JP2004266078A - Method of forming conductor pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form conductor patterns at a narrow pitch on a polymer film. <P>SOLUTION: A method of forming conductor patterns comprises a process of forming a conductive film 3 by printing conductive paste 6 over the entire surface of a polymer film 5, a process of forming an etching resist 8 on the conductive film 3 except for a conductor pattern formation section 9, a process of depositing pattern plating 4 on the conductor pattern formation section 9 using the conductive film 3 as an electrode, a process of removing the etching resist 8, and a process of removing the conductive film 3 except for the portion where the pattern plating 4 is deposited. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a conductor pattern on an insulating substrate, and more particularly, to a method for forming a conductor pattern having a narrow pitch using a semi-additive method.
[0002]
[Prior art]
Conventionally, when a conductive pattern is formed on a base substrate made of a glass cloth substrate, ceramics, a polymer film, or the like, a method of forming the film by sputtering on the base substrate and then performing photo-etching, A metal foil, such as a copper foil, is adhered via an adhesive, and the film is formed by photoetching.
[0003]
For example, as a base substrate of a flexible printed wiring board, a polymer film made of polyimide (PI), polyethylene terephthalate (PET), or the like is used. Among them, the PI film is excellent in heat resistance, so that when a conductive film is formed on the entire surface of the film, the film is formed by sputtering. This conductive film is formed by attaching a plurality of types of metal thin films, such as palladium (Pd), chromium (Cr), and copper (Cu), on the polymer film in order to enhance the adhesion to the polymer film. A film is formed by sputtering. Therefore, a conductive film having excellent adhesion can be obtained from the PI film. Thereafter, a conductor pattern is formed on the conductive film by photoetching using photolithography.
[0004]
[Patent Document 1]
JP 2001-196726 A
[Problems to be solved by the invention]
On the other hand, a printed wiring board using a PET film as a base substrate has better flexibility than a substrate using PI, but has a low heat resistance of the PET film. A conductive film is formed by attaching a metal foil such as a rolled copper foil with an adhesive and printing a conductive paste.
[0006]
When a resist pattern is formed on a conductive film made of this conductive paste and the conductive pattern is formed by wet etching, the etching proceeds to the lower portion of the resist, so-called undercut occurs, and the pitch of the pattern is reduced. Becomes difficult. If the thickness of the conductive film is reduced to suppress the undercut, the resistance value of the conductive film increases. In order to lower the resistance value, there is a method of further plating the formed conductive film. However, the pitch width of the conductor pattern is increased during plating growth, and it is difficult to reduce the pattern pitch. Become. Further, even if a conductor pattern is directly formed by a printing method such as screen printing, there is a limit to narrowing the pitch of the pattern.
[0007]
Therefore, an object of the present invention is to provide a conductive pattern forming method for forming a conductive pattern having a narrow pitch on a flexible polymer film on which a conductive film is printed or applied.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, a conductive pattern forming method according to the present invention is directed to a method of forming a conductive film by printing a conductive paste or conductive ink or applying a conductive paint over the entire surface of a polymer film. Forming an etching resist on a portion of the conductive film other than the conductive pattern forming portion, and depositing pattern plating on the conductive pattern forming portion using the conductive film as an electrode. A step of removing the etching resist; and a step of removing the conductive film except for a portion where the pattern plating is deposited.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a conductive pattern forming method to which the present invention is applied will be described in detail with reference to the drawings. The method for forming a conductor pattern to which the present invention is applied is used for forming a conductor pattern of a flexible printed wiring board 1, and prints a conductive paste such as silver on a base substrate 2 made of a polymer film. As shown in FIG. 1, a conductive pattern 3 having a pitch of several tens μm is formed on the conductive layer 3 by electroplating.
[0010]
As the base substrate 2, a polymer film 5 having excellent flexibility such as a polyethylene terephthalate (PET) film is used. In the method for forming a conductor pattern according to the present invention, since the conductive layer 3 is formed by screen printing or the like, the polymer film 5 is not exposed to a high temperature, and polyethylene terephthalate which is relatively poor in heat resistance. A (PET) film can be used. In addition, a polymer film such as a polyester film and a polyimide film may be used for the base substrate 2 in addition to the PET film.
[0011]
As shown in FIG. 2, the conductive layer 3 is formed on the entire surface of the base substrate 2 by printing the conductive paste 6 using a printing technique such as silk screen printing. In the present invention, the conductive layer 3 is used as a plating electrode in a later-described pattern plating deposition step.
[0012]
The conductive paste 6 is formed by mixing a single type of conductive metal particles such as a silver paste into a binder. Therefore, in the conductive layer 3, it is possible to form a conductor pattern made of a single metal by depositing a silver plating pattern in a plating step described later. This can prevent migration that may be caused by laminating a plurality of types of metal conductor layers.
[0013]
Further, since the conductive paste 6 is printed on the polymer film 5 having relatively low heat resistance such as a PET film, a binder fired at a low temperature is used.
[0014]
As such a binder, there is a binder using Ag + polyester + carbitol acetate or the like. As a binder for a polymer film having relatively low heat resistance such as a PET film, a so-called nanopaste having Ag particles of 50 nm or less is used. In the present invention, a nanopaste having a firing temperature of 140 ° C. was used as a binder.
[0015]
In addition, by using a polyester having a composition similar to PET as the binder, adhesion to the polymer film 5 such as a PET film is ensured.
[0016]
In addition, for a film of a material other than PET, a binder having a suitable sintering temperature and adhesion can be used.
[0017]
In addition, the conductive layer 3 needs to be formed as thin as possible so that etching can be completed in a short time in the etching step. That is, when the conductive layer 3 is formed thick, it takes a long time for etching, and erodes the plating deposited on the pattern forming portion. Therefore, a binder having a low viscosity is used as the binder of the conductive paste 6, and the conductive layer 3 is printed with a thickness of 5 μm or less.
[0018]
In addition to using the conductive paste 6, the conductive layer 3 supplies a conductive ink or a conductive paint mixed with conductive fine particles such as silver to the base substrate 2, and rotates the base substrate 2 at high speed. May be formed by a spin coating method of coating the conductive ink or the like used by the centrifugal force generated by the above, or a roll coating method of applying the conductive ink or the like on the base substrate 2 using a roller.
[0019]
The conductive layer 3 formed on the base substrate 2 is cured by firing. At this time, since the polymer film 5 having a relatively low heat resistance such as a PET film is used for the base substrate 2, the conductive paste 6 is fired at a temperature lower than the heat resistance of the polymer film 5. As the conductive paste 6, a binder fired at such a temperature is selected, and the conductive paste 6 is adhered onto the polymer film 5 by firing.
[0020]
If it is difficult to etch in a wet etching step to be described later when the conductive paste 6 is completely baked, the conductive paste 6 may be temporarily baked in this baking step and completely baked after the wet etching step. .
[0021]
The baked conductive layer 3 is coated with a photosensitive etching resist and exposed and developed through a mask film on which a conductive pattern is formed, thereby curing the resist 8 other than the pattern forming portion where the conductive pattern is formed. Then, the uncured resist corresponding to the pattern forming portion is removed. Thereby, as shown in FIG. 3, the conductive layer 3 has a pattern forming portion 9 where a plating pattern is deposited in a plating step on a portion where the resist 8 is not formed.
[0022]
Next, a plating pattern 4 is formed by depositing plating on the pattern forming portion 9 by an electroplating method. First, in order to remove oxides on the surface of the conductive layer 3, the surface is washed with sulfuric acid and washed with water. Thereafter, the base substrate 2 is immersed in a plating bath, and electrodes are connected to both ends of the conductive layer 3 via the pattern forming portion 9 to conduct electricity. When a plating current flows, as shown in FIG. 4, silver plating is deposited on the pattern forming portion 9, and the plating pattern 4 is formed. At this time, the conductive layer 3 formed over the entire surface of the polymer film 5 is used as a plating electrode. The thickness of the silver plating forming the plating pattern 4 is 15 to 20 μm.
[0023]
Next, as shown in FIG. 5, the resist 8 is peeled off from the polymer film 5 on which the plating pattern 4 is formed, and the silver plating pattern 4 is obtained. The resist 8 is stripped by spraying a stripping solution.
[0024]
Next, as shown in FIG. 6, the conductive paste 6 other than the silver plating pattern 4 is removed by wet etching. At this time, as described above, the conductive layer 3 is formed with a thickness of 5 μm or less by using a binder having a low viscosity as the binder of the conductive paste 6. Therefore, according to the method for forming a conductor pattern to which the present invention is applied, since the time required for wet etching can be short, side etching of the conductive paste 6 remaining under the silver plating pattern 4 can be prevented. Accordingly, a conductor pattern having a reduced pitch can be formed. Thereby, as shown in FIG. 1, the plating pattern 4 having a pitch width and a pitch width of 10 to 30 μm can be formed.
[0025]
As described above, according to the method for forming a conductive pattern to which the present invention is applied, the conductive layer 3 is formed by printing the conductive paste 6 on the polymer film 5 having poor heat resistance, such as a PET film. A conductor pattern is formed by applying pattern plating on the layer 3. Therefore, it is possible to prevent under-etching which has occurred in the conventional method of forming a conductive pattern by photo-etching a polymer film formed by printing a conductive layer, and to form a narrow-pitch conductive pattern. it can.
[0026]
According to the method of forming a conductive pattern to which the present invention is applied, the conductive layer 3 formed on the base substrate 2 is formed by printing the conductive paste 6 in which conductive fine particles such as silver are mixed in a binder. It is formed by. Since the binder of the conductive paste 6 is selected to have a low firing temperature, adhesion to the base substrate 2 is ensured even at a low firing temperature. Thus, according to the present invention, the conductive layer 3 made of a single metal can be formed without laminating a plurality of types of metal foils. In addition, by forming a plating pattern made of the same metal as the conductive layer 3, a conductive pattern made of a single metal can be formed. In addition, since the flexible printed wiring board 1 on which the conductive pattern is formed by the method of the present invention has a plating pattern formed on the conductive layer 3, even if the conductive layer 3 is formed to be thin, The resistance does not matter.
[0027]
In the method of forming a conductor pattern to which the present invention is applied, the conductive layer 3 is formed by sandwiching a different metal film such as palladium (Pd), chromium (Cr), or copper (Cu) between the base substrate and the silver paste. It may be formed to further improve the adhesion between the conductive layer 3 and the base substrate made of a PET film or the like.
[0028]
【The invention's effect】
As described in detail above, according to the method for forming a conductive pattern according to the present invention, a conductive layer is formed by printing a conductive paste on a polymer film having poor heat resistance, and the conductive layer is used as a plating electrode. A conductor pattern is formed by pattern plating on the conductive layer. Therefore, a narrow-pitch conductive pattern can be formed on a polymer film having poor heat resistance such as a PET film. Further, it is possible to prevent under-etching which has occurred in a method of forming a conductive pattern by photo-etching a polymer film formed by printing a conventional conductive layer, and to form a conductive pattern having a narrow pitch. it can.
[Brief description of the drawings]
FIG. 1 is a plan view showing an example of a conductor pattern to which the present invention is applied.
FIG. 2 is a cross-sectional view showing a base substrate on which a conductor layer is formed.
FIG. 3 is a cross-sectional view showing a base substrate provided with a resist and a pattern forming unit.
FIG. 4 is a sectional view showing a base substrate on which a plating pattern is formed.
FIG. 5 is a cross-sectional view showing the base substrate from which the resist has been removed.
FIG. 6 is a cross-sectional view showing a base substrate from which a conductive layer has been removed.
[Explanation of symbols]
1 Flexible printed wiring board, 2 Base board, 3 Conductive layer, 4 Plating pattern, 5 Polymer film, 6 Conductive paste, 8 Resist, Pattern forming part

Claims (3)

A step of printing a conductive paste or conductive ink over the entire surface of the polymer film, or forming a conductive film by applying a conductive paint,
A step of forming an etching resist on the conductive film except for the conductive pattern forming portion,
Using the conductive film as an electrode, a step of depositing a pattern plating on the conductive pattern forming portion,
Removing the etching resist;
Removing the conductive film except for the portion where the pattern plating is deposited. 2. The method according to claim 1, wherein the conductive film is a single type of metal film. 2. The method according to claim 1, wherein the conductive film is made of one of silver, gold, and copper.

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