JPH0529754A - Solder resist mask formation method of printed wiring board - Google Patents

Abstract

PURPOSE:To reduce the number of factors which are responsible to quality degradation and perform rational follow-up by treating a developing process or a curing process once. CONSTITUTION:The surface of a wiring board is cleaned by a surface cleaning process in (a). A first solder resist film 3 is formed by a coating process based on a curtain coater system in (b). A second solder resist film 4 is formed all over the surface by the coating process in (c). The exposure based on a light source equivalent to the second solder resist film 4 is carried out by a second exposure process with a first photo mask 75 in (d). Non-exposed portions of the first and second solder resist films are molten and eliminated by a developing process in (f). This construction makes it possible to reduce factors which are responsible to quality degradation by turning the flow of product handing in one direction.

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 mask of a printed wiring board which is a substrate of an electronic device for mounting and wiring electronic parts constituting an electronic circuit.

[0002]

2. Description of the Related Art Conventionally, a solder resist mask formed on a printed wiring board having a circuit pattern is used to prevent a solder bridge between adjacent circuits when soldering by a flow method or to use an extra copper which does not need to be soldered. The purpose was to protect the solder from the foil and to protect the circuit copper foil from the environment in which the electronic equipment was used.

However, as the surface mounting technology has become popular, the soldering technology has become mainstream from the flow method to the reflow method, which makes it easy to control the amount of solder. Although the reflow method is a method that allows more precise control of the amount of solder compared to the flow method, it is still difficult to solder due to the pitch of the target surface mount component pad width, and therefore the solder resist mask is unnecessary. In addition to the conventional purpose, there is a demand for an embankment to prevent solder from flowing out to the adjacent pads.

However, in order not to impair the cleanability,
Trapezoidal cross section rather than just thickening the dark resist film
A structure such as is desirable. Conventional solder register
As shown in FIG. 3, the strike mask forming method is performed in the previous step.
Surface cleaning of printed wiring boards with road patterns
Process and material for forming solder resist mask
Photosensitive solder resist coating process
Touch-drying process, which cures to a non-greasy
Ruder resist mask pattern is formed by photographic method.
Exposure process for solder mask pattern
Phenomenon process to remove unnecessary ink, solder resist
A curing process that completely cures the ink that forms the turn
After doing, stack more solder resist ink
In order to realize a shape with a trapezoidal cross section,
Change the strike mask pattern and
Oh, another process up to the process is performed serially 2
It required one processing step.

[0005]

As described above, in the conventional method of forming a solder resist mask, there is a redundancy that a series of processing steps is required twice serially, and the steps must be reversed. There was a problem that process management was difficult due to quality problems due to the troublesome handling and the timing of the second processing step input, and as a result delivery time management could not be rationalized.

[0006]

A method of forming a solder resist mask for a printed wiring board according to the present invention comprises first and second solder resist masks having different photosensitivity after cleaning the surface of the wiring board on which a circuit pattern is formed. A step of sequentially forming a solder resist film, a step of sequentially exposing the second and first solder resist films using first and second masks having different patterns, and a step of exposing the exposed second
And a step of developing the first solder resist film to remove the unexposed portion.

[0007]

The present invention will be described below with reference to the drawings. 1 (a) to 1 (f) and FIG. 2 are a sectional view and a process diagram of a wiring board for explaining an embodiment of the present invention.

First, as shown in FIG. 1 (a), the surface of the wiring board on which the circuit pattern 2 after the patterning of the copper foil is formed is cleaned in a surface cleaning process. Next in FIG.
As shown in (b), in order to apply a solder resist ink having a thickness of 20 to 40 μm, which is almost the same as the height of the copper foil of the printed wiring board, a curtain coater method is used to apply
A first solder resist film 3 having photosensitivity having a sensitivity peak at ˜250 nm is formed by a coating process. Then, drying is performed to the extent that the surface is not sticky in the finger touch drying step.

Next, as shown in FIG. 1C, a second solder resist film 4 having a photosensitivity having a sensitivity peak at 300 to 400 nm is formed on the entire surface by a spray method to a thickness of 10 to 20 μm. It is formed in the coating process. Next, the second solder resist film 4 is processed in a touch-drying process. Next, as shown in FIG. 1D, the first photomask 5 is used to perform exposure in a first exposure step using a light source that is aligned with the second solder resist film 4.

Next, as shown in FIG. 1 (e), a second photomask 6 is used to perform exposure in a second exposure step using a light source matched to the first solder resist film 3. Next, as shown in FIG. 1 (f), unexposed portions of the first and second solder resist films are simultaneously dissolved and removed by a solvent such as 1-1-1 trichloroethane in a developing process, and then exposed in a curing process. The portions 3A and 4A are completely cured and fixed, and the solder resist mask 7 having a two-layer structure is formed.

The first solder resist film 3 may be formed by a screen coater method. Further, the first solder resist film 3 may be exposed first.

[0012]

As described above, according to the present invention, the formation of the solder resist mask, which has conventionally required a series of two processes, is integrated into a process having the same function, and the same developing process is performed. Since the curing process and the curing process can be performed once, the redundant process of the conventional technique can be omitted. Therefore, the handling of the product becomes a one-way flow, and it is possible to reduce the factors that deteriorate the quality. It also has the effect of simplifying process management and rationalizing delivery date management.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a wiring board showing the order of steps for explaining an embodiment of the present invention.

FIG. 2 is a process drawing for explaining an embodiment of the present invention.

FIG. 3 is a process drawing for explaining a conventional example.

[Explanation of symbols]

 1 wiring substrate 2 circuit pattern 3 first solder resist film 4 second solder resist film 5 first photomask 6 second photomask 7 solder resist mask

Claims (1)

Claim: What is claimed is: 1. A step of cleaning a surface of a wiring board on which a circuit pattern is formed and then sequentially forming first and second solder resist films having different photosensitivity, and a step of forming a different pattern. Steps of sequentially exposing the second and first solder resist films by using the first and second masks, and developing the exposed second and first solder resist films to remove unexposed portions A method for forming a solder resist mask for a printed wiring board, comprising: