JP2002008444A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an conductive paste which has a high quality in electronic conductivity, workability, and reliability. SOLUTION: An electric conductive paste contains conductive powder, binder, and solvent, and the conductive powder contains dissolved spherical or semi- spherical conductive powder and dissolved fish-scale like conductive powder, and the ratio of dissolved spherical or semi-spherical conductive powder and dissolved fish-scale like conductive powder is in weight proportion of 40:60-95:5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste used by being embedded in a through-hole of a through-hole wiring board.

[0002]

2. Description of the Related Art As one method of forming a conductive circuit on a printed wiring board, there is a method of using a conductive paste as described in Electronic Materials, pp. 42-46 of October 1994. In particular, a conductive paste using silver powder as the conductive powder is used for forming a conductive layer to be a wiring conductor or an electrode of a printed wiring board, an electronic component or the like because of its good conductivity.

A method of using a conductive paste is to form a conductive layer as shown in FIG. 1 by dispersing a conductive powder in a binder, applying a paste of the conductive paste to the surface of the substrate or filling the through holes. is there. In FIG. 1, reference numeral 1 denotes a conductive paste. As another means for forming a conductive layer in a through hole of a printed wiring board, there is a method of forming a conductive layer by applying copper plating 2 to an inner wall of the through hole as shown in FIG.

However, when a conductive layer is formed on the inner wall of a through hole using a conductive paste, the inside of the through hole is filled with a conductive paste containing a large amount of a solvent.
It is inevitable that voids are generated in the through holes due to drying of the solvent. In addition, it is inevitable that voids are generated by the method shown in FIG. Therefore, as shown in FIG. 3, a multilayer circuit in which an insulating layer 6 is formed on a through-hole and a jumper conductive layer is further formed with a jumper conductive paste 7 eliminates voids in the through-hole and provides a highly reliable conductive layer. In order to form a conductive paste,
There is a drawback that the through-hole must be filled by using. In FIG. 3, 3 is a substrate, 5 is a copper foil, and 8 is an overcoat layer.

When a multilayer circuit as shown in FIG. 3 is formed, the insulation resistance and the migration between the conductive paste 4 filling the through holes and the jumper conductive paste 7 pose a problem. A conductive paste using silver powder has good conductivity, but has a disadvantage that when electrolysis is applied in a high-temperature and high-humidity atmosphere, migration occurs and a short circuit occurs. Therefore, when the inside of the through-hole is filled with a filling conductive paste using silver powder, insulation resistance between the conductive paste 4 and the jumper conductive paste 7 may be reduced and migration may occur.

If the cover plating 9 is applied to the conductive paste 4 in which the through-holes are filled as shown in FIG. 4 instead of the above method, a decrease in insulation resistance and the occurrence of migration can be prevented, but the number of steps is increased. It is not preferable because the cost increases.

Further, as shown in FIG. 5, there is a method in which a conductive layer is formed on the inner wall of a through hole by applying copper plating 2 and a void is filled with a resin 10. However, this method also requires a large number of steps, so that the cost is increased. However, there is a disadvantage that the cost is high.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a conductive paste excellent in conductivity, workability and reliability. The second aspect of the present invention provides a conductive paste having excellent migration properties and reliability. The third aspect of the present invention provides a conductive paste which is particularly excellent in the effect of improving conductivity among the first aspect of the present invention. A fourth aspect of the present invention provides the conductive paste according to the first aspect of the invention, which is particularly excellent in the effect of improving conductivity and reliability. Claim 5
The invention described above provides a conductive paste which is particularly excellent in the effect of improving conductivity and workability among the inventions described in claim 1.

[0009]

According to the present invention, there is provided a conductive paste containing a conductive powder, a binder, and a solvent, wherein the conductive powder includes a spherical or substantially spherical conductive powder in which the conductive powder is pulverized, and a flake-like conductive powder in which the conductive powder is pulverized; A conductive paste in which the ratio of the crushed spherical or substantially spherical conductive powder to the crushed flaky conductive powder is 40:60 to 95: 5 by weight ratio of spherical or substantially spherical conductive powder: flaky conductive powder. About. In addition, the present invention provides a silver coating in which the pulverized spherical or substantially spherical conductive powder and the pulverized flaky conductive powder expose a part of the copper powder or the copper alloy powder and the surface is substantially coated with silver. The present invention relates to a conductive paste that is copper powder or silver-coated copper alloy powder.

Further, in the present invention, the main component of the binder includes an epoxy resin, a phenol resin and a curing agent thereof, and the ratio of the epoxy resin to the phenol resin is 10:90 to 90:90 by weight. 10 relating to the conductive paste. Further, according to the present invention, the ratio of the conductive powder to the binder is 83:17 by weight ratio of the conductive powder: the binder.
９５95: 5. Furthermore, the present invention relates to a conductive paste in which the solvent is one kind or a mixed solvent of two or more kinds, and the content of the solvent is 2 to 10% by weight based on the conductive paste.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As the conductive powder used in the present invention, metal powder such as silver, copper, nickel, zinc, tin and lead or an alloy powder thereof can be used. It is preferable to use silver-coated copper powder or silver-coated copper alloy powder whose surface is substantially covered with silver by exposing a part of the powder, because it is possible to prevent a decrease in insulation resistance and to prevent migration.

In the present invention, it is necessary to use conductive powder that has been pulverized in order to fill the through holes at a high ratio. The method for pulverizing the conductive powder is not particularly limited. For example, agglomeration of the conductive powder and 1 kg of zirconia balls having a diameter of 0.5 mm in a ball mill container and rotating for about 2 hours is performed. be able to.

As the conductive powder, it is necessary to use a composite conductive powder obtained by combining a spherical or substantially spherical conductive powder and a flaky conductive powder. When the conductive powder is spherical or substantially spherical only, the filling rate of the conductive powder into the through holes is higher than that of the flaky conductive powder, and the viscosity of the conductive paste is also lower. However, there is a disadvantage that the resistance change rate after the reliability test becomes high. It is considered that the phenomenon that the conductive powders in the conductive paste come into contact with or separate from each other due to expansion and contraction of the base material due to thermal stress is remarkable, so that the conduction resistance increases and the resistance change rate increases. Therefore, a conductive paste using only spherical or substantially spherical conductive powder is not preferable in terms of reliability.

On the other hand, when the conductive powder is only in the form of scale, there are disadvantages that the filling rate in the through hole is lower and the viscosity of the conductive paste is higher than that of spherical or substantially spherical conductive powder. Therefore, a conductive paste using only flaky conductive powder is not preferable in terms of conductivity and workability. However, there is an advantage that the rate of change in resistance after a reliability test such as a thermal shock test is low.

The spherical or substantially spherical conductive powder and the flaky conductive powder used in the present invention have the above-mentioned relationship. From such a relationship, the spherical or substantially spherical conductive powder and the flaky conductive powder are used in combination. If this is the case, it is possible to make up for the drawbacks of both conductive powders, and it is possible to obtain a conductive paste that has solved the above drawbacks.

The ratio of the spherical or substantially spherical conductive powder and the scale-like conductive powder is 40:60 to 95: 5, preferably 50:50 to 9 by weight.
When the ratio is 5: 5 and the spherical or substantially spherical conductive powder is less than 40% by weight, the viscosity of the conductive paste is increased, the printing workability is deteriorated, and the spherical or substantially spherical conductive powder is 95% by weight.
If it exceeds, the conductivity tends to vary, and the connection reliability deteriorates.

In the conductive paste, the conductive paste using the flaky conductive powder has a random vertical and horizontal direction, and has a large variation in the through-hole conduction resistance and the resistance change rate after the reliability test. The composite conductive powder obtained by combining the spherical or substantially spherical conductive powder and the flaky conductive powder has a small through-hole conduction resistance and a small rate of change in resistance after a reliability test. That is, it is considered that the scale-like conductive powder is present between the spherical or substantially spherical conductive powders as shown in FIG. 6 even though the orientation is random, thereby improving the conduction resistance and the reliability. In FIG. 6, 11
Is a spherical or substantially spherical conductive powder, and 12 is a scaly conductive powder.

In the present invention, when a silver-coated copper powder or a silver-coated copper alloy powder whose surface is substantially covered with silver by exposing a part of the copper powder or the copper alloy powder is used as the conductive powder, if necessary, Silver powder can be used in combination. When silver powder is used in combination, the ratio is 30: composite conductive powder: silver powder in weight ratio.
A range from 70 to less than 100: more than 0 is preferable, and 50:
More preferably, it is in the range of 50 to less than 100: 0.

As the copper powder or copper alloy powder, powder produced by an atomizing method is preferably used, and the smaller the particle size, the more preferable. For example, a powder having an average particle size of 1 to 20 μm is preferable, and 1 to 10 μm The use of the powder is more preferable because even if the surface is coated with silver and then flattened, it can be easily dispersed uniformly in the conductive powder.

There are methods such as displacement plating, electroplating, and electroless plating for coating the surface of the copper powder or copper alloy powder with silver, and the copper powder or copper alloy powder has high adhesion to silver and running. Since the cost is low, it is preferable to cover with displacement plating. The amount of silver coating on the surface of the copper powder or copper alloy powder is 5 to 25% by weight based on the copper powder or copper alloy powder from the viewpoints of migration resistance, cost, and improvement in conductivity.
Is more preferable, and the range of 10 to 23% by weight is more preferable. Further, the exposed area of the copper powder or copper alloy powder is preferably in the range of 10 to 60%, more preferably 25 to 55%, from the viewpoints of migration property, conductivity and the like.

The substantially spherical conductive powder according to the present invention has an aspect ratio of 1 to 1.5 and an average long particle diameter of 1 to 20.
It is preferable to use conductive powder of μm, and it is more preferable to use conductive powder having an aspect ratio of 1 to 1.3 and a long diameter having an average particle diameter of 1 to 10 μm. The average particle size mentioned above can be measured by a laser scattering type particle size distribution measuring device. In the present invention, the measurement was performed using a master sizer (manufactured by Malvern) as the device.

The aspect ratio in the present invention refers to the ratio of the major axis to the minor axis (major axis / minor axis) of the conductive powder particles. In the present invention, the particles of the conductive powder are mixed well in the curable resin having a low viscosity, and the resin is cured while allowing the particles to settle by standing, and the obtained cured product is cut in the vertical direction. The shape of the particles appearing on the cut surface is observed under magnification with an electron microscope, and the major axis / minor axis of each particle is obtained for at least 100 particles, and the average value thereof is defined as the aspect ratio.

Here, the minor axis is selected so that a particle appearing on the cut surface is sandwiched by a combination of two parallel lines in contact with the outside of the particle, and two of the combinations having the shortest interval are selected. The distance between the parallel lines. On the other hand, the major axis is the two parallel lines perpendicular to the parallel line that determines the minor axis, and is the distance between the two parallel lines that are the longest among the combinations of the two parallel lines that contact the outside of the particle. is there. The rectangle formed by these four lines is sized to fit the particle exactly inside it. The specific method used in the present invention will be described later.

In the present invention, the main component of the binder is preferably a mixture of an epoxy resin, a phenol resin and a curing agent thereof. Epoxy resins have good adhesion to copper foil, but have poorer conductivity than phenolic resins, while phenolic resins have better conductivity, but have poorer adhesion to copper foil than epoxy resins. Therefore, it is preferable to use both resins in combination.

The phenol resin may be a known one such as a novolak type or a resol type, and the mixing ratio of the epoxy resin and the phenol resin is such that the weight ratio of epoxy resin: phenol resin is in the range of 10:90 to 90:10. Preferably
More preferably, it is in the range of 10:90 to 60:40. When the compounding ratio of the epoxy resin is less than 10% by weight, the adhesion to the copper foil tends to decrease, and when the compounding ratio of the epoxy resin exceeds 90% by weight, the conductivity tends to decrease.

The epoxy resin is preferably liquid at room temperature. Those that crystallize at room temperature can avoid crystallization by mixing with a liquid. The epoxy resin that is liquid at ordinary temperature in the present invention includes, for example, a resin that is solid at ordinary temperature and becomes liquid at ordinary temperature by mixing with an epoxy resin that is liquid at ordinary temperature. In the present invention, normal temperature means a temperature of about 25
Means ° C.

As the epoxy resin, a known epoxy resin is used, and a compound containing two or more epoxy groups in the molecular weight, for example, bisphenol A, bisphenol AD, bisphenol F, novolak, cresol novolaks and polychlorophenol obtained by reaction with epichlorohydrin. Glycidyl ether, dihydroxynaphthalenediglycidyl ether,
Aliphatic epoxy resins such as butanediol diglycidyl ether and neopentyl glycol diglycidyl ether; heterocyclic epoxies such as diglycidyl hydantoin; vinylcyclohexene dioxide; dicyclopentanedienedoxide; and alicyclic diepoxy adipate Alicyclic epoxy resins.

If necessary, a flexibility-imparting agent is used.
The flexibility-imparting agent may be a known one, and a compound having only one epoxy group in its molecular weight, for example, n-butyl glycidyl ether, glycidyl versatate, styrene oxide, ethylhexyl glycidyl ether,
Usual epoxy resins such as phenyl glycidyl ether, cresyl glycidyl ether, butyl phenyl glycidyl ether and the like can be mentioned. These epoxy resins and flexibility-imparting agents can be used alone or in combination of two or more.

Examples of the curing agent added to the binder include amines such as mensendiamine, isophoronediamine, metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, methylenedianiline, phthalic anhydride, trimellitic anhydride, Pyromellitic anhydride, succinic anhydride, acid anhydrides such as tetrahydrophthalic anhydride, imidazole, compound-based curing agents such as dicyandiamide, polyamide resins, and resin-based curing agents such as urea resins are used. It may be used in combination with a curing agent such as a latent amine curing agent, and is generally known as a curing accelerator for an epoxy resin and a phenol resin such as a tertiary amine, imidazoles, triphenylphosphine, and tetraphenylphosphenyl borate. Even if the compound is added There.

The content of these curing agents depends on the glass transition point (Tg) of the cured product of the conductive paste.
It is preferably in the range of 0.1 to 20 parts by weight, more preferably 1 to 10 parts by weight, based on 00 parts by weight.

To the binder used in the present invention, a thixo agent, a coupling agent, an antifoaming agent, a powder surface treating agent, an anti-settling agent, etc. are added, if necessary, in addition to the above-mentioned materials, followed by uniform mixing. can get. Thixotropic agents added as needed,
The content of the coupling agent, the defoaming agent, the powder surface treating agent, the anti-settling agent and the like is preferably in the range of 0.01 to 1% by weight based on the conductive paste, and is preferably 0.03 to 0.5% by weight. % Is more preferable.

The mixing ratio of the conductive powder and the binder is such that the conductive powder: binder has a weight ratio of 8 to the solid content of the conductive paste.
It is preferably in the range of 3:17 to 95: 5, and 8
More preferably, it is in the range of 5:15 to 93: 7. When the proportion of the conductive powder is less than 83% by weight, the conductivity tends to decrease, and when the proportion of the conductive powder exceeds 95% by weight, the viscosity, the adhesive strength, and the strength of the conductive paste decrease, and the reliability decreases. Tends to be inferior.

Generally, a conductive paste for filling holes is of a non-solvent type containing no solvent because voids are not preferably generated in through holes. However, the inclusion of a solvent improves conductivity and reduces dispersion. This is preferable because it reduces the number of the components.

The conductive paste containing a solvent has a larger volume reduction than the conductive paste containing no solvent when printed and coated and after heat treatment and hardening, as much as the solvent contains the solvent. . In the heat treatment process, the viscosity of the conductive paste containing the solvent is significantly reduced in the conductive paste containing the solvent, and the conductive powder contained in the conductive paste becomes dense in the conductive layer. Due to these factors, it is considered that the conductive paste containing the solvent has better conductivity and less variation than the conductive paste containing no solvent.

The solvent to be used is preferably a solvent which greatly reduces the viscosity of the conductive paste in the heat treatment. When the evaporation rate of butyl acetate is 100, the evaporation rate of the solvent to be contained is in the range of 28 or less without including 0. , Boiling point 150-26
Solvents in the range of 0 ° C., for example, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol butyl ether, dipropylene glycol isopropyl methyl ether, dipropylene glycol isopropyl ethyl ether, tripropylene glycol methyl ether, propylene glycol tertiary Butyl ether, propylene glycol ethyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether, diethylene glycol methyl ether, triethylene glycol methyl ether, diethylene glycol ethyl ether, ethylene glycol butyl ether, diethylene glycol butyl ether, 3-methyl-3-
Examples include methoxybutanol, 3-methyl-3-methoxybutyl ether, ethyl lactate, butyl lactate and the like.

The solvent to be contained is one kind or, if necessary, two kinds.
A solvent in which at least one kind of solvent is mixed is used, and the content of the solvent is preferably in the range of 1 to 10% by weight, and more preferably in the range of 1.5 to 7.5% by weight based on the conductivity and workability. More preferred.

The conductive paste of the present invention may be used together with the binder, conductive powder and, if necessary, a thixotropic agent, a coupling agent, a defoaming agent, a powder surface treating agent, an anti-settling agent, etc. It can be obtained by uniformly mixing and dispersing with a kneader, three rolls or the like.

[0038]

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

Example 1 Phenol resin (manufactured by Kanebo Co., Ltd., trade name Bellpearl S-8)
90) 40 parts by weight, bisphenol A type epoxy resin (manufactured by Yuka Shell Epoxy Co., Ltd., trade name: Epocoat 82)
7) 60 parts by weight and 2-phenyl-4-methyl-imidazole (Curesol 2P4MZ, manufactured by Shikoku Chemicals) 5
The parts by weight were added and mixed uniformly to obtain a binder. The ratio of the epoxy resin to the phenol resin was 60:40 in the weight ratio of epoxy resin: phenol resin.

Next, spherical copper powder (trade name: SFR-Cu, manufactured by Nippon Atomize Processing Co., Ltd.) having an average particle size of 5.1 μm produced by an atomizing method was washed with dilute hydrochloric acid and pure water. 18% by weight of silver based on spherical copper powder in a plating solution containing 80 g of AgCN and 75 g of NaCN
, And washed with water and dried to obtain silver-plated copper powder (silver-coated copper powder). Five particles of the obtained silver-plated copper powder were taken out and quantitatively analyzed by a scanning Auger electron spectrometer to examine the exposed area of the copper powder.
The average was 21% in the range of 2-28%.

Thereafter, 750 g of the silver-plated copper powder obtained above and 3 kg of zirconia balls having a diameter of 5 mm were put into a 2 liter ball mill container, and the mixture was rotated for 40 minutes. Average particle size is 5.5 μm
Was obtained. On the other hand, 400 g of the silver-plated copper powder obtained above and 3 kg of zirconia balls having a diameter of 10 mm were put into a 2 liter ball mill container, and rotated for 3 hours. A 7.5 μm flaky silver-coated copper powder was obtained.

To 50 g of the binder obtained above, a diameter of 0.1 g was added.
1 kg of 5 mm zirconia balls are put into a ball mill container, and 330 g of the above-mentioned roughly spherical silver-coated copper powder which has been rotated for 2 hours and crushed, and the flakes which have been crushed by the same method as above. 120 g of silver-coated copper powder and 30 parts by weight of 3-methyl-3-methoxybutanol (manufactured by Kuraray Co., Ltd., Solfit) as a solvent were added, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill. A conductive paste was obtained.

The weight ratio of the substantially spherical silver-coated copper powder to the flaky silver-coated copper powder is 73:27 in terms of the weight ratio of approximately spherical silver-coated copper powder: scale-like silver-coated copper powder, and 73:27 for the silver-coated copper powder and silver powder. The weight ratio is 100: 0 of silver-coated copper powder: silver powder, the ratio of conductive powder to binder is 90:10 of conductive powder: binder by weight ratio, and the content of solvent is 5.7 with respect to the conductive paste. % By weight.

Next, using the conductive paste obtained above,
A glass epoxy copper clad laminate having a thickness of 1.0 mm shown in FIG. 7 (manufactured by Hitachi Chemical Co., Ltd., trade name: MCL-E-670)
13, a through hole 14 having a diameter of 0.5 mm was formed, and the through hole 14 was filled with a conductive paste and printed between the through holes 14 to produce a wiring board A.

On the other hand, as shown in FIG. 8, on the surface of the same glass epoxy copper-clad laminate 13 from which the copper foil was removed by etching, a circuit 1 was formed using the conductive paste obtained above.
5, an undercoat material layer 16 is formed thereon using a thermosetting odorless solder resist (manufactured by Taiyo Ink Co., Ltd., trade name: S-40), and a migration-resistant jumper conductive paste is formed on the upper surface thereof. (Hitachi Chemical Industries, Ltd.
A jumper circuit 17 is formed using the trade name MP-200C), and an overcoat material layer 18 is formed on the upper surface of the undercoat material layer 16 and around the jumper circuit 17 using the same solder resist as described above. And a wiring board B crossing the jumper circuit 17 was obtained.

Thereafter, each of the wiring boards A and B was dried at 80 ° C. for 1 hour, and then subjected to a heat treatment at 165 ° C. for 1 hour to obtain wiring boards A ′ and B ′. The initial characteristics of the obtained wiring boards A 'and B' were evaluated. as a result,
The maximum resistance value per through hole in the wiring board A 'was 187 mΩ / hole, the minimum was 169 mΩ / hole, and the average was 172 mΩ / hole. Circuit 15 of wiring board B '
When a voltage of 50 V DC was applied between the circuit and the jumper circuit 17, the insulation resistance was measured and found to be 10 ⁸ Ω or more.

Further, as a result of performing a thermal shock test on wiring board A ', the rate of change in resistance was 67%. On the other hand, as a result of performing a moisture and medium load test on the wiring board B ′, the insulation resistance was 10 ⁸ Ω or more. The thermal shock test condition was 1
100 cycles of 25 ° C. for 30 minutes to −65 ° C. for 30 minutes and a load test under a humidity and humidity condition of 40 ° C. and 90% RH applied a voltage of 50 V DC between the circuit 15 and the jumper circuit 17 for 1000 hours.

The specific method of measuring the aspect ratio in this embodiment is described below. 8 g of a base material (No. 10-8130) of a low-viscosity epoxy resin (manufactured by Buehler) and 2 g of a curing agent (No. 10-8132) are mixed, and 2 g of conductive powder is mixed and dispersed well, and the mixture is left as it is. After defoaming in vacuo at 10 ° C., the particles were allowed to stand at 30 ° C. for 10 hours to settle and harden the particles. Thereafter, the obtained cured product was cut in the vertical direction, the cut surface was magnified 1000 times with an electron microscope, and the long diameter / short diameter of 150 particles that appeared on the cut surface was obtained. Ratio.

Example 2 220 g of substantially spherical silver-coated copper powder obtained by subjecting 60 g of the binder obtained in Example 1 to the pulverization treatment of Example 1 and 220 g of flake-shaped silver-coated copper powder subjected to the pulverization treatment of Example 1 And as a solvent 3-
35 parts by weight of methyl-3-methoxybutanol was added, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste.

The weight ratio of the substantially spherical silver-coated copper powder to the flaky silver-coated copper powder is 50:50, and the ratio of the substantially spherical silver-coated copper powder to the flaky silver-coated copper powder is 50:50. The conductive powder: binder was 88:12 in weight ratio, and the content of the solvent was 6.5% by weight based on the conductive paste.

Next, a wiring board was manufactured through the same steps as in Example 1, and the characteristics of the obtained wiring board were evaluated. As a result, in the wiring board corresponding to FIG.
Maximum resistance per hole is 201 mΩ / hole, minimum is 18
8 mΩ / hole and the average was 195 mΩ / hole. on the other hand,
When a voltage of 50 V DC was applied between the circuit of the wiring board corresponding to FIG. 8 and the jumper circuit, the insulation resistance was measured.
It was ⁸ Ω or more.

Further, as a result of performing a thermal shock test on the wiring board corresponding to FIG. 7 in the same manner as in Example 1, the resistance change rate was 82%. On the other hand, FIG.
As a result of conducting a wet and medium load test of the wiring board corresponding to the above, the insulation resistance was 10 ⁸ Ω or more.

Example 3 50 g of the binder obtained in Example 1 was subjected to the crushing treatment of Example 1 and 270 g of substantially spherical silver-coated copper powder was obtained, and the average particle size was subjected to crushing treatment in the same manner as in Example 1. 180 g of 7.8 μm flaky silver powder (manufactured by DMC Square Japan Co., Ltd., trade name SF-69) and 3-methyl-3 as a solvent
30 parts by weight of -methoxybutanol was added, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste.

The ratio of the substantially spherical silver-coated copper powder to the flaky silver powder is 60:40 for the roughly spherical silver-coated copper powder: scale-like silver powder, and the ratio of the silver-coated copper powder to the silver powder is the weight ratio of silver-coated copper powder. The ratio of the powder: silver powder was 60:40, the ratio of the conductive powder to the binder was 90:10, and the content of the solvent was 5.7% by weight based on the conductive paste.

Next, a wiring board was manufactured through the same steps as in Example 1, and the characteristics of the obtained wiring board were evaluated. as a result,
In the wiring board corresponding to FIG. 7, the maximum resistance value per through hole is 171 mΩ / hole, and the minimum resistance value is 134 m.
Ω / hole and the average was 143 mΩ / hole. On the other hand, FIG.
DC 50 between the circuit of the wiring board and the jumper circuit corresponding to
When a voltage of V was applied and the insulation resistance was measured, it was 10 ⁸ Ω
That was all.

Further, as a result of performing a thermal shock test on the wiring board corresponding to FIG. 7 in the same manner as in Example 1, the resistance change rate was 70%. On the other hand, FIG.
As a result of conducting a wet and medium load test of the wiring board corresponding to the above, the insulation resistance was 10 ⁸ Ω or more.

Comparative Example 1 To 50 g of the binder obtained in Example 1, 450 g of the roughly spherical silver-coated copper powder subjected to the pulverization treatment of Example 1 and 30 parts by weight of 3-methyl-3-methoxybutanol as a solvent were added and stirred. The mixture was uniformly mixed and dispersed with a grinder and a three-roll mill to obtain a conductive paste.

The weight ratio of the substantially spherical silver-coated copper powder to the flaky silver-coated copper powder is 100: 0 in the weight ratio of the substantially spherical silver-coated copper powder: the flaky silver-coated copper powder, and the ratio of the silver-coated copper powder to the silver powder. The ratio was 100: 0 in weight of silver-coated copper powder: silver powder, the ratio of conductive powder to binder was 90:10 in weight ratio of conductive powder: binder, and the content of solvent was 5. 7% by weight.

Next, a wiring board was manufactured through the same steps as in Example 1, and the characteristics of the obtained wiring board were evaluated. As a result, in the wiring board corresponding to FIG.
The maximum resistance per hole is 262 mΩ / hole and the minimum is 17
The dispersion was large at 1 mΩ / hole and the average was 188 mΩ / hole. On the other hand, when a voltage of DC 50 V was applied between the circuit of the wiring board corresponding to FIG. 8 and the jumper circuit, and the insulation resistance was measured, it was 10 ⁸ Ω or more.

Further, as a result of performing a thermal shock test on the wiring board corresponding to FIG. 7 in the same manner as in Example 1, the rate of change in resistance was 587% in 10 cycles, and became unmeasurable in 100 cycles. On the other hand, the wiring board corresponding to FIG. 8 was subjected to a wet and medium load test in the same manner as in Example 1, and as a result, the insulation resistance was 10 ⁸ Ω or more.

Comparative Example 2 To 50 g of the binder obtained in Example 1, 450 g of flaky silver-coated copper powder subjected to the pulverization treatment of Example 1 and 30 parts by weight of 3-methyl-3-methoxybutanol as a solvent were added and stirred. The mixture was uniformly mixed and dispersed with a grinder and a three-roll mill to obtain a conductive paste.

The weight ratio of the substantially spherical silver-coated copper powder to the flaky silver-coated copper powder is 0: 100 for the substantially spherical silver-coated copper powder: scale-like silver-coated copper powder, and 0: 100 for the silver-coated copper powder and the silver powder. The ratio was 100: 0 in weight of silver-coated copper powder: silver powder, the ratio of conductive powder to binder was 90:10 in weight ratio of conductive powder: binder, and the content of solvent was 5. 7% by weight.

Next, a wiring board was manufactured through the same steps as in Example 1, and the characteristics of the obtained wiring board were evaluated. As a result, in the wiring board corresponding to FIG.
The maximum resistance per hole is 279 mΩ / hole and the minimum is 14
The dispersion was large at 6 mΩ / hole and the average was 220 mΩ / hole. On the other hand, when a voltage of DC 50 V was applied between the circuit of the wiring board corresponding to FIG. 8 and the jumper circuit, and the insulation resistance was measured, it was 10 ⁸ Ω or more.

Further, as a result of performing a thermal shock test on the wiring board corresponding to FIG. 7 in the same manner as in Example 1, the rate of change in resistance was 312% at 10 cycles, and became unmeasurable at 100 cycles. On the other hand, the wiring board corresponding to FIG. 8 was subjected to a wet and medium load test in the same manner as in Example 1, and as a result, the insulation resistance was 10 ⁸ Ω or more.

REFERENCE EXAMPLE 1 50 g of the binder obtained in Example 1 was subjected to the crushing treatment of Example 1 and 50 g of substantially spherical silver-coated copper powder, and the average particle size was subjected to crushing treatment in the same manner as in Example 1. 280 g of approximately spherical silver powder (manufactured by DMC Square Japan Co., Ltd., trade name: SFC20-ED) having a particle size of 4.2 μm, 120 g of flaky silver powder used in Example 3 which had not been pulverized, and 3 as a solvent.
-Methyl-3-methoxybutanol (30 parts by weight) was added, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste.

The ratio of the substantially spherical silver-coated copper powder and the ratio of the substantially spherical silver powder to the flaky silver powder is 73:27 by weight, and the ratio of the substantially spherical silver-coated copper powder to the flaky silver powder is 73:27. The weight ratio of silver-coated copper powder: silver powder is 11:89, the ratio of conductive powder to binder is 90:10 by weight of conductive powder: binder, and the content of solvent is 5.7% by weight of the conductive paste. %Met.

Next, a wiring board was manufactured through the same steps as in Example 1, and the characteristics of the obtained wiring board were evaluated. As a result, in the wiring board corresponding to FIG.
The maximum resistance value per hole is 117 mΩ / hole, and the minimum value is 10
The average was 2 mΩ / hole and the average was 109 mΩ / hole. on the other hand,
When a voltage of 50 V DC was applied between the circuit of the wiring board corresponding to FIG. 8 and the jumper circuit, the insulation resistance was measured.
It was ⁸ Ω or more.

A wiring board corresponding to FIG. 7 was subjected to a thermal shock test in the same manner as in Example 1, and as a result, the rate of change in resistance was 66%. On the other hand, FIG.
As a result of performing a moisture load test on a wiring board corresponding to
Migration occurred in 9 hours.

[0069]

The conductive paste according to the first aspect has excellent conductivity, workability and reliability. The conductive paste according to claim 2 has the effect of the conductive paste according to claim 1,
Furthermore, it is excellent in migration property and reliability. The conductive paste according to the third aspect has the effects of the conductive paste according to the first or second aspect, and is particularly excellent in improving the conductivity.
The conductive paste according to the fourth aspect has the effects of the conductive paste according to the first, second, or third aspect, and is particularly excellent in improving the conductivity and reliability. The conductive paste according to claim 5,
The effect of the conductive paste according to the first, second, third or fourth aspect is exhibited, and particularly, the effect of improving conductivity and workability is excellent.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which through holes are connected by a conductive paste.

FIG. 2 is a cross-sectional view showing a state in which through holes are connected by copper plating.

FIG. 3 is a sectional view of a multilayer wiring board.

FIG. 4 is a cross-sectional view showing a state in which a lid plating is applied to a conductive paste filling a through hole.

FIG. 5 is a cross-sectional view showing a state in which the through holes are connected by plating and a resin is embedded in the voids of the through holes.

FIG. 6 is a schematic diagram showing a state of contact between a spherical or substantially spherical conductive powder and a flaky conductive powder in a through hole.

FIG. 7 is a plan view of the wiring board showing a state where conductive paste is filled in through holes formed in the glass epoxy copper clad laminate and printed and connected between the through holes.

FIG. 8: A circuit is formed using a conductive paste on a glass epoxy copper-clad laminate, and an undercoat material layer is formed on the upper surface of the circuit.
It is sectional drawing of the wiring board which shows the state in which the jumper circuit and the overcoat material layer were formed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conductive paste 2 Copper plating 3 Base material 4 Conductive paste 5 Copper foil 6 Insulating layer 7 Jumper conductive paste 8 Overcoat layer 9 Lid plating 10 Resin 11 Spherical or substantially spherical conductive powder 12 Scaly conductive powder 13 Glass epoxy copper clad laminate 14 through hole 15 circuit 16 undercoat material layer 17 jumper circuit 18 overcoat material layer

Claims (5)

[Claims] 1. A conductive paste containing a conductive powder, a binder, and a solvent, wherein the conductive powder contains a pulverized spherical or substantially spherical conductive powder and a pulverized flaky conductive powder, and the pulverized spherical or substantially spherical powder. A conductive paste in which the ratio of the spherical conductive powder to the flaked conductive powder is 40:60 to 95: 5 by weight in a ratio of spherical or substantially spherical conductive powder: scale conductive powder. 2. A silver-coated copper powder, wherein the pulverized spherical or substantially spherical conductive powder and the pulverized flaky conductive powder expose a part of the copper powder or the copper alloy powder and have a surface substantially coated with silver. The conductive paste according to claim 1, which is a powder or a silver-coated copper alloy powder. 3. The main component of the binder includes an epoxy resin, a phenolic resin and a curing agent thereof, and the ratio of the epoxy resin to the phenolic resin is 10:90 to 90:10 by weight in a ratio of epoxy resin: phenolic resin. Item 1 or 2
The conductive paste as described in the above. 4. The conductive paste according to claim 1, wherein the ratio of the conductive powder to the binder is 83:17 to 95: 5 by weight in a ratio of conductive powder: binder. 5. The conductive paste according to claim 1, wherein the solvent is one or a mixture of two or more solvents, and the content of the solvent is 2 to 10% by weight based on the conductive paste.