JPH11209662A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a conductive paste excellent in electric conductivity, printabilty, migration resistance, etc., by specifying the compounding ratio of a conductive powder to a binder, using no solvent, and imparting a specified viscosity to the same. SOLUTION: The compounding ratio of a conductive powder to a binder is pref. (75:25)-(90-10), and the paste does not contain a solvent and has a viscosity prf. of 10-150 Pa.s. The conductive powder is pref. a copper powder or copper alloy powder of which 10-50% of the surface is exposed and almost all the surface is covered with 5-25 wt.% silver and which is in the form of flakes having an aspect ratio of 3-20 and an average length of 5-30 μm. Pref., the binder comprises a compsn. cosisting of an epoxy resin liq. or solid at normal temp. and a diluent in a wt. ratio of (50:50)-(70:30) and a curig agent therefor.

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 multilayer printed wiring board.

[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 on a multilayer substrate manufactured through a multi-layer lamination process by pressurizing and heating, and plating is performed on the hole. Or by printing or embedding a conductive paste.

Conventional conductive pastes include electronic materials, 199
As described in the October, 4th issue, paragraphs 42-46,
It has been prepared by using a conductive powder of gold, silver, copper, carbon or the like, adding a binder, an organic solvent, and an additive as needed, and mixing them into a paste. Particularly in a field where high conductivity is required, gold powder or silver powder is generally used. A conductive paste containing silver powder is used for forming an electric circuit or an electrode of a printed wiring board, an electronic component, etc. because of its good conductivity, but when an electric field is applied in an atmosphere of high temperature and high humidity. Further, there is a disadvantage that silver deposition called migration occurs in an electric circuit or an electrode and a short circuit occurs between the electrodes or between the wirings. Several measures have been taken to prevent this migration, and measures such as applying a moisture-proof paint to the surface of the conductor or adding a corrosion inhibitor such as a nitrogen-containing compound to the conductive paste have been studied. It was not enough effect.

Also, in order to obtain a conductor having good conduction resistance, the amount of silver powder must be increased, and the silver paste is expensive, so that the conductive paste becomes expensive. The use of silver-coated copper powder can improve migration, and the use of silver-coated copper powder results in an inexpensive conductive paste. However, if the silver coating is uniformly and thickly coated, there is no effect of improving migration. In addition, plating is an inexpensive method of coating. For example, silver plating of spherical or substantially spherical copper powder can be easily performed with less aggregation, but the conductive paste using this has a drawback that resistance is high. was there. In order to obtain a conductor having good conduction resistance using the silver-plated copper powder as described above, flat copper powder may be used. However, since this flat copper powder is expensive, the conductive paste is also expensive. There were drawbacks.

[0005]

SUMMARY OF THE INVENTION The first aspect of the present invention provides a conductive paste having excellent conductivity and printability. The invention according to claim 2 provides a conductive paste which is particularly excellent in the effect of improving conductivity among the migration resistance and the invention according to claim 1. The third and fourth aspects of the present invention provide a conductive paste having an excellent effect of improving conductivity and printability.

[0006]

According to the present invention, in a conductive paste containing a conductive powder and a binder, the mixing ratio of the conductive powder and the binder is 75% by weight of the conductive powder: binder relative to the solid content of the conductive paste. : 25 to 90:10,
The present invention relates to a conductive paste containing no solvent having a viscosity of 10 to 150 Pa · s. Further, according to the present invention, the conductive powder exposes a part of the copper powder or the copper alloy powder and the surface is generally covered with silver,
The present invention relates to a solvent-free conductive paste having a flat shape.

[0007] The present invention also relates to a conductive paste containing no solvent, the binder comprising an epoxy resin composition and a curing agent thereof. Further, the present invention provides an epoxy resin composition, which comprises a liquid epoxy resin at room temperature or an epoxy resin solid at room temperature and a reactive diluent, and the mixing ratio of the epoxy resin and the reactive diluent is epoxy by weight. Resin: relates to a solvent-free conductive paste having a reactive diluent of 50:50 to 70:30.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Copper powder or copper alloy powder is easy to handle in a spherical or substantially spherical shape. For example, it is preferable to use a powder produced by an atomizing method. The smaller the particle size is, the more preferable it is. It is preferable to use a powder having a diameter of 1 to 20 μm, preferably 1 to 10 μm, because even if the surface is coated with silver and then flattened, it is easily dispersed uniformly in the composite conductive powder.

To cover the surface of copper powder or copper alloy powder with silver, there are methods such as displacement plating, electroplating, and electroless plating. However, since the plating is easy and the running cost is inexpensive, replacement is difficult. It is preferable to coat by a plating method. The coating amount of silver on the surface of the copper powder or the copper alloy powder is preferably in the range of 5 to 25% by weight based on the copper powder or the copper alloy powder from the viewpoint of migration resistance, cost, improvement in conductivity, and the like.
The range of 10 to 23% by weight is more preferable.

The conductive powder used in the present invention is a silver-coated copper powder or a silver-coated copper alloy powder in which a part of the above-mentioned copper powder or copper alloy powder is exposed and the surface is substantially covered with silver. Yes,
If a copper powder or a copper alloy powder whose entire surface is coated with silver without exposing a part thereof is used, migration of silver is likely to occur, and the object of the present invention cannot be achieved. The exposed area of the copper powder or copper alloy powder is preferably in the range of 10 to 50%, more preferably 10 to 30%, in order to obtain good conductivity. As the above copper alloy powder, for example, it is preferable to use an alloy of copper and tin, copper and zinc, or the like.

The mixing ratio of the conductive powder and the binder is such that the conductive powder: binder is 7% by weight based on the solid content of the conductive paste.
5:25 to 90:10, preferably 77.5: 22.5
When the amount of the conductive powder is less than 75 and the binder exceeds 25, the conductivity is reduced.
If the ratio is more than 0 and the solventless binder is less than 10, the printability deteriorates, and defects such as blurring and voids are easily generated inside the through holes.

The viscosity is preferably from 10 to 150 Pa · s, more preferably from 30 to 90 Pa · s. If the viscosity is less than 10 Pa · s, bleeding is likely to occur,
If it exceeds 50 Pa · s, voids are liable to occur inside the through holes and through holes. The viscosity can be adjusted by adding a reactive diluent or changing the mixing ratio of the epoxy resin.

In the present invention, when the conductive powder is spherical, the resistance tends to be high because the number of contact points is small. Therefore, it is preferable to apply an impact to the conductive powder to deform the shape of the particles into a flat shape. Specifically, it can be deformed by a method such as a ball mill and a vibration mill. The flat conductive powder in the present invention is a conductive powder composed of fine particles that are substantially flat in shape and include, for example, flat conductive powder. As the flat conductive powder, the aspect ratio is 3 to 20 and the average diameter of the major axis is 5 to 5.
It is preferable to use conductive powder having a thickness of 30 μm, and it is more preferable to use conductive powder having an aspect ratio of 5 to 15 and a long diameter having an average particle diameter of 5 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, for a particle appearing on the cut surface, a combination of two parallel lines that are in contact with the outside of the particle is selected so as to sandwich the particle, and two parallel lines that become the shortest interval among those combinations Is the distance. 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 conductive paste contains a binder in addition to the conductive powder. As the binder in the present invention, it is preferable to use a binder containing, for example, an epoxy resin and a curing agent thereof. 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 which is liquid at room temperature in the present invention includes, for example, a resin which is solid at room temperature and which becomes a liquid epoxy resin stably at room temperature by being mixed with the epoxy resin which is liquid at room temperature. In the present invention, the normal temperature means a temperature of about 25 ° C.

As the epoxy resin used in the present invention, known resins are used, and compounds having two or more epoxy groups in the molecular weight, for example, bisphenol A, bisphenol A
Aliphatic epoxy resins such as polyglycidyl ether, dihydroxynaphthalenediglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and diglycidyl hydantoin obtained by reacting D, bisphenol F, novolak, cresol novolaks with epichlorohydrin; Alicyclic epoxy resins such as vinylcyclohexene dioxide, dicyclopentadiene dioxide, alicyclic diepoxy-adipate or low molecular weight compounds having only one epoxy group, e.g. n-butyl Glycidyl ether, glycidyl versatate, styrene oxide, ethylhexyl glycidyl ether, phenyl glycidyl ether, cresyl glycidyl Ether, there is an epoxy resin used as an ordinary epoxy resin reactive diluents such as butyl phenyl glycidyl ether, these epoxy resins may be used alone or in combination.

The epoxy resin composition contains a liquid epoxy resin at room temperature or an epoxy resin solid at room temperature and a reactive diluent. When a solid epoxy resin is used, a reactive diluent is added. The mixing ratio of the resin and the reactive diluent is preferably from 50:50 to 70:30 by weight of epoxy resin: reactive diluent,
The ratio is more preferably from 5:35 to 55:45. If the epoxy resin is less than 50 and the reactive diluent exceeds 50, the conductivity tends to decrease.
If the reactive diluent exceeds 30 and the reactive diluent is less than 30, printability tends to decrease, and blurring and voids tend to occur easily in the through holes.

Examples of the curing agent added to the binder include amines such as mensendiamine, isophoronediamine, metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, methylenedianiline, phthalic anhydride, trimellitic anhydride, Acid anhydrides such as pyromellitic anhydride, succinic anhydride, and 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 or the like, and generally an epoxy resin such as a tertiary amine, imidazoles, triphenylphosphine, tetraphenylphosphine tetraphenylborate or the like and a phenol-based curing agent. As a curing accelerator for The known compounds may be added. The content of these curing agents depends on the binder 1 in terms of workability.
It is preferably in the range of 0.01 to 2 parts by weight, more preferably 0.05 to 1.5 parts by weight, based on 00 parts by weight.

Further, the conductive paste is obtained by adding a thixotropic agent, a coupling agent, a defoaming agent, a powder surface treating agent, an anti-settling agent and the like, as required, in addition to the above-mentioned materials, and uniformly mixing them. When a solvent is contained in these materials, they are used after performing a solvent removal treatment. The content of the thixotropic agent, the coupling agent, the defoaming agent, the powder surface treating agent, the anti-settling agent and the like added as necessary may be in the range of 0.01 to 1% by weight based on the conductive paste. Preferably
More preferably, it is in the range of 0.03 to 0.5% by weight.

The conductive paste of the present invention comprises the above conductive powder,
Thickener, coupling agent, defoaming agent, powder surface treating agent, anti-settling agent, etc. added together with binder and thixo agent if necessary
Can be obtained in a dispersed manner.

[0021]

Embodiments of the present invention will be described below. Example 1 Bisphenol A type epoxy resin (oiled shell epoxy)
58 parts by weight, manufactured by Asahi Denka Kogyo Co., Ltd., trade name: ED
-503) 42 parts by weight, 2-ethyl-4-methylimidazole (manufactured by Shikoku Chemicals Co., Ltd., trade name: Curesol 2E4M)
HZ) 6 parts by weight and dicyandiamide 4 parts by weight were added and uniformly mixed to obtain a binder.

Next, spherical copper powder (trade name: SF-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 with water 1
Substitution plating was performed with a plating solution containing 80 g of AgCN and 75 g of NaCN per liter 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 rotated for 10 hours to deform the shape. A flat silver-plated copper powder having an average particle diameter of No. 5 and a major axis of 7.1 μm 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 30% in the range of 10 to 50%. 110 g of the above-obtained binder was added with 470 g of the flat silver-plated copper powder described above, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste containing a solvent having a viscosity of 65 Pa · s. . The mixing ratio of the conductive powder and the binder is such that the weight ratio of the conductive powder to the solid content of the conductive paste is:
The binder was 81:19. The viscometer used for the viscosity measurement was an HBT type manufactured by Brookfield, and the measurement was performed with the temperature in the small chamber set to 25 ° C. (The same method was used for the following Examples and Comparative Examples). .

Next, using the conductive paste obtained above, the copper foil of a 1.0 mm thick glass epoxy copper clad laminate (manufactured by Hitachi Chemical Co., Ltd., trade name: MCL-E-670) was etched. The test pattern 1 shown in FIG. 1 was printed on the removed surface. In FIG. 1, reference numeral 2 denotes a glass epoxy copper clad laminate. Further, as shown in FIG. 2, a through hole 3 having a diameter of 0.3 mm is formed in the above-mentioned glass epoxy copper clad laminate 2, and the through hole 3 is filled with a conductive paste and printed between the through holes 3 for connection. 3. A comb-shaped test pattern 4 having a width between electrodes of 1.2 mm as shown in FIG. The copper foil 5 of the epoxy copper-clad laminate 2 was replaced with the copper foil 5 shown in FIGS.
5 and partially etched to a thickness of 50 as shown in FIGS. 5 (a) and 5 (b).
μm epoxy resin film (trade name: AS3000, manufactured by Hitachi Chemical Co., Ltd.) 6
Heat and pressure were applied under the conditions of MPa, and a test pattern 7 was printed on the upper surface.

Thereafter, the printed test patterns different from each other were left at 25 ° C. for 10 minutes, and then subjected to a heat treatment at 155 ° C. for 45 minutes to obtain a wiring board. As a result of evaluating the characteristics of the obtained wiring board, the specific resistance of the conductor was 2.7 mΩ · cm and the resistance value per hole of the through hole was 0.3 Ω / hole, and voids were found inside the through hole. Did not. The insulation resistance of the wiring board obtained from FIGS. 3 and 5A and 5B is 10%.
It was ⁸ Ω or more.

Further, FIGS. 3 and 5 (a) and 5 (b)
The wiring board obtained from the above was subjected to a moisture and medium load test for 2000 hours, and as a result, the insulation resistance was 10 ⁸ Ω or more. The wet load test was performed at 40 ° C. and 90% RH by applying a DC voltage of 50 V between adjacent lines (the same method was applied to the following Examples and Comparative Examples).

The specific method of measuring the aspect ratio in this embodiment is described below. 8 g of the 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 vacuum degassing at 30 ° 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 Bisphenol A type epoxy resin 61 used in Example 1
Parts by weight, 39 parts by weight of the aliphatic diglycidyl ether used in Example 1, 2-phenyl-4-methylimidazole 6
Parts by weight and 4 parts by weight of dicyandiamide were added and uniformly mixed to obtain a binder. Next, 750 g of the silver-plated copper powder obtained in Example 1 was rotated by a ball mill for 15 hours in the same manner as in Example 1 to deform the shape, and the average aspect ratio was 4.4 and the average particle diameter of the major axis was 8.8. 6 μm flat silver-plated copper powder was obtained. 5 particles of the obtained flat silver-plated copper powder
The individual pieces were taken out and quantitatively analyzed by a scanning Auger electron spectrometer to examine the exposed area of the copper powder.
In the range of%, the average was 41%.

Further, 630 g of the above-mentioned flat silver-plated copper powder was added to 110 g of the binder obtained above, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to give a viscosity of 87 Pa.
・ A conductive paste containing no s solvent was obtained. The mixing ratio of the conductive powder and the binder was 85.1: 14.9 in terms of weight ratio of the conductive powder to the binder with respect to the solid content of the conductive paste.

Next, a wiring board was manufactured through the same steps as in Example 1, and its characteristics were evaluated. As a result, the specific resistance of the conductor was 1.9 mΩ · cm, the resistance value per through hole was 0.2 Ω / hole, and no void was found inside the through hole. The insulation resistance of the wiring board obtained from FIGS. 3 and 5A and 5B was 10 ⁸ Ω or more. In addition, as a result of conducting a moisture and medium load test
The insulation resistance of the wiring board obtained from FIGS. 3 and 5A and 5B was 10 ⁸ Ω or more.

Comparative Example 1 470 g of the flat silver-plated copper powder obtained in Example 1 was added to 35 g of the binder obtained in Example 1, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to have a viscosity of 217 Pa · s. A conductive paste containing no solvent was obtained. The mixing ratio of the conductive powder and the binder was 93.1: 6.9 in terms of weight ratio of the conductive powder to the binder with respect to the solid content of the conductive paste.

Next, a wiring board was manufactured through the same steps as in Example 1, and its characteristics were evaluated. As a result, the specific resistance of the conductor was 1.2 mΩ · cm, the resistance per through hole was 0.3 Ω / hole, voids were found inside the through hole, and the occurrence probability was 77%. . The insulation resistance of the wiring board obtained from FIGS. 3 and 5A and 5B was 10 ⁸ Ω or more. Further, as a result of performing a moisture and medium load test on the wiring board, the insulation resistance of the wiring board obtained from FIGS. 3 and 5A and 5B was 10 ⁸ Ω or more.

Comparative Example 2 280 g of the flat silver-plated copper powder obtained in Example 1 was added to 110 g of the binder obtained in Example 1, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a viscosity of 41 Pa. A conductive paste containing no solvent was obtained. The mixing ratio of the conductive powder and the binder was 71.8: 28.2 in a ratio of conductive powder: binder by weight relative to the solid content of the conductive paste.

Next, a wiring board was manufactured through the same steps as in Example 1, and its characteristics were evaluated. As a result, the specific resistance of the conductor was 8.9 mΩ · cm, the resistance per through hole was 1.2 Ω / hole, and no void was found inside the through hole. The insulation resistance of the wiring board obtained from FIGS. 3 and 5A and 5B was 10 ⁸ Ω or more. In addition, as a result of conducting a moisture and medium load test
The insulation resistance of the wiring board obtained from FIGS. 3 and 5A and 5B was 10 ⁸ Ω or more.

[0035]

The conductive paste according to the first aspect of the present invention is
Excellent conductivity and printability. The conductive paste according to the second aspect of the invention is particularly excellent in the migration resistance and the effect of improving the conductivity among the conductive pastes according to the first aspect. The conductive paste of the invention according to claim 3 or 4 is excellent in the effect of improving conductivity and printability.

[Brief description of the drawings]

FIG. 1 is a plan view showing a state where a test pattern is printed on a surface of a glass epoxy copper clad laminate where copper foil is etched.

FIG. 2 is a plan view showing a state in which conductive paste is filled into through holes formed in a glass epoxy copper clad laminate and printed and connected between the through holes.

FIG. 3 is a plan view showing a state in which a comb-shaped test pattern is printed on the surface of the glass epoxy copper-clad laminate on which the copper foil has been etched;

4A is a plan view showing a state where a copper foil of a glass epoxy copper clad laminate is partially etched, and FIG. 4B is a front view thereof.

FIG. 5A is a plan view showing a state in which an epoxy resin film is overlaid on the surface of a glass epoxy copper-clad laminate obtained by partially etching a copper foil, and further a test pattern is printed on the upper surface thereof, and FIG. It is the top view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Test pattern 2 Glass epoxy copper clad laminated board 3 Through hole 4 Comb-shaped test pattern 5 Copper foil 6 Epoxy resin film 7 Test pattern

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H05K 1/09 H05K 1/09 A 3/46 3/46 SN

Claims (4)

[Claims] In a conductive paste containing a conductive powder and a binder, the mixing ratio of the conductive powder and the binder is 7 in a weight ratio of the conductive powder: binder to the solid content of the conductive paste.
5:25 to 90:10 and a viscosity of 10 to 150
Conductive paste containing no solvent that is Pa · s. 2. The conductive paste containing no solvent according to claim 1, wherein the conductive powder has a surface which is substantially covered with silver by exposing a part of the copper powder or the copper alloy powder, and has a flat shape. 3. The solvent-free conductive paste according to claim 1, wherein the binder comprises an epoxy resin composition and a curing agent thereof. 4. The epoxy resin composition contains a liquid epoxy resin at room temperature or an epoxy resin solid at room temperature and a reactive diluent, and the mixing ratio of the epoxy resin and the reactive diluent is weight ratio of the epoxy resin. : 50: 5 reactive diluent
The conductive paste containing no solvent according to claim 1, 2, 3 or 4, wherein the ratio is 0 to 70:30.