JPH0537141A - Formation of solder resist of circuit substrate - Google Patents

Abstract

PURPOSE:To form solder resist readily in a solid circuit having irregularites on a circuit surface. CONSTITUTION:After liquid photosolder resist 3 is applied to and dried in a circuit formation side 11 of a circuit substrate 1 having irregularities by a spray coat method, light screening ink 4 is printed to a specified pattern by pad print. Then, exposure and development are performed to dissolve and remove solder resist at a part whereto light screening ink 4 is applied and to form solder resist of an accurate pattern readily on an irregular surface. Thereby, it is possible to form a solder resist effectively by a simple operation without requiring a complicated and expensive device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a solder resist on a circuit board having irregularities.

[0002]

2. Description of the Related Art Solder resist is applied to parts that do not require soldering so that solder does not adhere to unnecessary parts when soldering mounting parts to land, pads, terminals, etc. of a circuit board. Form. There are various methods for forming the solder resist, but in the case of a circuit board having irregularities, applying a liquid photo solder resist,
A general method is to form a resist by arranging a planar mask in a non-contact state and exposing and developing only a required portion with parallel rays.

[0003]

However, when the circuit board has irregularities on the surface, the exposure apparatus is complicated and expensive with a flat mask, and the handling is not easy. There is also known a method of exposing a spot light source by moving it three-dimensionally using a robot, but the apparatus is also complicated and expensive.

[0004]

SUMMARY OF THE INVENTION The present invention solves these problems and provides a method for easily forming a solder resist on a three-dimensional circuit board, which is to form a circuit on an uneven circuit board. This is a method for forming a solder resist for a circuit board, which comprises applying a liquid photo solder resist on the surface, printing a light-shielding ink in a predetermined pattern, exposing and developing. That is, by forming the light-shielding mask directly on the photo solder resist, it is possible to form the light shielding mask on the solder resist on the uneven surface of the circuit board by a simple operation without using a special exposure device.

The present invention will be described in detail below with reference to the drawings. 1 is a cross-sectional view showing a state in which a liquid photo solder resist is applied on a circuit board in the present invention, FIG. 2 is a cross-sectional view in a state in which light-shielding ink is printed, and FIG. 3 is a cross-sectional view in a state after exposure and development. FIG. 4 is a front view showing a state where the light-shielding ink is printed on the circuit board.

As the circuit board 1 having the irregularities on the circuit forming surface which is the object of the method of the present invention, a three-dimensional board formed by injection molding or the like, or a three-dimensional board formed by pressing or bending a plane circuit board The material of the base material is not particularly limited. The circuit 2 is formed on the circuit forming surface 11 of the circuit board 1 by copper foil etching or the like.

In the method of the present invention, first, as shown in FIG. 1, the liquid photo solder resist 3 is applied to the circuit forming surface 11. As the liquid photo solder resist 3, a liquid photo solder resist 3 which is usually soluble to insoluble when exposed to ultraviolet rays or the like (negative type) is used. However, when the ratio of the portion left as a solder resist is small, the liquid photo solder resist 3 is exposed to soluble. In some cases, the one that becomes (positive type) is used. Examples of the material of the liquid photo solder resist include acrylic type, epoxy acrylate type and urethane acrylate type.

As a method for applying the photo solder resist 3, a spray coating method is preferable because the circuit forming surface 11 has irregularities, and any method such as an air spray method, an airless spray method and a bell spray method can be used. It may be. It is preferable that the coating thickness is usually 5 to 10 μm on the circuit copper foil and 10 to 100 μm on the substrate as a dry coating. After coating, the photo solder resist 3 is dried to the extent that pad printing can be performed on the surface.

Next, as shown in FIG. 2, the light-shielding ink 4 is printed in a predetermined pattern on the dried photo solder resist 3. Although the pad printing is preferable as the printing method, the printing method is not limited to this, and other methods can be used depending on the shape, position, and area of the printing pattern. Here, pad printing means that a predetermined pattern of ink is attached to a pad having a curved surface made of an elastic material such as silicon rubber, and the ink is pressed against an object to deform the pad according to the shape of the object. This is a method of transferring the ink by performing.

The light-shielding ink is printed on the pattern of the portion requiring soldering in the usual case where the photo solder resist is a negative type, and is printed on the shape of the portion not requiring solder in the case of the positive type. To do. The light-shielding ink needs to have a relatively thin thickness to sufficiently block ultraviolet rays and the like, and the ink layer has a thickness of 0.5 to 5 as a dry film.
The thickness is 100 μm, preferably 1 to 30 μm. The light-shielding ink may be one that is soluble or expands in the developer of the solder resist.

Next, the circuit forming surface 11 on which the light-shielding ink is printed in a predetermined pattern is exposed by ultraviolet rays or the like. In the present invention, since the light-shielding pattern is directly printed on the photo solder resist, a special device for exposure is used. Is unnecessary, and it suffices only to ensure that the exposure amount necessary for the inclined portion of the circuit formation surface 11 is secured.

Next, development is carried out. Depending on the type of the photo solder resist, solvent development with trichloroethane or the like, or alkali development with an aqueous solution of sodium carbonate or the like can be performed. As a result, in the negative type, the photo solder resist in the portion where the light-shielding ink is printed is dissolved and removed, and the solder resist 5 is formed in the required portion as shown in FIG. Then, if necessary, post-baking the remaining solder resist 5
It is possible to improve chemical resistance and electrolytic corrosion resistance.

[0013]

Example A circuit board shown in FIG. 4 was prepared using a polyphenylene sulfide resin as a base material. This board has dimensions 12
It has 0 × 132 mm and has recesses 12 in the shape of an inverted truncated pyramid having a 30 mm square and a depth of 3 mm at four places, and the circuit 2 is formed in a region including the inside of the recess 12. A liquid photo solder resist (Solder Rex K1000; manufactured by Toyo Ink Mfg. Co., Ltd.) was applied to the circuit surface by a conveyor type spray coater, and then dried at 75 ° C. for 25 minutes. The coating thickness was such that the dry coating was 40 μm.

A black aqueous light-shielding ink (Aqua King S 92 ink; trade name Toyo Ink Mfg. Co., Ltd.)
(Manufactured by the same company) was printed on a portion shown in black in FIG. 4 by a pad printer. Then, using a parallel light exposure device, an exposure amount of 40
It was exposed to 0 mj / cm ² and developed with a developer (1 wt% sodium carbonate aqueous solution) at 30 ° C. for a development time of 60 seconds. Further, a good solder resist pattern was obtained by post-baking at a temperature of 140 ° C. for 40 minutes.

[0015]

According to the method of the present invention, since the light-shielding mask is printed directly on the photo solder resist, the parallel ray projection exposure using a plane mask or the robot is used.
It is possible to easily and efficiently form a solder resist having an accurate pattern on an uneven surface without requiring complicated operations and devices such as a method using a dimensionally moving light source.

[0016]

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which a liquid photo solder resist is applied on a circuit board in the present invention.

FIG. 2 is a cross-sectional view of a state in which light-shielding ink is printed.

FIG. 3 is a sectional view of a state after exposure and development.

FIG. 4 is a front view showing a state in which light-shielding ink is printed on a circuit board.

[Explanation of symbols]

1 circuit board 11 Circuit formation surface 3 Liquid photo solder resist 4 Light-shielding ink 5 Solder resist

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kunitoshi Kamata             2-5-3 Marunouchi 2-chome, Chiyoda-ku, Tokyo             Ryo Jushi Co., Ltd. (72) Inventor Hiroaki Tsuruta             2-3-13, Kyobashi, Chuo-ku, Tokyo Toyo             Nki Manufacturing Co., Ltd. (72) Inventor Masujiro Sumita             2-3-13, Kyobashi, Chuo-ku, Tokyo Toyo             Nki Manufacturing Co., Ltd.

Claims (3)

[Claims] 1. A circuit forming surface of a circuit board having irregularities,
A method for forming a solder resist for a circuit board, which comprises applying a liquid photo solder resist, printing a light-shielding ink in a predetermined pattern, exposing and developing. 2. The method for forming a solder resist according to claim 1, wherein the light-shielding ink is printed in a predetermined pattern by pad printing. 3. The light-shielding ink is soluble in or expands in a solder resist developing solution.
Alternatively, the method for forming a solder resist as described in 2.