JP2001236827A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste of superior in solderability, embedding property, and migration, that is embedded in layers interconnection through holes or blind holes of multi-layered printed circuit board for connecting layers. SOLUTION: The conductive paste is composed of a binder and conductive powder which does not contain solvents. The paste when cured shows a glass transition temperature of 40 to 180 deg.C. The binder preferably consists of an epoxy resin and its curing agent, where the epoxy resin is preferably liquid at room temperature. The conductive powder may be copper or copper alloy powder almost coated with silver, but exposed in part, having an aspect ratio in the range of 1 to 1.5 and the average longer diameter of the particles of 1 to 20 μm.

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 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, through holes or non-through holes for interlayer connection are formed in a multilayer substrate obtained through a multi-layer lamination process by heating and pressing, as shown in FIG. In this method, copper plating 1 is applied to the holes, or a conductive paste 2 is printed or filled. In FIG. 1, reference numeral 3 denotes a copper foil.

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.

[0004] A conductive paste containing silver powder is used for forming electric circuits and electrodes of printed wiring boards and electronic parts because of its good conductivity. However, these pastes can be applied with an electric field in a high-temperature and high-humidity atmosphere. In this case, silver deposition called migration occurs in an electric circuit or an electrode, resulting in a short circuit between the electrodes or the wiring. 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.

Further, 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 coated uniformly and thickly, there is no effect of improving migration. In addition, there is a disadvantage that soldering cannot be directly applied to the obtained conductive paste coating film.

[0006] Since the known conductive paste cannot be directly applied by soldering as described above, the coating of the conductive paste is subjected to an activation treatment to perform electroless plating, or a plating solution is formed by using the coating as a cathode. After electroplating inside, it is soldered onto the copper surface. In such a case, it is not practical unless bonding between the coating film and the copper plating is ensured.
Therefore, if a solderable conductive paste that does not need to be subjected to electroless plating or electroplating is developed, the circuit forming process is greatly shortened, and the merit thereof is great.

[0007]

SUMMARY OF THE INVENTION The first aspect of the present invention provides a conductive paste having excellent solderability. The second and third aspects of the present invention provide a conductive paste which is excellent in the effect of improving the embedding property into a through hole or a non-through hole for interlayer connection and the solderability. The invention according to claims 4, 5 and 6 provides a conductive paste which is excellent in conductivity, migration property, effect of improving the embedding property in through holes or non-through holes for interlayer connection, and effect of improving solderability. It is.

[0008]

According to the present invention, in a conductive paste containing a binder and a conductive powder, the cured product of the conductive paste has a glass transition point (hereinafter referred to as Tg) of 40 to 180 ° C.
And a conductive paste containing no solvent. Further, the present invention relates to a conductive paste comprising a binder containing an epoxy resin composition and a curing agent thereof. Further, the present invention provides an epoxy resin composition containing a liquid state epoxy resin at room temperature or a solid state epoxy resin at room temperature and a flexibility-imparting agent, and the mixing ratio of the epoxy resin and the flexibility-imparting agent is epoxy. 50 to 90% by weight of resin and 10 of flexibility imparting agent
５０50% by weight.

The present invention also relates to a conductive paste in which the conductive powder exposes a part of the copper powder or the copper alloy powder and has a surface substantially covered with silver and a substantially spherical shape. In addition, the present invention provides a substantially spherical conductive powder in which the conductive powder has an aspect ratio of 1 to 1.5, an average major particle diameter of 1 to 20 μm, and an exposed area of copper powder or copper alloy powder of 10 to 60%. A conductive paste. Further, in the present invention, the blending ratio of the binder and the conductive powder is such that the binder is 5 to the solid content of the conductive paste.
The present invention relates to a conductive paste containing 15% by weight and 85 to 95% by weight of a conductive powder.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION For directly soldering to a conductive paste coating, the cured conductive paste has a Tg of 40 to 40.
The temperature is set in the range of 180 ° C, preferably in the range of 40 to 140 ° C. If the temperature is lower than 40 ° C, the conductivity and the reliability are reduced.
On the other hand, when the temperature exceeds 180 ° C., there is a disadvantage that soldering cannot be performed. Tg of cured conductive paste is 40 to 180
When the temperature is in the range of ° C, when the soldering flux is applied to the surface of the conductive paste coating and then soldered, the Tg of the cured conductive paste is lower than the temperature of the solder. It is considered that the proportion of the conductive powder on the surface of the paste coating film is larger than that of the binder, so that soldering can be directly performed on the conductive paste coating film.

The Tg of the cured conductive paste is 40 to 180.
In order to control the temperature in the range of ° C., it is preferable to use an epoxy resin composition containing a flexibility-imparting agent in addition to the epoxy resin. The mixing ratio of the epoxy resin and the flexibility-imparting agent is preferably in the range of 50 to 90% by weight of the epoxy resin and 10 to 50% by weight of the flexibility-imparting agent, and 60 to 80% by weight of the epoxy resin. Flexibility imparting agent is 20 to
Those in the range of 40% by weight are more preferred.

The binder in the present invention preferably uses an epoxy resin composition and a curing agent therefor. 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, 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 containing two or more epoxy groups in the molecular weight, such as bisphenol A, bisphenol AD, bisphenol F, novolak, cresol novolaks and epichlorohydrin Aliphatic epoxy resins such as polyglycidyl ether, dihydroxynaphthalenediglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and heterocyclic epoxies such as diglycidyl hydantoin, vinylcyclohexene dioxide, Alicyclic epoxy resins such as cyclopentanedienedoxide 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 can be used alone or in combination of two or more.

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. 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, and generally, a tertiary amine, imidazoles, triphenyl phosphine, tetraphenyl phosphenyl borate, and the like can be 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 the above curing agent is preferably in the range of 0.1 to 20 parts by weight with respect to 100 parts by weight of the epoxy resin in terms of Tg of the cured conductive paste.
More preferably, it is in the range of 10 parts by weight.

To the binder used in the present invention, a thixotropic 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.

As the copper powder or copper alloy powder, powder produced by an atomizing method is preferably used, and the smaller the particle size, the better. For example, a powder having an average particle size of 1 to 20 μm is preferable, and a powder having an average particle size of 1 to 10 μm is preferable. Is more preferable.

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. 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.

As the conductive powder used in the present invention, a silver-coated copper powder or a silver-coated copper alloy powder, which is partially exposed and whose surface is substantially covered with silver, is used as the conductive powder. preferable. If a copper powder or a copper alloy powder whose entire surface is coated with silver without exposing a part thereof is used, the solderability tends to deteriorate. In addition, the use of a material whose entire surface is covered with silver tends to deteriorate the migration property.

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%, from the viewpoints of solderability, oxidation of the exposed portion, conductivity and the like. Note that, as the copper alloy powder, an alloy of copper and tin, copper and zinc, or the like is preferably used.

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 an impact to the conductive powder to deform the shape of the particles into a flat shape, but the conductive paste using the flat conductive powder is substantially spherical. Viscosity is higher than conductive paste using conductive powder. Since the conductive paste of the present invention does not contain a solvent, the viscosity is not reduced by adding a solvent. Therefore, when the viscosity is high, the embedding work becomes difficult. From the viewpoint of workability and conductivity in the Y-axis direction of the hole when the conductive paste is embedded in the hole, it is preferable to use a conductive paste using substantially spherical conductive powder.

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 particles of the conductive powder. 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 such that particles appearing on the cut surface sandwich a combination particle 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.

The mixing ratio of the binder and the conductive powder is preferably 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, and 7 to 13% by weight of the binder. The conductive powder is more preferably in the range of 87 to 93% by weight. If the binder is less than 5% by weight and the conductive powder exceeds 95% by weight, the adhesive strength between the paste and the copper foil tends to decrease. If the binder exceeds 15% by weight and the conductive powder is less than 85% by weight. , Solderability and conductivity tend to decrease.

The conductive paste of the present invention can be used together with the binder, conductive powder and, if necessary, a thixotropic agent, a coupling agent, an antifoaming 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. Further, since the conductive paste of the present invention does not contain a solvent, it is possible to prevent the generation of voids in through holes or non-through holes.

[0028]

The present invention will be described below with reference to examples. Example 1 Bisphenol A type epoxy resin (oiled shell epoxy)
72 parts by weight, manufactured by Asahi Denka Kogyo Co., Ltd., trade name: ED
-503) 18 parts by weight, 2-phenyl-4-methyl-5
6 parts by weight of hydroxymethylimidazole (manufactured by Shikoku Chemicals Co., Ltd., trade name: Curazole 2P4MHZ) 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. 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.

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 40 minutes. Average particle size is 5.5 μm
Was obtained. Five particles of the obtained substantially spherical 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 20% in the range of 10 to 50%. Was.

To 50 g of the above-obtained binder was added 450 g of the above-mentioned substantially spherical silver-plated copper powder, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste. The conductive paste was cured by heating at 170 ° C. for 90 minutes, and the Tg of the cured product was measured using a TM manufactured by Seiko Denshi Kogyo.
It was 86 ° C. as a result of measurement at A120 with a load of 3 g and a heating rate of 5 ° C./min. The mixing ratio of the epoxy resin and the flexibility-imparting agent is 80% by weight of the epoxy resin and 20% by weight of the flexibility-imparting agent, and the mixing ratio of the binder and the conductive powder is 10% by weight of the binder and the conductive powder. The powder was 90% by weight.

Next, a 0.8 mm thick glass epoxy copper-clad laminate (manufactured by Hitachi Chemical Co., Ltd., trade name: MCL-E-670) is shown in FIG. 2 using the conductive paste obtained above. A through-hole 5 having a diameter of 0.3 mm is formed as described above, and the through-hole 5 is filled with a conductive paste and printed between the through-holes 5 and allowed to stand at room temperature for 10 minutes.
Heat treatment was performed at 170 ° C. for 90 minutes to obtain a wiring board.

Next, a soldering flux is applied to the conductive paste on the through-hole 5 of the obtained wiring board, soldered thereon, left at room temperature and cooled, and then the soldered portion of the through-hole is soldered. The tape test was performed. As a result, it was confirmed that the solder was not attached to the tape and was soldered to the conductive paste in the through-hole portion.

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 Bisphenol A type epoxy resin 55 used in Example 1
Parts by weight, 35 parts by weight of aliphatic diglycidyl ether, 2-
Ethyl-4-methylimidazole (manufactured by Shikoku Chemicals Co., Ltd., trade name: Curesol 2E4MZ) (6 parts by weight) and dicyandiamide (4 parts by weight) were added and uniformly mixed to prepare a binder. 465 g of the substantially spherical silver-plated copper powder obtained in Example 1 was added to 35 g of the above-mentioned binder, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste.

After the obtained conductive paste was cured under the same conditions as in Example 1, the Tg of the cured product was measured by the same method as in Example 1, and the result was 65 ° C. The mixing ratio of the epoxy resin and the flexibility-imparting agent is 6 for the epoxy resin.
1% by weight and the flexibility imparting agent were 39% by weight, and the mixing ratio of the binder and the conductive powder was 10% by weight of the binder and 90% by weight of the conductive powder.

Next, after a wiring board was obtained through the same steps as in Example 1, a tape test was performed in the same manner as in Example 1. As a result, no solder was attached to the tape, and It was confirmed that soldering was performed on the conductive paste.

Comparative Example 1 Bisphenol A type epoxy resin 90 used in Example 1
Parts by weight, 6 parts by weight of 2-phenyl-4-methyl-5-hydroxymethylimidazole and 2 parts by weight of dicyandiamide were added and uniformly mixed to obtain a binder. Approximately spherical silver-plated copper powder 450 obtained in Example 1 was added to 50 g of the above binder.
g was added, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste.

After the obtained conductive paste was cured under the same conditions as in Example 1, the Tg of the cured product was measured by the same method as in Example 1, and as a result, it was 182 ° C. The mixing ratio of the binder and the conductive powder was 10% by weight of the binder and 90% by weight of the conductive powder.

Next, after a wiring board was obtained through the same steps as in Example 1, a tape test was performed in the same manner as in Example 1, and as a result, solder was attached to the tape, and the conductive paste in the through-hole portion was removed. It was confirmed that it was not soldered.

[0041]

The conductive paste according to the first aspect of the present invention is
Excellent solderability. The conductive paste according to the second and third aspects of the present invention is excellent in the effect of improving the embedding property into a through hole or a non-through hole for interlayer connection and the solderability. The conductive paste according to the fourth, fifth, and sixth aspects of the invention is excellent in conductivity, migration property, an effect of improving embedding into a through hole or a non-through hole for interlayer connection, and an effect of improving solderability.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view showing a state in which copper plating is applied to a through hole for interlayer connection of a multilayer printed wiring board, and FIG. 1B is a view showing a state in which a conductive paste is applied to the through hole for interlayer connection of the multilayer printed wiring board. It is sectional drawing which shows the state which was embedded.

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

[Explanation of symbols]

 1 copper plating 2 conductive paste 3 copper foil 4 glass epoxy copper clad laminate 5 through hole

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01B 1/00 H01B 1/00 H H05K 1/09 H05K 1/09 A 3/46 3/46 SNF Terms (reference) 4E351 DD04 DD21 DD52 EE02 EE16 GG16 4J002 CC032 CC162 CD011 CD021 CD051 CD061 CD131 CL002 DA077 DC007 EL028 EL136 EN036 EN076 ET006 EU116 FB077 FD117 FD142 FD146 GQ02 4J038 DB001 EA0109B09 CC03 EA011 HA066 CC DA06 DA57 DD01

Claims (6)

[Claims] In a conductive paste containing a binder and a conductive powder, the cured product of the conductive paste has a glass transition point of 40 to 40.
A conductive paste containing no solvent at 180 ° C. 2. The conductive paste according to claim 1, wherein the binder comprises an epoxy resin composition and a curing agent thereof. 3. The epoxy resin composition contains an epoxy resin which is liquid at room temperature or an epoxy resin which is solid at room temperature and a flexibility-imparting agent, and the mixing ratio of the epoxy resin and the flexibility-imparting agent is epoxy resin. The conductive paste according to claim 1, wherein the content of the conductive paste is 50 to 90% by weight and the content of the flexibility-imparting agent is 10 to 50% by weight. 4. The conductive paste according to claim 1, wherein the conductive powder exposes a part of the copper powder or the copper alloy powder and has a surface substantially covered with silver, and has a substantially spherical shape. 5. The conductive powder is an approximately spherical conductive powder having an aspect ratio of 1 to 1.5, an average long diameter of 1 to 20 μm, and an exposed area of copper powder or copper alloy powder of 10 to 60%. The conductive paste according to claim 1, 2, 3, or 4. 6. The compounding ratio of the binder and the conductive powder is such that the binder is 5 to 15% by weight and the conductive powder is 85 to 95% by weight based on the solid content of the conductive paste.
6. The conductive paste according to 4 or 5.