JP3142484B2 - Conductive copper paste composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive copper paste composition excellent in the reliability of a through-hole portion in a printed circuit board, and more particularly, to a paper-based phenol resin substrate or a glass-based epoxy resin. After embedding copper paste into the through-holes provided on a printed circuit board such as a resin board by screen printing, it is heated and cured to give good conductivity in the through-holes, and it is resistant to aging, especially thermal shock. The present invention relates to a conductive copper paste composition which does not cause a poor conductive property in a through hole portion.

[0002]

2. Description of the Related Art Through holes are provided in the lands of a printed circuit board such as a paper-based phenolic resin substrate or a glass-based epoxy resin substrate, and a conductive silver paste (hereinafter, referred to as a silver paste) is embedded therein by screen printing. Thereafter, a method of manufacturing a printed wiring board by heat curing has become popular recently. However, when a silver paste is used, migration problems frequently occur especially in a pattern circuit which has recently been made finer in pitch. Also,
Silver is an expensive metal although having excellent conductivity.

[0003] For this reason, a conductive copper paste (hereinafter, referred to as a copper paste) as an alternative has recently attracted attention. However, copper is easily oxidized, and since the oxide is an insulator, it is necessary to mix a substance having a reducing action in order to effectively suppress the oxidation of copper. As measures for preventing such oxidation, for example, JP-A-61-3154 and JP-A-63-3154.
No. 286,577 is known. Furthermore, in the case of copper paste, if the copper powder does not sufficiently contact each other, an ohmic contact cannot be obtained and the silver paste cannot be replaced.

[0004]

Accordingly, attempts have been made to sufficiently contact copper powders by using, for example, a resol type phenol resin having a large curing shrinkage as a binder. Further, in order to effectively exert the binding force, a heterocyclic compound is added as disclosed in JP-A-5-179164. However, especially in the case of small-diameter through-holes, unlike the circuit on a plane, the stress due to the curing and shrinkage of the resin, the thermal expansion in the Z-axis direction of the substrate, and the shrinkage stress due to the evaporation of the solvent immediately cause cracks, causing conduction. Easy to be defective.

The present inventors have studied to improve the drawbacks of these conventional copper pastes. As a result, excellent properties are exhibited by using a thermosetting resin, a polyhydric phenol monomer, and an imidazole compound as binders as essential components. I found something. Moreover, by imparting flexibility to the imidazole compound, the generation of cracks, which was the biggest problem in the prior art, is suppressed, and the contact between copper powders due to resin curing shrinkage is generated very efficiently, and is not inferior to silver paste. A copper paste for through-holes having achieved conduction performance and high reliability was completed, and a patent application was filed (Japanese Patent Application No. 6-207824).

A through-hole board which has obtained electrical connection after hardening with a copper paste or a silver paste requires severe soldering heat resistance in component mounting. Completed copper paste with dramatically improved thermal shock resistance such as solder heat resistance,
A patent application was filed (Japanese Patent Application No. 6-295384).

Further, since the paper-based phenolic resin substrate, which is most frequently used, undergoes greater shrinkage due to heat in the Z-axis direction than the glass-based epoxy resin substrate, the through holes that conduct in the Z-axis direction are more resistant to thermal shock. On the other hand, high reliability is desired. In the present invention, it has been found that the reliability against the thermal shock is significantly affected not only by the resin binder but also by the particle size, blending amount, and shape of the copper powder. A copper paste for through holes was completed.

An object of the present invention is to enable screen printing,
Another object of the present invention is to provide a copper paste composition having good conductivity comparable to that of silver paste and migration resistance that cannot be obtained with silver paste, and having long-term reliability and suitable for fine pitch compatible through holes. .

[0009]

The present invention provides a conductive copper paste composition comprising copper powder, a thermosetting resin, a polyhydric phenol monomer, an imidazole compound, a reactive rubber elastomer, and a solvent as essential components, The copper powder has an average particle diameter of 3 to 7 μm and a maximum particle diameter of 20 μm or less, the shape is a dendritic electrolytic copper powder, and the compounding amount of the copper powder is 50 to 75% by weight of the whole composition. It is a conductive copper paste composition characterized by the above-mentioned.

The maximum particle diameter of the electrolytic copper powder exceeds 20 μm
A gap is formed between the metal powder and the copper powder, and the contact area is reduced, so that the thermal shock resistance is deteriorated. Further, when the average particle diameter is 3
When it is less than μm, uniform dispersibility is excellent, but the number of contact points is too large, so that the contact resistance increases and the conductive performance decreases. Conversely, if it exceeds 7 μm , the number of contact points decreases, and thermal stress due to thermal shock separates the contacted copper powder, and the number of isolated copper powder increases, so that thermal shock resistance decreases. Therefore,
More preferably, the average particle size is 5 μm.

When the amount of the electrolytic copper powder is less than 50% by weight, the proportion of the thermosetting resin occupies so much that the conductive performance is not sufficiently exhibited. If it exceeds 75% by weight, the thermal shock resistance tends to decrease due to insufficient bonding strength of the thermosetting resin.

As the thermosetting resin used in the present invention, an epoxy resin, a melamine resin, an unsaturated polyester resin, a phenol resin and the like can be used. In particular, a so-called resol type phenol resin obtained by converting phenol and formaldehyde to methylol under an alkali catalyst. Is preferred.

As the polyhydric phenol monomer used in the present invention, any of catechol, resorcin, hydroquinone and the like can be used, but hydroquinone is particularly preferable. The polyhydric phenol monomer, for example, hydroquinone forms the following redox system. This facilitates electron conduction, and hydrogen released from the oxidation-reduction system can reduce copper oxide, and long-term reliability can be obtained.

[0014]

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In the present invention, it is preferable to mix an imidazole compound for improving the curability. As the imidazole compound, for example, one or more imidazole compounds having a long-chain aliphatic hydrocarbon such as N, N '-{2-methylimidazolyl- (1) -ethyl} -eicosandioildiamide are preferably used. . The imidazole compound buffers internal stress due to curing shrinkage of the resin itself and volatilization of the solvent, prevents cracks due to thermal stress such as heat resistance of the cured product in the through hole and the cured solder, and maintains reliability. In addition, since the imidazole compound forms a chelate compound with copper powder, the adhesion is improved, the contact between the copper powder and the copper powder becomes strong, and very good electrical conductivity is obtained.

In the present invention, it is preferable to further incorporate a reactive rubber elastomer. As the reactive rubber elastomer, usually, one or more of a pobutadiene-based or a polyacrylonitrile-butadiene-based one having a reactive group at a terminal is used. The terminal reactive group of the reactive rubber elastomer may be a carboxyl group, an amino group, an epoxy group, a hydroxyl group, an amide group, or the like, as long as it can react with the phenol resin upon heating. Epoxy groups are preferred in terms of the performance of the copper paste. This reactive rubber elastomer imparts flexibility to the cured product without lowering the reliability as a copper paste, and can greatly improve the reliability of thermal shock resistance.

The solvent used in the present invention is, for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monopropyl ether, Dipropylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether,
Diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether,
Ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol mono 2-ethylhexyl ether, ethylene glycol monoallyl ether, ethylene glycol monophenyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether , And glycol ether derivatives such as esterified products thereof are used in one kind or in a mixture of two or more kinds.

Although various methods can be applied to the method of producing the conductive copper paste composition, it is generally obtained by mixing the constituent components and kneading the mixture with a three-roll mill. Also, if necessary, various antioxidants in the composition, a dispersant,
It is possible to add fine fused silica, a coupling agent, an antifoaming agent, a solvent and the like.

[0019]

EXAMPLES The present invention will be described below with reference to examples. A resole type phenol resin was used as a thermosetting resin, and kneaded with a three-roll mill according to the mixing ratio shown in Table 1 to obtain a copper paste composition. The copper paste prepared in this manner was used as a paper base phenolic resin substrate PL of Sumitomo Bakelite Co., Ltd.
A 0.4 mmφ through hole of C-2147RH (sheet thickness 1.6 mm) was filled by a screen printing method, and cured at 150 ° C. for 30 minutes by a box-shaped hot air dryer.

The conduction performance of each of the test pieces per through hole was confirmed by measuring a resistance value. Thereafter, a solder heat resistance test in which dip is performed five times at 260 ° C. for 5 seconds, and a temperature shock test (1000 cycles) at −65 ° C., 30 minutes ← → 125 ° C., 30 minutes are performed, and each changes from the initial conduction resistance. The rate was determined.

[0021]

[Table 1]

[0022]

The copper paste according to the present invention is embedded in the through-holes provided in a printed circuit board such as a paper-based phenolic resin substrate or a glass-based epoxy resin substrate by screen printing, and then is heated and cured.
It is possible to obtain a copper paste which gives good conductivity in the through-hole portion and hardly undergoes a change with time, particularly after a long-term thermal shock test.

Claims (1)

(57) [Claims] 1. Copper powder, thermosetting resin, polyhydric phenol monomer, imidazole compound, reactive rubber elastomer
-, And a conductive copper paste composition containing a solvent as an essential component, the copper powder has an average particle diameter of 3 to 7 μm, a maximum particle diameter of 20 μm or less, the shape is a dendritic electrolytic copper powder, A conductive copper paste composition, wherein the amount of the copper powder is 50 to 75% by weight of the whole composition.