JPS6340328B2 - - 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, noble metals such as Au, Ag, and Pd have been used as conductive powder in this type of conductive paste.
Generally, Ag is used for this conductive powder, and borosilicate glass frit and Bi ₂ O ₃ , ZnO, PbO
A paste dispersed in a vehicle is applied to a ceramic substrate using a method such as screen printing, and then fired at a high temperature to form electrodes for ceramic capacitors, piezoelectric elements, semiconductor ceramics, etc., or wiring for electronic circuits. It has been used as a conductor. However, in recent years, due to the sharp increase in the price of precious metals, especially Ag, conductive pastes using inexpensive conductive powder are being used as substitutes for conductive Ag paste, and Cu and Ni plating are being used as electrodes for baking ceramics. Many proposals have been made, including electrodes. For example, as a substitute for Ag powder, conductive pastes made using inexpensive base metal powders such as Ni and Cu, or conductive metal compounds such as TiN and SnO ₂ have been developed, and some are now commercially available. I'm getting used to it. However, base metal conductive pastes such as Ni and Cu can have good initial characteristics;
It is unsatisfactory due to its poor corrosion resistance, and since it is a base metal powder, it has drawbacks such as the need for a non-oxidizing atmosphere for firing. Also,
With conductive pastes such as TiN and _SnO2 , the powder itself has a relatively high resistance, so it is difficult to obtain a conductive paste with low resistance.
It has the disadvantage that it cannot be used when fired in air because it oxidizes. On the other hand, there is a conductive paste using conductive powder coated with Ag on Al ₂ O ₃ powder. This conductive paste made of Ag-coated powder of Al ₂ O ₃ is excellent in terms of economy, but Al ₂ O ₃ is made of Ag-coated powder.
The adhesion is poor due to poor wettability with the paste, and the Ag peels off during paste kneading, resulting in poor conductivity. Further, powder of this type of oxide coated with Ag or conductive paste using 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 substitutes for Ag, but none of them are satisfactory in terms of conductivity, corrosion resistance, solderability, etc. The emergence of a type conductive paste is desired. The present inventors investigated and investigated alloy powders mainly composed of base metals in order to satisfy the above-mentioned conductivity, corrosion resistance, solderability, and furthermore, economic efficiency. It has been found that an alloy to which Al, Zn, and even Sn are added satisfies the above properties to a considerable degree. Next, the configuration of the present invention will be explained in detail. In the conductive paste according to the present invention, the conductive powder thereof is a Cu-Al-Zn-Sn alloy powder. Its composition ratio is Al2~8% by weight, Zn10~40% by weight,
It consists of 0.5 to 5% by weight of Sn and the balance is Cu. Inferred, the desirable conditions for this kind of conductive paste, especially the powder that serves as the conductive medium for high-temperature baking type conductive paste, are (a) electrical conductivity, (b) thermal oxidation resistance, ( c) Must be able to be soldered. Although Cu, which is the main component of the conductive powder in the present invention, is a metal with excellent conductivity, it cannot be said to have good corrosion resistance and thermal oxidation resistance. In particular, it is unsuitable as a conductive medium for high-temperature baking pastes because a large amount of oxide scale is generated on its surface and conductivity cannot be obtained. Al is added as a way to improve these weaknesses of Cu. Even when Cu-Al alloy is heated in an oxidizing atmosphere, the proportion of scale formation is small. It has Al ₂ O ₃ on the surface
It is thought that a thin, strong layer is formed to prevent the progress of oxidation of the alloy. However, in such a state, in a paste fired film that forms a conductive path through contact with powder, not only the conductivity deteriorates but also the solderability deteriorates. However, such weaknesses of Cu-Al alloy powder can be greatly improved by adding Zn. That is, Cu-Al-Zn alloy powder is recognized to have characteristics such as relatively good conductivity and soldering capability when made into a paste fired film. It is not clear why the addition of Zn brings about such an improvement, but Zn sublimes from the alloy surface during high-temperature heating.
It is also speculated that the Zn phenomenon prevents the formation of an Al ₂ O ₃ film more than necessary. It is also possible that Zn is dissolved into the glass frit even if it is slightly oxidized. Next, the addition of Sn improves the solderability of the Al--Zn--Cu alloy fired film. However, when the amount added increases, the oxidation resistance may decrease. The Cu-Al-Zn-Sn alloy powder forms a conductive path through the above-mentioned functions, but conduction is maintained by the contact between the alloy powders, and if the alloy powders are fired in a state where they are melted and sintered together, Since the Al ₂ O ₃ film is destroyed, the alloy powder is oxidized and becomes nonconductive. For the above reasons, the composition ratio at which Cu-Al-Zn-Sn alloy can find its effect is Al2~8
% by weight, 10 to 40% by weight of Zn, 0.5 to 5% by weight of Sn, and the remainder Cu. The lower limit of the amount added is the minimum amount in which the above-mentioned effect can be found. The upper limit is an amount that is restricted from the viewpoints of conductivity, solderability, and deterioration of corrosion resistance. According to the present invention, the Cu-Al-Zn-Sn alloy powder is used as a core to improve the contact between the Cu-Al-Zn-Sn alloy powder and reduce the sheet resistance of the fired conductive film. , it is possible to coat the surface with Ag. The thickness of the Ag coating is determined by considering the particle size of the alloy powder, conductivity, and economic efficiency.If the particle size of the alloy powder is approximately 0.5 to 5μ, the thickness of the Ag coating is 0.05 μm. The effect can be recognized above μ. Normally, for high-temperature baking pastes that use Ag powder as a conductive medium, the baking conditions include holding heating in air at 800 to 900℃ for 10 minutes, and cycles of about 1 hour, including rising and falling before and after. but,
Since the alloy powder coated with Ag contains Ag,
Depending on the amount of coating, it is desirable to heat at a temperature slightly lower than the eutectic temperature of the Ag-Cu binary alloy, 780°C. According to the present invention, the above-mentioned Cu-Al-Zn-Sn alloy powder or this powder coated with Ag,
It is used as a conductive medium in a conductive paste, but generally the powder is dispersed in a glass frit and a vehicle and homogeneously kneaded to form a paste. At this time, as the glass frit, Bi ₂ O ₃ ,
Those containing PbO etc. are not preferred. This is because these oxides tend to corrode the alloy powder when melted during firing. The kneaded paste is applied to a substrate such as ceramic by a method such as screen printing, and then baked at a high temperature to be used as an electrode or a conductive path. The particle size of the powder is
A range of 0.05 to 10μ, preferably about 0.5 to 5μ is good. When the thickness exceeds 10μ, printability during screen printing deteriorates, and sheet resistance after firing increases. Next, examples will be described in order to make the present invention more concrete. Cu, Al, Zn, according to the composition according to the invention
Each Sn material was weighed to give a total weight of 1 kg. As materials, Cu-Al master alloy and Cu-Zn master alloy were used as appropriate. This was dissolved in nitrogen gas and further pulverized by a molten metal spray method. As a spray medium,
It was cooled by putting it into water using nitrogen gas. The particle size of the obtained powder is approximately 5 to 100μ, but this is re-pulverized using a mechanical crusher to reduce the average particle size to approximately
It was set to 2μ. Then, it was used as a conductive paste. Some of the powders were further coated with Ag in an electroless Ag plating solution containing a 1:1 mixture of an ammonia silver nitrate solution containing 25 g of AgNO ₃ and a reducing solution containing 140 g of Rothsiel's salt. It was then plated for 90 minutes while stirring at 20°C (Ag thickness was about 0.1μ). This plating powder was thoroughly washed with water, dried at 120° C. for 1 hour, and used as a powder for conductive paste. The paste was prepared by kneading 3 g of the above powder with a vehicle consisting of ethyl cellulose (100 CPS) and terpineol and a glass frit consisting of B ₂ O ₃ , SiO ₂ , Na ₂ O, ZnO, Al ₂ O ₃ etc. using a Hubermala. did. hoover mala load
I did 100 pounds and 20 rotations three times. The amount of powder was 80% by weight of the total amount. After printing the paste prepared above into a predetermined shape on an alumina substrate using a screen printing method,
Dry at 120℃ for 10 minutes, then dry at 750℃ in the air.
It was baked at 830°C for 10 minutes. As a result of measuring the resistance value between both ends of the above printed pattern, the values shown in the following table were obtained. For reference, the table shows Cu powder, Ag powder, and Cu powder produced by the same method.
Pastes were made from powder coated with an Ag layer, and the characteristics of the fired films are also shown. The solderability of the fired film surface is also shown in the table as ○ for easy soldering, △ for relatively easy soldering, and × for difficult soldering.

[Table] As is clear from the table, the paste using the powder according to the present invention shows comparable values to the paste using Ag powder. On the other hand, pastes using Cu powder are not completely satisfactory. As described above, the conductive paste according to the present invention is
It has sufficient performance for practical use, and economically, it can be manufactured at low cost by reducing Ag.
Its industrial value is enormous.

Claims (1)

[Claims] 1 Al2-8% by weight, Zn10-40% by weight, Sn 0.5-8% by weight
An alloy powder with a composition of 5% by weight and the balance Cu,
A conductive paste characterized by being dispersed in a vehicle together with glass frit. 2 Al2~8wt%, Zn10~40wt%, Sn0.5~
A powder consisting of an alloy powder with a composition of 5% by weight and the balance Cu as a core, and its surface coated with an Ag layer,
A conductive paste characterized by being dispersed in a vehicle together with glass frit.