JPH0619075B2 - Conductive paint that can be soldered - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a conductive coating material containing copper powder and having good conductivity, and more specifically, forming a conductive circuit on an insulating substrate by screen printing or the like. The present invention relates to a conductive paint capable of directly soldering a coating film of a circuit after heating and curing the coating film by using a flux agent.

(Prior Art) Since the specific resistance of silver paste has good conductivity of 10 ⁻⁴ Ω · cm class, it has been widely used as a material for printed circuits of electronic devices, but silver powder is expensive. Since the ratio of the cost to the cost is high, and a direct current voltage is applied to the conductive circuit formed of silver paste in a humid atmosphere, silver migration may occur and the circuit may be short-circuited.
There is a strong demand for the appearance of an inexpensive copper paste that can replace the silver paste.

When the coating film of the conductive paste consisting of the copper powder and the thermosetting resin is heat-cured, since the oxidizability of copper is large, oxygen contained in the air and the resin of the binder is combined with the copper powder, An oxide film is formed on the surface thereof, and the conductivity thereof is significantly impaired, or the conductivity disappears with time. Therefore, various kinds of copper pastes have been disclosed in which various additives are added to prevent the copper powder from being oxidized and have stable conductivity. However, their conductivity is often in the 10 ⁻³ Ω · cm class, and there is a problem in long-term stability of conductivity. Moreover, there is a problem that soldering cannot be directly applied to the obtained copper paste coating film.

(Problems to be Solved by the Invention) Since a conductive circuit formed on an insulating substrate by a known copper paste cannot be directly applied with soldering as described above, an activation treatment is applied to a coating film of the circuit. It is applied and electroless plated, or electrolytic copper plating is performed in a plating solution using the coating film as a cathode, and then soldering is performed on the copper surface. If it is not certain, it will not be put to practical use.

Therefore, if a solderable copper paste that does not require electroless plating and / or electroplating is developed, the process of forming a printed circuit can be greatly shortened, and its economic merit becomes significant. . Here, the problems that the copper paste should have are that it has the same conductivity as silver paste, that it can be screen-printed, intaglio-printed, brushed and spray-coated, and that the adhesion of the coating film on the insulating substrate is good. That is, a fine wire circuit can be formed, solderability on the coating film is excellent, and the conductivity of the conductive circuit of the solder coat can be maintained for a long period of time.

The present invention has an object to solve such a problem, and an object thereof is to provide a solderable conductive paint.

(Means for Solving Problems) As a result of intensive studies to solve the above problems, the present inventors have added metal copper powder to a thermosetting resin obtained by mixing an amino resin with an acrylic resin, Further, when a conductive coating material in which a saturated fatty acid or unsaturated fatty acid or a metal salt thereof and a metal chelate forming agent are arranged is provided, the conductivity is improved, and extremely good soldering can be applied to the entire surface of the cured coating film. The present invention has been completed by finding the above.

According to the present invention, 85 to 95% by weight of metallic copper powder and 15 of resin mixture are contained.
1 to 8 parts by weight of saturated fatty acid or unsaturated fatty acid or metal salt thereof based on 100 parts by weight (total of 5 to 30% by weight (acrylic resin 70 to 30% by weight, resin mixture consisting of the balance of amino resin)). And a metal chelate forming agent in an amount of 1 to 15 parts by weight.

Here, the metal copper powder used in the present invention is a piece,
It may have any shape such as a tree shape, a spherical shape, or an indefinite shape, and the particle size thereof is preferably 100 μm or less, and particularly,
It is preferably 1 to 30 μm. If the particle size is less than 1 μm, it is easily oxidized, and the resulting coating film has low conductivity and poor solderability.

The amount of metal copper powder blended is 85 when blended with the resin mixture.
Used in the range of 95 to 95% by weight, preferably 87 to 93
% By weight.

When the content is less than 85% by weight, the solderability becomes poor. On the other hand, when it exceeds 95% by weight, the metal copper powder is not sufficiently bound, the resulting coating film becomes brittle, and the conductivity decreases. Screen printability also deteriorates.

The resin mixture binds the metallic copper powder and other components in the conductive paint according to the present invention, and is made into a polymer substance by heat curing.
It is a mixture blended in a proportion of 0 to 30% by weight and 30 to 70% by weight of an amino resin.

The acrylic resin used in the present invention has an acid value (-
COOH) 10 to 80 mg / g, hydroxyl value (-OH) 40 to 250 mg / g, particularly, the hydroxyl value is in the range of 60 to 150 mg / g, and the acid value is 30.
A range of up to 70 mg / g is preferred. In order to improve the water resistance of the coating film, it is desirable to use an acrylic resin having a hydroxybutyl group, and a molecular weight of 2500 or more is used, but a range of 4000 to 15000 is preferable. The molecular weight is not related to the solderability which is the object of the present application, but if the molecular weight is less than 2500, the resulting coating film becomes brittle, which is not preferable. On the other hand, if an acrylic resin having a large molecular weight is used, the conductivity will decrease.

The amino resin used in the present invention is a urea resin, a butylated urea resin, a methylated melamine resin, a butylated melamine resin, a benzoguanamine resin, or the like, which acts as a cross-linking agent for an acrylic resin used in combination and has a three-dimensional network structure. To form.

The blending amount of the resin mixture obtained above is used in the range of 15 to 5% by weight in the blending with the metallic copper powder, and the total amount of the metallic copper powder and the resin mixture is 100 parts by weight.

In such a case, if the blending amount of the resin mixture is less than 5% by weight, the metal copper powder is not sufficiently bound, the resulting coating film becomes brittle, the conductivity is lowered, and the screen printability is deteriorated. When it exceeds 15% by weight, solderability is not preferable.

The saturated fatty acid or unsaturated fatty acid or metal salt thereof used in the present invention is a saturated fatty acid having 1 carbon atoms.
6-20 palmitic acid, stearic acid, arachidic acid, or unsaturated fatty acids such as zomarinic acid having 16 to 18 carbon atoms, oleic acid, linolenic acid, etc., and their metal salts, sodium, Potassium, copper, zinc,
It is a salt with a metal such as aluminum. The use of these dispersants is preferable since it facilitates fine dispersion of the metal copper powder in the resin mixture in the blending of the metal copper powder and the resin mixture, and forms a coating film having good conductivity.

The amount of the saturated fatty acid or unsaturated fatty acid or metal salt thereof used is within the range of 1 to 8 parts by weight, preferably 2 to 100 parts by weight based on 100 parts by weight of the total amount of the metal copper powder and the resin mixture.
6 parts by weight.

If the compounding amount of the dispersant is less than 1 part by weight, fine dispersibility of the metal copper powder cannot be expected, and conversely, if it exceeds 8 parts by weight, the conductivity of the coating film is lowered, and the coating film and the substrate are It is not preferable because it causes deterioration of the adhesiveness.

The metal chelate forming agent used in the present invention is at least one selected from aliphatic amines such as monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, triethylenediamine, and triethylenetetramine.

The metal chelate forming agent added prevents oxidation of the metal copper powder, contributes to maintaining conductivity, and further improves solderability. For example, in the combination of the metal copper powder and the resin mixture used in the present invention, it can be soldered on the coating film,
By adding a metal chelate forming agent, good and practically excellent soldering can be carried out, and therefore, its role as an addition effect is great.

The compounding amount of the metal chelate forming agent is 1 to 15 parts by weight, preferably 2.5 to 7.5 parts by weight, based on 100 parts by weight of the total amount of the metal copper powder and the resin mixture. When the amount of the metal chelate forming agent is less than 1 part by weight, the conductivity is lowered and the solderability is not preferable. On the other hand, when it exceeds 15 parts by weight, bleeding occurs from the cured coating film, which is not preferable.

For the conductive paint according to the present invention, a normal organic solvent can be appropriately used in order to adjust the viscosity. For example,
Butyl carbitol, butyl carbitol acetate,
It is a known solvent such as butyl cellosolve, methyl isobutyl ketone, n-butyl cellosolve acetate, cellosolve acetate.

(Examples) Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to these Examples.

Firstly, a tree-like metal copper powder having a particle diameter of 5 to 10 μm, a resin mixture (70 to 30% by weight of an acrylic resin, a resin mixture consisting of the balance amino resin), potassium oleate, copper oleate, and triethanolamine, respectively. The components were blended (parts by weight) in the proportions shown in the table, n-butyl cellosolve acetate was added as a solvent, and the mixture was kneaded with a triaxial roll for 20 minutes to prepare a conductive paint. An S-shaped conductive circuit having a width of 0.4 mm, a thickness of 30 ± 5 μm and a length of 520 mm is formed on a glass / epoxy resin substrate by screen printing, and the temperature is 130 to 180 ° C.
The coating film was cured by heating for 10 to 60 minutes.

Subsequently, in order to apply soldering on the formed conductive circuit,
The substrate was dipped in an organic acid type flux bath for 4 seconds, then dipped in a molten solder bath (Pb / Sn = 40/60) at 250 ° C. for 5 seconds and pulled up to solder the entire surface of the conductive circuit.

Table 1 shows the results of examining various characteristics of the conductive circuit obtained in the above process.

Here, the electroconductivity of the coating film is a value obtained by measuring the volume resistivity of the coating film which has been heat-cured.

Adhesiveness of a coating film is defined by JIS K5400 (1979), which is based on the basic test method, and is perpendicular to the coating film in a vertical and horizontal direction.
Draw 1 parallel line at 1 mm intervals and 1 in 1 cm ^2.
This is the number of base stitches of the coating film remaining on the insulating substrate when a base-like cut is made to make 00 cells and the coating film is peeled off from it with cellophane tape. .

The solderability was evaluated by observing the state of soldering on the coating film with a stereoscopic microscope at a low magnification and by the following criteria.

○ mark: The surface is smooth and solder is attached to the entire surface △ mark: The coating film is partially exposed × mark: The solder is attached only partially The printability is When a conductive circuit was formed by a screen printing method using the conductive paint, the ease of printing was observed and evaluated according to the following criteria.

◯: Good conductive circuit shape X: Difficult to form conductive circuit The thickness of the solder coat soldered to the coating film according to the example of Table 1 is 10 μm on average. As can be seen from the results, in Examples 1 to 4, since the specific compounding materials used in the present invention are properly combined, the conductivity of the coating film, the adhesion of the coating film, the solderability, the printability, etc. The various characteristics of are improved. In particular, since the obtained cured coating film can be directly soldered using an organic acid flux agent, the conductivity of the conductive circuit can be changed from 10 ^-4 Ωcm to 10 ^-5 Ωcm. It can be improved and a larger current can be passed through the conductive circuit.

In addition, the conductivity of the solder coating is excellent in heat resistance and moisture resistance,
Since its resistance change rate is also small, it can be used in an atmosphere of heating and high humidity.

Next, in Comparative Examples 1 and 2, since the metal chelate forming agent was not added and the compounding amount of the resin mixture was larger than the proper amount,
Solderability becomes poor, which is not preferable. In Comparative Examples 3 and 4, although the metal chelate forming agent was blended,
Since the blending amount of the resin mixture is larger than the proper amount, the solderability becomes poor. In Comparative Example 5, since the blending amount of the resin mixture with respect to the metal copper powder is insufficient, the resulting coating film has poor conductivity and solderability is also unfavorable.

Although not described in the above examples, the composition of the conductive coating material according to the present invention, a metal surface activated resin (for example, active rosin or partially hydrogenated rosin, fully hydrogenated rosin, esterified rosin, maleated At least one selected from modified rosins such as rosin, disproportionated rosin, and polymerized rosin is used. The preferred rosin is active rosin or maleated rosin. Sex is obtained.

As another example, the coating film thickness of the conductive paint according to the present invention is 30 ± 5.
Area resistance is 0.01 Ω / □ or less when solder plating with a thickness of 5 to 10 μm is applied, and when used for electromagnetic shielding, it is allowed by the Federal Communications Commission (FCC) Class B (for consumer use). A value well below the value (30 to 100 MHz
Of 100 μV / m or less) was obtained.

Therefore, a heat-curable or UV-curable solder resist ink is applied onto a conductive circuit formed by a copper-clad laminate by an etched fork method to form an insulating layer, and the conductive coating material according to the present invention is used on the insulating layer. Then, a pattern that is almost the same as the underlying conductive circuit is formed on the resist by screen printing, the coating film is heated and cured, and then solder coated on the entire surface of the coating circuit with a solder leveler machine to form an effective electromagnetic shielding layer. In addition, it can be effectively used as an electrostatic shield layer.

(Effects of the Invention) As described above, the conductive coating material according to the present invention can be directly soldered on a coating film by forming a conductive circuit on an insulating substrate and then heat-curing the coating film. Therefore, it is possible to further improve the conductivity of the conductive circuit, and it is not necessary to perform electroless plating by performing activation treatment on the coating film of the circuit or electroplating as in the conventional case. Is greatly shortened, and the economic merit is great.
Further, the conductive paint of the present invention is used not only for forming a conductive circuit but also for electronic equipment parts, electrodes of circuit parts, through-hole connecting agents, electromagnetic waves, electrostatic shield layers, etc., and has a high industrial utility value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisatoshi Murakami 2-3-1, Iwata-cho, Higashi-Osaka City, Osaka Prefecture Tatsuta Electric Wire Co., Ltd. (72) Inventor Tsunehiko Terada 2-3, Iwata-cho, East Osaka No. 1 in Tatsuta Electric Wire Co., Ltd. (56) Reference JP-A-58-117606 (JP, A) JP-B-60-58268 (JP, B2)

Claims (1)

[Claims] 1. A resin mixture 1 containing 85 to 95% by weight of metallic copper powder.
1 to 8 parts by weight of saturated fatty acid or unsaturated fatty acid or metal salt thereof based on 100 parts by weight in total of 5 to 5% by weight (70 to 30% by weight of acrylic resin, resin mixture consisting of balance of amino resin). Parts and metal chelate forming agents 1 to 15
Solderable conductive paint consisting of parts by weight.