JPH10208547A - Conductive copper paste composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive copper paste composition having high contact between copper powders and good conductivity. The present invention is a conductive copper paste composition having copper powder and a binder resin as essential components, the copper powder having a dendritic shape, and the following characteristics. A conductive copper paste composition containing 40% by weight. (B) Average particle size 1 to 25 μm (b) Apparent density 1.0 to 4.0 g / cm ³

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.

[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 copper pastes for through holes, Japanese Patent Application Nos. 6-207824, 6-295384, 7-161224 and 7-161224 have been used.
As described in the specification of Japanese Patent Application Nos. 7-177822 and 7-224401, after embedding by screen printing, by heating and curing, good conductivity of the through-hole portion is given. A copper paste has been provided which does not cause poor conductivity in through holes due to thermal shock such as a thermal shock test or a solder dip test.

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, attention is paid to the fact that in order to keep the conduction resistance low when the copper powders are pressed together, it is sufficient to increase the contact area, and the average particle diameter of the copper powder is 1 μm or more and 25 μm or less. And apparent density is 1.0
４4.0 g / cm ³ is preferred.

[0007]

The present invention provides a conductive copper paste composition comprising copper powder and a binder resin as essential components, wherein the copper powder has a dendritic shape and has the following characteristics. More preferably, the conductive copper paste composition comprises 10 to 40% by weight of a binder resin based on the copper powder. (B) Average particle size 1 to 25 μm (b) Apparent density 1.0 to 4.0 g / cm ³

The copper powder used in the present invention is a dendritic electrolytic copper powder having an average particle size of 1 to 25 μm and an apparent density of 1.0 to 4.0 g / cm ³ . Average particle size is 1μm
If less, the number of contact points between the copper powders increases, but at the same time the contact area decreases. As a result, the conduction resistance increases. In addition, the surface is easily oxidized and handling becomes difficult. If the average particle size exceeds 25 μm, the particles cannot pass through the screen printing eyes, which is likely to cause clogging.

On the other hand, if the apparent density is less than 1.0, the dendritic branches and leaves are too large and the gaps existing in one copper powder are increased.
Since the contact area when the copper powders are pressed against each other is reduced, the conduction resistance is increased. On the other hand, if the apparent density exceeds 4.0, the gap is reduced, but the dendritic branches and leaves are reduced (that is, closer to a sphere), so that the contact area is also reduced and the conduction resistance is increased.

The binder resin used in the present invention may be an epoxy resin, a melamine resin, an unsaturated polyester resin, a phenol resin, or the like. In particular, a so-called resol type phenol resin obtained by converting phenol and formaldehyde to methylol under an alkali catalyst. 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 becomes insufficient, the copper powders are not pressed sufficiently, and good conductivity is not exhibited. Also, a small amount of the compound leads to a decrease in reliability. If the 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 decreases. As a result, the initial conduction resistance becomes high, and it becomes practically unusable.

In the case of using a solvent in the present invention, it is necessary to select a screen printing plate which suppresses the drying of the plate and also facilitates 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) Copper powder having an average particle size of 1-2
A mixture of electrolytic copper powder having a thickness of 5 μm and an apparent density of 1.0 to 4.0 g / cm ³ , a resol type phenol resin as a binder resin, and ethylene glycol monobutyl ether, propylene glycol monobutyl ether and propylene glycol monopropyl ether as solvents. Using a solvent, the mixture was kneaded with a three-roll mill in accordance with the mixing ratio shown in Table 1 to obtain a conductive copper paste composition. The copper paste prepared as described above was filled into a 0.5 mmφ through-hole provided on a paper base phenolic resin substrate PLC-2147RH (sheet thickness 1.6 mm) manufactured by Sumitomo Bakelite Co., Ltd. by a screen printing method. 150 ℃ by hot air dryer, 3
Cured in 0 minutes. 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.

(Measurement method) Moisture absorption solder test: A sample subjected to a moisture absorption treatment at 95% at 40 ° C. for 96 hours is dipped in a solder bath at 260 ° C. for 5 seconds. Do this twice. 2. Temperature shock test: -65 ° C, 30 minutes ← → 125 ° C, 3
Repeat the 0 minute thermal shock test for 1000 cycles.

[0017]

[Table 1]

(Comparative Example 1) The composition of the compounded copper paste shown in Table 2 was the same as that of the Example except that the electrolytic copper powder having an average particle diameter of 50 μm and an apparent density of 1.0 g / cm ³ was used as the copper powder used. Was obtained and evaluated in the same manner as in the examples. (Comparative Example 2) A compounded copper paste composition shown in Table 2 was obtained in the same manner as in Example except that electrolytic copper powder having an average particle diameter of 10 µm and an apparent density of 6.1 g / cm ³ was used as the copper powder used. Evaluation was made in the same manner as in Examples. (Comparative Example 3) A compounded copper paste composition of Table 2 was obtained in the same manner as in Example except that electrolytic copper powder having an average particle diameter of 10 µm and an apparent density of 0.3 g / cm ³ was used as the copper powder used. Evaluation was made in the same manner as in Examples. (Comparative Example 4) A compounded copper paste composition of Table 2 in the same manner as in Example except that an electrolytic copper powder having an average particle size of 0.5 µm and an apparent density of 2.8 g / cm ³ was used as the copper powder used. Get
Evaluation was performed in the same manner as in the examples.

[0019]

[Table 2]

[0020]

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.

Claims (2)

[Claims] 1. A conductive copper paste composition comprising copper powder and a binder resin as essential components, wherein the copper powder has a dendritic shape and has the following characteristics. (B) Average particle size 1 to 25 μm (b) Apparent density 1.0 to 4.0 g / cm ³ 2. The method according to claim 1, wherein the binder resin is 10 to 4 with respect to the copper powder.
The conductive copper paste composition according to claim 1, which is blended at 0% by weight.