JPH06260015A - Conductive powder and paste fro connecting lsi chip to board electrode - Google Patents

Abstract

PURPOSE:To provide the conductive powder and paste excellent in environmental resistance and junction property, having conductivity, and easily deformed for directly mounting LSI chips on a board. CONSTITUTION:The conductive powder expressed by the general formula AgxCu1-x, where 0.02<=x<=0.4 in atomic ratio, having the silver concentration on the grain surface 2.3 times or above the average silver concentration, the average grain size of 3-20mum, the abundance ratio of 75% or above for the powder having the average grain size + or -2mum, and the content oxygen concentration of 2,000ppm or below or the paste using this powder is used to connect LSI chips to board electrodes. The conductive powder having conductivity, excellent in environmental resistance and migration resistance, and easily deformed for mounting LSI chips on a board and the paste using this conductive powder are obtained.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The conductive powder of the present invention and the paste using the conductive powder of the composition are used for directly connecting an LSI chip to a substrate electrode, and are used on a printed circuit board circuit, a hybrid IC board. Circuit, liquid crystal panel (C
OG: Chip-on-glass), IC cards, and conductive powder for electrical connection to solar cells.

[0002]

2. Description of the Related Art Recently, it has become necessary to increase the density and fine wiring of printed wiring boards, liquid crystal displays, hybrid ICs and the like. Therefore, instead of mounting the conventional IC package on the substrate, the LSI chip has been mounted directly. When mounting an LSI chip on the surface of a substrate, known methods include a method of connecting by soldering an indium component between an IC or LSI chip electrode and a substrate electrode, or an LSI in which a gold bump is formed.
The chip electrode is heat-cured or UV-cured on the substrate electrode with a conductive paste containing silver or silver-palladium conductive powder.
There are a connecting method for curing and a method for mechanically connecting the LSI chip electrode portion on which the gold bump is formed to the substrate electrode with a UV curable resin.

Conductive powders, for example, from several μm to 2
This is a method of interposing gold-plated resin particles and gold-plated nickel particles of about 0 μm between the LSI chip electrode and the substrate electrode to ensure electrical connection only in the direction between the electrodes. in this case,
Photothermosetting resin is coated on the electrodes of the LSI chip, the parts other than the electrodes are photo-cured, and the conductive powder is attached only to the electrodes using adhesiveness, and the bonding surface of the LSI chip faces downward. Bonded on the substrate electrode. At this time, the adhesive is applied on the substrate other than the electrodes in advance to wake up the LSI.
It protects the adhesion between the chip and the substrate and further cures by heating to fix the conductive powder present between the LSI chip electrode and the substrate electrode. At this time, if necessary, a method of stabilizing the conductivity by slightly deforming the conductive powder between the electrodes with a pressure of several tens Newton / electrode. Gold or solder bumps may be used for the LSI chip electrode portion.

As another method of interposing the conductive powder between the electrodes, the conductive powder is dispersed in a photocurable resin, a thermosetting resin, or a thermoplastic resin organic binder and coated on a substrate electrode or an LSI chip. Then, after the electrodes are aligned and bonded, they are heated or photocured, and simultaneously pressed to secure both contacts of the conductive powder existing between the electrodes. In this case, the particles dispersed in the organic binder are not electrically conductive with each other, and are electrically conductive only in the direction between the electrodes.

[0005]

The known mounting methods described above have the following drawbacks. IC by soldering
Chip mounting is not preferable because cracks easily form between itself and the substrate due to heat cycles. When the LSI chip on which the gold bumps are formed is directly bonded to the substrate by using the photo-curable resin, the bonding is performed only by the curing shrinkage of the resin, and thus the stable stable conductivity cannot be obtained. When the conductive paste is applied only to the LSI chip electrode portion and is bonded to the substrate electrode to secure the conductivity, a short circuit between adjacent electrodes is likely to occur due to dripping of the paste.

The present inventor has paid attention to a method of interposing conductive powder between the LSI chip electrode and the substrate electrode. L
In order to interpose the above-mentioned known conductive powder between the electrodes for SI chip connection, the conductive powder is present between the LSI chip electrode and the substrate electrode to apply pressure and heat for electrical connection. Gold plated resin particles, gold plated nickel particles,
Silver particles and the like have been used. However, when the gold-plated resin particles are used, not only the cost of gold plating on the resin is high, but also the plated gold is easily separated from the resin at the time of bonding,
It may cause poor contact. Further, even when using a conductive powder plated with gold on a nickel ball, in order to ensure sufficient conductivity, it must be plated thick.
Since nickel intervenes, there is a problem that nickel is oxidized at the interface of plated gold at high temperature and high humidity. In the case of silver particles, there is a problem of leakage due to migration of silver between the substrate electrodes.

[0007]

Means for Solving the Problems The present invention, by interposing a conductive powder between LSI chip electrode and the substrate electrode, as to how to ensure the only conductive in the inter-electrode direction, the general formula Ag _x Cu
_1-x (where 0.02 ≦ x ≦ 0.4, atomic ratio), and the silver concentration on the grain surface is higher than 2.3 times the average silver concentration. An excellent conductive powder for connecting an LSI chip electrode and a substrate electrode, which has a region where the silver concentration increases and which has an average particle size of 3 to 20 μm and an average particle size of ± 2 μm is 75% or more. A paste in which the composition powder is dispersed in an organic binder, and a liquid crystal panel mounted with an IC bare chip,
A hybrid IC and a printed circuit board are provided.

The conductive powder of the present invention may be produced by a known method, but US Pat. No. 5,011,140, which has already been filed by the present applicant, is preferable. According to the disclosure, it is obtained by atomizing a melt of silver and copper having such a composition with a high-pressure inert gas, but it is particularly preferable to use nitrogen gas or helium gas. The purity of the inert gas is preferably high, but the purity is preferably 99.9% or higher, and more preferably 99.99% or higher.

The conductive particles of the present invention have the general formula Ag _x Cu.
_{Although represented by 1-x} (however, 0.02 ≦ x ≦ 0.4, atomic ratio), if x is less than 0.02, sufficient oxidation resistance cannot be obtained. When x exceeds 0.4, silver migration between the base electrodes becomes a problem. Preferably 0.0
2 ≦ x ≦ 0.3. The conductive particles of the present invention have a silver concentration on the surface higher than 2.3 times the average silver concentration, but if the silver concentration is less than 2.3 times, sufficient oxidation resistance at the electrode particle contact cannot be obtained. It is preferably three times or more. Also, the particle shape is preferably spherical, but if the particle shape is far from the spherical shape, some of the particles existing between the substrate electrode and the LSI chip electrode may or may not have both contact points and may be electrically connected. It is easy to generate a combination that does not have

The surface silver concentration and average silver concentration used in the present invention are the values measured by the following method. Surface silver concentration measurement is X
PS (X-ray photoelectron spectroscopy analyzer: manufactured by KRATOS, X
SAM 800) was used. Etching conditions: 10 ^{over 7} torr argon accelerating voltage 2k
eV 5 minutes Measurement Conditions: 10 ^{over 8} torr argon magnesium Kα
Line voltage 12 KeV, current 10 mA measurement, etching was repeated 5 times, and the average value of the first 2 measurements was taken as the surface silver concentration, that is, surface silver concentration Ag / (Ag + Cu) (atomic ratio).

The average silver concentration was determined by dissolving the conductive powder in a concentrated nitric acid solution and then using ICP (high frequency inductively coupled plasma emission spectrometer, Seiko Denshi JY38P2). Also,
The average particle size is 3 to 20 μm, and the existence ratio of the average particle size ± 2 μm is 75% or more, but the pitch between the LSI chip electrodes is usually as narrow as about 20 to 150 μm, and the average particle size is 20 μm. If it exceeds, the existing particles are too large to have a contact with an adjacent electrode when crushed, and a leak current is generated, which is not preferable. When the average particle diameter is less than 3 μm, the particles between the electrodes are smaller than the thickness of the electrodes, and the contact becomes insufficient. The thickness is preferably 3 to 12 μm, more preferably 3 to 10 μm.

Further, 75% of powders have an average particle diameter of ± 2 μm.
As described above, if it is less than 75%, the particle size distribution is too wide, and a combination in which particles do not exist between the electrodes occurs. It is preferably at least 85%. Regarding the average particle size and particle size distribution of the conductive powder of the present invention, a laser diffraction type particle size distribution measuring device (SALD1100: manufactured by Shimadzu Corporation) was used to add the conductive powder to an ethylene glycol solution in an amount of 0.01 to 1 g / It was measured by dispersing with an ultrasonic transmitter at a concentration of cc. As the measured value, a particle size distribution based on volume was used. As the average particle diameter, a value of 50% was used on the basis of volume integration.
The amount of oxygen contained in the conductive powder is preferably small due to oxidation resistance and conductivity at the contact, and is preferably 2000 ppm or less.
Furthermore, it is preferably 1000 ppm or less. The oxygen content means the total content on the surface and inside of the powder. Oxygen / nitrogen analyzer (EMGA65
0: manufactured by Horiba Seisakusho) and heated up to 2000 ° C. The measuring method is shown below.

When the conductive powder of the present invention is used for joining an LSI chip electrode and a substrate electrode, a known method may be used.
For example, apply photo-curable resin on the electrode part on the substrate,
Furthermore, after curing the parts other than the connecting electrode part using a mask and further sticking the conductive powder to the electrode part using the adhesive property (FIG. 1), an adhesive is applied to the part other than the electrode part to apply pressure, heat or It is used after being photocured (FIG. 3). In addition, a known method in which conductive powder is dispersed in a conductive powder using an appropriate organic binder is applied to an LSI chip electrode or a substrate electrode, heated or photocured, and if necessary, pressurized by LSI. It is possible to join the chip electrode and the substrate electrode. As the size of the LSI chip electrode in this case, one having a normal LSI chip electrode of about 30 μm to 150 μm can be used. Further, an LSI chip electrode having gold bumps or solder bumps formed thereon can also be used.

The present invention relates to a conductive powder having the above composition,
Further, the present invention also provides a paste containing an organic binder. The paste of the present invention contains 0.2 to 15 parts by weight of an organic binder with respect to 1 part by weight of the conductive powder, but a thermosetting resin, a thermoplastic resin, or a photocurable resin can be used. As the thermoplastic resin, thermoplastic acrylic resin, butyral resin, vinyl chloride resin,
Examples thereof include urethane resin, polyester resin, polycarbonate resin, and styrene resin. If the organic binder is less than 0.2, it is difficult to form a paste and an adhesive for joining the substrate and the IC chip is required as in the method of using the conductive powder. If it exceeds 15 parts by weight, the probability of the conductive powder existing between the electrodes becomes low, which is not preferable. It is preferably 0.3 to 10 parts by weight, and more preferably 0.3 to 7 parts by weight.

The thermosetting resin may be at least one selected from epoxy resin, resol type phenol resin, amino resin, polyurethane resin, polyimide resin and thermosetting acrylic resin. Examples of the epoxy resin include bisphenol A type, bisphenol F type, brominated bisphenol A type, alicyclic epoxy, chain type epoxy, epoxy acrylate, fatty acid modified epoxy, polyalkylene ether type, and diglycidyl ester type. A liquid epoxy resin and, if necessary, a known reactive diluent can be used. Examples thereof include diglycidyl ether, ethylene glycol diglycidyl ether, 1,3 butanediol diglycidyl ether, and diethylene glycol diglycidyl ether.

Examples of the resol type phenol resin include phenol / formaldehyde type resol type resin, alkylphenol resol type resin, xylene resin modified resol type resin and rosin modified phenol resin.
Examples of the polyimide resin include condensation type polyimide, bismaleide type resin, and addition type polyimide resin.

As the polyurethane resin, urethane prepolymers that form urethane can be used, but it is preferable to mainly use a block isocyanurate prepolymer in which a terminal active isocyanate group is blocked with an active hydrogen compound. Among these thermosetting resins, those using an epoxy resin are preferable. Of these, bisphenol A-type and F-type epoxy resins are preferable. Above all, it is preferable to use a solventless epoxy resin.
A curing agent can be used if necessary, and it is preferable to use a known one such as imidazole type curing agent, organic polyamine, acid anhydride, dicyandiamide, benzoguanamine and the like.

When the ultraviolet curable resin is used, a photopolymerizable oligomer and a photopolymerizable monomer are used together with a photoinitiator and a photoinitiator aid. The photopolymerizable oligomer is a low-molecular weight reactive molecule (several hundreds to thousands) and has two or more acrylic groups and methacrylic groups as functional groups added to the skeleton of polyester, epoxy, urethane, etc. Examples thereof include epoxy acrylate, urethane acrylate, polyester acrylate, and polyether acrylate.

As the photopolymerizable monomer, an acryloyl group (CH ₂ = CHCO-) or a tacryloyl group (C
1 or 2 H ₂ C (CH ₃ ) CO-) per molecule
It is preferable to use one having one or more, a monofunctional acrylate (meth) having one or more, a polyfunctional acrylate having two or more, and another having a vinyl group (CH ₂ ═CH—). Examples thereof include allyl acrylate, allyl methacrylate, benzyl acrylate (meth), N, N-dimethylaminoethyl acrylate, glycidyl methacrylate, lauryl acrylate, polyethylene acrylate 90 methacrylate, and trifluoroacrylate. As the polyfunctional acrylate, for example,
1,4 butanediol diacrylate, diethylene glycol diacrylate, neopentyl glycol acrylate, polyethylene glycol 400 diacrylate, tripropylene glycol diacrylate, bisphenol A diethoxydiacrylate, tetraethylene glycol diacrylate, trimethylolpropane acrylate, pentaerythritol triacrylate Acrylate etc. are mentioned. Examples of the reactive monomer having a vinyl group include styrene, vinyltoluene, vinyl acetate,
Monofunctional monomers such as N-vinylpyrrolidone can be used.

The photoinitiator used together with the photopolymerizable oligomer or monomer is preferably a substance which easily absorbs ultraviolet rays to generate radicals, and known acetophenone-based, thioxanthone-based, benzoin-based or peroxide-based substances are used. be able to. As a photoinitiator aid, it is not itself activated by UV irradiation, but when used together with a photoinitiator, the initiation reaction is promoted more than the photoinitiator alone, and the curing reaction is made more efficient. Known photoinitiator aids such as aromatic amines can be used. Examples thereof include triethanolamine, N-methyldiethanolamine, Michler's ketone, 4,4-diethylaminophenone and the like. When an ultraviolet curable resin is used, it is preferably solvent-free in the same manner as the heat curable resin, from the viewpoint of preventing gas generation of the solvent.

When an ultraviolet curable resin is used, it is preferable to use it without a solvent in order to prevent gas generation due to volatilization of the solvent, like the heat curable resin. However, some known solvents can be used as long as the characteristics are not impaired. When a solvent is used, methyl carbitol, ethyl carbitol, butyl carbitol and their acetates, methyl cellosolve, ethyl cellosolve, butyl cellosolve and their acetates, 2,
Examples thereof include, but are not limited to, 2,4-trimethyl-1,3-pentanediol monoisobutyrate, terpenol, xylene, butyl acetate, toluene, ethyl acetate, methyl ethyl ketone, and methyl isobutyl ketone.

When used as a paste, known coupling agents, anti-settling agents, antioxidants and the like can be used. Examples include, but are not limited to, silane coupling agents, titanium coupling agents, aluminum coupling agents, colloidal silica, polyethylene oxides, higher fatty acids, hydroquinone compounds, phenol compounds, alkanolamines and the like. . The amount of these additives is 0.00 with respect to 1 part by weight of the conductive powder.
1 to 0.1 parts by weight is preferable.

The substrate electrode used as a paste is also
Similar to the case of using as conductive powder, glass epoxy resin substrate, paper phenol resin substrate, alumina substrate, small aluminum substrate, polyimide resin substrate, polyphenylene sulfide resin substrate, glass substrate and other rigid or flexible substrate, low temperature It means a conductor circuit and electrodes formed on a circuit board such as a fired ceramics substrate, and ITO (indium tin oxide) and IO (indium oxide) electrodes formed on a liquid crystal panel. When coating a paste having such a composition on a substrate electrode, a known coating method may be used.
For example, spin coating, screen printing, microdispenser method and the like can be mentioned, but they are not particularly specified. The coating thickness is the particle size of the conductive powder,
Although it depends on the thickness of the electrode, it is preferable to coat the electrode with a thickness of about 5 to 1000 μm. Furthermore, 10-200 micrometers is preferable and 10-50 micrometers is the most preferable. After being coated, it is dried at 100 ° C. or lower if necessary. Further, electrodes of the LSI chip (electrodes on which gold bumps or solder bumps are formed in some cases) are set at the substrate electrode bonding positions (FIG. 2). Next, they are joined and heated and dried, and heat-cured or light-cured under pressure (FIG. 4). At this time, the heat curing is preferably performed according to the curing conditions of the organic binder described above. However, when the substrate cannot be used at a high curing temperature like a liquid crystal panel, it is preferable to cure at a low temperature. In the case of a liquid crystal panel substrate, the temperature is preferably 200 ° C or lower, more preferably 130 ° C or lower, and most preferably 100 ° C or lower. The curing time is also preferably a short time from the stability of the LSI chip and the stability of the substrate. For example, when the LSI chip is mounted on a liquid crystal panel, it may be performed in a few seconds to a few minutes. The heating method is not particularly specified, and examples thereof include a far infrared furnace, a hot air dryer, a near infrared furnace, and a VPS furnace. When pressurizing, it is necessary to apply pressure of about 0.2 to 100 Newton / electrode per electrode.

The organic binder is a photocurable resin such as UV.
When a curable resin is used, the irradiation method differs depending on the substrate, and it is preferable that the liquid crystal panel substrate is irradiated from the opposite side of the panel. If the substrate does not have sufficient transparency, it is preferable to irradiate it from the side. Also in this case, it is preferable to apply pressure simultaneously to stabilize the joining. As indicated above, LS
The case where the I-chip is directly bonded by using the conductive powder, or the case where the conductive powder is dispersed in the organic binder in a necessary amount and heat-cured or light-cured is used for bonding, but in the bonded state, the LSI chip electrode ( It also means that the conductive powder exists between the substrate electrode and the gold and solder bumps) and the conductive powder exists at both points. Is in contact with both electrodes on the surface.
Depending on the type of the LSI chip electrode, the size of one piece of the electrode is as small as 30 μm to 120 μm, and the distance between the electrodes (electrode pitch) is as narrow as 30 μm to 200 μm.
In the contact state on the surface, sufficient conduction can be obtained as compared with the case where the particles are simply in point contact.

The conductivity between the LSI chip electrode and the substrate electrode depends on the size of the electrode, but is 0.1 mΩ to 4 mΩ / c.
It is preferable to obtain a resistance value of about m2 between the electrodes. Resistance value between electrodes (or 60 ° C for conductive environment resistance test)
1000 hours in 90% humidity, -55 ° C 30 minutes 12
The change in resistance value between both electrodes was measured at 1000C cycles of 5 minutes for 30 minutes. The case where the rate of change was less than twice the initial resistance value was regarded as good. In the migration test, with 10 V applied between the adjacent electrodes on the substrate, the insulation property was measured after leaving for 1000 hours in 60 ° C. and 90% humidity, and a value of 10 ⁸ ohms or more was taken as a normal value. Also, it was determined that migration (dielectric breakdown) occurred at 10 ⁷ ohms or less. The shape and state of the conductive powder between the electrodes were observed by cutting the cross section with a diamond cutter, polishing and then observing with an electron microscope.

The present invention will be described below with reference to examples.

[0027]

【Example】

Powder Preparation Example 1 571.5 g of copper particles (purity 99.9% or higher) and 108 g of silver particles (purity 99.9% or higher) were mixed and dissolved in a graphite crucible up to 1700 ° C. using high frequency induction heating. The melt is ejected from the tip of the crucible, and at the same time as the ejection, 50k
A nitrogen gas of g / cm ² was jetted to the melt for atomization. The obtained powder was spherical and had an average particle size of 10 μm. Among them, 7 to 10 μm particles were classified by an air stream classifier. The obtained classified powder had an average of 8.5 μm.
The existence ratio of classified powder contained in 8.5 ± 2 μm is 99.9.
% Or more. The silver concentration on the grain surface is 0.8 from the surface,
It was 0.78, 0.7, and 0.65, and the surface silver concentration was 0.79. The average silver concentration was 0.1, and the surface silver concentration was 7.9 times the average silver concentration. The oxygen content was 200 ppm.

Powder Preparation Example 2 Copper particles (412.5 g) and silver particles (378 g) were mixed and heated to 1700 ° C. in a graphite crucible and melted. The melt was jetted from the tip of the crucible, and at the same time as the jetting, 50 kg / cm 2 helium gas was jetted to atomize the melt. The obtained powder was spherical and had an average particle diameter of 5 μm. Using an airflow classifier, classification was performed at 3 to 6 μm. Average particle size 5 μm
And the existence ratio of particles of 5 ± 2 μm was 90% or more. The silver concentration on the grain surface is 0.9, 0.84 from the surface,
It was 0.78, 0.76 and 0.7, and the surface silver concentration was 0.87. The average silver concentration was 0.35, and the surface silver concentration was twice the average silver concentration. The oxygen content was 300 ppm.

Powder Preparation Example 3 603 g of copper particles and 54 g of silver particles were mixed and heated to 1750 ° C. in a graphite crucible and melted. The melt was ejected from the tip of the crucible, and at the same time as the ejection, an argon gas of 60 kg / cm 2 was ejected to atomize the melt. The obtained powder was spherical and had an average particle size of 8 μm. The obtained powder was classified with an air stream classifier at 10 to 14 μm. A powder having an average particle diameter of 12 μm and an abundance ratio of particles of 12 ± 2 μm of 90% or more was obtained. The silver concentration on the surface of the powder was 0.3, 0.26, 0.24, 0.2, 0.18 from the surface, and the silver concentration on the surface was 0.28. The average silver concentration was 0.05, and the surface silver concentration was 5.6 times the average silver concentration. The oxygen content of the powder is 200
It was ppm.

[0030]

[Example 1] Electrodes on an LSI chip (50 x 50 µm)
A UV curable resin was applied thereon to a thickness of 1 μm. Further, a portion other than the electrode portion was photo-cured using a mask. The conductive powder obtained in Powder Preparation Example 1 was dispersed and adhered onto the electrode portion of the chip without overlapping. The LSI chip was vacuum-adsorbed and set so that the electrode portions faced each other on the liquid crystal panel on which the ITO electrodes (80 to 100 μm) were already formed. At this time, a photothermal curing combined type adhesive for connecting the IC chips was applied between the ITO electrodes, and after bonding the IC chips, UV irradiation curing was performed. Further, 2 Newton / electrode was pressed and cured at 100 ° C. for 20 seconds.

The bonding state after curing is as follows:
Conductive particles exist between the TO electrodes, and the resistance value is 0.2.
It was good at mΩ / cm 2. Furthermore, after the environmental test, the change rate was within 50%, which was good.

[0032]

Example 2 The LSI chip of Example 1 was used for bonding under the same conditions except that the conductive powder obtained in Powder Preparation Example 2 was used. In the bonded state after curing, particles were present between the LSI chip electrode and the ITO electrode, and the resistance value between the electrodes was as good as 1 mΩ / cm 2. After the environmental test, the rate of change was good within 40%.

[0033]

[Example 3] 5 parts by weight of epoxy acrylate, 2 parts by weight of allyl methacrylate, 0.2 part of thioxanthone-based initiator to 1 part by weight of the conductive powder obtained in Powder Preparation Example 3
Part by weight and a small amount of solvent were mixed to form a paste. The prepared paste was uniformly coated with a thickness of 20 μm on a liquid crystal panel on which ITO electrodes (thickness 1000 Å, width 50 μm × 80 μm) were already formed. 22 electrode pads (aluminum 50 × 80 μm)
An LSI chip (7 × 13 mm) having 7 pads was joined so that the connection electrodes faced each other, and UV irradiation was performed from the liquid crystal panel side to cure. Further, while heating at 100 ° C. for 10 seconds, each electrode pad was pressurized with a pressure of 0.7 Newton to bond the electrodes. At this time, the conductive powder was present between the electrodes, the conductive particles between the electrodes were deformed by curing and pressure, and the particles were in contact with the electrodes on the surface. Except between the electrodes, the particles were not in contact with each other and were insulating.

[0034]

[Example 4] 1 part by weight of the conductive powder obtained in Powder Preparation Example 3 was mixed with 6 parts by weight of polyester acrylate, 1 part by weight of vinyl acetate, 0.02 part by weight of an acetophenone initiator, and a small amount of a solvent. The prepared paste has a thickness of 70μ on which a circuit has been formed by etching the copper foil.
2 evenly on flexible printed circuit board of m-polyimide
It was coated with 0 μm. Further, an LSI chip (6 × 6 mm) having 2260 electrodes of electrode pads (gold plating 50 × 80 μm) was set on a copper pad of 50 × 80 μm so that the connection electrodes face each other, and UV irradiation was performed from the lateral direction of the connection. Further, it was cured by heating at 100 ° C. for 20 seconds. At this time, it was simultaneously cured at a pressure of 1 Newton / electrode. It was confirmed that the conductive powder was present between the electrodes. The inter-electrode conductivity was good at 0.2 ohms. It was confirmed that the conductive powder between the electrodes was deformed, and both electrodes were in surface contact with each other. As a result of the environment resistance test, the rate of change was as low as 40%. Insulation was observed at locations other than between the electrodes.

[0035]

Example 5 1 part by weight of the conductive powder prepared in Example 1 was mixed with 5 parts by weight of a liquid epoxy resin, 0.1 parts by weight of an imidazole-based curing agent, and 0.1 parts by weight of triethanolamine. It was a paste. The prepared paste was coated on a circuit on which a copper thick film conductor had already been prepared on a low temperature fired ceramics substrate. Further, an LSI chip (6 × 6 mm) (electrode pad gold bump 75 μm diameter) was aligned and bonded onto the copper thick film electrode. Furthermore, 15
It was cured by heating at 0 ° C. for 30 seconds. At this time, a pressure of 50 Newton / electrode was simultaneously applied to bond. The resistance value between the electrodes was as good as 0.3 mΩ / cm 2. Even after the environmental test, the rate of change in resistance was as good as 40%.

[0036]

Example 6 An LSI chip was mounted in the same manner as in Example 5, except that the gold bumps of the LSI chip of Example 5 were solder bumps. The resistance value between the electrodes was 0.4 mΩ / cm 2, which was good. The rate of change in resistance value after the environmental test is 30.
% Was good.

[0037]

[Embodiment 7] An LSI chip was mounted under the same conditions as in Embodiment 4, except that the copper conductor on the flexible substrate of Embodiment 4 was tin-plated and used. Resistance value between electrodes is 0.4
It was good as mΩ / cm 2. The change in resistance value after the environmental test was as good as 20%.

[0038]

[Example 8] 1 part by weight of the conductive powder obtained in Powder Preparation Example 1 with 1 part by weight of polyester resin, 1 part by weight of butyl carbitol, 0.5 part by weight of toluene, and 0.002 part by weight of titanium coupling agent. A part was added to form a paste. The copper foil was etched and coated onto a flexible polyimide substrate with the circuit already made. The LSI chip (the same example 1) was bonded and dried at 50 ° C. At this time, at the same time, a pressure of 0.1 Newton / electrode was applied for bonding. The resistance value was as good as 0.2 mΩ / cm 2.
The rate of resistance change after the environment resistance test was good at 20%. It was confirmed that the conductive powder was present between the electrodes, and the powder was deformed to some extent and was in surface contact with the electrodes.

[0039]

[Comparative example]

Powder Preparation Example 4 317 g of copper particles and 540 g of silver particles were mixed to obtain 1700
It was heated and melted in a graphite crucible in a graphite crucible under nitrogen atmosphere. The melt was atomized with nitrogen gas (50 kg / cm ² ). The obtained powder was spherical and had an average particle diameter of 11 μm. 10 to 13 μm powder was classified with an air flow classifier. The obtained classified powder had an average particle size of 11 μm, and the existence ratio of 11 ± 2 μm was 99%. The average silver concentration of the classified powder was 0.5 and the average copper concentration was 0.5, and the silver concentration was 0.9, 0.
8, 0.7, 0.6, 0.55, and the surface silver concentration is 0.
It was 85. The silver concentration on the surface was 1.6 times the average silver concentration. The contained oxygen concentration was 300 ppm.

Powder Preparation Example 5 1000 g of copper particles were heated to 1700 ° C. and melted in a graphite crucible under a nitrogen atmosphere. Nitrogen gas (40 kg /
cm2) was atomized. The obtained powder was spherical and had an average particle diameter of 12 μm. 11-13μm with air flow classifier
It was classified in. The obtained classified powder is 12 ± 2 μm at 12 μm.
The abundance ratio of the powder was 99%. Oxygen content is 10
It was 00 ppm.

Powder Preparation Example 6 Copper particles 571.5 g and silver particles g108 were mixed to obtain 17
It was melted by heating in a graphite crucible under a nitrogen atmosphere up to 00 ° C. The melt was atomized with nitrogen gas (60 kg / cm 2). The obtained powder was spherical and had an average diameter of 10 μm, and was classified with an air stream classifier at 2 to 12 μm. Average particle size 6
The powder existence ratio of 6 ± 2 μm in μm was 50%. The average silver concentration was 0.1, the surface silver concentration was 0.7, and the surface silver concentration was 7 times the average. The oxygen content was 100 ppm.

Powder Preparation Example 7 The conductive powder obtained in Powder Preparation Example 1 was treated at 100 ° C. 1000
When left for a period of time, a conductive powder having an oxygen content of 5000 ppm was obtained. The average particle size did not change, but the surface silver concentration decreased, and the surface silver concentration was as low as 0.1 times the average silver concentration.

[0043]

Comparative Example 1 Example 1 except that the conductive powder of Powder Preparation Example 1 used in Example 1 was replaced with the conductive powder of Powder Preparation Example 4.
The LSI chip was mounted by the same method as described above. The resistance value between the electrodes was as good as 0.2 mΩ / cm 2, but as a result of the migration test, migration between the electrodes of the LSI chip was observed and a defective product was generated.

[0044]

Comparative Example 2 An LSI chip was mounted in the same manner as in Example 1 except that the conductive powder of Powder Preparation Example 1 used in Example 1 was replaced with the copper conductive powder of Powder Preparation Example 5. The resistance between the electrodes was as high as 100 mΩ / cm 2, and the resistance change rate between the electrodes after the environmental test was as large as 500%.

[0045]

[Comparative Example 3] The conductive powder used in Example 5 was prepared as Powder Preparation Example 6
An LSI chip was mounted under the same conditions as in Example 5, except that the conductive powder in Example 1 was used instead. Resistance between electrodes is 50m
Although it was as high as Ω / cm 2, the resistance change rate between the electrodes after the environmental test was as large as 200%.

[0046]

[Comparative Example 4] 200 parts by weight of a liquid epoxy resin, 1 part by weight of an imidazole-based curing accelerator, and 0.001 part by weight of a silane coupling agent were added to 1 part by weight of the conductive powder of Powder Preparation Example 1 to prepare a paste. . After coating the paste on the copper conductor electrodes formed on the flexible alumina substrate, gold bumps (75 μm diameter, 220 electrodes)
0) formed LSI chips were connected so as to face each other. It was heat-cured at 150 ° C. for 20 seconds. At this time, at the same time, a pressure of 0.3 Newton / electrode was applied to cure. Probably because the concentration of the conductive powder was low, there was an electrode with the conductive powder present between the electrodes and an electrode without the conductive powder, and the conductivity was as high as 20 mΩ / cm 2 ohm.

[0047]

Comparative Example 5 The same method as in Comparative Example 4 was used except that 0.01 part by weight of a liquid epoxy resin was used with respect to 1 part by weight of the conductive powder used in Comparative Example 4. Probably because the concentration of the conductive powder was too high, the conductive powder existed not only between the electrodes but also between the adjacent electrodes and short-circuited between the adjacent electrodes.

[0048]

Comparative Example 6 An LSI chip was mounted under the same conditions as in Comparative Example 1 except that gold-plated polystyrene particles (average particle size 5 μm) were used as the conductive powder. Resistance value is 0.3mΩ / c
Although the resistance was as low as m2, there were particles in which gold plating was partly peeled off between the electrodes. The rate of change in resistance after the environmental test was as high as 150%.

[0049]

Comparative Example 7 An LSI chip was mounted under the same conditions as Comparative Example 1 except that gold-plated nickel particles (average particle size 10 μm) were used as the conductive powder.

[0050]

COMPARATIVE EXAMPLE 8 The conductive powder was manufactured under the same conditions as in Example 1, except that the powder manufacturing example 6 was used. The resistance between the electrodes is as high as 20 mΩ / cm 2, and the conductive powder between the electrodes is sparse.
Many conductive powders without contacts were found.

[0051]

[Comparative Example 9] The conductive powder was prepared under the same conditions as in Example 1 except that the conductive powder of Powder Preparation Example 7 was used. The resistance value between the electrodes was 3000 mΩ / cm 2, which was extremely high.

[0052]

INDUSTRIAL APPLICABILITY The present invention relates to a conductive powder used as a conductive contact when mounting an LSI chip, and is excellent in stable low resistance bonding with moderate flexibility without using the conventional expensive gold plating powder. It is a conductive powder that provides environmental resistance and a paste that uses the conductive powder.

[Brief description of drawings]

FIG. 1 shows a state in which conductive powder is placed on an LSI chip.

[Fig. 2] A state in which a paste state is coated on a substrate electrode

FIG. 3 shows a state in which conductive powder placed on an LSI chip electrode is joined to a substrate electrode.

FIG. 4 shows a state where an LSI chip is mounted on a paste-coated substrate and cured.

[Explanation of symbols]

 1 ... Substrate electrode 2 ... LSI chip 3 ... Chip electrode 4 ... Conductive powder 5 ... Organic binder 6 ... Adhesive 7 ... Photocurable resin

Claims (6)

[Claims] 1. The general formula Ag _x Cu _1-x (provided that 0.0
2 ≦ x ≦ 0.4, atomic ratio), the silver concentration on the grain surface is higher than 2.3 times the average silver concentration, and there is a region near the surface where the silver concentration increases toward the grain surface. And the average particle size is 3 to 20 μm, the existence ratio of the average particle size ± 2 μm is 75% or more, and the oxygen content is 2000 ppm or less.
Conductive powder for connecting the SI chip electrode and the substrate electrode. 2. 0.1 to 15 parts by weight of one or more kinds of organic binders selected from photocurable resins, thermosetting resins and thermoplastic resins with respect to 1 part by weight of the conductive powder according to claim 1. Partial paste for connecting the LSI chip electrode and the substrate electrode. 3. The substrate electrode according to claim 1 or 2 is copper,
The conductive powder or paste according to claim 1 or 2, which is one or more selected from tin-plated copper, gold, solder-plated copper, ITO, and IO glass electrode. 4. The conductive powder or paste according to claim 1, wherein the conductive powder is present between the LSI chip electrode and the substrate electrode and has contacts with both electrodes. LCD display. 5. The conductive powder or paste according to claim 1, wherein the conductive powder is present between the LSI chip electrode and the substrate electrode and has contacts with both electrodes. Hybrid IC board that does. 6. The conductive powder or paste according to claim 1, wherein the conductive powder is present between the LSI chip electrode and the substrate electrode and has a contact with both electrodes. Printed circuit board.