JPH09147625A - Conductive paste and printed wiring board using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board which can prevent the increase in the resistance against electric conduction due to the oxidation of copper powder contained in a conductive paste even when it is used for a long time under the environment of high-temperature and high-humidity, corrosive gases or the like. SOLUTION: A conductive paste 4 which has a number of pores and in which a porous copper powder comprising particles 42 made to adsorb a material having the action of reduction on oxides is mixed and dispersed into a synthetic resin liquid, is applied to one side or both sides of an insulating base material 1 and/or the wall surface of a through-hole perforated in the insulating base material 1 and then dried to form a conductive film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board mounted on a signal processing circuit or the like of a television receiver, and a conductive paste used therefor.

[0002]

2. Description of the Related Art A conventional printed wiring board manufactured using this type of conductive paste uses a conductive resin paste in which copper powder is mixed and dispersed in a synthetic resin liquid. According to the method described above, the conductive film is formed by applying on the surface of the base material or the wall surface of the through hole formed in the base material and drying to form the conductive film, and the surface contact between the copper metal particles provides conductivity. Conductive paste is generally 60-90% in the paste
The metallic copper powder is blended in a weight ratio of.

[0003]

However, metallic copper, which is easily oxidized even in a normal metal form, is still easily oxidized in a shape having a large surface area, and since copper oxide is a poor conductor, it becomes conductive by contact between copper powders. In a printed wiring board using a conductive paste that obtains electrical conductivity, the electrical conduction resistance value gradually increases under the environment of high temperature and high humidity and corrosive gas in which electrical equipment is used, and it is several tens of percent to the initial resistance value. There was a problem in practical use after rising several times or several tens of times.

On the other hand, in the spherical copper powder having a relatively flat surface state, since the area of interparticle contact is the smallest point contact, the conduction resistance value of the dry film also depends on the difference in the dry conditions.
There is a drawback that the variation becomes large from several tens of milliohms / square to several hundreds of tens of milliohms / square.

Therefore, the present invention uses a conductive paste and a conductive paste capable of increasing the contact area between copper powder particles to obtain a low resistance value and preventing an increase in the conduction resistance value due to the formation of oxides. It is an object of the present invention to provide a printed wiring board that has been used.

[0006]

In order to achieve the above object, the conductive paste of the present invention is a conductive paste in which copper powder is mixed and dispersed in a synthetic resin liquid, and the copper powder has a large number of pores. It is characterized in that it is made of porous particles, and a substance having a reducing action on an oxide is adsorbed in the pores.

The copper powder mainly contains particles having a diameter of about 0.5 to 20 μm, and the pores are mainly about 20 to 20 on the surface of the particles.
Those having openings with a diameter of 0Å are preferable. Formalin or the like is a substance having a reducing action on oxides.

According to this structure, by making the copper powder porous, the contact area between the particles is increased, the contact resistance is reduced, and a low resistance paste can be obtained. Further, since the substance having a reducing action on the oxide is adsorbed in the pores, the generation of the oxide can be suppressed and the initial low resistance can be maintained.

In the printed wiring board of the present invention, the conductive paste is applied to one surface or both surfaces of the insulating base material and / or the wall surface of the through hole formed in the insulating base material and dried to form a conductive coating. It is characterized by having done.

According to this structure, even if the printed wiring board is used for a long time in an environment of high temperature and high humidity or corrosive gas, the reducing component adsorbed in the pores is continuously supplied, and the oxide Suppresses the rise of electrical conduction resistance,
Or keep it to a minimum.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 and 2
Shows a printed wiring board using a conductive paste according to an embodiment of the present invention, where 1 is an insulating substrate, 2 is a copper foil pattern, 3 is an insulating resin, and 4 is a conductive paste.

Next, the method for manufacturing the printed wiring board in the present embodiment will be described in detail. First, in FIG. 1 (a), a desired pattern is formed on a copper foil deposited on one side or both sides of an insulating base material 1 by an ordinary subtractive method to obtain a copper foil pattern 2. In addition, holes 5 penetrating the front and back are provided at required portions of the insulating base material 1 by a drill or the like.

Then, as shown in FIG. 1 (b), an insulating resin 3 is formed into a pattern by a screen printing method in a pattern shape opened so as to expose a part of the copper foil, and after temporary drying. Further, as shown in FIG. 1 (c), the conductive paste 4 containing the porous copper powder according to the present invention is formed by a screen printing method so as to be overlapped with a required circuit pattern. At this time, a film of the conductive paste 4 is also formed on the inner wall surface of the through hole 5, and the copper foil patterns 2 on the front and back are electrically connected by the conductive film obtained by drying them.

Here, as shown in FIG. 2, the conductive paste 4 is made by mixing and dispersing copper powder consisting of porous particles 42 having a large number of pores 41 in a synthetic resin liquid. A substance having a reducing action on the oxide, for example, formalin is adsorbed in the hole 41. An insulating resin 6 may be further coated on the conductive paste 4.

The conductive paste 4 configured as described above
When the copper powder has a porous form, the contact area between particles is increased several times as compared with a mere spherical one, and the contact resistance is reduced, resulting in a low resistance paste. Also,
Since the substance having a reducing action on the oxide is adsorbed in the pores 41, the generation of the oxide can be suppressed and the initial low resistance can be maintained.

Further, as a printed wiring board using the conductive paste 4, even if it is used for a long period of time in an environment such as high temperature and high humidity or corrosive gas, the reducing component adsorbed in the pores 41 continues. Therefore, it is possible to suppress the generation of oxides and prevent an increase in electrical conduction resistance, or to suppress it to a minimum.

The copper powder contained in the conductive paste 4 mainly has a particle diameter of about 0.5 to 20 μm, and the fine pores 41
Preferably has an opening mainly having a diameter of about 20 to 200Å on the particle surface. The particle size of the copper powder is set to about 0.5 to 20 μm because a desired film thickness and pattern accuracy can be obtained by screen printing, and a large number of pores for adsorbing a substance having a reducing action on oxides are formed. It is in a range suitable for formation, and if the particle size is too large, the printability decreases, and if it is too small, the adsorptivity of the substance decreases. In addition, the reason why the opening diameter on the particle surface is approximately 20 to 200Å is that the substance that has a reducing effect on oxides is adsorbed in the pores, its function is maintained permanently, and it is unnecessary. In addition, it is a range in which the substance is not released from the pores.

In the embodiment, the base material provided with the copper foil pattern has been described, but it goes without saying that a multilayer wiring made of a conductive paste may be formed instead of the copper foil pattern.

[0019]

As described above, according to the conductive paste of the present invention, the contact area between particles of copper powder is increased to obtain a low resistance value, and at the same time the conduction resistance value is prevented from increasing due to the formation of oxide. Therefore, the printed wiring board using the conductive paste is of low cost and high quality, that is, it maintains stable quality even if it is used for a long time in an environment such as high temperature and high humidity or corrosive gas. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view in a manufacturing process of a printed wiring board according to an embodiment of the present invention.

FIG. 2 is a partially enlarged cross-sectional view of an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Insulating base material, 2 ... Copper foil pattern, 3,6 ... Insulating resin, 4 ... Conductive paste, 5 ... Through hole, 41 ... Pore, 42 ... Particle.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01B 1/00 9459-5L H01B 1/00 A H05K 1/09 H05K 1/09 A

Claims (4)

[Claims] 1. A conductive paste in which copper powder is mixed and dispersed in a synthetic resin liquid, wherein the copper powder is composed of porous particles having a large number of fine pores, and has a reducing action on oxides in the fine pores. An electrically conductive paste, characterized in that it adsorbs a substance having 2. The copper powder mainly contains particles having a diameter of about 0.5 to 20 μm, and the pores are mainly about 20 to 200 Å on the surface of the particles.
The conductive paste according to claim 1, wherein the conductive paste has an opening having a diameter of. 3. The conductive paste according to claim 1, wherein the substance having a reducing action on the oxide is formalin. 4. A large number of pores containing particles with a diameter of about 0.5 to 20 μm and having openings with a diameter of about 20 to 200Å are provided on the surface of the particles, and the pores are reduced with respect to an oxide. A conductive paste obtained by mixing and dispersing a porous copper powder in which a substance having an action is adsorbed in a synthetic resin liquid, on one side or both sides of an insulating base material, or on a wall surface of a through hole formed in the insulating base material. A printed wiring board having a conductive coating formed by coating and drying.