JPH0216172A - Solderable conductive paint - Google Patents

Abstract

PURPOSE:To obtain a solderable paint having good conductivity by mixing a metallic copper powder, a specified resol phenolic resin, a fatty acid or its metallic salt, and a metal-chelating agent. CONSTITUTION:The title conductive paint consists of 85-98wt.% metallic copper powder (A), 15-5wt.% resol phenolic resin (B), 0.5-8pts.wt., based on 100pts.wt. A + B, saturated or unsaturated fatty acid, or metallic salt thereof, and 1-50pts. wt., based on 100pts.wt. A + B, metal-chelating agent. Said resol phenolic resin B is one wherein the following relationships shall hold: l/n = 0.8 to 1.2; m/n = 0.8 to 1.2; b/a = 0.8 to 1.2; c/a = 1.2 to 1.5 when the values of infrared transmittance, determined by infrared spectroscopy, of the 2-monosubstituted product, 2,4-disubstituted product, 2,4,6-trisubstituted product, methylol group, dimethylene ether, group and phenyl group thereof are represented respectively by l, m, n, a, b, and c.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a conductive paint containing copper powder and having good conductivity, and more specifically, to a conductive paint containing copper powder and having a conductive circuit formed on an insulating substrate by screen printing or the like. , relates to a conductive paint that can be directly soldered by applying a flux agent onto the circuit coating film after heating and curing the coating film.

(Prior art) Silver paste has a resistivity of 10-'Ωcm class and has good conductivity, so it has been widely used as a material for printed circuits in electronic devices, but silver powder is expensive and has good conductivity. , it accounts for a large proportion of the cost, and if a DC voltage is applied to a conductive circuit formed with silver paste in a humid atmosphere, silver migration will occur and the circuit will short-circuit. There is a strong demand for the emergence of a copper paste.

When a conductive paste coating made of copper powder and thermosetting resin is heated and cured, since copper is highly oxidizable, oxygen contained in the air and in the binder resin combines with the copper powder. An oxide film is formed on the surface, significantly inhibiting its conductivity, or the conductivity completely disappears over time. Therefore, various copper pastes have been disclosed in which various additives are added to prevent copper powder from oxidizing and to provide stable conductivity. However, the conductivity thereof is often on the order of 104 Ω·cm, and there is a problem in the long-term stability of the conductivity. Moreover, there is a problem in that the resulting copper paste coating cannot be directly soldered.

(Problems to be Solved by the Invention) Conductive circuits formed on insulating substrates using known copper pastes cannot be soldered directly as described above, so it is necessary to apply activation treatment to the coating film of the circuits. After electroless plating or electrolytic copper plating in a plating solution using the coating film as a cathode, soldering is performed on the copper surface. In such a case, it cannot be put to practical use unless the bond between the coating film and the copper plating is reliable.

Therefore, if a solderable copper paste were developed that did not require electroless plating and/or electroplating, the economic benefits would be significant as it would greatly shorten the printed circuit formation process. . Here, the problems that copper paste must have are: ■ It must have conductivity equivalent to that of silver paste, ■ It must be able to be applied by screen printing, intaglio printing, brushing and spray painting, and ■ Adhesion of the coating film to the insulating substrate. (1) The ability to form fine wire circuits; (2) Excellent solderability and soldering strength on the coating film; and (2) The ability to maintain the conductivity of the four-conductor circuit of the solder coat over a long period of time.

The present invention aims to solve this problem and provides a solderable conductive paint.

(Means for Solving the Problems) In order to solve the above problems, the present inventors previously applied for a solderable conductive paint in Japanese Patent Application No. 61-75303. The present invention was completed by discovering that by using a phenolic resin, a conductive paint that has excellent conductivity and soldering strength and can be soldered can be obtained without adding a soldering accelerator.

In the present invention, saturated fatty acid or unsaturated fatty acid or The resol type phenolic resin is composed of 0.5 to 8 parts by weight of these metal salts and 1 to 50 parts by weight of a metal chelate forming agent.
-2-substituted product, 2.4.6-3-substituted product, methylol group, dimethylene ether, and phenyl group, when the infrared transmittance measured by infrared spectroscopy is l, m, n, a, b, and c, respectively. Between the transmittance (a) -= 0.8 to 1.2 (b) -= 0.8 to 1.2 (c) = 0.8 to 1.2 (d) □ 1.2 to 1 It is characterized by being a resol type phenolic resin that satisfies the following relationship:

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

The metallic copper powder used in the present invention is flaky, dendritic, spherical,
It may have any shape, such as an irregular shape, and its particle size is preferably 100 μm or less, and in particular, those with a particle size of less than 1 μm, preferably 1 to 30 μm, are easily oxidized.
The electrical conductivity of the resulting coating film decreases, resulting in poor solderability.

The amount of metallic copper powder mixed with the resol type phenolic resin is in the range of 85 to 95% by weight, preferably 87 to 93% by weight.

If the amount is less than 85% by weight, solderability will be poor, whereas if it is more than 95% by weight. In this case, the metallic copper powder is not sufficiently bound, and the resulting coating film becomes brittle, the desired soldering strength cannot be obtained, the conductivity decreases, and the screen printability also deteriorates.

Regarding the resol type phenolic resin used, its chemical amount, the amount of 2-1 substitution product is λ, the amount of 2.4-2 substitution product is μ, 2
．． 4.6-3 The amount of substituent is ν, the amount of methylol group is α, and the amount of dimethylene ether is μ m. That is, compared to ν 2-1 substitution product amount λ and 2.4-2 substitution product amount μ, 2.
．． 4.6-3 It means that the amount of substituents ν is large.

α α becomes. That is, it means that the amount α of methylol groups is larger than the amount α of dimethylene ether and the amount of phenyl groups γ.

In general, when the 2.4.6-3W conversion amount ν increases, the frame Ii of the resol type phenolic resin! density is n
n The conductivity of the coating film is improved. However, on the contrary, the coating film tends to be hard and brittle, and its physical properties are poor.

β Also, if the value is small, the solderability of the paint film will be poor. If □ is large, the conductivity of the coating film is poor and α Become.

Therefore, in the resulting conductive paint, as a resol type phenolic resin that makes the hardness of the coating film appropriate and has both good conductivity and solderability, n n
a each 0.8 to 1.2, □ 1.2 to 1.5
It is appropriate to

The blending amount of the resol type phenolic resin is used in the range of 15 to 5% by weight in the same formulation (metal), and the total amount of the metal copper powder (A) and the resol type phenolic resin (B) (
A+B) is 100 parts by weight. If the resol-type phenolic resin is less than 5% by weight, the metallic copper powder will not be sufficiently bound, and the resulting coating film will become brittle, resulting in decreased electrical conductivity and poor screen printability. On the other hand, if it exceeds 15% by weight, the solderability will not be favorable.

The saturated fatty acids, unsaturated fatty acids, or metal salts thereof used in the present invention refer to saturated fatty acids having 16 carbon atoms.
Unsaturated fatty acids such as valmitic acid, stearic acid, and arachidic acid with ~20 carbon atoms include seamaric acid, oleic acid, and lylunic acid with 16 to 18 carbon atoms, and their metal salts include potassium, copper, and aluminum. It is a salt with metals such as , sodium, zinc, etc.

The use of these dispersants is preferable in blending the metallic copper powder with the resol-type phenolic resin because it promotes fine dispersion of the metallic copper powder into the resin and forms a coating film with good conductivity.

The blending amount of saturated fatty acids, unsaturated fatty acids, or metal salts thereof is in the range of 0.5 to 8 parts by weight, preferably 1 to 8 parts by weight, based on 100 parts by weight of the total amount of metallic copper powder and resol type phenolic resin. It is 3 parts by weight.

If the amount of the dispersant is less than 0.5 parts by weight, fine dispersibility of the metallic copper powder cannot be expected, and if it exceeds 8 parts by weight, the conductivity of the coating film will be reduced and the coating film will be damaged. This is undesirable because it leads to a decrease in the adhesion between the film and the substrate.

The metal chelate forming agent used in the present invention is at least one selected from aliphatic amines such as 1,000-ethanolamine, jetanolamine, 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 compounding amount of the metal chelate forming agent is 1 to 1 to 100 parts by weight of the total amount of metallic copper powder and resol type phenolic resin.
It is used in a range of 50 parts by weight. If the amount of the metal chelate forming agent is less than 1 part by weight, the conductivity will decrease and the solderability will not be favorable. On the other hand, when it exceeds 50 parts by weight, the viscosity of the paint itself decreases too much, which impairs printability, which is not preferable.

In the conductive paint according to the present invention, ordinary organic solvents can be appropriately used to adjust the viscosity. For example, butyl carpitol, butyl carpitol acetate, butyl cellosolve, methyl isobutyl ketone, toluene,
Known solvents such as xylene.

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

Dendritic metallic copper powder with a particle size of 5 to 10 μm, a resol type phenolic resin with an infrared transmittance ratio shown in Table 1, potassium oleate, and triethanolamine are blended in the proportions shown in Table 2 (parts by weight), A small amount of butylcarpitol was added as a solvent, and the mixture was kneaded with a three-wheel roll for 20 minutes to prepare a conductive paint. This was printed onto a glass epoxy resin substrate using the screen printing method to a thickness of 110.4mm and a thickness of 30±.
An S-type conductive circuit with a length of 5 μm and a length of 520 m+ was formed, and 1
The coating film was cured by heating for 30 to 30 minutes.

Subsequently, in order to apply soldering on the formed conductive circuit,
The board was passed through a solder leveler machine used in the actual process, immersed in an organic acid flux bath for 4 seconds, and then
5 in a molten solder bath (Pb/5n=40/60) at 50°C.
2 to 6.0 atm, 220
After blowing hot air at ~230'C, it was cleaned and soldered over the entire surface of the conductive circuit. The average thickness of the solder coat soldered to the paint film is lOμm.

The results of investigating the characteristics of the conductive circuit obtained through the above process are summarized in the first section.
Shown in the table.

Here, the electrical conductivity of a coating film is a value obtained by measuring the volume resistivity of a heat-cured coating film.

The adhesion of a coating film is defined by JIS K5400 (1979
), 11 vertical and horizontal parallel lines are drawn at 11 intervals on the coating film, and 1c11
! When I made a cut in the shape of a substrate so that there were 100 squares inside, and then peeled off the coating film with cellophane tape, wAiI! The number of substrates of the coating film remaining on the substrate was determined.

Solderability was evaluated by observing the soldered state on the paint film using a low magnification stereoscopic microscope and using the following criteria.

○ mark: The surface is smooth and the solder is adhered to the entire surface. Δ mark: The coating film is partially exposed. × mark: The solder is only partially attached. Printability refers to viscosity adjustment. When forming a conductive circuit by screen printing using the conductive paint obtained in this manner, the ease of printing was observed and evaluated according to the following criteria.

○: Good conductive circuit formation Δ: Slightly difficult conductive circuit formation × ×: Conductive circuit formation difficult For example, a land with a diameter of 3 mmφ and a thickness of 2 mm on G10).
After forming a coating film with a thickness of 5 to 30 μm and curing the coating film by heating at 130 μm, a lead wire (0
, 8Jl-φ tin-plated annealed copper wire) vertically soldered (63
(use Sn eutectic solder), fix the board and
The strength was determined by pulling the lead wire vertically at a pulling speed of +sm/min.

As can be seen from the results, in Examples 1 to 4, the specific compounding materials used in the present invention were appropriately combined, so that the conductivity of the coating film, the adhesion of the coating film, the solderability, and the solderability of the coating film were improved. The properties such as strength and printability are improved. In particular, it is possible to directly solder the obtained cured coating film using an ordinary organic acid fluxing agent, so that the conductivity of the conductive circuit can be increased to 1.
The resistance can be improved from 0-4 Ω·cm class to 10-′ Ω·cm class, and a larger current can be passed through the conductive circuit.

Next, looking at the comparative examples, in Comparative Examples 1, 2, and 3, the infrared transmittance ratio of the resol type phenolic resin used is inappropriate, so a coating film with desirable solderability cannot be obtained, and in Comparative Example 4, a coating film with desirable solderability cannot be obtained. However, since the amount of metallic copper powder is small, the solder adheres only to a portion of the conductive circuit during soldering, which is not preferable. Comparative Example 5 is preferable because there is a large amount of metallic copper powder and the metallic copper powder is not sufficiently bound, so the conductivity of the coating film is unstable, the resulting coating film is also brittle, and screen printing is somewhat difficult. do not have.

(Effects of the Invention) As explained above, the conductive paint according to the present invention can be soldered directly onto the coating film by forming a conductive circuit on an insulating substrate, then curing the coating film by heating. Therefore, the conductivity of the conductive circuit can be further improved, and there is no need to activate the coating film of the circuit and perform electroless plating or electroplating as in the past, so the process of forming the printed circuit can be improved. can be shortened to a large extent, resulting in significant economic benefits.

In addition to forming conductive circuits, the conductive paint of the present invention can also be used for electronic equipment parts, electrodes of circuit parts, through-hole connecting agents, electromagnetic,
It is also used in electrostatic barrier layers and has high industrial value.

Patent applicant: TAC Electric Wire Co., Ltd.

Claims (1)

[Claims] 85 to 95% by weight of metallic copper powder (A), 15 to 5% by weight of resol type phenolic resin (B), and a total of 100 parts by weight of (A) and (B), The resol type phenolic resin (B) is composed of 0.5 to 8 parts by weight of a saturated fatty acid or an unsaturated fatty acid or a metal salt thereof, and 1 to 50 parts by weight of a metal chelate forming agent, and the resol type phenolic resin (B) is The infrared transmittance of the 2,4-2-substituted product, 2,4,6-3-substituted product, methylol group, dimethylene ether, and phenyl group by infrared spectroscopy is expressed as l, m, n, a, b, c. When, between each transmittance (a) l/n = 0.8 to 1.2 (b) m/n = 0.8 to 1.2 (c) b/a = 0.8 to 1 .2 (d) A solderable conductive paint characterized by being a resol type phenolic resin that satisfies the following relationship: c/a = 1.2 to 1.5.