JP2000261116A - Hardening conductive paste for bump connecting printed wiring board layers - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide hardening conductive paste for a bump connecting printed wiring board layers which is used for formation of an electronic circuit where bonding force to base material, heat resistance and hardness are required. SOLUTION: This hardening conductive paste for a bump connecting printed wiring board layers contains epoxy resin, hardener, conducting powder and solvent. The epoxy resin is composed of 40-100 wt.% of multifunctional epoxy resin which is at least trifunctional and 0-60 wt.% of bifunctional epoxy resin. Softening point of the epoxy resin which is measured with a METTLER FP-90 automatic softening point measuring device at a temperature rising speed of 1 deg.C/minute is in a range of 80-130 deg.C. The hardener is latent hardener.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a curable conductive paste, and more particularly to a curable conductive paste for use in an electronic circuit molding which requires adhesion to a substrate, heat resistance and hardness. Regarding paste.

[0002]

2. Description of the Related Art Curable conductive pastes are used in the electronics field for many applications such as IC circuits, conductive adhesives, and electromagnetic wave seals. Especially recently,
A first substrate provided with a conical conductive bump made of a conductive paste at a predetermined position on at least one surface and a second substrate provided with a wiring pattern on at least one surface are provided with the conductive bump. The surface provided with the wiring pattern and the surface on which the wiring pattern is provided are opposed to each other, and an insulator layer is arranged between the first substrate and the second substrate to form a laminate. There has been proposed a method of manufacturing a printed wiring board in which conductive bumps are formed by stacking and pressing through the bumps in the thickness direction of the insulator layer to form conductive wiring portions.

In order to form the conductive bumps, a binder component such as melamine resin, phenol resin and polyimide resin is mixed with a conductive powder such as silver, gold, copper, solder powder and alloy powder thereof. A conditioned curable conductive paste is used.

[0004]

When the above-mentioned curable conductive paste is used in the production of the above-mentioned printed wiring board, there are the following problems.

[0005] The first problem is that connection failure occurs due to poor penetration of the insulating layer of the conical bump formed from the curable conductive paste. The penetration temperature of the conductive bumps must be set in an optimum range depending on the type of the insulating layers. For example, FR-4 having a relatively low softening point (NEM, USA)
A: national electrical manufacuturers associatio
n standard) type prepreg with glass cloth
It penetrates in a temperature range of 0 to 120 ° C. For this reason, the bump must have a softening point and hardness that do not deform within this temperature range, and if deformed, the bump cannot penetrate the insulator layer, resulting in poor connection between layers.

[0006] The second problem is that a defective connection occurs due to cracking of the bump at the time of laminating press, and a short circuit of the circuit occurs due to a jump of the tip of the bump. This tended to occur when the binder resin was brittle or when fillers such as conductive powder and thixotropy were not properly blended.

[0007] The third problem is poor adhesion between the bump contact portion and the wiring pattern after the laminating press. In addition to the case where the adhesive force of the binder itself is weak, the tendency tends to occur when the degree of curing of the bump is excessively advanced.

[0008]

Means for Solving the Problems The present inventors have intensively studied to solve the above problems. As a result, as a binder component of the curable conductive paste, by using a high adhesive strength epoxy resin and a latent curing agent having a large temperature dependence, and by arbitrarily controlling the degree of curing of the conductive bump before penetrating the insulating layer, The present invention has been completed.

That is, the present invention comprises an epoxy resin, a curing agent, a conductive powder, and a solvent, wherein the epoxy resin comprises 40 to 100% by weight of a trifunctional or higher polyfunctional epoxy resin and 0 to 60% by weight of a bifunctional epoxy resin. And an epoxy resin having a softening point in the range of 80 to 130 ° C. measured by a METTLER FP-90 automatic softening point measuring apparatus at a rate of 1 ° C./min.
The present invention relates to a curable conductive paste for a printed wiring board interlayer connection bump, wherein the curing agent is a latent curing agent.

The epoxy resin used in the present invention is ME
An epoxy resin having a softening point of 80 to 130 ° C., preferably 85 to 125 ° C., as measured by a TTLER FP-90 automatic softening point measuring device. It is preferable that the epoxy resin has such a softening point because the insulator has good penetration of the bumps and there is no crack in the bumps.

The mixing ratio of the polyfunctional epoxy resin having three or more functional groups in 100% by weight of the total epoxy resin is preferably 40 to 100% by weight, particularly preferably 60 to 100% by weight. Therefore, the mixing ratio of the bifunctional epoxy resin is 0-6.
0% by weight is preferable, and particularly preferably 0 to 40% by weight. When the mixing ratio of the trifunctional or higher polyfunctional epoxy resin is as described above, the hardness of the bump does not become insufficient, and the heat resistance does not decrease.

The trifunctional or higher polyfunctional epoxy resin is preferably a trisglycidyl type, a tetraglycidyl type or a novolak type, particularly preferably a novolak type epoxy resin. As the bifunctional epoxy resin, for example, a bisphenol-type epoxy resin is preferable, and a bisphenol-type epoxy resin having a softening point of 100 ° C. or more is particularly preferable.

[0013] The curing agent used in the present invention is a latent curing agent. A latent curing agent is a curing agent that is stable for a long time as long as it is blended with an epoxy resin and left at room temperature, but starts a curing reaction immediately after the latch is released by the action of heat. Such latent curing agents include dicyandiamide, diaminodiphenylsulfone, polyhydric phenols, latent imidazole, and the like. Examples of latent imidazoles include 2-phenyl-4,5-hydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole,
2. 4-Diamino-6- [2'-methylimidazole- (1 ')]-ethyl-S-triazine isocyanuric acid adduct, 2-heptadecylimidazole and the like. Among the latent curing agents, 2-phenyl-4,5-hydroxymethylimidazole is preferred.

These curing agents can be used alone or in combination. These curing agents have a long pot life, easy control of the degree of bump curing, a curing temperature equivalent to that of a printed wiring board, and an extremely small amount of by-products that cause voids. Suitable as the curing agent of the present invention.

The amount of the curing agent to be added may be selected in a usual amount according to the type of the curing agent to be used. Generally, 0.3 to 1 equivalent of epoxy group of epoxy resin.
1.1 equivalent, preferably 0.4 to 1.0 equivalent. When the addition amount of the curing agent is as described above, the crosslinked density of the obtained cured product does not decrease, and sufficient heat resistance, hardness, and good conductivity are obtained.

The glass transition point (Tg), which is an index of the heat resistance of the conductive paste, is preferably 135 to 200 ° C., more preferably 150 to 180 ° C. The hardness is 30 ~
About 45 is preferable. When the hardness is at this level, the conductive bump can penetrate the insulator layer and does not become brittle.

In the present invention, it is preferable to use a curing accelerator such as imidazole or amine adduct in combination. After printing the bump, dry the bump to remove the solvent,
It is necessary to have a bump hardness that allows the insulating layer to penetrate during the drying, and to control the degree of curing that allows the wiring pattern of the abutting portion and the bump to strongly adhere under the same pressing conditions as FR4 after the penetration. By using a curing agent and a curing accelerator together,
It becomes easy to control the degree of curing. The amount of curing accelerator used is
Depending on the type of the epoxy resin and the curing agent, about 0.05 to 3 parts by weight is appropriate for 100 parts by weight of the epoxy resin.

In the present invention, as the conductive powder, for example, metal powder such as silver, gold, copper, solder powder, alloy powder or mixed metal powder thereof can be used. Among these, silver and copper are preferred in terms of hardness. The amount of the conductive powder used is 300 to 1900 parts by weight, preferably 400 parts by weight, based on 100 parts by weight of the total amount of the epoxy resin and the curing agent.
It is used in a proportion of up to 1000 parts by weight.

When the proportion of the conductive powder is as described above, good conductivity can be obtained, and at the same time, the fluidity of the paste does not decrease so that the printability does not deteriorate. Is sufficient because cracking of the bump and jumping of the tip of the bump are less likely to occur, and connection failure and short circuit do not occur.

As the solvent in the present invention, known solvents can be used without any particular limitation. For example, ethyl acetate, esters such as butyl acetate, ethyl cellosolve, cellosolves such as butyl cellosolve, ethyl carbitol, carbitols such as butyl carbitol, isopropanol,
Alcohols such as butanol. The above-mentioned solvents may be used alone or as a mixture of two or more kinds. However, when bumps are formed by screen printing, carbitols and cellosolves are preferable in consideration of plate drying. The amount of the solvent used varies depending on the target viscosity, but is usually about 5% to 15% of the whole paste.

In the present invention, known additives can be blended as long as their properties are not significantly reduced. Such additives include, for example, thixotropy-imparting agents, defoamers, dispersants, rust inhibitors, reducing agents, and the like.

The method for producing the curable conductive paste of the present invention is not particularly limited. For example, the above-mentioned epoxy resin, curing agent, conductive powder and solvent are premixed and kneaded using a three-roll mill to obtain a paste. And degassing under vacuum.

In the present invention, the viscosity of the curable conductive paste measured at 25 ° C. at 10 rotations / minute with a spiral viscometer manufactured by Malcolm Co. is preferably 1000 to 3500 Pa · s.
s, more preferably 1500 to 3000 Pa · s
Is appropriate.

In addition, log (10 min-1 viscosity / 5 m
The thixo ratio calculated by (in-1 viscosity) log (5/10) is such that the apparent viscosity increases while standing and prevents sedimentation of the pigment, and the viscous stirring lowers the apparent viscosity to make it easier to apply. And preferably represents 0.2 to
1.0, and more preferably 0.3 to 0.9.

When the viscosity and the thixo ratio of the curable conductive paste are as described above, the screen is well wetted, the holes in the plate are easily passed, and a sufficient bump height is obtained when printing.

The curable conductive paste of the present invention is not particularly limited, and can be printed by a known method such as screen printing or a dispenser. Screen printing is preferred.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The mixing ratio is part by weight, and the evaluation and measurement were performed according to the following methods.

(1) Softening Point The epoxy resin was melted and measured at a heating rate of 1 ° C./min using a METTLER FP-90 automatic softening point measuring apparatus.

(2) Glass transition point (Tg) The paste was applied to the S surface of the copper foil (the glossy surface on the rotating cathode side of the electrolytic copper foil) to a thickness of 300 μm.
Dried for 0 minutes. A copper foil with the S side facing down was placed on the application surface, and cured by pressing at 170 ° C. for 60 minutes to obtain a sample. The glass transition point (Tg) was measured by differential scanning calorimetry (DSC) at a heating rate of 10 ° C./min.

(3) Hardness After applying the paste to the M surface of the copper foil (the surface of the electrolytic copper foil having no gloss on the electrolyte side) to a thickness of 300 μm, the paste was heated at 160 ° C. for 20 minutes.
The sample was dried to obtain a sample. Hardness is micro hardness tester MXT50
(Matsuzawa Seiki Co., Ltd.), test temperature 23 ° C, test load 25
The measurement was performed at kgf and a load holding time of 15 seconds.

(4) Peeling strength of copper foil After applying the paste to the M surface of the copper foil to a thickness of 300 μm,
Dried at 160 ° C. for 20 minutes. A copper foil was placed on the application side with the M side facing down, and cured with a press at 170 ° C. for 60 minutes to obtain a sample. The copper foil peeling strength (N / cm) was measured according to JIS C6481.

(5) Printability The conductive paste was printed on an 18 μm-thick electrolytic copper foil through a 0.5 mm-thick metal screen plate having holes of 0.3 mm in diameter at predetermined positions. . Good: Bumps can be printed through all holes of the metal screen, and the shape and application height are uniform. Bad: Some holes in the metal screen are clogged, and printing is not possible with all holes. Or, the shape and application height vary.

(6) Penetration A conductive paste was printed on a 18-μm-thick electrolytic copper foil through a 0.5-mm-thick metal screen plate in which holes having a diameter of 0.3 mm were formed at predetermined positions. . The printed conductive paste was dried at 160 ° C. for 10 minutes, and then printed and dried at the same position using the same metal screen plate three times. After the third printing, drying was performed at 160 ° C. for 20 minutes to form conical conductive bumps. Then, an FR4 type prepreg impregnated with an epoxy resin in a glass cloth was placed on the electrolytic copper foil provided with the conductive bumps, and the bumps were pierced through the prepreg through a special penetrating machine to check the penetrability. Good: All bumps penetrate the prepreg, and the shape and height of the protruding bumps are uniform. Bad: Some bumps do not penetrate the prepreg.

[0034]

Example 1 70 parts of a naphthalene novolak type epoxy resin having a softening point of 95 ° C. (NC7000 manufactured by Nippon Kayaku Co., Ltd.)
And 30 parts of bisphenol A type epoxy resin (R367 manufactured by Mitsui Chemicals, Inc.) having a softening point of 125 ° C. are mixed and dissolved in 70 parts of diethylene glycol monobutyl ether acetate at 130 ° C. while heating. 19 parts of diaminodiphenyl sulfone and 2-phenyl-4,5 were added to the resin solution cooled to 25 ° C.
-0.5 parts of dihydroxymethyl imidazole, silver powder 67
7 parts and 18 parts of Aerosil (# 200) are added and premixed with a universal mixer for 30 minutes. Thereafter, the mixture was kneaded with three rolls to obtain a conductive paste.

The viscosity, thixotropy, hardness, peel strength, printability,
The height of one-time printing of the bump and the prepreg penetration of the bump were measured. The results are shown in Table 1.

[0036]

Examples 2 to 5 Conductive pastes of Examples 2 to 5 having the composition shown in Table 1 were obtained in the same manner as in Example 1.
The viscosity of the obtained conductive paste was determined by the method described above.
The thixo ratio, hardness, peel strength, printability, one-time printing height of the bump, and penetration were measured. The results are shown in Table 1.

[0037]

Comparative Example 1 100 parts of bisphenol A type epoxy resin (R367 manufactured by Mitsui Chemicals, Inc.) having a softening point of 125 ° C. was added to 70 parts of diethylene glycol monobutyl ether acetate.
Mix and dissolve under heating at 130 ° C. To the resin solution cooled to 25 ° C., 1 part of dicyandiamide, 2-phenyl-4,5-
0.25 parts of dihydroxymethyl imidazole, silver powder 55
A conductive paste was obtained by mixing in the same manner as in Example 1 except that 0 parts and 14 parts of Aerosil (# 200) were added. By the method described above for the obtained conductive paste, the viscosity,
The thixo ratio, hardness, peel strength, printability, one-time printing height of the bump, and prepreg penetration were measured. Table 1 shows the results
It was shown to.

[0038]

COMPARATIVE EXAMPLES 2-3 The composition shown in Table 1 and Comparative Example 1
In the same manner as in the above, conductive pastes of Comparative Examples 2 and 3 were obtained.
The obtained conductive paste was measured for viscosity, thixotropy, hardness, peel strength, printability, bump single-print height, and prepreg penetrability by the methods described above. The results are shown in Table 1.

The abbreviations in the table mean the following, respectively. Epoxy resin R367: BPA type solid epoxy resin (SP = 125 ° C), Mitsui Chemicals, Inc. VG3101: Trifunctional type epoxy resin (SP = 61 ° C), Mitsui Chemicals, Inc. NC7000: Naphthalene type novolak epoxy resin ( SP = 95 ° C), Nippon Kayaku Co., Ltd. EOCN104S: Orthocresol type novolak epoxy resin (SP = 96 ° C),
Curing agent PSM4326 manufactured by Nippon Kayaku Co. , Ltd .: Phenol novolac resin, DDS manufactured by Gunei Chemical Co., Ltd. Dcy: aminoaminophenyl sulphone Dicy: cyanocyanic acid amido hardening accelerator 2PHZ: 2-phenyl-4,5-thiocyanoxymethyl imitasol, Shikoku Chemicals Co., Ltd. ) PN23: Ethoxyamine Attach, manufactured by Ajinomoto Co., Inc.

[0040]

When the curable conductive paste of the present invention is used, printability is good and bumps can be printed at a high level.
In addition, it is possible to manufacture a penetrating conductive wiring portion which has a good adhesiveness between the bump and the wiring pattern after penetrating and has high heat resistance while having good bump penetration. As a result, in manufacturing a printed wiring board having a penetrating conductive wiring portion, the yield is improved and the connection reliability is improved.

[0041]

[Table 1]

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4J036 AA05 AD08 AF05 AF06 AF08 DA04 DA05 DA10 DB06 DC03 DC10 DC31 DC41 FA02 FA05 FA10 KA03 5E317 AA21 BB01 BB11 BB12 BB13 BB14 BB18 BB19 BB25 CC22 CD21 CD36 GG05 GG16GG20

Claims (4)

[Claims] 1. An epoxy resin comprising an epoxy resin, a curing agent, a conductive powder and a solvent, wherein the epoxy resin comprises 40 to 100% by weight of a polyfunctional epoxy resin having three or more functions and 0 to 60% by weight of a bifunctional epoxy resin, and METTLER FP-90 automatic softening point measuring device has a softening point of 80 to 13 measured at a heating rate of 1 ° C / min.
A curable conductive paste for printed circuit board interlayer connection bumps, which is an epoxy resin at a temperature of 0 ° C. and a curing agent is a latent curing agent. 2. The method according to claim 1, wherein the latent curing agent is dicyandiamide,
The curable conductive paste according to claim 1, wherein the paste is at least one selected from diaminodiphenyl sulfone, polyhydric phenol, and latent imidazole. 3. The conductive powder is silver powder or copper powder, and 300 to 1 parts by weight based on 100 parts by weight of the total amount of the epoxy resin and the curing agent.
The curable conductive paste for a printed wiring board interlayer connection bump according to claim 1, wherein the curable conductive paste is contained in a proportion of 900 parts by weight. 4. A viscosity at 25 ° C. of 1,000 to 3,500.
The curable conductive paste for a printed wiring board interlayer connection bump according to any one of claims 1 to 3, wherein Pa · s and a thixotropy ratio are 0.2 to 1.0.