JP2010007172A - Nickel electroplating liquid and plating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plating liquid and a plating method which can suppress the erosion of an element assembly and the generation of an insulation defect, and can efficiently apply nickel plating only to the part to be plated. <P>SOLUTION: The plating liquid is a nickel electroplating liquid for a ceramic electronic component and comprises nickel ions and ammonium ions of ≤0.3 mol/L, its pH is 5 to <7, and the ion concentration of alkali metal is ≤0.03 mol/L. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric nickel plating solution suitably used for ceramic electronic components and a plating method using the plating solution.

  Conventionally, Ni electroplating has been used in the manufacture of ceramic electronic parts made of thermistors, capacitors, inductors, LTCC (Low Temperature Co-fired Ceramics), varistors and their composites. For example, after applying a conductive paste such as silver or copper to the surface of a ceramic electronic component having an internal electrode and firing to form a base electrode, the Ni layer and Sn are selectively applied to the surface of the base electrode by electric barrel plating. A terminal electrode made of a layer is formed.

  Conventionally, for example, a watt bath or a chloride bath is used for electroplating of the Ni layer. Watt bath is a plating solution whose main component is nickel sulfate, nickel chloride and boric acid, and whose pH is adjusted to 4-5 with sodium hydroxide (NaOH), and is used at a temperature of 40-60 ° C. It is. The chloride bath is a plating solution mainly composed of nickel chloride, boric acid, and sodium sulfate and adjusted to pH 4 to 5 with sodium hydroxide, and is used at a temperature of 40 to 60 ° C. .

  Conventionally, semiconductor parts such as varistors and thermistors have poor chemical resistance, and there has been a problem that the element body is greatly eroded (etched) by a nickel plating solution typified by a watt bath or a chloride bath. In addition, with LTCC and chip capacitors, with the recent miniaturization and high performance, the chemical resistance of the element body becomes poor, and the same problem has arisen. Therefore, as shown in Patent Document 1, a method has been adopted in which a chelating agent is added to the plating solution to adjust the pH to, for example, 4 to 9, and to prevent erosion of the element body.

JP 2003-193285 A

  However, even when the plating solution described in Patent Document 1 is used, there is a problem in that insulation failure occurs in ceramic electronic components such as capacitors. This is because a specific component of the chelating agent and the plating solution dissolves the frit (glass component) of the base electrode, the plating solution passes through the base electrode and reaches the exposed body of the internal electrode, and between the internal electrodes. This is considered to be caused by melting of the element body and releasing the thermal stress generated between the internal electrode and the element body to generate cracks.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide an electro nickel plating solution and a plating method capable of suppressing the erosion of the element body and the occurrence of insulation failure. .

  In order to achieve the above object, an electro nickel plating solution of the present invention is an electro nickel plating solution for ceramic electronic components, which contains nickel ions and ammonium ions of 0.3 mol / L or less, and has a pH of 5. Higher than 7 The alkali metal ion concentration is 0.03 mol / L or less.

  In the present invention configured as described above, since the alkali metal ion concentration is suppressed to 0.03 mol / L or less, insulation failure and etching of the element body are suppressed. Further, by adjusting the pH to be higher than 5 and lower than 7, deterioration of the element body due to the plating solution can be suppressed. When the pH is less than 5, the etching of the element body with the plating solution is remarkable. When the pH is less than 7, the plating solution can be constituted without adding a chelating agent. Furthermore, when the concentration of ammonium ions is lowered to 0.3 mol / L or less, insulation failure and erosion of the element body can be suppressed.

  The concentration of ammonium ions is preferably 0.01 mol / L or more. Thereby, the erosion of the element body is further suppressed.

  It is preferable that sulfate ions are not contained as much as possible, and the concentration is preferably 0.01 mol / L or less. Thereby, the erosion of the element body is further suppressed. For example, a nickel ion supply source other than nickel sulfate is preferably used, and for example, nickel chloride is preferably used.

  It is preferable that chelating agents other than ammonia are not contained as much as possible, and the concentration is preferably 0.05 mol / L or less. Thereby, dissolution of the frit of the base electrode is suppressed, and insulation failure after plating is reduced.

  The concentration of nickel ions is preferably 1 mol / L or less and 0.1 mol / L or more. In order to make the pH 5 to 7 basically without containing a chelating agent, it is preferable that the Ni ion concentration is low as described above.

  The present invention has a remarkable effect when applied to a ceramic electronic component including an element body containing Zn. Since the element containing Zn has poor chemical resistance, the conventional plating solution causes large corrosion of the element and may cause defects such as poor insulation. However, the present invention suppresses defects. can do.

  In order to achieve the above object, an electro nickel plating solution of the present invention is an electro nickel plating solution for a ceramic electronic component, which contains nickel chloride, boric acid, and ammonia, and has a pH higher than 5 and lower than 7. It is.

  According to the above configuration, erosion of the element body is suppressed by using nickel chloride instead of nickel sulfate as a nickel ion supply source. In addition, by using ammonia instead of sodium hydroxide for pH adjustment, poor insulation and erosion of the element due to the presence of alkali metal ions are suppressed. Boric acid is used as a buffer that suppresses fluctuations in pH.

  The plating method according to the present invention is for electroplating nickel onto a ceramic electronic component using the above-described electro nickel plating solution. Thereby, the corrosion of the element body by the plating solution and the occurrence of insulation failure are suppressed.

  According to the plating solution and the plating method of the present invention, a plating solution containing nickel ions and a predetermined concentration of ammonium ions is used, and the ion concentration of alkali metal or the like in the plating solution is suppressed to a predetermined concentration or less. Therefore, it is possible to suppress the corrosion of the element body due to the plating solution and the occurrence of insulation failure.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios. Further, the following embodiments are exemplifications for explaining the present invention, and are not intended to limit the present invention only to the embodiments. Furthermore, the present invention can be variously modified without departing from the gist thereof.

<Examples of ceramic electronic components>
FIG. 1 is a perspective view showing an example of a ceramic electronic component to be subjected to electroplating processing according to the present invention. 2 is a cross-sectional view taken along line II-II in FIG.

  The ceramic electronic component 1 has a laminated body 4 including an element body 2 made of ceramics and a plurality of internal electrodes 3 formed in the element body 2. In other words, the element body 2 and the internal electrodes 3 are laminated. At least one unit structure 10 is provided. More specifically, the internal electrodes 3 having end portions exposed on one side surface of the multilayer body 4 and the internal electrodes 3 having end portions exposed on the other side surface of the multilayer body 4 are alternately stacked. . Base electrodes 5 and 5 are provided on both side surfaces of the laminate 4 so as to cover the side surfaces, and each base electrode 5 is a group of internal electrodes 3 exposed from one side surface of the laminate 4 or It is electrically connected to the group of internal electrodes 3 exposed from the other surface of the laminate 4.

  The element body 2 of the ceramic electronic component 1 is made of ceramics, specifically, semiconductor ceramics or dielectric ceramics. In both cases of semiconductor ceramics and dielectric ceramics, the element body 2 may contain Zn. In semiconductor ceramics, Zn is preferably used as the main component of varistors, thermistors, etc., and in dielectrics, Zn is used as a sintering aid. In particular, in the latter case, the thinning of the LTCC has progressed, and as a result, the sintering temperature has further decreased and the number of use cases has increased.

  For the internal electrode 3, for example, a material mainly composed of Ag, Pd, Ni, Cu, or Al is used in terms of enabling reliable ohmic contact with the element body 2. There is no limitation.

  The base electrode 5 is obtained, for example, by applying and baking a conductive paste on the side surface of the multilayer body 4. Examples of the conductive paste for forming the base electrode 5 mainly include glass powder (frit), organic vehicle (binder), and metal powder. By firing the conductive paste, the organic vehicle is The base electrode 5 that volatilizes and finally contains a glass component and a metal component is formed. In addition, you may add various additives, such as a viscosity modifier, an inorganic binder, and an oxidizing agent, to an electrically conductive paste as needed. For example, the base electrode 5 contains Ag, Cu, and Zn as metal components.

  As shown in FIG. 3, terminal electrodes 7 and 7 are further formed on the surfaces of the base electrodes 5 and 5 of the ceramic electronic component 1 by electroplating. These terminal electrodes 7 and 7 are joined to, for example, electrodes on the wiring board by solder or the like. Each terminal electrode 7 has, for example, a two-layer structure including a Ni layer 7a and a Sn layer 7b that are stacked from the base electrode 5 side. The Ni layer 7a functions as a barrier metal that prevents the Sn layer 7b and the base electrode 5 from contacting each other and prevents corrosion of the base electrode 5 by Sn, and has a thickness of, for example, about 2 μm. Further, the Sn layer 7b has a function of improving the wettability of the solder, and the thickness thereof is, for example, about 4 μm.

<Plating solution>
The plating solution and the plating method according to this embodiment are suitably used for forming electrodes of ceramic electronic components such as the Ni layer 7a described above. Hereinafter, the plating solution and the plating method according to the present embodiment will be described.

  The electric nickel plating solution of this embodiment contains nickel ions and 0.3 mol / L or less ammonium ions, and has a pH higher than 5 and lower than 7.

  Among these, the concentration of nickel ions is preferably 1 mol / L or less and 0.1 mol / L or more. In order to make the pH 5 to 7 basically without containing a chelating agent, it is preferable that the Ni ion concentration is low as described above.

  The reason why the concentration of ammonium ions is as low as 0.3 mol / L or less is to suppress poor insulation and erosion of the element body. Ammonium ions are contained in conductive salts such as ammonium chloride, chelating agents such as ammonium citrate, pH adjusters such as ammonia and TMAH. However, it is preferable that the concentration of these ions is 0.01 mol / L or more than not containing ammonium ions completely. This is because it has been found in the following examples that the erosion of the element body is suppressed.

  Further, by adjusting the pH to be higher than 5 and lower than 7, corrosion of the element body during plating can be suppressed.

  In order to reduce the corrosion of the element body by the plating solution, the temperature of the plating solution is preferably as low as possible, for example, at room temperature.

  Examples of unnecessary components in the plating solution according to the present embodiment include alkali metal ions. It is preferable not to contain alkali metal ions as much as possible, and the ion concentration is preferably 0.03 mol / L or less. Thereby, the insulation defect and the etching of the element body are suppressed.

  Alkali metal ions are contained in a conductive salt such as sodium sulfate, a chelating agent such as sodium citrate, and a pH adjuster such as sodium hydroxide. Preferably no components are used.

  The plating solution preferably contains as little sulfate ion as possible, and the concentration is preferably 0.01 mol / L or less. Thereby, the erosion of the element body is further suppressed. For example, a nickel ion supply source other than nickel sulfate is preferably used, and for example, nickel chloride is preferably used.

  Furthermore, it is preferable that a chelating agent other than ammonia is not contained in the plating solution as much as possible, and the concentration is preferably 0.05 mol / L or less. Thereby, dissolution of the frit of the base electrode is suppressed, and insulation failure after plating is reduced.

  An example of the electro nickel plating solution that satisfies the above-described conditions includes a plating solution that contains nickel chloride, boric acid, and ammonia, and has a pH adjusted to be higher than 5 and lower than 7. Thus, by using nickel chloride instead of nickel sulfate as a nickel ion supply source, erosion of the element body is suppressed. In addition, by using ammonia instead of sodium hydroxide for pH adjustment, poor insulation and erosion of the element due to the presence of alkali metal ions are suppressed. Boric acid is used as a buffer that suppresses fluctuations in pH.

  The plating solution according to this embodiment may contain known additives such as brighteners and surfactants as necessary, but in these cases as well, the additive It is preferable to select the type and adjust the amount.

  The plating method according to the present embodiment is a method in which nickel is electroplated on a ceramic electronic component with the above-described electronickel plating solution. As a plating method, for example, barrel plating can be used. If necessary, the agitation can be carried out by a method of flowing the plating solution by air agitation, cathode swing, pump or the like.

  Known conditions can be used as the plating conditions. As the anode, nickel metal is usually used, but insoluble electrodes such as a titanium plate plated with platinum can also be used in some cases. The bath temperature is preferably 10 ° C to 30 ° C. The plating conditions such as the cathode current density and the plating time can be appropriately determined by those skilled in the art according to the required thickness of the nickel layer. According to the plating method according to the present embodiment, the corrosion of the element body by the plating solution and the occurrence of insulation failure are suppressed.

  The plating solution and the plating method according to this embodiment can be preferably used for a ceramic electronic component including an element body containing Zn. This is because, when Zn is contained, the chemical resistance of the element body becomes poor, so that the effect of the plating solution according to the present embodiment becomes more remarkable.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  1000 pieces of 1608 sized capacitor chips made of a strontium titanate main composition and containing 2% ZnO were plated by a barrel plating apparatus having a capacity of 300 mL. 80 mL of Φ1.2 steel media was added as a medium, and plating was performed at room temperature for 20 hours at a current value of 1.5 A with a barrel rotation speed of 20 rpm. The composition of the plating solution is as shown in Experiment No. 1 in Table 1 below. The main composition is nickel chloride and boric acid, and the pH is adjusted with ammonia. Ten chips after plating were extracted, and the thickness of the corrosion layer on the surface of the element body was evaluated by SEM cross-sectional observation. As a result, the average was 0.7 μm. Further, when 100 chips were plated and the insulation resistance was measured, the number of insulation failures (IR failures) was 0/100.

  Next, sodium sulfate was added to this plating solution, and the same evaluation as above was performed (experiment numbers 2 to 11). It can be seen that as the amount of sodium sulfate increases, insulation failure and corrosion distance increase. The relationship between the Na ion concentration, the insulation failure, and the corrosion distance is shown in FIGS. It can be seen that both the insulation failure and the corrosion distance increase when the Na ion concentration exceeds 0.03 mol / L.

  Analysis of the cross section of the poorly insulated chip confirmed that cracks occurred between the electrodes. Moreover, the result of cleaving from the crack part and analyzing the electrode surface with a time-of-flight secondary ion mass spectrometer (TOF-SIMS) is shown in FIG. In FIG. 6, the analysis results in the cracked part (Crack area) and the cracked part (Flesh area) are shown vertically. From the results shown in FIG. 6, the cause of the crack is that sodium ions in the plating solution move to the periphery of the terminal electrode during plating to form a highly alkaline region, and this solution passes through the void of the base electrode to expose the internal electrode. It is considered that cracks are generated by reaching the surface of the element body, melting the element body, and releasing the thermal stress generated between the internal electrode and the element body.

  Next, ammonium chloride was added to the plating solution of Experiment No. 1 and the same evaluation as in Example 1 was performed (Experiment Nos. 13 to 18). Note that the plating solution of Experiment No. 12 is the same as the plating solution of Experiment No. 1. It can be seen that as the amount of ammonium chloride increases, the insulation failure and the corrosion distance increase. The relationship between the ammonium ion concentration, insulation failure, and corrosion distance is shown in FIGS. It can be seen that both the insulation failure and the corrosion distance increase when the ammonium ion concentration exceeds 0.3 mol / L.

  Next, the same evaluation as Example 1 was performed by adding ammonium citrate as a chelating agent to the plating solution of Experiment No. 1 (Experiment Nos. 20 to 24). In addition, the plating solution of experiment number 19 is the same as the plating solution of experiment number 1. It can be seen that as the amount of ammonium citrate increases, insulation failure and corrosion distance increase. The relationship between chelate ion concentration, insulation failure, and corrosion distance is shown in FIGS. It can be seen that the insulation failure increases when the chelate ion concentration exceeds 0.05 mol / L.

  The pH of Example 1 was adjusted with Ni carbonate, a plating solution containing no alkali metal was prepared, and the same evaluation as in Example 1 was performed (Experiment No. 25). In this case, no insulation failure occurs, but the corrosion distance increases. It can be seen that there is less corrosion of the element body with a small amount of ammonium ions.

  Next, Ni sulfate was added to the plating solution of Experiment No. 1 and the same evaluation as in Example 1 was performed (Experiment Nos. 27 to 30). In addition, the plating solution of experiment number 26 is the same as the plating solution of experiment number 1. Here, the amount of Ni chloride is adjusted so that the Ni ion concentration in the plating solution remains unchanged. It can be seen that the corrosion distance increases as the amount of Ni sulfate increases. The relationship between the sulfate ion concentration and the corrosion distance is shown in FIG. It can be seen that the corrosion distance increases when the sulfate ion concentration exceeds 0.1 moL / L.

  As shown in Examples 1 to 5 described above, a cation (alkali metal, ammonium ion), an anion (sulfate ion), and a chelating agent that promote dissolution of the base and electrode frit (glass component) in the plating solution. Since almost no inclusion, the erosion of the element body after plating was small, and the occurrence of insulation failure could be greatly reduced.

  INDUSTRIAL APPLICABILITY The present invention can be widely used for plating treatment of ceramic electronic parts including thermistors, capacitors, inductors, LTCC (Low Temperature Co-fired Ceramics), varistors, and composite parts thereof.

It is a perspective view which shows schematic structure of a ceramic electronic component. It is sectional drawing of the II-II line | wire of FIG. It is a schematic sectional drawing which shows the structure where the terminal electrode was formed by plating on the outer side of the base electrode of the ceramic electronic component. It is a figure which shows the relationship between Na ion concentration in a plating solution, and insulation (IR) defect. It is a figure which shows the relationship between Na ion concentration in a plating solution, and a corrosion distance. It is a figure which shows the result of cleaving from the part of a crack and analyzing the electrode surface by TOFSIMS. It is a figure which shows the relationship between the ammonium ion concentration in a plating solution, and insulation defect. It is a figure which shows the relationship between the ammonium ion concentration in a plating solution, and a corrosion distance. It is a figure which shows the relationship between the chelating agent density | concentration in plating solution, and insulation defect. It is a figure which shows the relationship between the chelating agent density | concentration in plating solution, and insulation defect. It is a figure which shows the relationship between the sulfate ion concentration in a plating solution, and a corrosion distance.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,9 ... Ceramic electronic component, 2 ... Element body, 3 ... Internal electrode, 4 ... Laminated body (sintered body), 5 ... Base electrode, 7 ... Terminal electrode, 7a ... Ni layer, 7b ... Sn layer, 10 ... Unit structure.

Claims (8)

An electro nickel plating solution for ceramic electronic components,
With nickel ions,
Containing 0.3 mol / L or less of ammonium ions,
pH is higher than 5 and lower than 7, and the alkali metal ion concentration is 0.03 mol / L or less,
Electro nickel plating solution. The ammonium ion concentration is 0.01 mol / L or more,
The electrolytic nickel plating solution according to claim 1. The concentration of sulfate ions is 0.01 mol / L or less,
The electro nickel plating solution according to claim 1 or 2. The concentration of nickel ions is 1 mol / L or less,
The electro nickel plating solution according to claim 1. The concentration of the chelating agent other than ammonia is 0.05 mol / L or less,
The electro nickel plating solution according to claim 1. Applied to a ceramic electronic component comprising a body containing Zn,
The electro nickel plating solution according to claim 1. An electro nickel plating solution for ceramic electronic components,
Nickel chloride,
Boric acid,
Including ammonia,
pH is higher than 5 and lower than 7.
Electro nickel plating solution.   A plating method in which nickel is electroplated on a ceramic electronic component with the electric nickel plating solution according to claim 1.

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