JP2000080271A - Dielectric paste and dielectric film obtained therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject paste capable of being easily coated and having a low viscosity even with a high solid ratio by bringing the paste to contain dielectric powder in a specific polyimide precursor varnish. SOLUTION: The objective paste is obtained by bringing 100 pts.wt. of (A) a polyimide precursor varnish obtained by dissolving 5-80 wt.% of a mixture, which constitutes a polyimide precursor, of (i) a diamine expressed by formula I [R1 and R2 are each formula II or the like, formula III or the like; R3 and R4 are each H or a 1-5C alkyl; (m) is 0-10] with (ii) a tetracarboxylic acid (ester) expressed by formula IV (R5 to R8 are each H or a 1-5C alkyl) to contain preferably 0.5-200 pts.wt., more preferably 10-150 pts.wt. of (B) dielectric powder having preferably 0.05-10 μm. The blended amount of the ingredient (i) in 100 pts.wt. of the mixture of the ingredient (i) with the ingredient (ii) is preferably 20-99 pts.wt. As the ingredient B, barium titanate, strontium titanate, etc., are cited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric paste containing a dielectric powder in a polyimide precursor varnish and a dielectric film obtained therefrom.

[0002]

2. Description of the Related Art In recent years, with the demand for smaller and lighter information communication devices and various electronic devices, new component forming technologies such as capacitors, inductors, and resistors mounted on various substrates, mounting technologies, and circuit design technologies. Is being developed. Further, in order to increase the transmission capacity of information communication circuits and to increase the frequency with an increase in speed, a circuit having a small transmission loss is required. It is well known that a ceramic substrate has a smaller transmission loss in a high frequency range than a conventional printed circuit board.
In addition, capacitors, inductors,
Attention has been paid to the fact that forming a resistor as a thin film enables a reduction in transmission loss and a reduction in size and weight due to a reduction in signal wiring length.

Among the conventional methods for forming a thin film capacitor, a vapor deposition method and a sputtering method are used as dry methods.
As a wet method, a sol-gel method is well known, and a ferroelectric thin film such as strontium titanate, barium titanate, or tantalum oxide is formed by using these methods to form a thin film capacitor. However, in the conventionally used vapor deposition or sputtering method, the relative permittivity changes depending on the film forming temperature, so that strict control of the film forming temperature is required, and a high temperature of 500 ° C. or more is required. Further, in the sol-gel method, a high temperature exceeding 700 ° C. is required to promote crystallization of the ferroelectric thin film, and therefore, deterioration of an electrode material connecting a capacitor due to high temperature has been a problem. Furthermore, according to these methods, it is necessary to perform patterning of a thin film using a resist agent in advance, and there is a problem that complicated steps of patterning a substrate, forming a thin film, and removing a resist are required. Was. From such a problem, a dielectric paste capable of forming a dielectric thin film simply by coating or printing on a substrate and performing heat treatment has been required.

On the other hand, a polyimide precursor solution in which polyamic acid is dissolved using dimethylformamide or N-methylpyrrolidone as a solvent has been well known, and various fillers are dispersed in such a polyimide precursor varnish. This is also known from various documents. By applying this technique, it is considered possible to produce a dielectric paste in which a dielectric powder is dispersed in a polyimide precursor varnish.

However, the varnish using a polyamic acid as a polyimide precursor has a high degree of polymerization and a low solubility, so that it is difficult to increase the solid content ratio in the varnish. Dielectric pastes prepared using varnishes require complicated operations such as repeated printing and coating to obtain a thin film having a predetermined thickness, and there has been a problem in productivity. Furthermore, the varnish made of polyamic acid as a precursor has a high viscosity even at a low solid content, so that when a dielectric powder is mixed to form a dielectric paste, the viscosity further increases, and a predetermined dielectric constant is obtained. When the ratio of the dielectric is increased in order to obtain a dielectric thin film having characteristics, there has been a problem that print coating becomes difficult.

[0006]

In view of the above, it is an object of the present invention to provide a dielectric material which has a low viscosity and is easy to apply even when a polyimide precursor and a dielectric powder are contained in an organic solvent at a high solid content ratio. It is an object of the present invention to provide a body paste and to provide a dielectric film obtained from this dielectric paste and having a smooth surface and a uniform film thickness.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a polyimide precursor obtained by dissolving a specific diamine and a specific carboxylic acid in an organic solvent. The dielectric paste containing the dielectric powder in the body varnish has a low viscosity even if it has a high solid content ratio.Furthermore, a dielectric film using a polyimide obtained from this dielectric paste as a binder is a dielectric film. It was found that the surface was smooth and the film thickness was uniform, and the present invention was reached.

That is, the gist of the present invention is that, first, a diamine represented by the formula (1) and a tetracarboxylic acid and / or an ester thereof represented by the formula (2) for forming a polyimide precursor are dissolved in an organic solvent. And these concentrations are 5-8
A dielectric paste, wherein a dielectric powder is contained in a polyimide precursor varnish of 0% by weight.

[0009]

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(Wherein R ₁ and R ₂ are each selected from Structural Formula Group 1 and Structural Formula Group 2; R _{3 to} R ₈ each represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms; -10
Indicates an integer. Second, a dielectric film using polyimide as a binder, which is obtained by applying this dielectric paste to a substrate and heating the polyimide, the polyimide being composed of a repeating unit represented by formula (3).

[0011]

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(In the formula, R ₁ and R ₂ are each selected from Structural Formula Group 1 and Structural Formula Group 2, and n is an integer of 10 to 5000.)

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the dielectric paste of the present invention, a diamine represented by the formula (1) and a tetracarboxylic acid and / or an ester thereof represented by the formula (2) for forming a polyimide precursor are dissolved in an organic solvent. In the polyimide precursor varnish, the dielectric powder is contained, wherein R ₁ and R ₂ are respectively selected from Structural Formula Group 1 and Structural Formula Group 2, and R _{3 to} R ₈ are Represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and m represents an integer of 0 to 10.

The concentration of the polyimide precursor in the polyimide precursor varnish is 5 to 80% by weight, and the concentration is 5% by weight.
If it is lower, it is difficult to obtain a predetermined dielectric film thickness only by adjusting the coating apparatus, and it is necessary to perform coating repeatedly, and the advantage in terms of productivity is lost.
Conversely, if the concentration is higher than 80% by weight, it is difficult to stably dissolve the polyimide precursor, and even if the dissolution can be achieved by selecting an organic solvent, the dielectric powder is added to the polyimide precursor varnish. The viscosity of the contained dielectric paste increases, making it difficult to apply the paste, resulting in poor productivity of the dielectric film. A more preferred concentration range is from 20 to 5
It is 5% by weight, and within this range, the printability of screen printing used for forming a fine pattern is excellent.

[0015] In the polyimide precursor varnish, 100 parts by weight of the total of the diamine represented by the formula (1) and the tetracarboxylic acid and / or ester thereof represented by the formula (2) is mixed with the diamine represented by the formula (1). The amount is preferably from 20 to 99 parts by weight, and if it is outside this range, it may not be possible to form a film.

The dielectric paste of the present invention is obtained by adding a dielectric powder to the polyimide precursor varnish as described above. Examples of the dielectric powder include barium titanate,
Strontium titanate, solid solution of barium titanate and strontium titanate, titanates such as lead titanate, tantalum nitride, tantalum oxide, tantalum nitride oxide,
In addition to tantalum compounds such as tantalum strontium bismuth oxide, alumina, aluminum nitride, silicon carbide and other dielectric powders having a relative dielectric constant of 5 or more can be mentioned. Among them, barium titanate, strontium titanate, barium titanate and titanate Preferred are a strontium solid solution and thallium oxide. These can be used alone or in combination of two or more.

The amount of the dielectric powder contained in the polyimide precursor varnish is preferably 0.5 to 200 parts by weight based on 100 parts by weight of the polyimide precursor varnish. If the amount is less than 0.5 part by weight, the effect of adding the dielectric powder is small, and if it exceeds 200 parts by weight, the effect of the polyimide in the dielectric film as a binder is low, and the film strength may be reduced. Furthermore, the compounding amount of the dielectric powder is 10 to 15
0 parts by weight is more preferred. The particle diameter of the dielectric powder is preferably 0.05 to 10 μm.

The organic solvent used in the dielectric paste of the present invention includes N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, hexamethylphosphoryltriamide, sulfolane,
Polar solvents containing N, S, P atoms in molecules such as N, N'-dimethylimidazolidinone and N-methylcaprolactam, cellsolves such as cellsolve, phenylcellsolve, ethyl acetate cellsolve, butyl acetate cellsolve, etc. Sorbitol acetate, carbitols such as methyl carbitol, ethyl carbitol, carbitol acetates such as ethyl carbitol, butyl carbitol acetate, carbitol diethers such as dimethyl carbitol (diglyme), diethyl carbitol , Cyclohexanol, alcohols such as benzyl alcohol,
Examples thereof include ketones such as cyclohexanone and isophorone and esters such as γ-butyrolactone, and are preferably organic solvents having a boiling point of 150 ° C. or higher. This is because, when an organic solvent having a boiling point of less than 150 ° C. is used in performing continuous production, volatilization of the organic solvent is remarkable, and the viscosity of the dielectric paste is not stabilized.

The type of the organic solvent can be appropriately selected depending on the desired evaporation rate and the viscosity of the paste.
The use of a strong polar organic solvent containing S or P in the molecule increases the solubility of the polyimide precursor resin, so if you want to increase the film thickness, obtain a higher concentration polyimide precursor varnish. Therefore, it is preferable to use a strongly polar organic solvent.

Further, other inorganic particles may be added to the dielectric paste for the purpose of adjusting the capacitance value, the film hardness, the friction coefficient, the viscosity and the like, as long as the effects of the present invention are not impaired. As the inorganic particles, silica, zinc white, iron oxide, ferrite, and the like are used. The shape of the inorganic particles may be a true sphere, a needle, a flake, or the like.

When the above-mentioned dielectric paste is applied to the substrate and the solvent is removed, a coating film composed of a polyimide precursor and a dielectric powder is obtained. When this is heated, the polyimide precursor is imidized to obtain the formula (3) A dielectric film comprising a polyimide composed of the repeating units shown as a binder is obtained. In the formula (3), R ₁ and R ₂ are each represented by the structural formula group 1
And n is an integer of 10 to 5000. The conditions for imidization vary depending on the type of the polyimide precursor, but are preferably performed at 250 to 400 ° C.

As a method of applying the dielectric paste of the present invention on a substrate, a known method such as a spin coating method, a bar coating method and a spray coating method is employed, but a fine pattern can be easily formed. Screen printing is preferred. Since the dielectric paste of the present invention has a low viscosity despite having a high solid content in the organic solvent, it is applied to a substrate, the solvent is removed, and a dielectric material obtained by heat imidization is obtained. The body film has a smooth surface and becomes a uniform dielectric film.

[0023]

The present invention will be described below in more detail with reference to examples. Examples 1 to 3 As components forming a polyimide precursor, R ₁ in the formula (1) is shown in the following formula (4), R ₂ is shown in the following formula (5), and R ₃ and R ₄ = H. , a diamine is m = 3, in the formula (2) R ₂ represents the following formula (5), R ₅
= H, R ₆ = H, R ₇ = H, and tetracarboxylic acid with R ₈ = H are used in a weight ratio of 85:15, and these are added to dimethylacetamide in a ratio of 30, 35, and 40% by weight. In addition to the above, a polyimide precursor varnish was prepared, and its viscosity was measured. Table 1 shows the results. The viscosity was measured at 20 ° C. using a B-type viscometer.

[0024]

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15 parts by weight of strontium titanate powder (average particle size: 1 μm) was blended with 100 parts by weight of these polyimide precursor varnishes, kneaded and dispersed to produce three types of dielectric pastes. The viscosity of the dielectric paste was measured, and the results are shown in Table 1. Further, this dielectric paste was printed on a ceramic insulating substrate using a 350-mesh screen plate, dried, and then heated and imidized at 300 ° C. for 2 hours to produce a dielectric film. Table 1 shows the characteristics of the dielectric film. As shown in Table 1, a dielectric film having a smooth surface and a uniform film thickness was obtained using any of the pastes.

[0026]

[Table 1]

In the above embodiments, strontium titanate was used as the dielectric powder, but the same effect could be obtained by using barium titanate or tantalum oxide powder. Also, as the compounding ratio of the dielectric powder,
Although 15 parts by weight was used with respect to 100 parts by weight of the polyimide precursor varnish, a similar effect could be obtained by using a mixing ratio of 0.5 part by weight and 150 parts by weight.

[0028]

As described above, the dielectric paste of the present invention has a low viscosity and can be easily applied even if the polyimide precursor and the dielectric powder are contained in the solvent at a high solid content ratio. Therefore, a dielectric film could be manufactured with high productivity from this dielectric paste, and the obtained dielectric film had a smooth surface and a uniform film thickness.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshiaki Echigo 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Central Research Laboratory F-term (reference) 4J002 CM001 DE096 DE146 DE186 DF016 DJ006 FD206 GQ00 HA08 4J038 DJ031 HA216 HA246 KA06 KA06 KA20 NA17

Claims (5)

[Claims] 1. A diamine represented by the formula (1) for forming a polyimide precursor and a tetracarboxylic acid represented by the formula (2) and / or
Alternatively, a dielectric paste is characterized in that a dielectric powder is contained in a polyimide precursor varnish in which an ester thereof is dissolved in an organic solvent and the concentration thereof is 5 to 80% by weight. Embedded image (Wherein R ₁ and R ₂ represent structural formula group 1 and structural formula group 2 respectively.
R _{3 to} R ₈ each represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and m represents an integer of 0 to 10. ) 2. A sum of a diamine represented by the formula (1) and a tetracarboxylic acid and / or an ester thereof represented by the formula (2):
2. The dielectric paste according to claim 1, wherein the compounding amount of the diamine represented by the formula (1) is 20 to 99 parts by weight with respect to 0 parts by weight. 3. The dielectric paste according to claim 1, wherein the amount of the dielectric powder is 0.5 to 200 parts by weight based on 100 parts by weight of the polyimide varnish. 4. The dielectric powder according to claim 1, wherein the dielectric powder is at least one powder selected from barium titanate, strontium titanate, a solid solution of barium titanate and strontium titanate, and tantalum oxide. The dielectric paste as described. 5. A dielectric film comprising a polyimide having a repeating unit represented by the formula (3) obtained by applying the dielectric paste according to claim 1 to a substrate and heating the dielectric paste. Embedded image (Wherein R ₁ and R ₂ represent structural formula group 1 and structural formula group 2 respectively.
And n is an integer of 10 to 5000. )