JPH0753843B2 - Conductive paint that can be soldered - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a conductive paint containing copper powder and having good conductivity, and more specifically, a conductive circuit formed on an insulating substrate by screen printing or the like. The present invention relates to a conductive paint which can be directly soldered after a circuit coating film is heated and cured and then a flux agent is applied onto the coating film.

(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. However, if the DC voltage is applied to the conductive circuit formed of the silver paste in a humid atmosphere, it may cause silver migration and cause a short circuit to the circuit.
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.

As described above, since the conductive circuit formed on the insulating substrate by the known copper paste cannot be directly applied by soldering, the coating film of the circuit is subjected to an activation treatment to be electroless plated or coated. After performing electrolytic copper plating in a plating solution using the film as a cathode, soldering is performed on the copper surface. In such a case, practical use cannot be achieved unless the interlayer connection between the coating film and the copper plating is reliable.

Therefore, if a solderable copper paste that does not require electroless plating and / or electroplating is developed, the process of forming a printed circuit is greatly shortened, and the economic merit thereof is great. . 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, concave plate-printed, brushed and spray-coated, and that the adhesion of the coating film on the insulating substrate is What is good is that a fine wire circuit can be formed, solderability on the coating film and soldering strength are excellent, and the conductivity of the conductive circuit of the solder coat can be maintained for a long period of time.

Therefore, as a result of repeated experiments and studies, the present inventors have found that
As means for somehow solving the above technical problem, metallic copper powder, resin mixture (resin mixture consisting of metal surface-activating resin and granular phenol resin and thermosetting resin), saturated fatty acid or A solderable conductive paint comprising a saturated fatty acid or a metal salt thereof, a metal chelate forming agent and a soldering accelerator has been proposed (Japanese Patent Laid-Open No. 62-2706).
(See Japanese Patent Publication No. 74).

This invention is the conductivity of the paint, the adhesion of the coating film, solderability,
Various properties such as crack resistance and printability of the coating film are good, and in particular, the obtained cured coating film can be directly soldered by using an ordinary organic acid-based flux agent. The conductivity can be improved from 10 ^-4 Ωcm to 10 ^-5 Ωcm, a larger current can be applied to the conductive circuit, and the conductivity of the soldering coating is heat resistant, Since it has excellent moisture resistance and a small rate of change in resistance, it has an exceptional effect that it can be used in an atmosphere of heating and high humidity.

(Problems to be Solved by the Invention) However, the above-mentioned invention proposed by the present inventors was a very effective means for solving the conventional problems, but the present invention itself has the following problems. It was found to be internal for subsequent use.

That is, the invention previously proposed by the present inventors, as described above, the resin that binds the metal copper powder is composed of a metal surface activating resin, a granular phenol resin and a thermosetting resin, This is a point that the work of mixing the resin mixture is required before the kneading of the conductive paint, and the work of adding the soldering accelerator is inevitable.

Therefore, the present invention has been completed as a result of further experiments and studies in order to solve this problem, and it is possible to highly improve the convenience and greatly improve the productivity. The necessary properties as a "possible conductive paint" are intended to provide one that is well equipped.

(Means for Solving the Problems) In order to achieve the above object, the solderable conductive paint of the present invention comprises a metal copper powder (A) of 85 to 95% by weight and a resol type phenol resin (B). And (A) and (B) total 100
The resol type phenolic resin has 2-1 to 5 parts by weight of saturated fatty acid or unsaturated fatty acid or a metal salt thereof and 1 to 50 parts by weight of a metal chelate forming agent. Substitutes, 2,4-2 Substitutes, 2,
4,6-3 substituted product, methylol group, dimethylene ether,
The infrared transmittance of the phenyl group by infrared spectroscopy is 1, m,
When n, a, b, c, between the transmittances It is a resol type phenolic resin that satisfies the following relationship.

Next, the configuration of the present invention will be further described.

Metallic copper powder used in the present invention, flaky, woodworking, spherical,
It may have any shape such as an irregular shape, and its particle size is preferably 100 μm or less, and particularly 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 the copper metal powder is used in the range of 85 to 95% by weight in the blending with the resol-type phenol resin, preferably
87 to 93% by weight.

If the blending amount is less than 85% by weight, the solderability will deteriorate, and conversely
If it exceeds 95% by weight, the metallic copper powder is not sufficiently bound, the resulting coating film becomes brittle, the desired soldering strength is not obtained, the conductivity is lowered, and the screen printability is deteriorated.

Regarding the resol type phenolic resin used, its stoichiometry, 2-1 substitution amount is λ, 2,4-2 substitution amount is μ, 2,4,6
If the -3 substitution product amount is ν, the methylol group amount is α, the dimethylene ether amount is β, and the phenyl group amount is γ, then
Larger l / n and m / n mean smaller λ / ν and μ / ν. That is, the amount of 2-1 substitution product λ, 2,
This means that the amount of 2,4,6-3 substituted product ν is larger than the amount of 4-2 substituted product μ.

In addition, the fact that b / a and c / a in the above configuration are large means that β /
This means that α and γ / α are small. That is, it means that the amount α of methylol groups is larger than the amount β of dimethylene ether and the amount γ of phenyl groups.

Generally, when the 2,4,6-3 substitution product amount ν increases, the crosslinking density of the resol-type phenol resin increases,
The smaller / ν and μ / ν, that is, the larger l / n and m / n, the better the conductivity of the coating film. However, on the contrary, the coating film tends to be hard and brittle, and the physical properties are poor.

Also, if β / α is small, the solderability of the coating film deteriorates, and γ
If / α is large, the conductivity of the coating film becomes poor.

Therefore, in the conductive paint obtained, the hardness of the coating film is appropriate, and as the resol-type phenol resin having both good conductivity and solderability, 1 / n, m / n, and b / n shown in the above-mentioned constitution are provided.
It is suitable that a is 0.8 to 1.2 and c / a is 1.2 to 1.5, respectively.

The compounding amount of the resol type phenol resin is used in the range of 15 to 5% by weight in the compounding with the metal copper powder, and the total amount (A + B) of the metal copper powder (A) and the resol type phenol resin (B) is 100%. Parts by weight. If the amount of the resol-type phenol resin 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. On the other hand, when it exceeds 15% by weight, the 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 16 to 16 carbon atoms.
Unsaturated fatty acids such as 20 palmitic acid, stearic acid, and arachidic acid are zomarinic acid having 16 to 18 carbon atoms, oleic acid, linolenic acid, and the like, and those metal salts are potassium, copper, aluminum, It is a salt with metals such as sodium and zinc.

The use of these dispersants is preferable because in the blending of the metallic copper powder and the resol-type phenol resin, the fine dispersion of the metallic copper powder in the resin is promoted and a coating film having good conductivity is formed.

The amount of the saturated fatty acid or unsaturated fatty acid or the metal salt thereof used is in the range of 0.5 to 8 parts by weight based on 100 parts by weight of the total amount of the metal copper powder and the resol type phenol resin,
It is preferably 1 to 3 parts by weight.

When the compounding amount of the dispersant is less than 0.5 part by weight, the fine dispersibility of the metal copper powder cannot be expected, and when 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.

The amount of the metal chelate forming agent is 1 to 50 with respect to 100 parts by weight of the total amount of the metal copper powder and the resol-type phenol resin.
Used in the range of parts by weight. 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, if it exceeds 50 parts by weight, the viscosity of the coating material itself is excessively lowered and the printability is impaired, which is not preferable.

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

(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.

Blending (parts by weight) of a tree-like metal copper powder having a particle size of 5 to 10 μm, a resole-type phenol resin having an infrared transmittance ratio shown in Table 1, potassium oleate, and triethanolamine at a ratio shown in Table 2, respectively. Then, some butyl carbitol was added as a solvent, and the mixture was kneaded with a triaxial roll for 20 minutes to prepare a conductive paint. This is screen-printed onto a glass / epoxy resin substrate with a width of 0.4 mm, a thickness of 30 ± 5 μm, and a length of 5
A 20 mm S-shaped conductive circuit was formed and heated at 130 to 180 ° C. for 10 to 60 minutes to cure the coating film.

Subsequently, in order to apply soldering on the formed conductive circuit,
Pass it through the solder leveler machine used in the actual process, immerse the substrate in an organic oxygen-based flux bath for 4 seconds, and then
Immerse in a molten solder bath (Pb / Sn = 40/60) at 250 ° C for 5 seconds and pull it up, and at the same time blow hot air at 2 to 6.0 atm and 220 to 230 ° C, and then wash the entire conductive circuit. Soldered.
The thickness of the solder coat soldered to the coating film is 10 μm on average.

The results of examining various characteristics of the conductive circuit obtained in the above process
The results are shown in Tables and Table 2.

Here, the infrared transmittance ratio was obtained as a result of performing a spectroscopic analysis by a liquid film method on the resol-type phenol resin shown in Table 2 using a Shimadzu Fourier transform infrared spectrophotometer (FTIR-4100). It is obtained by examining the ratio of transmittances at absorption positions (wave numbers) corresponding to the respective substituents with respect to the chart.

The relationship between the positions of the spectra and the substituents required to determine the resol type phenolic resin shown in Table 2 is as follows.

As shown in the above table, the transmittance of each substituent is 1, m,
Expressed as n, a, b, c.

Here, the transmittance (T) is the ratio of the intensity (I ₀ ) of the incident light and the intensity (I) of the transmitted light obtained by drawing a baseline on the background of each absorption peak. In general, It is represented by a formula.

As described above, the transmittance is obtained at the wavelength specified for each substituent. By examining the magnitude relationship of the transmittance, as mentioned above, among the resol type phenolic resins, there are many dimethylene ether bonds, and
A type with many 3-substitutions could be identified.

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.

Adhesion of a coating film is defined by the JIS K5400 (1979) cross-cut test method, and draws 11 parallel and 11 horizontal and vertical lines on the coating film at intervals of 1 mm to give 100 in 1 cm ^2. This is the number of cross-cuts of the coating film remaining on the insulating substrate when the cross-cutting cuts are made so that individual cells can be made and the coating film is peeled off with cellophane tape.

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

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

○ mark: Good formation of conductive circuit △ mark: Difficulty forming conductive circuit × mark: Difficulty forming conductive circuit Next, the soldering strength is the glass / epoxy resin substrate ( For example, a land with a diameter of 3 mm on G10) and a thickness of 25-30 μ
m, a coating film is formed and heated at 130 to 180 ° C for 10 to 60 minutes to cure the coating film, and then the lead wire (0.8 mm
φ tin-plated annealed copper wire) was vertically soldered (using 63Sn eutectic solder), the board was fixed, and the lead wire was pulled vertically with a tensile continuity of 50 mm / min, and the strength was obtained. It is a thing.

As can be seen from the results, in Examples 1 to 4, since the specific compounding materials used in the present invention are appropriately combined, the conductivity of the coating film, the adhesion of the coating film, the solderability, and the soldering strength. , Various properties such as printability become good. In particular, since the obtained cured coating film can be directly soldered by using a normal organic acid-based flux agent, the conductivity of the conductive circuit can be reduced to 10%.
It can be improved from ^-4 Ω ・ cm class to 10 ^-5 Ω ・ cm class,
Larger current can be passed through the conductive circuit.

Next, regarding Comparative Examples, in Comparative Examples 1, 2, and 3, since the infrared transmittance ratio of the resol-type phenolic resin used is not appropriate, preferably a coating film having solderability cannot be obtained. Comparative Example 4 is not preferable because the amount of metallic copper powder is small and the solder is only partially attached to the conductive circuit during soldering. Comparative Example 5 is preferable because the amount of metallic copper powder is large and the amount of metallic copper powder is not sufficiently bound, the conductivity of the coating film is unstable, the resulting coating film is brittle, and the screen printability is difficult. Absent.

(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.
In addition to the conductive circuit formation, the conductive coating material of the present invention is used for electronic device parts, circuit part electrodes, through-hole connecting agents, electromagnetic agents,
It is also used for electrostatic shield layers and has a high industrial utility value. And, in particular, in the present invention, a resin for binding the metal copper powder in the step before kneading the conductive coating, which has been previously proposed by the present inventors, is a metal surface activating resin and a granular phenol resin and a thermosetting resin. Unlike the ones that must be obtained by kneading or that a soldering accelerator must be added, the resol-type phenol resin is the only resin that binds metallic copper powder, and Since a specific resol type phenolic resin is used, there is no need to mix the resin mixture before the conductive paint is kneaded. In addition, sufficient soldering is possible without adding a soldering accelerator. Because it can be attached
The convenience can be further improved and the productivity can be greatly improved, and as described above, it is possible to provide a soldering conductive paint having the necessary characteristics sufficiently.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication C08K 5/17 (72) Inventor Hisatoshi Murakami 2-3-1 Iwata-cho, Higashiosaka-shi, Osaka Prefecture Tatsuta Electric Wire Co., Ltd. In-house (72) Inventor Tsunehiko Terada 2-3-1 Iwata-cho, Higashi-Osaka City, Osaka Prefecture Tatsuta Electric Wire Co., Ltd. (56) Reference JP-A-62-270674 (JP, A)

Claims (1)

[Claims] 1. A saturated copper powder (A) of 85 to 95% by weight, a resole type phenolic resin (B) of 15 to 5% by weight, and a total of 100 parts by weight of (A) and (B) are saturated. 0.5 to 8 parts by weight of fatty acid or unsaturated fatty acid or metal salt thereof,
1 to 50 parts by weight of a metal chelate forming agent, and the resol type phenol resin (B) has a 2-1 substitution product, a 2,4-2 substitution product, a 2,4,6-3 substitution product, which it has. When the infrared transmittance of methylol group, dimethylene ether, and phenyl group by infrared spectroscopy is 1, m, n, a, b, c, A solderable conductive paint, which is a resol-type phenolic resin that satisfies the following relational expression.