JPH06318778A - Protective coating method for printed wiring boards - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if the circuit conductor has a thickness of 30 μm or more, it is possible to protect the surface circuit by completely adhering the insulating layer to the surface and maintaining the thickness of the insulating layer. To [Structure] A step of sealing the circuit 2 by laminating an insulating sheet 3 having an insulating layer 4 formed on the surface of the photosensitive film 5 on the surface of the conductor circuit 2, and the photosensitive film 5
Is selectively exposed to light and developed to remove a required portion, and the insulating layer 4 in a portion where the photosensitive film 5 is removed is dissolved and removed with an alkaline aqueous solution to remove a land portion in a required portion. 8 and the component mounting portion 7 are exposed, and a step of peeling the film 5 to cure the insulating layer 4 is characterized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a printed wiring board.

[0002]

2. Description of the Related Art Solder resist coatings have stable electrical insulation, excellent heat resistance, impact resistance, moisture resistance, solvent resistance, and high adhesion to surface circuits and base materials. Utilizing its characteristics, it has been conventionally used as a permanent mask for the purpose of preventing solder from adhering to unnecessary parts of a conductor circuit and protecting the surface circuit of a printed wiring board from the external environment. I am.

As a method of applying a solder resist, a resist ink having a creamy viscosity is generally used to apply a required portion of a printed wiring board by a screen printing method.

[0004]

In a general printed wiring board, as shown in the example of the single-sided printed wiring board in FIG. 6, the thickness of the circuit conductor 12 formed on the surface of the substrate 11 is usually 30 μm.
The solder resist 13 on the circuit conductor of this thickness.
In the case of applying, the solder resist 13 adheres to the entire surface of the circuit conductor, and the thickness thereof can be evenly formed.

However, the thickness of the circuit conductor is 35 μm.
As mentioned above, when the thickness becomes 105 μm, 150 μm, etc.,
As shown in FIG. 7, since the end surface of the circuit conductor 12 rises higher than the surface of the substrate 11, it is difficult to form a uniform film thickness by closely contacting the entire surface of the circuit conductor 12.
As a result, the corner portion 14 formed by the end surface of the circuit conductor 12 and the surface of the substrate 11 may have poor adhesion, or the film thickness 15 near the upper end portion of the circuit conductor 12 is likely to be thin, and the circuit conductor 12 at that portion is exposed. There is a risk of

Therefore, the present invention has been made in consideration of the above circumstances, and the circuit conductors 12 formed on the surface of the substrate 1 are three.
Even in the case of a thickness of 0 μm or more, the insulating layer 13 is completely adhered to the entire surface of the circuit conductor 12 while ensuring a sufficient thickness of the insulating layer 13 and exhibits the function as a solder resist, and the surface circuit is externally connected. An object of the present invention is to provide a protective coating method for a printed wiring board that enables protection from the environment.

[0007]

In order to achieve the above object, the present invention provides a printed wiring board having a circuit conductor thicker than usual on one or both sides of a substrate, wherein a photosensitive film is formed on the surface of the circuit conductor. A step of sealing the circuit by laminating an insulating sheet having an insulating layer formed on its surface, a step of selectively removing the photosensitive film in a required portion by exposing and developing the photosensitive film, Of removing the insulating film in the portion where the photosensitive film is removed by dissolving with an alkaline solution to expose the land portion and the component mounting portion in the required portion, and a step of peeling the photosensitive film and curing the insulating layer It is characterized by consisting of.

The insulating sheet is formed by forming an insulating layer made of an insulating resin soluble in an alkaline solution on the surface of the photosensitive film.

[0009]

According to the protective coating method for a printed wiring board of the present invention, the insulating layer has a thickness of 30 μm or more to sufficiently cope with the thickness of the circuit conductor to seal the circuit conductor and to cover the entire surface of the circuit conductor. It has a function of reliably adhering and protecting the surface circuit from the external environment, and also functions as a solder resist.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings in accordance with a manufacturing process of a single-sided printed wiring board. FIG. 1 shows a printed wiring board in which a circuit conductor 2 is formed on one surface of a substrate 1.

As shown in FIG. 2, an insulating sheet having an insulating layer 4 made of an insulating resin soluble in an alkaline aqueous solution formed on the surface of a photosensitive film 5 is heated on a surface of a substrate on which a circuit conductor 2 is formed. And laminate. This allows
The circuit conductor 2 is filled with the insulating layer 4 without any void, and is cast by the insulating layer 4. Further, in order to ensure the adhesion of the insulating resin when the insulating sheet is laminated on the substrate surface, chemical treatment of the printed circuit or adhesion treatment of the adhesive layer can be added.

Next, as shown in FIG. 3, a desired portion of the photosensitive film 5 is exposed and developed to selectively remove the photosensitive film 5 in that portion.

The edge layer 4 of the required portions 7 and 8 exposed by selectively removing the photosensitive film 5 is chemically dissolved and removed by an alkaline aqueous solution as shown in FIG. The component mounting portion 7 is exposed to enable electrical connection.

Finally, as shown in FIG. 5, after the photosensitive film is peeled off, the insulating layer 4 is irradiated with an electron beam to be temporarily cured, and further heat-treated at 160 ° C. for 25 minutes to be fully cured. By doing so, the circuit conductor 2 is completely sealed by the insulating layer 4, and the circuit is protected.

As described above, when the insulating layer is applied in this embodiment, the adhesion of the insulating layer to the surface of the circuit conductor may be poor, or the thickness of the insulating layer may be reduced, resulting in the destruction of the film thickness. There is no risk that the protection of the circuit conductor will be incomplete.

[0016]

According to the present invention, an insulating sheet having an insulating layer formed on the surface of a photosensitive film is laminated on the surface of a substrate of a printed wiring board on which a circuit conductor is formed, so as to have a thickness of 30 μm or more. Even if the circuit conductor is thick, the thickness of the insulating layer sufficiently corresponds to the embedding of the circuit conductor, and the necessary thickness of the insulating layer can be maintained while completely adhering to the circuit conductor. That is, the insulating layer enables the surface circuit of the printed wiring board to be protected from the external environment, and at the same time, the insulating layer also functions as a solder resist.

[Brief description of drawings]

FIG. 1 is a diagram showing steps in a protective coating method for a printed wiring board according to the present invention.

FIG. 2 is a diagram showing steps in a protective coating method for a printed wiring board according to the present invention.

FIG. 3 is a diagram showing steps in a protective coating method for a printed wiring board according to the present invention.

FIG. 4 is a diagram showing steps in a protective coating method for a printed wiring board according to the present invention.

FIG. 5 is a diagram showing steps in a protective coating method for a printed wiring board according to the present invention.

FIG. 6 is a view showing a state in which a solder resist is applied on a conventional printed wiring board.

FIG. 7 is a diagram showing a solder resist application state in a conventional printed wiring board.

[Explanation of symbols]

 1 substrate 2 circuit conductor 3 insulating sheet 4 insulating layer 5 photosensitive film 6 chip 7 component mounting portion 8 land portion

Claims (2)

[Claims] 1. A printed wiring board in which a conductor circuit thicker than usual is formed on one surface or both surfaces of a substrate, by laminating an insulating sheet having an insulating layer formed on the surface of a photosensitive film on the surface of the conductor circuit. The step of sealing the circuit, the step of selectively removing the photosensitive film in the required portion by exposing and developing the photosensitive film, and the insulating layer in the portion where the photosensitive film is removed in an alkaline aqueous solution. Protective coating of a printed wiring board, comprising: a step of dissolving and removing the land part and the component mounting part to the required portion by removing the photosensitive film; and a step of peeling the photosensitive film to cure the insulating layer. Method. 2. The protective coating method for a printed wiring board according to claim 1, wherein the insulating sheet has an insulating layer made of an insulating resin soluble in an alkaline solution formed on the surface of a photosensitive film.