JPS639996A - Method of forming solder resist layer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION 1-21 The present invention relates to a method for forming a solder resist layer for preventing solder from adhering to unnecessary portions on a conductive pattern of a printed circuit board.

An electronic circuit device generally has electronic components mounted on a printed circuit board, and the electronic components are electrically connected using conductive patterns to form a circuit.

FIG. 3 shows an example of a printed circuit board. In the figure, 1 is an insulating substrate such as resin, 2 is a conductive pattern formed by etching copper foil laminated on the insulating substrate 1, and 3 is a conductive pattern 2.
A through hole penetrating the substrate 1 is shown in the upper main part.

Since the conductive pattern 2 of this printed circuit board is exposed, when it is soldered using a solder bath, the solder adheres to the entire surface of the conductive pattern 2, resulting in a large amount of solder being used. Generally, a solder resist layer 4 is formed as shown in FIG. 4 so that only necessary portions of the conductive pattern 2 are exposed.

Heat-resistant resin is generally used for this solder resist, and it is formed by screen printing using a mask with apertures in only desired areas of liquid solder resist material.

[1, (', -c! By the way, the resist layer 4 has conventionally been formed all at once using one mask.

However, when the inside of the conductive pattern 2 is narrowed and the distance between the conductive patterns 2 is narrowed in order to increase the mounting density of electronic components, the following problems occur.

That is, the conductive pattern formed along the advancing direction of the squeegee during screen printing, for example, the conductive pattern 2a shown in FIG.
A good solder resist layer 4 is formed both above and between the conductive patterns 2at2a, but the thickness of the resist layer is smaller than that of the conductive pattern (conductive pattern 2b in FIG. 3) that is perpendicular to the advancing direction of the squeegee. If the thickness of the resist layer is approximately the same as or thinner than the conductive pattern 2b, the thickness of the resist layer becomes thinner at the cross-sectional edge portion of the conductive pattern 2b, as shown in FIG.
In extreme cases, there is a problem that the conductive pattern 2b is exposed and does not function as a solder resist.

. The present invention has been proposed in view of the above-mentioned problems, and is based on the fact that the conductive patterns are drawn in substantially the same direction on the conductive pattern surface of the substrate.
The above problem is solved by dividing the paper into sections and screen printing along the drawing direction for each section.

Embodiments of the present invention will now be described with reference to FIG. 1 by applying them to the printed circuit board shown in FIG.

First, masks 5 and 6 for screen printing shown in FIG. 1 are prepared.

In actual practice, a plurality of printed circuit boards 1 are connected to improve workability, and a portion to be held in a carrier during mounting or soldering of electronic components is connected to the outer periphery of the printed circuit board 1. The second masks 5 and 6 are also larger than the above-mentioned substrates, and their peripheral edges are stretched over a frame (not shown), but for the sake of simplicity, one substrate 1 and its corresponding mask portion are shown in the figure. It shows.

These masks 5 and 6 are made by coating a photosensitive resin on a screen such as a silk mesh, exposing the desired area to light, and closing the eyes of the mensch by leaving the resin 7 on the area where you do not want to form a solder resist layer. 1 mask 5 is printed circuit board 1
The mesh in the shaded area a in the figure is opened corresponding to the area A where the conductive pattern 2a along the X direction of the printed circuit board 1 is formed, and the second mask 6 forms the conductive pattern 2b along the Y direction of the printed circuit board 1. The mesh in the shaded area in the figure is opened corresponding to the area B that has been removed.

Using such first and second masks 5 and 6, first, the first mask 5 is placed on the substrate 1, and although not shown, a solder resist is supplied onto the mask 5 and the solder resist is applied in the X direction with a squeegee. Then, a solder resist layer is formed in area A on the substrate 1.

Next, using the second mask 6, the solder resist is extended in the Y direction to form a solder resist layer in region B on the substrate 1.

In addition, in the illustrated example, in order to simplify the explanation, the conductive pattern 2
a + 2 b is formed only in the orthogonal direction, but in the case of a complicated shape, either the first or second mask 5 or 6 can be used to create a squeegee resist l in the direction of movement of the squeegee.
In this way, the pattern shape of the region C1C" of the first and second masks 5, 6 can be determined based on the pattern shape of the region C (not shown in FIG. 1). However, as shown in FIG. 2, the solder resist layer 4 can be coated with a uniform thickness.

Thereafter, the substrate 1 is perforated and cut into predetermined dimensions to produce a printed circuit board.

The above explanation was about a single-sided printed circuit board, but
Needless to say, it can also be applied to double-sided printed circuit boards.

According to the present invention, the thickness of the solder resist can be made uniform regardless of the direction in which the conductive pattern is drawn, and in extreme cases, the thickness of the solder resist can be made uniform at the edges of the cross-section of the conductive pattern. This eliminates the problem of conductive patterns being exposed due to edge overlapping, and eliminates the problem of solder bridging between conductive patterns.

Therefore, the distance between the conductive patterns can be made smaller, and the solder cyst can be made thinner than the thickness of the conductive patterns.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a printed circuit board and a mask for explaining the present invention, FIG. 2 is a sectional view of a printed circuit board embodying the present invention, FIG. 3 is a perspective view of the printed circuit board, and FIGS. 4 to 6
The figure shows a perspective view of a printed circuit board on which a solder resist layer is formed. 1... Substrate, 2a12b... Conductive pattern, 4...
・Solder resist layer. l. Patent applicant: Kansai NEC Corporation (Fig. 1, Fig. 2)

Claims (1)

[Claims] When forming a solder resist layer by screen printing on a printed circuit board on which a conductive pattern is formed on the substrate, the drawing direction of the conductive pattern is divided and screen printing is performed along the drawing direction for each section. A method for forming a solder resist layer.