JPS5853966A - Electrically-conductive coating compound using ni powder - Google Patents

Abstract

PURPOSE:The titled inexpensive coating compound applicable to jumper line of printed circuit board, etc., capable of being soldered, having improved strength, obtained by adding Ni powder as an electrically-conductive substance to a coating compound consisting of a thermosetting resin having high heat resistance, an organic solvent, and an unsaturated fatty acid. CONSTITUTION:For example, (A) (i) a thermosetting resin (preferably, polyimide type resin having a heat resistance of >=200 deg.C) is dissolved in (ii) an organic solvent and (iii) an unsaturated fatty acid (e.g., oleic acid, etc.) in an amount to give 10-70wt% based on pure resin weight of the component i to give a coating compound. (B) Ni powder as an electrically-conductive substance is uniformly dispersed into the coating compound, to give the desired coating compound. USE:Useful for covering the terminal draw lead of print resistance, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conductive paint made by dispersing fine metal powder (hereinafter referred to as powder) as a conductive substance in a resin paint.

Conventional conductive paints that use thermosetting resin as a binder are
Most of them used Ag powder. Although Ag paints have many advantages, they have major drawbacks, such as the fact that their paint films tend to undergo migration under high humidity and pressure, and that they are expensive.

As conductive paints are now used in a wide variety of fields, especially in electronic components (e.g. jumper wires using printed distribution boards, terminal lead-out wires for printed resistors, etc.), the above-mentioned drawbacks have become a serious problem. It is well known that it has gained attention as a

Therefore, research on conductive paints using Cu powder has recently been conducted vigorously, and the results have been announced.
It seems that it has not yet been used as a substitute for paint.

In particular, conductive paints that are resin-based paints and can be soldered not only to resin laminated boards but also to ceramic substrates, etc. have been announced, but they are not yet in general use. The metal glaze conductive paint used is the main product. The main reason for this is the following.

(a) Soldering is difficult.

(b) Soldering has insufficient properties, especially strength.

(c) A method using Ag powder cannot avoid the disadvantage of migration and is expensive.
G-paints have common drawbacks.

SUMMARY OF THE INVENTION An object of the present invention is to provide a resin-based conductive paint which can significantly improve the above-mentioned drawbacks, has excellent properties, can be soldered, and is inexpensive and has low friction.

In order to achieve the above object, the conductive paint according to the present invention has the following features:
Ni is used as a conductive material in a paint made by adding a suitable organic solvent and a small amount of unsaturated fatty acids to a highly heat-resistant thermosetting resin.
It is characterized by using powder and uniformly dispersing it in the paint.

Next, the configuration of the present invention will be explained in detail.

First, a conductive paint using Cu powder as a conductive material will be briefly explained. This is because the theory regarding conductive paints other than Ag paints used at so-called medium and low temperatures also applies to high-temperature paints.

An important condition for a conductive paint is that when it forms part of an electrical circuit by printing, spraying, brush painting, etc., its surface specific resistance (abbreviated as specific resistance) should be less than c and the value of ρ' (abbreviated as specific resistance) should be less than 1Ω, preferably The resistance should be 0.1Ω/mouth or less.

According to our research, in order to manufacture conductive paints using metal powders other than noble metal powders such as Ag, Au, Pt, etc., such as Cu powder, the following two conditions are required: Satisfied thermosetting properties It is necessary to select a resin.

(+) Even when stored as a paint, the metal powder does not oxidize, but rather has reducing properties.

(11) When the paint is cured at high temperature, it absorbs oxygen and undergoes a polycondensation reaction.

Condition (1) is because the metal powder contained in it is not oxidized during storage.Q, condition (11) is that the metal powder is not oxidized during coating baking, but rather a thin oxide film forms on the surface of the powder. Even if it is wrapped, it is necessary to reduce it and form a low-resistance film.

Based on the above idea, the main invention is as follows.

(1) JP-A-51-93:394, (1 Conductive Composition) (2) JP-A-51-115691 (Conductive Composition) The present inventor has detailed the conditions of (s) and (ti) above. As a result of further investigation, it was determined that other conditions were necessary in order to reduce the value of ρ'.As a result, it was confirmed that the above two conditions were necessary conditions, but not sufficient conditions.

Through this research, the present inventor invented a Cu conductive paint that can be used as a substitute for Ag conductive paint, and filed the following series of patent applications by the same applicant as the present inventor.

(a) Japanese Patent Application No. 55-098778 (b) % Application No. 1988-129115 (C) Japanese Patent Application No. 154-073-1973 (d) Japanese Patent Application No. 172645-1987 (e) Japanese Patent Application No. 56-010843 In the above application, it was confirmed that the sufficient conditions mentioned above are that when the resin undergoes a curing reaction at a high temperature, the metal powder is not oxidized and the metal powder is tightly and firmly bonded.

Through the above research, the present inventors were able to provide an inexpensive Cu conductive paint with excellent properties, but soldering cannot be performed using this paint. This is a regrettable point.

After that, the present inventor developed a paint that could be used with soldering, and finally reached completion. In this case as well, it is still necessary to satisfy the two necessary conditions and one sufficient condition.

Next, the above conditions regarding the present invention will be explained.

In the order of explanation, the physicochemical characteristics of Ni powder will be described. It is well known that Ni powder is used as a catalyst in polymer synthesis. When Ni powder is dispersed in a solution containing a weak acid, it exhibits a reversible reaction in which it becomes ionized from a molecular state, and the ionized material becomes molecular again.

On the other hand, as a result of Auger electron spectroscopy and thermal analysis of Ni powder, it is confirmed that the surface of ordinary Ni powder is covered with an extremely thin oxide film. Therefore, even if Ni powder is analyzed by differential thermal analysis, no endothermic reaction associated with oxidation is observed up to 300°C. [T] Nl powder surrounded by a thin oxide group does not oxidize even when heated at around 600°C. The properties of this stiff Ni powder are different from those of Ag and Cu powders; when Ag or Cu is heated to around 250° C., the oxidation reaction extends to the center, making it a poor conductor of electricity.

Next, we will describe the chemical characteristics that unsaturated fatty acids have on Ni powder. For example, in a solution containing a small amount of oleic acid, N1
When the powder is dispersed, the thin oxide layer on the surface of the N1 powder is destroyed by oleic acid, resulting in a pure metallic Ni surface. In addition, N1 eluted into the solvent by oleic acid
The + ions concentrate on Ni molecules existing in molecular form and form part of fine scale-like Ni powder.

That is, it can be seen that among paints containing weakly acidic organic fatty acids, the Ni conductive paint satisfies all of the above conditions (1).

Next, Ni powder was dispersed in a paint containing oleic acid.
A case in which conductive paint is heated to a high temperature will be described. For example, when the high temperature heat resistant resin is a polyimide resin, the solvent starts to evaporate when the temperature reaches 70°C or higher, and the oleic acid starts to evaporate at about 120°C. cease to exist. Incidentally, up to this stage, the above-mentioned action of removing the blocking film of the N1 powder is continued.

On the other hand, Ni powder begins to crystallize at around 170°C through fine scale-like Ni powder whose active layer becomes thick and the activity is further increased. That is, sintering between the powders progresses.

At the same time, the ring-closing polycondensation reaction of the polyimide resin is started, so the Ni powder is tightly bound without being oxidized. That is, the contact area of the hardened Ni powder during N exchange increases, and as a result, the contact resistance between the Ni powders decreases.

Therefore, conductivity is significantly improved.

From the above explanation, the necessary conditions (11) that a conductive paint should have are due to the special physicochemical properties inherent in Nl powder.
It will be understood that and sufficient condition (iii) is satisfied. '& Since the product during the ring-closing polycondensation reaction, ie, the resin curing reaction, is mainly H2O, the conductivity of the Ni powder is not affected.

According to experiments, the weight of the unsaturated fatty acid is preferably 10 to 70 per 100 of the pure resin weight. The general structure of polyicide resin is shown below.

Next, examples of the highly heat-resistant resin according to the present invention include polyimide resin; polyimide amide resin; polyimide ester resin; polybenzimidazole imide resin; polymethylene phenylene oxide resin; polyimidazopyrrolone; acid anhydride-cured alicyclic epoxy resin, etc. There is. These resins can be used alone or in combination.

Next, embodiments of the present invention will be described in detail.

(Example 1 to Example 6) Table 1 shows the formulations of Examples 1 to 2.

Note 1: Polyimide face (manufactured by Mitsui Toatsu Chemical) Note 2: Polyimide enamel (manufactured by Westenghouse) Note 6: Electrolytic N
1 powder, average particle size -7 μm The ingredients listed in Table 1 above were blended and thoroughly mixed, and the resulting Ni conductive paint was applied to a 150-mesh nylon screen on an alumina porcelain substrate. A zigzag pattern of 50 μm, 2 mm in width, and 368 mm in length was printed. The sample was placed in a sintering furnace at 600° C. for 60 minutes to dry and sinter. After taking it out and allowing it to reach room temperature, a Sn-plated copper wire with a diameter of Q, 5 Jll + a length of 6 Jll was placed vertically at any point on the NI conductive film in the zigzag pattern, and an area of 2 mm x 2mm
I made a test sample by soldering the parts.

The conditions for soldering are as follows.

Solder used: Commercially available Pb-8n solder.

0 Soldering iron temperature: 220℃~240℃ 0 Soldering takes 2 to 5 seconds The strength test method using this sample is the following S).

Sn plating et win perpendicularly to the board 1oo, y/
The strength of soldering is defined as the tensile strength at a rate of % and the strength at break.

The test results are shown in Table 2 together with the results of other characteristic tests.

Next, the moisture resistance and heat resistance characteristics of the Ni conductive coating film will be described.

(11) (Note: 0 in the table is good, O is slightly good, X is bad) Note 1: Average value of 2Q samples, Note 2: Average value of 10 samples 3 is a graph showing the results of a moisture resistance test of a sample of clothing according to Example 2. The test conditions were that the sample was left in a constant temperature and humidity chamber at a temperature of 60°C and a relative humidity of 96% for up to 1000 hours, and the change in resistivity was measured, and the rate of change Sρ' was calculated using the following formula.

Here ρ6. ρ′ is the specific resistance before the test and at the time of measurement, respectively. The curve was an average value of 10 samples, and the variation was small. This can be said to be a good result.

FIG. 2 is a graph showing the results of the resistance (12) heat test of the sample according to Example 2 in Table 2. Test conditions are room temperature,
The sample was left in a constant temperature chamber at 100°C for up to 1000 hours, the change in resistivity was measured, and the rate of change bρ' was calculated according to both formulas. The curve was an average value of 10 samples, and the variation was small. What should be noted is that the resistivity decreases with time. This is thought to be due to an aging effect or, although it is extremely small, to the progress of the curing reaction of the resin, but this has not been determined. In any case, it is a desirable tendency that the specific resistance becomes small.

Next, the effects of the present invention will be briefly described.

(1) The resin-based Ni conductive paint according to the present invention is different from conventional Ag.
It has a low resistivity comparable to that of conductive paints.

(2) It has high-temperature heat resistance that cannot be obtained with conventional resin-based conductive paints.

(3) Good soldering has properties and soldering has strength.

This was a difficult point with conventional resin-based paints.

(4) Good moisture resistance. Although omitted for simplicity, other electrical properties are also comparable to conventional Ag conductive paints.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the moisture resistance properties of the coating film of the Ni conductive paint according to the present invention, and FIG. 2 is a graph showing the heat resistance properties of the coating film. Enter Figure 2 (H) - (15) Procedural Amendment (Ministry)) July 1982! Mr. Kazuo Wakasugi, Commissioner of the Japanese Patent Office on the f day, 1, Indication of the case, 1982, Patent Application No. 152134, 2, Title of the invention: N, Conductive paint using powder 3 Relationship with the person making the amendment: Patent applicant representative number 2 Masao Mura 4゛ Agent 〒-1,3 (telephone) 460
-6072 Name (7862) Patent Attorney Oka
1) Go Part 5, Date of amendment order 6 Number of inventions increased by the amendment None 7, "Detailed explanation of the invention column" of the specification subject to the amendment In the detailed explanation of the invention in the statement of contents of the amendment, the following Correct as shown. (1) Page 14, lines 1 and 2. "...at normal temperature..." should be replaced with "...at normal humidity,"
"..." I corrected myself. (2) 6th line from the bottom of page 14. The statement ``This was difficult to achieve with conventional resin-based paints'' has been corrected to ``This characteristic is difficult to obtain with conventional resin-based paints.''

Claims (1)

[Claims] 1. Ni powder is used as a conductive substance in a paint made by adding a suitable organic solvent and a small amount of unsaturated fatty acid to a highly heat-resistant thermosetting resin, and this is added to the paint. A conductive paint using Ni powder that is characterized by uniform dispersion. 2. A conductive paint using Ni powder according to claim 1, wherein the thermosetting resin according to claim 1 has a heat resistance of at least 200°C or higher. 6. A conductive paint using Ni powder according to claim 2, wherein a polyimide resin is used as the thermosetting resin according to claim 2. 4. A conductive paint using Ni powder according to claim 2, characterized in that a polyamide-imide resin is used as the thermosetting resin according to claim 2. 5. Claims 1 to 4, characterized in that oleic acid is used as the unsaturated fatty acid described in claim 1.
A conductive paint using the Ni powder described in any one of the items. 6. Claims 1 to 4, characterized in that linoleic acid is used as the unsaturated fatty acid described in claim 1.
A conductive paint using the Ni powder described in any one of the items. Z A conductive paint using Ni powder according to any one of claims 1 to 4, characterized in that lylunic acid is used as the unsaturated fatty acid described in claim 1. 8. Claims 1 to 7, characterized in that the content of unsaturated fatty acids in the thermosetting resin according to claim 1 is 10 to 70% by weight based on the pure resin weight of the resin. A conductive paint using the Ni powder described in item 1.