JPH04186792A - Printed wiring board and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent the excessive adhesion in soldering or bridge inferiority by flow up by selectively leaving hole stopping ink inside a T/H exclusively used for continuity. CONSTITUTION:An insulating board 1 lined with copper is plated with a conductor 2, and a through hole is made, and then the through hole is filled up with hardening hole stopping ink 3, and then it is hardened. Next, a circuit pattern is printed with an etching resist 4, and then etching treatment by cupric chloride solution or the like to get a conductor circuit 2b. Furthermore, only the etching resist 4 is selectively exfoliated and removed by aqueous sodium hydroxide, and then photosensitive SR ink 5 is applied on the insulating substrate 1 by screen coating method, and then it is dried. After this, using a mask film, ultraviolet rays are applied selectively to the T/H 2a part exclusively used for continuity, etc., and further with an organic solvent, the photosensitive SR ink 5 at the unexposed part and the thermosetting hole stopping ink 3 are dissolved and removed to get a printed wiring board.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a printed wiring board and a method of manufacturing the same, and more particularly to a printed wiring board having through holes dedicated to conduction and a method of manufacturing the same.

[Conventional technology]

In recent years, as electronic devices have become lighter, thinner, shorter, and more sophisticated, the wiring circuits of printed wiring boards (hereinafter referred to as PWBs) are becoming more densely packed. This has been addressed by narrowing the width of the wiring circuit and through holes for conduction only (hereinafter referred to as T/'H for conduction only).

Among these, the conduction-only T/H is an effective means for eliminating channel necks in high-density wiring and dramatically increasing wiring capacity, and has been adopted in various PWBs.

In general, conduction-only T/Hs are often arranged closely together in order to secure wiring area, and when soldering mounted components using flow soldering method, etc., the solder is
), (b), there are many troubles where adjacent conduction-only T/H2a comrades are short-circuited.

Figure 2 (a) shows a case where excessive solder adheres to the soldering surface, and Figure 2 (b) shows a case in which T/H2 is used only for conduction.
This is a case where the solder that flowed up a caused a short circuit.

Therefore, in order to control solder adhesion to the conduction-only T/H and prevent short-circuit defects caused by solder, the conduction-only T/H
It is necessary to block the solder resist (hereinafter referred to as SR), but conventionally, a method of forming a tenting-like SR film on the conductive T/H using a photosensitive dry film was often used. .

That is, through-holes are formed in the copper-clad insulating substrate as shown in FIG. 3(a) by a known panel plating method consisting of drilling holes in the copper-clad insulating substrate and copper plating. Furthermore, as shown in FIG. 3(b), thermosetting hole-filling ink 3 is filled into the inside of the through hole and cured, and a predetermined circuit is formed on both the front and back surfaces of the insulating substrate 1 with etching resist 4 as shown in FIG. 3(c). After printing the pattern, a conductor circuit 2b is formed by etching as shown in FIG. 3(d).

Thereafter, as shown in FIG. 3(e), the etching resist 4 and the thermosetting hole-filling ink 3 are simultaneously peeled off and removed.

Furthermore, as shown in FIG. 3(f), a photosensitive dry film 8 is pasted on the entire surface of the insulating substrate, exposed and baked using a mask film having a predetermined pattern, and then the unexposed areas are exposed to light through a development process. The dry film 8 is dissolved and removed to obtain a printed wiring board having a tenting-like SR as shown in FIG. 3(g).

[Problem to be solved by the invention]

However, the above method using a photosensitive dry film has the following problems.

In other words, when attaching a photosensitive dry film to the surface of an insulating substrate, it is difficult to fill in the irregularities on the surface of the insulating substrate due to the conductor circuit, and air traps are likely to occur, which requires countermeasures such as special processing such as lamination under vacuum. be.

Additionally, in order to completely cover the conductor circuit, the thickness of the dry film material must be greater than the thickness of the conductor, and generally a material with a thickness of 70 to 100 μm is required, making the material cost extremely high. Moreover, since the SR is significantly thicker than the pad in the vicinity of the surface mounting pad, gas is trapped on the pad surface during flow soldering, impairing soldering performance.

An object of the present invention is to provide a printed wiring board that is inexpensive in material cost, has good soldering properties, and is highly reliable, and a method for manufacturing the same.

[Means to solve the problem]

The present invention provides a printed wiring having a conduction-only through hole used for connecting a front wiring circuit and a back wiring circuit and connecting at least one of the front wiring circuit and the back wiring circuit to an inner layer wiring circuit. In the board, a filler ink is filled in a predetermined through hole exclusively for conduction, and a predetermined portion of a surface layer and a back layer containing the filler ink inside the through hole exclusively for conduction is coated with a solder resist. There is.

The method for manufacturing a printed wiring board of the present invention includes the steps of: drilling a hole in a copper-clad insulating substrate; forming a through hole by plating the inner wall of the hole and the surface of the insulating substrate; and applying thermosetting hole-filling ink to the through hole. a step of filling the inside of the hole and curing it; a step of printing a predetermined circuit pattern on both the front and back sides of the insulating substrate with an etching resist; and a step of peeling off only the etching resist after obtaining a conductive circuit by etching treatment; a step of applying photosensitive solder resist ink to the entire surface of the insulating substrate; a step of exposing and baking using a mask film having a predetermined pattern;
The method includes a step of selectively removing the photosensitive solder resist ink in unexposed areas and the thermosetting hole-filling ink in unexposed areas by a development process.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1(a) to 1(g) are cross-sectional views showing the steps of a manufacturing method according to an embodiment of the present invention.

First, as shown in Fig. 1(a), a conductor 2 is plated on a copper-clad insulating substrate 1 by a known panel plating method to form a through hole, and then a viscosity of 200 to 500 voids is formed as shown in Fig. 1(b). The through holes are filled with thermosetting hole-filling ink 3 and cured at 80 to 150°C for 20 to 50 minutes.

Next, a predetermined circuit pattern is printed using the etching resist 4 as shown in FIG. 1(c), and then etching is performed using a cupric chloride solution or the like to obtain a conductive circuit 2b as shown in FIG. 1(d).

Furthermore, as shown in Figure 1(e), 1 to 3% at 45 to 65°C.
After selectively removing only the etching resist 4 with an aqueous sodium hydroxide solution, photosensitive SR ink 5 is coated and dried on both the front and back surfaces of the insulating substrate 1 by a screen coating method, as shown in FIG. 1(f).

After that, using a mask film with a predetermined pattern, ultraviolet rays of 200 to 1,000 millijoules per square centimeter are selectively irradiated to the T/H2a part dedicated for conduction, and then the non-conductive layer is treated with an organic solvent such as 1.1.1 trichloroethane. The photosensitive SR ink 5 and thermosetting hole-filling ink 3 in the exposed area are dissolved and removed to obtain the printed wiring board shown in FIG. 1(g).

In the printed wiring board shown in FIG. 1(g), the T/H2a for continuity and the conductor circuit 2b that does not require soldering are covered with 5R5a, and the T/H2-c for component mounting and the conductor circuit necessary for soldering are covered with 5R5a. A state where part 2b is exposed is shown.

In FIG. 1(f), as a method for applying the photosensitive SR ink, in addition to the screen coating method, a spray coating method, a curtain coater method, and a roller coating method can be used.

〔Effect of the invention〕

As is clear from the above, according to the present invention, the conduction-only T/
Since the hole-filling ink selectively remains inside the H, the T/H can be easily closed without the need for tenting with expensive photosensitive dry film, and bridges due to excessive adhesion or flow-up during soldering can be avoided. This has the effect of preventing defects.

Furthermore, since a liquid ink can be used as the photosensitive SR, the SR film thickness near the surface mounting pads does not become excessively thick, and highly reliable soldering can be achieved for the pads as well.

[Brief explanation of the drawing]

Figures 1 (a) to (g) are cross-sectional views showing the manufacturing method according to an embodiment of the present invention in the order of steps, and Figures 2 (a) and (b) show that the conduction-only T/H is sometimes soldered. A sectional view showing an example of a solder bridge, and FIGS. 3(a) to 3(g) are sectional views shown in order of steps to explain a conventional manufacturing method.

Claims (2)

[Claims] 1. In a printed wiring board having through-holes exclusively for conduction used for connecting a front wiring circuit and a back wiring circuit and connecting at least one of the front wiring circuit and the back wiring circuit to an inner layer wiring circuit. Filling ink is filled into the inside of a predetermined conduction-only through hole, and further, predetermined portions of the surface layer and the back layer containing the hole-filling ink inside the conduction-only through hole are coated with a solder resist. printed wiring board. 2. a step of drilling a hole in a copper-clad insulating substrate; a step of forming a through hole by plating the inner wall of the hole and a surface of the insulating substrate; a step of filling and curing the inside of the through hole with a thermosetting hole-filling ink; A process of printing a predetermined circuit pattern with etching resist on both the front and back surfaces of the insulating substrate, a process of peeling off only the etching resist after obtaining a conductor circuit by etching, and a process of applying photosensitive solder resist ink to the entire surface of the insulating substrate. a step of exposing and baking using a mask film having a predetermined pattern; and a step of selectively applying the photosensitive solder resist ink in unexposed areas and the thermosetting hole-filling ink in unexposed areas through a development process. A method for producing a printed wiring board, the method comprising: removing the printed wiring board.