JPH1166955A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide easily printable and hardly sagging paste by including conductive powder and a thermosetting resin composed of a specific rate of a low molecular weight thermosetting resin and a high molecular weight thermosetting resin having weight average molecular weight not less than two times the low molecular weight thermosetting resin, as an essential component. SOLUTION: In a thermosetting resin, among 100 pts.wt. in total, a high molecular weight thermosetting resin is composed of 20 to 80 pts.wt., and a low molecular weight thermosetting resin is composed of 80 to 20 pts.wt. It is desirable that weight average molecular weight is 5000 to 100 thousand in the high molecular weight thermosetting resin and is 350 to 3500 in the low molecular weight thermosetting resin. A phenol resin and an expoxy resin are used in combination as the thermosetting resin. Copper powder, copper alloy powder, silver powder or silver alloy powder are used as conductive powder, and particularly, in scale-shaped silver powder or sliver alloy powder, the grain size is desirable to be in a range of 0.5 to 40 μm. It is desirable to blend the conductive powder by 80 to 90 wt.% to the total quantity of the conductive powder and the thermosetting resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a conductive paste.

[0002]

2. Description of the Related Art One method of forming a conductive circuit on a printed wiring board is to use a conductive paste. In particular, a conductive paste using silver powder as the conductive powder is used for forming a conductive layer such as a wiring conductor or an electrode of a printed wiring board or an electronic component because of its good conductivity. The method using a conductive paste is a method in which a conductive powder is dispersed in a binder, a paste-form conductive paste is applied to a substrate, and a conductive layer having a predetermined pattern is formed. A conventional conductive paste is a paste formed by using a curable resin such as an epoxy resin or a phenol resin as a binder component, dissolving the binder component in an organic solvent, adding a conductive powder such as silver powder to the binder, and kneading the paste. .

[0003]

The conductive paste needs to have a viscosity suitable for being printed on the substrate and filling the through holes. However, conventionally known conductive pastes are not sufficient because the cross-sectional shape after printing tends to be drooped. In particular, when a conductive paste is applied, dried, and hardened on the periphery and the inner wall surface of the through hole formed in the substrate to form a conductive layer, the shoulder portion of the through hole may be thinned and the conduction resistance may be increased. Was.

[0004] In order to lower the conduction resistance, a method of increasing the amount of silver powder in the conductive powder to increase the viscosity of the conductive paste to prevent dripping has been studied. However, coating or filling operations are difficult. It did not satisfy both the prevention of drooping and the ease of the application or filling operation.

Accordingly, the first aspect of the present invention is to provide a conductive paste which is easy to print and has less dripping. The invention described in claim 2 provides a conductive paste in which, among the inventions described in claim 1, there is particularly little drooping and the shoulder thickness of the through hole can be stably obtained.

[0006]

The invention according to claim 1 comprises conductive powder, a high molecular weight thermosetting resin and a low molecular weight thermosetting resin as essential components, and the molecular weight of the high molecular weight thermosetting resin is reduced. The present invention relates to a conductive paste that is at least twice as large as a low molecular weight thermosetting resin. In the present invention, the high molecular weight means that the weight average molecular weight is 5,000 or more,
Low molecular weight means that the weight average molecular weight is 3,500 or less. The weight average molecular weight is obtained by gel permeation chromatography in terms of standard polystyrene, and is hereinafter simply referred to as molecular weight.

[0007] When a high molecular weight thermosetting resin is used alone, the viscosity rise accompanying the evaporation of the solvent during the drying process is large, and a smooth conductor surface cannot be formed. When a low-molecular-weight thermosetting resin is used alone, the viscosity rises slowly during the drying process, and the reproducibility of the shape of the printed conductor surface is poor. In order to obtain preferable viscosity characteristics in the drying process, it is necessary that the difference in molecular weight between the high-molecular-weight thermosetting resin and the low-molecular-weight thermosetting resin be at least twice, more preferably at least three times. It is particularly preferred that the ratio be twice or more.

[0008] Since the high molecular weight thermosetting resin and the low molecular weight thermosetting resin are used together, the viscosity in the paste state and the increase in the viscosity during the drying process can be easily and arbitrarily controlled. By incorporating a high molecular weight thermosetting resin, the curing reaction can be accelerated, and the viscosity rise can be accelerated. For this reason, with the drying in the drying / curing process, the viscosity is rapidly increased, and dripping is prevented. Further, since the low-molecular-weight thermosetting resin is used in combination, the surface of the conductive circuit is smoothed. Therefore, the conductivity can be obtained stably.

The invention described in claim 2 is the first invention.
In the invention described in the above, the high molecular weight thermosetting resin is 20 to
The present invention relates to a conductive paste containing 80 parts by weight, 80 to 20 parts by weight of a low molecular weight thermosetting resin, and 100 parts by weight of the total amount of a high molecular weight thermosetting resin and a low molecular weight thermosetting resin.

The compounding amount of the high molecular weight thermosetting resin is less than 20 parts by weight, that is, the compounding amount of the low molecular weight thermosetting resin is 8 parts by weight.
When the amount exceeds 0 parts by weight, the curing of the thermosetting resin is delayed,
There are problems such as blistering when the adsorbed gas of the article is released. The blending amount of the high molecular weight thermosetting resin is 80
If the amount is more than 80 parts by weight, that is, if the compounding amount of the low-molecular-weight thermosetting resin is less than 80 parts by weight, the viscosity rapidly increases due to the progress of drying, and irregularities during printing remain as it is. For this reason, the high-molecular-weight thermosetting resin is 30 to 7
It is more preferable that 0 part by weight and the low molecular weight thermosetting resin be blended in the range of 70 to 30 parts by weight.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the thermosetting resin used in the present invention include a phenol resin and an epoxy resin, and a curing agent, a curing catalyst and the like are used in combination.

The high molecular weight thermosetting resin used in the present invention has a molecular weight of 5,000 to 100,000.
Is preferably within the range. If the molecular weight exceeds 100,000, the viscosity is high and the reaction is fast, so that the viscosity tends to increase during storage. Further, the molecular weight of the low-molecular-weight thermosetting resin is preferably from 350 to 3,500 from the viewpoint of a curing reaction or dripping. Note that a molecule containing less than 350 molecules may be included.

As the conductive powder, a conductive powder conventionally used in a conductive paste such as copper powder, copper alloy powder, silver powder or silver alloy powder is used. In particular, scaly silver powder or silver alloy powder is preferable from the viewpoint of conductivity. It is preferable to use flaky conductive powder and irregular-shaped conductive powder in combination, since the conductivity can be particularly improved. The particle size of the conductive powder is 0.5 to 6 because the powder is uniformly dispersed in the paste and the conductivity in the conductive layer formed by the conductive paste is uniform.
It is preferably in the range of 0 μm, more preferably in the range of 0.5 to 40 μm.

The thermosetting resin (A) and the conductive powder (B)
In order to improve the conductivity, it is preferable that (B) is blended so as to be 75% by weight or more with respect to (A + B), more preferably 80% by weight or more, Further, from the viewpoint of the adhesion and strength of the conductive layer to be formed, it is preferable that (B) is blended so as to be 93% by weight or less with respect to (A + B), and 90% by weight or less. More preferably, it is blended.

[0015] In addition to the thermosetting resin and the conductive powder, components such as a coupling agent, a copper corrosion inhibitor, and a dispersant can be added as required.

A thermosetting resin, a curing agent, a curing catalyst, a conductive powder and, if necessary, a coupling agent, a copper corrosion inhibitor, a dispersant, etc., are mixed with a solvent using a stirrer or a three-roll mill. Into a paste. As a solvent to be used, ethyl carbitol, butyl carbitol butyl cellosolve and the like can be used alone or in combination. Further, since the solvent is volatilized in the process of drying and curing the conductive paste, it is preferable to use a small amount of the solvent as long as the paste can be formed.

[0017]

Examples of the present invention will be described below. Example 1 As a thermosetting resin, a bisphenol A type epoxy resin having a molecular weight of 2,500 (manufactured by Yuka Shell Epoxy Co., Ltd.)
5 parts by weight of Epicoat 1007 (trade name) and resol type phenol resin having an average molecular weight of 450 (Hitanol 4010 (trade name) manufactured by Hitachi Chemical Co., Ltd.)
10 parts by weight) were mixed in advance, 0.3 parts by weight of 2-ethyl-4-methylimidazole was added and mixed, and 30 parts by weight of a mixed solvent of equal amounts of ethyl carbitol and butyl cellosolve was added. This was mixed to form a resin solution. 55 parts by weight of silver powder (using TCG-1 (trade name) manufactured by Tokurika Kagaku Kenkyusho Co., Ltd.) as scaly conductive powder, and reduction of an irregularly shaped conductive powder having an average particle size of 5 μm as an irregularly shaped conductive powder. 30 parts by weight of silver powder was added, and the mixture was uniformly dispersed with a stirrer to prepare a conductive paste.

The copper foil of the paper phenol copper-clad laminate (using MCL-437F (trade name) manufactured by Hitachi Chemical Co., Ltd.) is removed by etching, and then dried using the obtained conductive paste. A test pattern having a thickness of 12 μm, a width of 1 mm, and a length of 130 mm after curing was printed, and the temperature was 30 ° C.
After drying for 30 minutes, the temperature was raised to 150 ° C. over 30 minutes, and the temperature was maintained at 150 ° C. for 30 minutes to cure the thermosetting resin, thereby forming a conductive circuit. As a result, the circuit width was 6 μm, and the surface was smooth and good.

Example 2 As a thermosetting resin, a bisphenol A type epoxy resin having a molecular weight of 1,500 (manufactured by Yuka Shell Epoxy Co., Ltd.)
5 parts by weight of Epicoat 1004 (trade name) and a resol type phenol resin having an average molecular weight of 20,000 (Hitanol 4011B manufactured by Hitachi Chemical Co., Ltd.)
(Use of trade name) A conductive paste was prepared in the same manner as in Example 1 except that 10 parts by weight was used.

A through hole having a diameter of 0.5 mm is formed in a paper phenol copper-clad laminate (using MCL-437F (trade name) manufactured by Hitachi Chemical Co., Ltd.), and the obtained conductive paste is filled in the through hole. , Dried at 70 ° C. for 45 minutes, and then heated to 150 ° C. over 30 minutes,
The thermosetting resin was cured at a temperature of 0 ° C. for 30 minutes to form a through-hole connection. As a result, the conductive paste is hardened at a sufficient thickness even at the shoulder of the through hole,
The resistance of the through-hole connection was 17.5 mΩ / hole.

COMPARATIVE EXAMPLE 1 As a thermosetting resin, the resol-type phenol resin used in Example 1 was dissolved alone in 15 parts by weight, and an equal amount of ethyl carbitol and butyl cellosolve was dissolved in 30 parts by weight of a mixed solvent. A conductive paste was prepared in the same manner as in Example 1.

Thereafter, a conductive circuit was formed in the same manner as in Example 1. As a result, the circuit width was 10 μm, and the surface was smooth and good.

Comparative Example 2 A through-hole connection was formed in the same manner as in Example 2 using the conductive paste obtained in Comparative Example 1. As a result, the resistance of the through-hole connection was 34 mΩ / hole.

[0024]

According to the present invention, the conductive paste according to the present invention can form a stable conductive layer without any printed matter being reduced, particularly without reducing the thickness of the conductive layer at the shoulder of the through hole. .

Continuing on the front page (72) Inventor Ryoji Tashiro 3-3-1 Ayukawacho, Hitachi City, Ibaraki Prefecture Inside the Yamazaki Plant of Hitachi Chemical Co., Ltd. (72) Inventor Shuichiro Shimoda 3-1-1 Ayukawacho, Hitachi City, Ibaraki Prefecture No. Hitachi Chemical Co., Ltd. Yamazaki Factory

Claims (2)

[Claims] Claims: 1. An electroconductive powder, a high molecular weight thermosetting resin and a low molecular weight thermosetting resin are contained as essential components, and the weight average molecular weight of the high molecular weight thermosetting resin is at least twice that of the low molecular weight thermosetting resin. Some conductive paste. 2. A total of 100 parts by weight of the high molecular weight thermosetting resin and the low molecular weight thermosetting resin, 20 to 80 parts by weight of the high molecular weight thermosetting resin and 80 to 80 parts by weight of the low molecular weight thermosetting resin.
The conductive paste according to claim 1, which is 20 parts by weight.