JPH07162134A - Solder resist film coated printed wiring board - Google Patents

Abstract

PURPOSE:To flatly finish the surface of the title printed wiring board by a method wherein a photosensitive solder resist film is provided on the whole surface of the printed wiring board, it is exposed and developed by closely adhering a mask film, and a hardening type solder resist film is provided on the resist film left between circuits. CONSTITUTION:A circuit 2 is provided on a printed circuit board 1 by photoetching the upper film of an epoxy resin laminated sheet. A photosensitive solder resist film 3 is formed on the whole surface of the printed wiring board 1. An exposing operation is conducted by closely adhering a mask film on which circuit pattern transmits no light, and the photosensitive film is developed and removed. Then, hardening type solder resist is applied on the whole surface, and a hardening type solder resist film 6 is formed. Accordingly, a printed wiring board on which a circuit pattern is not seen and unrecognized is obtained. As a result, the metal foil and the photosensitive solder resist film become even with each other, and as hardening type solder resist is applied on it, surface can be finished flat and a thin film can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board whose wiring circuit cannot be discriminated from its appearance and a manufacturing method thereof.

[0002]

2. Description of the Related Art A printed wiring board is a metal foil of a glass-based epoxy resin laminated plate having a metal foil such as a copper foil attached thereto and a circuit provided by a photoetching method or the like. In a printed wiring board such as an IC card or a game of a personal computer, an unspecified user can touch it, and if the shape of the circuit is known, the circuit may be tampered with. For this reason, an opaque curable solder resist (thermosetting resin such as epoxy resin) film colored in black, green, or the like is applied to the circuit of the printed wiring board so that the circuit of the wiring cannot be distinguished from the appearance. It is necessary to cover the entire surface of the wiring except the terminal portion of the wiring by screen printing or the like so as to cover it, conceal the circuit so that it cannot be seen, and smooth the surface so that the swell of the circuit cannot be seen. Screen printing is used because it can be printed partially or relatively thickly. Generally, the screen mesh used is # 80 to # 200, and the viscosity of the screen ink is 100 to 700 poise (2
5 ° C).

[0003]

However, the circuit has a thickness of about 35 μm, a line width of 100 μm, and an interval of 100 μm. The circuit having a step of about 35 μm is coated with solder resist screen ink to form a circuit. It is necessary to make the entire surface smooth so that the rise of is not known. For this reason, in the screen printing, a method in which the screen ink is printed several times is used by utilizing the property that the screen ink is slightly deformed after printing (flowing to the lower side). However, in the case of a circuit having a step of about 35 μm, it is necessary to perform overprinting at least 5 to 6 times or more in order to prevent the rise of the circuit from being recognized. In addition, this increases the thickness of the solder resist film,
You will use more solder resist screen ink than necessary. Naturally, the productivity is deteriorated and the defect occurrence rate is also increased.

The present invention has been made in view of the above points, and an object of the present invention is to provide a printed wiring board having a solder resist film and a smooth surface, and a method for manufacturing the same. Is.

[0005]

According to the present invention, a photosensitive solder resist film is provided on the entire surface of a printed wiring board having a circuit made of a metal foil so as to have a thickness substantially equivalent to the thickness of the metal foil. On the resist film, a mask film having a pattern having the same shape as the pattern of the circuit, which is a light opaque portion, is brought into close contact with the pattern of the circuit, and exposed.
Next, development is performed to remove the photosensitive solder resist film on the circuit, and a curable solder resist film is further provided on the entire surface of the circuit and the photosensitive solder resist film between the circuits. It is a method for manufacturing a coated printed wiring board.

The present invention is also a method for producing a solder resist film-covered printed wiring board, characterized in that screen deposition is performed to provide the photosensitive solder resist film or the curable solder resist film.

The present invention is also the method for producing a solder resist film-covered printed wiring board, characterized in that the curable solder resist film is provided by screen printing twice or less times.

According to the present invention, in a printed wiring board having a circuit made of a metal foil, a photosensitive solder resist film is provided between the circuits so as to have a thickness corresponding to the thickness of the metal foil. A solder resist film-covered printed wiring board, characterized in that a curable solder resist film is provided on the entire upper surface.

The present invention is also a solder resist film-covered printed wiring board characterized in that the photosensitive solder resist film and / or the curable solder resist film are provided by screen printing.

The present invention is also a printed wiring board characterized in that the curable solder resist film is provided by screen printing twice or less times.

[0011]

[Function] By embedding the photosensitive solder resist film in the thickness of the metal foil between the circuits made of the metal foil, the thickness of the circuit and the thickness of the photosensitive solder resist film become almost the same,
The surface can be finished smooth by simply printing the curable solder resist once or twice.

[0012]

EXAMPLES The present invention will be described in detail below with reference to examples.

The printed wiring board 1 is, as shown in FIG. 2, a copper foil of a glass-based epoxy resin laminated plate on which a copper foil is pasted as a metal foil having a thickness of 33 μm, and a circuit 2 is provided by a photoetching method. is there.

As shown in FIG. 3, except for the soldering points, P is a product of Taiyo Ink Mfg. Co., Ltd. as an ink for the photosensitive solder resist film on the entire surface of the printed wiring board 1.
The photo-SR ink was printed twice on the entire surface by screen printing to a thickness of 30 μm to 33 μm, and dried to form a photosensitive solder resist film 3. The screen mesh used is # 100, and the ink viscosity is 700 poise (2
5 ° C).

As shown in FIG. 4, a mask film 5 having the same shape as the circuit pattern (not shown) and having the light opaque portion 4 is prepared.
The pattern of Circuit 2 was adhered onto the printed film surface.

After exposure, the photosensitive film on the circuit 2 is removed by developing with a 5% aqueous sodium bicarbonate solution. In this way, as shown in FIG. 5, a photosensitive film having a thickness close to the thickness of the circuit was embedded between the circuits.

Next, as shown in FIG. 1, a black thermosetting SR manufactured by Asahi Kaken Co., Ltd. was used as a curable solder resist.
The ink (epoxy resin) was applied by screen printing to a thickness of 20 μm on the entire surface and dried to form a curable solder resist film 6. Thus, there was obtained one in which the circuit pattern on the surface could not be seen and the circuit pattern could not be recognized.

[0018]

As described above, the present invention is characterized in that in the printed wiring board, the photosensitive solder resist film is embedded between the circuits, and the metal foil and the photosensitive solder resist film are flush with each other. Since a curable solder resist is applied on top of it, the photosensitive solder resist film is 2
The surface can be smoothed less than twice, as a curable solder resist less than twice, and as the solder resist is applied less than four times in total. The thickness of the solder resist screen ink is also small, which reduces the material cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a solder resist film-covered printed wiring board according to an embodiment of the present invention.

FIG. 2 is a sectional view of a printed wiring board according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view in which a photosensitive solder resist film is formed on a printed wiring board in the example of the present invention.

FIG. 4 is a cross-sectional view in which a photosensitive solder resist film is formed on a printed wiring board and a mask film is further adhered thereto in the example of the present invention.

FIG. 5 is a cross-sectional view showing a state in which a photosensitive film is embedded between circuits in the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Printed wiring board 2 ... Circuit 3 ... Photosensitive solder resist film 4 ... Light-impermeable part 5 ... Mask film 6 ... Curable solder resist film

Claims (6)

[Claims] 1. A photosensitive solder resist film is provided on the entire surface of a printed wiring board having a circuit made of a metal foil so as to have a thickness substantially equivalent to the thickness of the metal foil, and the circuit of the circuit is provided on the photosensitive solder resist film. A mask film having a pattern of the same shape as the pattern, which is a light opaque portion, is brought into close contact with the pattern of the circuit, exposed to light, and then developed to remove the photosensitive solder resist film on the circuit. A method for producing a solder resist film-covered printed wiring board, characterized in that a curable solder resist film is provided on the entire surface of the circuit and a photosensitive solder resist film between the circuits. 2. The method for producing a solder resist film-covered printed wiring board according to claim 1, wherein the photosensitive solder resist film or the curable solder resist film is provided by screen printing. 3. The method for producing a solder resist film-covered printed wiring board according to claim 1, wherein the curable solder resist film is provided by screen printing twice or less times. . 4. A printed wiring board having a circuit made of a metal foil, wherein a photosensitive solder resist film is provided between the circuits to a thickness corresponding to the thickness of the metal foil, and the photosensitive solder resist film between the circuit and the photosensitive solder resist film is provided between the circuits. A solder resist film-covered printed wiring board, characterized in that a curable solder resist film is provided on the entire surface. 5. The printed wiring board according to claim 4, wherein the photosensitive solder resist film or the curable solder resist film is provided by screen printing. 6. The printed wiring board according to claim 4 or 5, wherein the curable solder resist film is provided by screen printing twice or less.