JPH0826251B2 - Silver powder for baking type conductive paint and baking type conductive paint using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silver powder for conductive paint and a conductive paint using the same, and more particularly to a conductive paint suitable for baking thin ceramic elements to form electrodes or conductors. is there.

[0002]

2. Description of the Related Art Various silver powders for conductive paints are commercially available, and various conductive paints using the same have been developed. However, recently, when electrodes or conductors are formed on a thin ceramic element having a thickness of 100 μm or less by using a conventional conductive coating material, the ceramic element may be deformed or destroyed. The cause of this deformation or destruction of the ceramic element is not clear, but because the ceramic element is thin, its strength is low, and with conventional conductive paint, only a coating film with a thickness of 4 μm or more can be formed. It is considered that the ceramic element is shrunk due to contraction and the stress deforms the ceramic element or exceeds the breaking strength of the ceramic element.

[0003]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted various studies in order to prevent the above-mentioned ceramic element from being deformed or destroyed on the conductive paint side. As a result, the conductive paint film is baked to form the paint film. The thickness of the coating film should be 2 μm or less in order to minimize the shrinkage when performing, and the silver powder for conductive paint used in this case has flake-shaped silver particles to ensure conductivity, and the maximum flake diameter / flake When the thickness ratio is 100 or more and 300 or less, even if the coating thickness is 2 μm or less, the contact points between silver particles are secured, good conductivity is obtained, and the obtained coating film is The present invention has been completed by finding out that a shrinkage during firing is small, and at the same time, a dense coating film having a uniform coating film thickness can be formed.

[0004]

Means for Solving the Problem That is, the present invention is a flake powder having a maximum particle size of 40 μm or less and a flake thickness of 2 μm or less, and a maximum flake diameter / flake thickness ratio of 1
Silver powder for conductive paint containing at least 80% by weight of flake particles of 00 or more and 300 or less, and this silver powder for conductive paint 3
The conductive coating material is characterized in that 0 part by weight or more and 60 parts by weight or less, low melting point glass frit is 1 part by weight or more and 10 parts by weight or less, and the rest is organic varnish.

[0005]

[Function] The silver powder for conductive paint of the present invention has a maximum particle size of 40 μm.
In the following, it is necessary that the flaky powder has a flake thickness of 2 μm or less. This is because when the maximum particle size is 40 μm or more, the thixotropy of the paint becomes large when used as a conductive paint, a uniform coating surface cannot be obtained, and the flake thickness is 2 μm or more. This is because when the powder is contained, a coating film of 2 μm or less cannot be formed due to the thickness of the silver particles themselves.

Further, it is necessary to contain a minimum of 80% by weight of flake-like particles having a maximum flake diameter / flake thickness ratio of 100 or more and 300 or less. When particles having a maximum flake diameter / flake thickness ratio of 100 or less were included, when a coating film was formed as a conductive paint, the shrinkage during firing was large and the contact between silver particles was reduced, resulting in a dense and uniform thickness. The electrode cannot be obtained, and as a result, the ceramic element is destroyed and conduction failure occurs, which is not preferable.

Further, when particles having a ratio of maximum flake diameter / flake thickness of 300 or more are contained, the thixotropy of the paint becomes large when it is used as a conductive paint, and the printability such that the coating film thickness cannot be formed uniformly. Is not preferable because it deteriorates. The maximum flake diameter / flake thickness ratio is 100 or more, 3
Flake-shaped particles of 00 or less are all. Silver powder for conductive paint is preferable, but when it is 80% by weight, it does not substantially affect the properties of the conductive paint. If it is less than 80% by weight, the above-mentioned deformation or breakage of the ceramics element, poor conduction, and increase in thixotropy deteriorate printability, which is not preferable.

The conductive paint of the present invention comprises the above-mentioned silver powder for conductive paint of the present invention, a low melting point glass frit and an organic varnish, and the content of each is specified as follows. 30 parts by weight or more of the silver powder for conductive paint of the present invention,
The amount of 60 parts by weight or less is because when it is less than 30 parts by weight, a gap is formed on the surface of the coating film and a uniform coating film cannot be obtained. This is because printing becomes difficult and printing is difficult, and it is impossible to form a coating film having a thickness of 2 μm or less with the current screen technology. Furthermore, 1 part by weight or more of a low melting point glass frit,
The amount of 10 parts by weight or less is because when the amount is less than 1 part by weight, the strength of the ceramic element and the electrode layer is weakened, and when the amount is more than 10 parts by weight, the solder wettability is deteriorated.

The silver powder for conductive coating of the present invention is obtained by flattening a lump or spherical powder produced by a chemical reduction method, an atomizing method or the like in a ball mill containing an anti-adhesive agent such as an organic solvent. However, it is necessary to select conditions that are fine and flat. The silver powder for conductive paint of the present invention can also be obtained by crushing a thin film by vapor deposition or sputtering.

[0010]

EXAMPLES Examples will be described below. Formalin (60 ml) is added to a silver nitrate aqueous solution (AgNO ₃ 100 g / H ₂ O 3000 ml), and then a caustic soda aqueous solution (NaOH 50 g / H ₂ O 200 ml) is added to form a white precipitate. The precipitate thus obtained was thoroughly washed with water by decantation, filtered, and dried at low temperature. The powder thus obtained was put into a ball mill, and a higher fatty acid and a steel ball were simultaneously put into the ball mill as an anti-adhesion agent and flattened to form flaky particles. By changing 14 kinds of conditions at this time, powder having maximum flake diameter / flake thickness shown in Table 1 was obtained. The silver powders obtained in this example are all flaky powders having a maximum particle size of 40 μm or less and a flake thickness of 2 μm or less, and a flake having a maximum flake diameter / flake thickness ratio of 100 or more and 300 or less. It contained 80% by weight or more of particulate particles.

The measurement of the maximum flake diameter / flake thickness ratio and the content rate were observed by an electron microscope.
The maximum particle size was measured using a laser diffraction particle sizer. The silver powder for conductive paint obtained as described above was prepared to have a viscosity of 200 poise as the conductive paint of the examples having the component compositions shown in Table 1. Clean printing of each paste composition
(250 mesh screen)
(φ, thickness 100 μm) and printed in 19φ size. This was placed in a drier and dried at 150 ° C. for 10 minutes.
Next, this coating layer was baked for 15 minutes at a temperature of 700 ° C. in the atmosphere. At this time, a total of 60 including the temperature rise and fall times
The ceramic element was placed in the furnace for a minute. As a result, a conductive coating film as shown in Table 2 was formed.

[0012]

[Table 1]

[0013]

[Table 2]

The film thickness was measured by an electron microscope, and the roughness was measured as the surface roughness of the coating film. The solderability was evaluated by the solder eating crack and the solder wetting rate, and the small solder eating crack was evaluated as ○, the small eating crack was evaluated as Δ, and the large solder eating crack was evaluated as ×. The soldering conditions at this time are S206, 23.
It was immersed at 0 ° C. for 5 seconds. The porosity indicates the ratio of the gap on the surface of the coating film, and when the porosity is 20% or more, the electrical characteristics cannot be obtained. Regarding the strength, the adhesive strength between the coating film and the ceramics element was measured, and the one that destroyed the element was ◯ and the one that caused the interface destruction was x.

[0015]

COMPARATIVE EXAMPLE Among the examples of the present invention, 8 kinds of powders shown as comparative examples in Table 1 were manufactured by the same method as in the example except that the conditions of the bow mill were changed, and the conductive paint was prepared by the same method as the example. Then, a conductive coating film was formed on the ceramic element.
The characteristics of this conductive coating film are shown in Table 2.

From Table 1 and Table 2, in the examples of the present invention, no element deformation due to the stress caused by the film thickness was observed, and since the porosity was small, there was little solder erosion and the predetermined electrical characteristics were obtained. Also, the adhesive strength with the ceramic element is improved. That is, a uniform and dense coating film having a film thickness of 2 μm or less can be obtained. On the other hand, in Comparative Example 1, in Comparative Example 1, the maximum particle size exceeds 40 μm, so that a uniform coating film surface cannot be obtained. The film thickness increases, and the element is deformed. In Comparative Example 2, the content of the silver powder having a maximum flake diameter / flake thickness ratio of 100 or more and 300 or less is less than 80% by weight, so that the shrinkage during firing becomes large, resulting in defective conduction or element deformation. In Comparative Example 3, the maximum flake diameter /
Since the ratio of the flake thickness is 100 or less, the shrinkage during the formation of the coating film is large, resulting in poor conduction, or the element is deformed due to the large film thickness. In Comparative Example 4, since the ratio of maximum flake diameter / flake thickness is 300 or more, the thixotropy of the coating material becomes large and the printability becomes poor, so the coating film roughness becomes large and the film thickness becomes large. The stress at the time increases and the element is deformed. In Comparative Examples 5 and 6, the low-melting-point glass frit was 1 part by weight or less, or 10 parts by weight or more. Therefore, Comparative Example 5 had low adhesive strength, and Comparative Example 6 had poor solder wettability. In Comparative Example 7, the content of silver powder was 30.
Since it is less than the weight part, the porosity is large and the electrical characteristics cannot be obtained, and the solder crack is large. In Comparative Example 8,
Since the content of the silver powder is more than 60 parts by weight, the viscosity characteristics of the coating material are poor, resulting in a large coating film roughness and a large film thickness, which causes element deformation. Therefore, it is clear that the silver powder for conductive paint which lacks the constituent features of the present invention cannot be applied to thin ceramic elements.

[0017]

As described above, the silver powder for baking type conductive paint or the baking type conductive paint of the present invention forms a uniform coating film with a thickness of 2 μm or less and can be soldered. It is very effective for forming electrodes or conductors of thin elements, especially thin ceramic elements, which could not be applied. Further, the silver powder for baking type conductive paint of the present invention can be applied to baking type conductive paint for low temperature firing (500 ° C).

Claims (2)

[Claims] 1. A flake-like powder having a maximum particle size of 40 μm or less and a flake thickness of 2 μm or less, containing 80% by weight of flake-shaped particles having a maximum flake diameter / flake thickness ratio of 100 or more and 300 or less. Baking type conductive powder silver powder. 2. A flake-like powder having a maximum particle size of 40 μm or less and a flake thickness of 2 μm or less, containing 80% by weight of flake-shaped particles having a maximum flake diameter / flake thickness ratio of 100 or more and 300 or less. baking-type electroconductive paint silver 30 parts by weight or more to 60 parts by weight or less, the low-melting glass frit 1 part by weight or more, 10 parts by weight or less, baking-type electroconductive coating material, wherein the remainder is an organic varnish.