JPH02155114A - Conductive copper paste - Google Patents

Abstract

PURPOSE:To obtain a monoliquid conductive copper paste with low electrical resistance, good adhesion to a substrate, screen-printability, heat resistance, humidity and heat-soldering resistance, and thermal shock resistance by using modified hydroquinone resin and modified epoxy resin together as a binder of the conductive copper paste. CONSTITUTION:The title paste is comprised of a copper-based conductive powder, a reductive resin of a modified hydroquinone resin, and a modified epoxy resin. As the modified hydroquinone resin, hydroquinones, catechols, and their alkyl and alkenyl-substituted ones may be used. Also, as the modified epoxy resin, a glycidyl compound-novolak epoxy resin such as phenol-novolak, cresol- novolak, etc., is preferably used owing to its heat resistance and electric properties. As a result, a monoliquid conductive copper paste with low resistance, good screen-printability and adhesion to a substrate, and stable resistance against heat and humidity is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a conductive copper paste used for single-sided and double-sided printed circuit boards called single-sided multilayer boards or jumper circuits among printed circuit boards. be.

[Conventional technology]

There are three types of printed circuit boards: single-sided boards, double-sided boards, and multilayer boards. Y! Functions required by the device,
In consideration of reliability and cost, materials such as resistant reinforced phenolic resin laminated sheets and glass fiber reinforced epoxy resin laminated sheets are being used. Among these, single-sided board O
In order to improve the processing efficiency, if both sides are used, it is inevitable that the material will be changed and the number of processing steps will increase, resulting in an increase in cost. A way to avoid this is to apply insulating ink (undercoat agent) to the circuit part on the single-sided board, except for the necessary terminals, by screen printing, and then screen-print a conductive paste on top of this! A common method is to draw a circuit using a wafer, connect it to the terminals of the original circuit, and then apply insulating ink (overcoat agent) to the entire surface of the circuit to complete the finished product. The pattern drawn using this conductive paste is called a jumper gland, and the completed printed wiring board is called a single-sided multilayer board. One finger is used as a binder and silver powder is used as conductive particles. However, as the use of conductive coatings for magnetic shielding, including jumper circuits, has expanded in recent years, high reliability has been required. It's starting to happen. In other words, fine patterning of circuits is becoming a priority in order to make electronic devices lighter, thinner, and smaller. This phenomenon occurs and the circuit is short-circuited, which not only destroys the electronic equipment but also causes various adverse effects. To avoid this, various measures have been devised.1 For example, some of the powder may be replaced with an alloy such as vanadium. Suppress the degree of migration phenomenon. A2.
It is common practice to use a conventional silver paste and apply an undercoat agent and an overcoat many times to suppress the silver migration phenomenon.However, both methods have a limit to their effectiveness. On the other hand, as a way to avoid the silver migration phenomenon, it is recommended not to use silver powder as conductive particles, that is, to replace silver powder with conductive particles such as nickel or copper. Both nickel and silver are base metals and are cheaper than silver, but those using nickel powder have excellent stability over time but are poor in conductivity, while those using copper powder have poor conductivity. Although the initial conductivity of the conductive paste is satisfactory, the oxidation of the copper powder gradually progresses over time and the conductivity decreases, making the long-term reliability unsatisfactory.
It must be carried out under an atmosphere of inert gas such as nitrogen, which poses difficulties in terms of handling methods and equipment.

[Problems to be Solved by the Invention] Needless to say, the performance required of conductive copper paste used for jumper circuits is low electrical resistance, good screen imprintability, and high adhesion to the substrate. However, as its uses have expanded in recent years, high reliability has become required, especially resistance stability against insulation coating agents such as undercoat agents and overcoat agents, heat resistance, etc.
The requirements for resistance stability against 7 degrees are becoming stricter.

However, since conventional conductive copper paste for jumper circuits uses epoxy resin and phenol resin alone, the electrical resistance value is not very low, and it also has poor coating hardness, mechanical strength, and solvent resistance. Although these resins have excellent impact resistance, they have a weak point against impact, and
There was a large change in resistance when immersed in a solder bath, and there were problems with electrical and mechanical properties against thermal shock.

In addition, a conductive copper paste that has low electrical resistance and is well-balanced in printability, adhesion properties, insulation coating resistance, soldering heat resistance, heat and moisture resistance stability, and thermal shock resistance has not yet been obtained. This is the current situation.

-Means for Solving the Problems] In view of the above circumstances, the present inventors conducted intensive research to obtain a paste free of such defects, and as a result, they arrived at the present invention.

That is, by using modified hydroquinone resin and modified epoxy resin together as a binder for conductive copper paste,
Low electrical resistance, improved adhesion to substrates, good screen printability, heat resistance, single ink resistance, soldering heat resistance, and thermal shock resistance. Requires curing in an inert atmosphere. The present invention was completed based on the discovery that a one-component conductive copper paste that does not

That is, the conductive copper paste of the present invention is a conductive powder mainly composed of copper powder, a reducing agent such as modified hydroquinone resin,
Fingers, change [':, epoxy resin as the main component 4!
It is a conductive paste with a

The modified hydroquinone compound used in the present invention can be obtained as follows.

Modified Hydroquinone Resin-2 Hydroquinones used include hydroquinone, catechol, alkyl thereof, and fulkenyl substituted products thereof. These substituted compounds include t-butylhydroquinone and urushiolthithiol, of which three compounds except L-butylhydroquinone are the main components of lacquer and are natural products. The purity and composition ratio of natural lacquer differs depending on where it is produced, such as Japan, China, Korea, Burma, or Thailand.

It is known that these two natural lacquers produce coatings with a three-dimensional structure through repeated oxidative coupling reactions between urushiolquinone and urushiol catalyzed by the enzyme laccase. In addition, the enzyme roughcase is a copper complex that participates in the redox action between urushiol and urushiolquinone. The idea of using these redox mechanisms to reduce copper powder, which is easily oxidized, into a paste using hydroquinone and catechol, which are industrially produced, easily available, and stable in terms of quality. A reducing resin was originally obtained.

First, hydroquinone was dissolved in a solvent such as ethylene glycol monomethyl ether along with phenols, and 37
A resol type resin is obtained by condensation reaction with an aqueous formalin solution of about % by weight under an alkaline catalyst. The phenols used here include phenol, p-cresol,
Examples include t-butylphenol. Any alkali catalyst may be used as long as it causes a condensation reaction to produce a resol type resin, but an ammonia aqueous solution is preferred because it is easily available and inexpensive.

The modified epoxy resin used in the present invention can be obtained as follows.

That is, the epoxy resin used for the modified epoxy resin is
Polyhydric epoxy resins are suitable; any epoxy resin used can be used, and novolac epoxy resins such as glycidyl compounds such as phenol novolac and cresol novolac are preferred from the viewpoint of heat resistance and electrical properties. Other compounds having 2 or more S active hydrogens in one molecule, such as bisphenol A, polyhydric phenols such as bishydroxydiphenylmethane, resorcinol, bishydroxydiphenyl ether, and tetrabromobisphenol A: ethylene glycol, neopentyl glycol ,
Polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, triethylene glycol, polypropylene glycol, bisphenol-ethylene oxide adduct, trishydroxyethyl isocyanate; Polyhydric alcohols such as ethylenediamine and aniline; adipic acid, phthalic acid , glycidyl-type epoxy resins obtained by reacting polyvalent carboxy compounds such as isophthalic acid with epichlorohydrin or 2-methylepichlorohydrin, aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxide, butadiene dimer diepoxide, etc. One or more selected epoxy resins can be used.

Next, the isotropic epoxy resin used in the present invention is typically produced by polymerizing a vinyl monomer in the presence of the epoxy resin described above to first produce a graft polymer of the epoxy resin and the vinyl monomer.

Vinyl monomers used here include alkenyl aromatic R such as styrene and vinyltoluene; methyl methacrylate, dodecyl methacrylate, methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl JL/7 acrylate, trimethylolpropane Acrylic esters such as acrylates: Acrylic compounds without ester groups such as acrylonitrile, acrylic acid, butoxymethylacrylamide, methacrylamide; vinyl acetate, vinyl laurate, vinyl persate, vinyl chloride, vinylidene chloride, ethylene, allyl acetate, etc. Non-conjugated vinyl compounds: Typical examples include conjugated diene compounds such as butadiene, isoprene, and chlorobrene, and polymerizable vinyl compounds such as dibutyl fumarate, monomethyl maleate, and diethyl itaconate can also be used. In order to polymerize the above-mentioned vinyl hexamer to obtain a vinyl polymer, a radical initiator such as lauroyl peroxide, benzoyl peroxide, tert-butyl benzoate, dimethylbenzoyl peroxyhexane, kusha leaf thyl barbylate is usually used. , ditert-butyl peroxide, 1,1-bis-tert-butyl-8-rubberoxy-3,3,5-)limethylcyclohexane, dimethyl di-tert-butyl peroxyhexane, cumyl peroxide, cumene hydroperoxide, Typically, radical polymerization is performed using a peroxide such as tert-butyl peroxymaleic acid, succinic acid peroxide, tert-butyl peroxyisopropyl carbonate, hydrogen peroxide, or an azo compound such as azobismethylvaleronitrile. . Further, if necessary, a reducing agent may be used in combination to carry out so-called redox polymerization, and a polymerization initiator such as hydroquinone or a chain transfer agent such as dodecyl mercaptan may be used.

In addition, in order to promote grafting, it is effective to introduce polymerizable double bonds or graftable chemical bonds into epoxy lubricant. Acid, acrylamide, methylol acrylamide, butoxymethyl acrylamide, hydroxyethyl methacrylate, maleic anhydride, monobutyl fumarate, monobutyl fumarate, chloromethylstyrene, phosphoxyethyl methacrylate, chlorohydroxybutyl methacrylate, parahydroxypropyl methacrylate A typical method is to react a compound having a functional group and a polymerizable double bond, such as parahydroxystyrene, dimethylaminoethyl methacrylate, with an epoxy tree or a finger in advance.

In the present invention, it is not acceptable even if the epoxy resin or the vinyl polymer remains free without being grafted into the graft polymer.

Modified epoxy resin 2 is obtained by subjecting an addition-reactive silicone polymer to an addition reaction in the presence of the above-mentioned graft polymer of an epoxy resin and a vinyl polymer by a conventional method. That is, silicone rubber is a rubber produced by an addition reaction of a vinyl-modified silicone polymer having a vinyl group in the molecule and a hydrogen-modified silicone polymer having an active hydrogen in the molecule through a silylation reaction.
The particle size is 1.0μ or less, preferably 0.5μ or less,
More preferably, it is 0°01μ or more and 0.2μ or less. If the particle size of the silicone rubber exceeds 1.0 μm, the object of the present invention cannot be achieved and the heat resistance cannot be improved.

A vinyl-modified silicone polymer refers to a polysiloxane with a small number (one or more) of 5i-CToCHz bonds at the end or inside of the molecule, and a hydrogen-modified silicone polymer refers to a polysiloxane with 5i-CToCHz bonds at the end or inside of the molecule.
A polysiloxane having at least two or more nv3 groups is usually commercially available in combination.
Examples include E-1821 and KE-1204 manufactured by Shin-Etsu Chemical Co., Ltd.

The particle size of the silicone rubber obtained by the addition reaction and the difference in the double bonds introduced into the epoxy resin can also be controlled.

The composition of the present invention may contain epoxy resin (or fat) if desired. As the epoxy resin, all of the above-mentioned epoxy resins can be used, and the two may be the same or different.

In addition, the silicone rubber obtained by addition reaction is required to be at least 5% by weight based on the total amount of epoxy resin, and especially 1% by weight or more based on the total amount of epoxy resin.
0 to 20% by weight is preferred. Is it possible to achieve low stress with less than 5% by weight? C: If it exceeds 20% by weight, the strength will drop significantly and it will be difficult to put it into practical use.

In order to adjust the amount of silicone rubber mentioned above to a desired level, the amount of vinyl nitrate used in producing the modified epoxy resin may be adjusted, but it is best to adjust the amount of the silicone rubber by changing the amount of epoxy resin. It is easier and from this point of view, it is preferable to use an epoxy resin in combination.

The present inventors have implemented the above-mentioned idea of improving the modified epoxy resin using a vinyl polymer mainly composed of alkyl acrylate having an alkyl group of 04 or more, and have published the patent application 1983-
No. 79728, but the present invention goes beyond that.

The copper powder used in the present invention may be flake-like powder, spherical powder, or round-shaped powder (also known as high-grade fatty acids such as stearic acid, silane camping agents, titanate coupling agents, etc.). The copper powder may be treated with an aluminum coupling agent, an antioxidant such as a benzotriazole, etc. Copper powder may be mixed with silver by adding m powder, but the ratio of !!There is an appropriate range.

In other words, if silver powder is used in combination, good results will be obtained in terms of conductivity and its retention, but if the amount exceeds a certain range, the disadvantages of silver paste, such as an increase in price and the occurrence of silver migration phenomenon, will become apparent and the conductivity will be reduced. This deviates from the original purpose of using sex paste.

In other words, it is necessary to keep the silver ratio within a range that does not have a significant impact on costs and does not cause silver migration.
Its upper limit: about 20%. These conductive powders may be used alone or in combination.

The solvent used in the paste of the present invention must: 1) be a good solvent for both the reducing resin and the modified epoxy resin, that is, dissolve both resins together and not cause phase separation between the resin and the solvent; It must meet the following conditions: (1) It must have a high boiling point that does not significantly change the solid content concentration when it is heated, (2) It must not significantly interfere with the curing speed, and (2) It must be free from odor and toxicity.

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 diptyle ether, diethylene glycol dimethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, etc. Ethylene glycol and diethylene glycol derivatives, butyl acetate, amyl acetate, cyclohexyl acetate, methyl acetoacetate, methyl acetoacetate, dimethyl adipate, dimethyl glutarate, dimethyl succinate, and other esters, cyclohexanone, methylcyclohexanone, diisobutyl ketone, isophorone, etc. ketones, α-terpineol, and the like. These solvents may be used alone or in combination.

It should be noted that various compounds may be added as long as the properties of the conductive copper paste are not affected. The compound referred to herein means a resin as a binder, a coating additive, and an adhesion improver.

Examples of the resin as a binder include general epoxy resins, phenol resins, acrylic resins, polyester resins, polyurethane resins, ketone resins, phenoxy resins, and the like.

Examples of paint additives include fine-particle silica used for the purpose of imparting and optimizing printability, non-precipitated substances such as bentonite, those treated with organic substances, silicon-based substances, and fluorine-based substances.

Further, adhesion improvers include silicone coupling agents, titanate coupling agents, and aluminum.Next, the blending amounts of each component will be explained.

The amount of modified epoxy resin blended is 10 to 80 parts by weight, preferably 2 parts by weight, per 100 parts by weight of modified hydroquinone resin.
0 to 50 parts by weight are suitable. Less than 10 parts by weight,
The effect of the addition of the modified epoxy resin did not appear, and no improvements were made in adhesion, heat resistance/i'It humidity, and soldering heat resistance.
If the amount exceeds 50%, there is a limit to the amount of conductive powder that can be added due to the high viscosity of the modified epoxy resin, and not only will high conductivity not be achieved, but problems will arise in printability and adhesion.

The amount of conductive powder to be blended is 40 parts by weight for a total of 100 parts by weight of reducing resin and modified epoxy resin, although it depends on its type.
0 to 900 parts by weight, preferably 500 to 800 parts by weight are suitable. If it is less than 400,311 parts, high conductivity will not be achieved, and if it exceeds 900 parts by weight, it will not become paste-like.

The blending amount of the solvent for forming the paste of the present invention is the total amount of reducing resin, modified epoxy resin, and conductive powder: 1
5 to 25 parts by weight per 00 parts by weight, preferably 12 to 1 parts by weight
It is suitable to add 8 parts by weight. If the paste is less than 5 parts by weight, the paste will become highly viscous and printing will be difficult. On the other hand, if it exceeds 25 parts by weight, the viscosity will be too low and the fine pattern will not fade during screen printing, or the thickness of the transferred pattern will be too thin and it will be difficult to print. Multiple printing is required to obtain conductivity.
This may cause some inconvenience, such as having to rotate it.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

These are merely examples, and are not intended to limit the technical scope of the present invention! +! It is j. That is, it must be clearly understood that the present invention is not limited to these examples.
In addition, in Examples and Comparative Examples, parts mean parts by weight.

Various tests were conducted as follows.

(1) on the phenolic surface of the air resistance value root reinforced phenolic resin copper clad laminated number,
Hand-printed 5-line pattern of 2a+m (spring) x 80mta (length) on machine 011 (Screen mesh! 2)
25. Emulsion thickness: 10 μW) After marking 11, harden at 150°C for 30 minutes in a heat-calf cycle; -1000, three-phase meter (manufactured by S Seisakusho), the electrical resistance values were measured, and the average value thereof was determined.

(2) Adhesion reinforced phenolic resin copper cladding on the copper foil surface of the number of laminated layers, 501
After printing the rectangular pattern of 1＠
0 minute defecation, 1m+sXl+u+ with a cutter knife
<7) Make a square of 100 pieces Apply lysero tape and peel it off vigorously. At this time, the adhesion of the coating film was evaluated by the number of lines remaining (JIS-5400).

(3) Insulating coating properties After printing and curing i5 in the same manner as in (1), insulating coating agent (Regicoat TMD-430, manufactured by Acheson Japan Co., Ltd.) was cured with silver paste so that 5 mII was left on both ends of the pattern. The pattern was printed and cured from above, and the electrical resistance of each pattern was measured using a 4-terminal resistance meter. The rate of change in electrical resistance before and after coating with the insulating coating agent was determined and used as a guideline for 1m edge coatability.

(4) Reliability After printing and curing and measuring the electrical resistance value in the same manner as in (1), the following reliability test was conducted.

I, heat resistant heat y! , 1 at a constant temperature of 80°C using a WI ring dryer.
000 hours of testing was conducted. Heat resistance was determined by determining the rate of change in electrical resistance after 1000 hours, and used as a guideline.

4Q'C in an environment of 295% RH using a thermostatic constant temperature and humidity chamber.
000 hours of testing was conducted. Moisture resistance was determined by determining the rate of change in electrical resistance after a 1000 hour test.

(5) Solder heat resistance After printing and curing in the same manner as in (1) and measuring the electrical resistance value, the rate of change in electrical resistance value was measured after immersion in a 260"C solder bath for 5 seconds twice. I searched for it and used it as a guideline.

(6) Thermal sealing type vine property After printing and curing in the same manner as in (1) and measuring the electrical resistance value, leave it in a thermostat at 120°C for 1 hour, then -30°C.
Leave it in a constant temperature bath for 1 hour. After repeating this operation 100 times, the rate of change in the electrical resistance value was determined and used as a guideline.

Example 1 105.6 parts of hydroquinone and 26.4 parts of p-cresol
Convenient diethylene glycol 7 methyl ether 49.5
Department! : Dissolve, dissolve, add 174.0 parts of 37 wt% formalin and raise the temperature to 60''C. Then, react at 85°C for 6 hours using 4.5 parts of 28 wt% aqueous ammonia as a catalyst.

Next, the water produced in the condensation reaction was completely removed under reduced pressure to obtain reducing resin A (solid content 80%).

The reducing ratio thus obtained is a diethylene glycol mononotyl ether solution of fat 4 too+:solid content 8
0%), 15 parts of the modified epoxy resin obtained earlier was uniformly dissolved, and CE-1110 was added as the i-th powder to this.
(manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd., trade name), 100 parts of diethylene glycol monomethyl ether was added as a viscosity adjusting solvent, and the mixture was thoroughly mixed.
A conductive paste was obtained by kneading with a wooden roll. The various evaluations described above were performed on the obtained paste. The results are shown in Table 1.

Example 2 An experiment similar to Example 1 was conducted except that bisphenol A diglycidyl ether was used instead of orthocresol novolac epoxy resin and 2-ethylhexyl acrylate was used instead of glycidyl methacrylate. . The results are shown in Table 1.

Example 3 The same procedure as in Example 1 was carried out except that t-butylphenol was used instead of p-cresol.

The results are shown in Table 1.

Example 4 The same procedure as in Example 1 was carried out except that 10 parts of particulate silica, Aerosil FF300 (1 trade name, manufactured by Nikki Aerosil Co., Ltd.) was added to Example 1. The results are shown in Table 1.

Example 5 Copper-silver composite powder Cu-Ag (8X) (manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd.) was used instead of copper powder CE-1110 in Example 1.
The same procedure as in Example 1 was carried out except that the product (trade name) was used. The results are shown in Table 1.

Example 6 Aminosilane coupling agent 5 was added as an additive to Example 1.
The same procedure as in Example 1 was carried out except that 1 part of H-6020 (manufactured by Toshi Silicone Co., Ltd., trade name) was added. The results are shown in Table 1.

Comparative Example 1 Fruit! except that in Example 1, phenol tree and fingers were used instead of modified hehydroquinone resin! The same procedure as in Example 1 was carried out. 8
Eight results are shown in Table 1. In this case, it can be seen that since the binder has no reducing ability, the initial conductivity is poor and the reliability is also poor.

Comparative Example 2 The same procedure as in Example 1 was carried out except that in the experiment σ111, urethane-modified epoxy resin Adekalezin EP-4000 (manufactured by Asahi Denka Kogyo Co., Ltd., trade name) was used instead of the modified epoxy resin. The results are shown in Table 1, and it is clear that even modified epoxy resins that do not contain a vinyl polymer give extremely poor results in all items.

Comparative Example 3 In Example 1, 10 parts of vinyl-modified polysiloxane and 10 parts of hydrogen-modified polysiloxane were replaced with 5 parts of epoxy-modified silicone oil (manufactured by Toshi Silicone Co., Ltd.) and 15 parts of dimethylpolysiloxane rubber (manufactured by Toshi Silicone Co., Ltd.). The same experiment as in Example 1 was conducted except for the following.The results are shown in Table 1. In this case, the particle size of the vinyl polymer was 0.5 μl.
It can be seen that the effect of addition is much inferior to that of example 1, in which the particle size exceeds 0.5 μm.

(Bottom, margin,) [Effects of the invention] As is clear from the results in Table 1, the conductive copper paste of the present invention has excellent reliability in terms of conductivity, printability, adhesion, heat resistance, moisture resistance, etc. It is excellent and inexpensive, and is suitable for forming conductive circuits such as jumper boards and conductive coatings for 'TL magnetic wave shields.

Patent applicant: Mitsui Toatsu Chemical Co., Ltd.

Claims (6)

[Claims] (1) A conductive copper paste whose main components are a conductive powder mainly composed of copper powder, a reducing resin, and a modified epoxy resin. (2) The conductive copper paste according to claim 1, wherein the reducing resin is a modified hydroquinone resin. (3) The modified epoxy resin is a silicone rubber obtained by reacting an addition reaction type silicone polymer with a graft polymer of an epoxy resin and a vinyl polymer, and uniformly dispersed with a particle size of 1.0 μm or less. The conductive copper paste according to claim 1 or claim 2. (4) The conductive copper paste according to any one of claims 1 to 3, wherein the conductive powder is a copper powder or a copper-silver composite powder. (5) The ratio of reducing resin and modified epoxy resin is reducing resin: modified epoxy resin = 100:10 to 100:30.
The conductive copper paste according to any one of claims 1 to 4. (6) A claim in which the ratio of the conductive powder to the total amount of reducing resin and modified epoxy resin is conductive powder: [reducing resin ÷ modified epoxy resin] = 400:100 to 900:100. The conductive copper paste according to any one of claims 1 to 5.