JPH03176904A - Conductive paste - Google Patents

Abstract

PURPOSE:To realize conductive paste having excellent performance and burnable in the atmosphere at a low cost by using predetermined quantities of respective Cu powder, B powder, boric acid or borate powder, glass frit and organic vehicle. CONSTITUTION:Low cost Cu is used to substitute for expensive Ni. A predetermined ratio is provided between respective compositions. Namely, the ratio of B powder against 100 weight part of the total weight of Cu powder and B powder is 3.5-3.9 weight part. The ratio of boric acid or borate against 100 weight part of the total weight of Cu powder and B powder is 2.0-50.0. The ratio of glass frit against 100 weight part of the total weight of Cu powder and B powder is 10-30 weight part. A conductive composition having excellent fluidity, formability, printing property and high conductivity can be manufactured with this paste composed in that method.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a conductive paste, and more particularly to a conductive paste that uses Cu powder as a conductive powder and can be fired in the atmosphere.

(Prior art) Generally, conductive paste is used for conductor circuits, electrodes of ceramic capacitors, radio I wave shield materials, electrodes of plasma displays, etc., and is particularly promising for use as electrodes for DC type plasma displays. being watched.

For example, in a plasma display, an electrode (cathode) is printed on a glass back plate substrate, and a transparent electrode is formed on the cover plate side facing the cathode.
A voltage is applied between both electrodes to cause discharge and color development.This is done by screen printing a metal conductive paste such as Ni on the back plate substrate to form a thick film, then drying it and baking it in the air. to form an electrode.

In this type of conductive paste, Ni is easily oxidized and loses its conductivity when it is baked in the air to form electrodes, etc., during manufacture, so B is included in the conventional base composition to oxidize the Ni. The idea is to prevent hitting. Examples are Special Publication No. 51285-1985 and Special Publication No. 51285-1983.
It is disclosed in Japanese Patent No. 16041. Among these, the former is Ni and B (N13'B)a (Ni3Sl
) b (') It is contained in the form of a composition, and the latter is in the form of B powder added to Ni powder,
In either case, the oxidation reaction of Ni is prevented by the selective oxidation reaction of B.

(Problems to be Solved by the Invention) However, these conventional conductive pastes have the following problems in terms of their manufacturing method and characteristics.

That is, in the case of the former described in Japanese Patent Publication No. 55-51285, (N 13B) a (N 13Si
) To produce the composition b, it is necessary to add B to Ni, dissolve it, solidify it, and then crush it. At this time, since the Bρ specific gravity is about 1/4 lighter than Ni, a uniform composition can be obtained. It is difficult to manufacture, and the manufacturing cost is high because it is crushed into granular powder (in addition, the powder shape is angular, making it difficult to print the paste on a substrate). It's bad.

In addition, in the case of the latter described in Japanese Patent Publication No. 60-16041, since a relatively large amount of B is added (the amount of B added is 4 to 50%), the oxidized B20 floats on the surface in a glass-like manner. However, there is a problem in that a large amount of B2O3 becomes an impurity and increases the electrical resistance value.

The present invention has been made to solve these problems, and the problem to be solved by the present invention is to use relatively inexpensive Cu instead of Ni, and improve fluidity, moldability, and printability. An object of the present invention is to provide a conductive paste that can be fired in the atmosphere, and can produce a conductive composition with high conductivity.

(Means for Solving the Problems) The present invention has been made to solve the above problems, and
Its gist is that it is a conductive paste consisting of Cu powder, B powder, boric acid or borate powder, glass frit, and organic vehicle, the composition of which is (a).
The B powder is 3.5 to 3.9 parts by weight based on 100 parts by weight of the total weight of the Cu powder and B powder, and (b) the boric acid or borate powder is 100 parts by weight of the total weight of the Cu powder and B powder. (c) The amount of the glass frit is 10 to 30 parts by weight based on 100 parts by weight of the total weight of Cu powder and B powder.

Since the conductive paste according to the present invention uses Cu powder as the main component, the manufacturing cost is lower than when using Ni powder, and the content of B powder is reduced to 100 parts by total weight of Cu powder and B powder. Since the amount of Cu powder is increased by that much in the range of 3.5 to 3.9 parts by weight, the conductivity is improved. Therefore, when the present invention is applied to electrode formation of a plasma display, the image clarity becomes good.

The average particle size of the Cu powder is desirably in the range of 1 to 30 μm, more preferably in the range of 5 to 20 μm. This is because when the average particle size is less than 1 μm, the surface area of the Cu particles becomes relatively large (the oxidation reaction of Cu is likely to be promoted and the electrical resistance value tends to increase), and the average particle size is 30 μm.
The reason why the thickness is set to be less than μm is because if it exceeds 30 gm, the fluidity of the conductive paste deteriorates, and printability and filling performance deteriorate.

The reason for adding B powder is to prevent Cu from oxidizing.
For this purpose, at least 3.5 parts by weight of B powder is required per 100 parts by weight of the total weight of B powder and Cu powder,
If it exceeds 3.9 parts by weight, the Cu content decreases and the resistance value increases accordingly, so the amount of B powder is set in the range of 3.5 to 3.9 parts by weight.

That is, B is selectively oxidized to B2O3 at high temperatures as described below, but the melting point of this B2O3 is 57
Since the temperature is about 7℃, if the amount of B is large, selectively oxidized B203 floats to the surface when the paste is fired in the atmosphere at a firing temperature of about 600 to 620℃, causing a glittering state, which deteriorates the electrode properties. This causes a decrease in image clarity in plasma displays. This boundary region that reduces image clarity occurs when the amount of B added is 4.0 parts by weight, and if it is more than this, B2O3 will float to the electrode surface and the surface will become glittery. be. On the other hand, if the amount of B added is less than this, the glittering effect on the electrode surface disappears, floating of B2O3 is not observed, and the image clarity of the plasma display becomes high.

Further, the raw material powder form of B is preferably an amorphous powder, or preferably a powder with an average particle size of 50 LLm or less. This is because if the average particle size exceeds 50 Ht.m, the fluidity, printability, etc. of the conductive paste will deteriorate.

The amount of boric acid or borate powder is in the range of 20 to 50 parts by weight based on 100 parts by weight of the total weight of Cu powder and B powder. Adding boric acid or borate powder is at a temperature of 300
This is to form a glassy substance in the range of ~500°C and effectively suppress the oxidation of Cu, and for this purpose, at least 2.
0 parts by weight are required. Moreover, if it exceeds 50 parts by weight, B
This is because the base I becomes like a glass film and forms an insulator, increasing the resistance value of the base I.

In boric acid, for example, the reaction shown in the following formula is promoted at 300°C.

2H3BO2□→B203+3H20 Here, ■ boric acid is orthoboric acid (H3BO.

), metaboric acid (HBO2), tetraboric acid (H□B4O7
)including. ■Borates include orthoborate, diborate, metaborate, tetraborate, pentaborate, heborate, etc., which correspond to the general formula % formula % 5/2.4. be. For example, Co B 407 , CuB
4O? , Na2B407 , Li2B4O, ,2Zn
0 ・3B203 ・3.5H20, K2 B40?
'4■]10. CaB4O?・6H20, MnB
a 0? -8820 etc.

The glass frit has a total weight of Cu powder and B powder of 100
It is desirable that the amount is in the range of ]0 to 30 parts by weight. Glass frit is added (J, this is because glass frit becomes vitrified at temperatures in the range of 400 to 600°C during firing, forms a protective layer around Cu powder, and plays a role in preventing oxidation of Cu. In this case, 10 parts by weight or more of glass frit is required. Too much glass frit makes it easy to form a glass film-like insulator (and the conductivity decreases), so it should be within 30 parts by weight.

The organic vehicle is added to ensure the fluidity of the conductive paste.

The conductive paste having the composition described above can be fired in the air, that is, in an oxidizing atmosphere. Further, firing can be performed at a maximum temperature of 600°C.

Next, how the oxidation of Cu is prevented by the various additives when the conductive paste is fired in the atmosphere will be explained based on FIG. 1. The additives in the range of the arrows shown in FIG. 1 show that their antioxidant effect mainly works within that temperature range.

When the temperature is gradually increased from room temperature during firing after pre-calcination, the organic vehicle prevents the oxidation of Cu in the range C' from room temperature to about 350°C. and from 300℃ to 3
In the range of 50°C, Cu oxidation prevention by the organic vehicle (movement) and the formation of a glassy layer around Cu as boric acid or borate powder changes to glassy state prevents Cu oxidation. from 350°C to 400°C
℃ range, boric acid or borate powder B2O
Vitrification to 3 prevents oxidation of Cu.

When the temperature ranges from 400° C. to 550° C., the oxidation of Cu is further prevented by the glass frit forming borosilicate glass. When the temperature exceeds 550°C, oxidation of Cu is suppressed as B is selectively oxidized. At around 600°C, the effect of B is significant, and the oxidation of Cu is effectively suppressed.

These organic vehicles, boric acid or borate powder, glass frit, and B each effectively prevent Cu from oxidizing in a predetermined temperature range. As a result, 600
The oxidation-suppressing effect is significant even at temperatures around or near °C, making it possible to sinter while maintaining electrical properties.

(Example) Examples of the present invention will be described below.

0 As a raw material for conductive paste, the average particle size is 10°4 μm.
A spherical Cu powder, an amorphous B powder, a boric acid or borate powder, a glass frit was added thereto, and an organic vehicle in which ethyl cellulose was dissolved in terpineol was used. After kneading these using a three-roll mill, lines with a line width of 0.5 mm and a length of 100 mm were printed on an alumina substrate using a #200 screen. After drying this at 120℃ for 10 minutes,
It was baked in the atmosphere at 650°C for 15 to 20 minutes. The average film thickness after firing was 50 μm.

When the surface condition of the obtained fired part was observed and the surface oxidation state was observed from the hue of the fired part, the hue of the fired part was as shown in Table 1. When the specific resistance value of the fired part was measured, the results were as shown in Table 1.

(The following is a blank space.) (1) In Table 1, in Examples 1 to 10, the specific resistance value of the fired portion was 2]Xl0-'Ωcm or less, indicating that the conductivity was high.

On the other hand, in Comparative Examples 1 to 4, the content of B deviates from the scope of the present invention, and in Comparative Examples 5 and 6, for reasons such as not containing boric acid or borate powder,
The specific resistance value is extremely large or unmeasurable (50Ω)
The result was that the resistance was higher than cm. Further, in Comparative Examples 7 and 8, the specific resistance values were large because the firing temperatures were as high as 620° C. and 650° C., respectively. This is presumed to be because oxidation was excessively accelerated at high temperatures.

(Effect of the invention) As explained above, in the conductive paste 1 of the present invention, J:
A1 is a paste with good fluidity, filling properties, and printability, and the oxidation prevention effect works properly even during high-temperature atmospheric firing, so the resulting conductor not only has a low electrical resistance value but also has good compatibility with the substrate. Simultaneous firing becomes possible, and a good conductor can be obtained through a simple production process.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram for explaining the antioxidant effects of various additives added to the conductive paste.

Claims (1)

[Scope of Claims] A conductive paste consisting of Cu powder, B powder, boric acid or borate powder, glass frit, and an organic vehicle, the composition of which is: (a) the B powder is composed of Cu powder and B powder; Total weight of powder 10
(b) The boric acid or borate powder is 2.0 to 50.0 parts by weight relative to 100 parts by weight of the total weight of Cu powder and B powder. (c) The conductive paste is characterized in that the glass frit is present in an amount of 10 to 30 parts by weight based on 100 parts by weight of the total weight of the Cu powder and the B powder.