JPS626284B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a conductive paste, and an object of the present invention is to provide a conductive paste that is inexpensive and has excellent conductivity and corrosion resistance. Conventionally, conductive powder in conductive paste contains
Noble metals such as Au, Ag, and Pd have been used.
Generally, Ag powder is used as the conductive powder, and it is dispersed in a vehicle together with borosilicate glass frit, lead oxide, bismuth oxide, zinc oxide, etc. to form a paste, and this is applied to a substrate such as ceramics by screen printing, etc. After being applied by a method and then fired at a high temperature, it has been used as electrodes for capacitors, piezoelectric elements, semiconductor elements, etc., or as wiring conductors for electronic circuits. However, in recent years, due to the rising prices of precious metals, especially Ag, as an alternative to conductive Ag paste, conductive paste using inexpensive conductive powder, and Cu, Ni as electrodes for baking ceramics are being used.
Many proposals have been made, including the glazed electrode.
For example, as a substitute for Ag powder, cheap Ni,
Conductive pastes made of powders of base metals such as Cu or powders of conductive metal compounds such as TiN and SnO ₂ have been developed and some are now commercially available. However, although conductive pastes using base metal powders such as Ni and Cu have good initial properties, they are unsatisfactory due to poor corrosion resistance, and because they are base metal powders, they are not resistant to firing. However, there are drawbacks such as the need for a non-oxidizing atmosphere. In addition, conductive pastes using conductive metal compound powders such as TiN and SnO ₂ have a relatively high resistance, so it is difficult to obtain conductive pastes with low resistance. Conductive paste has the disadvantage that it cannot be used for high-temperature baking types because TiN oxidizes when baked in air. On the other hand, there is a conductive paste using conductive powder in which Al ₂ O ₃ powder is coated with Ag. This Ag coating
A conductive paste using Al ₂ O ₃ powder is excellent in terms of economy, but because Al ₂ O ₃ has poor wettability with Ag, the adhesion between Al ₂ O ₃ and Ag is poor. During the kneading of the paste, the coated Ag peeled off, resulting in deterioration of the conductivity. Further, a conductive paste using powder of this type of oxide coated with Ag or the aforementioned powder of TiN or SnO ₂ has a problem in that the conductive film after firing does not have solderability. As mentioned above, various conductive pastes have been proposed as Ag substitutes, but none of them are satisfactory in terms of conductivity, corrosion resistance, solderability, etc. The emergence of type conductive pastes is desired. The present inventors investigated various alloy powders mainly composed of base metals in order to satisfy the above-mentioned conductivity, corrosion resistance, solderability, and economic efficiency. We have also found that a conductive paste using a mixed powder of an alloy powder containing Zn as a main component and Ag powder as a conductive medium satisfies the above-mentioned properties to a considerable degree. However, depending on the chemical composition of the glass frit, there remains the problem that the fired film of the conductive paste does not fully satisfy the above-mentioned characteristics. In this type of conductive paste, the strength of the fired film is maintained by melting and solidifying the glass frit during firing. However, glass melt is generally corrosive to metals,
The effect on Cu-Al-Zn alloys is particularly remarkable, and as mentioned above, Cu-Al-Zn alloy powder and Ag
When using a conductive paste that uses a mixed powder as a conductive medium, if the glass frit used is a highly corrosive glass frit, the alloy powder will be corroded by the glass melt during firing, and as a result, the paste will not be fired. The conductivity and solderability of the film cannot be obtained. As a result of research and study on borosilicate glass, the present inventors found that B ₂ O ₃ , SiO ₂ , and Na ₂ O,
Glass whose main component is at least one alkali metal oxide selected from K ₂ O and Li ₂ O is Cu,
It has been found that a mixed powder of alloy powder mainly composed of Al and Zn and Ag powder is effective as a glass frit for a conductive paste using a conductive medium. The corrosivity of glass frit is Al8% by weight,
Cu-Al-Zn with a composition of 25% by weight Zn and the balance Cu
The alloy powder and glass frit were dispersed in a vehicle to form a paste, which was screen printed on an alumina substrate, fired at 850°C in the atmosphere, and evaluated based on the appearance of the fired film. The results are shown in Table 1.

【table】

[Table] In Table 1, those with severe blackening of the fired paste film due to corrosion by the glass melt are ×, and those with black spots observed here and there are △, where almost no black spots are observed. Mark things with a circle.
B ₂ O ₃ is not corrosive, but when added in large amounts it tends to deteriorate the water resistance of glass. SiO ₂ is not corrosive, but when added in large amounts it raises the softening point of the glass, which tends to impose operational constraints. Addition of alkali metal oxides such as Na ₂ O, Li ₂ O, and K ₂ O lowers the softening point of glass and makes it less susceptible to operational constraints, but it tends to increase corrosivity. Addition of Al ₂ O ₃ tends to reduce corrosivity, but increases the softening point of the glass. CaO, Mg
The addition of alkaline earth metal oxides such as O, SrO, BaO, and BeO tends to significantly reduce the corrosivity of glass and increase its water resistance, but it has the disadvantage of raising the softening point. The chemical composition that complements the advantages and disadvantages of the glass frit materials mentioned above and is satisfactory in terms of both workability and corrosion resistance is B ₂ O ₃ 10-70.
mol%, SiO ₂ 15-60 mol%, Al ₂ O ₃ 0-15 mol%, total alkali metal oxides of Na ₂ O, Li ₂ O, K ₂ O 5-50 mol %, CaO, MgO, BaO,
The total amount of alkaline earth metal oxides such as SrO and BeO is 0 to 30 mol%. In addition, an Ag paste using the glass frit according to the present invention and an Ag paste using a commercially available glass frit (PbO-B ₂ O ₃ -SiO _2- based glass frit) were prepared, and the baked films of both were subjected to a moisture resistance test to determine the change in sheet resistance. As a result of follow-up investigation, no difference was found between the two, so the water resistance of the glass frit according to the present invention is satisfactory. In addition, in the case of glass frit materials, the starting raw material of the material may be a substance with a predetermined chemical formula during the vitrification reaction process, such as Na ₂ CO ₃ changing to Na ₂ O during the vitrification reaction process. Well, it doesn't matter what you choose. According to the present invention, a mixed powder of alloy powder and Ag powder is dispersed in a vehicle together with glass frit to form a conductive paste. This paste is a regular A
Similar to g-paste, it is applied to a substrate such as ceramics by a method such as screen printing, and then baked in the atmosphere at high temperature to be used as an electrode or conductive path. The particle size of powder and glass frit ranges from 0.05 to 10μ,
Preferably, the thickness is about 0.5 to 5μ. When the thickness exceeds 10μ, printability during screen printing deteriorates, and sheet resistance after final firing increases. Next, in order to make the present invention more specific, examples will be described in detail. The glass frit according to the present invention was produced as follows. In accordance with the chemical composition according to the invention
Each material such as B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ was weighed to give a total amount of 20 g. As a material, Na ₂ CO ₃ ,
Li ₂ CO ₃ , K ₂ CO ₃ and the like were used. After thoroughly mixing the mixture and vitrifying it in a platinum crucible, the mixture was poured into water to obtain glass. Vitrification at 1300℃2
I spent time. The obtained glass was mechanically crushed to obtain glass frit with an average particle size of about 2 μm. The alloy powder was melted, sprayed with molten metal, and mechanically pulverized to obtain a powder with an average particle size of about 2 μm. Glass frit and alloy powder obtained by the above method, and commercially available silver powder (average particle size of about 2
μ) were weighed to achieve a predetermined mixing ratio, and the total amount was 3 g. The weight of the glass frit is 15% of the total amount.
It was expressed as weight%. Vehicle 1 consisting of ethyl cellulose (100 cps) and terpineol
ml using a Hubermala. Kneading with Hoover Mara, load 100 lbs., 40 lbs.
Rotation was repeated four times. After printing the paste prepared above into a predetermined shape on an alumina substrate using a screen printing method,
It was dried at 120°C for 10 minutes and fired in air at 750-850°C for 10 minutes, followed by a 1-hour cycle including temperature increases and decreases. Table 2 shows the results of measuring the resistance values between both ends of the printed pattern. Table 2 also shows the solderability of the fired films, with those that are easy to solder marked as ○, those that are relatively easy to solder as △, and those that cannot be soldered as ×. Further, in Table 2, the composition of alloy powder A is 8% by weight of Al, 25% by weight of Zn, and the balance is Cu, and the composition of alloy powder B is 4% by weight of Al, 30% by weight of Zn, 0.1% by weight of B, and the balance is Cu. In addition, No. 22 glass fritz has
Commercial products based on ZnO, B ₂ O ₃ and SiO ₂ were used, and commercial products based on PbO, B ₂ O ₃ and SiO ₂ were used for glass frit No. 23.

【table】

[Table] As is clear from the above explanation and Table 2, the conductive paste according to the present invention has conductivity,
In terms of solderability, it exhibits sufficient properties for practical use, and furthermore, it has the excellent effect of being able to be fired in air. In addition, economically, by specifying the chemical composition of the glass frit, it is possible to use a mixed powder of base metal alloy powder and Ag powder as the conductive powder, which is extremely superior to conventional Ag paste. Since the conductive paste can be produced at low cost, it has great industrial value.

Claims (1)

[Scope of Claims] 1. An alloy containing at least three elements of Cu, Al, and Zn is mixed with Ag powder, and this is dispersed in a vehicle together with a glass frit, and as the glass frit, B ₂ O ₃ ,
1. A conductive paste characterized by using a paste mainly containing SiO ₂ and at least one alkali metal oxide selected from Na ₂ O, Li ₂ O, and K ₂ O. 2 As glass frit, B ₂ O ₃ 10 to 70 mol%, SiO ₂ 15 to 60 mol%, Al ₂ O ₃ 0 to 15 mol%,
5 to 60 mol% of at least one component from the alkali metal oxide group of Na ₂ O, Li ₂ O, K ₂ O, CaO,
The conductive material according to claim 1, characterized in that the conductive material has a chemical composition of 0 to 30 mol % of one or more components from the group of alkaline earth metal oxides such as MgO, BaO, SrO, and BeO. sex paste.