JP5141980B2 - Electro nickel plating solution and method for manufacturing electronic component - Google Patents

Description

  The present invention relates to an electric nickel plating solution suitably used for a ceramic electronic component and a method for producing an electronic component 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. The Watt bath is a plating solution containing nickel sulfate, nickel chloride and boric acid as main components and having a pH adjusted to 4 to 5, and is used at a temperature of 40 to 60 ° C. The chloride bath is a plating solution mainly composed of nickel chloride and boric acid and adjusted to a pH of 4 to 5, and is used at a temperature of 50 to 70 ° 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, dielectric products such as LTCCs and chip capacitors have become less prone to chemical resistance due to recent miniaturization and higher performance, and the same problems have arisen. Therefore, as shown in Patent Document 1, a method has been proposed in which a chelating agent is added to a 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 the chelating agent and a specific component of the plating solution dissolve 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 the element on the surface of the internal electrode. It is presumed that the body is melted and the thermal stress generated between the internal electrode and the element body is released to cause cracks. Besides such inconvenience, generally, a stable plating solution that does not cause decomposition or the like when energized in electroplating is required.

  Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to suppress the erosion of the element body and the occurrence of insulation failure and to have a highly stable electric nickel plating solution and the electric An object of the present invention is to provide a method for manufacturing an electronic component using a nickel plating solution.

  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, comprising nickel ions and an alkali having a concentration of 0.005 mol / L to 0.1 mol / L. It is characterized in that it contains metal ions, has a pH greater than 5 and less than 7, and an ion concentration of ions containing ammonium or ammonia is 0.2 mol / L or less.

  In the present invention having the above configuration, since the ion concentration of the alkali metal is suppressed to 0.1 mol / L or less, insulation failure and etching of the element body are suppressed. Moreover, although the detailed mechanism of action is still unclear, it was confirmed that the decomposition of the plating solution due to energization is satisfactorily suppressed when the ion concentration of the alkali metal is 0.005 mol / L or more. Furthermore, by adjusting the pH to be greater than 5 and less than 7, deterioration of the element body due to the plating solution can be suppressed. More specifically, by making the pH higher than 5, the etching of the element body by the plating solution is further suppressed, and if the pH is less than 7, the plating solution is constituted without adding a chelating agent. There is an advantage that can be. Furthermore, by suppressing the concentration of ions containing ammonium or ammonia as low as 0.2 mol / L or less, insulation failure and erosion of the element body are further suppressed.

  Here, as a component of the electro nickel plating solution, it is preferable not to contain sulfate ions 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. Specifically, for example, it is preferable to use a source other than nickel sulfate as a nickel ion supply source. More specifically, for example, nickel chloride is suitably used.

  Moreover, it is preferable not to contain chelating agents other than ammonia 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 effectively suppressed, and the occurrence of insulation failure after plating is reduced.

  Furthermore, the concentration of nickel ions is preferably 0.1 mol / L or more and 1 mol / L or less. If it is 0.1 mol / L or more, the plating current can be increased, and the productivity of nickel plating can be improved. Moreover, if it is 1 mol / L or less, it will become easy to adjust pH to 5-7 essentially without including a chelating agent as a component.

  Still further, in order to achieve the above object, a method for manufacturing a ceramic electronic component according to the present invention includes a step of forming a nickel layer by electro nickel plating on a base electrode of a ceramic element, wherein in the step, nickel ions, An alkali metal ion having a concentration of 0.005 mol / L or more and 0.1 mol / L or less, a pH of greater than 5 and less than 7, and an ion concentration of ions containing ammonium or ammonia of 0.2 mol / L or less. A certain electro nickel plating solution is used.

  In particular, when using a ceramic body containing Zn, the effect of the present invention is remarkable. Since the element body containing Zn is poor in chemical resistance of the element body, the corrosion of the element body becomes undesirably large in the treatment with the conventional plating solution, and there are cases where defects such as defective insulation are likely to occur. On the other hand, this problem can be sufficiently suppressed by using the method for manufacturing a ceramic electronic component according to the present invention.

  According to the present invention, plating is performed by using a plating solution containing nickel ions and alkali metal ions at a predetermined concentration, and suppressing the concentration of ions containing ammonium or ammonia in the plating solution to a predetermined concentration or less. It is possible to provide a highly stable electric nickel plating solution that suppresses corrosion of the element body due to the solution and occurrence of insulation failure. And productivity of a ceramic electronic component can be improved by using such an electric nickel plating solution.

It is a perspective view which shows schematic structure of a ceramic electronic component. It is sectional drawing of the II-II line 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 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.

  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. Particularly in the latter case, as the LTCC (parts) is miniaturized, the layer thickness is reduced. For this reason, the sintering temperature is further lowered, and the use examples are further increased.

  For the internal electrode 3, for example, a material mainly composed of Ag, Pd, Ni, Cu, or Al is used from the viewpoint 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 according to the present embodiment is suitably used for forming an electrode of a ceramic electronic component such as the Ni layer 7a described above. Hereinafter, the plating solution according to the present embodiment will be described.

  The electro nickel plating solution of the present embodiment contains nickel ions and alkali metal ions having a concentration of 0.005 mol / L or more and 0.1 mol / L or less, and has a pH greater than 5 and less than 7, ammonium or ammonia The ion concentration of ions containing is 0.2 mol / L or less.

  Among these, it is preferable that the density | concentration of nickel ion is 0.1 mol / L or more and 1 mol / L or less. In the case of less than 0.1 mol / L, the current value at the time of plating tends to decrease excessively, and the productivity of nickel plating tends to decrease. In addition, by setting the Ni ion concentration to 1 mol / L or less, basically, the pH can be appropriately adjusted to 5 to 7 without including a chelating agent.

  In this embodiment, the pH of the plating solution is adjusted to be larger than 5 and smaller than 7 in order to suppress corrosion of the element body during plating. The pH of the plating solution can be adjusted using an appropriate pH adjuster.

  The alkali metal ion is contained in an appropriate pH adjuster such as a conductive salt such as sodium sulfate, a chelating agent such as sodium citrate, or sodium hydroxide.

  Here, the concentration of the alkali metal ions is preferably 0.005 mol / L or more and 0.1 mol / L or less, more preferably 0.03 mol / L or more and 0.1 mol / L or less. If the alkali metal ion concentration is 0.005 mol / L or more, decomposition of the plating solution by energization can be effectively suppressed, and if the alkali metal ion concentration is 0.1 mol / L or less. It becomes easy to suppress poor insulation and inconvenient etching of the element body. Moreover, if the density | concentration of an alkali metal ion is 0.03 mol / L or more, the lifetime of a plating solution will become long and is more preferable.

  Further, ions containing ammonium or ammonia are contained in conductive salts such as ammonium chloride, chelating agents such as ammonium citrate, and pH adjusters such as ammonia and TMAH.

  The reason why the concentration of ions containing ammonium or ammonia is lowered to 0.2 mol / L or less is to suppress poor insulation and erosion of the element body.

  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.

  Further, it is preferable that sulfate ions are not contained in the plating solution as much as possible, and the concentration is more preferably 0.1 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, chelating agents other than ammonia have a large complex ion formation constant and a large amount of ceramic dissolution, so that they are preferably not contained in the plating solution as much as possible, and the concentration is more preferably 0.05 mol / L or less. . Thereby, dissolution of the frit of the base electrode is suppressed, and the occurrence of insulation failure after plating can be sufficiently reduced.

  An example of the electronickel plating solution that satisfies the above-described conditions includes a plating solution that includes nickel chloride, boric acid, and sodium hydroxide and has a pH adjusted to be greater than 5 and less than 7. Thus, by using nickel chloride instead of nickel sulfate as a nickel ion supply source, it becomes easy to suppress erosion of the element body. Further, by using sodium hydroxide instead of ammonia or nickel carbonate as a pH adjuster, a stable plating solution without decomposition after energization can be easily formed. At this time, by defining the upper limit value of the amount of sodium hydroxide added, poor insulation and erosion of the element body due to the presence of alkali metal ions are further suppressed. Moreover, boric acid acts (functions) effectively as a buffer that suppresses fluctuations in pH.

  The plating solution according to the present embodiment may contain a known additive such as a brightener or a surfactant as necessary, and even in that case, the type of additive is selected so as to satisfy the above-described conditions. It is preferable to select 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 not particularly limited, and 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 film 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. In the case where 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.

  Presence or absence of liquid decomposition at the initial stage of plating, corrosion distance of the ceramic electronic component (chip), poor insulation after plating when electroplating was performed on the ceramic electronic component using the plating solution of Experiment No. 1-32 shown in Table 1 Rate was evaluated. The corrosion distance is an average value when 10 chips after plating are sampled (sampled) and the thickness of the corrosion layer on the element body surface is measured by SEM cross-sectional observation. The insulation failure rate indicates the proportion of insulation failure when 100 chips after plating are extracted and insulation resistance is measured. The results are discussed below in order of experiment number. In Table 1, the blank part indicates 0.

(Experiment number 1: Ammonia is used as a pH adjuster)
1000 pieces of 1608 size capacitor chips made of a strontium titanate main composition and containing 2% ZnO were plated using a barrel plating apparatus having a capacity of 700 mL. Using the plating solution of composition No. 1 (pH adjusting agent is ammonia), 120 mL of Φ0.5 steel media is added as media, 90 mL of zirconia Φ5 media is added for stirring, and the barrel rotation speed is 20 rpm. Although a current of 5 A was applied, the bath voltage increased, severe bubbles were generated from the cathode, and a large amount of precipitation occurred after 10 minutes. The composition of the precipitate was nickel hydroxide Ni (OH) ₂ .

This is a composition in which the overvoltage of the plating solution is large and hydrogen is likely to be generated, and hydrogen is generated from the cathode after energization, and this raises the pH, thereby presuming that nickel hydroxide Ni (OH) ₂ was generated. Is done.

(Experiment No. 2: Use nickel carbonate as a pH adjuster)
Next, a similar experiment was performed by changing the pH adjuster of Experiment No. 1 to nickel carbonate (Experiment No. 2), and the result was the same as that of Experiment No. 1. Thus, even when nickel carbonate was used as a pH adjuster, the plating solution was decomposed after energization.

(Experiment No. 3-15)
Therefore, an experiment was conducted by replacing part of the pH adjuster with sodium hydroxide (Experiment No. 2-5). From these results, it was found that if the ion concentration of the alkali metal is 0.005 mol / L or more, decomposition of the plating solution immediately after energization does not occur. Furthermore, without adding nickel carbonate as a pH adjuster, sodium chloride was added to examine the effective upper limit of the alkali ion concentration (Experiment No. 6-15). As a result, it was found that as the alkali metal ion concentration increases, the corrosion distance increases, and when it exceeds 0.1 mol / L, insulation failure after plating occurs. The relationship between Na ion concentration, insulation failure, and corrosion distance is shown in FIGS. 4 and 5, respectively. It was confirmed that both the insulation failure and the corrosion distance increased when the Na ion concentration exceeded 0.1 mol / L.

  Moreover, when the cross section of the chip | tip with poor insulation was analyzed, it was confirmed that the crack has generate | occur | produced between electrodes. Moreover, the result of having analyzed the electrode surface cleaved from the crack part with the 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. As a result, it is estimated that the element body is dissolved, and as a result, the element body is melted, and the thermal stress generated between the internal electrode and the element body is released to cause a crack. However, the action is not limited to this.

(Experiment No. 16-21)
Next, ammonium chloride was added to the plating solution of Experiment No. 6, and the relationship between the ammonium ion concentration, corrosion of the element body, and insulation failure was examined (Experiment No. 16-21). In addition, the plating solution of experiment number 16 is the same as the plating solution of experiment number 6. It was found that the insulation failure and the corrosion distance increased as the amount of ammonium chloride increased. The relationship between the ammonium ion concentration, insulation failure, and corrosion distance is shown in FIGS. 7 and 8, respectively. When the ammonium ion concentration exceeded 0.2 mol / L, it was confirmed that both the insulation failure and the corrosion distance increased.

(Experiment No. 22-27)
Next, ammonium citrate was added as a chelating agent to the plating solution of Experiment No. 6, and the relationship between the concentration of the chelating agent, corrosion of the element body, and insulation failure was examined (Experiment No. 22-27). In addition, the plating solution of experiment number 22 is the same as the plating solution of experiment number 6. It can be seen that poor insulation and corrosion distance increase with increasing amount of ammonium citrate. The relationship between the chelate ion concentration, insulation failure, and corrosion distance is shown in FIGS. 9 and 10, respectively. It was confirmed that the insulation failure increased when the chelate ion concentration exceeded 0.05 mol / L.

(Experiment No. 28-32)
Next, nickel sulfate was added to the plating solution of Experiment No. 6, and the relationship between the sulfate ions and the corrosion of the element body and insulation failure was examined (Experiment Nos. 28 to 32). In addition, the plating solution of experiment number 28 is the same as the plating solution of experiment number 6. Here, the amount of Ni chloride was adjusted so that the Ni ion concentration in the plating solution remained unchanged. From these results, it was found that the corrosion distance increased as the amount of Ni sulfate increased. The relationship between the sulfate ion concentration and the corrosion distance is shown in FIG. It was confirmed that the corrosion distance increased when the sulfate ion concentration exceeded 0.1 mol / L.

  As shown in the above-described embodiments, there are few cations (alkali metal, ammonium ion), anions (sulfate ions), and chelating agents that promote dissolution of the element body and the electrode frit (glass component) contained in the plating solution. Therefore, it was confirmed that the erosion of the element body after plating was small and the occurrence of insulation failure could be greatly reduced. It has also been found that a stable and highly productive plating solution can be provided by containing an appropriate amount of alkali metal ions in the plating solution.

  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.

  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 (4)

An electro nickel plating solution for ceramic electronic components,
With nickel ions,
An alkali metal ion having a concentration of 0.005 mol / L or more and 0.1 mol / L or less,
pH is larger than 7 than 5, wherein the ion concentration of ammonium Mui on is not more than 0.2 mol / L,
Electro nickel plating solution. The concentration of sulfate ions is 0.1 mol / L or less,
The electro nickel plating solution according to claim 1. Comprising a step of forming a nickel layer on the base electrode of the ceramic element by electro nickel plating;
In the step, a nickel ion, and a alkali metal ions in the following concentrations 0.005 mol / L or more 0.1 mol / L, a larger than 7 than pH 5, the ion concentration of ammonium Mui on 0. Use an electro nickel plating solution that is 2 mol / L or less,
Manufacturing method of ceramic electronic components. The ceramic body contains Zn;
The method for manufacturing a ceramic electronic component according to claim 3 .

Images