JP3061309B2 - Curable conductive composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel curable conductive composition. Specifically, in the formation of a circuit pattern on a circuit board, the formation of a pattern for electromagnetic wave shielding, the formation of a conductive through-hole, etc., there is no occurrence of cracks at the time of curing and a curable material having good conductivity can be obtained. It is a conductive composition.

[0002]

2. Description of the Related Art A curable conductive composition is used as a pattern forming material such as a circuit pattern forming material and a pattern forming material for electromagnetic wave shielding, or is filled into a conductive through hole of a circuit board and cured to form a conductive through hole. It is used as a filling material for

As a problem of the curable conductive composition, cracks generated after curing may cause defects such as a decrease in conductivity and disconnection. This is considered to be due to the brittleness of the cured product obtained by curing the curable conductive composition.

Conventionally, to solve such a problem, there is a method of curing the curable conductive composition under mild conditions to lower the crosslinking density of the binder. However, in such a method, the shrinkage due to the curing reaction is insufficient, and the conductivity and the moisture resistance are reduced.

As another method, there is a method in which a flexible insulating resin is used for an undercoat layer and an overcoat layer, and a curable conductive composition is sandwiched.
However, in such a method, a pattern, a through-hole, and the like formed by the curable conductive composition are vulnerable to impact, and thus the above problem has not been essentially solved. In addition, the above method cannot be applied when the curable conductive composition is filled into the through holes and cured.

[0006]

Therefore, there is no crack after curing, and the heat history is durable .
An object of the present invention is to provide a curable conductive composition capable of obtaining a cured body having good conductivity.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, as the copper powder, dendritic copper powder and flakes, which are copper powder having a specific long shape, are used. It has been found that a curable conductive composition containing a specific amount of a copper powder and / or a fibrous copper powder shows excellent conductivity after curing, and that the generation of cracks is extremely effectively suppressed. The invention has been completed.

That is, the present invention provides a curable polymer binder 10
A total copper powder amount of 150 to 2500 parts by volume is used with respect to 0 parts by volume.
0 to 95 parts by volume and (b) a flaky copper powder having a major axis of 10 to 100 μm and an aspect ratio of 5 to 1000 and / or a diameter of 0.5
5 to 3 μm, length of 50 to 5000 μm fibrous copper powder 5 to 3
The curable conductive composition is a copper powder mixture having a composition of 0 volume parts.

The capacity of the copper powder is a value calculated based on the apparent density. In addition, the apparent density is determined according to JIS
It was measured according to the method described in K2504.

In the present invention, the dendritic copper powder has an effect of giving good conductivity to a cured product of the curable conductive composition.
The shape of the dendritic copper powder has a known shape in which a large number of branches protrude in a three-dimensional direction, and can be generally produced by an electrolytic method.

The dendritic copper powder used in the present invention has an average particle size of 1 to 50 μm, preferably 5 to 20 μm. That is, when the average particle size is less than 1 μm, the oxidation rate becomes excessively high, and when the curable conductive composition is used, the copper powder is significantly oxidized, and the conductivity of a cured product obtained by curing the copper powder decreases. . Further, when the average particle size exceeds 50 μm, not only does the curability of the curable conductive composition decrease, but also the sedimentation of the copper powder becomes severe and a uniform dispersion state cannot be obtained. Cannot be obtained stably.

The flaky copper powder used in the present invention has a major axis of 10 to 100 μm, preferably 20 to 50 μm.
μm, flatness of 5 to 1000, preferably 50 to 500
Copper powder. The “flatness” is a value obtained by dividing the major axis of the flake-like copper powder by the thickness. When the major diameter of the flake-form copper powder is smaller than 10 μm, the effect of suppressing the occurrence of cracks during curing is not sufficient. Further, when the major axis exceeds 100 μm, dispersibility in the curable conductive composition is poor, and adversely affects the dispersibility of other copper powder.
A curable conductive composition that gives a cured product having good conductivity cannot be obtained. On the other hand, when the flattening ratio is smaller than 5, the effect of suppressing the occurrence of cracks during curing decreases. Further, when the flattening ratio exceeds 1000, the thickness of the copper powder becomes thin, so that the copper powder is easily broken at the time of kneading the curable polymer, and not only cannot maintain the shape, but also is broken due to shrinkage at the time of curing. As a result, the effect of suppressing cracks tends to decrease.

Further, the flake-form copper powder having a ratio of the minor axis to the major axis (major axis / minor axis) of 1 to 3 has a stable effect of preventing cracks regardless of the dispersion state of the copper powder. It is preferable because it can be expressed.

The fibrous copper powder used in the present invention has a diameter of 0.5 to 5 μm, preferably 1 to 3 μm, and a length of 50 to 50 μm.
Those having a size of 5000 μm, preferably 500 to 2000 μm are used. When the diameter of the fibrous copper powder is smaller than 0.5 μm, the strength in the fiber axis direction is weak, and a sufficient effect of suppressing cracks during curing cannot be obtained. Further, even when the length of the fibrous copper powder is shorter than 50 μm, no effect of suppressing the generation of cracks during curing of the curable conductive composition is observed. On the other hand, when the diameter of the fibrous copper powder exceeds 5 μm, or when the length exceeds 5000 μm, not only the dispersibility in the curable conductive composition is reduced, but also the dispersion of other copper powder is reduced. As a result, a cured product having good conductivity cannot be obtained.

[0015] In the curable conductive composition of the present invention, the copper powder mixture is prepared by mixing 5 to 30 parts by volume of flake copper powder and / or fibrous copper powder with 70 to 95 parts by volume of dendritic copper powder. Become. When the dendritic copper powder is less than 70 parts by volume,
The contact between the copper powders at the time of curing becomes insufficient, and the conductivity is reduced. Further, when the dendritic copper powder exceeds 95 parts by volume, the absolute amount of the flake copper powder and / or the fibrous copper powder is insufficient, so that the effect of suppressing cracks during curing of the curable conductive composition becomes insufficient. . Among the proportions of the copper powder, the proportion of flake copper powder and / or fibrous copper powder of 25 to 10 parts by volume with respect to the dendritic copper powder of 75 to 90 parts by volume is particularly effective for the effect of the present invention. It can be preferable.

In the present invention, the flaky copper powder and the fibrous copper component, which are components of the copper powder mixture, can be used alone or in combination, respectively. It is more effective for the expression of body conductivity and prevention of cracks during curing. A preferred ratio of the flake copper powder is such that the ratio of the flake copper powder to the total amount of the flake copper powder and the fibrous copper powder is 60 to 100% by volume, particularly 70 to 100% by volume.

If necessary, the copper powder used in the present invention may be subjected to various known surface treatments, for example, various surface treatments for the purpose of removing an oxide layer, preventing oxidation, improving dispersibility, and the like. After being washed with an unsaturated fatty acid, treated with various coupling agents such as a silane coupling agent and a titanium coupling agent, and rust-proofed with an imidazole derivative or the like, it is mixed with a curable polymer binder.

In the present invention, the curable polymer binder is
A resin composition that shrinks upon curing is used without any particular limitation. Typical examples include thermosetting resins such as epoxy resin, phenolic resin, urea resin, and melamine resin, and polymerizable ethylenically unsaturated bonds such as nylon, unsaturated polyester, and (meth) acrylate. Examples thereof include a photosensitive composition comprising a compound having the compound and various photocrosslinking agents, a photosensitive resin such as polyvinyl cinnamate and a resin having a cinnamate ester in a side chain, and an electron beam curable resin such as an acrylate.

In the present invention, among the above curable polymer binders, an epoxy resin is particularly preferred. Examples of such epoxy resins include glycidyl ethers such as bisphenol A type, bisphenol F type, novolak type, resole type, aromatic / aliphatic type, cycloaliphatic type, glycidyl ester type, glycidylamine type, and heterocyclic epoxy type. These various epoxy resins can be used alone or as a mixture of two or more. Also,
As the curing agent, amine-based, acid anhydride-based, polyamide resin, phenol resin, urea resin, imidazoles, dicyandiamide, and other commonly used curing agents for epoxy resins can be used.

When an epoxy resin is used as the curable polymer binder, a curable conductive composition having excellent adhesion to circuit board materials, copper foil, insulating resin, and the like, heat resistance, and insulating properties can be obtained. Can be Furthermore, the curable conductive composition using an epoxy resin as a curable polymer binder has no by-products during curing, so it is necessary to form a relatively thick cured body layer or fill the through hole forming holes. It is particularly suitable for use in applications in which electrical conduction between the front and back is obtained, since voids due to curing are small.

The curable conductive composition of the present invention has a total copper powder content of 150 to 2 per 100 parts by volume of the curable polymer binder.
500 parts by volume, preferably 180 to 500 parts by volume are used. When the amount of the copper powder is less than 150 parts by volume, good conductivity cannot be obtained because the absolute amount of the copper powder is insufficient. If the total amount of copper powder exceeds 2500 parts by volume, kneading becomes difficult because the absolute amount of the curable polymer binder as a binder is insufficient, workability is remarkably reduced, and the obtained cured product is practically usable. The strength cannot be obtained.

The viscosity of the curable conductive composition of the present invention may be adjusted using an appropriate organic solvent, if necessary. Generally, the curable conductive composition preferably has a viscosity of 200 to 450 poise (ps). As the organic solvent used for adjusting the viscosity, a known organic solvent is used without any particular limitation. For example, aromatic hydrocarbons such as toluene and xylene; alcohols such as isopropanol and butanol;
Esters such as ethyl acetate and butyl acetate; cellosolves such as ethyl cellosolve and butyl cellosolve; and carbitols such as ethyl carbitol and butyl carbitol. The organic solvent can be used alone or in combination of two or more depending on the kind of the binder and the like.

The curable conductive composition of the present invention may further contain, if necessary, known components such as a rust inhibitor, an antifoaming agent, a thixotropic agent, a leveling agent, a lubricant, a reducing agent, etc. Additives may be blended.

The method for producing the curable conductive composition of the present invention is not particularly limited. Generally, using a usual dispersing device or pulverizer, for example, a homogenizer, a Henschel mixer, an automatic mortar, a three-roll mill, a ball mill, a sand mill, a flow jet mixer, etc., a copper powder mixture, a curable polymer binder, and other additives It is manufactured by mixing agents, solvents and the like.

[0025]

The curable conductive composition of the present invention is obtained by mixing a specific amount of a copper powder mixture obtained by adding a specific flake copper powder and / or a fibrous copper powder to a dendritic copper powder as a conductive material, It is possible to suppress the occurrence of cracks during curing and to stably obtain a cured body having good conductivity.

[0026] Further, by blending the flake-like copper powder and / or the fibrous copper powder, the thermal conductivity of the cured product of the curable conductive composition is improved. When used in an application in which the holes are filled and cured to obtain conduction between the front and back surfaces, there is also an effect that heat dissipation in the thickness direction of the through-hole substrate is improved. .

[0027]

The effect of the curable conductive composition of the present invention exhibiting the above-described excellent crack prevention effect while maintaining good conductivity is not clear.
The expression of conductivity by the dendritic copper powder and the flake-like copper powder and / or the fibrous copper powder and the anchor effect at the time of curing by the flake-like copper powder and / or the fibrous copper powder act synergistically. It is estimated that.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Examples 1 to 14, Comparative Examples 1 to 14 Tables A-1 (Examples 1 to 10), A-2 (Examples 10 to 1)
4), B-1 (Comparative Examples 1 to 8), and B-2 (Comparative Example 9)
To 14), linoleic acid was blended at a rate of 0.5 × 10 ⁻⁵ mmol / cm ² with respect to the surface area of the copper powder, and preliminarily mixed with a mortar under a nitrogen atmosphere for 15 minutes. . The pre-treated copper powder obtained in this manner was mixed with bisphenol A type epoxy resin (epoxy equivalent = 176) / novolak type phenol resin (hydroxy equivalent = 105) = 7.
280 parts by volume were added to 100 parts by volume of a binder of 7.5 / 22.5 (weight ratio), and 2-ethyl-4-
2.8 parts by weight of methylimidazole was added to 100 parts by weight of the binder, and kneaded with a three-roll mill for 30 minutes to obtain a curable conductive composition. In order to adjust the viscosity of the curable conductive composition to 200 to 450 PS, an appropriate amount of butyl cellosolve was added as a solvent during kneading.

The obtained curable conductive composition was 1.6 mm thick.
A 0.8 mmφ through-hole provided on a thick glass epoxy substrate is printed and filled by screen printing, dried with a hot air drier at 80 ° C. for 2 hours, and heated in an IR furnace adjusted to 180 ° C. for 20 hours. Cured in minutes. After curing, the through-hole resistance was measured by a four-terminal method. The through-hole resistance is
The measurement was performed on 64 holes per sample, and the average and standard deviation were calculated. After measuring the resistance, observe the cross section of the through hole,
The number of cracked through-holes out of 64 through-holes per sample was counted. A hot oil test was performed on each sample at 20 ° C.
The test was carried out under the conditions of 15 seconds, transfer time of 20 seconds, 260 ° C. for 5 seconds, and 100 cycles, and the change rate of the through-hole resistance before and after the hot oil test was measured. Hot oil test evaluation
◎, 10 to 30%
Was evaluated on a four-point scale, ○, 30 to 100% Δ, and 100% or more ×. These evaluation results are shown in Tables C-1 (Examples 1 to 10), C-2 (Examples 10 to 14), and D-1.
(Comparative Examples 1 to 8) and D-2 (Comparative Examples 9 to 14).

Examples 15 and 16 Using a copper powder having the composition shown in Table A-2, a binder 100
A curable conductive composition was prepared in the same manner as in Example 1 except that 160 parts by volume of linoleic acid-treated copper powder (Example 15) and 2,000 parts by volume (Example 16) were added to the volume part. And evaluated. The evaluation results are shown in Table C-2.

Examples 17 and 18 Using a copper powder having the composition shown in Table A-2, a phenol novolak type epoxy resin (epoxy equivalent =
176) / Novolak type phenol resin (hydroxy equivalent = 105) = 77.5 / 22.5 (weight ratio) (Example 17), neopentyl glycol diglycidyl ether (epoxy equivalent = 150) / dicyandiamide = 96 /
4 (weight ratio) (Example 18), only Example 18
Except that no -ethyl-4-methylimidazole is added
A curable conductive composition was prepared in the same manner as in Example 1 and evaluated. The evaluation results are shown in Table C-2.

Examples 19 and 20 The copper powders shown in Table A-2 were used in the form of dendrites: flakes: fibrous = 90: 8: 2 (Example 19) and 90: 2: 8 (Example 20). A curable conductive composition was prepared and evaluated in the same manner as in Example 1 except that the mixture was a mixture. The evaluation result is
The results are shown in Table C-2.

Comparative Examples 15 and 16 Using a copper powder having the composition shown in Table B-2, a binder 100
A curable conductive composition was prepared in the same manner as in Example 1 except that 120 parts by volume of linoleic acid-treated copper powder (Comparative Example 15) and 2800 parts by volume (Comparative Example 16) were added to the parts by volume. And evaluated. The evaluation results are shown in Table D-2.

Comparative Examples 17 to 19 Instead of dendritic copper powder, granules produced by the atomizing method
Copper powder was used. That is, Comparative Example 17 is compared to Example 2.
Example 18 corresponds to Example 9 and Comparative Example 19 corresponds to Example 19.
Other than using the corresponding copper powder having the composition shown in Table B-3,
A curable conductive composition was prepared in exactly the same manner as in Example 1,
evaluated. The evaluation results are shown in Table D-3.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

[0041]

[Table 6]

[0042]

[Table 7]

[0043]

[Table 8]

[0044]

[Table 9]

[0045]

[Table 10]

Claims (1)

(57) [Claims] 1. A total of 150 to 2500 parts by volume of copper powder is used for 100 parts by volume of a curable polymer binder, and said copper powder is (a) 70 to 95 parts by volume of dendritic copper powder having a particle diameter of 1 to 50 μm. Part and (b) major axis 10 to 100 μm, flatness 5 to 100
Curable conductive composition, which is a flake-like copper powder and / or a copper powder mixture having a composition of 5 to 30 parts by volume of fibrous copper powder having a diameter of 0.5 to 5 μm and a length of 50 to 5000 μm. .