JPS6340327B2 - - 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 for this type of conductive powder. Generally, Ag is used as the conductive powder, and a paste is dispersed in a vehicle together with borosilicate glass frit, bismuth oxide, zinc oxide, lead oxide, etc., and then applied to a substrate such as ceramic by a method such as screen printing. After that, they are fired at high temperatures and used as electrodes for capacitors, piezoelectric elements, semiconductor elements, etc., or as wiring conductors for electronic circuits. However, in recent years, due to the high price of precious metals, especially Ag, as an alternative to conductive Ag paste, conductive paste using inexpensive conductive powder and electrodes for baking ceramics such as Cu and Ni have been developed. Many proposals have been made, including plated 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 compound powders such as TiN and SnO ₂ have been developed and some are commercially available. It has become like that. However, although base metal conductive pastes such as Ni and Cu can have good initial properties, they are unsatisfactory due to poor corrosion resistance, and because they are base metal powders, they cannot be fired in a non-oxidizing atmosphere. There are some drawbacks, such as the need for Also, TiN,
Conductive pastes such as SnO ₂ have a relatively high resistance as a powder, so it is difficult to obtain a conductive paste with low resistance. TiN is a high-temperature baking type, but baking in air oxidizes, so There are drawbacks that make it unusable. On the other hand, there is a conductive paste using conductive powder coated with Ag on Al ₂ O ₃ powder. This Al ₂ O ₃
Conductive paste made of Ag-coated powder is excellent in terms of economy, but Al ₂ O ₃ has poor adhesion due to poor wettability with Ag, and when the paste is kneaded, Ag
has peeled off and the conductivity has deteriorated. Further, there is a problem that the powder of this type of oxide coated with Ag or the conductive paste using TiN or SnO ₂ has no solderability in the conductive film after firing. As mentioned above, various conductive pastes have been proposed as a substitute for Ag, but none of them are satisfactory in terms of conductivity, corrosion resistance, solderability, etc. The emergence of conductive paste is desired. The present inventors have achieved the above-mentioned conductivity, corrosion resistance,
In order to satisfy both solderability and economic efficiency, we investigated various alloy powders containing base metals as the main component.
The core is an alloy containing Al and Zn, and the surface is coated with Ag.
It has been found that the coated powder satisfies the above characteristics as a conductive medium for a conductive paste and is economically advantageous. Next, the present invention will be explained in detail. The powder for conductive paste in the present invention is Cu-
It consists of a core made of Al-Zn alloy powder and a layer of Ag coated on its surface. The following is the core
The Cu-Al-Zn alloy powder will be explained. Cu is a metal with excellent conductivity, but it also has corrosion resistance and
It is difficult to say that the thermal oxidation resistance is good. In particular, when heated in an oxidizing atmosphere, a large amount of scale is generated on the surface. One way to improve this weakness of Cu is to add Al. Even when Cu-Al alloy becomes red hot in an oxidizing atmosphere, the proportion of scale formation is small. This is presumed to be due to the formation of a thin, strong layer of Al ₂ O ₃ on the surface, which retards the progress of oxidation on the alloy surface. However, in such a state, it is difficult to say that the solderability is excellent. Inferred, in the case of the powder that serves as the conductive medium for conductive pastes, especially high-temperature baking type conductive pastes, the conditions desired for the core powder in the case of the aforementioned oxide powder coated with Ag. Examples of these include a) conductivity, b) thermal oxidation resistance, c) good adhesion to the Ag layer, and d) solderability. Therefore, if the aforementioned Al ₂ O ₃ powder is used as a core, only item b can be satisfied among the above conditions, so a powder coated with Ag on Al ₂ O ₃ is desirable. It can be said that it is not a thing. From this point of view, the Cu-Al alloy has some drawbacks in item d, and is insufficient as a powder for conductive paste. Depending on how you think about it, it seems that the core powder does not need solderability because the Ag coating material has good solderability, but from a practical standpoint, the thickness of the Ag layer is Since it is less than 1μ at most, and 2 to 3μ at most,
Solder is eaten away and solderability becomes almost impossible. However, according to the present invention, soldering of Cu--Al alloys is significantly improved by the addition of Zn.
It is not clear why the addition of Zn brings about such an improvement, but the so-called de-Zn phenomenon, in which Zn sublimes from the alloy surface during high-temperature heating, is likely to cause Al ₂ O ₃
It is also surmised that this prevents the formation of more film than necessary. Therefore, for example, a Cu-Al-Zn alloy ingot is heated and burned in air, then rolled,
Since it appears that a wire-drawn material already has a strong Al ₂ O ₃ film formed on its surface, solderability is extremely poor. In order to obtain the solderability as described above, it is necessary to use mechanically strained fractured surfaces, sheared surfaces, etc. with little Al ₂ O ₃ film or peeling.
More desirable results are obtained on surfaces with less Zn. For the above reasons, according to the present invention, Cu-Al
-The composition ratio at which the Zn alloy can find its effect is
1 to 15% by weight of Al, 2 to 40% by weight of Zn, and the remainder Cu. The lower limit of the amount added is the minimum amount that can provide the above-mentioned effect, and the upper limit is the amount that is restricted from the viewpoint of conductivity and segregation in producing the alloy material. However, for practical use, an appropriate composition must be selected depending on the thickness of the Ag coating and the firing conditions of the paste. Normally, for high-temperature baking pastes that use Ag powder as a conductive medium, the baking conditions include holding heating in air at 850℃ to 920℃ for 10 minutes, and cycles of about 1 hour, including rising and falling before and after that. However, under such conditions, the amounts of Al and Zn added are preferably 3 to 7% by weight of Al and 10 to 20% by weight of Zn. When the amounts of Al and Zn added are in this range, the specific resistance of the alloy material is about 5 to 10 μΩ-cm, which is a value that can be said to be a good conductive material. Next, the Ag layer will be explained. There is no particular problem with the Ag layer to be coated, as long as it is uniformly coated on the Cu--Al--Zn alloy powder, such as by electroless Ag plating or vapor deposition. The thickness of the Ag layer is determined by taking into consideration the particle size of the Cu-Al-Zn alloy powder, economic efficiency, conductivity, etc. If the particle size of the Cu-Al-Zn alloy powder is about 0.5 to 5μ, the effect can be seen when the thickness of the Ag layer is 0.05μ or more. According to the present invention, the above-mentioned Ag-coated Cu-Al-
Zn alloy powder is used as a conductive medium for a conductive paste, but generally the powder is dispersed in a vehicle with glass frit, metal oxide, etc. to form a conductive paste. Similar to pastes using normal Ag powder, this paste is applied to a ceramic substrate using a method such as screen printing, then baked at high temperature and used as an electrode or conductive path. The particle size of the powder ranges from 0.05 to 10μ, preferably 0.5
~5μ is good. When the thickness exceeds 10μ, printability during screen printing deteriorates, and sheet resistance after final firing increases. Next, examples will be described in detail in order to make the present invention more concrete. The Cu-Al-Zn alloy according to the present invention was weighed according to the composition ratio, and the total amount of 1 kg was powdered by a molten metal spraying method. N ₂ gas was used as a spray medium and cooled by cooling it in water. The particle size of the obtained powder was about 5 to 100 μm, but it was mechanically processed and ground again using a pin mill to give an average particle size of about 2 μm. This powder was then mixed with an ammonia silver nitrate solution consisting of 25 g of AgNO ₃ and 140 g of Rothsiel's salt.
Electroless with a 1:1 mixture of reducing solution consisting of g/
Pour into the Ag plating solution, and stir at 20°C until 90°C.
Ag plating was carried out for a minute. The obtained Ag plating powder was thoroughly washed with water, dried at 120° C. for 1 hour, and used as a powder for conductive paste. To prepare a paste, 3 g of this powder was kneaded with a vehicle consisting of ethyl cellulose (100 CPS) and televisionneol, and a glass frit consisting of boron oxide and silicic acid using a Hubermala. Huber Mara performed three repetitions of 20 rotations with a load of 100 pounds. Further, the amount of powder made of Cu-Al-Zn alloy powder as a core and covered with an Ag layer was 80% by weight of the total amount. After printing the paste prepared above into a predetermined shape on an Al ₂ O ₃ substrate using a screen printing method,
After drying for 10 minutes, further dry in the air at 850℃~950℃
Bake for 10 minutes. As a result of measuring the resistance value between both ends of the above printed pattern, the values shown in the table were obtained. For reference, the table shows the results of baked films of pastes prepared using the same method, such as Cu powder coated with an Ag layer, Ni powder coated with an Ag layer, and Ag powder as a conductive medium. The characteristics of are also shown in the same way. In addition, regarding the solderability of the fired film surface, the table shows those that are easy to solder with ○, those that are relatively easy to solder with △, and those that cannot be soldered with ×.

[Table] As is clear from the table, the paste using the powder according to the present invention shows values comparable to the paste using Ag powder. On the other hand, a paste using a powder made of Ni or Cu as a core and coated with an Ag layer does not give satisfactory results. As described above, the powder and its paste according to the present invention have sufficient performance for practical use, and can be economically produced at a much lower cost than pastes using Ag powder (in practice). In this example, the thickness of the Ag layer is 0.1μ, and the silver saving rate is 75%), so its industrial value is great.

Claims (1)

[Claims] 1. A conductive paste characterized in that a powder consisting of a Cu-Al-Zn alloy powder as a core and a surface coated with an Ag layer is dispersed in a vehicle together with glass frit. . 2 The composition ratio of the Cu-Al-Zn alloy described in claim 1 is Al1 to 15% by weight, Zn2 to 40% by weight,
A conductive paste characterized by the balance being Cu.