2. The electroplating solution according to claim 1, used for electroplating articles containing zinc.

3. The electroplating solution according to claim 1 or 2, wherein, The sulfonic acid or its salts include methanesulfonic acid, 2-hydroxyethanesulfonic acid and / or their salts.

4. The electroplating solution according to any one of claims 1 to 3, wherein, It contains inorganic halogen compounds.

5. The electroplating solution according to claim 4, wherein, The inorganic halogen compound comprises chlorides and / or bromides, and / or, The concentration of halide ions is above 0.03 mol / L and less than 1.7 mol / L.

6. The electroplating solution according to claim 4 or 5, wherein, The nickel ion supply source has a nickel ion molar concentration C. Ni molar concentration C of halide ions Halo The ratio of C Ni / C Halo Greater than 1 and less than 57.

7. The electroplating solution according to any one of claims 4 to 6, wherein, The nickel ion supply source has a nickel ion molar concentration C. Ni The molar concentration C of the sulfonic acid or its salt sulfo and the molar concentration C of halide ions Halo The following relationship must be satisfied: 0≤(C sulfo +C Halo -2×C Ni )≤0.6。 8. The electroplating solution according to any one of claims 1 to 7, wherein, The concentrations of each component are as follows: The nickel ion supply source is calculated to be 0.15 mol / L to 1.7 mol / L; and / or For the sulfonic acid or its salt, the concentration is 0.3 mol / L to 4 mol / L.

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, wherein, It does not actually contain any or all of sulfate ions, aminosulfonic acid or its salts, ammonia, and chelating agents.

11. The electroplating solution according to any one of claims 1 to 10, wherein, The pH is 4.5–5.

5.

12. A method for electroplating an article, comprising: The process of applying electricity 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 item contains zinc.

14. The method according to claim 12 or 13, wherein, The item in question is a ceramic electronic component.

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

Images