JP2010275613A - Tin electroplating solution and method of manufacturing electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tin electroplating solution preventing a deterioration in electrical characteristic of a ceramic electronic component by suppressing the corrosion of an element assembly in plating, and to provide a method of manufacturing the electronic component using the tin electroplating solution. <P>SOLUTION: The tin electroplating solution for the ceramic electronic component contains tin ion and has pH≥5 and ≤8, ≤0.3 mol/L concentration of ammonia and ammonium ion, and (molar concentration of chelate agent)/(molar concentration of tin ion) of ≤2.5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  Electrical Sn plating is used in the process of forming terminal electrodes of ceramic thermistors composed 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 on 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. Layers are formed continuously to form terminal electrodes. A neutral tin plating solution having a pH of 4 to 8 is often used for the electroplating of the Sn layer.

  Conventionally, there has been a problem that the electrical characteristics of a ceramic electronic component after plating are deteriorated as compared with the electrical characteristics before plating. One of the reasons is that the plating solution penetrates into the element body through a large number of pores present in the element body mainly made of ceramics and corrodes the element body. From such a viewpoint, as shown in Patent Document 1, a method has been proposed in which the viscosity of the plating solution is increased to suppress the penetration of the plating solution into the pores.

Japanese Patent Publication No. 7-23554

  However, according to the inventor's research, it has been found that the technique of simply adjusting the viscosity of the plating solution cannot sufficiently suppress the corrosion of the element body. Therefore, there is a demand for a plating solution that can sufficiently suppress corrosion of the element body and prevent deterioration of electrical characteristics of the ceramic electronic component due to plating.

  Accordingly, the present invention has been made in view of the above circumstances, and an object thereof is an electrolytic tin plating solution capable of suppressing corrosion of an element body during plating and preventing deterioration of electrical characteristics of a ceramic electronic component. Another object of the present invention is to provide an electronic component manufacturing method using the electrotin plating solution.

  In order to achieve the above object, the electrotin plating solution of the present invention is an electrotin plating solution for ceramic electronic components, contains tin ions, has a pH of 5 or more and 8 or less, and has a concentration of ammonia and ammonium ions. The ratio of the molar concentration of the chelating agent / the molar concentration of tin ions (the value of the ratio of the molar concentration of the chelating agent to the molar concentration of tin ions) is 2.5 or less.

  As in the above configuration, the corrosion of the ceramic electronic component body can be suppressed by minimizing the concentrations of the chelating agent, ammonia, and ammonium ions and increasing the pH as much as possible. If possible, it is preferred not to contain chelating agents, ammonia and ammonium ions.

  Preferably, the concentration of divalent tin ions is 0.15 mol / L or less. In an environment where the pH is high and the concentration of the chelating agent is low, if the tin ion concentration is higher than 0.15 mol / L, precipitation occurs during standing or energization, resulting in fluctuations in the composition of the plating solution, Stable plating tends to be difficult.

  Preferably, the sulfamate ion concentration is less than 0.5 mol / L. When the concentration of sulfamate ions is as high as 0.5 mol / L or more, precipitation occurs during energization, the composition of the plating solution varies, and stable plating tends to be difficult.

  The concentration of the cation having a solubility of hydroxide in water of 0.5 mol / L or more is preferably 0.5 mol / L or less, more preferably 0.3 mol / L or less. Examples of the cation having such a high solubility of hydroxide with respect to water include alkali metal ions such as Li ion, Na ion and K ion, and ammonium ion. Such cations move to the cathode periphery when energized and are concentrated to generate strong alkali and corrode the ceramic electronic component body. Therefore, the concentration can be suppressed to 0.5 mol / L or less. desirable.

  From this viewpoint, a chelating agent or a conductive salt made of a salt of Sr, Ca, or Mg may be included. Sr, Ca and Mg salts have very low solubility of hydroxide in water, so even when energized, they are concentrated in the periphery of the cathode and do not produce strong alkali, nor do they corrode the element. is there. The solubility of the alkaline earth metal is Mg <Ca <Sr <Ba.

  Furthermore, in order to achieve the above object, the method for producing a ceramic electronic component according to the present invention is a method that can be suitably carried out using the electrotin plating solution according to the present invention. A step of forming a tin layer by plating, wherein in the step, tin ions are included, the pH is 5 or more and 8 or less, the concentration ratio of ammonia and ammonium ions is 0.3 mol / L or less, An electrotin plating solution having a molar concentration / a molar concentration of tin ions of 2.5 or less 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 inconveniently large by 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, corrosion of the element body by the plating solution can be suppressed by minimizing the concentrations of the chelating agent, ammonia and ammonium ions in the plating solution and making the pH as high as possible. Thereby, deterioration of the electrical characteristics of the ceramic electronic component after plating can be suppressed.

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 the chelating agent density | concentration in a plating solution, and a corrosion distance. It is a figure which shows the relationship between ammonium ion concentration and 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 sides (ends) of the multilayer body 4 so as to cover the side surfaces thereof, and each ground electrode 5 is formed of the internal electrode 3 exposed from one side surface of the multilayer body 4. A group or a group of internal electrodes 3 exposed from the other surface of the laminate 4 is electrically connected.

  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. For semiconductor ceramics, glass containing Zn as a main component of varistors, thermistors and the like, and for dielectrics as a sintering aid is preferably used. 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, or Zn as a metal component.

  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 poor solderability due to mutual diffusion between the Sn layer 7b and the base electrode 5 due to heat during soldering, 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 Sn layer 7b described above. Hereinafter, the plating solution according to the present embodiment will be described.

  In the electrotin plating solution of this embodiment, the pH is set as high as possible to suppress the corrosion of the element body, and the concentrations of the chelating agent, ammonia and ammonium ions are minimized.

  The chelating agent is preferably not contained as much as possible, and may not be contained at all. Since the chelating agent has a large complex ion formation constant, when the chelating agent is contained, the element body itself made of ceramics tends to be easily dissolved. Specifically, when the ratio of the molar concentration of the chelating agent / the molar concentration of tin ions is 2.5 or less, the corrosion of the element body is significantly suppressed.

  The material of the chelating agent is not limited, and examples thereof include gluconic acid, glucoheptonic acid, gluconolactone, glucoheptonolactone, citric acid, pyrophosphoric acid, and salts with these alkali metals and alkaline earth metals. . Specific examples include sodium gluconate, magnesium gluconate, calcium citrate, and strontium pyrophosphate. Of these, gluconate is preferred because it can enhance the stability of the plating solution.

  Ammonia and ammonium ions are preferably not contained as much as possible, and may not be contained at all. When ammonia or ammonium ions are included, the corrosion of the element itself tends to proceed. Specifically, when the ammonium ion is 0.3 mol / L or less, the corrosion of the element body is significantly suppressed.

  Also, in plating solutions that contain as little chelating agent as possible and have a high pH, if the Sn concentration is high, the composition of the plating solution fluctuates due to precipitation during standing or energization, making stable plating difficult. It tends to be. For this reason, the Sn concentration is preferably small. However, if the Sn concentration is too small, the plating current decreases, the plating time becomes longer, and the productivity tends to be lowered. From such a viewpoint, the Sn concentration in the plating solution is preferably 0.05 to 0.15 mol / L.

  As the supply source of Sn, tin alkane sulfonate such as tin methanesulfonate, tin sulfate, tin sulfamate, tin chloride, stannous acetate, stannous oxide, stannous borofluoride, 2-hydroxyethanesulfone Examples include stannous acid, stannous 2-hydroxypropane sulfonate, and stannous phenol sulfonate. Among these, tin sulfate and tin sulfamate are unstable in the raw materials themselves and have a problem in handleability. Further, when tin sulfamate is used, there is a further problem that precipitation is likely to occur during continuous energization. Accordingly, among those described above, it is preferable to use tin methanesulfonate.

  Furthermore, in order to improve the electroconductivity of a plating solution, it is preferable that a conductive salt is included. Examples of the conductive agent include alkali metal, alkaline earth metal, or ammonia, alkanesulfonic acid such as methanesulfonic acid, sulfuric acid, sulfamic acid, acetic acid, borofluoric acid, 2-hydroxyethanesulfonic acid, and 2-hydroxypropanesulfone. Examples include acids and salts with acids such as phenolsulfonic acid, or chlorides. Specific examples include magnesium methanesulfonate, ammonium methanesulfonate, calcium chloride, strontium sulfate, sodium sulfate, ammonium chloride, sodium sulfamate and the like. Among these, ammonium salts such as ammonium chloride tend to corrode the element body, and sulfamate such as sodium sulfamate tends to precipitate when energized. In order to prevent such precipitation of sulfamate, the sulfamate ion concentration is preferably less than 0.5 mol / L.

  Furthermore, the concentration of the cation having a hydroxide solubility in water of 0.5 mol / L or more is preferably 0.5 mol / L or less, and more preferably 0.3 mol / L or less. Such cations can arise from, for example, chelating agents, conductive salts, or ammonium ions. Examples of cations whose hydroxide solubility in water is 0.5 mol / L or more include alkali metal ions such as Li ions, Na ions, K ions, and ammonium ions. Such cations move to the periphery of the cathode when energized and are concentrated to generate strong alkali, which tends to corrode the ceramic electronic component body. Therefore, it is desirable to suppress the concentration thereof.

For example, sodium gluconate is often used as a chelating agent. In this case, a large amount of sodium ions are present in the plating solution, and these sodium ions together with Sn ²⁺ ions during plating are around the ceramic electronic component (chip). , And a concentrated solution of sodium hydroxide is generated to become a strong alkali and the element body tends to be corroded. The same tendency occurs when the chelating agent is an alkali salt such as K or Li, or an ammonium salt.

  Therefore, among the materials exemplified as the chelating agent or the conductive salt, when a salt such as an alkali metal ion such as Li ion, Na ion or K ion or ammonium ion is used, the concentration of these salts is 0.5 mol / L or less is desirable, and 0.3 mol / L or less is more desirable. An example of such a chelating agent is sodium gluconate. Examples of the conductive salt include sodium sulfate, ammonium chloride, sodium sulfamate, and ammonium methanesulfonate.

  Alternatively, among the materials exemplified as the chelating agent or the conductive salt, a metal salt such as Sr, Ca, or Mg can be preferably used. As a result, corrosion of the element body is significantly suppressed without generating strong alkali around the chip during plating. Examples of such a chelating agent include magnesium gluconate, calcium citrate, strontium pyrophosphate, and the like. Examples of such a conductive salt include magnesium methanesulfonate, calcium chloride, strontium sulfate and the like.

  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 tin is electroplated on a ceramic electronic component with the above-described electrotin 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 using a cathode swing or a pump.

  Known conditions can be used as the plating conditions. For example, tin metal is usually used as the anode, but insoluble electrodes such as platinum-plated titanium plates may be used in some cases. The bath temperature is not particularly limited, and is preferably 10 ° C to 30 ° C. Plating conditions such as cathode current density and plating time can be appropriately determined by those skilled in the art according to the required film thickness of the tin layer. According to such a plating method according to the present embodiment, it is possible to suitably suppress the corrosion of the element body by the plating solution.

  Moreover, the plating solution and the plating method according to the present 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.

Example 1
In advance, five types of electrotin plating solutions A to E shown in Table 1 were prepared. The base electrode 7 of the chip capacitor (laminated body 4) having a main composition of the element body 2 of barium titanate and an outer shape of 1.6 × 0.8 × 0.8 mm is first subjected to nickel plating in a watt bath to 2 μm. The Ni layer 7a was formed, followed by tin plating with the plating solutions A to E to form a 4 μm Sn layer 7b. The corrosion distance of the element body was examined for the chips treated with each plating solution. The corrosion distance indicates an average value when ten chips after plating are sampled (sampled), and the thickness of the corrosion layer on the element body surface is measured by cross-sectional observation of the SEM. Table 2 and FIG. 4 show the measurement results of the corrosion distance together with the chelating agent / Sn ion molar ratio. The unit of numerical values in Table 1 is mol / L.

  As shown in Table 2 and FIG. 4, it was found that when the amount of chelating agent exceeds 2.5 times that of Sn ions, the corrosion distance tends to increase significantly. From this, it was confirmed that the molar ratio of chelating agent / Sn ion should be 2.5 or less.

(Example 2)
Ammonium methanesulfonate is added as a conductive salt to the plating solution B shown in Table 1 to prepare plating solutions B0 to B4, and the Sn layer 7b is formed using the plating solutions B0 to B4 under the same conditions as in Example 1. Ceramic electronic components were produced. The corrosion distance of this ceramic electronic component (chip) was examined. Table 3 and FIG. 5 show the results of the corrosion distance together with the ammonium ion concentration. In Table 3, the unit of numerical values in which the unit is not specified is mol / L.

  As shown in Table 3 and FIG. 5, when the ammonium ion concentration exceeds 0.3 moL / L, it has been found that the corrosion greatly increases. From this, it was confirmed that the ammonium ion concentration is preferably suppressed to 0.3 mol / L or less.

(Example 3)
Plating solutions B5 to B8 were prepared by adding sodium sulfamate as a conductive salt to the plating solution B0 shown in Table 3. And the presence or absence of precipitation was investigated after energizing 100 Ah / L to plating solution B0 and B5-B8. The results are shown in Table 4. In Table 4, the unit of numerical values is mol / L.

  As shown in Table 4, it was confirmed that precipitation occurred when the sulfamate ion concentration exceeded 0.5 mol / L. This precipitate is presumed to be nickel sulfamate.

Example 4
An electrotin plating solution having the main composition shown in Table 5 was prepared. The method for preparing the plating solution is as follows. 0.11 mol / L tin methanesulfonate, 1.10 mol / L gluconic acid, and 1.86 mol / L methanesulfonic acid are mixed, and the pH is adjusted to 4.0 with strontium hydroxide. Since the valence of Sr is 2, it is necessary to add twice the amount of gluconic acid and methanesulfonic acid in order to make the amount of chelating agent and conductive salt the same in terms of moles. Then, the main composition is composed of the element body 2 containing strontium titanate and 2% of Zn, and the 4 μm Sn layer 7b is formed on the base electrode 7 of the capacitor chip having a size of 1.6 × 0.8 × 0.8 mm. Formed. Thirty of these chips were randomly extracted and subjected to a high temperature load test under conditions of 140 ° C., 6.3 V, and 12 hours, and the insulation resistance (IR) before and after the test was measured. The proportion of chips with reduced insulation resistance after plating was 0/30. Here, when the resistance of the chip fell below 5 × 10 ⁸ Ω, it was considered that the resistance had decreased.

(Example 5)
Next, Sr was replaced with Mg in the plating solution of Example 4. The method for preparing the plating solution is as follows. The same amount of tin methanesulfonate, gluconic acid and methanesulfonic acid as in Example 4 were mixed, and the pH was adjusted to 4.0 with magnesium hydroxide. An Sn layer 7b was formed on the capacitor chip under the same conditions as in Example 4 using the plating solution. And the high temperature load test was done by the method similar to Example 4, and the insulation resistance before and behind a test was measured. The proportion of chips with reduced insulation resistance after plating was 0/30.

  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 ... Ceramic electronic component, 2 ... Element body, 3 ... Internal electrode, 4 ... Laminated body, 5 ... Base electrode, 7 ... Terminal electrode, 7a ... Ni layer, 7b ... Sn layer, 10 ... Unit structure.

Claims (7)

An electrotin plating solution for ceramic electronic components,
Contains tin ions,
pH is 5 or more and 8 or less,
The concentration of ammonia and ammonium ions is 0.3 mol / L or less,
The ratio of the molar concentration of the chelating agent / the molar concentration of tin ions is 2.5 or less,
Electro tin plating solution. The concentration of tin ions is 0.15 mol / L or less,
The electrotin plating solution according to claim 1. The sulfamate ion concentration is less than 0.5 mol / L,
The electrotin plating solution according to claim 1 or 2. The concentration of the cation having a solubility of hydroxide in water of 0.5 mol / L or more is 0.5 mol / L or less.
The electrotin plating solution according to claim 1. Including a chelating agent or a conductive salt comprising a salt of Sr, Ca, or Mg,
The electrotin plating solution according to claim 1. A step of forming a tin layer by electrotin plating on the base electrode of the ceramic element is provided.
In the step, tin ions are included, the pH is 5 or more and 8 or less, the concentration of ammonia and ammonium ions is 0.3 mol / L or less, and the ratio of the molar concentration of the chelating agent / the molar concentration of tin ions is 2.5. Use the following electrotin plating solution:
Manufacturing method of ceramic electronic components. The ceramic body contains Zn;
The manufacturing method of the ceramic electronic component of Claim 6.

Images