JPH02180089A - Forming method for conductive circuit - Google Patents

Abstract

PURPOSE:To obtain a printed board having high reliability and an inexpensive cost even when a complicated circuit pattern is formed by forming a liquid latent image according to a picture signal on a board, and forming a conductive circuit on the liquid latent image. CONSTITUTION:A step of forming a latent image 4 with liquidlike substance by discharging liquid droplet 3 from a liquid droplet source 2 in response to a picture signal according to a circuit pattern formed on the surface of a board 1, and a step of sticking powder 6 formed of a conductive material on the latent image 4 are provided. Accordingly, a complicated step is not required, and etching liquid, etc., having toxicity may not be employed. Thus, even if small number of many kinds of complicated patterns of conductive circuits are manufactured, it can be manufactured inexpensively in a short period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of forming a conductive circuit on a substrate.

[Prior Art] In the production of printed circuit boards, etc., conventional methods for forming circuit patterns (hereinafter referred to as conductive circuits) using conductive materials on boards include a wet process using an etching method,
There was a dry process using screen printing methods.

A wet process using an etching method is a thin film layer of a conductive material on a substrate made of an electrically insulating material.
For example, a copper thin film layer) is formed, a photoresist layer is formed on top of the photoresist layer, exposure is performed from above the photoresist layer according to the desired circuit pattern, and finally an etching solution is used to separate the photoresist layer and the conductive material. This is a method of removing unnecessary parts of the thin film layer.

In addition, the dry process using the screen printing method involves layering a screen original plate with openings corresponding to the desired circuit pattern on a substrate made of an electrically insulating material, and then mixing binder resin and conductive particles on top of it. In this method, a desired conductive circuit is formed on a substrate by coating a conductive ink formed by the method and transmitting the conductive ink through openings on the screen original.

As a printed circuit board produced by screen printing, one is known in which an alumina ceramic substrate is used as an electrically insulating substrate and an ink containing a binder resin and tungsten conductive powder is used as a conductive ink. this is,
The alumina substrate and tungsten conductive powder are metallized and bonded by baking the alumina substrate on which a conductive circuit is formed by screen printing at high temperature.

[Problems to be Solved by the Invention] However, these printed circuit board forming methods had the following problems.

First, the etching method had the following problems.

■It is not suitable as a method for producing many types of printed circuit boards in small quantities.

■The process is complicated, resulting in poor productivity and high costs.

- A toxic processing solution must be used as the etching solution.

■Copper in unnecessary parts must be removed, resulting in a large loss of copper, resulting in high costs.

In addition, the screen printing method had the following problems.

(2) Since it is necessary to prepare a screen master having a desired conductive circuit pattern in advance, this method is not suitable for producing many types of printed circuit boards in small quantities.

■It is difficult to form a conductive circuit with a narrow line width (for example, 200 μm line width).

The present invention was tried to solve these problems, and has excellent productivity and safety, is highly reliable even when forming complex circuit patterns, and can be manufactured in small quantities. [Means for Solving the Problems] The gist of the present invention is to provide a method for forming a conductive circuit that can provide a printed circuit board that is inexpensive even if A method for forming a circuit pattern by forming a latent image of a liquid substance on the surface of the substrate by ejecting droplets from a droplet supply source in accordance with an image signal according to the circuit pattern to be formed. A method for forming a conductive circuit is characterized in that it includes at least the following steps: A step of attaching powder formed of a conductive material to the latent image.

Hereinafter, the present invention will be explained in detail.

(Droplet supply source) As a droplet supply source, for example, an inkjet head known as an inkjet recording method may be used. Inkjet recording methods include the ``bubble jet method,'' in which droplets are ejected from the tip of a nozzle using the force of bubble generation caused by temperature rise, and the ``piezo method,'' in which droplets are ejected from the tip of the nozzle using the electrostrictive force of a piezoelectric element.・Jet method”, and also “electrostatic force method”, which uses electrostatic force to eject droplets from the tip of the nozzle.
Sheet method is known, and any method can be used as the droplet supply source of the present invention.

The piezo method is advantageous in that the type of liquid substance that forms the droplets can be selected from a relatively wide range of types.

When using the electrostatic cashier method, the specific electrical ratio is 5 or more,
Alternatively, it is preferable to use a liquid substance having an electrical conductivity of 1010 Ω·Cm or less.

When using the bulb-jet method, it is preferable to use a liquid substance with a film boiling temperature of about 350° C. or lower in terms of heater life and the like.

(?1i, type substance) As the liquid substance to be used, for example, a liquid obtained by dissolving 6 wt % to 25 wt % of a water-soluble adhesive resin such as POVAL in water may be used. After forming a liquid latent image on a substrate (for example, a polyimide substrate) with this liquid substance, and attaching powder made of a conductive material such as metal (hereinafter referred to as metal conductive powder) to the liquid latent image, By drying this, a conductive circuit can be formed.

Further, as the liquid substance used, a liquid substance that does not contain adhesive resin can also be used. For example, as a liquid substance, 5 wt% of ethylene glycol as a thickener is added to water.
Using an aqueous solution in which ~20 wt% is dissolved, a latent image is formed on the substrate by this liquid material, and after the metal conductive powder is attached to this, a short film is placed in a chamber filled with a gaseous adhesive resin (e.g., isocyanate). By leaving it for a while, a chemical reaction between isocyanate and water can occur, and the metal conductive powder attached to the liquid reservoir image can be fixed to the substrate.

That is, this method is a method in which the metal conductive powder is fixed by post-treatment.

As explained above, the liquid substance that forms the liquid latent image is
The adhesive resin may be dissolved from the beginning, or after the metal conductive powder is attached to the liquid latent image, another substance may be applied to give it a fixing function through a chemical reaction.

Alternatively, for example, a thermosetting resin or an ultraviolet curable resin may be used as the adhesive resin, and the adhesive may be fixed by heating or applying energy such as ultraviolet rays after development.

(Substrate) The present invention does not particularly limit the substrate on which the conductive circuit is formed. That is, all commonly used electrical circuit boards can be used. Furthermore, in the present invention,
A desired conductive circuit can also be formed on the surface of a three-dimensional object having a complicated curved surface.

(Metal conductive powder) As the metal conductive powder used in the present invention, for example, copper powder having an average particle size of about several tens of microns can be used.

(Method of attaching metal conductive powder) As a method of attaching metal conductive powder to a liquid latent image (hereinafter referred to as development), for example, a fur brush made from "rabbit hair" with soft bristles with an average diameter of about 50 μm is used. Using a brush with an appropriate amount of copper powder attached, lightly rub the fur brush with this copper powder attached on the liquid latent image on the substrate.
Copper powder may be applied to the liquid latent image area and developed.

[Function] According to the present invention, a liquid latent image is formed on the substrate according to an image signal, and a conductive circuit is formed on this liquid latent image, so it is possible to form a complex circuit pattern with excellent productivity and safety. It is possible to provide a printed circuit board that is highly reliable even when manufactured, and is inexpensive even when manufactured in small quantities.

[Example] (Example 1) FIG. 1 is a diagram showing an example of the present invention. In the figure, 1 is a polyamide substrate as a base, 2 is a piezo type inkjet head as a droplet supply source, 3 is a droplet ejected by the droplet supply source 2, and 4 is a liquid droplet formed on the polyamide substrate 1. A liquid latent image made of a substance, 5 a developing device for developing the liquid latent image (in this case, a fur brush developing device using rabbit hair), and 6 metal conductive powder attached to and developed on the liquid latent image 4.

A polyimide substrate with a thickness of 100 μm was used. The liquid substance used was one in which 15 wt % of poval resin was dissolved in water. Further, as the metal conductive powder 6, copper powder having an average diameter of 50 μm was used.

Hereinafter, the method for forming a conductive circuit according to this embodiment will be explained in the first part.
This will be explained according to the diagram.

(2) Droplets 3 were ejected from the droplet supply source 2 onto the surface of the polyimide substrate 1 (FIG. 1(a)), and a liquid latent image 4 according to a desired circuit pattern was formed on the surface of the substrate 10 ( Figure 1(b)).

(2) Next, using a developing device 5 using a fur brush, an appropriate amount of copper powder was applied to the fur brush, and the surface of the polyimide substrate 1 was developed by rubbing lightly (FIG. 1(C)). copper powder 6
was firmly attached to the liquid material latent image 4 and developed.

(2) Finally, the liquid latent image 4 was dried by heating, and the metal conductive powder 6 was fixed to the polyamide substrate 1.

In the manner described above, a conductive circuit could be formed on the surface of the polyimide substrate 1.

(Example 2) A printed circuit board was created in the same manner as in Example 1, using an alumina substrate with a thickness of 500 μm as the substrate and setting the width of the circuit pattern to 100 μm. Width 100μm
The circuit pattern was sufficiently and reliably formed on the substrate.

(Example 3) As Example 3, a case will be described in which a liquid substance that does not contain adhesive resin is used as the liquid substance. FIG. 2 is a conceptual diagram for explaining the method of fixing the liquid latent image in this case.

In the figure, 7 is a chamber. Further, 8 is an isocyanate gas supply source provided inside the chamber 7, and specifically, the liquid adhesive "Aron Alpha" is used.
(registered trademark) in an opened glass container.

In this example, a liquid substance made by mixing 12 wt% of ethylene glycol in water was used as the liquid substance, a polyimide substrate with a thickness of 200 μm was used as the base, and a non-woven material with an average particle size of 60 μm was used as the metal conductive powder 6. Shaped copper powder was used.

First, after performing the same steps as in Example 1,
This substrate was left for 5 minutes inside a chamber 7 filled with "Aron Alpha" gas (isocyanate gas) as shown in FIG. As a result, the liquid substance forming the liquid latent image 4 on the surface of the substrate caused a chemical reaction with water in the isocyanate gas atmosphere, and the metal conductive powder 6 could be reliably fixed to the substrate.

It could be satisfactorily used as a conductive circuit on a printed circuit board formed by the above method.

In addition, at this time, it is better to use a non-spherical conductive powder, especially one with needle-like protrusions on the surface, as the metal conductive powder (copper powder), because the number of electrical contact points between the conductive powders increases, and the conductive path increases. Our advantage was that we could reduce the electrical resistance of the (conductive circuit).

(Example 4) As Example 4, a case where a cascade development method is used will be described. The developer used was a spherical ferrite carrier whose surface was coated with an acrylic resin having an average particle size of 100 μm, mixed with 20 wt % of copper powder having an average particle size of 30 μm.

First, a liquid latent image is formed on the polynate substrate in the same manner as in the process of Example 1, and then a conductive component is deposited by the cascade development method to form a conductive circuit. A conductive circuit was fixed in the same manner.

In this way, a printed circuit board could be manufactured using the cascade development method.

(Example 5) A case where the developing device shown in Example 1, the liquid substance shown in Example 3, and the developer shown in Example 4 are used will be described. First, after carrying out the same steps as in Example 1 and 2, this substrate is left in the chamber 7 filled with "Aron Alpha" (registered trademark) gas for 5 minutes as in Example 3. By this, the metal conductive powder is fixed,
A conductive circuit was formed.

The printed circuit board manufactured in this manner was also a conductive circuit that could be put to practical use.

[Effects of the Invention] As explained above, according to the present invention, a screen original having a desired conductive circuit pattern can be prepared in advance without requiring complicated processes or using toxic etching liquid. A method for forming a conductive circuit that does not require preparation can be provided.

Therefore, even when manufacturing a small number of conductive circuits with various types of complicated patterns, they can be manufactured in a short time and at low cost. Furthermore, a desired conductive circuit can be formed on the surface of a three-dimensional object having a complicated curved surface.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the present invention, and FIG. 2 is a diagram for explaining another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Droplet supply source, 3... Droplet, 4
... Liquid latent image, 5... Developing device, 6... Metal conductive powder, 7... Chamber, 8... Isocyanate gas supply source diagram (b) /-P-1 〒i = 艷 = ii ko (C) et al.

Claims (1)

[Claims] A method for forming a circuit pattern using a conductive material on the surface of an electrically insulating substrate, the method comprising: forming a droplet on the surface of the substrate according to an image signal according to the circuit pattern to be formed; The method is characterized in that it includes at least the steps of: forming a latent image of a liquid substance by discharging a liquid extractor from a supply source; and attaching powder formed of a conductive material to the latent image. Method of forming a conductive circuit.