JP2004152934A - Circuit board and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently, inexpensively forming a circuit board having a fine conductive circuit with a high aspect ratio, and to provide the circuit board formed by the method. <P>SOLUTION: The manufacturing method of the circuit board includes a process for applying a conductive paste containing metal powder onto an insulating board formed in a recess shape, curing the paste, polishing the surface of the insulating board, and removing the paste at a place other than a recess, thus efficiently, and inexpensively forming the circuit board having the fine conductive circuit with a high aspect ratio. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a conductive circuit on an electronic circuit board and a circuit board on which a conductive circuit obtained by the method is formed, and more particularly to a circuit board having fine wiring with a high aspect ratio.
[0002]
[Prior art]
Conventionally, in a method of manufacturing a circuit board, a conductive circuit is formed by applying or laminating a photoresist on a copper foil of a copper-clad laminate in which a copper foil is bonded to an insulating substrate, and performing exposure, development, and etching. (Subtractive method). However, in recent years, the miniaturization of conductive circuits has progressed as electronic devices have become lighter, thinner and shorter, and the subtractive method causes erosion from the side surfaces of conductors during etching, resulting in a trapezoidal cross-sectional shape, making it difficult to form fine wiring. The only solution to this problem is to reduce the thickness of the copper foil to be used. However, if the thickness is reduced, the aspect ratio becomes small, and the current value that can be passed is limited. In order to solve this problem, a photoresist layer is formed on an insulating substrate in the same manner as described above, and after exposure and development, a conductive circuit is formed by performing electroless copper plating and / or electrolytic copper plating (additive method). . However, even with the additive method, the formation of fine conductive circuits with a high aspect ratio has limitations due to poor resolution of photoresist, and the formation of conductive circuits by copper plating requires time, is inefficient and expensive. And so on.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for efficiently and inexpensively forming a circuit board having a fine and high aspect ratio conductive circuit as described above, and to provide a formed circuit board.
[0004]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have completed the present invention.
That is, the present invention applies a conductive paste containing metal powder on an insulating substrate having a concave shape in a conductive circuit portion, and after curing the paste, polishing the surface and removing the paste other than the concave portion. And a circuit board obtained by the method. Alternatively, a conductive paste containing metal powder is applied on an insulating substrate having a concave shape in the conductive circuit portion, the paste is dried, the surface is polished, and the paste other than the concave portions is removed, and then the paste is cured. A method of manufacturing a circuit board formed by forming a conductive circuit and a circuit board obtained by the method.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for forming the concave shape in the insulating substrate having a concave shape in the conductive circuit portion of the present invention is not particularly limited, but a method using a mold or a method using a laser is preferable. When a mold is used, a mold having a convex shape corresponding to the concave shape is prepared, and an insulating substrate having a concave shape in the conductive circuit portion is obtained by a transfer molding method or an injection molding method in which resin is injected or compressed. Is preferred. As a method for forming the mold, a thick resin film layer is usually formed on a glass plate, and is exposed and developed to form a concave resin mold. Next, after nickel plating is performed on the surface, the photosensitive resin is removed to obtain a convex mold.
[0006]
In the case of using a laser, a concave shape may be formed by directly irradiating a laser beam such as a carbon dioxide gas laser or a YAG laser to a conductive circuit portion on a planar insulating substrate. When a mold is used as the resin constituting the insulating substrate, a thermoplastic resin such as a polyimide resin, a polyamide resin, a polyester resin, a polyether sulfone resin, a polyether ether ketone resin, a polyphenylene oxide resin, or an epoxy resin, or a phenol resin And a thermosetting resin such as a bismaleimide resin. Among them, a liquid crystal polymer is particularly desirable in terms of heat resistance and dimensional stability. When a laser is used, there is no particular limitation, and examples thereof include a glass / epoxy substrate, a glass / polyimide substrate, a glass / polyphenylene oxide substrate, and a polyimide film. In any case, as the shape of the concave portion of the fine wiring formed on the insulating substrate, the ratio of the depth to the opening width (aspect ratio) of the concave portion is preferably 0.5 or more from the viewpoint of flowing a current to the fine conductive circuit. .
[0007]
The metal powder of the conductive paste containing the metal powder of the present invention is silver, copper, gold, nickel or the like, and has a particle diameter of 10 μm or less, preferably 100 nm or less. These may be used alone or in combination of two or more. If the particle diameter is 10 μm or more, it is difficult to fill the fine concave portions, which may not be preferable. The metal powder is dispersed and kneaded together with a resin, a solvent and a dispersant to obtain a conductive paste.
[0008]
The resin to be used is not particularly limited, but from the viewpoint of heat resistance, usually, an epoxy resin, a phenol resin, a polyimide resin, a polyamide resin, a polycyanate resin, a polyphenylene oxide resin, and the like are used. Resins such as resins, hydrogenated NBR resins, SBR resins, hydrogenated SBR resins, silicone resins, and the like. These may be used alone or in combination of two or more.
The weight ratio between the metal powder and the resin is usually 98: 2 to 70:30. Examples of the method for applying the present conductive paste include screen printing, dip coating, roll coating, spray coating, and ink-jet methods, and the like. Yes, reasonable and preferred.
[0009]
The step of applying the conductive paste after application, after drying or after curing may be repeated a plurality of times.
Before applying the conductive paste, the surface of the insulating substrate may be treated so as to be easily wetted with the paste. Examples of the treatment method in this case include a dry treatment such as a plasma treatment, a UV treatment, and a corona discharge treatment, and a wet treatment with a permanganic acid solution, an alkali solution, and the like.
[0010]
After the conductive paste containing the metal powder is applied on the insulating substrate having the concave shape in the conductive circuit portion in this manner, the paste is dried or cured, and the paste other than the concave portions is removed by polishing the surface. .
Drying, polishing, and curing steps are performed at 50 to 120 ° C., preferably at 80 to 100 ° C. for 15 to 60 minutes, and then polished. Is cured. When the curing and polishing steps are performed, the polishing is performed after curing at a temperature of 180 ° C. to 300 ° C. for 30 minutes to 180 minutes.
[0011]
Polishing is performed under the conditions of a load of 0.5 to 10 kg / cm ² , a rotation speed of 30 to 100 rpm, and a polishing time of 2 to 30 minutes while flowing the slurry on the conductive paste application surface with a platen polishing machine. The main polishing step may be performed using a buffing machine, a belt sander, or the like.
[0012]
It is, of course, possible to manufacture a multilayer circuit board by repeating this manufacturing process a plurality of times.
[0013]
【Example】
Next, specific examples of the present invention will be described.
[Example 1]
FIG. 1 shows a manufacturing process of the circuit board of the present invention. In FIG. 1, transfer molding was performed using a mold having a convex shape in the conductor circuit portion and using an epoxy resin (Epox, trade name, manufactured by Mitsui Chemicals, Inc.) as the resin for the mold. The molding conditions were a mold pressing pressure of 200 kg / cm ² , a resin pressure of 45 kg / cm ² , and a filling temperature of 180 ° C. Thus, an insulating substrate having a concave portion on the surface was obtained.
A silver paste was printed in the recesses on the thus obtained insulating substrate by an inkjet method. The silver paste used was obtained by mixing and dispersing 2 parts by weight of an epoxy resin (trade name: Epox, manufactured by Mitsui Chemicals, Inc.) and 100 parts by weight of tetradecane as a solvent with 98 parts by weight of silver powder having a particle size of 7 nm.
After heating the substrate at 200 ° C. for 1 hour to cure the silver paste, the paste printed surface was polished and removed with a surface plate polisher to remove excess paste on the concave surface. The conditions of the polishing machine were a load of 1 kg / cm ² , a rotation speed of 70 rpm, and a polishing time of 20 minutes.
The conductor circuit width in the fine wiring portion of the conductor circuit of the circuit board thus obtained was 10 μm, and the conductor circuit thickness was 12 μm.
[0014]
[Example-2]
Using an YAG laser on the surface of a glass / epoxy substrate as an insulating substrate, a recess was formed in the conductor circuit portion. Thereafter, 25 parts by weight of copper powder having a particle diameter of 10 nm, 55 parts by weight of copper powder having a particle size of 2 μm, 10 parts by weight of phenol resin (Mirex XLC, manufactured by Mitsui Chemicals, Inc.), and 10 parts by weight of epoxy resin (EOCN-4400, manufactured by Nippon Kayaku Co., Ltd.) A copper paste mixed and dispersed with 30 parts by weight of decanol as a solvent was printed in the recesses by a screen method. After drying at 100 ° C. for 5 minutes, the printing surface was polished with a belt sander to remove excess copper paste. Polishing conditions were a pressurized load current of 5 A and a feed rate of 1 m / mim. The substrate was heated at 180 ° C. for 1 hour in a nitrogen atmosphere to cure the paste. The conductor circuit width in the fine wiring portion of the circuit board thus obtained was 20 μm, and the conductor circuit thickness was 12 μm.
[0015]
[Example-3]
An insulating layer having a concave portion was further formed on the circuit board prepared in Example 1 by molding, and a two-layer circuit board was prepared in the same manner as in Example-1. Figure 2 shows the manufacturing process.
[0016]
【The invention's effect】
According to the method of the present invention, a circuit board having a fine and high aspect ratio conductive circuit can be efficiently and inexpensively formed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a circuit board manufacturing process. FIG. 2 is a diagram illustrating an example of a circuit board manufacturing process.

Claims (8)

A conductive paste containing metal powder is applied on an insulating substrate having a concave shape, and after the paste is cured, the surface of the insulating substrate is polished to remove the paste other than the concave portion. Production method. After applying a conductive paste containing metal powder on an insulating substrate having a concave shape, drying the paste, polishing the surface of the insulating substrate, removing the paste other than the concave portion, and curing the paste. A method for manufacturing a circuit board, comprising: The method according to claim 1, wherein the metal powder has a particle size of 10 μm or less. 4. The organic resin substrate according to claim 1, wherein the insulating substrate is an organic resin substrate formed by transfer molding or injection molding using a mold having a convex shape corresponding to the concave portion. The method for manufacturing the circuit board described in the above. The method for manufacturing a circuit board according to any one of claims 1 to 3, wherein the concave shape is formed by a laser. The method for manufacturing a circuit board according to any one of claims 1 to 5, wherein the conductive paste is applied to the concave portions by an inkjet method. The method for manufacturing a circuit board according to any one of claims 1 to 6, wherein an aspect ratio (conductive circuit thickness / conductive circuit width) of the formed conductive circuit is 0.5 or more. A circuit board obtained by the manufacturing method according to claim 1.

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