JPH07118575B2 - Thick film circuit board and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thick film circuit board having a large-capacity printed capacitor and a method for manufacturing the same.

[Technical background of the invention and its problems]

In recent years, hybrid ICs have been widely used to reduce the size and weight of electronic devices. In general, this hybrid IC is a chip-type passive element with no lead wire or active element on a thick film circuit board where wiring patterns and resistors are formed by printing and firing conductive paste or resistance paste on an insulating substrate such as alumina. An element (hereinafter referred to as a chip component) is mounted. In order to further increase the density and functionality of the above hybrid ICs, a thick film circuit board with a printed capacitor, in which a large-capacity capacitor of the above chip components is printed and fired with a dielectric paste to form a film, has been put into practical use. It is coming.

In FIG. 3 showing such a conventional thick film circuit board,
Reference numeral 30 is an insulating substrate formed of a ceramic material such as alumina. This insulating substrate 30 has silver / palladium (Ag / P
The lower electrode 31 and the wiring pattern layer 32 of the membrane capacitor are formed by printing and firing a d) type conductive paste. Next, a high dielectric constant dielectric paste such as barium titanate containing lead glass is printed and fired on the lower electrode 31 to form the dielectric layer 33. Then, a silver / palladium-based conductive paste is printed again on the dielectric layer 33.
The upper electrode 34 is formed by firing. As described above, the printed capacitor is formed on the insulating substrate 30. The thick film material is fired in air at about 900 ° C.

The thick film circuit board having the above-mentioned conventional printed capacitor uses a silver / palladium-based conductive paste as its wiring material. Since this conductive paste has a high sheet resistance of 20 to 50 mΩ / □, the conductivity of the wiring pattern layer 32 is low, that is, the pattern resistance is high. Moreover, since a migration phenomenon of silver occurs due to moisture absorption, insulation deterioration between patterns is likely to occur. Further, since it is a noble metal, there is a drawback that the paste cost becomes high.

Therefore, in recent hybrid ICs, a copper-based conductive paste is used as a wiring material, and low-temperature firing is performed in an inert atmosphere such as nitrogen gas so as not to oxidize it. This conductive paste has a sheet resistance of 2-5mΩ /
It has the advantages that it is as low as □ and that the transition phenomenon is unlikely to occur.

However, the copper-based conductive paste cannot be replaced with a silver / palladium-based conductive paste in a thick film circuit board having a conventional printed capacitor.
In general, since a high-dielectric-constant dielectric paste contains a lead-based compound, the lead compound is reduced to metallic lead when fired in an inert atmosphere. Therefore, simply applying the manufacturing process using a copper-based conductive paste will significantly reduce the capacitance of the membrane capacitor and also significantly reduce the insulation resistance between the upper and lower electrodes, and the function as a membrane capacitor will not be fulfilled. Will end up.

As explained above, it has a large-capacity printed capacitor,
In addition, it has not been possible to realize a thick film circuit board having excellent wiring pattern characteristics.

In particular, in electronic tuning tuners for television receivers that have a large number of large-capacity pass capacitors of several thousand pF, high-density mounting by thickening the capacitor is desired, but the conventional silver / palladium-based conductive paste was used. For thick film circuit boards,
Since the conductivity of the circuit wiring pattern is low, the high-frequency characteristics are poor, and practical application is impossible.

[Object of the Invention]

An object of the present invention is to provide a thick film circuit board having a large capacity printed capacitor and excellent wiring pattern characteristics, and a method for manufacturing the same.

[Outline of Invention]

In this invention, a large-capacity printed capacitor is formed by using an in-air firing type conductive paste for the lower and upper electrodes so that the dielectric layer formed of the high dielectric constant paste containing a lead-based compound is not reduced, and The conductor wiring layer including the lead wiring patterns for the lower and upper electrodes is formed of a copper-based conductive paste that is fired in an inert atmosphere to improve the characteristics of the wiring pattern. In order to prevent reduction of the dielectric layer that occurs during firing, the printed capacitor is covered with a coating layer to achieve the above object.

Example of Invention

An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1 (a), 10 is an insulating substrate formed of a ceramic material such as alumina, which is printed with an air-baking type conductive paste such as silver / palladium and is heated in the air at 900 ° C to 950 ° C.
The lower electrode 11 of the capacitor is formed by firing at 1 ° C. for about 1 hour. Next, as shown in FIG. 1 (b), a high dielectric constant dielectric paste containing a lead-based compound is printed on the lower electrode 11 and fired in air at 900 ° C. to 950 ° C. for about 1 hour. Forming the dielectric layer 12. Then, on this dielectric layer 12, the upper electrode
13 is printed and fired in the same manner as the lower electrode 11 to form as shown in FIG. By the above, the membrane capacitor is printed / formed.

Next, as shown in FIG. 1 (d), an insulating paste containing crystalline glass or the like as a main component is printed so as to almost cover the lower electrode 11, the dielectric layer 12 and the upper electrode 13, and a 90
The coating layer 14 is formed by baking at about 0 ° C. for about 1 hour. At this time, in order to draw out the wiring pattern from the lower electrode 11 and the upper electrode 13, the coating layer 14 is provided with openings 15 and 16, respectively. Further, the dielectric layer 12 prevents the above-mentioned reduction,
Must be completely covered.

Thereafter, as shown in FIG. 1 (e), the electrode lead-out wiring patterns 17 and 18 connected to the lower electrode 11 and the upper electrode 13 through the openings 15 and 16 and the wiring pattern 19 of the circuit board are made of copper-based material. It is formed by printing using an electrically conductive paste and firing at 600 ° C. to 900 ° C. for about 1 hour in an inert atmosphere such as nitrogen gas.

If necessary, an overcoat layer (not shown) that covers the entire thick film circuit described above is formed. This is generally
It is performed by printing a low-melting-point glass insulating paste and baking it at a low temperature of 600 ° C. or lower in nitrogen gas, or by printing and curing an organic insulating resin paste.

In the above embodiment, since the lower and upper electrodes 11 and 13 are formed of the air-baking type conductive paste, reduction of the dielectric layer 12 does not occur when the electrodes 11 and 13 are formed. Furthermore, the coating layer
14 completely covers the dielectric layer 12 and separates it from the inert atmosphere. Therefore, the dielectric layer 12 formed of the high-dielectric-constant paste containing the lead-based compound has the wiring patterns 17 to 19 of the circuit.
It is possible to form a large-capacity printed capacitor without being reduced even when the copper-based conductive paste required for the formation of the above is baked.

Next, the characteristics of the printed capacitor formed by the above embodiment will be described.

Here, considering the compatibility such as the matching of each layer, the electrodes 11, 1
DuPont's # 9843 as the silver / palladium-based conductive paste of No. 3, # 5217 as the high dielectric constant paste containing the lead-based compound of the dielectric layer 12, and # 5 as the crystalline glass-based overcoat forming the coating layer 14. 9688, wiring patterns 17-19
As a low temperature firing type copper-based conductive paste that forms
6001D was used.

The following table shows various characteristics of the printed capacitor when the film thickness of the dielectric layer 12 after firing is formed to about 50 μm. As a comparative example, various characteristics of the printed capacitor when the wiring patterns 17 to 19 are printed without forming the reduction preventing coating layer 14 and fired in nitrogen gas are also shown.

From this table, according to the example, it is possible to form a printed capacitor having a large capacity, a large insulation resistance between the upper and lower electrodes, and an excellent withstand voltage characteristic, while the lead compound of the dielectric layer 12 is reduced in the comparative example. , It can be seen that the performance of the capacitor is not practical.

As described above, according to this embodiment, even if a high dielectric constant paste containing a lead-based compound is used, reduction of the lead-based compound can be prevented by the coating layer 14, so that a large-capacity thick film capacitor is formed. be able to.

A copper-based conductive paste was used as the wiring material, and was baked at a low temperature in an inert atmosphere so that it would not be oxidized. This makes it possible to use a copper-based conductive paste, so that the occurrence of the migration phenomenon can be suppressed.

Further, since the main wiring patterns 17 to 19 of the circuit are formed by using the copper-based conductive paste, the impedance of the wiring pattern can be made extremely low and the high frequency characteristics are improved. Therefore, it is possible to obtain a thick film circuit board that can be practically used for a high frequency circuit such as an electronic tuning tuner having a large number of large-capacity bus capacitors of several thousand pF.

Furthermore, the silver / palladium-based conductive paste is used for the upper electrode.
11. Since it is applied only to a limited part of the lower electrode 13, it has an advantage that insulation deterioration between patterns due to a transition phenomenon is extremely unlikely to occur.

It should be noted that the formation of a printed resistor commonly used as a thick film circuit board may be combined with the present invention to obtain a thick film circuit board having a printed resistor and a printed capacitor.

Next, another embodiment of the present invention will be described with reference to FIG.

The structure shown in FIG. 2 does not have openings in the coating layer 24 to draw out the wiring pattern from the lower electrode 21 and the upper electrode 23, but exposes the ends 25 and 26 of the electrodes 21 and 23, respectively.
Formed 24. In this case also, the dielectric layer 22
Is completely covered by the coating layer 24. Also in this embodiment, the same effect as the previous embodiment can be obtained.

〔The invention's effect〕

According to the present invention, it is possible to provide a thick film circuit board having a large-capacity printed capacitor and excellent wiring pattern characteristics, and a method for manufacturing the same.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention, FIG. 2 is a side sectional view showing another embodiment of the present invention, and FIG. 3 is a side sectional view showing a conventional thick film circuit board. . 10 ... Insulating substrate, 11 ... Lower electrode, 12 ... Dielectric layer, 13 ... Upper electrode, 14 ... Covering layer, 15,16 ... Opening, 17-19 ... Wiring pattern.

Claims (2)

[Claims] 1. An insulating substrate, a lower electrode layer, a dielectric layer made of a lead-based compound, and an upper electrode layer made of the same material as the lower electrode layer are laminated on the insulating substrate and formed by firing in air. A printed capacitor, a coating layer that covers a part of the lower and upper electrode layers, and a lead-out wiring pattern that connects to the lower and upper electrode layers that are not covered with the coating layer, and is made of an inert gas. A thick film circuit board, comprising: a conductor wiring layer formed of a copper-based conductive paste that is fired in an atmosphere. 2. A first step of printing a firing type conductive paste in an air atmosphere on an insulating substrate and firing the paste to form a lower electrode layer, and a high conductivity containing a lead-based compound on the lower electrode layer. A second step of printing and firing a paste to form a dielectric layer; and a third step of printing and firing a conductive paste of the same material as the lower electrode layer on the dielectric layer to form an upper electrode layer. A fourth step of forming a coating layer on the printed capacitor including the lower electrode layer, the dielectric layer and the upper electrode layer; and a conductor wiring including a lead wiring pattern of the lower and upper electrodes coated with the coating layer. A fifth layer is formed by printing and firing a copper-based conductive paste that is fired in an inert gas atmosphere.
And a step of manufacturing the thick film circuit board.