JPH09165685A - Method for plating on ceramics and dielectric resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to efficiently produce a dielectric resonator having excellent characteristics by making it possible form an electrode layer at adequate adhesive strength on the surface of a ceramic even if the ceramic surface is not roughened. SOLUTION: The dielectric ceramic 1 is first immersed into an aq. zinc acetate soln. and, thereafter, the ceramic is dried and calcined, by which the zinc oxide thin film 2 is formed on the surface of the dielectric ceramic 1. The dielectric ceramic 1 is then immersed into an aq. palladium chloride soln. to form a catalyst film 3. The dielectric ceramic 1 is thereafter immersed into an aq. copper sulfate soln. and is subjected to electroless plating, by which a copper plating layer (electrode layer) 4 is formed thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of plating a ceramic, which is preferably used when an electrode layer is formed on the surface of a dielectric ceramic to form a dielectric resonator.

[0002]

2. Description of the Related Art Conventionally, when a dielectric resonator or a dielectric filter is made of a dielectric ceramic, a Cu plating layer is deposited on the surface of the dielectric ceramic by electroless plating to form an electrode layer. Is known to do. Conventionally, such electroless copper plating on the ceramic surface has been performed by the procedure shown in FIG. 3, for example.

First, the surface of the ceramic 11 (FIG. 3 (a)) is roughened by etching with an etching solution such as strong acid or strong alkali (FIG. 3 (b)). Next, as a pretreatment for increasing the reactivity (Cu deposition reaction) of the electroless copper plating on the surface of the ceramic 11, sensitization using Sn ²⁺ ions 12 (FIG. 3C) was performed, and subsequently, Pb ²⁺ ion 13
Is used for catalysis (FIG. 3 (d)). Then, after this, the copper plating layer 14 on the surface of the ceramic 11 is deposited by electroless plating (FIG. 3E).

[0004]

By roughening the ceramic surface prior to electroless plating as described above, the adhesion strength between the ceramic and the plating layer is improved by the anchor effect, and an appropriate adhesion strength is obtained. It is necessary to get it. However, when the plated layer formed on the roughened ceramic surface is used as an electrode layer of a dielectric resonator or the like, the conductor loss increases due to the effect of the skin effect. Therefore, the obtained dielectric resonator has a disadvantage that the Q (Qu) value at the time of no load is low. Moreover, the influence of the conductor loss of the electrode layer increases as the size and frequency of the dielectric resonator increase, which is one of the obstacles to the size reduction and frequency increase of the dielectric resonator. . Further, the etching solution of a strong acid or a strong alkali used for roughening the ceramic surface has a variation in surface roughness due to compatibility with the ceramic material to be etched, and as a result, Qu varies depending on the ceramic material. There are inconveniences such as large variation in the values, and time and labor required to develop etching solutions having compositions suitable for various ceramic materials.

The present invention has been made in view of the above circumstances, and enables the dielectric layer having excellent characteristics to be formed by forming an electrode layer on the surface of the ceramic with an appropriate adhesion strength without roughening the surface. It is an object of the present invention to provide a method for plating ceramics that enables efficient manufacture of a container.

[0006]

In order to solve the above-mentioned problems, the method of plating a ceramic according to claim 1 of the present invention comprises depositing a zinc oxide thin film on the surface of the ceramic, and then applying the zinc oxide thin film surface. It is characterized in that electroless copper plating is applied to. The method of plating a ceramic according to claim 2 further comprises a step of forming the zinc oxide thin film on the surface of the ceramic by immersing the ceramic in an aqueous solution of zinc acetate, followed by drying and firing, and after the step of forming the binder layer. A catalytic step of immersing the ceramic in an aqueous palladium chloride solution to catalyze it, and an electroless plating step of immersing the ceramic in an aqueous solution of copper sulfate to form a copper plating layer after the catalytic step. It is characterized by. The dielectric resonator according to claim 3, wherein the dielectric ceramic formed into a columnar shape, a through hole penetrating from one end surface to the other end surface of the dielectric ceramic, and an internal electrode layer provided on the inner surface of the through hole. And an external electrode layer provided on an outer peripheral surface other than one end surface of the dielectric ceramic, wherein at least one of the internal electrode layer and the external electrode layer forms a zinc oxide thin film on the dielectric ceramic. It is characterized by comprising a copper plating layer formed through the above. The dielectric resonator according to claim 4 is characterized in that at least a part of the zinc oxide thin film is a catalyst film substituted with palladium ions, and the copper plating layer is formed thereon. To do.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
FIG. 1 is a schematic process diagram showing an example of a method for plating a ceramic according to the present invention. First, ceramic 1 (Fig. 1 (a))
A zinc oxide (ZnO) thin film 2 serving as a binder layer is adhered to the surface of the (the binder layer forming step, FIG.
(B)). This binder layer forming step can be performed by using various methods as long as the zinc oxide thin film 2 can be adhered to the ceramic surface with an appropriate adhesion strength. If the zinc oxide thin film 2 is too thick, it takes time to form the film.
If it is too thin, the adhesion strength with the plating cannot be obtained.
The thickness is preferably about 5 to 2 μm. For example, first, with the ceramic 1 immersed in an aqueous solution of zinc acetate,
After defoaming using a vacuum pump, return to normal pressure and leave. After soaking, the zinc oxide thin film 2 is formed by drying and further baking. The zinc oxide thin film 2 is preferably dried at a heating temperature of 100 to 120 ° C. and a drying time of about 5 to 30 minutes. The zinc oxide thin film 2 is preferably fired at a heating temperature of 400 to 600 ° C. and a firing time of about 10 to 60 minutes. Then, the dipping, drying and firing are repeated until the zinc oxide thin film 2 has a preferable thickness.

Next, as a pretreatment for increasing the reactivity (Cu deposition reaction) of the electroless copper plating on the surface of the ceramic 1, catalysis is performed (catalyzing step, FIG. 1 (c)). This catalyzing step is carried out by immersing the ceramic on which the zinc oxide thin film 2 is formed in an aqueous solution of palladium chloride and substituting part of the zinc oxide thin film 2 with palladium ions to form the catalyst coating 3 on the surface. . Here, since the surface of the zinc oxide thin film 2 is replaced with palladium ions, the thickness of the zinc oxide thin film 2 itself becomes thin.
If the film thickness is too thin, the adhesion strength with the plating cannot be obtained. Therefore, in the catalysis process, the film thickness is 0.1 μm.
It is necessary to control the reaction conditions so that the zinc oxide thin film 2 of m or more remains. After catalyzing in this way, the ceramic is thoroughly washed with water.

Subsequently, electroless plating is performed on the ceramic surface on which the catalyst coating 3 is formed to form a copper plating layer 4 (electroless plating step, FIG. 1D). This electroless plating step is performed by immersing the ceramic in an appropriately prepared electroless copper plating bath. As the electroless copper plating bath, for example, an aqueous copper sulfate solution having an appropriate composition is used. Then, the deposition rate and the density of the copper plating layer are changed by changing the composition and the temperature. For example, if electroless plating is performed at room temperature using a plating bath with a relatively low concentration of copper sulfate, a dense plating layer with a low deposition rate is obtained, and a plating bath with a relatively high concentration of copper sulfate is used. If the electroless plating is performed by heating the plating bath, the plating layer becomes rough but the deposition rate becomes faster.

Therefore, in order to increase the production efficiency and to form a relatively high quality copper plating layer, first, electroless plating is performed at room temperature using a plating bath having a relatively low concentration of copper sulfate to form a ceramic surface. A method for obtaining a copper plating layer 4 having a desired film thickness by performing thin copper plating on the substrate, subsequently increasing the concentration of copper sulfate, and performing thick copper plating using a plating bath heated to about 50 ° C. Is used. For example, when forming a copper plating layer 4 having a thickness of about 4 to 6 μm as an electrode layer of a dielectric resonator, first, thin copper plating is performed to a thickness of 1 μm.
It is preferable to form a copper plating layer 4 having a thickness of about μm and further perform thick copper plating on the copper plating layer 4. After completion of electroless plating, annealing treatment is performed in a N ₂ atmosphere furnace. The annealing temperature is preferably about 300 to 500 ° C.

By thus forming the copper plating layer 4 on the surface of the ceramic 1 with the zinc oxide thin film 2 interposed therebetween, a suitable adhesion strength can be obtained without roughening the surface of the ceramic 1 prior to electroless plating. Obtainable. Further, the surface of the zinc oxide thin film 2 formed on the surface of the ceramic 1 is not roughened, but the surface of the zinc oxide thin film 2 is flattened more than the surface of the ceramic 1, which is sufficiently smooth. Therefore, the surface roughness of the interface between the copper plating layer 4 formed on the zinc oxide thin film 2 and the zinc oxide thin film 2 below it is the same as that of the conventional roughened ceramic 11 and copper plating layer 14. In comparison, it is sufficiently small. Therefore, when the copper plating layer 4 formed on the ceramic 1 is used as an electrode layer of a dielectric resonator or the like, the adverse effect of the skin effect is reduced and the conductor loss can be reduced. Further, since the zinc oxide thin film 2 as the binder layer is basically free of incompatible materials and can be easily applied to various ceramic materials having different compositions, it is troublesome to develop a conventional etching solution. It is possible to improve the manufacturing efficiency by eliminating the disadvantage that it takes time. Also, the variation in surface roughness due to the difference in the type of material is small.

The ceramic plating method of the present invention is suitable for forming an electrode layer of a dielectric resonator. FIG. 2 is a perspective view showing an embodiment of the dielectric resonator. The dielectric resonator of this example is a dielectric ceramic 2 formed in a columnar shape.
1 is formed with a through hole penetrating from the upper end surface to the lower end surface, the internal electrode layer 22 is provided on the inner surface of the through hole, and the external electrode layer 23 is provided on the outer surface other than the upper end surface of the dielectric ceramic 21.
Is provided. The internal electrode layer 22 and the external electrode layer 23 are composed of a copper plating layer formed on the dielectric ceramic 21 via a zinc oxide thin film (not shown).

The dielectric resonator of this embodiment can be manufactured as follows. First, for example, an organic binder is added to a dielectric ceramic material powder such as Ba-Ti system or Ba-Ti-Nd system, and the mixture is molded by a method such as extrusion molding, and then fired at a high temperature of several thousand and several hundred degrees Celsius. The cylindrical dielectric ceramic 21 is molded by using a sintered body. Next, according to the procedure shown in FIG.
A copper plating layer is formed on the entire surface of the sheet by electroless plating.
That is, after depositing a zinc oxide thin film on the entire surface of the dielectric ceramic 21, a catalytic film is formed on at least a part of the zinc oxide thin film by performing a catalytic treatment using palladium ions. Then, electroless copper plating is applied thereon to form a copper plating layer (including the internal electrode layer 22 and the external electrode layer 23). The thickness of the electrode layers (copper plated layers) 22 and 23 in the dielectric resonator is generally set to be equal to or larger than the required thickness because the required thickness is determined by the frequency band used. Thereafter, the copper plating layer on the upper end surface of the dielectric ceramic 21 is removed by cutting and polishing, and the one end surface is further cut and polished to change the length of the internal electrode layer 22 to adjust the resonance frequency. .

In the dielectric resonator thus formed, the surface of the dielectric ceramic 21 is not roughened,
Since the internal electrode layer 22 and the external electrode layer 23 are formed through the binder layer made of a zinc oxide thin film, the surface roughness of the interface between these electrode layers 22 and 23 and the zinc oxide thin film as the lower layer is Is sufficiently smaller than the interface between the roughened ceramic 11 and the electrode layer 14. Therefore,
The adverse effect of the skin effect on the electrode layers 22 and 23 is reduced, and the increase in conductor loss is suppressed. As a result, the characteristics (Qu value) of the dielectric resonator are improved. In particular, when the surface roughness of the ceramic 21 itself is smaller than the thickness of the electrode layers 22 and 23, the adverse effect of the skin effect becomes extremely small, so that Qu close to the theoretical value can be obtained even when the operating frequency becomes high. be able to. Further, the improvement of Qu enables downsizing when a dielectric resonator made of the same material as the conventional one and having the same use frequency is formed. Furthermore, since the surface of the dielectric ceramic 21 is not roughened by using an etching solution, variations in surface roughness due to differences in the types of ceramic materials are small, and as a result the characteristics (Qu value) of the dielectric resonator are stable. To do.

[0015]

【Example】

(Example 1) Using the plating method of the present invention, a rectangular tube-shaped dielectric resonator as shown in FIG. 2 was produced. First, a dielectric ceramic molded into a rectangular tube shape and a 0.1 mol / l zinc acetate aqueous solution were prepared. The size of the dielectric ceramic is an outer diameter of 2 mm × 1.8 mm, an inner diameter of 0.4 mm square, and a length of 5.3 mm.
It was used at a ratio of 50 ml per piece. Then, the dielectric ceramic is dipped in an aqueous solution of zinc acetate, defoamed for about 1 minute using a vacuum pump, then returned to normal pressure and dipped 1
It was left for 0 minutes. Next, it was dried at 120 ° C. for about 5 minutes and then baked at 400 ° C. for 30 minutes. These dipping, drying and firing were repeated 10 times to form a ZnO (zinc oxide) thin film having a film thickness of 0.5 μm or more on the surface of the dielectric ceramic. Next, the dielectric ceramic to which the ZnO thin film was deposited was immersed in an aqueous palladium chloride solution for about 5 minutes to replace a part of the ZnO thin film with palladium ions to carry out catalysis.

After washing with running water for 10 minutes or more, electroless copper plating was performed. That is, OPC-at about 25 ° C
The catalyzed dielectric ceramic was immersed in an electroless copper plating bath of 700 electroless copper plating M (manufactured by Okuno Chemical Industries Co., Ltd.) for about 30 minutes to form a copper plating layer having a thickness of about 1 μm. This dielectric ceramic was O
The copper plating layer was further thickened by further immersing it in an electroless copper plating bath called PC Copper T (manufactured by Okuno Chemical Industries Co., Ltd.), and finally a copper plating layer having a film thickness of 10 μm was formed on the entire surface of the dielectric ceramic. Then, after annealing at 400 ° C. in an N ₂ atmosphere furnace, the copper plating layer on one end face of the dielectric ceramic was removed by cutting and polishing to obtain a dielectric resonator. The resonance frequency was adjusted to 1470 MHz by further cutting and polishing one end surface of the dielectric resonator. With respect to the 10 obtained dielectric resonators, the Qu value and the adhesion strength of the copper plating layer were evaluated. The results are shown in Table 1 below. The adhesion strength of the copper plating layer was evaluated by the tensile strength measured as follows. That is, first, a metal wire is soldered to the surface of the copper plating layer. At this time, the area to be soldered is 4 mm ² . Then, the stress used for pulling the metal wire to peel off the copper plating layer is measured.

[0017]

[Table 1]

Comparative Example 1 A dielectric resonator was produced by a conventional method, that is, a method of electroless plating after roughening a ceramic surface. First, a dielectric ceramic molded in a rectangular tube shape similar to that in the above-mentioned Example 1 was prepared, and 98% thereof was prepared.
Sulfuric acid ... 750 ml / l, 55% hydrofluoric acid ... After immersing in an etching solution having a composition of 250 ml / l to roughen the surface,
Sensitization was performed by immersing in a stannous chloride aqueous solution. Then, after sufficiently washing with water, catalysis, electroless copper plating, annealing, and cutting and polishing were sequentially performed in the same manner as in Example 1 to fabricate a dielectric resonator having a resonance frequency of 1470 MHz. Regarding the obtained dielectric resonator, the above-mentioned Example 1 was used.
When the Qu value and the tensile strength were examined in the same manner as
The u value was about 150, and the tensile strength was about 8 kg / 4 mm ² .

From the results of Example 1 and Comparative Example 1 above,
In Comparative Example 1, the Qu value is 150 (about 50 of the theoretical value).
%), In Example 1, the average Qu value increased to about 190 (about 80% of the theoretical value),
It can be seen that the characteristics of the dielectric resonator are improved. Regarding the tensile strength, the average value obtained in Example 1 and Comparative Example 1
It was almost the same as the value obtained in. Further, the minimum value of the tensile strength in Example 1 is smaller than the value obtained in Comparative Example 1, but it is usually within the permissible range in the field.
It can be said that there is no problem in practical use because it has secured at least kg / 4mm ² . As described above, according to the present invention, the electrode layer (copper plating layer) can be formed with appropriate adhesion strength without roughening the surface of the ceramic dielectric, and as a result,
It was confirmed that the characteristics of the dielectric resonator can be improved.

In the above embodiment, the method of forming the zinc oxide thin film is the method of immersing in the zinc acetate aqueous solution, but the method is not limited to this and various methods can be used.
Also, although the rectangular resonator is taken as an example of the dielectric resonator, the method of the present invention is not limited to this, and the dielectric ceramic is molded into a cylindrical shape, and a plurality of resonators are integrally formed. It is also applicable to various modifications such as the ones that are open, and the structure of the electrode layer is such that the internal electrode layer and the external electrode layer are not short-circuited at both ends of the ceramic dielectric and are open. Can also be applied.

[0021]

As described above, the ceramic plating method of the present invention is characterized in that the surface of the ceramic is coated with a zinc oxide thin film, and the surface of the zinc oxide thin film is subjected to electroless copper plating. Is. Further preferably, the ceramic is dipped in an aqueous solution of zinc acetate, then dried and baked to form a zinc oxide thin film on the surface of the ceramic layer, and a ceramic layer is dipped in the aqueous solution of palladium chloride after the step of forming the binder layer. The method is characterized by comprising a catalyzing step of catalyzing and then performing an electroless plating step of immersing the ceramic in a copper sulfate aqueous solution to form a copper plating layer after the catalyzing step.

Therefore, it is possible to form a copper plating layer having an appropriate adhesion strength without roughening the surface of the ceramic prior to electroless copper plating. Further, since the copper plating layer is formed on the ceramic surface without roughening the surface of the ceramic through the zinc oxide thin film, it is possible to reduce the surface roughness of the interface between the copper plating layer and the zinc oxide thin film thereunder. it can. Therefore, when the copper plating layer formed on the ceramic is used as an electrode layer of a dielectric resonator or the like, the adverse effect of the skin effect is reduced and the conductor loss can be reduced. Further, since the zinc oxide thin film to be the binder layer can be easily applied to various ceramic materials having different compositions,
It is possible to improve the manufacturing efficiency by eliminating the conventional inconvenience that it takes time and effort to develop an etching solution. Also, the variation in surface roughness due to the difference in the type of material is small.

The dielectric resonator of the present invention comprises a dielectric ceramic molded in a columnar shape, a through hole penetrating from one end surface to the other end surface of the dielectric ceramic, and an internal electrode provided on the inner surface of the through hole. And an external electrode layer provided on an outer peripheral surface other than one end surface of the dielectric ceramic, wherein at least one of the internal electrode layer and the external electrode layer is a zinc oxide thin film on the dielectric ceramic. It is characterized by comprising a copper plating layer formed through. Further, preferably, at least a part of the zinc oxide thin film is a catalyst film substituted with palladium ions, and the copper plating layer is formed thereon.

Therefore, since the internal electrode layer and the external electrode layer are formed through the binder layer composed of the zinc oxide thin film without roughening the surface of the dielectric ceramic, the oxidation of these electrode layers and the layers below them is performed. The surface roughness of the interface with the zinc thin film can be reduced. Therefore, the adverse effect of the skin effect on the electrode layer is reduced and the increase of the conductor loss is suppressed, and as a result, the characteristics (Qu value) of the dielectric resonator can be improved. In particular, when the surface roughness of the ceramic itself is smaller than the thickness of the electrode layer, the adverse effect of the skin effect becomes extremely small, so that even if the operating frequency becomes high, Qu closer to the theoretical value can be obtained.
Further, the improvement of Qu enables downsizing when a dielectric resonator made of the same material as the conventional one and having the same use frequency is formed. Furthermore, since it is not necessary to roughen the surface of the dielectric ceramic using an etching solution, the variation in surface roughness due to the difference in the type of ceramic material is small,
As a result, the characteristic (Qu value) of the dielectric resonator can be stabilized.

[Brief description of the drawings]

FIG. 1 is a schematic process diagram showing an example of a method for plating a ceramic according to the present invention.

FIG. 2 is a perspective view showing an embodiment of the dielectric resonator of the present invention.

FIG. 3 is a schematic process diagram showing an example of a conventional method for plating ceramics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic 2 Zinc oxide thin film (binder layer) 3 Catalyst coating 4 Copper plating layer 21 Dielectric ceramic 22 Internal electrode layer 23 External electrode layer

Claims (4)

[Claims] 1. A method for plating ceramics, which comprises depositing a zinc oxide thin film on the surface of a ceramic and subjecting the surface of the zinc oxide thin film to electroless copper plating. 2. A binder layer forming step of forming a zinc oxide thin film on a ceramic surface by immersing the ceramic in an aqueous solution of zinc acetate, followed by drying and firing, and after the binder layer forming step, the ceramic is placed in an aqueous solution of palladium chloride. Plating on a ceramic, comprising a catalyzing step of dipping and catalyzing, and an electroless plating step of dipping the ceramic in a copper sulfate aqueous solution to form a copper plating layer after the catalyzing step. Method. 3. A columnar dielectric ceramic,
A through hole penetrating from one end surface to the other end surface of the dielectric ceramic, an internal electrode layer provided on the inner surface of the through hole, and an external electrode layer provided on an outer peripheral surface other than the one end surface of the dielectric ceramic. At least one of the internal electrode layer and the external electrode layer comprises a copper plating layer formed on the dielectric ceramic with a zinc oxide thin film interposed therebetween. 4. The dielectric film according to claim 3, wherein at least a part of the zinc oxide thin film is a catalyst film substituted with palladium ions, and the copper plating layer is formed thereon. Body resonator.