JPH11224532A - Conductive copper paste composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the mutual contact of copper powder and reduce the continuity resistance to provide satisfactory conductivity by providing a composition containing copper powder, a binder resin and a solvent as essential components, the copper powder having branch form, and having specified characteristics. SOLUTION: The copper powder preferably consists of a branch electrolytic copper powder with an average particle size of 1-25 μm and a BET specific surface area of 3900-6300 cm<2> /g. Further, a binder resin is blended to the copper powder in an amount of 10-40 wt%, preferably, 20-30 wt%. The binder resin preferably consists of a resol type phenol resin. The solvent preferably consists of glycol ether, and a mixed system of two or more is also usable. This composition is obtained by mixing these components followed by kneading by use of three rolls, and various antioxidants, dispersants, coupling agents, defoaming agents and the like can be added as occasion demands.

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 through holes in a printed circuit board, and more particularly to a paper-based phenolic resin substrate or a glass cloth substrate. After embedding copper paste into the through-holes provided on a printed circuit board such as an epoxy resin board by screen printing, it is heated and cured to give good conductivity in the through-holes and to provide thermal shock even after absorbing moisture The present invention relates to a conductive copper paste composition which does not cause poor conductivity in a through hole portion accompanying the above. Of course, as a use, it can be used as a circuit conductor other than a through hole, for example, a BVH (buried via hole) or a jumper circuit.

[0002]

2. Description of the Related Art A through hole is provided in a land portion of a printed circuit board such as a paper-based phenolic resin substrate or a glass cloth-based epoxy resin substrate, and a conductive silver paste is embedded therein by screen printing and then cured by heating. Recently, a method of manufacturing a printed wiring board has become popular. However, when a silver paste is used, migration problems frequently occur especially in a pattern circuit which has recently been made finer in pitch. Further, silver is an expensive metal although having excellent conductivity.

[0003] For this reason, conductive copper paste has recently attracted attention as an alternative. However, since copper is easily oxidized and its oxide is an insulator, it is necessary to effectively suppress the oxidation of copper and further incorporate a substance having a reducing action. As measures for preventing such oxidation, for example, JP-A-61-3154 and JP-A-63-286577
Publications are known. However, in the case of copper paste, ohmic contact cannot be obtained unless the copper powders are in sufficient contact with each other, and there is still no substitute for silver paste.

[0004]

Until now, as a copper paste for through holes, Japanese Patent Application Laid-Open No. 8-73780,
JP-A-8-153942, JP-A-9-12937
JP, JP-A-9-92032, JP-A-9-69
After embedding by screen printing as described in the specification of Japanese Patent Publication No. 314, etc., by heating and curing, good conductivity of the through-hole portion is given, and thermal shock such as a thermal shock test or a solder dip test is performed. Copper paste which does not cause poor conductivity at the through-hole portion accompanying the above.

In order to exhibit this conductivity, it is necessary to press the copper powder in the paste and the copper powder by the shrinkage of the binder resin existing around the copper powder. For that purpose, it is necessary to optimize the blending amount of the copper powder and the binder resin according to the degree of shrinkage of the binder resin. In addition, the shape of the copper powder is an important factor for increasing the conductivity, that is, for reducing the conduction resistance value.

In the present invention, the BET specific surface area is 3900 to 6300 cm ² / as an element for determining the shape of the copper powder for suppressing the conduction resistance value when the copper powders are pressed together.
g has been found to be preferred.

[0007]

According to the present invention, there is provided a conductive copper paste composition comprising copper powder, a binder resin and a solvent as essential components, wherein the copper powder has a dendritic shape and has the following characteristics. More preferably, there is provided a conductive copper paste composition comprising 10 to 40% by weight of a binder resin based on the copper powder. (A) Average particle size 1 to 25 μm (B) BET specific surface area 3900 to 6300 cm ² / g The BET specific surface area is measured by the “BET one-point method”.

The copper powder used in the present invention is a dendritic electrolytic copper powder. If the BET specific surface area exceeds 6,300, the dendritic branches and leaves are too large and the gaps existing in one copper powder are increased. Since the contact area when the members are pressed against each other is reduced, the conduction resistance is increased. When the BET specific surface area is less than 3900, the gap existing in one copper powder particle is small, but the dendritic branches and leaves are small (that is, they are close to spherical).
Therefore, the contact area is also small, and the conduction resistance is high. However, since the larger the BET specific surface area, the more easily it is oxidized, the degree of oxidation of the surface is preferably as low as possible in order to exhibit high conductivity. The hydrogen reduction loss of the copper powder is desirably 1.0% or less. Hydrogen reduction weight loss is measured by “MPIF Standard 02”.

The average particle size of the electrolytic copper powder used in the present invention is preferably 1 to 25 μm. Average particle size is 1
If it is less than μm, the surface is easily oxidized and handling becomes difficult. On the other hand, if the average particle size exceeds 25 μm, the particles cannot pass through the screen printing eyes, which is likely to cause clogging.

The binder resin used in the present invention may be a thermosetting resin such as an epoxy resin, a melamine resin, an unsaturated polyester resin and a phenol resin. In particular, phenol and formaldehyde are converted into methylol under an alkali catalyst. A so-called resol type phenol resin is preferred.

The amount of the binder resin is preferably 10 to 40% by weight based on the copper powder. More preferably, 2
0 to 30% by weight. 10% by weight based on copper powder
If it is less than 3, the binding force is insufficient, and the copper powders are not sufficiently pressed against each other, so that good conductivity is not exhibited. Also, a small amount of the compound leads to a decrease in reliability. If the compounding amount of the binder resin exceeds 40% by weight of the copper powder, the insulating layer becomes excessive and the contact between the copper powders is reduced, so that the initial conduction resistance is increased, and practical use becomes difficult.

In the present invention, the solvent to be used must be selected so as to suppress drying of the screen printing plate and to facilitate drying after printing. The following glycol ethers are preferable, and are appropriately selected according to equipment capacity and use conditions. 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 monomethyl ether Isopropyl 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 the like, and esters thereof are used. Appropriate boiling point depending on the solubility and drying conditions of the binder resin
One having a vapor pressure can be selected, and a mixed system of two or more types is also possible.

Although various methods can be applied as a method for producing the conductive copper paste composition, it is general that the components are mixed and then kneaded with a three-roll mill. Also, if necessary, various antioxidants in the composition, a dispersant,
It is also possible to add fine fused silica, a coupling agent, an antifoaming agent, a leveling agent and the like.

[0014]

The present invention will be described below with reference to examples and comparative examples.

Examples 1 to 3 Copper powder having an average particle diameter of 10 μm and a BET specific surface area of 3900 to 6300 cm ²
/ G, an electrolytic copper powder having a hydrogen reduction loss of 1% or less, a resol type phenol resin as a binder resin, and a mixed solvent of ethylene glycol monobutyl ether, propylene glycol monobutyl ether and propylene glycol monopropyl ether as a solvent. The mixture was kneaded with three rolls according to the mixing ratio of 1 to obtain a conductive copper paste composition. The copper paste prepared in this manner is applied to a paper base phenolic resin substrate PL manufactured by Sumitomo Bakelite Co., Ltd.
0.1 mounted on C-2147RH (sheet thickness 1.6mm).
A 5 mmφ through hole was filled by a screen printing method, and cured at 150 ° C. for 30 minutes by a box-shaped hot air drier. The conduction performance per through hole of this test piece was measured and confirmed as a resistance value. Thereafter, a moisture absorption solder heat resistance test and a temperature shock test were performed, and the rate of change from the initial conduction resistance was determined. Then, a cross section of the inside of the through hole of this test piece was observed, and it was confirmed whether cracks or peeling had occurred in the copper paste. Table 1 shows the above results.

(Comparative Example 1) An electrolytic copper powder having an average particle diameter of 10 μm, a BET specific surface area of 1100 cm ² / g and a hydrogen reduction loss of 1% was used in the same manner as in the example, except that the copper powder used was copper. A copper paste composition having the composition shown in Table 1 was obtained and evaluated in the same manner as in the examples. (Comparative Example 2) The copper powder used had an average particle diameter of 10 µm,
Except for using electrolytic copper powder having a BET specific surface area of 8800 cm ² / g and a weight loss of hydrogen reduction of 1%, a copper paste composition having the composition shown in Table 2 was obtained in the same manner as in Example, and evaluated in the same manner as in Example. .

(Measurement method) Moisture-absorbing solder test: A sample subjected to a moisture-absorbing treatment at 40 ° C. and a humidity of 95% for 96 hours is dipped in a 260 ° C. solder bath for 5 seconds.
Do this twice. 2. Temperature impact test: 1000 cycles of the temperature impact test at -65 ° C for 30 minutes ← → 125 ° C for 30 minutes.

[0018]

[Table 1]

[0019]

The conductive copper paste composition according to the present invention is a conductive copper paste composition having excellent reliability in through-hole portions of a printed circuit board, and more specifically, a paper-based phenol resin substrate or glass. After embedding copper paste in the through-holes provided on a printed circuit board such as a cloth-based epoxy resin substrate by screen printing, and then curing it by heating, it gives good conductivity to the through-holes and solder heat resistance after moisture absorption Since there is no occurrence of poor conductivity in the through-hole portion due to heat resistance and thermal shock, highly reliable electrical connection is possible. Of course, as a use, it can be used as a circuit conductor other than a through hole, for example, a BVH (buried via hole) or a jumper circuit.

Claims (4)

[Claims] 1. A conductive copper paste composition comprising copper powder, a binder resin and a solvent as essential components, wherein the copper powder has a dendritic shape and has the following properties. (B) Average particle size 1 to 25 μm (b) BET specific surface area 3900 to 6300 cm ² / g 2. The conductive copper paste composition according to claim 1, wherein the binder resin is a resol type phenol resin. 3. The conductive copper paste composition according to claim 1, wherein the copper powder has a hydrogen reduction loss of 1% or less. 4. A copper powder containing 10 to 4 binder resins.
The conductive copper paste composition according to claim 1, wherein the composition is 0% by weight.