JP2001266644A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and highly conductive paste to be filled into a through hole or non-through hole for the connection between layers. SOLUTION: The paste includes a binder, conductive powders and a solvent. The evaporation rate of the solvent is 30 or less, and the boiling point of the solvent is in the range from 150 to 260 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste for embedding in a through-hole or a non-through-hole for interlayer connection of a build-up multilayer printed wiring board or the like.

[0002]

2. Description of the Related Art In a conventional multilayer printed wiring board, a through-hole or a non-through-hole for interlayer connection is formed in a multilayer board manufactured through a multi-layer lamination process by heating and pressing, and then plating is performed on the hole. It is manufactured by printing or embedding a conductive paste as shown in FIG. In FIG. 1, 1
Is a conductive paste and 2 is a copper foil.

[0003] Generally, it is preferable that the hole-filling conductive paste generate a gap between the wall surface of the hole and the paste due to a decrease in volume during the drying and curing processes, and the generation of voids due to gas generated by drying of the solvent or curing of the resin. Therefore, a conductive paste containing no solvent and containing an epoxy resin as a main component has been used.

[0004] However, compared with phenolic resins and the like, epoxy resins have a small amount of heat-induced shrinkage, and thus have the drawback that the resistance of the conductive paste containing epoxy resin as a main component is not easily reduced. To lower the resistance,
If the proportion of the conductive powder in the conductive paste is increased or a highly conductive metal powder such as silver is used, the disadvantage can be compensated for, but the conductive paste also becomes expensive.

[0005]

An object of the present invention is to provide a conductive paste which is inexpensive and has excellent conductivity. The inventions according to claims 2, 3, 4, 5, and 6 provide a conductive paste having an excellent effect of improving conductivity.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a conductive paste containing a binder, conductive powder and a solvent having an evaporation rate of 30 or less (excluding 0). Further, the present invention relates to a conductive paste in which the solvent has a boiling point of 150 to 260 ° C. Further, the present invention relates to a conductive paste in which the solvent is one kind or a mixed solvent of two or more kinds.

[0007] The present invention also relates to a conductive paste containing a solvent in an amount of 2 to 10% by weight based on the conductive paste. Further, the present invention relates to a conductive paste comprising a binder containing an epoxy resin composition and a curing agent thereof. Further, in the present invention, the mixing ratio of the binder and the conductive powder is such that the binder is 5 to 15 with respect to the solid content of the conductive paste.
% Of the conductive paste and 85 to 95% by weight of the conductive powder.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, a solvent-free conductive paste containing no solvent is used as a conductive paste for filling holes. By including a solvent, conductivity is improved and variation is reduced. The conductive paste containing a solvent has a larger volume reduction than the conductive paste not containing a solvent when printed and applied and after being cured by heat treatment by the amount of 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 a solvent has better conductivity and less variation than the conductive paste containing no solvent. The solvent is preferably a solvent having a large decrease in the viscosity of the conductive paste at the time of heat treatment. Conversely, a solvent having a high drying property, drying of the solvent at the time of heat treatment progressing, and a small decrease in the viscosity of the conductive paste is not preferred.

For the above reasons, it is necessary to use a solvent having an evaporation rate of 30 or less, preferably 28 or less, more preferably 25 or less (both not including 0) as the solvent used in the present invention. When a solvent exceeding 30 is used, since the drying of the solvent during the printing and the heat treatment process of the conductive paste is fast, the decrease in the viscosity of the conductive paste is small. Therefore, the conductive powder does not become dense in the conductor layer, and the conductivity after the heat treatment is reduced, and the dispersion is increased. In the present invention, the evaporation rate means that the temperature is 25 ° C and the relative humidity is 5 ° C.
The relative speed is shown assuming that the weight loss of butyl acetate per unit time under the condition of 5% RH is 100.

The evaporation rate is determined by dropping 10 g of the solvent used in the present invention into a glass Petri dish having a diameter of 90 mm, leaving it for 1 hour in an atmosphere at normal temperature and normal pressure, and letting the amount of dry weight of the solvent after 1 hour be A, Also, 10 g of butyl acetate was dropped on a glass Petri dish having a diameter of 90 mm in the same manner as described above, and left for 1 hour in an atmosphere at normal temperature and normal pressure. be able to.

[0012]

(Equation 1)

The boiling point of the solvent is preferably from 150 to 260 ° C., more preferably from 170 to 240 ° C., from the viewpoint of lowering the viscosity of the conductive paste.

Examples of the solvent suitable for the above conditions include dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol butyl ether, dipropylene glycol isopropyl methyl ether, dipropylene glycol isopropyl ethyl ether, and tripropylene glycol methyl ether. , Propylene glycol tert-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-methoxybutanol, 3-
Examples thereof include methyl-3-methoxybutyl ether, ethyl lactate, and butyl lactate.

As the solvent described above, one kind or a mixture of two or more kinds of solvents as required is used. The content of the solvent is preferably in the range of 2 to 10% by weight with respect to the conductive paste from the viewpoint of conductivity and filling and filling of holes.
More preferably, it is in the range of 2 to 7.5% by weight.

The binder used in the present invention contains an epoxy resin composition and its curing agent. Also,
As the epoxy resin composition, a composition containing an epoxy resin and a flexibility-imparting agent is used. The epoxy resin is preferably liquid at room temperature. What crystallizes at room temperature
Crystallization can be avoided by mixing with a liquid material.

The epoxy resin which is liquid at ordinary temperature in the present invention includes, for example, those which are solid at ordinary temperature and which become stable at ordinary temperature when mixed with epoxy resin which is liquid at ordinary temperature. In the present invention, the normal temperature means a temperature of about 25 ° C.
Means the following.

As the epoxy resin used in the present invention, 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 epichlorohydrin is used. Polyglycidyl ether obtained by the reaction, dihydroxynaphthalenediglycidyl ether, butanediol diglycidyl ether, heterocyclic epoxy such as diglycidyl hydantoin and aliphatic epoxy resin such as neopentyl glycol diglycidyl ether, vinyl cyclohexene dioxide,
Alicyclic epoxy resins such as dicyclopentanedienedoxide and alicyclic diepoxy adipate are exemplified.

As the flexibility-imparting agent, known ones are used, and compounds having only one epoxy group in the molecular weight, for example, n
And ordinary epoxy resins such as butyl glycidyl ether, versidic acid glycidyl ester, styrene oxide, ethylhexyl glycidyl ether, phenyl glycidyl ether, cresyl glycidyl ether, butylphenyl glycidyl ether and the like. These epoxy resins and flexibility imparting agents may be used alone or
A mixture of more than one species can be used.

Examples of the curing agent to be added to the binder include amines such as mensendiamine, isophoronediamine, metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, methylenedianiline, phthalic anhydride, trimellitic anhydride, and the like. Pyromellitic anhydride, succinic anhydride, acid anhydrides such as tetrahydrophthalic anhydride, compound-based curing agents such as imidazole and dicyandiamide, and resin-based curing agents such as polyamide resins, phenol resins, and urea resins are used. Accordingly, it may be used in combination with a curing agent such as a latent amine curing agent, and generally, a tertiary amine, imidazoles, triphenyl phosphine, tetraphenyl phosphenyl borate, and the like are generally used in combination with an epoxy resin and a phenolic curing agent. Known as a curing accelerator The compound may be added.

The content of these curing agents may be in the range of 0.1 to 20 parts by weight based on 100 parts by weight of the epoxy resin in terms of the glass transition point (hereinafter referred to as Tg) of the cured conductive paste. Preferably, it is more preferably in the range of 1 to 10 parts by weight.

To the binder used in the present invention, a thixo agent, a coupling agent, a defoaming 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.

As the conductive powder, silver powder, copper powder or copper alloy powder is used, and the smaller the particle size, the better. For example, a powder having an average particle size of 1 to 20 μm, preferably 1 to 10 μm is preferable. If the conductive powder has few contact points, the resistance tends to increase. In order to obtain high conductivity by increasing the contact area between the conductive particles, it is preferable to apply a shock to the conductive powder to deform the shape of the particles into a flat shape, but the conductive paste using flat conductive is substantially spherical conductive. The viscosity is higher than that of the conductive paste using powder, and the embedding work becomes difficult. A conductive paste using a substantially spherical conductive powder is more preferable in terms of workability and conductivity in the Y-axis direction of the hole when the conductive paste is embedded in the hole.

The substantially spherical conductive powder of 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 contacting 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.

The mixing ratio of the binder and the conductive powder is preferably in the range of 5 to 15% by weight of the binder and 85 to 95% by weight of the solid content of the conductive paste, and 7 to 14% by weight of the binder and the conductive powder. More preferably, the powder is in the range of 86 to 93 wt%. When the conductive powder is less than 85% by weight, the conductivity tends to decrease, and when the conductive powder exceeds 95% by weight, the adhesive strength and the strength of the conductive paste tend to decrease.

The conductive paste according to the present invention is prepared by uniformly mixing the above-mentioned materials such as the binder, the conductive powder, and the solvent having an evaporation rate of 30 or less (excluding 0) by using a grinder, kneader, three rolls or the like. Mixed and dispersed.

[0029]

The present invention will be described below with reference to examples. Example 1 Bisphenol A type epoxy resin (oiled shell epoxy)
80 parts by weight of an aliphatic diglycidyl ether (trade name: EDOPAT 827, manufactured by Asahi Denka Kogyo KK)
-503) 8 parts by weight, 2-phenyl-4-methyl-5-
8 parts by weight of hydroxymethylimidazole (trade name: Curesol 2P4MHZ, manufactured by Shikoku Chemicals Co., Ltd.) and 4 parts by weight of dicyandiamide were added and uniformly mixed to obtain a binder.

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, and then washed per liter of water. Substitution plating was performed using a plating solution containing 80 g of AgCN and 75 g of NaCN so that the amount of silver was 18% by weight with respect to the spherical copper powder, washed with water and dried to obtain a silver-plated copper powder.

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. 5.5μ average particle size
m of substantially spherical silver-plated copper powder was obtained. 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 copper.
The average was 20% in the range of 0-50%.

To 65 g of the binder obtained above, 450 g of the substantially spherical silver-plated copper powder obtained above and 25 g of diethylene glycol ethyl ether having an evaporation rate of 0.7 and a boiling point of 202 ° C. as a solvent were added. The conductive paste was obtained by uniformly mixing and dispersing with a three-roll mill. In addition,
The content of the solvent (diethylene glycol ethyl ether) was 4.6% by weight based on the conductive paste, and the mixing ratio of the binder and the conductive powder (substantially spherical silver-plated copper powder) was 12.6% by weight of the binder and the conductive powder. Was 87.4% by weight.

Next, using the conductive paste obtained above, a test pattern 3 shown in FIG. 2 was printed on a polyethylene terephthalate film which had been preshrinked at 168 ° C. in advance, and was further heated at 80 ° C. for one hour in air. 1 at 165 ° C
Heat treatment was performed for a time to obtain a wiring board. As a result of evaluating the characteristics of the obtained wiring board, the maximum specific resistance of the conductor was 47 μΩ ·
m, the minimum value was 35 μΩ · m, and the average value was 39 μΩ · m.

The specific method of measuring the aspect ratio in this embodiment will be 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 To 50 g of the binder obtained in Example 1 was added 450 g of the substantially spherical silver-plated copper powder obtained in Example 1 and 3-methyl-3-methoxybutanol having an evaporation rate of 7 and a boiling point of 174 ° C. as a solvent. 35 g was added, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste. The solvent (3
-Methyl-3-methoxybutanol) was 6.5% by weight with respect to the conductive paste, and the mixing ratio of the binder and the conductive powder (substantially spherical silver-plated copper powder) was 10% for the binder.
% By weight and 90% by weight of conductive powder.

Next, as a result of fabricating a wiring board through the same steps as in Example 1 and evaluating the characteristics, the maximum specific resistance of the conductor was 6%.
2μΩ ・ m, minimum value is 49μΩ ・ m and average value is 57μ
Ω · m.

Example 3 To 50 g of the binder obtained in Example 1 was added 450 g of the substantially spherical silver-plated copper powder obtained in Example 1, and the evaporation rate was 25 as a solvent.
Propylene glycol tertiary with a boiling point of 151 ° C
37 g of butyl ether was added, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste.
The content of the solvent (propylene glycol tertiary butyl ether) was 6.9% by weight with respect to the conductive paste, and the mixing ratio of the binder and the conductive powder (substantially spherical silver-plated copper powder) was 10% by weight of the binder. And 90% by weight of conductive powder.

Next, a wiring board was manufactured through the same steps as in Example 1 and the characteristics were evaluated. As a result, the maximum specific resistance of the conductor was 7%.
2μΩ ・ m, minimum value is 44μΩ ・ m and average value is 63μ
Ω · m.

Comparative Example 1 450 g of the substantially spherical silver-plated copper powder obtained in Example 1 was added to 65 g of the binder obtained in Example 1, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill. A paste was obtained. The mixing ratio of the binder and the conductive powder (substantially spherical silver-plated copper powder) was 12.6% by weight for the binder and 8 for the conductive powder.
It was 7.4% by weight.

Next, as a result of fabricating a wiring board through the same steps as in Example 1 and evaluating the characteristics, the specific resistance of the conductor has a large variation and the maximum value is 178 μΩ · m and the minimum value is 88 μΩ · m.
And the average value was 149 μΩ · m.

COMPARATIVE EXAMPLE 2 450 g of the substantially spherical silver-plated copper powder obtained in Example 1 and a solvent having an evaporation rate of 46 g were added to 65 g of the binder obtained in Example 1.
Then, 25 g of propylene glycol methyl ether acetate having a boiling point of 146 ° C. was added, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste. The content of the solvent (propylene glycol methyl ether acetate) was 4.6% by weight based on the conductive paste.
The mixing ratio of the binder and the conductive powder (substantially spherical silver-plated copper powder) was 12.6% by weight for the binder and 87.4% for the conductive powder.
% By weight.

Next, as a result of fabricating a wiring board through the same steps as in Example 1 and evaluating the characteristics, the specific resistance of the conductor has a large variation and the maximum value is 211 μΩ · m, and the minimum value is 125 μΩ · m.
m and the average value were 170 μΩ · m.

Comparative Example 3 450 g of the substantially spherical silver-plated copper powder obtained in Example 1 and a solvent having an evaporation rate of 32 g were added to 50 g of the binder obtained in Example 1.
Then, 25 g of ethylene glycol ethyl ether having a boiling point of 135 ° C. was added, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste. The content of the solvent (ethylene glycol ethyl ether) was 4.6% by weight with respect to the conductive paste, and the mixing ratio of the binder and the conductive powder (substantially spherical silver-plated copper powder) was 12.6 in the binder.
% By weight and 87.4% by weight of conductive powder.

Next, as a result of fabricating a wiring board through the same steps as in Example 1 and evaluating the characteristics, the specific resistance of the conductor has a large variation and the maximum value is 181 μΩ · m and the minimum value is 95 μΩ · m.
And the average value was 154 μΩ · m.

[0045]

The conductive paste according to claim 1 is inexpensive and has excellent conductivity. The conductive paste according to claims 2, 3, 4, 5, and 6 is excellent in the effect of improving conductivity.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which through holes for interlayer connection of a multilayer printed wiring board are connected by a conductive paste.

FIG. 2 is a plan view showing a state where a test pattern is printed on a polyethylene terephthalate film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conductive paste 2 Copper foil 3 Test pattern 4 Polyethylene terephthalate film

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4E351 BB31 EE16 GG16 4J038 DA002 DA142 DB031 DB071 DB081 DB261 DH002 HA066 JA18 JA26 JA35 JA56 JB04 JB07 JB14 JB32 KA03 KA12 KA20 LA03 MA06 MA09 NA20 PA19 PB12 BB19 BB19 BB19 5G301 DA03 DA06 DA57 DD01

Claims (6)

[Claims] 1. A conductive paste comprising a binder, conductive powder and a solvent having an evaporation rate of 30 or less (excluding 0). 2. The conductive paste according to claim 1, wherein the solvent has a boiling point of 150 to 260 ° C. 3. The conductive paste according to claim 1, wherein the solvent is one kind or a mixed solvent of two or more kinds. 4. The solvent is used in an amount of 2 to 10 with respect to the conductive paste.
4. The conductive paste according to claim 1, wherein the conductive paste is contained by weight. 5. The conductive paste according to claim 1, wherein the binder comprises an epoxy resin composition and a curing agent thereof. 6. The compounding ratio of the binder and the conductive powder is 5 to 15% by weight of the binder and 85 to 95% by weight of the conductive powder based on the solid content of the conductive paste.
Or the conductive paste according to 5.