JPH10279903A - Electroconductive adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject adhesive, sufficiently adhesive and electroconductive simultaneously and also reworkable, by including two types of specific particles and an organic binder. SOLUTION: This adhesive comprises (A) particles of a low-melting metal melting at 300 deg.C or lower, preferably selected from the group consisting of Sn, Zn, In, Bi, Pb, Cd and Sb, (B) electroconductive particles, preferably of a metal selected from the group consisting of Cu, Ni, Au, Ag, Al, Pd and Pt, melting at higher temperature than the component A, wherein the component A/component B wt. ratio is set at (5:95) to (50:50), and total of the components A and B accounts for 70 to 95 wt.% of the whole adhesive, (C) an organic binder of a thermoplastic resin, preferably having a hydrogen bond, mixed, as required, with a thermosetting resin, and (D) a setting accelerator, flame retardan, pigment, tackifier or the like, as required. The components A and B work as the electroconductive fillers. The component A preferably has a smaller particle size than the component B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive adhesive used for assembling ICs, LSIs, other semiconductor devices, and various electric and electronic parts or bonding them to a substrate.

[0002]

2. Description of the Related Art Conventionally, Sn-Pb eutectic solders have been widely used for assembling ICs, LSIs, other semiconductor devices, and various electric and electronic components, or bonding them to substrates, from the viewpoint of excellent conductivity and high reliability. Have been used. In recent years, as devices have become lighter, thinner and smaller, semiconductor devices such as LSIs have become smaller and more sophisticated, and accordingly, a large number of connection terminals having a fine pitch in which the width and interval of connection terminals have been narrowed have been used. Have been. As the number of connection terminals having a fine pitch increases, solder has a risk of causing a bridging phenomenon at the time of soldering. In addition, since solder has a high reflow temperature, there are restrictions on the members that can be joined, and there is also a problem from the viewpoint of environmental protection in that it contains lead.

[0003] A conductive adhesive has attracted attention as a next-generation bonding material replacing solder. Such a conductive adhesive requires conductivity and adhesion of a fine circuit, and varies depending on a member to which the conductive adhesive is applied. For example, the volume specific resistance is 5 × 10 ⁻³ Ωcm or less. , Adhesive strength is 5
kgf or more is required. On the other hand, recent conductive adhesives are required to have not only conductivity and adhesiveness but also reworkability when used as an adhesive. Reworkability means that when a part where conductivity is insufficient occurs once in a circuit that has been bonded, the member at that part is peeled off using known means, the inconvenient part is improved, and the part is re-bonded accurately again This is a property required when connecting a complicated circuit board.

There is also an example in which a thermoplastic resin binder and a spherical conductive filler coated with low melting point tin are used to achieve both adhesive strength and reworkability (JP-A-8-227613). There is a problem that a complicated filler is required and the process is complicated.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a conductive adhesive having both sufficient adhesiveness and conductivity, and further provide a conductive adhesive having both the above-mentioned properties and reworkability. Is to do.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, as a conductive filler, particles (A) made of a low melting point metal having a melting point of 300 ° C. or less and the particles (A). The inventors have found that by mixing and using the conductive particles (B) having a melting point higher than the melting point of the low-melting-point metal, they have sufficient adhesiveness and conductivity, and have reached the present invention.

That is, the present invention provides: A low-melting-point metal particle (A) having a melting point of 300 ° C. or less, a conductive particle (B) having a melting point higher than the low-melting-point metal, and a conductive adhesive comprising an organic binder. The total amount of the metal particles (A) and the conductive particles (B) is 70 to 95% by weight, and the mixing ratio of the low melting metal particles (A) and the conductive particles (B) is 5:95.
1. a conductive adhesive characterized by being in the range of 50:50 (weight ratio); Particles (A) made of low melting point metal are Sn, Zn, I
a metal containing at least one selected from the group consisting of n, Bi, Pb, Cd, and Sb, wherein the conductive particles (B) are Cu, Ni, Au, Ag, Al, Pd, and Pt. 2. The conductive adhesive according to 1 above, wherein the conductive adhesive is a metal containing one or more kinds selected from the group consisting of: 3. The conductive adhesive according to 1 above, wherein the particle size of the low melting point metal (A) is smaller than the particle size of the conductive particle (B). The above-mentioned 1, 2 wherein the organic binder comprises a thermoplastic resin.
Or 3 conductive adhesive; 5. The conductive adhesive according to the above 1, 2, or 3, wherein the organic binder comprises a mixture of a thermoplastic resin and a thermosetting resin; The above-mentioned item 4, wherein the thermoplastic resin is a resin having a hydrogen bond.
Or 5 conductive adhesive; The conductive adhesive according to the above item 5, wherein the thermoplastic resin and the thermosetting resin are compatible with each other.

Hereinafter, the present invention will be described in detail. The particles (A) composed of a low melting point metal used in the present invention include S
A single metal or two or more metals selected from the group consisting of n, Zn, In, Bi, Pb, Cd, and Sb can be used. Sn and a metal containing Sn are particularly preferable because they can easily form an intermetallic compound with an electrode metal such as copper, silver, or gold.

As the conductive particles (B) used in the present invention, one or more metals selected from the group consisting of Cu, Ni, Au, Ag, Al, Pd and Pt can be used. Further, as such conductive particles (B), those obtained by forming a layer made of the above metal on the surface of a polymer material can also be used. Examples of the polymer material include a polyester resin and a polyvinyl acetal resin.

The conductive particles (B) are copper alloy powders represented by an average composition of Ag _x Cu _1-x (0.01 ≦ x ≦ 0.4, where x represents an atomic ratio). A powder having a region in which the silver concentration of the copper alloy powder surface is larger than the average silver concentration and having a region where the silver concentration gradually increases from the inside toward the surface can also be preferably used. Thus, sufficient oxidation resistance and migration resistance can be obtained. If x is less than 0.01, sufficient oxidation resistance cannot be obtained, and if it exceeds 0.4, electromigration resistance is insufficient. Copper alloy powder can be obtained by a known method (Japanese Patent Laid-Open No. 1-205).
No. 561). Among them, a copper alloy powder produced by an inert gas atomizing method is particularly preferable. The copper alloy powder has a region where the silver concentration on the surface is higher than the average silver concentration and the silver concentration gradually increases from the inside toward the surface, but the silver concentration on the surface of the copper alloy powder is the average silver concentration. 2.
It is preferably at least 1 and more preferably at least 3 and at most 30.

[0011] The selection of a conductive filler is important for the conductive adhesive to have both sufficient adhesive strength and high conductivity. In the present invention, the melting point of the conductive filler is 300 ° C. or less, preferably 40 ° C. or more.
It is necessary to use a mixture of particles (A) made of a low melting point metal having a melting point of 00 ° C. or lower and conductive particles (B) having a melting point higher than the melting point of the low melting point metal.

The particles (A) comprising the low melting point metal as described above
When the conductive particles (B) having a higher melting point than the low melting point metal are used in combination, when heated to a temperature higher than the melting point of the low melting point metal,
The particles (A) made of the low melting point metal are melted and adhere around the conductive particles (B). Upon further heating, the low-melting-point metals are bonded to each other, and the adjacent conductive particles (B) are welded to each other and connected in a chain. Further, at the contact interface with the electrode, the particles (A) made of the low melting point metal are melted to form an intermetallic compound with the electrode metal and are firmly bonded. Therefore, the chain-like connection structure formed by the conductive filler formed between the opposing electrodes is firmly connected mechanically and electrically by fusion bonding of the metals.

In the present invention, particles (A) composed of a low melting point metal
And the mixing ratio of the conductive particles (B) is 5:95 to 50:50.
(Weight ratio). If the amount of the particles (A) made of a low melting point metal is less than 5% by weight, no electrical conduction path is formed between the electrodes. If the amount of the particles (A) made of a low melting point metal is more than 50% by weight, a leak failure occurs in which the adjacent electrodes are electrically connected when heated above the melting point.

The conductive particles (B) used in the present invention may have any shape such as a sphere or a scale. It is also possible to use a mixture of two or more types of fillers. If the particle size of the conductive particles (B) used in the present invention is too large, a leak failure occurs. If the particle size is too small, a plurality of particles aggregate to form secondary particles. For this reason, the spherical conductive particles preferably have a particle size of 0.1 μm or more and 10 μm or less. The average diameter of the plate surface of the flaky conductive particles (the average of both major and minor diameters, if any) is 1 μm.
It is preferably from m to 30 μm.

The particles (A) made of a low melting point metal used in the present invention may have any shape such as a sphere or a scale. If the particle size is too large, a leak failure occurs. If the particle size is too small, it is difficult to form an electrical conduction path. For this reason, it is preferable that the spherical low melting point metal has a particle size of 0.1 μm or more and 10 μm or less. Further, it is preferable that the average diameter of the plate surface of the flaky low melting point metal is 1 μm or more and 30 μm or less. Further, the particle diameter of the particles (A) made of a low melting point metal is
It is more preferable that the particle diameter is smaller than the particle diameter of the conductive particles (B) because the above-described chain-like connected structure is easily formed.

Although any thermoplastic resin can be used as the thermoplastic resin used in the organic binder of the present invention, those having a functional group having a hydrogen bond in the structure are excellent in adhesiveness. preferable. As the functional group having a hydrogen bonding property, a hydroxyl group, an amide group, a urea group,
Imide group, ester group, ether group, thioether group,
And a sulfone group and a ketone group. Examples of such a thermoplastic resin include, for example, phenoxy resin, thermoplastic polyurethane, polyvinyl butyral, polyamide, thermoplastic polyimide, polyimide siloxane, polyamide imide, polycarbonate, polyphenylene ether, polyvinyl ether, polysulfone, polyvinyl alcohol, polyvinyl formal, poly Examples include vinyl acetate, methacrylic resin, and ionomer resin. The reason why a thermoplastic resin having a functional group having hydrogen bonding properties is particularly excellent is not clear, but it is considered that hydrogen bonding with a metal improves wettability.

The thermoplastic resin used in the present invention preferably has a glass transition temperature of 300 ° C. or less. When the glass transition temperature exceeds 300 ° C., it is necessary to raise the temperature to 300 ° C. or more during use as an adhesive and during thermal rework, and thus there is a problem such as deterioration of a member to be bonded, which is not preferable. Among such thermoplastic resins, phenoxy resin, thermoplastic polyurethane, and polyvinyl butyral are more preferable, and phenoxy resin is particularly preferable.

The thermosetting resin used in the organic binder of the present invention includes epoxy resin, phenol resin, polyimide, polyurethane, melanin resin, urea resin and the like. Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, (cresol) novolak type epoxy resin, halogenated bisphenol type, resorcinol type, tetrahydroxyphenolethane type, polyalcohol polyglycol type, glycerin triether Type, polyolefin type, epoxidized soybean oil, cyclopentadiene dioxide, vinylcyclohexene dioxide and the like. Among them, bisphenol A type epoxy resin, bisphenol F type epoxy resin and (cresol) novolak type epoxy resin are preferable.

C12,13 mixed alcohol glycidyl ether, 2-ethylhexyl glycol glycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, Polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin diglycidyl ether, trimethylolpropane triglycidyl ether, hydrogenated bisphenol A diglycidyl ether, 2,2-dibromoneopentyl Low molecular weight epoxy compounds such as glycol diglycidyl ether Etc. can also be used. Among them, neopentyl glycol diglucidyl ether, 1,
6-Hexanediol diglycidyl ether, glycerin diglycidyl ether, and trimethylolpropane triglycidyl ether are preferred.

The epoxy curing agent used in the present invention includes:
General epoxy curing agents can be used. For example, aliphatic polyamines include triethylenetetramine and m-xylenediamine; aromatic amines include m-phenylenediamine and diaminodiphenylsulfone; and tertiary amines include benzyldimethylamine and dimethylamino. Examples include methylphenol, acid anhydrides include phthalic anhydride and hexahydrophthalic anhydride, and boron trifluoride amine complexes include BF ₃ -piperidine complex. Alternatively, a bisphenol compound such as bisphenol A may be used. Also, dicyandiamide,
2-ethyl-4-methylimidazole, tris (methylamino) silane and the like are also included. Examples of the resin-based curing agent include a polyamide resin made from linolenic acid dimer and ethylenediamine, a polysulfide resin having a mercapto group at both ends, a novolak phenol resin, and the like. These may be used alone or in combination of two or more.

The amount of the curing agent to be added varies depending on the type of the curing agent. For example, when reacting with a glycidyl group stoichiometrically such as an acid anhydride type, the optimum addition amount is determined from the epoxy equivalent. When reacting catalytically, 3 to 30
% By weight is common. When the reactivity of these curing agents at room temperature is high, a liquid containing an initiator is mixed with the adhesive immediately before use, or the curing agent is encapsulated in a gelatin or other capsule of about 100 μm and used as microcapsules. Is preferred.

In the present invention, as the organic binder,
Thermoplastic resins can be used alone. The use of a thermoplastic resin alone has the advantage that the conductive adhesive can be easily reworked. That is, heating to a temperature higher than the glass transition temperature of the thermoplastic resin softens the thermoplastic resin and reduces the strength of the cured product, so that rework can be performed.
In addition, by using a solvent that dissolves the thermoplastic resin,
Rework can be performed because the strength of the cured product is weakened.

[0023] In the present invention, the term "rework" means that an adhesive is heated at a temperature not lower than the glass transition temperature of a thermoplastic resin and not higher than the deterioration temperature of a member to be bonded, or a solvent having a shear strength of 3 kgf or less. It means that the adherend detaches from the member by applying a slight force such as pulling with tweezers. In the present invention, the organic binder may be used by mixing a thermoplastic resin and a thermosetting resin. By mixing, the cross-linking structure of the thermosetting resin develops sufficient strength, and the rework can be achieved by heating to a temperature higher than the glass transition temperature of the thermoplastic resin or by using a solvent that weakens the strength of the cured product. Will be possible.

When the thermoplastic resin and the thermosetting resin are mixed, the content of the thermosetting resin is preferably 97% by weight or less based on the total weight of the thermosetting resin and the thermoplastic resin. If the content of the thermosetting resin is more than 97% by weight, rework cannot be performed. Further, in order to exhibit sufficient adhesive strength, it is preferable to select a combination in which the thermosetting resin and the thermoplastic resin are compatible with each other, and to use a combination in which the thermosetting resin and the thermoplastic resin are compatible. In the present invention, the term "compatible" means that both resins are not turbid after mixing alone without using a solvent, or after dissolving and mixing in a solvent and not distilling off the solvent. Say. Examples of such a combination of resins include an epoxy resin and a phenoxy resin.

In the present invention, the conductive filler comprises 7
It is necessary to contain 0 to 95% by weight. If the amount of the conductive filler is less than 70% by weight, sufficient conductivity cannot be obtained. If the amount exceeds 95% by weight, workability and conformability with a semiconductor chip deteriorate. In the conductive adhesive of the present invention, a curing accelerator, a flame retardant, a leveling agent, a thixotropy-imparting agent, an anti-settling agent, a coupling agent, a monoepoxy compound, a pigment, an antifoaming agent, a corrosion inhibitor, and an adhesive are used as additives. Various additives such as a property imparting agent can be used.

For use as a conductive adhesive, viscosity during use is an important factor. In order to adjust the viscosity, a monoepoxy compound such as dimethylformamide, dimethylacetamide, N-methyl-pyrrolidone,
A solvent such as methyl ethyl ketone, methyl cellosolve, methyl carbitol, carbitol, carbitol acetate, butyl cellosolve, ethyl acetate, methyl cellosolve acetate, butyl cellosolve, ethyl cellosolve, ethyl cellosolve, methyl cellosolve, etc. may be used alone or in an appropriate amount of a mixture of plural solvents. It is possible. It is preferable from the viewpoint of workability that the viscosity of the obtained solution or paste is 5,000 to 400,000 cp, more preferably 20,000 to 70,000 cp.

The conductive adhesive of the present invention can be obtained by kneading the above-mentioned various components using various kneaders such as a ball mill, a roll mill, and a planetary mixer in a conventional manner, for example, for 10 to 60 minutes. The kneaded conductive adhesive is applied to an insulating substrate or a lead frame by a method such as screen printing or dispenser application.

The conditions for heat curing of the conductive adhesive of the present invention are as follows:
There is no particular limitation as long as the resin is sufficiently cured and deterioration due to heat is not a problem. The general temperature range is 150 ° C. to 220 ° C., but preheating may be performed at a lower temperature for the purpose of melting the solid curing agent or preventing the formation of voids.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described with reference to the following Examples and Comparative Examples. In the examples and comparative examples, evaluation was performed as follows. Shear strength: Conductive adhesive on copper plate with film thickness of 70-100μ
Apply 2 cm width and 2 mm length while keeping m, cure 5 pieces of copper chips (2 mm x 2 mm x 1 mm) at a predetermined temperature, push the tip of the push-pull gauge into the cured product, and remove the tip Was measured by reading the intensity of the sample. Reworkability: The cured product prepared above was heated at 180 ° C in an oven.
Immediately after heating for 10 minutes, the copper chip was pulled with tweezers to evaluate whether the copper chip was dropped. Volume specific resistance: conductive adhesive on FR4 substrate with film thickness of 5
The resistance (R) of 1 cm of the conductor prepared by applying and curing at a predetermined temperature with a width of 1 cm and a length of 7 cm while maintaining 0 to 100 μm is measured using a digital multimeter, and the numerical value is substituted into the following equation. Was calculated. Volume specific resistance value = R × t × 10 ⁻⁴ Ωcm R: resistance value t: film pressure μm In performing each example, it was visually confirmed that the respective components were compatible with each other at the mixing ratio of the resin of each example. .

[0030]

Example 1 Phenoxy resin (manufactured by PAPHEN Co., Ltd.)
333.3 parts by weight of a 30% by weight solution of PKHC) in DMF,
A paste obtained by kneading 810 parts by weight of spherical copper powder having an average particle diameter of 5 μm and 90 parts by weight of spherical tin powder having an average particle diameter of 3 μm was kneaded with a metal spatula for 5 minutes. When this conductive adhesive was cured at 230C for 30 minutes at 80C for 15 minutes and evaluated by the above method, the cured product was reworkable. The shear strength was 7.8 kgf and the volume resistivity was 5.5 × 10 ⁻⁵ Ωcm. It is a conductive adhesive which has both sufficient strength and conductivity, and has reworkability.

[0031]

Example 2 Phenoxy resin (PAPHEN Co., Ltd.)
333.3 parts by weight of a 30% by weight solution of PKHC) in DMF,
And a paste obtained by kneading 810 parts by weight of a spherical copper powder having an average particle diameter of 5 μm and 90 parts by weight of a spherical solder (Sn60-Pb40) powder having an average particle diameter of 3 μm with a three-roll mill.
Kneaded for minutes. This conductive adhesive is applied at 80 ° C. for 15 minutes.
When cured at 230 ° C. for 30 minutes and evaluated by the above method, this cured product was reworkable. The shear strength is 8.
2 kgf, the volume resistivity was 5.3 × 10 ⁻⁵ Ωcm. It is a conductive adhesive which has both sufficient strength and conductivity, and has reworkability.

[0032]

Example 3 Phenoxy resin (manufactured by PAPHEN Co., Ltd.)
333.3 parts by weight of a 30% by weight solution of PKHC) in DMF,
And an average particle size of 5 μm represented by an average composition Ag _x Cu _1-x
810 parts by weight of a spherical copper alloy powder (x = 0.168) and 90 parts by weight of a spherical tin powder having an average particle diameter of 3 μm were kneaded with a three-roll mill and kneaded with a metal spatula for 5 minutes. When this conductive adhesive was cured at 230C for 30 minutes at 80C for 15 minutes and evaluated by the above method, the cured product was reworkable. The shear strength was 7.8 kgf and the volume resistivity was 5.0 × 10 ⁻⁵ Ωcm. It is a conductive adhesive which has both sufficient strength and conductivity, and has reworkability.

[0033]

Example 4 Phenoxy resin (PAPHEN Co., Ltd.)
16.7 parts by weight of a 30% by weight solution of PKHC) in DMF and bisphenol A type epoxy resin (AE, manufactured by Asahi Ciba Co., Ltd.)
R2664) 95 parts by weight, and 810 parts by weight of spherical copper powder having an average particle diameter of 5 μm and 90 parts by weight of spherical tin powder having an average particle diameter of 3 μm were kneaded with a three-roll mill, and a microcapsule-type epoxy curing agent ( 36 parts by weight of Novacure HX3613 manufactured by Asahi Kasei Kogyo Co., Ltd. was added and kneaded with a metal spatula for 5 minutes. Apply this conductive adhesive at 80 ° C. for 30 minutes,
When cured at 30 ° C for 1 hour and evaluated by the above method,
This cured product was reworkable. Shear strength is 19.7
kgf and volume resistivity were 2.0 × 10 ⁻⁵ Ωcm. It is a conductive adhesive which has both sufficient strength and conductivity, and has reworkability.

[0034]

Comparative Example 1 Phenoxy resin (manufactured by PAPHEN CORPORATION)
333.3 parts by weight of a 30% by weight solution of PKHC) in DMF,
A paste obtained by kneading 900 parts by weight of spherical copper powder having an average particle size of 5 μm with three rolls was kneaded with a metal spatula for 5 minutes. This conductive adhesive is applied at 80 ° C. × 15 minutes, 230 ° C. ×
When cured for 30 minutes and evaluated by the above method, this cured product was reworkable. The shear strength was 3.2 kgf and the volume resistivity was 8.2 × 10 ⁻³ Ωcm. A conductive adhesive that does not satisfy the required values in both strength and volume resistivity.

[0035]

Industrial Applicability The conductive adhesive of the present invention has both sufficient adhesiveness and good conductivity, and can also have reworkability by using an organic binder containing a thermoplastic resin, so that it can be used industrially. Very useful.

Claims (7)

[Claims] 1. A conductive adhesive comprising a particle (A) made of a low melting point metal having a melting point of 300 ° C. or lower, a conductive particle (B) having a melting point higher than the melting point of the low melting point metal, and an organic binder. The total amount of the low melting point metal particles (A) and the conductive particles (B) is 70 to 95% by weight, and the mixing ratio of the low melting point metal particles (A) and the conductive particles (B) is 5:95 to
An electrically conductive adhesive characterized by being in the range of 50:50 (weight ratio). 2. Particles (A) made of a low melting point metal are Sn,
A metal containing at least one selected from the group consisting of Zn, In, Bi, Pb, Cd and Sb, wherein the conductive particles (B) are Cu, Ni, Au, Ag, A
The conductive adhesive according to claim 1, wherein the conductive adhesive is a metal containing one or more selected from the group consisting of l, Pd, and Pt. 3. The conductive adhesive according to claim 1, wherein the particle size of the low melting point metal particles (A) is smaller than the particle size of the conductive particles (B). 4. The conductive adhesive according to claim 1, wherein the organic binder comprises a thermoplastic resin. 5. The conductive adhesive according to claim 1, wherein the organic binder comprises a mixture of a thermoplastic resin and a thermosetting resin. 6. The conductive adhesive according to claim 4, wherein the thermoplastic resin is a resin having a hydrogen bond. 7. The conductive adhesive according to claim 5, wherein the thermoplastic resin and the thermosetting resin are compatible with each other.