JPH08148374A - Capacitor - Google Patents

Abstract

PURPOSE: To facilitate the mounting of a capacitor on a circuit board and to obtain the excellent withstand voltage characteristics by covering both main surfaces of a dielectric ceramic plate with thin film electrodes, and covering at least one surface of the electrodes with a thin film brazing material. CONSTITUTION: A dielectric ceramic plate 1 is covered on both main surfaces with a pair of thin film electrodes 2. When the plate 1 is formed by barium titanate ceramics, the electrodes 2 covering both the main surfaces are formed in a three layer structure in which a titanium layer 2a, a palladium layer 2b and a metallic layer 2c are sequentially covered from the plate 1 side. Further, the plate 1 in which both the main surfaces are covered with the electrodes 2, is covered at least on the one surface of the films 2 with a thin film brazing material 3. The material 3 is made of gold-tin alloy with a thickness of 0.5 to 10.0μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor, and more particularly to a surface mount type capacitor directly mounted on a wiring board.

[0002]

2. Description of the Related Art Conventionally, a large number of capacitors have been used as circuit parts constituting a transmission / reception circuit for electric signals in communication devices such as mobile phones and satellite communications.

In general, such a capacitor is constructed by depositing a pair of electrodes made of silver-palladium or the like on both main surfaces of a dielectric porcelain plate, and one electrode being a brazing material such as solder on a wiring conductor of a wiring board. And the other electrode is electrically connected to another wiring conductor of the wiring board via a bonding wire to be mounted on the wiring board.

In the capacitor, a conductive paste obtained by adding and mixing an organic solvent and a solvent to silver-palladium on both main surfaces of a dielectric porcelain plate is applied by printing to a predetermined thickness and is baked at a high temperature. Produced by.

A specific method for mounting the capacitor on the wiring board is to first prepare a brazing foil having a thickness of about 30 μm, and then sandwich the brazing foil on the wiring conductor of the wiring board. Then, the capacitor is placed so that one electrode of the capacitor faces the wiring conductor, and then the brazing material disposed between the wiring conductor of the wiring board and the capacitor is heated to a predetermined temperature, By melting and melting the brazing material, one electrode of the capacitor is electrically connected to the wiring conductor, and finally the other electrode of the capacitor is connected to the other wiring conductor of the wiring board through the bonding wire. Be seen.

[0006]

However, in this conventional capacitor, it is necessary to separately prepare a foil-shaped brazing material for joining the wiring conductor of the wiring board and one electrode of the capacitor when mounting on the wiring board. Since it is necessary to accurately align the wiring conductor of the wiring board, the foil-shaped brazing material, and one electrode of the capacitor, the mounting of the capacitor on the wiring board is troublesome and the workability is poor, and It had the drawback of being expensive.

Further, since the foil-shaped brazing material has the smallest thickness of 15 μm, when one electrode of the capacitor is joined to the wiring conductor of the wiring board, the brazing material becomes excessive and a part of the dielectric ceramic material is used. There is also a drawback in that it crawls up to the side surface of the plate, and as a result, the distance between the pair of electrodes of the capacitor becomes substantially short, and the withstand voltage characteristic of the capacitor deteriorates significantly.

[0008]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks, and an object of the present invention is to provide a capacitor which is easy to mount on a wiring board and has excellent withstand voltage characteristics.

[0009]

The capacitor of the present invention comprises:
It is characterized in that both main surfaces of a dielectric ceramic plate are coated with thin film electrodes and at least one surface of the thin film electrodes is coated with a thin film brazing material.

The capacitor of the present invention is characterized in that the dielectric porcelain plate is made of barium titanate, and the thin film electrode has a three-layer structure of a titanium layer, a palladium layer and a gold layer.

Further, in the capacitor of the present invention, the thin-film brazing material is made of gold-tin alloy and has a thickness of 0.5 to 10 μm.
It is characterized by being m.

[0012]

According to the capacitor of the present invention, since the thin film brazing material is applied to the surface of at least one of the electrodes, when the capacitor is mounted on the wiring board, the capacitor is simply placed on the wiring conductor of the wiring board. Thus, the wiring conductor of the wiring board and the electrode of the capacitor can be extremely accurately aligned with the brazing material sandwiched therebetween, and the mounting on the wiring board is easy and the workability is good.

Further, according to the capacitor of the present invention, since the brazing material deposited on at least one electrode surface is formed of a thin film, the amount of the brazing material is small, and as a result, one electrode of the capacitor is wired. When joining to the wiring conductor of the board, brazing material is not excessive and part of it does not crawl up to the side surface of the dielectric porcelain plate, making the distance between the pair of electrodes of the capacitor long and increasing the withstand voltage characteristics of the capacitor. Can be improved.

[0014]

The present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment of the capacitor of the present invention, in which 1 is a dielectric ceramic plate and 2 is a thin film electrode attached to both main surfaces of the dielectric ceramic plate 1. A capacitor A is composed of this dielectric porcelain plate and the pair of thin film electrodes 2.

The dielectric porcelain plate 1 is made of barium titanate porcelain, strontium titanate porcelain, or the like.
When composed of barium titanate porcelain, raw powders of barium carbonate, titanium oxide, magnesium titanate, etc. are calcined,
Barium titanate is reacted to obtain fine powder, and then an appropriate organic solvent and solvent are added and mixed to form a sludge, and finally the sludge is green by a doctor blade method or a calendar roll method. It is made by forming a sheet and firing it at a high temperature.

The dielectric porcelain plate 1 has a pair of thin film electrodes 2 and 2 deposited on both main surfaces thereof, and the relative dielectric constant of the dielectric porcelain plate 1 is between the pair of thin film electrodes 2 and 2. A corresponding constant capacitance is formed.

The pair of thin film electrodes 2 and 2 attached to both main surfaces of the dielectric porcelain plate 1 are the dielectric porcelain plates when the dielectric porcelain plate 1 is made of barium titanate porcelain. 1
A three-layer structure in which a titanium layer 2a, a palladium layer 2b, and a gold layer 2c are sequentially deposited from the side is preferably used.

The pair of thin film electrodes 2 and 2 are connected to the titanium layer 2.
In the case of a three-layer structure of a, palladium layer 2b, and gold layer 2c, the titanium layer 2a acts as an adhesion layer for firmly attaching the electrode 2 to the dielectric ceramic plate 1, and titanium is used as the dielectric ceramic plate 1. It is formed by depositing a film having a thickness of 0.05 μm to 0.3 μm on both main surfaces by a thin film forming means such as a sputtering method or an ion plating method.

The titanium layer 2a has a thickness of 0.05 μm.
If it is less than m, it tends to be difficult to firmly adhere the pair of electrodes 2, 2 to both main surfaces of the dielectric ceramic plate 1, and if it exceeds 0.3 μm, the titanium layer 2a is formed. Since a large stress is inherent in the titanium layer 2a, cracks or the like are likely to occur in the dielectric ceramic plate 1 due to the intrinsic stress. Therefore, it is preferable that the titanium layer 2a forming the pair of electrodes 2, 2 has a thickness in the range of 0.05 μm to 0.3 μm.

A palladium layer 2b is deposited on the surface of the titanium layer 2a, and a part of a thin film brazing material 3 to be described later is diffused into the titanium layer 2a of the palladium layer 2b, and the palladium layer 2b is applied to the dielectric ceramic plate 1. It has an effect of effectively preventing the deposition strength of the electrode 2 from being lowered, and palladium is formed on the surface of the titanium layer 2a by a thin film forming means such as a sputtering method or an ion plating method so as to have a thickness of 0.05 to 2.0 μm. It is formed by depositing on.

The palladium layer 2b has a thickness of 0.0
If the thickness is less than 5 μm, the diffusion of the brazing material 3 into the titanium layer 2a cannot be effectively prevented, and the adhesion strength of the electrode 2 on the dielectric ceramic plate 1 tends to decrease, and the thickness of 2.0 μm
When it exceeds m, a large stress is inherent in the palladium layer 2b when the palladium layer 2b is formed, and the palladium layer 2b is more easily peeled from the titanium layer 2a due to the intrinsic stress. Therefore, the palladium layer 2b has a thickness of 0.05 μm.
It is preferable to set it in the range of 2.0 to 2.0 μm.

Further, a gold layer 2c is deposited on the surface of the palladium layer 2b, the gold layer 2c acts as a main conductor layer of the electrode 2, and gold is deposited on the surface of the palladium layer 2b by a vapor deposition method.
The thickness is 0.2 μm to 6.0 μm by a thin film forming means such as a sputtering method, an ion plating method and a plating method.
It is formed by depositing on.

The gold layer 2c has a thickness of 0.2 μm.
If it is less than 6.0 μm or exceeds 6.0 μm, the reliability of the joining and connection tends to be low when the electrode 2 is joined and connected to the wiring conductor of the wiring board through the thin film brazing material 3 and the bonding wire. Therefore, the gold layer 2c has a thickness of 0.2.
It is preferably set in the range of μm to 6.0 μm.

Further, in the dielectric ceramic plate 1 having the thin film electrodes 2 adhered on both main surfaces, the thin film brazing material 3 is adhered on at least one surface of the thin film electrodes 2.

The thin film brazing material 3 functions to bond one electrode 2 of the capacitor A to the wiring conductor of the wiring board,
For example, it is made of a gold-tin alloy and has a thickness of 0.5 by a thin film forming means such as a sputtering method or an ion plating method.
It is formed by depositing a thickness of μm to 10.0 μm.

Since the thin film brazing material 3 is adhered to one electrode 2 of the capacitor A, when the capacitor A is mounted on the wiring board, the thin film brazing material 3 of the capacitor A is mounted on the wiring conductor of the wiring board. The wiring conductor of the wiring board and the electrode 2 of the capacitor A can be simply placed by making direct contact with each other.
Can be extremely accurately aligned with the thin film brazing material 3 interposed therebetween, and the mounting on the wiring board is easy and the workability is good.

Further, since the thin film brazing material 3 is deposited by the thin film forming technique, the amount of the thin film brazing material 3 is small, and as a result, one electrode 2 of the capacitor A is joined to the wiring conductor of the wiring board. At this time, a part of the thin film brazing material 3 does not excessively crawl up to the side surface of the dielectric ceramic plate 1, and the withstand voltage characteristic of the capacitor A is set by increasing the distance between the pair of electrodes 2 of the capacitor A. Can be greatly improved.

The thin film brazing material 3 has a thickness of 0.5.
If it is less than μm, the absolute amount of the brazing material decreases, and it tends to be difficult to firmly bond one electrode 2 of the capacitor A to the wiring conductor of the wiring board.
If m is exceeded, one electrode 2 of capacitor A is
When joining the wiring conductor to the wiring conductor of the wiring board, the thin film brazing material 3 becomes excessive and partly crawls onto the side surface of the dielectric ceramic plate 1, and the distance between the pair of electrodes 2 and 2 of the capacitor A is shortened. The withstand voltage characteristic of the capacitor A tends to deteriorate. Therefore, the thin film brazing material 3 has a thickness of 0.5 μm.
It is preferable to set it in the range of from 10.0 to 10.0 μm.

Thus, according to the capacitor of the present invention, as shown in FIG. 2, the capacitor A is mounted on the wiring conductor 5 of the wiring board 4 such that the thin film brazing material 3 of the capacitor A is in direct contact with the wiring conductor 5. Then, the thin film brazing material 3 is heated and melted to bond one electrode 2 of the capacitor A to the wiring conductor 5 of the wiring board 4 through the thin film brazing material 3 with an electrical connection, and the other electrode of the capacitor A. By electrically connecting the electrode 2 to another wiring conductor 6 of the wiring board 4 via a bonding wire, the electrode 2 is used in a transmission / reception circuit of a communication device such as a mobile phone.

The present invention is not limited to the above-mentioned embodiments, but various modifications can be made without departing from the gist of the present invention.

[0031]

According to the capacitor of the present invention, since the thin film brazing material is applied to the surface of at least one of the electrodes, the capacitor is mounted on the wiring conductor of the wiring board when the capacitor is mounted on the wiring board. Only by doing so, the wiring conductor of the wiring board and the electrode of the capacitor can be extremely accurately aligned with the brazing material interposed therebetween, and the mounting on the wiring board is easy and the workability is good.

Further, according to the capacitor of the present invention, since the brazing material deposited on at least one electrode surface is formed of a thin film, the amount of the brazing material is small, and as a result, one electrode of the capacitor is wired. When joining to the wiring conductor of the board, brazing material is not excessive and part of it does not crawl up to the side surface of the dielectric porcelain plate, making the distance between the pair of electrodes of the capacitor long and increasing the withstand voltage characteristics of the capacitor. Can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a capacitor of the present invention.

FIG. 2 is a sectional view for explaining mounting of the capacitor shown in FIG. 1 on a wiring board.

[Explanation of symbols]

 1 ・ ・ ・ ・ Dielectric porcelain plate 2 ・ ・ ・ ・ ・ ・ ・ ・ Thin film electrode 3 ・ ・ ・ ・ Thin film brazing material 4 ・ ・ ・ ・ Wiring board 5 ・ ・ ・ ・ ・ ・ ・ ・ Wiring conductor

Claims (3)

[Claims] 1. A capacitor characterized in that a thin film electrode is deposited on both main surfaces of a dielectric ceramic plate, and a thin film brazing material is deposited on at least one surface of the thin film electrode. 2. The capacitor according to claim 1, wherein the dielectric ceramic plate is made of barium titanate, and the thin film electrode has a three-layer structure of a titanium layer, a palladium layer and a gold layer. 3. The capacitor according to claim 1, wherein the thin-film brazing material is made of a gold-tin alloy and has a thickness of 0.5 to 10 μm.