JPS62230870A - Electrically conductive coating compound to be soldered - Google Patents

Abstract

PURPOSE:A soderable, electrically conductive coating compound containing copper powder, having improved electrical conductivity, consisting of metallic copper powder, a thermosetting resin, a metallic salt of fatty acid, a metallic chelate-forming agent and a soldering promotor. CONSTITUTION:(A) Metallic copper powder (preferably having 1-30mum particle diameter) is blended with (B) a thermosetting resin (e.g. resol type phenolic resin, etc.), (C) a metallic salt of a saturated or unsaturated fatty acid (e.g. potassium oleate, etc.), (D) a metallic chelate-forming agent (e.g. triethanolamine, etc.) and (E) a soldering promotor (e.g. glutamic acid, etc.) to give the aimed coating compound. The blending ratio is preferably 1-8pts.wt. component C, 1-50pts.wt. component D and 0.1-2.5pts.wt. component E based on 100pts.wt. total amounts of 85-95wt% component A and 15-5wt% component B.

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. , relates to a conductive paint that can be soldered directly onto a circuit coating film using a flux agent after the coating film is cured by heating.

(Prior art) The specific resistance of silver paste is! Because it has good conductivity of 0-4Ω・cm class, it has been widely used as a material for printed circuits in electronic devices, but silver powder is expensive and accounts for a large proportion of the cost, and silver paste When a DC voltage is applied to the formed conductive circuit in a humid atmosphere, silver migration occurs and the circuit is short-circuited. .

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, its conductivity is 10-3Ω・0111
Many of them are of the same grade, and the long-term stability of their conductivity is a problem.

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 coating film and the copper plating are firmly bonded to each other.

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 a copper paste must have are: ■ It must have conductivity equivalent to that of silver paste, ■ It must be able to be used in screen printing, intaglio printing, brushing and spray painting, and ■ Adhesion of the coating film to the insulating substrate. (1) The ability to form thin wire circuits, (2) Excellent solderability on coatings, and (2) The ability to maintain the conductivity of the conductive 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 Problem) If a conductive paint is prepared in which a metal salt of a saturated fatty acid or an unsaturated fatty acid, a metal chelate forming agent, and a soldering accelerator are added, the conductivity will be improved and its curing will be improved. The present invention was completed by discovering that extremely good soldering can be applied to the entire surface of the coating film.

The present invention consists of 85 to 95% by weight of metallic copper powder and 1 part of thermosetting resin.
1 to 8 parts by weight of a metal salt of a saturated or unsaturated fatty acid, 1 to 50 parts by weight of a metal chelate forming agent, and 0.1 to 2 parts by weight of a soldering accelerator, based on a total of 100 parts by weight of 5 to 5% by weight.
．． 5 parts by weight.

Here, the metallic copper powder used in the present invention refers to flaky,
It may have any shape such as dendritic, spherical, irregular shape, etc., and the particle size is preferably 100 μm or less, particularly,
1 to 30 μm is preferable. If the particle size is less than 1 μm, it is easily oxidized and the conductivity of the resulting coating film decreases, and the amount used in soldering is 85 to 95% by weight, preferably 87 to 93% by weight.

If the blending amount is less than 85% by weight, the conductivity will decrease and the solderability will deteriorate, whereas if the blending amount exceeds 95% by weight,
The metallic copper powder is not sufficiently bound, and the resulting coating film becomes brittle, resulting in decreased conductivity and poor screen printability.

The thermosetting resin used in the present invention binds the metallic copper powder and other components in the conductive paint according to the present invention, and is a polymeric substance that is liquid at room temperature and hardens by heating. For example,
Phenol, acrylic, epoxy, polyester, xylene resin, etc. are used, but are not limited to these.

Among them, resol type phenolic resins are preferably used.

The blending amount of thermosetting resin is 1 when mixed with metallic copper powder.
It is used in a range of 5 to 5% by weight, and the total amount of metallic copper powder and thermosetting resin is 100 parts by weight. If the blending amount of the thermosetting resin is less than 5% by weight, the metallic copper powder will not be sufficiently bound, the resulting coating film will become brittle, the conductivity will decrease, and the screen printability will deteriorate; If it exceeds this value, the conductivity decreases and the soldering process becomes unfavorable.

The metal salts of saturated fatty acids or unsaturated fatty acids used in the present invention refer to palmitic acid, stearic acid, and arachidic acid having 16 to 20 carbon atoms in the case of saturated fatty acids, or those having a carbon number of 16 to 20 in the case of unsaturated fatty acids. Potassium salts, copper salts, or aluminum salts of seamarinic acid, oleic acid, or lylunic acid of 16 to 18 are used. The use of these metal salts is
In blending the metallic copper powder and the thermosetting resin, it is preferable because it promotes fine dispersion of the metallic copper powder into the thermosetting resin and forms a coating film with good conductivity.

The blending amount of the metal salt of saturated fatty acid or unsaturated fatty acid is 1 to 1 to 100 parts by weight of the total amount of metallic copper powder and thermosetting resin.
It is used in an amount of 8 parts by weight, preferably 2 to 6 parts by weight.

If the amount of the metal salt is less than 1 part by weight, fine dispersibility of the metallic copper powder cannot be expected, and if it exceeds 8 parts by weight, it will reduce the conductivity of the coating film and cause problems between the coating film and the substrate. This is undesirable because it leads to a decrease in the adhesion of the film.

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

The metal chelate forming agent added prevents oxidation of the metallic copper powder, contributes to maintaining conductivity, and exhibits a synergistic effect with the soldering accelerator described later to further improve solderability. For example, a combination of metallic copper powder, thermosetting resin, and soldering accelerator does not allow for good soldering on the paint film, but good soldering can be achieved by disposing a metal chelate forming agent. Therefore, their role as a synergistic effect is significant.

The metal chelate forming agent is used in an amount of 1 to 50 parts by weight, preferably 5 to 30 parts by weight, based on 100 parts by weight of the metal copper powder and thermosetting resin. If the amount of the metal chelate forming agent is less than 5 parts 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.

The soldering accelerator used in the present invention is oxydicarboxylic acid or aminodicarboxylic acid or a metal salt thereof,
For example, at least one selected from tartaric acid, malic acid, glutamic acid, aspartic acid, or metal salts thereof is used.

The amount of the soldering accelerator used is in the range of 0.1 to 2.5 parts by weight, preferably 0.5 to 2.5 parts by weight, based on 100 parts by weight of the total amount of metallic copper powder and thermosetting resin. It is 0 parts by weight. If the amount of the soldering accelerator is less than 0.1 part by weight, the solderability of the coating film will be poor, and if it exceeds 2.5 parts by weight, the conductivity will decrease and the solderability will be unfavorable. It won't happen.

In order to adjust the viscosity, a conventional organic solvent can be appropriately used in the conductive paint according to the present invention. for example,
Butyl carpitol, butyl carpitol acetate,
Known solvents include butyl cellosolve, methyl isobutyl ketone, toluene, and 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 metal copper powder with a particle size of 5 to 10 μm, a thermosetting resin resol type phenolic resin, potassium oleate, triethanolamine, glutamic acid, and malic acid are blended in the proportions shown in Table 1 (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 screen printed to form an S-shaped conductive circuit with a width of 0.4 mm, a thickness of 30 ± 5 pm, and a length of 520 mm on a glass or epoxy resin substrate, and the coating was heated at 130~B for 0~60 minutes to form a coating film. hardened.

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 2.5 atm, 220
After blowing hot air at ~230°C, it was cleaned and soldered over the entire surface of the conductive circuit.

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

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

The adhesion of a coating film is defined by JIS K5400 (1979
), draw 11 vertical and horizontal parallel lines perpendicular to each other on the paint film at intervals of 1 cm.
``We made cuts in the shape of substrate so that there were 100 squares inside, and when the coating was peeled off with cellophane tape, we calculated the number of substrates remaining on the insulating substrate. It is something.

Solderability was evaluated by observing the soldered state on the paint film using a stereoscopic microscope with a magnification of Mr. I, and using the following criteria.

○ mark: The surface is smooth and the solder is adhered to the entire surface. △ mark: The coating film is partially exposed. × mark: The solder is only partially attached. Heat resistance and resistance change rate is the soldered coating film at 80℃
It was heated for 100 hours and the resistance change rate with respect to the initial resistance was determined.

Moisture resistance and resistance change rate refer to soldered coating film at 55℃ x 95%.
It was left in an atmosphere at a temperature of RHX 100O hours, and the rate of change in resistance with respect to the initial resistance was determined.

Printability was evaluated based on the following criteria by observing the ease of printing when forming a conductive circuit using the obtained conductive paint by screen printing.

○ mark: Good formation of N & electrical circuit △ mark: Partially difficult to form a conductive circuit × mark: Part where formation of a conductive circuit is difficult The average solder coat thickness is 10 μm. As can be seen from the results, in Examples 1 to 6, 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 printability were improved. Various properties such as these are improved. In particular, since the obtained cured coating film can be directly soldered using a normal organic acid fluxing agent, the conductivity of the conductive circuit can be increased from Xl0-'Ω・cm to Xl0-'Ω・cn.
It can be improved to + class, allowing a larger current to flow through the conductive circuit.

In addition, the solder coating has excellent conductivity, heat resistance, and moisture resistance.
Since the rate of change in resistance is also small, it can be seen that it can be used even in heated and high-humidity environments.

Next, looking at Comparative Examples, Comparative Example 1 has a large amount of metallic copper powder and a small amount of thermosetting resin, so the metallic copper powder is not sufficiently bound, and the resulting coating film is also brittle and difficult to screen print. So it's not desirable.

Comparative Example 2 is not preferable because the amount of metallic copper powder is small, so that the solder adheres only to a portion of the conductive circuit during soldering. In Comparative Example 3, since no metal salt of unsaturated fatty acid was added, the solderability was slightly lowered and the rate of change in resistance in heat resistance and moisture resistance was increased, which is not preferable. Comparative Example 4 has a large amount of metal salts of unsaturated fatty acids,
The adhesion of the coating film is poor, which is not desirable.

In Comparative Example 5, since no metal chelate forming agent was added, the solderability decreased and the resistance change rate in heat resistance and moisture resistance was large (which is undesirable). This is not preferable because the viscosity of the paint itself decreases too much, making printing difficult.

In Comparative Example 7, since no soldering accelerator was added, the solderability deteriorated and the rate of change in resistance in heat resistance and moisture resistance increased, which is not preferable. Comparative example 8.9
Since the amount of soldering accelerator is large, the conductivity of the coating film decreases and the solderability decreases, which is not preferable.

As another example, the coating thickness of the conductive paint according to the present invention is 30±5
When a solder paste is applied to μm with a thickness of 5 to 1011 m, the sheet resistance is less than 0.01 Ω/unit, and when used for electromagnetic shielding, it is classified as Class B (for consumer use) by the Federal Communications Commission (FCC). (30 to 100)
100 μV/m or less at 100 O) was obtained.

Therefore, an insulating layer is provided by coating a heat-curable or ultraviolet-curable solder resist ink on a conductive circuit formed from a copper-clad laminate by the etched-off method, and the conductive paint according to the present invention is applied on the insulating layer. Then, a pattern almost identical to the underlying conductive circuit is formed on the resist by screen printing, and the entire surface of the coated circuit is coated with solder using a soldering machine that heats and hardens the coated film, thereby creating an effective electromagnetic barrier layer. can be formed, and can also be effectively used as an electrostatic shielding layer.

(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 for circuit parts, through-hole connecting agents, electromagnetic,
It is also used in electrostatic barrier layers and has high industrial value.

Claims (2)

[Claims] (1) (i) Metallic copper powder, (ii) thermosetting resin, (ii)
A solderable conductive paint comprising: i) a metal salt of a saturated or unsaturated fatty acid; (iv) a metal chelate forming agent; and (v) a soldering accelerator. (2) The proportion of the components constituting the conductive paint is 85% of the metallic copper powder.
~95% by weight and 15-5% by weight of thermosetting resin, total 1
00 parts by weight, 1 to 8 parts by weight of a metal salt of a saturated fatty acid or an unsaturated fatty acid, 1 to 50 parts by weight of a metal chelate forming agent, and 0.1 to 2.5 parts by weight of a soldering accelerator. Solderable conductive paint as described in Scope 1.