JPH0661629A - Printed wiring board - Google Patents

Abstract

PURPOSE:To prevent solder bridge from being formed across adjacent land parts without causing increase of manhours or cost. CONSTITUTION:Land parts 2 for mounting components 5 are formed on a substrate 1. Solder resist 3 for blocking adhesion of solder is applied on the land pattern. Openings 4 are made through the solder resist 3 at positions corresponding with the land parts 2 thus exposing the land parts 2. Edge of the opening 4 is lapped, with width of at least 50mum, over the peripheral edge of the land part 2 at three sides thereof except one side where the component 5 is stuck. Consequently, the solder resist 3 rises partially along the periphery of the land part 2.

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 on which surface mount components are mounted, and more particularly to a printed wiring board for preventing the occurrence of solder bridges between adjacent land portions.

[0002]

2. Description of the Related Art In a printed wiring board, after a predetermined pattern is formed by a copper foil on a substrate, a surface of the printed wiring board is coated with a solder resist for preventing adhesion of solder on portions other than lands. 3 and 4 are enlarged views of a main part of a conventional printed wiring board. A plurality of lands 2 and line parts (not shown) are formed on the surface of a substrate 1 made of glass epoxy by, for example, a subtractive method. And the like are formed. Then, the solder resist 3 is coated thereon with an appropriate thickness.
The thickness of the solder resist 3 is usually smaller than the thickness of the copper foil forming the land 2. The solder resist 3 is coated by a so-called photographic method excluding the land portion 2. The land portion 2 to which the solder is to be attached has a rectangular opening 4 as shown in the figure. The land portion 2 is exposed. In particular, the opening 4 is generally set to be slightly larger than the intended size of the land 2 so that the land 2 is not covered even if there is some positional deviation or size error. .
It should be noted that, finally, various surface mount components 5 as illustrated by imaginary lines are mounted on these lands 2.

[0003]

A large number of the land portions 2 as described above are provided corresponding to various surface mount components 5, but at the locations where the land portions 2 are provided adjacent to each other, A so-called solder bridge in which the solder attached to the land portion 2 is short-circuited is likely to occur. This is the solder resist 3
If the thickness is smaller than the thickness of the land portion 2, it is particularly likely to occur.

In order to prevent such a solder bridge, so-called silk 6, which is printed by overlaying an insulating resin in a line shape, may be provided between the lands 2 as shown in the figure. However, since the silk 6 is formed separately from the solder resist 3, the process is complicated and the cost is increased.

[0005]

SUMMARY OF THE INVENTION Therefore, according to the present invention, in a printed wiring board in which a solder resist is coated on the surface of a substrate leaving a land portion and a surface mount component is mounted on the land portion, a component attaching direction is provided. It is characterized in that the solder resist opening edge is overlapped with a part of the peripheral edge of the land portion except for.

[0006]

The solder resist is coated with a constant thickness, but it is partially raised by overlapping the opening edge with the peripheral edge of the land. That is, there is a raised portion along the periphery of the land portion, which prevents solder bridges.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 and FIG. 2 are enlarged views of a main portion of a printed wiring board according to the present invention. A plurality of land portions 2 and lines are formed on the surface of a substrate 1 made of glass epoxy by a subtractive method. A portion (not shown) is formed. The wall thickness of the land portion 2 and the like is about 50 μm. Then, on this pattern, solder resist 3
Is coated with a thickness of about 30 μm. This solder resist 3 is formed with a rectangular opening 4 corresponding to each land 2 by a so-called photographic method, whereby each land 2 is exposed so that solder can be attached thereto.

Here, the three sides 4a, 4b of the opening 4,
The opening edge of 4c is at least 50μ on the periphery of the land portion 2.
Overlaid with a width of about m. The remaining one side 4d of the surface mount component 5 in the component attaching direction is opened with some allowance so as not to overlap the land portion 2. In order to overlap the land portion 2 and the solder resist 3 as described above, the opening portion 4 of the solder resist 3 may be set small, but conversely, the size of the land portion 2 may be slightly increased. .

By overlapping the peripheral edge of the land portion 2 and the opening edge of the solder resist 3 in this manner, the solder resist 3 is partially raised along the peripheral edge of the land portion 2. Therefore, the occurrence of solder bridges between the adjacent land portions 2 is prevented. That is, it is possible to prevent the solder bridge by using the solder resist 3 without requiring a separate process such as the conventional silk printing.

In the above embodiment, the solder resist 3 is raised on the three sides 4a, 4b, 4c excluding the component mounting direction. The land portion 2 and the solder resist 3 may be overlapped only in the direction where

[0012]

As is apparent from the above description, the printed wiring board according to the present invention prevents the occurrence of solder bridges between the adjacent land portions by the solder resist which is partially raised. The parts can be arranged close together. In particular, there is no need for a separate process like the conventional double resist, and the solder bridge can be easily prevented by simply changing the shape of the opening of the solder resist.
The man-hours and costs can be reduced.

[Brief description of drawings]

FIG. 1 is an enlarged plan view showing an essential part of an embodiment of a printed wiring board according to the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is an enlarged plan view showing a main part of a conventional printed wiring board.

FIG. 4 is a cross-sectional view taken along the line BB of FIG.

[Explanation of symbols]

 2 ... Land part 3 ... Solder resist 4 ... Opening part 5 ... Surface mount component

Claims (1)

[Claims] 1. In a printed wiring board in which a solder resist is coated on the surface of a substrate leaving a land portion and surface-mounted components are mounted on the land portion, a part of the peripheral edge of the land portion excluding the component mounting direction, A printed wiring board, characterized in that the edges of the solder resist are overlapped.