JP2001014944A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately form a shield wall of a circuit board by containing conductive metal, insulating inorganic material, photo-polymerization initiator, organic binder containing photo-curing resin and plasticizer, and organic solvent with specific ratio. SOLUTION: When a total amount of conductive metal, insulating inorganic material, organic binder is 100 wt.%, total amount of the conductive metal and insulating inorganic material is 70-95 wt.%, and amount of organic binder is 5-30 wt.%. It is preferable that a plasticizer of 5-25 wt.% be contained in a total organic binder, dibutylphthalate and/or dioctylphthalate. Before photo- curing, it is sufficiently filled into a through hole for a via hole or a through- groove for shield because it has low viscosity, solvent is dried, then photo-curing resin is polymerized and hardened, and therefore, a composition which hardly causes swelling deformation due to solvents can be provided. Occurrence of cracks on the surface of a shield conductor can be prevented, and a shield wall having superior vertical size accuracy can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a conductive paste, and more particularly, to a conductive paste used for forming a shield wall of a circuit board.

[0002]

2. Description of the Related Art In recent years, electronic devices have become smaller, lighter and more portable, and the circuit blocks used therein have been reduced in size, weight, and thickness, surface-mounted, and composited in accordance with the trend. .

In particular, in communication equipment utilizing high frequency such as portable communication, ceramic circuit blocks have been used more frequently than ever because of their excellent dielectric properties and multilayer technology, and these circuit blocks have a single function. Has been required to be compounded. For example, a voltage-controlled oscillator is formed into a block by providing a strip line inside a ceramic substrate, but there is a trend to incorporate a mixer unit into one block for the purpose of further increasing the degree of integration of the ceramic substrate.

However, a transmitting circuit in a high frequency region such as a voltage controlled oscillator is easily affected by external noise,
The only countermeasure was to separate the mixer section from the oscillation circuit, and this structure only impaired the advantage of compounding for miniaturization. In order to separate the circuit, there is a method of arranging a large number of via holes between the mixer and the oscillation circuit.However, it is difficult to sufficiently separate the circuit, and the oscillation circuit emits noise generated by the mixer. There was a problem that it was easily affected by

Conventionally, as a structure for preventing circuit interference, which is a problem when a plurality of circuit elements are formed into one block, a high-frequency composite circuit having a shield wall for preventing circuit interference in the thickness direction in addition to the plane direction of the substrate. A block is disclosed (see Japanese Patent Application Laid-Open No. 9-130045).

FIGS. 1 and 2 show high-frequency composite circuit blocks. In these figures, a block having two circuit functions of a voltage controlled oscillator X and a mixer unit Y is combined. In the drawing, reference numeral 1 indicates an insulating base.
An end face electrode 2 is formed on the insulating base 1. A surface electrode 3 is formed on the surface of the insulating substrate 1, and a chip component 6 such as a thick film resistor 4 and a capacitor is connected to the surface electrode 3. Further, a cavity portion is formed in the insulating base 1, and a semiconductor bare chip 7 is arranged in the cavity portion, and the semiconductor bare chip 7 is connected to the surface electrode 3 via a wire.

As shown in FIG. 2, the insulating substrate 1 is formed by laminating a plurality of insulating layers 10a to 10h, and includes two circuits formed by an internal wiring 11, a via hole conductor 13, a chip component 6, a semiconductor bare chip 7, and the like. Functions X and Y are formed. Here, the circuit function means that one circuit function may affect the other circuit function, and FIG. 2 illustrates the voltage controlled oscillator X and the mixer unit Y.

The internal wiring 11 between the insulating layers 10a to 10h may be connected by a via-hole conductor 13 formed in the thickness direction of the insulating layers 10a to 10h, or may be connected in a distributed manner by capacitive coupling or the like. Some are connected.

The insulating substrate 1 has an insulating layer 10a between the two circuit functions of the voltage controlled oscillator X and the mixer Y.
The shield wall 17 is formed in the stacking direction of 10 to 10 h.

The shield wall 17 is formed so as to cut off between the voltage controlled oscillator X and the mixer Y as shown in FIG. The circuit function X is shielded by the shield wall 17 and the end face electrode 2a. That is, the shield wall 17
Shields with the voltage controlled oscillator Y by the end face electrode 2a.
Shields the outside.

[0011] Such a high-frequency composite circuit block is formed by thinning and drying an insulating layer material made of ceramic or glass ceramic, a photocurable monomer, and a slip material containing an organic binder to form an insulating layer molded body. When,
Exposing the surface of the insulating layer molded body excluding the position where the shield wall is formed, and developing the insulating layer molded body to form a shield through groove at a position where the shield wall is formed by developing the insulating layer molded body; Forming a conductive paste in the shield through-groove; laminating the insulating layer molded body before the exposure processing on the exposed insulating layer molded body; and repeating the steps from exposure processing to lamination. And firing the laminated molded body.

For example, a ceramic slip material composed of a ceramic powder, a photocurable monomer, an organic binder, and a solvent is applied, dried, and exposed to form an insulating film 32a on the support substrate 31 as shown in FIG. Then, an insulating film 32b is formed on the insulating film 32a in the same manner, and the insulating film 32b is exposed and developed to form a through hole 33b for a via hole and a through groove 34b for a shield as shown in FIG. To form

As shown in FIG. 3C, a conductive paste is filled in the through-holes 33b and the through-grooves 34b thus formed by a screen printing method or the like, and dried. The via-hole conductor 35b and the shield conductor 36b are formed by curing the paste. Thereafter, a conductive paste containing a photocurable resin is applied to the upper surface of the insulating film 32b if necessary, dried, and then an internal wiring conductor film having a desired shape is formed by a photolithography process, and thereafter, as shown in FIG. As described above, the above-described ceramic slip material is applied to the insulating film 32c to be the next insulating layer, dried, exposed, and developed to form the through hole 33c for the via hole and the through groove 34c for the shield. By repeating the above steps, a laminated molded body as shown in FIG. 3 (e) is produced and fired to obtain a high-frequency composite circuit block.

The via holes 3 are formed in the insulating films 32b to 32d by a photolithography process.
For example, as the conductive paste filled in the through-hole 3 and the shielding through groove 34, the conductive paste proposed by the present inventors has been used (see Japanese Patent Application No. 10-242337).

The conductive paste contains a conductive metal, an insulating inorganic material, an organic binder containing a photopolymerization initiator and a photocurable resin, and an organic solvent. The total amount of materials and organic binder is 10
When the weight is 0% by weight, the total amount of the conductive metal and the insulating inorganic material is 70 to 95% by weight, and the weight of the organic binder is 5 to 30% by weight. After that, it is exposed and cured by ultraviolet irradiation.

As a result, the formed via hole conductor 3
5 and the shield conductor 36 have enhanced solvent resistance, and the conductor 3
When the slip material is applied on the conductors 5, 36, the conductors 35, 36
The organic solvent in the slip material permeates into the conductors 35 and 36.
Problems such as poor conduction due to swelling and deformation.

[0017]

When the above-mentioned conductive paste is used for a via-hole conductor, the via-hole is filled in the through-hole 33b, dried and exposed, and then a slip material is applied, dried, exposed and processed. A problem does not occur even if the process of performing the development process and forming the via hole through hole 33c in the insulating film 32c of the next layer is repeated, but when the conductive paste is used as the conductive paste filled in the shield through groove 34, However, there were the following problems.

That is, as shown in FIG. 4A, a slip material is applied on a support substrate 41, dried and exposed to light to form an insulating film 42.
is formed on the insulating film 42a, a slip material is applied, dried, exposed, and developed to form an insulating film 42b, and a shielding through groove 44b is formed in the insulating film 42b. Is filled with the conductive paste,
Insulating film 42b on which one layer of shield conductor 46b is formed
A slip material is applied thereon and dried to form an insulating film 42c.

After that, as shown in FIG. 4B, when a shield through groove 44c for forming a shield conductor is formed in the insulating film 42c by exposure and development processing,
As shown in (c), when the developing solution is dried after the developing process, the insulating film 42c contracts in the direction of the arrow in the figure. Since this contracting force is generated so as to tear the groove outwardly perpendicular to the shielding through groove 44c, the force is applied to the surface of the shield conductor 46b of the insulating film 42b which is pulled hard and becomes brittle. As shown in FIG. 4D, a crack x occurs, and even if the shield conductors are repeatedly laminated, there is a problem that a plurality of shield conductors 46 cannot accurately form a vertical shield wall continuous in the thickness direction. Was.

[0020]

According to the present invention, there is provided a conductive paste comprising a conductive metal, an insulating inorganic material, an organic binder containing a photopolymerization initiator, a photocurable resin and a plasticizer;
An organic solvent is contained, and when the total amount of the conductive metal, the insulating inorganic material, and the organic binder is 100% by weight, the total amount of the conductive metal and the insulating inorganic material is 70 to 95%. % By weight, and the organic binder is 5 to 30%.
% By weight.

Here, 5 parts of a plasticizer are contained in the total amount of the organic binder.
It is desirable to contain 〜25% by weight. Further, it is desirable that the plasticizer is dibutyl phthalate and / or dioctyl phthalate. The conductive paste of the present invention is desirably used particularly for forming a shield wall of a circuit board.

[0022]

According to the present invention, a through hole for a via hole and a through groove for a shield are formed by exposing and developing an insulating film containing a photocurable resin, and the conductive paste of the present invention is formed in such a through hole and a through groove. Is filled by screen printing, etc., heated to disperse the solvent, dried, and photo-cured so that the organic solvent contained in the slip material applied to the upper surface of the insulating film penetrates the via-hole conductor and the shield conductor. These conductors can prevent conduction failure, deformation, and cracks of these conductors, and can protrude from the surface of the insulating film even in the slip material drying process applied on the insulating film on which the via hole conductor and the shield conductor are formed. Or the lower insulating film or the laminated molded body from the supporting substrate can be prevented. Furthermore, the smoothness of the surface of the laminated insulating film above the via-hole conductor and the shield conductor can be improved, and the connection between the conductors can be reliably performed.

That is, since the conductive paste of the present invention has a low viscosity before photocuring, it can be sufficiently filled in a through hole for a via hole or a through groove for a shield. Since the curable resin is polymerized and cured, it is possible to obtain a structure in which an organic solvent does not easily penetrate and deformation due to swelling does not easily occur.

In addition, since the conductor is light-cured, even in the step of drying the slip material on the upper surface of the conductor, deformation of the conductor due to the contraction is small, and the upper surface of the conductor protrudes from the insulating film surface or peels off from the supporting substrate. Or disconnection of the connection part of the conductor formed on each insulating film can be prevented,
The smoothness of the laminate can be improved.

In the conductive paste of the present invention, since the organic binder contains a plasticizer, the dried and light-cured conductor contains a plasticizer. Therefore, even if a force to tear the conductor is applied from the outside of the conductor, the conductor can follow the force to some extent, thereby preventing the occurrence of cracks on the conductor surface. Therefore, even if the insulating film shrinks when the developing solution is dried after the developing process, and the shield conductor of the insulating film below the insulating film acts on the shield conductor in the thickness direction of the conductor, the shield conductive film is flexible. Cracks on the surface of the shield conductor can be prevented, and multiple shield conductors can form a shield wall with excellent vertical dimensional accuracy that is continuous in the thickness direction of the board, and multiple circuit functions with good shield properties A circuit board for a built-in high-frequency module can be provided.

Further, for example, dibutyl phthalate and / or
Alternatively, by including 5 to 25% by weight of a plasticizer composed of dioctyl phthalate in the total amount of the organic binder, generation of cracks on the surface of the shield conductor can be further prevented, and a vertical shield wall having better dimensional accuracy can be formed.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive paste of the present invention contains a conductive metal, an insulating inorganic material, an organic binder containing a photopolymerization initiator, a photocurable resin and a plasticizer, and an organic solvent. Things.

As the conductive metal, a low-temperature firing material (800 to 1100 ° C.) in which the substrate material is glass ceramics
In the case of baking to a certain degree, gold, silver, copper or an alloy material thereof is used, and when the substrate material is alumina, a metal such as tungsten or molybdenum is used. The average particle size of the conductive metal is desirably 5 to 10 μm from the viewpoint of dispersibility and sinterability during paste production.

Examples of the insulating inorganic material include borosilicate glass powder, borosilicate alkaline earth metal-based glass, quartz glass, and the like. A small amount improves the dispersibility of the conductive metal with the conductive metal. Desirably, the thickness is 5 to 10 μm.
Further, this insulating inorganic material has a role of controlling the sintering shrinkage behavior of the conductive metal. The insulating inorganic material is
0.1 to 1% by weight of the conductive metal is desirable.

Examples of the photopolymerization initiator constituting the organic binder include 2-methyl-1- [4- (methylthio) phenyl] -2-monforinopropanone-1 (Irgacure 907 manufactured by Ciba Geigy), diethylthioxanthone and the like. There is. It has the role of absorbing light and causing a photocuring reaction.

The photocurable resin may be either a monomer or a polymer. Examples of the photocurable resin include an alkyl acrylate or an alkyl methacrylate that can be thermally decomposed at a temperature of 500 ° C. or less, and a polymer compound thereof.

Examples of the photocurable monomer include compounds having an ethylenically unsaturated bond, which can be burned out at a low temperature and in a short time and are polymerized by irradiation with ultraviolet rays.
Specific examples include polyethylene glycol diacrylate such as tetraethylene glycol diacrylate, trimethylolpropane triacrylate, and methacrylate corresponding thereto. Examples of the photocurable polymer include high molecular weight compounds of the above monomers (molecular weight: 5
000 to 50,000).

The organic binder may contain a non-photocurable polyalkyl acrylate or methacrylate such as polymethyl methacrylate or poly (iso) butyl methacrylate.

In the present invention, the organic binder further contains a plasticizer. The plasticizer is used to weaken the strong bond of the resin by penetrating into the macromolecules that make up the photocurable resin, and to give the dried, cured, hard and brittle conductor a suitable flexibility. A substance that does not scatter at a temperature of about 80 to 100 ° C., which is the temperature at which the paste is dried, and that scatters at a low temperature and in a short time during firing, and has a good affinity for alkyl acrylate and alkyl methacrylate constituting the resin. Specifically, phthalic acid ester compounds such as dibutyl phthalate (DBP) and dioctyl phthalate (DOP) are optimal.

Examples of the organic solvent include butyl carbitol acetate, α-terpineol and the like, and have a role of adjusting the viscosity of the conductive paste to a viscosity suitable for screen printing.

In the conductive paste of the present invention, the total amount of the conductive metal, the insulating inorganic material and the organic binder is 1
When the content is 00% by weight, the total amount of the conductive metal and the insulating inorganic material is 70 to 95% by weight, and the organic binder is 5 to 30% by weight.
It is important that

When the weight of the organic binder is less than 5% by weight, that is, when the total weight of the conductive metal and the insulating inorganic material is more than 95% by weight, sufficient photocurability cannot be obtained, and This is because solvent penetration or deformation of the conductor may occur. When the weight of the organic binder exceeds 30% by weight, that is, when the total weight of the conductive metal and the insulating inorganic material is less than 70% by weight, This is because the organic binder does not sufficiently decompose during firing, adversely affects the sinterability of the conductive metal, and breaks the conductor.

For the reasons described above, the total weight of the conductive metal and the insulating inorganic material is preferably 70 to 95% by weight, and the weight of the organic binder is preferably 5 to 30% by weight. Is 80-90% by weight,
It is desirable that the weight of the organic binder is 10 to 20% by weight.

In the conductive paste of the present invention, it is preferable that the plasticizer contains 5 to 25% by weight based on the total amount of the organic binder. When the weight of the plasticizer contained in the organic binder is less than 5% by weight, sufficient flexibility is not provided to the conductor film, and a crack is easily generated on the conductor surface when a force for tearing the conductor is applied. If the content exceeds 25% by weight, the strength of the polymer compound constituting the organic binder and serving as the skeleton of the binder is excessively weakened, which may cause deterioration of the solvent resistance and dissolution of the conductor during the upper layer development. is there.
The amount of the plasticizer in the organic binder is preferably 10 to 20% by weight.
Is desirable.

The conductive paste of the present invention comprises a conductive metal, an insulating inorganic material, a photopolymerization initiator, a photocurable resin,
The organic binder is obtained by adding and mixing a predetermined amount of an organic binder containing a plasticizer and an organic solvent. The organic binder may be previously dissolved in an organic solvent to form an organic vehicle and mixed with an inorganic component.

The conductive paste of the present invention is formed by exposing and developing an insulating film containing a photocurable resin to form a through hole for a via hole and a through groove for a shield. The conductive paste is used for a multilayer ceramic circuit board formed by repeating a process of filling the conductive paste by a screen printing method or the like, heating to disperse the solvent, drying and photo-curing. The conductive paste can be efficiently cured in a short time by performing exposure while heating using a conveyor type UV furnace or the like as a light source.

[0042]

EXAMPLE Silver powder having an average particle size of 5 μm as a conductive metal, quartz glass powder having an average particle size of 2 μm as an insulating inorganic material, 2-methyl-1- [4-
(Methylthio) phenyl] -2-monforinopropanone-1 (Irgacure 907 manufactured by Ciba Geigy) and a mixture of diethylthioxanthone, trimethylolpropane triacrylate and its polymer as a photocurable resin, and other organic binders Prepare isobutyl methacrylate as a component, dioctyl phthalate (DOP) as a plasticizer, and butyl carbitol acetate as an organic solvent. The insulating inorganic material is 0.5% by weight of the conductive metal, and the insulating inorganic material and the conductive metal are mixed. A total weight of 70% by weight of the total amount, a mixture of 30% by weight of an organic binder composed of a photopolymerization initiator, a photocurable resin, isobutyl methacrylate, and dioctyl phthalate (DOP), and 20% by weight of an organic solvent in the total amount of the paste. Into a ceramic three-roll mill Ri kneaded to to prepare a conductive paste of the present invention. The amount of DOP in the organic binder is 1
0% by weight.

Further, a conductive paste was prepared by changing the total weight of the insulating inorganic material and the conductive metal, the amount of the organic binder, the amount of the plasticizer, and the amount of the organic solvent as shown in Table 1. The above example is described as Sample No. 2. Using the conductive paste, a circuit board was manufactured as follows.

A ceramic slip material for forming an insulating layer was prepared by mixing 50% by weight of alumina powder having an average particle size of 3 μm with 50% by weight of lead borosilicate glass powder having an average particle size of 3 μm as an insulating material. Using a photocurable monomer, polyethylene glycol dimethacrylate having an ethylenically unsaturated bond, a certain amount of carboxyl that is soluble in an alkaline aqueous solution in the development process for forming a through hole for a via hole and a through groove for a shield as an organic binder A poly (iso) butyl methacrylate containing a group was used, Irgacure 907 and diethylthioxanthone were used as a photopolymerization initiator, and diethylene glycol monobutyl ether acetate was used as an organic solvent. These were mixed and kneaded with a ball mill.

As shown in FIG. 3 (a), a ceramic slip material is applied on a supporting substrate 31 by a doctor blade method and dried to form an insulating film 32a having a thickness of 80 μm. As shown in FIG. 3B, a ceramic slip material was applied to the insulating film 32a and dried to form an insulating film 32b having a thickness of 80 μm. The insulating film 32b is subjected to an exposure process and a development process, and a through hole 33b for a via hole and a through groove 34b for a shield are formed at predetermined positions.
Was formed.

Specifically, the through hole 33b and the through groove 34
Using a photo target in which the area where b is to be formed is shielded from light, the area other than the area where the through hole 33b and the through groove 34b are formed is exposed to 100 mJ / cm ^{2 using} an ultra-high pressure mercury lamp, and the area is cured. The uncured area which was not removed was dissolved and removed by spray development using a weak alkaline aqueous solution of a triethanolamine aqueous solution, and the developing solution was dried at 80 ° C. for 10 minutes to form a through hole 33b and a through groove 34b.

As shown in FIG. 3C, the through-holes 33b and the through-grooves 34b are filled with the conductive paste by a screen printing method, heated at 100 ° C., and dried to form a via-hole conductor 35b and a shield. The conductor 36b was formed. The via-hole conductor 35b and the shield conductor 36b were irradiated with ultraviolet rays having an exposure amount of 1 to 5 J / cm ² using a UV light source such as a metal halide lamp to cure the via-hole conductor 35b and the shield conductor 36b.

Next, as shown in FIG. 3D, after the above-mentioned ceramic slip material is applied and dried to form an insulating film 32c, the surface of the insulating film 32c is observed, and the via-hole conductor 35b and the shield conductor 36b are observed. It was determined whether or not the upper insulating film 32c protruded. Regarding the presence or absence of protrusion,
Judgment was made based on whether or not protrusion could be confirmed with the naked eye. The results are shown in Table 1.

After that, by exposing and developing the insulating film 32c, the through hole 33c for the via hole and the through groove 3 for the shield are formed.
4c is formed and dried at 80 ° C. for 10 minutes, and then the via-hole conductor 3 below the through-hole 33c and the through-groove 34c is formed.
5b and the surface condition of the shield conductor 36b were observed, and the presence or absence of cracks was visually judged. The results are also shown in Table 1. Thereafter, as shown in FIG. 3E, filling of the conductive paste into the through-holes 33c and the through-grooves 34c, drying, and ultraviolet curing were performed to produce via-hole conductors 35c and shield conductors 36c. Further, the insulating film 32d, the via-hole conductor 35d and the shield conductor 3
6d, and a laminated molded body is produced.
Removed from 1.

Next, the via-hole conductors 35b to 35d and the shield conductors 36b to 36d in the cross section of the laminated molded product are shown.
Was observed. The results are shown in Table 1.

[0051]

[Table 1]

As shown in Table 1, in the sample of the present invention, the insulating film 32
There was no unevenness on the surface c, no cracks occurred on the surface of the shield conductor 36b, and no defect was found in the via hole conductor and the shield wall after firing.

On the other hand, the sample No. In 10, the insulating film 32c
After coating and drying, the upper ends of the via-hole conductor 35b and the shield conductor 36b protruded from the surface of the insulating film 32b, and protruded from the surface of the insulating film 32c. In addition, the sample No. In No. 4, a crack was confirmed along the center of the shield conductor 36b below the shield through groove 34c.

Thereafter, the laminate was debindered at 500 ° C., and then baked at 900 ° C. for 1 hour. Observation of the fired state of the via-hole conductor and the shield conductor of this fired body revealed that the via-hole conductor and the shield conductor filled with the conductive paste of the present invention had no problem of conduction in a dense sintered state, and the shield conductor was almost vertical. Sample No. In No. 4, no vertical shield wall was formed.

[0055]

According to the conductive paste of the present invention, an insulating film containing a photocurable resin is exposed to light and developed to prevent a through hole for a via hole and a through hole for shielding in a thickness direction of a substrate to prevent mutual interference between circuits. A groove is formed, and a conductive paste is filled in such a through-hole and a through-groove by a screen printing method or the like, heated, the solvent is scattered, dried, and light-cured, thereby coating the upper surface of the insulating film. The organic solvent contained in the slip material is less likely to penetrate into the via-hole conductor and the shield conductor, preventing poor conduction and deterioration of the via-hole conductor and the shield conductor, and also on the insulating film on which the via-hole conductor and the shield conductor are formed. Also in the slip material drying step to be applied, it is possible to prevent the conductor from protruding from the insulating film surface and peeling from the lower layer or the support substrate.

Furthermore, even if an insulating film is formed on the shield conductor, and a shield through groove is formed in the insulating film again by exposure and development, cracks are formed on the surface of the lower shield conductor by the force generated in the upper layer after the development. Does not occur, and a vertical and highly reliable shield wall can be formed. This makes it possible to provide a high-frequency module circuit board having a plurality of circuit functions with good shielding properties.

[Brief description of the drawings]

FIG. 1 is a perspective view of a high-frequency composite circuit block.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a process diagram illustrating a manufacturing method using a build-up multilayer method.

FIG. 4 is a process diagram for explaining generation of cracks on the surface of a shield conductor when a conventional conductive paste is used.

[Explanation of symbols]

 32a to 32d: insulating film 31: support substrate 33b to 33d: through hole for via hole 34b to 34d: through groove for shield 35b to 35d: via hole conductor 36b to 36d: shield conductor

Claims (4)

[Claims] An organic solvent containing a conductive metal, an insulating inorganic material, a photopolymerization initiator, a photocurable resin, and a plasticizer, and an organic solvent.
The total amount of the insulating inorganic material and the organic binder is 10
When the weight is 0% by weight, the total amount of the conductive metal and the insulating inorganic material is 70 to 95% by weight, and the organic binder is 5 to 5% by weight.
30% by weight of a conductive paste. 2. The conductive paste according to claim 1, wherein the total amount of the organic binder contains 5 to 25% by weight of a plasticizer. 3. The conductive paste according to claim 1, wherein the plasticizer is dibutyl phthalate and / or dioctyl phthalate. 4. The conductive paste according to claim 1, wherein the conductive paste is used for forming a shield wall of a circuit board.