JPH0461703A - Electroconductive paste for printing - Google Patents

Abstract

PURPOSE:To provide a printing paste exhibiting excellent printing characteristics, which contains no such a solvent as having strong polarity and presenting high moisture absorptiveness at all, by forming the paste from a specific solvent, thermosetting resin, and electroconductive metal powder. CONSTITUTION:Example of a solvent concerned is ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc., either solely or in combination. Example of thermosetting resin is polyimide resin, either single type or a combination of different types, having a dissolutiveness in the solvent no less than 10wt.% at room temp. The electroconductive metal poser consists of Au, Ag, Pd, Cu, Ni, Al or an alloy thereof with good conductivity. This allows removal of a conventional solvent, which has very strong polarity and presents high moisture absorptiveness, perfectly from the paste composition to lead to enhancement of the screen print characteristics to a great extent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a conductive paste that is used as a circuit that becomes a conductor part and as an electrode when forming a wiring circuit of an electronic device or the like.

BACKGROUND ART Conventionally, conductive pastes have been used for forming wiring circuits on printed circuit boards, etc., as disclosed in, for example, Japanese Patent Laid-Open No. 51-23639. Such conductive paste is
Approximately 60 to 90 wL% of conductive metal powder (fR or silver) and approximately 4
The conductive paste, which consists of a binder whose main component is a thermosetting resin such as epoxy resin or phenol resin, is applied to a film of about 15 to 35 μm on a substrate through a screen with a predetermined circuit pattern. After thick screen printing, the curing conditions of the binder resin (approximately 80-220℃
) A conductor wiring circuit has been formed by heating and curing.

Epoxy resins and phenolic resins used as binder resins have excellent adhesion, have a high degree of freedom in solvent selection, and are easy to handle, but they have drawbacks in heat resistance.
The reality is that reliability at high temperatures is insufficient, particularly when such pastes are used as electrodes, and connections such as soldering are not sufficiently reliable.

In recent years, for the purpose of improving the heat resistance of such pastes, for example, Japanese Patent Application Laid-Open No. 54-126999. JP-A-63-226
As disclosed in Japanese Patent Application No. 811, etc., polyimide resins are being considered as binder resins. The polyimide resin used as a binder here refers to polyamic acid as a polyimide resin precursor and N-methylpyrrolidone (hereinafter referred to as 11).
1N MP) or 2-pyrrolidone solvent, or bismaleimide or modified bismaleimide resin dissolved in NMP solvent, and highly conductive metal powder is added to the binder resin solution. A method is to transfer a paste containing the above onto a substrate by screen printing, and then form a conductor circuit on the substrate through ring-closing reaction of polyamic acid, thermal polymerization of bismaleimide resin, or addition reaction with polyamines. It has been taken.

However, conventionally used resins that generate imide groups in their molecular structure after curing or that contain imide groups in their molecular structure before curing are limited in soluble solvents, and in high boiling point solvents, NMP, 2 - Polyimide resins such as pyrrolidone, dimethyl sulfoxide, and sulfolane are highly hygroscopic, polar, and soluble only in solvents with strong dissolving power, and cannot be liquefied without these solvents.

For this reason, conductive pastes using polyimide resin as a binder contain a small amount or a large amount of such solvents, which causes changes in the composition or viscosity of the paste due to moisture absorption or volatilization during screen printing, resulting in continuous In addition to problems with printing, an even bigger problem is that such solvents swell or deteriorate organic parts such as the screen and squeegee rubber of screen printing machines, causing premature wear of the squeegee rubber. This leads to early errors in the screen and extremely shortens the life of the screen.

For this reason, conventional techniques, for example, as disclosed in JP-A-5478491, have improved the polyimide resin as a binder and reduced the content of solvents such as NMPs and dimethyl sulfoxide as much as possible. Much effort has been focused on the development or selection of polyimide resins that can be dissolved or dispersed by adding the solvent used, such as diethylene glycol monobutyl ether acetate (hereinafter referred to as BCA).

[Problems to be Solved by the Present Invention] As mentioned above, in the case of a printing conductive paste using polyimide resin as a binder, in the case of polyamic acid, there are problems such as a decrease in the average molecular weight of the raw material resin, a change in the molecular structure, and a change in the bismaleimide resin. In the case of , only the solubility in solvents was slightly improved by modification with epoxy resin, etc., so not only did the high heat resistance, which is the original characteristic of polyimide resin, be sacrificed, but the There was a desire to create a conductive paste using a polyimide resin as a binder, but since liquefaction was impossible without the presence of a polar solvent such as NMP, drastic improvements in printability were not achieved.
Compared to other types of resins or thick film pastes using glass frit as a binder, there is a clear difference in printability. It had poor performance and continuous printing performance, and was by no means common.

On the other hand, such polyimide resins have sacrificed heat resistance in pursuit of solubility in solvents. In particular, sufficient reliability could not be obtained even in connection such as the soldering described above.

[Object of the Invention] The present invention has been made in view of the problems of the electrically conductive paste for printing using the above-mentioned polyimide resin as a binder. That is, the first object of the present invention is to provide a conductive paste that has strong polarity like NMP and has excellent printability and does not contain any highly hygroscopic solvent. Another object of the present invention is to provide a conductive paste that can be made into a heat-resistant cured product with sufficient reliability.

[Means for Solving the Problem] In order to achieve the above-mentioned object, the inventors developed a solvent that has less hygroscopicity and less polarity than BCA, which is most commonly used in such thick film pastes. We started by looking for a soluble polyimide resin. As a result, they discovered a polyimide resin that is only slightly soluble in BCA but soluble in triethylene glycol dimethyl ether (hereinafter referred to as trigraino) and tetraethylene glycol dimethyl ether to a high concentration.

Such polyimide resins include (1) acetylene-terminated polyisoimide oligomers (the following structural formulas I and It) (2)
> Copolymer of bismaleimide and amino acid hydrazide (reaction formula I), (3) polyfunctional maleimide resin (structural formula ■)
, etc.

(Reaction Formula I) Moreover, such polyimide resins are not limited to high boiling point solvents that have a limit in water content, such as propylene glycol monophenyl ether (hereinafter referred to as PGPE), ethylene glycol monobenzyl ether, ethylene glycol monobenzyl ether, etc. It has been found that alkylene glycol ethers having a benzene ring such as 2-phenoxyethyl acetate can also be dissolved at a high concentration of at least 10 wL% at room temperature.

Such a polyimide resin is easily available as a commercial product, and as (1) TI+ermid IP-600F
A-7001 (Kanebo NSC), Compimide $183 as (2). $353. $
795 (The Boots Company
PLC, Technochemie GmbH),
(3) MP-2000X, MP-256, MP-
276 (Mitsubishi Yuka), etc.

One or more of the above-mentioned polyimide resins can be used as P
It is dissolved in alkylene glycol ethers having a benzene ring such as GPE and ethylene glycol monobenzyl ether in a range of 10 to 60 w%, and in this solution,
The present invention was achieved by adding one or more types of highly conductive metal powders made of gold, silver, balacidium, copper, nickel, aluminum, etc. or alloys thereof in a range of 60 to 90 wt%.

Furthermore, in addition to at least one solvent of alkylene glycol ethers having a benzene ring, a high boiling point solvent having a limited water content, such as BCA,
It is also possible to use in combination with at least one solvent selected from alkylene glycol ethers such as 2-butoxyethyl acetate, diethylene glycol dibutyl ether, and ethylene glycol dibutyl ether.

It is also possible to knead polyimide resin, solvent, and metal powder at the same time, and to improve viscosity and printability,
It is also possible to add various additives.

[Function] A polymer conductive paste consisting of one or more polyimide resins, an alkylene glycol ether having a benzene ring, and a highly conductive metal powder as main components is a conductive paste with a conventional polyimide resin binder. In comparison, it has excellent storage stability and screen printability has improved dramatically.

The conventionally used N
Because highly polar and hygroscopic solvents such as MP and dimethyl sulfoxide were completely removed from the paste composition, problems encountered during screen printing using conventional conductive pastes with polyimide resin binders were eliminated. This trouble is because the alkylene glycol ethers having a benzene ring mentioned above have a sufficiently slow evaporation rate at room temperature and have low hygroscopicity, so there is no change in the viscosity of the paste during printing, and the emulsion of the screen Since there is no adverse effect such as swelling, abrasion, or dissolution on the squeegee rubber of screens and printing machines, the life of screens and squeegee rubber in Japan will be dramatically increased, and as a result, the number of consecutive printings will also be increased dramatically.

Furthermore, the conductive paste of the present invention has higher heat resistance than conductive pastes containing other types of resins that have been proposed in the past, such as epoxy resins, phenol resins, acrylic resins, and polyurethane resins as binders. As a conductive paste, it has many excellent cured coating properties.

Some of its excellent features are: (1) It has a very low sheet resistance value of 5 to 10 transohms, so it can be used in thin wire circuits.

(2) The solder wettability is very good, and the soldering strength is also very high.

(3) Soldering was performed at 150℃ in a later heat aging test.
Even after 1,000 hours, the initial strength is maintained and there is no noticeable deterioration in strength.

(4) Conventionally, connections such as wire bonding were impossible only with conductive pastes using resin as a binder, but the conductive paste of the present invention has made it possible.

It has become a revolutionary conductive base not only in improving screen printability but also in the physical properties of cured coatings.

[Example] The present invention will be explained in detail below with reference to Examples.

Note that parts in the text mean parts by weight.

Example 1 Flake-like silver powder (average particle size 8μ, Kashi Metal Foil Powder Kogyo, A
[lC-L) 75 parts, Ther as polyimide resin
mid F A -700115 parts, PG as solvent
Weigh out 22 parts of PE, and thoroughly dissolve and mix using a stirrer. Furthermore, after thoroughly kneading in a three-roll mill, a small amount of leveling agent and antifoaming agent is added, and 3 parts of PGPE are added to adjust the viscosity to about 50 to 80 Kcps. 200 mesh
The paste screen-printed on an alumina substrate or polyimide film using a stainless steel screen did not deteriorate the screen emulsion or squeegee rubber, and had excellent printability and continuous printability.

After printing, it was dried at 120°C for 10 minutes and then cured at 360°C for 30 minutes to obtain a circuit with a film thickness of 15μ. The resistance value of the circuit was 6.1-Ω/hole, and the adhesive strength of the butt portion after soldering was 7ky or more, and all cases resulted in wire breakage or substrate destruction. Wire bonding strength is also 2
The strength was about 15 to 202 with a 5μ diameter gold wire.

Examples 2 to 4 Pastes were prepared in the same manner as in Example 1 and subjected to screen printing, except that the type of polyimide resin was changed and the amount of solvent PGPE was changed depending on the type of resin. The printing results are shown in Table 1, and the cured coating properties are shown in Tables 3 and 4.

Example 5 Flake silver powder (average particle size 5μ, Tokuyama Chemical Research Institute).

TCG-7N) 70 parts, palladium powder (average particle size 03μ
, Mitsui Kinzoku Mining) 5 parts, TI+e as polyimide resin
15 parts of rmid FA-7001, PG as a solvent
Weigh out 22 parts of PE and thoroughly dissolve and mix using a stirrer.

After further kneading in a three-roll mill, a small amount of leveling agent and antifoaming agent was added, and 8 parts of BCA were added.
The viscosity was adjusted to about 50-8°Kcps. Screen printing was performed in the same manner as in Example 1. The printing results are shown in Table 1, and the cured coating properties are shown in Tables 3 and 4.

Examples 6 to 11 Pastes were prepared in the same manner as in Example 5 and subjected to screen printing, except that the type of polyimide resin was changed and the amount of solvent BCA was changed depending on the type of resin.

The printing results are shown in Tables 1 and 2, and the cured coating properties are shown in Tables 3 and 4.

Example 12 Same as Example 5 except that 75 parts of TCG-7N was used as flaky silver powder, 8 parts of Thermid IP-600 and 7 parts of MP-256 were used as polyimide resin, and 11 parts of BCA was used as a solvent. A paste was prepared using the method described above and used for screen printing. The printing results are shown in Table 2, and the cured coating properties are shown in Tables 3 and 4.

Examples 13 to 14 Pastes were prepared in the same manner as in Example 12, except that the type of polyimide resin was changed and the amount of solvent BCA was changed, and the pastes were subjected to screen printing. Table 2 shows the print results.
The properties of the cured coating film are shown in Tables 3 and 4.

Example 15 35 parts of TCG-7N as flaky silver powder, AgC-
35 parts of L, 5 parts of palladium powder, 10 parts of TI+er+sid IP-600 as polyimide resin and MP
A paste was prepared in the same manner as in Example IJA13, except that 5 copies of -256 were added, and the paste was subjected to screen printing. The printing results are shown in Table 2, and the cured coating properties are shown in Tables 3 and 4.

Examples 16 to 17 Pastes were prepared in the same manner as in Example 15, except that the type of polyimide resin was changed, and were subjected to screen printing. The printing results are shown in Table 2, and the cured coating properties are shown in Tables 3 and 4.

Example 18 The flaky silver powder, polyimide resin, PGPE as a solvent, and BCA in Example 12 were
The same parts by weight were weighed out, thoroughly dissolved and mixed using a stirrer, and then thoroughly kneaded using a three-roll mill.

Example 12: Viscosity and other appearance of the obtained paste
was exactly the same. The printing results and cured coating properties were also similar to Example 12.

Table 4 Comparative Example 1 75 parts of flaky silver powder TCG-7N, 15 parts of Kelimide #601 (manufactured by Nippon Polyimide) as a polyimide resin
Weighed out 50 parts of NMP as a solvent, thoroughly dissolved and mixed with a stirrer, and then kneaded with a 3-roll mill.The viscosity of the 0-roll paste immediately after production was about 40 Kcps.
It gelatinized in about 7 days at room temperature.

Screen printing was performed immediately after production, but continuous printing was impossible because the printability was very poor and the squeegee rubber deteriorated quickly.

When curing was carried out at 260° C. for 30 minutes and the sheet resistance value was measured, it was impossible to measure because there was a short circuit due to sag in the line portion. It was a cured coating that did not get wet even with solder.

Comparative Example 2 As a polyimide resin, PS I-ZPS-1514 (Chisso, resin content 17%, solvent composition NMP/B CA
A paste was prepared in the same manner as in Comparative Example 1, except that 90 parts of the paste was used (=70150), and the viscosity immediately after production of the paste was about 4QKcps. Sedimentation of silver powder was observed after 2-3 days at room temperature.

Screen printing immediately after production was very poor, similar to Comparative Example 1, and continuous printing was also impossible.

The sheet resistance value after drying at 260°C for 30 minutes is that of Comparative Example 1.
Similarly, it was impossible to measure, and it did not get wet with solder.

Comparative Example 3 A paste similar to Comparative Example 1 was prepared except that 54 parts of LARC-TPT (Mitsui Toatsu Chemical, 28% triglyme solution) was used as the polyimide resin.

The viscosity of this paste immediately after production was about 50 Kcps. Similar to Comparative Example 2, sedimentation of powder was observed. The screen printing immediately after manufacturing was very poor, but there was no deterioration of the squeegee rubber, etc.

The coating properties after drying at 260° C. for 30 minutes were similar to those of Comparative Example 2.

Comparative Example 4 5R-5110 (Nissan Chemical Industries, Ltd.,
Resin concentration 60 wt%, NMP/BCA mixed solvent) at 25%
A paste was prepared in the same manner as in Comparative Example 1 except that 8 parts of BCA was further added to adjust the viscosity.The viscosity of the 6 pastes immediately after manufacture was about 60 K cps, and the storage stability was also about 20 K cps at room temperature. It was usable for days.

Table 5 Table 6 Table 7 Screen printing immediately after production had good printability, but continuous printing was poor due to deterioration of the squeegee rubber.

The coating film properties after curing are shown in Tables 6-7.

[Effects of the Invention] As explained above in the Examples and Comparative Examples, in the conductive paste using a polyimide resin as a binder, the specific solvent component is used, and the paste is soluble in such solvents, By using a highly heat-resistant thermosetting polyimide resin with a small imide group equivalent as a component, the storage stability of the paste is improved, making it suitable for screen printing.
The printability was very good, and continuous printing could be carried out in the same manner as other thick film pastes.

Furthermore, the properties of the cured coating film are equivalent to or better than those of thick film paste using glass frit as a binder.

However, with the conductive paste of the present invention, compared to the conventional conductive paste using glass frit as a binder, which was limited to ceramic substrates,
Its applications have expanded to include heat-resistant organic substrates mainly made of polyimide resin, and even glass substrates, and of course it is also versatile for ceramic substrates of all types.

Patent applicant: Hakutokaji Co., Ltd. (3 other people)

Claims (2)

[Claims] 1. In a conductive paste for forming circuits and electrodes, which is mainly composed of (A) a solvent, (B) a thermosetting resin (binder), and (C) a conductive metal powder, (A) the solvent is ethylene glycol monophenyl. The thermosetting resin (B) is composed of at least one solvent selected from the group consisting of ether, propylene glycol monophenyl ether, ethylene glycol monobenzyl ether, and 2-phenoxyethyl acetate. at least 10wt in
% or more of polyimide resin as a component, and (C) conductive metal powder consisting of gold, silver, palladium, copper, nickel, aluminum, or an alloy of these. 1. A printed conductive paste comprising one or more types of conductive metal powder as a component. 2. (A) As a solvent, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, ethylene glycol monobenzyl ether, 2-
A claim in which at least one solvent selected from the group consisting of phenoxyethyl acetate and at least one solvent selected from the group consisting of diethylene glycol monobutyl ether acetate, 2-butoxyethyl acetate, diethylene glycol dibutyl ether, and ethylene glycol dibutyl ether are used together. Item 1. Printed conductive paste according to item 1.