JPH07262821A - Conductive paste - Google Patents

Abstract

PURPOSE:To provide a conductive paste which has a high conductivity and excellent economically efficiency, and can prevent or reduce a short circuit between electrodes or between wirings under the ambiance of a high temperature and a high humidity, by including a ceramics powder whose surface is covered with a specific compound particle in the conductive paste. CONSTITUTION:This conductive paste contains a ceramics powder whose surface is covered with compound particles of a silver powder and a titanium powder. Although the form of the compound particles of the silver powder and the titanium powder is not limited, it is preferable to be a flake form whose mean aspect ratio is about 3 or higher, and it is more preferable to be the flake form with the aspect ratio 10 or higher. Although the form of the compound particles is not limited, it is favorable to have the undifined form having few projection, and its mean grain size is preferable less than 10mum, being more preferable to be less than 5mum. The manufacturing method of the compound particles is not limited, but a strong impact is applied to the particles after the silver powder and the titanium powder are mixed together evenly, or while mixing them evenly, so as to integrate plural particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste for forming an electric circuit.

[0002]

2. Description of the Related Art Conventionally, as a method for forming a wiring conductor of a printed wiring board, an electronic component, etc., a method of applying or printing a paste containing silver powder having excellent conductivity is generally known. .

[0003]

Since the conductive paste using silver powder has good conductivity, it is used as a wiring conductor or an electrode of a printed wiring board, an electronic component or the like, but these are used in a hot and humid atmosphere. When an electric field is applied to the wiring conductors and electrodes, silver electrodeposition called migration occurs, which causes a short circuit between electrodes or between wirings. Several measures have been taken to prevent this migration, and measures such as applying a moisture-proof coating to the surface of the conductor or adding a corrosion inhibitor such as a nitrogen-containing compound to the conductive paste have been studied. The effect was not sufficient.

Migration can be improved by using an alloy of silver and palladium, but since palladium is expensive, the conductive paste is also expensive, and in order to obtain a conductor having good conduction resistance, silver powder or a silver-palladium alloy powder is blended. The amount has to be increased, and since these raw materials are expensive, the conductive paste is also expensive.

The present invention provides a conductive paste that does not have such drawbacks.

[0006]

The present invention relates to a conductive paste containing ceramic powder whose surface is coated with composite particles of silver powder and titanium powder.

The shape of the composite particles of silver powder and titanium powder in the present invention is not limited, but it is preferable to have a flake shape having an average aspect ratio of about 3 or more, and a flake shape of 10 or more. The shape is more preferable. The average particle diameter of the major axis is preferably 20 μm or less, and more preferably 10 μm or less because printability is not deteriorated.

Although the shape of the ceramic powder is not limited, an irregular shape with few protrusions is suitable, and the average particle diameter is preferably 10 μm or less, more preferably 5 μm or less. Further, it is desirable that the entire surface of the ceramic powder is covered with the composite particles, but if the ceramic powder is substantially covered, no problem will occur. As the ceramic powder, alumina powder, silica powder, silicon carbide powder, aluminum nitride powder, silicon nitride powder, zirconia powder and the like are used. The method for producing the composite particles is not particularly limited, but after the silver powder and the titanium powder are mixed almost uniformly or while being mixed substantially uniformly, a strong impact force may be applied to the particles to integrate the plurality of particles. Specifically, a ball mill, a continuous bead mill, or the like may be used to mix them substantially uniformly, and then this may be treated with a device such as a vibration mill, a planetary ball mill, or an attritor that can apply a high shearing force, to form a composite integral. . The method for coating the composite particles on the ceramic powder is not particularly limited. For example, the composite particles are put into a ball mill together with a ball for pulverization, and the surface of the ceramic powder is dispersed by rotating the composite particles to disperse the aggregated composite particles. The coating method is preferable because a large amount can be processed.

The ratio of silver powder to titanium powder of the composite particles is preferably 100: 1 to 20: 1 (silver powder: titanium powder) in weight ratio from the viewpoint of resistance of conductor, migration prevention and soldering resistance. The volume ratio of composite particles to ceramic powder is 5: 1 to 1: 1 in terms of resistance of conductor, prevention of migration and price (composite particles: ceramic powder).
Is preferred.

In addition to the above materials, the conductive paste is a curing agent for an organic adhesive component such as liquid epoxy resin, phenol resin, unsaturated polyester resin, and the like, and an organic adhesive component such as 2 ethyl 4-methylimidazole, and if necessary. It contains a solvent such as terpineol, ethyl carbitol, carbitol acetate and butyl cellosolve, a corrosion inhibitor such as benzothiazole and benzimidazole, and fine graphite powder. The content of silver powder, titanium powder, and ceramics powder is preferably 20 to 60% by weight from the resistance of the conductor and economy with respect to the solid content of the conductive paste, and 30
More preferably, it is from about 60% by weight.

[0011]

EXAMPLES Examples of the present invention will be described below. Example 1 60 parts by weight of bisphenol A type epoxy resin (Oilized shell epoxy, trade name Epicoat 834) and 40 parts by weight of bisphenol A type epoxy resin (Oilized shell epoxy, trade name Epicoat 828) were dissolved by heating in advance. ,
Then, after cooling to room temperature, 5 parts by weight of 2 ethyl 4-methyl imidazole (manufactured by Shikoku Kasei), 20 parts by weight of ethyl carbitol (manufactured by Wako Pure Chemicals, reagent), 20 parts by weight of butyl cellosolve (manufactured by Wako Pure Chemicals, reagent) were added. The resin composition was mixed uniformly.

On the other hand, 110 g of flake-shaped silver powder (TCG-1 manufactured by Tokuriki Kagaku Kenkyusho) and an average particle size of 1 μm.
5.5 g of the following titanium fine powder (manufactured by Kojundo Chemical Co., Ltd.) was put into a ball mill together with a ball for pulverization and rotated for 100 hours. Further, this was transferred to a planetary ball mill (high-speed rotation ball mill), and a high shearing force was applied for 100 hours to integrate them, and the aspect ratio was 20 on average and the average diameter of major axis was 6 μm.
The composite particles of Next, the composite particles and alumina powder having an average particle size of 0.4 μm (trade name AES-, manufactured by Sumitomo Chemical Co., Ltd.
12) 35 g was put into a ball mill together with a ball for pulverization, rotated for 100 hours to be uniformly dispersed, and alumina powder having the surface coated with composite particles was produced. When the coverage of the composite particles on the alumina powder was observed with an optical microscope, the coverage was about 90%. Thereafter, 150.5 g of the alumina powder coated with the above composite particles was added to 145 g of the resin composition obtained above and uniformly dispersed by a stirrer and a triple roll to obtain a conductive paste.

Next, a paper phenol copper-clad laminate (made by Hitachi Chemical Co., Ltd., trade name MCL- with a thickness of 1.6 mm and a through hole having a diameter of 0.8 mm (φ) formed with the conductive paste obtained above. 437F) was printed with the test pattern shown in FIG. 1 and the through hole 1 was filled with the test pattern and heated at 60 ° C. for 30 minutes and 160 ° C. for 30 minutes to obtain a wiring board. In FIG. 1, 2 is a paper phenol copper clad laminate. Next, the resistance of the obtained wiring board was measured. As a result, through hole 1 excluding the resistance of copper foil
The resistance was 24 mΩ / hole, and the insulation resistance between adjacent through holes was 10 ⁸ Ω or more. As a result of the thermal shock test of the wiring board, the resistance of the through hole 1 is 30 m.
Ω / hole. Moreover, as a result of performing a wet and medium load test on the wiring board, the insulation resistance between the through holes was 10 ⁸ Ω or more. The cold heat test conditions are 125 ° C. 30 minutes to −65 ° C.
100 cycles of 30 minutes, 40 ° C 9
In 0% RH, a voltage of 50 V was applied between adjacent lines and held for 1000 hours. Also, solder resistance test (260
However, solder curl was not observed in the cured conductive paste in the land portion.

Example 2 Aspect ratio was 20 on average and the average diameter of major axis was 6 μm through the same steps as in Example 1 except that 200 g of the flake silver powder used in Example 1 and 5 g of titanium powder were blended. Composite particles were prepared, and then 40 g of the alumina powder used in Example 1 and the alumina powder used in Example 1 were put into a ball mill together with a ball for pulverization and rotated for 100 hours to uniformly disperse the alumina powder whose surface was coated with the composite particles. It was made. Then, 245 g of the alumina powder coated with the above composite particles was added to 145 g of the resin composition obtained in Example 1 and uniformly mixed and dispersed in the same manner as in Example 1 to obtain a conductive paste. A wiring board was manufactured through the same steps as in Example 1 and the characteristics thereof were evaluated. As a result, the resistance of the through hole is 22 mΩ.
/ Hole, and the insulation resistance between through holes was 10 ⁸ Ω or more. As a result of the thermal shock test of the wiring board, the resistance of the through holes was 28 mΩ / hole, and the result of the wet and medium load test showed that the insulation resistance between the through holes was 10 ^8.
It was more than Ω.

Example 3 The same aspect ratio as in Example 1 was used except that 730 g of the flake silver powder and 70 g of titanium powder used in Example 1 were blended, and the aspect ratio was 20 on average and the average diameter of major axis was 6 μm.
Composite particles and 70 g of the alumina powder used in Example 1 were put into a ball mill together with a ball for grinding, and the mixture was rotated for 100 hours to be uniformly dispersed and the surface of the alumina powder was coated with the composite particles. Was produced. Thereafter, 870 g of the alumina powder coated with the above composite particles was added to 145 g of the resin composition used in Example 1 and uniformly mixed and dispersed in the same manner as in Example 1 to obtain a conductive paste.
A wiring board was manufactured through the same steps as in Example 1 and the characteristics thereof were evaluated. As a result, the through hole resistance is 21
mΩ / hole, insulation resistance between through holes is 10 ⁸ Ω
That was all. As a result of the thermal shock test of the wiring board, the resistance of the through hole was 26 mΩ / hole, and the result of the wet and medium load test showed that the insulation resistance between the through holes was 10 mΩ / hole.
It was more than ⁸ Ω.

Comparative Example 1 To 145 g of the resin composition obtained in Example 1, 1000 g of the flake silver powder used in Example 1 was added and uniformly mixed and dispersed in the same manner as in Example 1 to obtain a conductive paste. A wiring board was manufactured through the same steps as in Example 1 and the characteristics thereof were evaluated. As a result, the resistance of the through holes was 22 mΩ / hole, and the insulation resistance between the through holes was 10 ⁸ Ω or more. As a result of a thermal shock test of the wiring board, the resistance of the through hole was 28 mΩ / hole. According to the result of the wet and medium load test, the insulation resistance between the through holes was 10 ^{7 for} 5 wiring boards. It had dropped to the Ω range. Further, when the same soldering resistance test as in Example 1 was carried out, solder nicks were observed in the conductive paste cured product in the land portion.

[0017]

EFFECT OF THE INVENTION The conductive paste according to the present invention is a highly conductive paste having a low resistance of through holes in a wiring board, and has a small decrease in insulation resistance between through holes after a wet and medium load test. It is a conductive paste that is economically excellent in that migration resistance and solder resistance can be improved without using expensive palladium.

[Brief description of drawings]

FIG. 1 is a plan view showing a state in which a conductive paste is printed on a paper phenol copper clad laminate and the through holes are filled.

[Explanation of symbols]

 1 Through hole 2 Paper phenol copper clad laminate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Wada 4-13-1, Higashimachi, Hitachi City, Ibaraki Prefecture Ibaraki Research Laboratory, Hitachi Chemical Co., Ltd. (72) Inventor Toshikazu Ono 3-chome, Ayukawacho, Hitachi City, Ibaraki No. 3 Sakuragawa Sangyo Co., Ltd.

Claims (1)

[Claims] 1. A conductive paste containing ceramic powder, the surface of which is coated with composite particles of silver powder and titanium powder.