JPH05194822A - Conductive paste - Google Patents

Abstract

PURPOSE:To provide a conductive paste excellent in conductivity and film properties, especially abrasion resistance, and also excellent in storage stability. CONSTITUTION:The objective paste is prepared by dispersing a conductive filler in a binder resin composition essentially consisting of a resol phenolic resin and dicyandiamide. The binder resin may further contain a bisphenol F epoxy resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste used for printed wiring boards, and more particularly to a conductive paste excellent in conductivity, adhesion and abrasion resistance.

[0002]

2. Description of the Related Art Properties required for conductive paste such as conductive carbon paste used for printed wiring boards are conductivity, printability, adhesion, solder heat resistance, high temperature heat resistance, moisture resistance, and thermal shock resistance. And wear resistance. However, in the current situation, there is no conductive paste that has been used in the past, which possesses these characteristics in a well-balanced manner. In particular, none of them simultaneously satisfy the conductivity and the coating property, especially the abrasion resistance. Therefore, in the case of a printed wiring board in which a jumper conductor and a pattern that is slid by a metal slider such as a slide switch are mixed, a complicated processing method such as printing the jumper conductor and the sliding pattern with different conductive pastes, respectively. I had to take it. Also, when a jumper conductor and a sliding pattern are formed at the same time, if a paste that considers the abrasion resistance of the sliding pattern is used, the conductivity will be low and it will be unsuitable for a jumper conductor. If a highly conductive paste is used, abrasion of the coating film and a short circuit due to abrasion powder (decrease in insulation between A and B in FIG. 1) may occur in the sliding pattern, or the abrasion powder may cause the slider to move. There is a problem that the contact resistance is increased due to the aggregation of the. In addition, the conductive paste,
As the binder resin, usually a resol-type phenol resin is widely used, but an acidic catalyst used for accelerating the curing of this resin, for example, phosphoric acid, p-
There is also a problem that toluene sulfonic acid or the like significantly reduces the storage stability of the conductive paste. Therefore, there has been a strong demand for the development of a conductive paste which is capable of simultaneously obtaining conductivity and coating film characteristics and which is excellent in storage stability.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation. That is, an object of the present invention is to provide a conductive paste which is excellent in conductivity and coating film characteristics, particularly abrasion resistance and storage stability.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to achieve the above-mentioned object, and as a result, by using a conductive paste using a specific binder resin composition containing a resol-type phenol resin, Found that can be achieved. That is, the present inventors have found that the differential scanning calorimeter (DS
C) It was observed by analysis that the curing of the resol type phenolic resin was accelerated by the amine compound. Then, it was found that certain amine compounds do not adversely affect storage stability, and that curing of the resol-type phenol resin is further promoted by addition of an epoxy resin,
The present invention has been completed.

That is, the first conductive paste of the present invention is characterized by using a binder composition comprising at least a resol-type phenol resin and dicyandiamide, and mixing and dispersing a conductive filler therein. ..
A second conductive paste of the present invention is characterized in that a binder composition comprising at least a resol-type phenol resin, a bisphenol F-type epoxy resin and dicyandiamide is used, and a conductive filler is mixed and dispersed in the binder composition. To do.

In the conductive paste of the present invention, the dicyandiamide acts to accelerate the curing of the resol-type phenol resin without adversely affecting the storage stability of the conductive paste. Further, conventionally, in a phenolic resin-based conductive paste, when an additive such as a curing accelerator is used, the electrical characteristics such as conductivity are deteriorated even in a small amount, but in the conductive paste of the present invention, The presence of dicyandiamide does not have any adverse effect on the electrical characteristics and rather brings about a good result on the conductivity.

The present invention will be described in detail below. The resol type phenolic resin, which is the main component of the conductive paste of the present invention, is specifically T-200 (manufactured by Showa High Polymer Co., Ltd.), PS-2180 (manufactured by Gunei Chemical Industry Co., Ltd.), Hitanol 4010 (Hitachi Chemical Co., Ltd.) Manufactured by the company) and the like.

In the present invention, it is preferable to use a bisphenol F type epoxy resin together with the above-mentioned resol type phenol resin, whereby the curing of the resol type phenol resin is promoted and flexibility which is a drawback of the phenol resin. It also contributes to the improvement of. Bisphenol F
Preferred examples of the type epoxy resin include Epicoat 807 (produced by Yuka Shell Co., Ltd.) and Epotote YDF-2001 (produced by Toto Kasei Co., Ltd.).

The mixing ratio (solid content ratio) of the bisphenol F type epoxy resin is 100 for the resol type phenol resin.
3 parts by weight of bisphenol F type epoxy resin
The amount is 0 parts by weight or less, preferably 15 parts by weight or less. Further, the mixing ratio of dicyandiamide is 1 to 7 parts by weight, and more preferably 1 to 5 parts by weight, relative to 100 parts by weight of the resol type phenol resin.

If desired, the thermosetting resin or the thermoplastic resin may be mixed with the binder resin composition containing these resol type phenolic resin and dicyandiamide as a main component.

Carbon powder is usually used as the conductive filler used in the conductive paste of the present invention, and conductive carbon black and graphite are particularly preferable.
The amount of the conductive filler used is set in the range of 50 to 120 parts by weight with respect to 100 parts by weight of the resol-type phenol resin. Particularly, it is preferable to set it in the range of 100 to 120 parts by weight.

The solvent used for the conductive paste of the present invention is a good solvent for the phenol resin and epoxy resin, and has a slow volatilization rate so as not to evaporate during screen printing and increase the viscosity of the conductive paste. There must be conditions such as the presence, odor, and nontoxicity. Solvents satisfying all of these conditions, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene Glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether Tellur, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether and other ethylene glycol and diethylene glycol derivatives, butyl acetate, amyl acetate, cyclohexyl acetate, methyl acetoacetate, ethyl acetoacetate, dimethyl adipate, dimethyl glutarate, dimethyl succinate, etc. Examples thereof include ketones such as esters, cyclohexanone, methylcyclohexanone, diisolketone, and isophorone. These solvents may be used alone or as a mixture of two or more kinds.

Various additives can be added to the conductive paste of the present invention as long as the characteristics are not impaired. For example, additives such as a defoaming agent, a thixotropic agent, and a coupling agent can be added.

[0014]

EXAMPLES The present invention will be specifically described below with reference to examples. In addition, "parts" means parts by weight unless otherwise specified. Examples 1 to 7 and Comparative Examples 1 to 3 The components shown in Table 1 below were mixed and dispersed with a three-roll mill to prepare a conductive paste.

[0015]

[Table 1]

Using a printed wiring board produced by using these conductive pastes, the sheet resistance value, adhesiveness, flexibility, reliability, high-temperature storage property, moisture resistance, and Solder resistance, boiling resistance and abrasion resistance tests were conducted. The results are shown in Table 2.

(1) Sheet resistance value The conductive paste of Examples 1 to 7 and Comparative Examples 1 to 3 was applied to a copper foil portion of a printed wiring board made of a paper phenol copper clad laminate having electrodes formed at intervals of 100 mm. Are respectively applied by the screen printing method, and the width is 1 mm × 100.
A mm pattern film was formed. Then, it was heated and cured at 150 ° C. for 30 minutes in a hot air circulation type drying furnace. The resistance value of the obtained cured film was measured with a digital multimeter (VOAC-7411 manufactured by Iwatsu Electronics Co., Ltd.),
The sheet resistance value was calculated. The sheet resistance value is preferably as small as possible, and as is clear from the results in Table 2, the addition amount of dicyandiamide of 1 to 5 parts by weight and the case where the bisphenol F type epoxy resin is 20 parts by weight or less are particularly preferable can get.

(2) Adhesiveness Paper phenol copper clad laminate copper foil surface 15 mm × 15
A mm pattern film was formed in the same manner as in (1) above, and heat-cured. 1 mm with a cutter knife on the obtained cured film
Adhesion was evaluated by making 100 squares having a size of 1 mm and checking the number of squares left on the substrate when the coating film was peeled off with a cellophane tape (JISK5400). The larger the number of squares, the more preferable the result.

(3) Flexibility A pattern was formed in the same manner as in the above (1), and after heating and curing, the formed printed wiring board was bent back and forth 10 times at a bending rate of 10%, and then cracked. Was examined and the flexibility was evaluated. Excellent resistance change rate of 1% or less, good resistance change rate of 10% or less, bad crack generation,
Indicates that there is a disconnection.

(4) Reliability After printing and curing in the same manner as in the above (1), the resistance value of the obtained cured film was measured, and a pattern film was formed in the same manner as in the above (2), followed by heat curing. The following reliability test was performed using the printed wiring board. The smaller the absolute value of the rate of change in both high temperature storage characteristics and humidity resistance, the better, and +
More preferred is −. B. High-temperature storage property The film was left in a hot-air circulation type drying oven at 85 ° C. for 1000 hours to determine the rate of change in resistance, and the adhesion was tested by the method (2) above. (B) Moisture resistance Use a thermo-hygrostat for 10 hours at 65 ° C and 95% RH.
After storage for 00 hours, the resistance change rate was determined, and the adhesion was tested by the method (2).

(5) Solder heat resistance A printed wiring board manufactured in the same manner as in the above (1) was used for 260
After being immersed in a solder bath at a temperature of 10 ° C. for 10 seconds, the rate of change in resistance was determined, and an adhesion test was conducted by the method (2).

(6) Boiling resistance A printed wiring board manufactured in the same manner as in (1) above was immersed in boiling water for 4 hours and boiled. The resistance change rate after boiling was determined, and the adhesion test was performed by the method (2).

(7) Abrasion resistance The abrasion resistance test was carried out using the apparatus shown in FIG. In FIG. 1, (a) is a partial plan view of an abrasion resistance test device including a printed wiring board and a slider, and (b) is a sectional view taken along the line aa. Reference numeral 1 is a base material of a paper-phenol copper-clad laminate, 2 is a copper foil formed on the base material, 3 is a cured film of a pattern film formed of a conductive paste, and 4 is a slider. Here, for the printed wiring board, the same conductive paste as used in (1) above was applied onto the copper foil portion of the base material made of paper phenol copper clad laminate, respectively, as shown in FIG. It was produced by heat curing. By sliding the slider (weight: 100 g) back and forth 20000 times between A and B (space: 1 mm) of the cured film of this printed wiring board, and measuring the insulation resistance value between A and B. I did. It is indicated that the larger the insulation resistance value, the greater the film strength.

[0024]

[Table 2]

[0025]

As described above, since the conductive paste of the present invention has the above-mentioned constitution, the cured film formed by using it has excellent abrasion resistance without impairing the conductivity. In addition, it has excellent adhesion and flexibility. Therefore, by using the conductive paste of the present invention, it is not necessary to form the jumper conductor and the sliding pattern with separate conductive pastes as in the conventional case, and a jumper conductor excellent in high conductivity, adhesion and flexibility is obtained. And, it becomes possible to easily manufacture a printed wiring board having a key contact and a sliding contact having excellent wear resistance.

[Brief description of drawings]

FIG. 1 is a partial plan view of an abrasion resistance test apparatus of the present invention and a sectional view taken along line aa.

[Explanation of symbols]

 1: Base material 2: Copper foil 3: Hardened film 4: Slider

Claims (4)

[Claims] 1. A binder resin composition comprising at least a resol-type phenol resin and dicyandiamide,
A conductive paste comprising a conductive filler mixed and dispersed. 2. The conductive paste according to claim 1, wherein the dicyandiamide is 1 to 7 parts by weight and the conductive filler is 50 to 120 parts by weight with respect to 100 parts by weight of the resol-type phenol resin. 3. At least a resol type phenolic resin,
A conductive paste comprising a binder resin composition composed of a bisphenol F type epoxy resin and dicyandiamide, and a conductive filler mixed and dispersed therein. 4. The bisphenol F type epoxy resin is 30 parts by weight or less, the dicyandiamide is 1 to 5 parts by weight, and the conductive filler is 50 to 120 parts by weight with respect to 100 parts by weight of the resol type phenol resin. The conductive paste according to claim 2.