JPS6232604B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a multilayer ceramic capacitor which has excellent electrode adhesion strength and solderability and is inexpensive.

Multilayer ceramic capacitors are small and highly reliable, and are suitable for automatic devices attached to printed wiring patterns. , demand is rapidly expanding.

FIG. 1 shows a cross-sectional view of a conventional multilayer ceramic capacitor. In the figure, 1 is a ceramic dielectric element body, 2 is an internal electrode made of noble metal such as platinum or palladium, and 3 and 4 are terminal electrodes provided on both sides of the ceramic dielectric element body 1, which separates the internal electrode 2. Each one is connected.

By the way, in forming the internal electrode 2 of this multilayer ceramic capacitor, an internal electrode paste is applied onto a plastic film made of barium titanate, titanium oxide, etc. to a thickness of about 50 to 100 μm. Then, superimpose this by the desired number of images.
It was designed to be sintered at a high temperature of 1100°C to 1400°C. Therefore, the internal electrodes must be made of an expensive metal with a high melting point that can withstand high temperatures of 1100 DEG C. to 1400 DEG C., such as noble metals such as platinum and palladium. However, when the terminal electrodes 3 and 4 connecting these internal electrodes 2 in parallel are formed by the baking method of frit-containing silver electrodes in order to provide soldering strength, they become different metals. In some cases, the internal electrode 2 and the terminal electrodes 3 and 4 are alloyed by diffusion migration due to metallurgical diffusion properties, and the connection between them is broken, resulting in an accident in which capacity is insufficient or no capacity is produced at all. In order to prevent such alloying, conventionally, 3% or more of platinum or palladium, which is the same as that of the internal electrodes, was mixed into the silver of the terminal electrodes. However, platinum, palladium, and the like are expensive noble metals, making the multilayer ceramic capacitor extremely expensive. Therefore, in order to eliminate the drawback of increased costs, it is desirable to form terminal electrodes using inexpensive base metals such as nickel, copper, or tin.

However, since these base metal pastes oxidize when sintered in an oxidizing atmosphere, it is impossible to bake them onto a ceramic dielectric body like silver-panadium electrodes. Furthermore, the base metal paste can be sintered in a reducing atmosphere, but in this case, the ceramic dielectric element is also reduced at the same time, making it difficult to obtain a ceramic capacitor with satisfactory characteristics. There was a problem that I couldn't do it.

In addition, in the silver baking method, after immersion in solder, silver diffuses into the solder and peels off, which lowers the electrode density strength and tends to become unstable, resulting in a decrease in capacitor capacity and tan δ
There was a drawback that it led to deterioration.

Furthermore, when printing and coating a frit-containing silver/palladium or platinum-based paste on a porcelain dielectric element, it is extremely difficult to control the coating thickness, and variations inevitably occur, resulting in variations in electrode thickness. It has become extremely difficult to control the external dimensions of the capacitor to a predetermined value. Moreover, since the electrode thickness becomes large, the amount of laminated ceramic capacitors that can be loaded into the magazine of the automatic laminated ceramic capacitor mounting machine is small, resulting in poor productivity. Incidentally, the electrode thickness of conventional multilayer ceramic capacitors is 15 to 50 mm.
It is about μ.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a method for manufacturing a laminated ceramic capacitor that is excellent in mass production, is inexpensive, and has good electrode adhesion strength and solderability.

In order to achieve the above object, the method for manufacturing a multilayer ceramic capacitor according to the present invention includes applying a first conductive layer of nickel by electroless plating to the entire surface of a ceramic dielectric element whose surface has been roughened by a chemical etching method. After etching the first conductive layer to leave only the portion that will become the terminal electrode and remove the other portions, a second conductive layer having tin as the outermost layer is formed on the first conductive layer by barrel plating. Characterized by electrodeposition of the layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The content of the present invention will be explained in detail below with reference to the accompanying drawings which are examples. FIGS. 2A to 2E are process explanatory diagrams of a method for manufacturing a multilayer ceramic capacitor according to the present invention.

As shown in FIG. 2A, the surface of the flat ceramic dielectric body 7 in which internal electrodes 5 and 6 are buried in layers is roughened by chemical etching to form an uneven layer 8 (FIG. 2B). The aforementioned chemical etching method uses, for example, a mixed solution of nitric acid (HNO ₃ ) and hydrofluoric acid (HF), but the role of each solution is that nitric acid increases the cleaning effect as an oxidizing agent, while hydrofluoric acid has a corrosive effect. Since it is strong, it is necessary to etch the base body 7. When the surface of the porcelain dielectric element 7 is roughened in this manner, when the first conductive layer 9 of nickel is formed on the surface of the porcelain dielectric element 7 as shown in FIG. Since it bites into the surface unevenness layer 8, the adhesion strength can be made good and stable. However, if the amount of hydrofluoric acid used for etching is too large,
If the etching time is too long, excessive etching will occur and the ceramic dielectric element body 7 will become brittle, resulting in a decrease in adhesion strength and instability, so care must be taken. It should be noted that mechanical surface roughening methods other than chemical etching methods are inappropriate because the adhesion strength against electroless methods is lost.

After the etching process, the porcelain dielectric element 7
Fluoric acid and nitric acid must be removed from the Fluoric acid and nitric acid are removed by washing with water, neutralizing or boiling, but if there is any residual
It activates and becomes sensitized, causing spots on the plating layer in the next step, so care must be taken when processing after etching.

Next, a first conductive layer 9 of nickel is formed on the entire surface of the uneven layer 8 of the ceramic dielectric body 7 by, for example, a barrel type electroless plating method (FIG. 2C).
When the material forming the first conductive layer 9 is a single metal, it has been confirmed that copper other than nickel is not suitable because the adhesion strength does not improve even if heat treatment is applied. Note that the layer thickness of the first conductive layer 9 is 3 to 5 μm.
It is possible to form a layer as thin as possible.

Next, a portion of the first conductive layer 9 that will become a terminal electrode,
That is, both sides S ₁ of the upper and lower surfaces of the ceramic dielectric element 7,
S ₂ and both side surfaces S ₃ and S ₄ connected thereto are masked with an organic resist containing TiO ₂ as an etching resist. Next, the other parts P ₁ and P ₂ are removed by chemical etching to expose the surface of the ceramic dielectric element 7 in the center, and the first conductive layer 9 that will become the terminal electrode is coated on both sides. A porcelain dielectric material obtained by this process is obtained (FIG. 2D). Note that ferric chloride (FeCl ₃ ) was used as the etching solution in this case.

After the etching process, it goes without saying that a post-processing process is performed to remove the resist and etching solution, but by forming the first conductive layer 9 described above, the first conductive layer 9 is formed in the form of a ceramic capacitor. . However, if only the first conductive layer 9 is made of nickel, it is susceptible to oxidation due to changes over time, resulting in poor soldering and peeling during processes such as solder dipping, resulting in deterioration of characteristics such as capacity loss.

Therefore, in order to prevent the nickel layer of the first conductive layer 9 from being oxidized and to improve solderability, in the present invention, a second conductive layer with tin as the outermost layer is formed on the first conductive layer 9 by barrel plating. Electrodeposit 10 (Fig. 2E).

FIG. 3 is a perspective view of the barrel plating device, and FIG. 4 is an enlarged view of the rotating barrel in the barrel plating device. As shown in the figure, the barrel plating device immerses a rotary barrel 13 in the form of a porous cylinder in an electrolytic solution 12 in an electrolytic bath 11, and gears 15 coaxially attached to the rotating shafts 14, 14 of the rotary barrel 13. To,
By meshing the gear 16 on the power source side,
A rotating barrel 13 is rotated in the electrolyte 12. A cathode 1 is installed inside the cylindrical body of the rotating barrel 13.
One of the cathodes 17 and 18, for example, the cathode 17, is supplied with electricity through a brush 20 that is in sliding contact with a current collector 19. 21 is an anode.

To perform barrel plating using the above-mentioned barrel plating device, the porcelain dielectric material on which the first conductive layer 9 is formed is housed in the rotating barrel 13 as shown in FIG. 2D,
Rotating barrel 13 is rotated in electrolyte 12 while supplying current to cathode 17 and anode 21 . Then, the porcelain dielectric material 22 flows through the electrolyte in the rotating barrel 13.
is rolled, and the second conductive layer 10 of tin is electrodeposited only on the surface of the first conductive layer 9.

As the electrolytic solution 12, a well-known one used in barrel tinning, for example, one having a composition mainly composed of sodium stannate is used. Also rotating barrel 1
It is desirable that the number of rotations for 3 is around 10 (R・P・M).

Since the barrel plating method is carried out as described above, it is possible to plate a large amount of small-shaped items such as multilayer ceramic capacitors at one time, and the productivity is very high. Moreover, as the rotating barrel 13 rotates, the porcelain dielectrics 22 come into contact with each other, rub against each other, and roll, and the cathode 1
Since it is plated by touching 7 and 18, even small and difficult to handle items such as porcelain capacitors can be plated easily. Note that the layer thickness of the second conductive layer 10 is 3 to 5 μm.
It will be about.

FIG. 5 shows another embodiment of a multilayer ceramic capacitor manufactured by the manufacturing method according to the present invention. The feature of this embodiment is that a copper conductive layer 10'a is electrodeposited on the first conductive layer 9' by barrel plating, and a tin conductive layer 10'b is further deposited on this conductive layer 10'a by barrel plating. It was electrodeposited by.

With such a configuration, a copper conductive layer whose linear expansion coefficient is between the two is placed between the nickel first conductive layer 9', which has a large difference in linear expansion coefficient, and the tin conductive layer 10'b. Since the copper conductive layer 10'a is present, the copper conductive layer 10'a acts as a linear expansion buffer and prevents the interfacial peeling phenomenon of the electrode layer. Furthermore, since the first conductive layer 9' made of nickel is covered with the conductive layer 10'a made of copper, oxidation of the first conductive layer 9' made of nickel is prevented, and furthermore, the conductive layer 10'b made of tin is covered with the conductive layer 10'a made of copper. Since it is the outer layer, the solderability is extremely good.

Note that the thickness of each conductive layer is very thin, about 3 to 5 μm, and is formed uniformly.

As detailed above, the method for manufacturing a multilayer ceramic capacitor according to the present invention includes forming a first conductive layer of nickel by electroless plating on the surface of a ceramic dielectric element whose surface has been roughened by a chemical etching method; Next, the first conductive layer is etched to leave only the part that will become the terminal electrode and remove the other parts, and then a second conductive layer with tin as the outermost layer is deposited on the first conductive layer by barrel plating. Since it is characterized by being worn, it has the following effects.

(1) By forming electrodes using a combination of low-cost base metals such as nickel, tin, or copper, the cost can be reduced to about 1/3 of the conventional cost.

(2) The first conductive layer is formed by an electroless plating method,
Since the second conductive layer is formed by the barrel plating method, it is possible to form a very thin and uniform electrode with a layer thickness of about 3 to 5 μm.

As a result (a) By making the electrode thickness uniform, it becomes very easy to manage the external dimensions of the multilayer ceramic capacitor.

(b) The electrode thickness was 6 to 10μ compared to the conventional 15 to 50μ.
The amount of laminated ceramic capacitors that can be packed into the magazine of an automatic magnetic capacitor mounting machine increases by about 9%.

(3) By roughening the surface of the porcelain dielectric body and attaching multilayer plating to the electrode, the solder durability of the terminal electrode has been improved by approximately 10%.
It can be strengthened twice as much. This makes it extremely easy to solder the multilayer ceramic capacitor to a printed circuit board or the like.

(4) Adopting the barrel plating method improves productivity and reduces costs.

(5) By electrodepositing a second conductive layer having tin as the outermost layer on the first conductive layer of nickel, it is possible to improve solderability while preventing oxidation of the nickel layer.

(6) As shown in the example, when a copper layer is provided between the nickel layer and the tin layer, the compatibility between the nickel layer and the tin layer is improved and the electrode strength is improved. .

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a conventional multilayer ceramic capacitor, Figs. 2 A to E are process explanatory diagrams of a method for manufacturing a multilayer ceramic capacitor according to the present invention, and Fig. 3 is a perspective view of a barrel plating device used in the present invention. figure,
FIG. 4 is an enlarged cross-sectional view of the rotating barrel, and FIG. 5 is a cross-sectional view of another embodiment of a ceramic capacitor manufactured by the manufacturing method according to the present invention. 7...Porcelain dielectric element body, 8...Irregular layer, 9...
1st conductive layer, 10...2nd conductive layer.

Claims (1)

[Claims] 1. A first conductive layer of nickel is formed by electroless plating on the entire surface of a porcelain dielectric element whose surface has been roughened by chemical etching, and then only the portions that will become terminal electrodes are left. After the first conductive layer is etched to remove other parts thereof, a second conductive layer having tin as the outermost layer is electrodeposited on the first conductive layer by a barrel plating method. Method of manufacturing magnetic capacitors. 2. The second conductive layer is formed by electrodepositing a copper conductive layer on the first conductive layer by barrel plating, and electrodepositing the tin outermost layer on the copper conductive layer. A method for manufacturing a multilayer ceramic capacitor according to claim 1.