JPH08302312A - Conductive adhesive - Google Patents

Abstract

PURPOSE: To obtain a conductive adhesive which can improve the strength of bonding to the surface of a metal, such as a copper foil. CONSTITUTION: This conductive adhesive comprises a copper alloy powder represented by the formula, Agx Cuy (wherein 0.01<=x<=0.30, 0.70<=y<=0.99 and x+y=1 provided that x and y represent the atomic ratio) with the silver concn. of the powder in its surface being higher than the average silver concn.; and a curable resin compsn., wherein the curable resin compsn. comprises any one member or a mixture of any two or more members selected from a polyvinyl acetal resin, a polyamide resin, and a rubber-modified 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 adhesive for fixing and bonding various electronic parts on a wiring circuit.

[0002]

2. Description of the Related Art As a method of fixing and joining electronic parts to a wiring circuit, a method of using a conductive adhesive has been studied instead of the conventional soldering method. This method eliminates the need for special treatment for waste by not using lead, and because it does not go through the melting process, it is suitable for high-density mounting without problems such as bridging in narrow pitch mounting. Another advantage is that it can be cured at a lower temperature than the soldering temperature.

The conductive adhesives which have been studied so far include a silver paste composed of silver powder and a curable resin and a copper paste composed of copper powder and a curable resin. When a silver paste is used, electromigration is high, so that a short circuit is likely to occur during long-term humidification. When a copper paste is used, the conductivity is likely to decrease in the environment resistance test. As a conductive powder that does not have such a defect, a conductive adhesive agent using a copper alloy powder containing silver and having a structure in which the surface concentration of silver powder is higher than the average concentration is already known (special feature: Kaihei 4-268381 report).

[0004]

In the conductive adhesive using the above-mentioned copper alloy powder, the adhesive surface becomes smaller as the size of the component becomes smaller, and the substantial fixing force decreases.
Since the reliability of bonding tends to decrease, a conductive adhesive having higher fixing strength than before has been required. Therefore, an object of the present invention is to provide a conductive adhesive having high adhesion strength to a metal surface such as a copper foil.

[0005]

[Means for Solving the Problems] As a result of earnestly studying to achieve the above-mentioned problems, as a result of earnestly studying the effect of adding various thermoplastic resins to conventionally known compositions, particularly polyvinyl acetal resin, polyamide resin or rubber. The present inventors have found that the addition of a modified epoxy resin can achieve a markedly improved adhesion to a metal surface as compared with other general thermoplastic resins, and have reached the present invention. That is, the present invention is based on the general formula Ag
_x Cu _y (0.01 ≦ x ≦ 0.30, 0.70 ≦ y ≦ 0.
99, x + y = 1, x and y are represented by an atomic ratio), and a conductive adhesive composed of a curable resin composition and a copper alloy powder in which the silver concentration on the powder surface is higher than the average concentration is cured. The present invention relates to a conductive adhesive containing a polyvinyl acetal resin, a polyamide resin, a rubber-modified epoxy resin, or a mixture thereof in a conductive resin.

There are no particular restrictions on the mounting parts using the conductive adhesive of the present invention, and various surface mounting parts (SM
D) is most suitable, but it can also be used for pin insertion type component fixing. The polyvinyl acetal resin used in the present invention can be used as long as the polymerization degree of polyvinyl alcohol in the polymer skeleton is 100 or more and the glass transition point is 0 ° C. or more. Polyvinyl acetal resins having different polymerization degrees and glass transition points may be mixed and used. From the viewpoint of heat resistance, the above-mentioned polymerization degree is preferably 200 or more, and particularly preferably 500 or more. From the viewpoint of adhesive strength, mol% of hydroxyl groups remaining in the molecule
Is preferably 5% or more, and particularly preferably 25% or more. The glass transition point is particularly preferably 50 ° C. or higher.

The structure of the aldehyde used for acetalization can be arbitrarily selected according to the required characteristics. For example, if it is an alkyl group, a methyl group, an ethyl group, a butyl group, or a mixture thereof can be used. An aryl group other than an alkyl group or a group having a substituent having an unsaturated skeleton introduced thereinto can also be used. In particular, butyral resin acetalized with butyraldehyde is preferable because of its large effect.

The polyamide resin used in the present invention has a glass transition point of -10 ° C. or higher and is soluble in alcohol, so that it does not matter. For example, -N of the amide skeleton in the resin
It is possible to use one in which the proton of the H group is alkoxylated to make it alcohol-soluble. Further, a polymer skeleton other than an amide skeleton may be introduced into the resin in order to make it soluble in alcohol. In this case, the mol% of the amide skeleton is preferably 30% or more, particularly preferably 50% or more. The polyamine forming the amide skeleton may be alicyclic or aromatic. Further, the skeleton of the polycarboxylic acid may be alicyclic or aromatic.

The rubber-modified epoxy resin used in the present invention is
A mixture of liquid rubber and epoxy resin, or a mixture of liquid rubber and epoxy resin can be used. The weight part of the rubber component in the blended resin is preferably 5 to 60%, particularly preferably 10 to 50%.
If the rubber content is less than 5%, sufficient shear strength cannot be obtained, and if it exceeds 60%, sufficient heat resistance cannot be obtained.

The rubber component used in the rubber-modified epoxy resin preferably has a molecular weight of 500 to 2500, and particularly preferably a molecular weight of 800 to 2000. The types of rubber include polybutylene, polybutadiene, butadiene-
One or more kinds of rubber selected from acrylonitrile rubber and silicone rubber can be used. Further, those having a skeleton in which a carboxyl group is introduced at the terminal or the molecule of rubber are particularly preferable. A known epoxy resin can be used as the rubber-modified epoxy resin. Examples thereof include bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, novolac-modified epoxy resin, and alicyclic epoxy resin.

The polyvinyl acetal resin, the polyamide resin or the rubber-modified epoxy resin may be used alone, or may be mixed and used if necessary. The content in the curable resin composition is preferably 2 to 40% by weight,
Further, 10 to 30% by weight is more preferable. If it is less than 2% by weight, sufficient adhesive strength cannot be obtained, and if it exceeds 40% by weight, sufficient cured film strength cannot be obtained.

The copper alloy used in the conductive adhesive of the present invention can be obtained by a known method (Japanese Patent Laid-Open No. 205/1990).
561). Among them, the inert gas atomizing method is particularly preferable. According to the disclosure, silver particles and copper particles having a predetermined composition are melted in a graphite crucible, and the melt is atomized in an inert gas atmosphere to form fine powder. The copper alloy powder that can be used in the present invention has a silver content x of 0.01 to 0.4 (atomic ratio). However, when it is less than 0.01, the contact resistance with the electrode is unsatisfactory due to the oxidation of the same component on the particle surface. Be stable. x is 0.4
If it exceeds the range, a short circuit due to silver migration between the electrodes easily occurs. The silver concentration on the grain surface is higher than the average silver concentration and is preferably 1.8 times or more. If it is less than 1.8 times, the oxidation resistance of the particle surface is not sufficient. The silver concentration used in the present invention is measured using XPS (X-ray photoelectron spectroscopy analyzer: XSAM800, manufactured by KRATOS).

The average particle size of the conductive particles used in the present invention is
The range of 0.1 to 50 μm is preferable, and the range of 1 to 10 μm is more preferable. If the particle size is less than 0.1 μm, the surface of the powder becomes active and the oxidation resistance decreases. If the particle size exceeds 50 μm, sedimentation in the paste becomes large and the stability decreases. The wider the particle size distribution, the higher the packing density of the powder in the cured product, and the better the conductivity, which is preferable.

The organic binder used in the curable composition of the present invention may be a thermosetting resin or a photocurable resin, and a thermoplastic resin may be added if necessary. Examples of the thermoplastic resin include thermoplastic acrylic resin, vinyl chloride resin, urethane resin, polyester resin, and styrene resin. Examples of the thermosetting resin include an epoxy resin and its curing agent, a resol-type phenol resin, an amino resin, a polyurethane resin, a polyimide resin, and a thermosetting acrylic resin, which may be used alone or in combination. May be. Also, various epoxy-based reactive diluents may be used. Various kinds of epoxy curing agents such as imidazole type and dicyandiamide can be used, but a latent curing agent formed by the reaction of an imidazole derivative and an epoxy compound is preferable.

When an ultraviolet curable resin is used, a polymerizable oligomer, a curable monomer, a photopolymerization initiator and the like are used in combination. Examples of the polymerizable oligomer include epoxy (meth) acrylate, urethane (meth) acrylate, polyester acrylate, and polyether acrylate. The polymerizable monomer has one or more acryloyl groups or methacryloyl groups in one molecule, and is usually used in a mixed system of monomers having different functional groups. The photoinitiator is generally one that initiates radical polymerization by light, and known ones such as acetophenone-based, thioxanthone-based, benzoin-based, and peroxide-based can be used.

Copper oxide film removing agents such as various organic carboxylic acids and alkylamines can be added to the curable resin composition, and various silane coupling agents and titanate cups can be used as surface treatment agents. A ring agent or the like can be added. A solvent may be used if necessary for the purpose of adjusting the viscosity of the resin composition, and there is no particular limitation as long as the solubility and the drying property satisfy the required characteristics. Examples thereof include methyl carbitol, ethyl carbitol, their acetates, methyl cellosolve, butyl cellosolve, and their acetates, methyl ethyl ketone, acetone, ethyl acetate, benzyl alcohol and the like.
In order to reduce the generation of bubbles during drying and curing, the smaller the amount of the solvent added, the better.

The method of fixing and joining electronic components using the above-mentioned conductive adhesive can be selected optimally depending on the conditions such as the shape of the substrate and the electronic components. For example, when surface-mounting components are fixedly joined, a conductive adhesive paste is applied to the component connection portion (pad portion) of the wiring board in advance by a screen printing method, a dispenser method, or the like. A mounting substrate can be obtained by pressing the bonding electrode portion of the electronic component onto the applied paste so that it adheres to the pad, and if necessary, drying and then heat curing. The optimum drying temperature can be selected depending on the boiling point of the solvent used, etc., but is generally in the range of 40 to 90 ° C. The curing temperature in the case of thermosetting can be selected as the optimum condition of the thermosetting resin used, but is generally 150 to 220 ° C. Also, apply the conductive adhesive paste to the bonding electrodes of electronic parts by printing or dipping in advance,
If necessary, the dried product may be adhered and fixed on the conductive adhesive paste applied to the wiring pad portion by the same procedure as above, and the adhesive strength is further improved, which is preferable. In this case, since the electrodes are formed on the component terminal portions with the conductive adhesive, it is possible to omit the conventional steps such as plating for forming the terminal electrodes. It is preferable to perform the drying under mild conditions because the generation of voids can be suppressed.
Further, after the preliminary curing after the drying, the continuity is checked, and if a defect is found, it is possible to peel off the component and reconnect it. Furthermore, even if a poor connection is found after curing, it is possible to peel and reconnect.

The conductor of the wiring board may be a wiring circuit formed by patterning a copper foil, or may be a wiring circuit formed of a conductive paste using silver powder or copper powder and the above copper alloy. Preparation Example of Copper Alloy Powder 603 g of copper particles (purity 99.9% by weight or more) and 54 g of silver particles (purity 99.9% by weight or more) were mixed, and heated and melted in a graphite crucible at 1700 ° C. under a nitrogen atmosphere. The melt was ejected from the crucible tip into a nitrogen atmosphere, and at the same time as the ejection,
A nitrogen gas of 50 Kg / cm ² G (purity of 99.9% by weight or more) was jetted to the melt and atomized. The obtained conductive powder was spherical and had an average particle size of 10 μm. Airflow classifier (TC-15N manufactured by Nisshin Engineering Co., Ltd.)
Was used to classify particles in a particle size range of 20 μm or less. The average particle diameter was 5 μm. The surface silver concentration was 0.55.
The average silver concentration was 0.05, and the surface silver concentration was 11 times the average silver concentration.

[0019]

Example 1 The copper alloy powder obtained in the above preparation example
g, 58 g of resole type phenol resin, 5.6 g of hydrogenated bis A type epoxy resin, 13 g of butyral resin (BM-
1, Sekisui Chemical Co., Ltd.), triethanolamine 1.5 g,
1.5 g of a silane coupling agent and 8 g of benzyl alcohol were mixed and kneaded with a three-roll mill to obtain a conductive paste (1).

A conductive paste (1) using a copper alloy powder was applied by screen printing to the pad portion (2 × 2 mm ² , pad spacing 2 mm) of the wiring obtained by patterning the glass epoxy copper clad laminated substrate. Then, a chip resistor for surface mounting was pressure-bonded to temporarily fix the adhesive. It was dried at 50 ° C. for 30 minutes and then heated at 170 ° C. for 30 minutes to be cured. The connection resistance between the chip resistor and the pad portion was 13 mΩ, which was in the usable range. The adhesive strength of the chip resistor was 2 Kg, which was sufficient. In addition, in the environment of 90 ℃, 80% relative humidity 1
Even if the DC voltage of 50 V was continuously applied for 000 hours, a short circuit did not occur and good migration resistance was exhibited. The connection resistance at this time was 15 mΩ, which showed good environment resistance.

[0021]

Example 2 The copper alloy powder obtained in the above preparation example
g, 58 g of resole phenolic resin, 5.6 g of hydrogenated bis A type epoxy resin, 13 g of polyamide resin (T-8,
Unitika Ltd.), triethanolamine 1.5 g, silane coupling agent 1.5 g, benzyl alcohol 8 g
Were mixed and kneaded with a triple roll to obtain a conductive paste (2).

After fixing the components to the substrate in the same manner as in Example 1, the connection resistance, the adhesive strength, the migration resistance,
The environment resistance of the connection resistance was evaluated. Table 1 shows the evaluation results.

[0023]

Example 3 The copper alloy powder obtained in the above-mentioned preparation example
g, 58 g of resole phenolic resin, 5.6 g of hydrogenated bis A type epoxy resin, 13 g of rubber modified epoxy resin, 1.5 g of triethanolamine, 1.5 g of silane coupling agent, 8 g of benzyl alcohol, and three The mixture was kneaded with a roll to obtain a conductive paste (3).

After fixing the components to the substrate in the same manner as in Example 1, connection resistance, adhesive strength, migration resistance,
The environment resistance of the connection resistance was evaluated. Table 1 shows the evaluation results.

[0025]

Comparative Example 1 The copper alloy powder obtained in the above preparation example
g, 71 g of resol type phenol resin, 5.6 g of hydrogenated bis A type epoxy resin, 1.5 g of triethanolamine,
1.5 g of a silane coupling agent and 8 g of benzyl alcohol were mixed and kneaded with a triple roll to obtain a conductive paste (4).

After fixing the components to the substrate in the same manner as in Example 1, connection resistance, adhesive strength, migration resistance,
The environment resistance of the connection resistance was evaluated. Table 2 shows the evaluation results.

[0027]

Comparative Example 2 The copper alloy powder obtained in the above preparation example
g, 58 g of resole phenolic resin, 5.6 g of hydrogenated bis A type epoxy resin, polyester resin (Findick M-8710, manufactured by Dainippon Ink and Chemicals, Inc.) 13
g, triethanolamine 1.5 g, silane coupling agent 1.5 g, and benzyl alcohol 8 g were mixed and kneaded with a three-roll mill to obtain a conductive paste (5).

After the components were fixed to the substrate in the same manner as in Example 1, connection resistance, adhesive strength, migration resistance,
The environment resistance of the connection resistance was evaluated. Table 2 shows the evaluation results.

[0029]

Comparative Example 3 50 g of electrolytic copper powder having an average particle size of 10 μm, 71 g of resol-based phenol resin, 5.6 g of hydrogenated bis-A type epoxy resin, 1.5 g of triethanolamine, 1.5 g of silane-based coupling agent, benzyl 8g of alcohol is mixed and kneaded with a triple roll to make conductive paste (6)
I got

After fixing the components to the substrate in the same manner as in Example 1, the connection resistance, the adhesive strength, the migration resistance,
The environment resistance of the connection resistance was evaluated. Table 2 shows the evaluation results.

[0031]

Comparative Example 4 50 g of scaly silver powder having an average particle size of 7 μm, 71 g of resol-based phenol resin, 5.6 g of hydrogenated bis-A type epoxy resin, 1.5 g of triethanolamine, 1.5 g of silane-based coupling agent, benzyl 8g of alcohol is mixed and kneaded with a triple roll to make conductive paste (7)
I got

After fixing the components to the substrate in the same manner as in Example 1, connection resistance, adhesive strength, migration resistance,
The environment resistance of the connection resistance was evaluated. Table 2 shows the evaluation results.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

According to the present invention, the bonding strength with a metal surface such as a copper foil can be improved as compared with the conventional conductive adhesive, so that the reliability of the mounting substrate can be improved.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area C09J 163: 00)

Claims (1)

[Claims] 1. The general formula Ag _x Cu _y (0.01 ≦ x ≦ 0.
30, 0.70 ≦ y ≦ 0.99, x + y = 1, x and y are atomic ratios), and a copper alloy powder in which the silver concentration on the powder surface is higher than the average concentration, and a curable resin composition A conductive adhesive comprising a substance, wherein the curable resin contains any one of a polyvinyl acetal resin, a polyamide resin, and a rubber-modified epoxy resin, or a mixture thereof.