JPH0611842B2 - Conductive resin paste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a conductive resin paste, which is a conductive resin used for joining a light emitting diode chip to a substrate, which particularly requires conductivity, and for conducting a liquid crystal substrate. It's about paste. More specifically, the present invention relates to a conductive resin paste which has a B-stage state when used and is excellent in conductivity and adhesiveness.

[Prior art]

Conventionally, a gold-silicon eutectic has been used for joining a semiconductor element such as an IC and an LSI to a lead frame, but recently, since gold is expensive, a conductive resin paste using silver powder is often used. It's starting to happen.

As the conductive resin paste of this kind, a silver paste in which an epoxy resin is used as a binder and silver powder is mixed with the binder is mainly used because of its good workability and adhesiveness.

The properties required for this conductive resin pace include workability, curability, adhesiveness, wire bonding method, conductivity, and reliability.

On the other hand, since pellets for light emitting diodes are small, 1/10 to 1/100, compared to chips such as ICs and SLIs, resin paste needs to have stronger adhesiveness, and since electrodes are taken from the back surface of the chip, conductivity is improved. Since the electrical conductivity of the resin paste is proportional to the characteristics of the light emitting diode, high electrical conductivity is required. Further, in the light emitting diode, since the creep failure occurs due to the creep of the paste onto the chip, it is necessary to eliminate the creep.

Further, a conductive resin paste is also used for the vertical conduction of the liquid crystal substrate, but the coating area is smaller than that of the LED chip and the stability of adhesion is required. Further, the conduction stability of the upper and lower substrates is the most important point in the function of the liquid crystal display, and high conductivity is required.

Heretofore, none of the conductive resin pastes for light emitting diodes and liquid crystal substrates have satisfactory adhesiveness and conductive stability.

[Object of the Invention]

The present invention, as a result of researching to obtain a conductive paste having excellent adhesiveness and conductivity in order to eliminate the above-mentioned drawbacks, the silver powder is a conductive silver powder by appropriately mixing flake silver powder, spherical silver powder and dendritic silver powder. It has high adhesiveness and is stable, and by using phenol novolac as a curing agent, it has high adhesive strength, and the adhesive strength is reduced even when subjected to temperature treatment such as heat cycle or temperature treatment such as high temperature and high humidity test. It was possible to achieve the purpose by discovering that there are many cases.

[Structure of Invention]

The present invention is a conductive thermosetting resin paste comprising silver powder, an epoxy resin, a curing agent, a curing accelerator, and a solvent,
(A) The silver powder is flaky silver powder, and the average particle size is 0.1 to 2 μ.
m is spherical silver powder and dendritic silver powder, and the mixing ratio is 100 parts by weight of flake silver powder, 5 to 70 spherical silver powder.
Parts by weight, a silver powder mixture in which the dendritic silver powder is 5 to 70 parts by weight,
(B) Epoxy resin is an epoxy resin that is liquid at room temperature,
(C) Curing agent is a polyhydric phenol having an average of 2.5 or more active hydrogen per molecule, (D) Curing accelerator is a tertiary amine or its salt, (E) Solvent is a derivative of glycols. The conductive resin paste is characterized in that it can be in a B stage state as a component.

The silver powder used in the present invention is a mixture of flake silver powder, spherical silver powder, and dendritic silver powder.

Conventionally, only flake-shaped silver powder has been mainly used as the silver powder used for the conductive paste of IC, LSI and the like, but this has many silver powder contacts and has excellent conductivity, and is necessary for applying the paste. This is because thixotropy is easily obtained and workability is excellent.

On the other hand, if the spherical silver powder is used alone, the number of contact points of the silver powder is small, so that the conductivity is deteriorated and the paste is hard to spread, resulting in poor workability.

Further, the flake-shaped silver powder is likely to be oriented in the horizontal direction after the pellet mounting, and may be inferior in the vertical direction, that is, the electrical connection between the chip and the lead frame that is truly necessary.

When spherical silver powder is used in combination with flake silver powder, electrical conductivity in the vertical direction can be improved without compensating electrical connection between the flake silver powders.

Spherical silver powder is 10 μm or less, average particle size is 2 μm or less,
It is preferably 0.1 μm or more. If the particle size is 10 μm or more and the average particle size is 2 μm or more, the coating thickness becomes thick and the adhesive strength is reduced. When the average particle size is 0.1 μm or less, the effect of electrical bonding between the flake-shaped silver powders is lost and the conductivity in the vertical direction is reduced. However, if the flake-shaped silver powder and the spherical silver powder are used together, the resin is easily separated and bleeding of the resin occurs, which is not preferable.

In order to prevent this, a dendritic silver powder, which is three-dimensionally bulky and has a large specific surface area, is used in combination to solve the problem. Since dendritic silver powder is bulky in three dimensions, it has the effect of compensating for conductivity in the vertical direction, and because of its large specific surface area, phenomena such as separation and bleeding do not occur. It is not preferable to use the flake-shaped silver powder and the dendritic silver powder together without using the spherical silver powder, because the viscosity becomes high. Therefore, the mixing ratio of flake silver powder, spherical silver powder and dendritic silver powder is 5 parts by weight of spherical silver powder to 100 parts by weight of flake silver powder.
The amount of dendritic silver powder is preferably 5 to 70 parts by weight. Here, if the amount of the spherical silver powder is 5 parts by weight or less, the conductivity in the vertical direction is deteriorated, but the viscosity is increased, which is not preferable. Further, when it is 70 parts by weight or more, separation and bleeding occur, which is not preferable. When the dendritic silver powder is 5 weight or less, the electrical conductivity in the vertical direction is deteriorated, but separation and bleeding occur, which is not preferable. Further, if it is 70 parts by weight or more, the viscosity becomes high, which is not preferable.

In the present invention, the content of the silver powder in the conductive resin paste is preferably 70 to 85% by weight, and those in this range are the easiest to use for applying the paste by a dispenser, screen printing, stamping, etc. , 70%
If it is less than the above range, the conductivity is deteriorated, which is not preferable.

The epoxy resin used in the present invention is limited to liquid at room temperature, but if not liquid at room temperature, the amount of solvent used increases, voids are generated, and the drying time becomes long, which is preferable. Absent.

Furthermore, the epoxy resin used in the present invention must contain an average of 2.5 or more epoxy groups per molecule. The number of epoxy groups per molecule is 2.
A value of 0 is not desirable because sufficient heat resistance and quick curing cannot be obtained. However, trifunctional or higher and 2
You may mix | blend with a functional thing and make it an average of 2.5 functionality or more, and may use it.

As the epoxy resin used in the present invention, any epoxy resin satisfying the above conditions can be used, but the following types are preferable.

Phloroglucinol triglycidyl ether, trihydrooxypiphenyl triglycidyl ether, tetrahydrocipiphenyl tetraglycidyl ether, tetrahydroxypisphenol F tetraglycidyl ether, tetrahydroxybenzophenone tetraglycidyl ether, epoxidized novolak, Epoxidized polypinylphenol, triglycidyl-luisocyanurate, triglycidyl-lucyanurate, triglycidyl S-triazine, triglycidyl aminophenol, tetraglycidyl diaminodiphenylmethane, tetraglycidyl metaphenylenediamine, tetraglycidylpyromellit Acid, triglycidyl trimellitic acid, and other polyfunctional epoxy resins having three or more functional groups Difunctional epoxy resins such as diglycidyl resorcin, diglycidyl pisphenol A, diglycidyl bisphenol F, diglycidyl bisphenol B, diglycidyl ether of dihydroxybenzophenone, diglycidyloxybenzoic acid, diglycidyl phthalate The acid (o, m, p), diglycidyl hydantoin, diglycidyl aniline, diglycidyl toluidine, or the like, or a condensation type resin of these.

Among these, polyglycidyl compounds (liquid form) of low molecular weight polyphenols are particularly preferable in terms of reactivity, workability and physical properties.

The curing agent used in the present invention needs to be a polyfunctional one having 2.5 or more active hydrogen groups per molecule which react with an epoxy group and participate in crosslinking.

Examples of such compounds having active hydrogen include polyhydric phenols, aromatic polybasic acids, and aromatic polyamines, and polyhydric phenols are particularly preferable from the viewpoint of curability and storage stability.

As the polyphenols, an amorphous resinous substance which is an initial condensate of phenols and aldehydes and contains as little free phenol as possible is preferable. For example phenol,
Low molecular weight liquid novolac mainly composed of di- and trinuclear compounds obtained by reacting monohydric phenols such as cresol and xylenol with formaldehyde in dilute aqueous solution and monohydric phenols and acrolein,
The initial condensate under acidic conditions with polyfunctional aldehydes such as glyoxal and the initial condensate under acidic conditions with polyhydric phenols such as resorcinol, catechol, hydroquinone and formaldehyde, etc., satisfying the above conditions. Any of them can be used similarly.

As the aromatic polybasic acid, there are polybasic acids such as pyromellitic anhydride and trimellitic anhydride, and 2 to 3 thereof.
A polybasic acid derivative in which the molecule is linked by an ester bond with a difunctional or trifunctional polyol, or a difunctional acid anhydride such as maleic anhydride, phthalic anhydride, endomethylenetetrahydrophthalic anhydride hexahydrophthalic anhydride, and the above It is a eutectic mixture with a polybasic acid, and any of them can be used in the same manner as long as the above conditions are satisfied.

Among the above polyphenols, those of novolak type are particularly preferable, and among them, those having a relatively low molecular weight, a small amount of free phenol and a narrow molecular weight distribution are particularly preferable. That is, Mn: 350 to 450, Mw / Mn: 2.0 to 3.5, free P: 0.5% or less, and softening point (microscopic method) of 80 to 110 ° C are suitable.

These types are compatible with epoxy resins,
Good reactivity, comparatively low viscosity as a mixture, high functionality and good curability, and good balance of performance in all aspects such as excellent physical properties of the cured product Is a major feature.

The ratio of the average epoxy equivalent of the epoxy resin used in the present invention to the average active hydrogen equivalent of the curing agent is 3.0 or less, preferably
It should be 0.5 or less, and 0.2 or more, preferably 0.5 or more. Here, if the equivalent ratio is 0.2 or less, the adhesive strength is significantly reduced, which is not preferable. Further, when it is 3.0 or more, the viscosity of the curing agent is high, so that the viscosity becomes high, which is not preferable.

The curing accelerator used in the present invention is a tertiary amine or a salt thereof, and at least one selected from the group consisting of dimethylbenzylamine, tris (dimethylaminomethyl) phenol, alicyclic superbases and imidazoles. A salt of a tertiary amine with a polyhydric phenol or a polybasic acid is desirable.

Alicyclic super base is trimethylenediamine, 1,8-diaza-bicyclo- (5,4,0) undecene-7, todecahydro-
Examples include 1,4,7,9b tetraazaphenalene.

The imidazoles are those in which a substituent such as methyl, ethyl, propyl or a long-chain alkyl group up to C ₁₇ or a phenyl group is introduced at the 2- and / or 4-position.

For forming a salt with these tertiary amines,
Polybasic acids such as phthalic acid (o, m, p), tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, hexahydrophthalic acid, trimellitic acid, adipic acid, succinic acid, maleic acid, itaconic acid, or resorcin, pyrogallol , Hydroquinone, pisphenol A, pisphenol F, pisphenol S, low molecular weight novolac, and other polyhydric phenols.

It is desirable that the salt of these tertiary amines is in the range of 0.1 to 10 parts with respect to 100 parts (weight, hereinafter the same) of the epoxy resin. If it is less than this, accelerated curing is insufficient,
If the amount is larger than this, curing is not promoted so much, but the storage stability may be deteriorated.

The solvent used in the present invention preferably has a boiling point of 170 ° C. or higher, and includes lower alkyl monoethers, diethers, monoether acetates, propionates of glycols such as cellosolves and carbitols.

When the boiling point is 170 ° C. or less, drying at the time of screen printing is quick and not preferable.

In the present invention, a defoaming agent or a coupling agent may be appropriately used.

As the defoaming agent and the cup agent, any of silicone type, fluorine type and others may be used.

The conductive resin paste of the present invention is adhered after coating,
Although it can be cured at 0 ° C., it may be cured by heating after application and, after passing through the B stage for a while, the adherend is subjected to thermocompression bonding. That is, by taking the B stage state, the coating shape becomes stable, so that the creeping amount of the LED can be suppressed and the leak failure can be prevented. In the case of a liquid crystal substrate, there is an advantage that the alignment of the substrate is easy. Further, since the solvent is scattered by further heating, voids are less likely to occur during curing, and the adhesive strength and conductivity can be further stabilized.

Here, the heating temperature for the B stage is preferably 50 ° C. to 150 ° C. When the temperature is 50 ° C. or less, the solvent is less likely to fly, and when the temperature is 150 ° C. or more, the reaction easily proceeds, which is not preferable. Further, the conditions for thermocompression bonding of the adherend can be 35 ° C to 150 ° C.

The manufacturing process of the mounting resin composition of the present invention is as follows.

First, a predetermined amount of an epoxy resin, a curing agent, a curing accelerator, and a solvent are individually weighed and kneaded to form a uniform solution. In this case, for kneading, an ordinary stirring layer, a crusher, a triple roll, an ink mill and the like may be appropriately combined and used.

Next, a predetermined amount of silver powder is weighed and kneaded with the above resin solution to form a completely uniform paste. Also in this case, a stirring tank, a crusher, a triple roll and the like are used in an appropriate combination. Next, the paste resin composition is weighed and distributed in a predetermined container and defoamed in a vacuum chamber to obtain a product.

〔The invention's effect〕

The conductive resin paste according to the present invention uses a silver powder mixture consisting of flake silver powder, spherical silver powder and resin silver powder as the silver powder, and phenol novolac as the curing agent, so that the conductive stability and the adhesion stability are improved as compared with the conventional paste. An excellent paste can be obtained, which is extremely excellent as a conductive resin paste for conducting light emitting diodes and liquid crystal substrates.

Example 1 Epoxidized phenol novolak as epoxy resin (number average molecular weight; 620, epoxy equivalent; 175, number / molecule of epoxy groups; 3.5,100 parts (weight, the same hereinafter), phenol novolac as curing agent (number average molecular weight; 750, active hydrogen equivalent; 105, number of active hydrogen groups / molecule; 5.5) 65 parts,
0.1 part of adipic acid salt of tris (dimethylaminomethyl) phenol as a curing accelerator, 80 parts of butyl carbitol acetate as a solvent, and 0.01 part of a silicone antifoaming agent are stirred to form a uniform solution.

60 parts by weight of flake-shaped silver powder having an average particle size of 2 μm, 10 parts by weight of spherical silver powder having an average particle size of 0.5 μm, and 10 parts by weight of dendritic silver powder having an average particle size of 0.5 μm are mixed with 20 parts by weight of the above-mentioned composition.
After mixing, the resin composition is obtained by passing through three rolls.

The data on the viscosity, adhesive strength, volume resistivity and workability of the obtained resin composition are summarized in Table 1.

Example 2 Epoxy resin is an epibis liquid epoxy resin (number average molecular weight; 380, epoxy equivalent 1; 190, number of epoxy groups / molecule; 2.0, hydrolyzable chloro group; 150 ppm) triglycidyl ether of phloroglucin (number) Average molecular weight: 360,
Epoxy equivalent: 120, number of epoxy groups / molecule; 2.8) and a mixture of 1.0 / 2.0 (weight) are used.

As a curing agent, resorcin-based novolak (number average molecular weight: 300, active hydrogen equivalent: 80, number of active hydrogen / molecule; 3.
8) is used.

The curing accelerator and the defoaming agent are the same as in Example 1.

The composition, paste properties, curing conditions, and performance of the cured product are as shown in Table 1.

Comparative Example 1 The resin composition of Table 1 in which the curing agent was changed from phenol novolac to dicyandiamide in Example 1, but the mounting strength was reduced by changing the curing agent,
Stickiness occurs in the B stage state, which is not preferable.

Comparative Examples 2 to 6 Compositions were prepared with the formulations shown in Table 1 using the resin formulation of Example 1, and the performance is shown in Table 1. In Comparative Example 2, only the flake-shaped silver powder was used and the conductivity was poor. Comparative Example 3
When used together with spherical silver powder, the viscosity is low and bleeding is easy. In Comparative Example 4, when flake-shaped silver powder and dendritic silver powder are used in combination, the viscosity is high and projections are generated, so that workability is not good. In Comparative Example 5, spherical silver powder having an average particle diameter of 5 μm was used, but bleeding is likely to occur. Although Comparative Example 6 uses a large amount of spherical silver powder,
The conductivity decreases and bleeding also occurs.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C09D 163/00 PJP 8830-4J H01B 1/22 A 7244-5G (56) References JP-A-62 -145602 (JP, A) JP 60-12222 (JP, A) JP 60-1221 (JP, A) JP 56-866 (JP, A) JP 62-145601 (JP, A) ) JP-A-61-208701 (JP, A) JP-A-59-132502 (JP, A)

Claims (1)

[Claims] 1. A conductive thermosetting resin paste comprising silver powder, an epoxy resin, a curing agent, a curing accelerator, and a solvent, wherein (A) the silver powder is flake silver powder and the average particle size is 0.1.
A spherical silver powder having a size of ˜2 μm and a dendritic silver powder, and a mixing ratio thereof is 5 to 70 parts by weight of spherical silver powder and 5 to 70 parts by weight of dendritic silver powder, relative to 100 parts by weight of flake silver powder, (B) Epoxy resin is a liquid epoxy resin at normal temperature, (C) curing agent is a polyhydric phenol having an average of 2.5 or more active hydrogen per molecule, (D) curing accelerator is a tertiary amine or its The conductive resin paste characterized in that the salt and the solvent (E) have a derivative of glycol as an essential component and can be in a B-stage state.