JPS6021591A - Method of producing conductive circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a conductive circuit using a copper conductive paste, and in particular, the present invention relates to a method for manufacturing a conductive circuit using a copper conductive paste. The present invention relates to a method for manufacturing a conductive circuit that can significantly improve performance.

Conventionally, the method of using copper for conductive circuits is to create a printed circuit by pasting copper foil over the entire printed circuit board and using an etching method to leave the circuit part and melt the other parts. However, there were disadvantages in that the amount of copper used was large and the manufacturing time was long, resulting in high manufacturing costs. There is a method of creating a circuit by sintering a metal paste such as silver or palladium conductive paste to create a twisted thick film circuit, but silver-fi has recently become very expensive and is not suitable for general electronic devices due to cost. It is becoming unusable.

Therefore, as a way to improve the shortcomings of the above-mentioned method, it is possible to use a copper conductive paste that is a mixture of copper powder and synthetic resin, but according to this method, heating is required to harden the paste. Due to its characteristics, it is extremely easy to oxidize, contrary to the paste, so this heating oxidizes the copper powder in the paste, increasing the electrical resistance and worsening solderability, so it has not been put into practical use. .

1) The 16 researchers succeeded in developing a copper conductive paste that can eliminate all of the above-mentioned drawbacks. Sofi is copper conductive paste AC made by Asahi Chemical Laboratory Co., Ltd., which is made by adding a small amount of special additives in addition to copper powder and synthetic resin.
P-020 and ACI)-(+30) have reached the stage of practical use.The copper conductive paste called ACP-020 is
The main components are copper powder 80 times 11 times thick and synthetic resin 2 times thick, and has extremely good electrical conductivity, but its soldering properties are somewhat poor. The copper conductive paste called ACP-030 is mainly composed of 85% by weight of copper powder and 15% by weight of synthetic resin, and its I/% conductivity is slightly inferior to that of ACP-020, but it has good soldering properties.

The present invention is based on the above L7? : In addition to eliminating the drawbacks of the conventional technology,
In order to effectively use the newly developed copper conductive paste mentioned above, the purpose is to create conductive circuits for electronic equipment (copper conductive paste). By applying it to an insulating substrate and curing it by heating, and applying an electroless metal plating treatment with good conductivity to the surface of the cured coating, the conductivity is significantly improved compared to a cured coating made only of copper conductive paste.
The object of this invention is to stabilize conductivity and obtain a conductor circuit that has no traces compared to conventional copper foil circuits. In addition, other purposes are
By making it possible to put such conductor circuits to practical use, we can eliminate the need for expensive silver conductive paste and etching methods, reduce the cost of printed circuits, and dramatically improve productivity. be.

In short, the present invention involves coating an insulating plate with a copper conductive paste that has good solderability, heating and curing it to form a conductive circuit with a cured coating, and immersing it in a weakly acidic solution to form a conductive circuit. The method is characterized in that the surface of the cured coating film is activated (1), and then the surface of the cured coating film is subjected to electroless gold dust plating treatment with good conductivity.

The present invention will be explained below based on examples. In order to put copper powder conductive paint into practical use, it is necessary that the electrical resistance value at the time of completion of the coating film be between lXl0-'' and lXl0''Ω-, and that it also has great resistance to humidity, and can withstand high humidity. It must show little change over time in the atmosphere, and its resistance-temperature characteristics at low and high temperatures centered around room temperature (20°C) must be comparable to conventional silver conductive paints.

Simply mixing and applying phenolic resin to copper powder 1-1 If this is simply heated and dried, the copper powder will oxidize and become copper monoxide due to this heating, resulting in an electrical resistance value of lXl0"Ω-m or more. .

In other words, the conductive mechanism of conductive paint is generally based on the conductive path formed by the mutual contact of the metal powder particles contained therein, but the surface of the constituent conductive particles is always covered with oxide. It is common knowledge that their electrical resistance becomes extremely high due to the presence of oxides and cannot be put to practical use. However, with respect to noble metals such as silver, which have a very small surface oxide film, there is no concern about oxides, and an increase in electrical resistance due to oxides was not considered. It is well known that in the case of powdered metals, a surface oxide film is instantaneously formed when the powder is exposed to air.

Therefore, during the first VC1 conductive coating, copper powder! final grain 5
- It is necessary to reduce the contact resistance of the child. To do this, it is necessary to remove the oxide during the process of forming a conductive film to form a conductive path through normal contact between metal atomic surfaces. For this purpose, oxides present on the surface of the copper powder must be removed by some method. Second, after the conductive mechanism is completed by copper powder on a normal surface from which oxides have been removed, the copper powder is oxidized by the influence of acid purple from the outside during heating or use, and the electrical resistance increases again. must be prevented from rising.

Therefore, the key to practical application of copper powder conductive paint is how to satisfy the first and second requirements above and prevent copper powder from oxidizing during storage at room temperature, heating, and use. It is what it is. That is, the selection and amount of special additives to be added to a material consisting of copper powder and resin is the most important issue in determining the performance of this type of material.゛The applicant of this application has conducted many experimental studies over many years in order to obtain the ideal additive that satisfies the above two requirements, and finally succeeded in determining the amount of machining and addition thereof. However, we succeeded in developing a copper powder-introducing paint that can be used in practical use in place of conventional copper foil and silver frost-conducting paints. As mentioned in M1, this is (41 Atsuhi Chemical?tll Kabuto Copper Powder Conductive Coating Phase A, CP-0
20 and ACJ)-030 and 1. This has led to the stage of practical application.

When using additives and [7], anthracene or its derivatives provide the best results.
t1'+ol and anthracenecarboxylic acid (C14HI
l (C00I month) is particularly excellent. Next, anthrazine (C2g''+nNz) is also excellent. Next to this is anthranilic acid (Cf111. (Nl(,) (C00
I)) is also valid.

In other cases, benzoic acid (C, H, .r:oOH) has an electrical resistance l that is an order of magnitude higher than that of anthracene and its derivatives.
Xl0-2Ω-m1. Therefore, it is difficult to put it into practical use.

The paint used in the method of the present invention contains 70 to 85% by weight of copper powder, phenolic resin, epoxy resin, and bottle powder.
) 15 to 30% by weight of at least one resin selected from the group consisting of nistyl resins and xylene resins, and a trace amount (preferably 0.23 to 30%) of the above-mentioned anthracene or its derivatives. It is made into a fluid by mixing 1.6% by weight (02 to 5% by weight as a practical addition amount) with an additive.

Anthracene or its derivatives, which are additives used in the present invention, dissolve compounds such as oxidized @ present on the surface of copper powder during heating and become a compound that is compatible with the coexisting resin, so it improves conductivity. In addition to increasing the resin η
It has been found that the additive and copper compound that are compatible with each other have the effect of lowering the moisture permeability and oxygen permeability of the resin. That is, the anti-oxidation mechanism of copper powder by anthracene or its derivative VC is as follows.

For example, anthracenecarboxylic acid (C04H, C00)
1), the following effects lead to good conduction 'I! It is assumed that a paint film is formed. That is, anthracenecarboxylic acid reacts with copper oxide present or formed on the surface of copper powder particles according to the following formula to produce anthracenecarboxylic acid steel salt.

Cuo+2c, 4H0COOII → (C,,)T, Co
o) Due to the chemical reaction that occurs in the coating film, which is shielded from the atmosphere by Cu1H,0 and the coexisting resin, the surface of the copper powder is exposed as a clean metal surface from which oxides have been removed. The conductive tubes are arranged in contact with each other, forming a conductive path with good properties, that is, high resistance to heat.

On the other hand, the anthracene carbon-intoxicated copper base produced by the above chemical reaction mixes with the coexisting phenol resin, epoxy resin, polyester resin, or xylene resin, and is uniformly dissolved and fractionated in the resin, resulting in the formation of copper particles. There is no harm to the alignment or formation of a coating film accompanied by the curing reaction of the resin. Furthermore, when an appropriate amount of anthracene derivative copper compound is mixed into the resin, it has been found that it actually reduces the moisture permeability and oxygen permeability of the filter resin, and slightly improves the moisture resistance and oxidation resistance. , which further enhances the effects of the present invention.

Here, it is most effective when the amount of the additive added is in the range of 0.23 to 1.5% by weight, and in practical terms, the amount added is 0.2 to 51% by weight. It has been experimentally confirmed that when the amount of anthracene or its derivatives added was varied and the film thickness was set to 40μ, the amount of anthracene or its derivatives added was 0.23 to 1.5V. In the case of 1f?, the electric resistance is almost constant at lXl0'-'Ω-on, and an extremely good solution is obtained. :
When the amount added is 0.2%, the electrical resistance value is 1.3X.
10='Ω-m, and 2X at addition amount of 51t%]
O-''Ω-m, and it was found that it is practical if the amount added is within this range.However, when the amount of L7 added is less than 0.2% by weight, the electrical resistance value sharply decreases.
At 01% by weight, the electric resistance value becomes 1 x 10-20-Fuchi, which is not practical V-, and the additive amount exceeds 5-fold f-'f.
In the case of rc, the electrical resistance increases rapidly, and when the amount added is 8 times higher, the electrical resistance value becomes 1 x 10-2 [7], making it impractical.

Further, the above experimental values have been similarly obtained for anthranilic acid and anthrazine other than anthracene or its derivatives.

The following mechanism is considered to be the reason why the critical value of the above-mentioned addition amount was confirmed through experiments. That is, as shown in the mechanism of action when anthracenecarboxylic acid is used, when the additive chemically reacts with oxides etc. present on the surface of the conductive copper powder particles and dissolves and removes them, the additive is added rapidly. Stoichiometry is established between the agent and the oxide. Therefore,
Even in the case of fc using copper powder with relatively low oxide content, it is impossible to completely prevent oxidation as long as the copper powder is handled in the air.

The fact that a minimum amount of 0.2% by weight of additive is required indicates that a minimum amount of oxide is present. ″−!
The fact that the maximum amount of fC added is limited to 5% by weight based on experiments indicates that the additive is compatible with the coexisting resin and does not have a negative effect on the properties of the resin. If the amount is more than this, it exceeds the amount necessary to promote the above-mentioned conductive effect, and is not only unnecessary, but may also deteriorate the properties of the coexisting resin.

According to the copper powder conductive paint configured as described above, in the case of a printed circuit with a film thickness of 40 μm, its electrical properties are astoundingly conductive, with an electrical resistance value of 1×10 Ω-tan. The electrical resistance value can be reduced to 1/1,000,000 times less than when no additives are used.Moreover, the moisture resistance is reduced by approximately 50% with only a slight increase in the electrical resistance value.
An equilibrium state was reached after 4 hours, and no further changes over time were observed, causing no practical problems.

In addition, regarding the resistance temperature characteristics, at temperatures below room temperature, the rate of change in electrical resistance is approximately 172, which is extremely superior to that of silver conductive paint, and even at temperatures above room temperature, the results are almost the same as silver conductive paint, making it practical. At the second temperature of about 60°C, it can be used without coloring.

Next, we will explain the method of manufacturing a conductive circuit using the above-mentioned powder-containing conductive paint. First, as an example of an insulating board, we will use copper conductive paint with good soldering properties on an organic board from which copper foil has been removed. Apply a paste (for example, the above-mentioned copper powder conductive paint ACP-030 manufactured by Asahi Chemical Research Institute) and heat it to a temperature of 13
It is cured by heating at 0° C. to 180° C. for 10 minutes to 60 minutes, and a conductive circuit is formed by a cured coating film on the substrate. In this case, the best heating temperature is 140°C, the heating time is 30 minutes, and the appropriate thickness of the cured coating is 25μ.

Next, the substrate is immersed in a weakly acidic solution to activate the surface of the cured coating. Then, conductor 1b is applied to the surface of the cured coating film.
: Electroless metal plating treatment with good properties, such as high-speed thickening, is the best of its kind! A plating treatment using an N copper plating solution is performed to form a layer of plated copper on the cured coating. In this case, the appropriate thickness of the plated copper layer is 25μ to 35μ.

In the electroless steel plating process, the copper powder particles in the cured coating film serve as the core, and the fine copper particles precipitated from the copper plating solution adhere around the core1,7, causing a separation between the cured coating film and the copper plating. Even at the boundary between the layers, the copper particles completely cover the resin, further improving the conductivity and cutting off the contact between the cured coating and the air. oxidation will not proceed.

These features provide a copper foil circuit with high conductivity that is practically practical, and the process is extremely simple and inexpensive compared to the gluing process, in which the thin surface becomes a plated copper layer.
Copper waste is incomparably less, and it is advantageous in all respects.

In addition, in the above example, the electroless metal plating was explained as electroless copper plating, but this is
It is also possible to perform the process by nickel plating, electroless solder plating, electroless silver plating or electroless gold plating1.
However, its application range is extremely wide.

Since the present invention is constructed as described above, -
A conductive circuit for installed electronic equipment is made by applying a copper conductive %f1 paste to an insulating plate and curing it by heating, and then applying electroless metal plating with good conductivity to the surface of the cured coating. It is possible to significantly improve conductivity compared to a cured coating film made of paste only, and it also makes it possible to stabilize conductivity, making it possible to obtain a conductor circuit with no body color compared to a copper foil circuit. There is. In addition, since it becomes possible to put such conductor circuits to practical use, the use of expensive silver conductive paste and etching methods become unnecessary, making it possible to reduce the cost of printed circuits and dramatically increasing their productivity. Six effects can be obtained by focusing on the target.

Patent Applicant: Azahi Chemical Research Institute Co., Ltd. Agent: Attorney-at-Law 1+1 Kazuo 15- 485-

Claims (1)

[Claims] 1 Copper conductive paste, which has good soldering properties, is applied to an insulating plate, heated (-2) to harden it to form a conductive circuit with a cured coating, and then soaked in a weakly acidic solution. A method for producing a conductive circuit, comprising immersing the cured coating film to activate the surface thereof, and then subjecting the cured coating film surface to electroless metal plating treatment with good conductivity. 2. 2. The method of manufacturing a conductive circuit according to claim 1, wherein the electrolytic metal plating is electroless copper plating.