JPH05315821A - Manufacture of coaxial dielectric resonator - Google Patents

Abstract

PURPOSE:To improve the adhesive force of a copper plating film in the coaxial dielectric resonator in which a copper film electrode is formed on a high frequency dielectric ceramic by chemical plating. CONSTITUTION:A dielectric ceramic 1 is made of a material using a TiO2ZrO2- SnO2 as a major content at least added with 2wt.% or over and 20wt.% or below of a Co oxide material, the Co oxide is depositted onto the surface of the dielectric ceramic 1 by sintering, and then Co is eliminated by the etching processing to form lots of recessed parts on the surface of the dielectric ceramic 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a coaxial dielectric resonator used for high frequency filters, high frequency oscillators and the like.

[0002]

2. Description of the Related Art FIG. 1 shows a conventional general coaxial dielectric resonator. In the figure, 1 is TiO ₂ -ZrO ₂ -SnO ₂
A rectangular parallelepiped having a cylindrical through hole 2 in the center, which is a dielectric ceramic made of a material containing 1% by weight of CoO and 2.5% by weight of Nb ₂ O ₅ as additives for promoting sinterability. Sintered into shape. 3 is an electrode layer, and the outer conductor 4, the inner conductor 5 and the short-circuited end 6 are formed by baking silver paste. That is, a glass frit, an organic binder and a solvent are mixed with silver powder, and a silver paste formed into a paste is attached to the dielectric ceramic by a method such as printing, coating or dipping, and then baked at a high temperature of about 800 ° C. It Reference numeral 7 is an open end where no electrode layer is formed.

By the way, a high Q is required for a high frequency dielectric resonator. When the unloaded Q of the dielectric resonator is Q _u , the Q of the dielectric ceramic material is Q _d , the Q due to the conductor loss of the electrode is Q _e , and the Q due to the radiation loss is Q _r , Q _u is expressed by the following equation.

[0004]

[Equation 1]

Usually, Q _d is about 10,000 to 20,000,
Q _e is about several hundreds. Further, when the surface of the dielectric resonator other than the open end is covered with the conductor, Q _r becomes infinite. Therefore, the value of Q _e greatly affects Q _u . Since the higher the conductivity of the metal that constitutes the electrode, the higher Q _e ,
In order to realize high Q _u , it is necessary to increase the conductivity of the electrode.

In the above-mentioned prior art, it is indispensable for the silver paste to have a glass frit mixed therein in order to obtain adhesiveness, and as a result, the intrinsic conductivity of silver is 6.06 × 10 ⁵ (Ω ⁻¹ c).
Since m ⁻¹ ) is reduced by 20 to 30%, there is a drawback that Q _u is lowered. Further, in the above-mentioned conventional technique, the outer conductor 4,
Although it is necessary to form electrodes on a total of 6 surfaces of the inner conductor 5 and the short-circuited end 6, the structure is complicated, so that the workability when applying the silver paste is poor and it is not suitable for mass production. Further, there are drawbacks that uneven coating is likely to occur and that Q _u is lowered and variations among elements occur.

For this reason, for example, Japanese Patent Laid-Open No. 54-
Recently, as described in Japanese Patent No. 108554 (H01P 7/00), instead of applying a silver paste,
A method of forming a copper coating on the dielectric ceramic by electroless plating has been proposed. In this conventional technique, a dielectric ceramic degreasing step (cleaning the ceramic surface to improve wettability with a surfactant) etching step (roughening the surface with a mixed solution of hydrofluoric acid, nitric acid, hydrochloric acid, etc.) Activation step (adding a catalyst) Plating step (plating bath containing copper sulfate, EDTA, formalin, NaOH, etc.) Washing and drying steps.

The adhesion of the copper coating formed by the above-mentioned conventional plating process is closely related to the surface roughness of the dielectric ceramic. The larger the surface roughness, the higher the adhesion strength of the copper coating, but the rougher the unloaded Q of the resonator, the worse the unloaded Q of the resonator is disclosed in JP-A-60-132402 (H01P 11 /
00). Therefore, the surface roughness is required to be such that the copper coating is sufficiently adhered and the unloaded Q is high, and the surface roughness must be uniform and uniform in any part of the dielectric ceramic.

[0009]

A material containing TiO ₂ —ZrO ₂ —SnO ₂ as a main component and 1% by weight of CoO and 2.5% by weight of Nb ₂ O ₅ as an additive for promoting sinterability is used as a dielectric material. Dielectric resonators used as body ceramics and made by electroless copper plating have poor adhesion of the copper film, many blisters occur on the copper plating surface, and the resonance frequency changes in high temperature storage test and humidity resistance test etc. There was a problem. This is because the surface of the dielectric ceramic is not sufficiently rough to obtain close contact, and the S of the dielectric ceramic shown in FIG.
This is because, as can be seen from the EM photograph, the particle size is as large as 10 μm or more, and it is not roughened by the etching solution.

[0010]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art, and provides a coaxial dielectric resonator in which a copper film electrode is formed on a high frequency dielectric ceramic by electroless plating. In the manufacturing method, the dielectric ceramic contains TiO ₂ —ZrO ₂ —SnO ₂ as a main component and contains 2% by weight.
20% by weight or more and at least 20% by weight of Co oxide are added to the surface of the dielectric ceramic by sintering.
It is characterized in that an oxide is deposited and then Co is removed by an etching treatment.

[0011]

[Function] A large number of concave portions are formed on the surface of the dielectric ceramic by roughening the surface of the dielectric ceramic in which Co oxide is added to TiO ₂ -ZrO ₂ -SnO ₂ by etching treatment. The adhesion of the plating film increases.

[0012]

EXAMPLES Examples of the present invention will be described below. TiO ₂ -ZrO ₂ -SnO ₂ system ceramic is used as the material of the dielectric ceramic, and the composition ratio of the main components is TiO ₂ 51 mol% and ZrO ₂ 41 m.
ol% and SnO ₂ are 8 mol%. In addition, CoO as an additive
0 wt% and Nb ₂ O ₅ 2.5 wt% are added. This material, 1 ~
It is shaped into a coaxial dielectric resonator at a pressure of ² ton / cm ² , and sintered at a peak temperature of 1430 ° C and a keeping time of 5 hours. The dimensions after sintering are 3 mm x 3 mm x 6 mm, and a large amount of CoO is deposited to a depth of 15 μm from the surface and is uniformly deposited on the entire surface. Figure 3
Is a surface SEM photograph of the sintered body.

Then, when this sintered body was etched for 5 minutes with a mixed solution of hydrofluoric acid and nitric acid (60 ° C.), Co was removed by etching, and the entire surface of the sintered body 8 was removed as shown in FIG. A large number of recesses 9 are formed in the. FIG. 5 is an SEM photograph of the sintered body after this etching.

The characteristics of the coaxial dielectric resonator formed by applying electroless copper plating of 10 μm to such a dielectric ceramic are shown in Table 1 when compared with the conventional product. In Table 1, the compounding ratio of the main component is the same as that of the present invention and the CoO
Of 1.0% by weight and Nb ₂ O ₅ of 2.5% by weight. Further, f ₀ is the resonance frequency, Q _u is the unloaded Q of the dielectric resonator, and ε _r is the dielectric constant. Further, the adhesive force means the force when the wire is soldered on the plated surface in an area of φ2 mm and pulled in the direction perpendicular to the plated surface to separate the plated surface.

[0015]

[Table 1]

Since the dielectric resonator according to the present invention has improved adhesion as compared with the conventional product, it has no blistering and Q _u.
Is high.

Table 2 compares the reliability of the coaxial dielectric resonator according to the present invention with that of a conventional product. The high temperature storage test at 110 ° C. and the humidity resistance test at 60 ° C., 95% RH are 500 each. It shows the changes in f ₀ and Q _u after time.

[0018]

[Table 2]

In the conventional product, the change in f ₀ is large in both tests. On the other hand, in the product of the present invention, the change of f ₀ is about 3 MHz in both tests.
And small. Also, the decrease in Q _u is small.

[0020]

As described above, in the coaxial dielectric resonator according to the present invention, a large number of recesses are formed on the surface of the dielectric ceramic, so that the electroless copper plating film adheres well and does not cause blistering. _u is high. Furthermore, there is little change in f ₀ in the high temperature storage test and the humidity resistance test, and a coaxial dielectric resonator having excellent characteristics can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional coaxial dielectric resonator.

FIG. 2 is a surface SEM photograph of a conventional dielectric ceramic.

FIG. 3 is a surface SEM photograph of a dielectric ceramic according to the present invention after sintering.

FIG. 4 is a diagram showing a coaxial dielectric resonator according to the present invention.

FIG. 5 is a SEM photograph of a surface of a dielectric ceramic according to the present invention after etching.

[Explanation of symbols]

 1 Dielectric Ceramic 2 Through Hole 3 Electrode Layer 4 Outer Conductor 5 Inner Conductor 6 Short-Circuiting End 7 Opening End 8 Sintered Body 9 Recess

Claims (1)

[Claims] 1. A method for manufacturing a coaxial dielectric resonator comprising a copper coating electrode formed on a high frequency dielectric ceramic by electroless plating, wherein the dielectric ceramic is TiO ₂ -ZrO.
_{It is} formed of a material containing _2- SnO ₂ as a main component and at least 2 wt% to 20 wt% of Co oxide added, and the Co oxide is deposited on the surface of the dielectric ceramic by sintering, and then etched. A method for manufacturing a coaxial dielectric resonator, characterized in that Co is removed by a treatment.