JPH03137173A - Electron radiation curing type electrically conductive paste - Google Patents

Abstract

PURPOSE:To obtain the subject paste, composed of fine powder, such as copper- based powder, an electron radiation curing resin and organic fatty acid in a specific proportion and excellent in initial electric conductivity with maintained reliability for a long period at high temperatures and humidities without migration. CONSTITUTION:The objective paste composed of a blend composed of (A) 60-90wt.%, preferably 70-90wt.% copper- and/or nickel-based fine powder and (B) 40-10wt.%, preferably 30-10wt.% electron radiation curing resin (e.g. an unsaturated polyester resin) and (C) an organic fatty acid (preferably oleic, linoleic or linolenic acid) in an amount of 0.05-10wt.%, preferably 0.1-5wt.% based on the total amount of the aforementioned blend.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an electron beam curing type conductive paste, and more specifically, it relates to an electron beam curing type conductive paste that is applied after being painted or printed on equipment such as electronic equipment parts and printed wiring boards. , relates to a conductive paste that is cured by irradiation with an electron beam.

(Prior art) In recent years, so-called paste-like conductive paints and adhesives, which are made by blending large amounts of fine particulate silver flakes, copper powder, or carbon particles with organic polymer binders and oligomers, have been put into practical use and are widely used. It is used for.

These conductive paints and adhesives are used to form conductor circuits in the manufacturing process of printed wiring boards or hybrid ICs.

It is also used as a resistor in circuit formation. Furthermore, this type of paste is used not only for the purpose of circuit formation mentioned above, but also for various electronic parts such as membrane switches and resistors, as well as for bonding paste, liquid crystal panel adhesive, and LED.
used as an adhesive.

In addition, as one of the measures to prevent electromagnetic waves, which has recently become a social issue, a method has been developed that coats conductive paint on printed wiring circuits to shield electromagnetic waves generated from inside the circuit and prevent crosstalk between wiring. , is gradually becoming common.

However, conventionally developed conductive pastes use thermosetting resins as binders. For this reason, upon application, it is necessary to apply or print this conductive paste onto a base material and then heat and harden it at a high temperature. In order to harden this paste, it is not only uneconomical as it requires a large amount of energy, time for heating, and large floor space for installing heating equipment, but the base material on which the paste is applied is also made of synthetic resin. In many cases, long-term heating causes deterioration and deformation of the base material, which may impair long-term reliability. Therefore, there is a strong demand for a material that can be cured by heating for a short time, but there is still no satisfactory material.

Therefore, expectations are high for a method of curing a conductive paste at or near room temperature by irradiation with active energy rays such as ultraviolet rays and electron beams.

However, curing with ultraviolet rays is difficult to apply to such highly concentrated metal-containing coatings because ultraviolet rays do not have the ability to penetrate metal parts. On the other hand, although curing with electron beams does not have any problems with curing properties, it has the drawback that it is significantly inferior to heat-curing types in terms of initial conductivity and a decrease in conductivity in high temperature and high humidity environments. Ta.

For these drawbacks, for example, Japanese Patent Application Laid-Open No. 56-9059
No. 0 recommends heating a coating film coated with a silver filler-containing electron beam curable paint after electron beam irradiation. The improvement in initial conductivity by this method is remarkable, but since i-triple is used as a filler,
There are problems with migration, and long-term reliability is still not satisfactory.

(One problem to be solved by the invention) The present invention is an electron beam-curable conductive material that has excellent initial conductivity, maintains long-term reliability even under high temperature and high humidity environments, and has no migration problem. It provides a paste.

(Means for Solving the Problems) That is, the present invention provides: (A) 60-90% by weight of copper-based and/or nickel-based fine powder; (B) 40-10% by weight of electron beam curable resin. and (C) an electron beam curable conductive paste characterized by comprising an organic fatty acid blended in a proportion ranging from 0.05 to 10% by weight based on the total amount of the blend.

The copper-based and/or nickel-based fine powder used in the present invention includes dendritic copper powder, scale-like copper powder, spherical copper powder, silver-plated copper powder, silver-copper composite powder, silver-copper alloy powder, and amorphous copper powder. Fine powder, carbonyl nickel powder, nickel-silver composite gold powder, silver-plated nickel powder, flaky nickel powder, silver-nickel composite powder, or a mixture thereof having an average particle size of 0.1 to 50 μm is used. Particularly preferred is a fine powder having an average particle diameter of 1 to 30 μm.

Note that the average particle diameter refers to a centrifugal sedimentation method or a mode diameter derived from a Stokes diameter measured by a sedimentation method.

Examples of the electron beam curable resin used in the present invention include resins having unsaturated groups within their molecular chains or in their side chains. Specifically, unsaturated polyester resin, polyester (meth)acrylate resin, epoxy (meth)
Examples include acrylate resins, polyurethane (meth)acrylate resins, polyether (meth)acrylate resins, polyallyl compounds, polyvinyl compounds, polyacrylated silicone resins, and polybutadiene. Preferably, it is an epoxy (meth)acrylate resin. These resins can be used alone or in combination.

In addition, 7mers and oligomers with unsaturated groups for the purpose of reducing viscosity, such as methyl (meth)acrylate, (meth)
Ethyl acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylic acid, dimethylaminomethyl (meth)acrylate, poly (methylene glycol) polyacrylate, poly ( Propylene glycol)
Polyacrylate, trimethylcolpropane triacrylate, triallyl trimellitate, triallyl isocyanurate, etc. may be used in combination.

The organic fatty acid used in the present invention is an aliphatic compound having one or more carboxyl groups in the molecule.

Examples include saturated carboxylic acids, unsaturated carboxylic acids, alicyclic carboxylic acids, and the like.

As specific examples, saturated carboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, lauric acid, myristic acid, palmitic acid, stearic acid, chelic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, crotonic acid, oleic acid, linoleic acid, linoleic acid, fumaric acid, maleic acid, etc. Alicyclic acid Examples of the carboxylic acid include cyclohexanecarboxylic acid, hexahydrophthalic acid, and tetrahydrophthalic acid. These can be used alone or in combination, and derivatives thereof can also be used.

Preferred are oleic acid, linoleic acid, and lylunic acid.

In the present invention, the blending ratio of (A) copper-based and/or nickel-based fine powder and (B) a compound having an electron beam reactive group is 60 to 90% by weight of (A) and 40 to 10% by weight of (B). (C) organic fatty acid is in the range of 0.05 to 10% by weight based on the total amount of (A) and (B).

When (A) is less than 60% by weight, the conductivity is insufficient, and when it exceeds 90% by weight, the coating film becomes brittle and the conductivity decreases. If the amount of (B) exceeds 40, no conductivity will be obtained, and if the amount is less than 10, the coating film will become brittle.

(C) is 0 for a formulation consisting of (A) and (B).
．． If the amount is less than 0.5% by weight, conductivity cannot be obtained, and if it exceeds 10% by weight, the coating film becomes brittle. Particularly preferably, (A) is 70 to 90% by weight and (B) is 30 to 1% by weight.
0% by weight, C) for a formulation consisting of (A) and (B)
The content is 0.1 to 5% by weight.

Volatile solvents can be added to adjust the workability of the conductive paste of the present invention. As a volatile solvent,
For example, ketones, aromatics, alcohols, cellosolves, esters, etc. can be used.

Specifically, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, ethanol, butanol,
Ethylene glycol, propylene glycol, methyl cellosolve, ethyl cellosolve, butyl cellosolve, propylene glycol monobutyl ether, butyl calpitol, ethyl acetate, butyl acetate, cellosolve acetate, etc.
Or a mixture of these.

The conductive paste of the present invention includes the above (A), (B), (
As necessary, within the range that does not impede the performance of C),
Thixotropic agents such as finely divided silica, calcium carbonate, magnesium carbonate, clay, talc, mica,
Inorganic fillers such as barium sulfate, adhesion improvers such as titanate compounds, etc. can be added.

The conductive paste of the present invention can be prepared by mixing (A), (B), and (C), and then using a method that is used in the production of ordinary conductive paste.
For example, it can be easily manufactured by a method using a three-roll device.

In particular, the order of mixing (A), (B), and (C) is not limited.

The conductive paste of the present invention may contain a thermosetting resin in addition to the electron beam curable resin, if necessary. Examples include epoxy resin, urethane resin, phenol resin, melamine resin, urea resin, benzoguanamine resin, diallyl phthalate resin, thermosetting silicone resin,
Mention may be made of maleimide resins. Among these resins, epoxy resins and urethane resins require the combined use of a curing agent or catalyst.

Although screen printing is the most suitable method for applying the conductive paste of the present invention to a substrate, it is also possible to use other printing and coating methods, such as spray coating and roller coating.

The conductive paste of the present invention can be printed or painted on a base material, and after removing volatile solvents at room temperature or by heating as necessary, irradiation with an electron beam in air or an inert gas atmosphere is performed. hardened by The conditions for electron beam irradiation are as follows: acceleration voltage 15 (1 to 300 kv, absorption line 'Ik
The conductive paste of the present invention may be heated during electron beam irradiation.

The conductive paste of the present invention can be put to practical use as it is after being cured by electron beam irradiation, but if necessary, it can also be subjected to heat aging treatment or coated with a protective paint. be.

In addition to so-called wiring circuits, it can also be used for the purpose of IUT wave shielding, and in some cases, it can be used as an adhesive.

Examples of how adhesives can be used include reinforcing screw lock caulks, repairing circuits, bonding waveguides, bonding liquid crystals, bonding LEDs,
Examples include adhesion of semiconductor elements, adhesion of potentiometers, adhesion of crystal resonators, and adhesion of carbon brushes of micromotors.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.
These are not limited.

fa) Preparation of conductive paste: Uniformly disperse the various ingredients at the compounding ratio shown in the table below using a triple roll. I arranged it.

) Preparation of cured coating film: The conductive paste was printed using a 200-mesh stainless steel screen plate on a single-sided copper-clad paper phenol laminate on which a copper foil electrode portion had been previously formed by etching and polishing.

The size of the conductive paste printed between w4 foil electrodes is
The length was ICl5 and the width was 1c11. Next, 200'CX
After drying with a far infrared dryer at 1 m 1 n, use an electron beam irradiation device (
Nisshin High Voltage 300kv Low Energy Accelerator)
The conductive paste was cured by irradiating it with an electron beam in an N gas atmosphere under the conditions of an acceleration voltage of 250 kV and an absorption line of 1110 Mrad.

Furthermore, a thermosetting solder resist (S-22 manufactured by Taiyo Ink Manufacturing Co., Ltd.) was printed on the conductive paste after curing.
It was cured at 160°C for 3 minutes.

(C) Test method for cured coating film; (i) Surface condition evaluation: The surface condition before printing the solder resist is visually observed and its smoothness is evaluated.

(ii) Solder immersion test: The cured coating was immersed in a 260°C molten solder bath (tin 60/lead 4
0) for 10 seconds.

(iii) Moisture resistance test: The cured coating film is left at a constant temperature of 60° C. and relative humidity of 90 to 95% for 500 hours.

The rate of change in volume resistivity after the test (11) and (if) was calculated from the following formula.

Rate of change (%) − Comparative examples 1 to 4 Table 3 shows formulation examples and their evaluations.

Examples 1 to 6 Table 1 shows formulation examples, and Table 2 shows the evaluation results (effects of the invention) In the present invention, organic fatty acids were used together with copper-based or /6 and nickel-based fine powders that are conductive powders. As a result of the blending, Migracigon's electro-curable conductive paste is provided which has excellent initial conductivity and maintains long-term stability under high temperature and high humidity conditions.

(1 other person)

Claims (1)

[Claims] (A) Copper-based and/or nickel-based fine powder 60-90
% by weight, (B) a compound consisting of 40 to 10% by weight of electron beam curable resin, and (C) 0.05 to 0.05 to the total amount of the compound.
An electron beam curable conductive paste characterized by comprising an organic fatty acid blended in a proportion in the range of 10% by weight.