JP3142465B2 - 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 through holes in a printed circuit board, and more particularly to a paper-based phenol resin substrate or a glass cloth epoxy resin. After embedding the conductive copper paste composition by screen printing in the through-holes provided on a printed circuit board such as a substrate, and then heating and curing it, it gives good conductivity in the through-holes and changes over time, especially heat. The present invention relates to a conductive copper paste composition (hereinafter, referred to as a copper paste) that does not cause poor conductivity in a through hole portion due to a mechanical impact.

[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 base phenol resin board or a glass cloth epoxy resin board, and a conductive silver paste (hereinafter, referred to as a silver paste) is embedded therein by screen printing. Recently, a method of manufacturing a printed wiring board by heat curing has become popular. However, when a silver paste is used, silver migration problems frequently occur, especially in recent fine-pitch patterned circuits. Further, silver is an expensive metal although having excellent conductivity.

[0003] For this reason, recently, an alternative copper paste has attracted attention. However, copper is easily oxidized, and since the oxide is an insulator, it is necessary to effectively suppress the oxidation of copper and further to mix a substance having a reducing action. As a measure for preventing such copper oxidation, for example, JP-A-61-315
No. 4, JP-A-63-286577, and the like 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]

For both silver paste and copper paste for through-holes, in addition to printing workability such as embedding into small-diameter holes, low bleeding properties, and low plate-drying properties, the shape that the paste produces in the through-holes Greatly affects reliability. These properties are influenced by the boiling point and vapor pressure of the solvent, the viscosity of the binder resin, and the curing speed. The balance between the increase in viscosity due to the curing of the binder resin and the rate of evaporation of the solvent is important. That is, if the curing of the resin is too fast when the solvent is volatilized, blisters are generated due to an increase in the viscosity of the resin, and voids are generated by the solvent trapped inside. It is sufficient that the solvent evaporates as quickly as possible in the process of hardening the resin binder. However, when the amount of the low boiling solvent increases, the solvent evaporates on the screen plate during printing, that is, the plate dries.

[0005] When the balance between the solvent volatilization rate and the resin curing rate was investigated, it was found that it is desirable that the total amount of the solvent in the copper paste be 20 to 40 parts by weight and the boiling point be 140 to 180 ° C. Thus, the above-mentioned problems could be overcome. The phenol resin used in combination with such a solvent has a gel time of 6 at 150 ° C.
It has been found that a resol type phenol resin having a time of 0 to 180 seconds is preferable. Specifically, from room temperature to the curing temperature of 15
The temperature was raised to 0 ° C. in 30 minutes, and the curing was completed in 30 minutes.

[0006]

DISCLOSURE OF THE INVENTION The present invention relates to a method for preparing a copper powder, a thermosetting resin , a polyhydric phenol monomer, and an imidazole compound.
Paste containing a product, a reactive rubber elastomer, ultrafine silica particles and a solvent as essential components, wherein the solvent has a boiling point of 14.
One or more mixed solvents at 0 to 180 ° C,
The amount of the solvent is 20 parts by weight based on 100 parts by weight of the copper powder.
It is a copper paste characterized by being で あ 40 parts by weight. And preferably, when a resol type phenol resin having a gel time of 150 to 60 seconds at 150 ° C. is used as the thermosetting resin, the balance between the solvent volatilization rate and the resin curing rate is further improved, and copper having excellent properties is obtained. A paste can be obtained.

If the total amount of the solvent is less than 20 parts by weight with respect to the copper powder, the viscosity tends to be too high for printing and embedding in a small-diameter through-hole, and the volume shrinkage due to the evaporation of the solvent is too small. In addition, the formability of the cured paste in the through-hole becomes problematic. If the amount exceeds 40 parts by weight, thinness is hardened and formed on the wall surface of the through hole, resulting in poor reliability. Regarding the boiling point of the solvent, if the temperature is 140 ° C or lower, drying on the screen plate becomes intense at the time of printing. Or

The thermosetting resin used in the present invention is preferably a so-called resol type phenol resin obtained by converting phenol and formaldehyde to methylol under an alkali catalyst, and preferably has a gel time of 150 ° C. for 60 to 180 seconds. When the time is less than 60 seconds, the resin hardens faster than the solvent evaporates, and blistering may occur. On the other hand, when the heating time is 180 seconds or more, heating for 30 minutes or more is required for curing sufficiently, which is not preferable in practical use.

As the copper powder used in the present invention, a commercially available product can be used as it is, and any shape such as scaly, dendritic, and spherical shapes can be used. Particularly, dendritic electrolytic copper powder is preferable. .

In the present invention, a polyhydric phenol monomer is used to prevent oxidation of the copper powder. As the polyhydric phenol monomer, any of catechol, resorcin, hydroquinone and the like can be used, but hydroquinone is particularly preferred for the above purpose. This hydroquinone forms an oxidation-reduction system, thereby facilitating electron conduction, and hydrogen released from the oxidation-reduction system can reduce copper oxide, and long-term reliability is obtained. The amount of the polyhydric phenol monomer is 1 to 100 parts by weight of copper powder.
~ 100 is preferred. If the amount is less than 1 part by weight, the reducing effect is small, and if the amount exceeds 100 parts by weight, no further improvement in the effect can be seen.

As the reactive rubber elastomer preferably used in the present invention, at least one of a polybutadiene-based or 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, etc., as long as it can react with the phenolic resin when heated, and is not particularly limited.
Carboxyl groups, amino groups, and epoxy groups are preferred in terms of copper paste performance. 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 compounding amount of the reactive rubber elastomer is 0.1.
1 to 20 parts by weight is preferred. If the amount is less than 0.1 part by weight, the improvement of the above characteristics cannot be expected. When the amount is more than 20 parts by weight, heat resistance such as solder heat resistance is lowered.

The ultrafine silica preferably used in the present invention imparts thixotropy to the copper paste, and is anhydrous silica represented by SiO 2 having a specific surface area of 50 m 2 / g or more having a particle diameter of 50 nm or less and having a hydrophobic surface. The processed one is good. The compounding amount of ultrafine silica is copper powder 100
It is 0.5 to 3 parts by weight based on parts by weight. When the amount is less than 0.5 part by weight, the effect of imparting thixotropy is small, and when the amount is more than 3 parts by weight, the cured paste becomes brittle, and the adhesion is reduced.
The reliability will be reduced.

Although various methods can be applied as a method for producing the copper paste composition, it is general that the components are mixed and kneaded with a three-roll mill. Further, it is possible to add various antioxidants, dispersants, coupling agents, defoaming agents and the like to the composition as needed.

[0014]

EXAMPLES The present invention will be described below with reference to examples. Electrolytic copper powder having an average particle diameter of 5 μm as copper powder, a resol type phenol resin having a gel time of 150 to 60 seconds at 150 ° C. as a thermosetting resin, and a solvent having a boiling point of 140 to 180 ° C. The mixture was kneaded with three rolls according to the ratio to obtain a copper paste. The copper paste thus prepared was applied to a paper-based phenolic resin substrate PLC-2147RH (sheet thickness 1.6 mm) manufactured by Sumitomo Bakelite Co., Ltd.
The through holes of 0.4 mmφ were filled by a screen printing method, and the temperature was raised from room temperature to a curing temperature of 150 ° C. in 30 minutes by a box-shaped hot air drier, and the curing was completed within this time.

The conduction performance per through hole of this test piece was confirmed by measuring the resistance value. Thereafter, a soldering heat test in which dip is performed 5 times at 260 ° C. for 5 seconds and a thermal shock test (1000 cycles) for 30 minutes at −65 ° C. for 30 minutes →→ 125 ° C. are performed, and the rate of change from the initial conduction resistance, respectively. I asked. Then, the inside of the through hole of this test piece was observed, and it was checked whether cracks, voids, or blisters had occurred in the copper paste.

[0016]

[Table 1]

Since the copper paste obtained in Comparative Example 1 had a low boiling point of the solvent, the copper paste was dried during screen printing, and printing was impossible except at the beginning.

[0018]

According to the present invention, the copper paste is embedded by screen printing in a through-hole portion provided on a printed circuit board such as a paper-based phenolic resin substrate or a glass cloth-based epoxy resin substrate, and then heated and cured. Gives good conductivity in the through-hole part, and changes with time are extremely small.Especially, by optimizing the balance between the increase in viscosity due to the curing of the binder resin and the rate of evaporation of the solvent, embedding into small holes, low bleeding, The present invention provides a highly reliable conductive copper paste composition which improves printing workability such as low plate drying property and has no cracks, voids, or blisters in a shape produced by a paste in a through hole.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ identification code FI C08L 101/00 C08L 101/00 (58) Field surveyed (Int.Cl. ⁷ , DB name) H01B 1/00-1/24 C08K 3/08 C08K 3/36 C09D 5/24

Claims (2)

(57) [Claims] 1. Copper powder, thermosetting resin, polyhydric phenol monomer, imidazole compound, reactive rubber elastomer
-A conductive copper paste composition containing ultrafine silica and a solvent as essential components, wherein the solvent has a boiling point of 140 to 180 ° C.
Or a mixed solvent of two or more of the above, wherein the compounding amount is 20 to 40 parts by weight based on 100 parts by weight of the copper powder. 2. The conductive copper paste composition according to claim 1, wherein the thermosetting resin is a resol-type phenol resin, and has a gel time at 150 ° C. for 60 to 180 seconds.