JPS6253034B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a conductive paint, and an object of the present invention is to provide a conductive paint that is inexpensive, has excellent conductivity, and has excellent migration resistance. Conventionally, noble metal powders such as Au, Ag, and Pd have been used as conductive powders in this type of conductive paint. Generally, Ag paint is mixed with a thermosetting resin such as phenolic resin, epoxy resin, or xylene resin, and a solvent such as ethyl carbitol using Ag as the conductive powder, and is screen printed on a phenolic resin substrate. After being applied by this method, it is cured by heating and used as electrodes for variable resistors and printed wiring conductors for electronic circuits. However, in recent years, as electronic devices have become smaller and thinner, there has been a strong demand for smaller electronic components. Interaction with a DC electric field causes a phenomenon in which Ag paint migrates between electrodes, so-called migration, which results in short circuits and is often a major cause of trouble. In order to compensate for such shortcomings of Ag paint,
Conductive paints using Ag-Pd powder are commercially available, but they are not yet perfect. Also, Ag―Pd
Conductive paint using powder is extremely disadvantageous in terms of economic efficiency in the recent situation where the price of Pd is extremely high compared to the price of Ag, and the price of precious metals, especially Ag, has skyrocketed in recent years. For the reasons mentioned above, there is a desire for an inexpensive conductive paint with good migration resistance. The present invention has been made in view of these points, and as a result of research and study on alloy powders mainly composed of base metals, the inventors have developed a conductive powder using Ag-Al-Cu alloy powder as a conductive powder. It has been discovered that the paint has excellent migration resistance and satisfies a considerable level of conductivity. Next, the configuration of the present invention will be explained in detail. In the conductive paint according to the present invention, the conductive powder contains at least 10 to 70% by weight of Ag and 0.1 to 10% by weight of Al.
This is an electrically conductive paint characterized by being an Ag-Al-Cu alloy powder with a composition of Ag-Al-Cu, and the balance being Cu. Desired conditions for the conductive powder of this type of resin-curing conductive paint include: a) electrical conductivity; and b) thermal oxidation resistance during heat curing. Cu, which is a component of alloy powder, is a metal with excellent electrical conductivity, but it cannot be said to have good thermal oxidation resistance or corrosion resistance. Therefore, a large amount of oxidized scale is often generated on the surface of the Cu powder due to the heating during the paint curing process, making it impossible to obtain sufficient conductivity of the cured paint film. These drawbacks of Cu powder can be improved by adding Ag as an alloying element. However, in terms of migration resistance, Ag--Cu alloy powder tends to be improved compared to Ag powder because Cu is less likely to cause migration, but sufficient migration resistance cannot be obtained. These drawbacks of Ag--Cu alloy powder can be greatly improved by further adding Al as an alloying element. It is not clear why alloying brings about such an improvement in migration resistance, but it is believed that Al itself is less prone to migration and that Al is an extremely base metal compared to Ag. ,Ag
-It is presumed that the Al-Cu alloy powder has excellent migration resistance when used as a conductive paint. Furthermore, the addition of Al as an alloying element tends to improve the heat oxidation resistance of Ag--Cu alloy powder. This is presumably because Al oxide prevents excessive oxidation of the alloy powder. Furthermore, due to the environmental resistance of Al itself,
It is thought that its addition provides corrosion resistance effects. However, if the amount of Al added exceeds an appropriate amount, the conductivity of the alloy powder itself decreases, making it impossible to obtain desirable characteristics. The alloy composition in which Ag-Al-Cu alloy powder can find the above-mentioned advantages as a conductive powder for conductive paint is 10 to 70% by weight of Ag, 0.1 to 10% by weight of Al, and the remainder Cu. The lower limit of Ag content is determined by the heat oxidation resistance of the alloy powder.
The upper limit is a quantity restricted from economic efficiency.
Further, the lower limit of the amount of Al is the minimum amount at which the effect of its addition can be found, and the upper limit is the amount limited by the electrical conductivity of the alloy powder. As described above, conductive paint using Ag-Al-Cu alloy powder can be found to have practically sufficient performance in terms of conductivity and migration resistance. However, in general, the corrosion resistance of Cu and Cu-based composites is not necessarily good in an excessively corrosive environment, and the alloy powder of the present invention does not necessarily have satisfactory corrosion resistance when left in such an atmosphere. It's not a thing. However, such drawbacks are caused by the 1, 2, 3-
This problem can be solved by a process (hereinafter referred to as benzotriazole treatment) in which benzotriazole is immersed in a solution of an organic solvent such as acetone, and then the solution is separated and dried. It is presumed that the benzotriazole treatment described above forms a thin chelate compound film on the surface of the alloy powder, thereby exerting an anticorrosion effect. According to the present invention, Ag-Al-Cu alloy powder or Ag-Al treated with benzotriazole
-Cu alloy powder is mixed with thermosetting resin and solvent to create conductive paint. This conductive paint is applied to a phenol resin substrate or the like by a method such as screen printing in the same way as ordinary Ag paint, and then heated and cured in the atmosphere to be used as electrodes or conductive paths. The particle size of alloy powder 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 heat curing increases. Next, examples will be described in detail in order to make the present invention more concrete. Ag-Al-Cu alloy powder according to the present invention was produced as follows. Each material of Ag, Al, and Cu was weighed according to the alloy composition according to the present invention, and the total amount was 1 kg.
And so. This was dissolved in nitrogen gas and further pulverized by a molten metal spray method. Nitrogen gas was used as a spray medium, and the mixture was cooled in water. The particle size of the obtained alloy powder is about 5 to 100μ, but this is powdered again using a mechanical crusher, and the average particle size is about 2.
It was set as μ. A portion of the alloy powder obtained by the above method was treated with benzotriazole. The benzotriazole treatment was carried out in the following manner.
1,2,3-benzotriazole 10mg in acetone
10 g of the alloy powder was immersed in this solution and thoroughly dispersed. After that, the alloy powder and the solution were separated, and the alloy powder was dried. 2g of alloy powder obtained by the above method or 2g of alloy powder treated with benzotriazole
g, xylene resin 1g, ethyl carbitol
It was kneaded with 0.2g using a Hubermala.
For kneading with a Hoover Mara, the load is 100 pounds,
40 rotations were repeated four times. The conductive paint prepared above was printed in a predetermined shape on a phenolic resin substrate using a screen printing method, and then cured by heating at 190° C. for 10 minutes in the atmosphere. The following table shows the results of measuring the resistance value between both ends of the above printed pattern, and the results after being left in a constant temperature and humidity chamber at 40°C and 95% RH for 120 hours. For reference, the table also shows the results when commercially available Ag powder and Cu powder were used as conductive powder.

【table】

[Table] In addition, as a migration resistance test, the paint prepared above was screen printed in a pattern with a gap of 0.5 mm on a phenolic resin substrate.
After heating and curing, 0.2ml of pure water was dropped into the gap, and a DC voltage of 3V was applied to the gap, and the current flowing through the gap was measured.The current value after 2 hours after voltage application was were about 10 μA in all cases. On the other hand, when a similar test was conducted on a paint using conductive Ag powder, migration of Ag was observed in the gap 1 minute after voltage application, causing a short circuit. Therefore, it can be said that the conductive paint according to the present invention has extremely superior migration resistance compared to conventional Ag paint. As is clear from the above explanation and table, although the conductive paint according to the present invention is somewhat inferior in terms of conductivity and corrosion resistance compared to conventional Ag paint, it has sufficient characteristics for practical use. It has particularly excellent migration resistance, and economically, it can be produced at a much lower cost than conventional Ag paints, so it has great industrial value.

Claims (1)

[Claims] 1. Consists of conductive powder, resin, and solvent, and the conductive powder contains at least 10 to 70% by weight of Ag and 0.1 to 10% by weight of Al.
% by weight, and the balance is Cu. 2. The alloy powder according to claim 1, wherein the alloy powder is obtained by immersing in a solution of 1,2,3-benzotriazole in an organic solvent, separating the solution, and drying it. conductive paint.