JPH0422037B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a printed wiring board.

[Conventional technology]

A widely used method is to print a copper clad laminate with an etching resist necessary to form a printed wiring board having a desired pattern, and then to etch the printed wiring board.

Further, after the printed wiring board is formed, after the etching is dissolved and removed, the solder resist layer is formed by leaving solder parts such as lands and performing solder resist printing.

[Problem that the invention seeks to solve]

However, the formation of the solder resist layer is carried out by silk printing, but as printed wiring parts become more precise and denser, the boundary line (surface) between the land part and the solder resist part is reduced to a unit of 1/100 mm. Because they are located close to each other, a slight misalignment or a gap with the copper foil thickness (usually 35μ) on the land in the printed wiring section can cause the solder resist ink to bleed onto the land, which can lead to poor soldering. This is a major factor.

Therefore, conversely, the occurrence of this bleeding phenomenon is also a factor that prevents higher density printed wiring boards.

That is, when a solder resist is formed by a screen printing method, bleeding and blurring of the resist ink are inevitable, and it is very difficult to prevent this from occurring.

To prevent this, it is necessary to periodically clean the screen (wipe the screen). However, the mechanism behind why bleeding occurs will be explained below with reference to FIGS. 3 to 9.

First, in the screen printing method, a gauze (screen) 21 woven from Tetron or stainless steel thread is stretched over a mouth-shaped frame called a plate frame 20 with high tension to form a flat surface.

By selectively covering the gauze 21 with a mask called an emulsion 24, the ink 22
Distinguish between where you want to print and where you do not want to print.

In fact, selective formation is achieved by first coating the entire surface with an emulsion and developing it with a film.

Next, add ink (as viscous as mayonnaise) 2
2 is placed on the plate, and the printed wiring board 10 placed underneath is rubbed out using a urethane resin squeegee 23 to remove the ink 22 on the plate.
Apply ink 22 on top (FIG. 3).

At this time, press the squeegee 23 with a very large printing pressure.
runs on the plate, the gauze 21 is also printed with a slight distortion in the running direction of the squeegee 23, and this error appears as a printing misalignment, but naturally the positional relationship between the plate and the printed wiring board 10 below It is included in the calculation.

However, as mentioned above, the gauze 21 itself is formed by knitting with threads such as Tetoron, and immediately before the squeegee 23 runs, a force acts on the contraction side, and immediately after the squeegee 23 runs, a force acts on the elongation side.

Furthermore, when printing the solder resist after pattern formation, as shown in FIG. 4, there are already unevenness due to the 35 μm thick copper foil, and this, combined with the expansion and contraction of the gauze 21 mentioned earlier, causes the gauze 21 when printing near land 4 to be uneven. As the squeegee 23 is stroked for tens or hundreds of sheets, although the amount is extremely small in reality, the ink 22 on the plate will move downwards from the edge of the emulsion (on the printed circuit board). side) (Figure 5).

Looking at the printed wiring board 10 after printing, as shown in FIG. 6, smearing gradually appears, and as the printing progresses further, smearing appears on the land 4 as shown in FIG.
It becomes NG.

It is also possible that the printing alignment between the land 4 and the solder resist layer 6 is misaligned 26, and when the land edge comes into contact with the resist edge (Fig. 8), due to the difference in level between the emulsion of the plate and the copper foil, This makes bleeding 25 more likely to occur (Figure 9).

As described above, in the screen printing method, the occurrence of bleed 25 is inevitable due to its principle, and even now, the reality is that many defects due to this phenomenon occur, and this is a future issue.

Therefore, the present invention has been made with attention to these problems, and it is an object of the present invention to propose a method for manufacturing printed wiring boards that can prevent the occurrence of bleeding phenomenon due to solder resist printing and eliminate soldering defects. It is something to do.

[Means for solving problems]

In the present invention, a solder resist layer is formed prior to etching a copper-clad laminate in manufacturing a printed wiring section.

[Effect]

By applying solder resist printing to the copper-clad laminate before etching, which leaves the soldered parts such as lands in the printed wiring part, the solder resist can be printed in a state that prevents the bleeding phenomenon caused by the gap in the copper foil thickness. Resist printing can be performed.

〔Example〕

Hereinafter, the method for manufacturing a printed wiring board of the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view of a printed wiring board manufactured by the manufacturing method of the present invention, and FIGS. 2 a to 2e are explanatory diagrams showing the method of manufacturing the printed wiring board.

In FIG. 1, 1 is an insulating plate, 2 and 3 are printed wiring parts, 4 is a land part in the printed wiring parts, and 5 is a part in the formation of the printed wiring parts 2 and 3.
The solder resist layer applied at the time of etching resist printing, and 6, represent the solder resist layer applied after etching.

Now, a method for manufacturing printed wiring board 10 having the following configuration will be explained with reference to FIG. 2. First, as shown in FIG. 2a, solder resist printing 13 is performed as etching resist printing necessary for forming printed wiring portions on the surface of the copper foil 12 of the copper clad laminate 11.

However, when printing this solder resist printing 13, printing is performed so that soldered parts such as land parts in the printed wiring part remain.

Thereafter, as shown in FIG. 2b, the soldering parts such as lands left in the solder resist printing 13 are covered with an alkali-soluble ink 14. Note that the soldering portions such as lands can also be covered with the alkali-soluble ink 14 by silk printing.

Therefore, after completing the etching resist printing necessary for the printed wiring board by the solder resist printing 13 and coating with the alkali-soluble ink 14, the printed wiring is etched by etching the copper foil 12 of the copper clad laminate 11. 2, 3 and a land 4 (see FIG. 2c).

Further, after the etching is completed, the alkali-soluble ink 14 on the land portion 4 is peeled off (see Fig. 2d).
As shown in FIG. 2e, the printed wiring board 10 shown in FIG. 1 can be formed by applying solder resist printing 15 to the printed wiring parts 2 and 3.

〔Effect of the invention〕

According to the present invention, since the solder resist for a printed wiring board is applied directly to the copper-clad laminate before etching, it is possible to improve the bleeding phenomenon without the gap caused by the thickness of the copper foil when applying it after etching, and to improve the printing process. It is possible to provide a highly accurate printed wiring board that is compatible with higher density wiring boards.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the method for manufacturing a printed wiring board of the present invention, FIGS.
The figure is an explanatory diagram of a conventional method. 2, 3...Printed wiring part, 4...Land part, 5,
6...Solder resist layer.

Claims (1)

[Claims] 1. In a method for manufacturing a printed wiring board in which etching resist is printed on a copper-clad laminate and then etched, soldering parts such as lands in the wiring pattern remain during the etching resist printing. At least perform solder resist printing and cover the soldered parts such as the land portions with alkali-soluble ink or other solvent-soluble ink, and then perform etching.
Furthermore, the alkali-soluble ink or other solvent-soluble ink that coats the soldered parts such as the land parts is peeled off after etching and leaves the soldered parts such as the lands in the printed wiring part, A method for manufacturing a printed wiring board, which comprises performing solder resist printing after etching.