JPH04365394A - Manufacture of printed wiring board - Google Patents

Abstract

PURPOSE:To obtain a printed wiring board for enabling securing, unification, and yield in manufacturing process of a film thickness of a solder resist of a printed wiring board with a high-density conductor pattern which is used for various kinds of electronic equipment to be improved extremely and reliability of the electronic equipment to be also improved. CONSTITUTION:In a curtain coater application method of a liquid solder resist ink to a printed-wiring board, coating is performed by increasing ink viscosity according to the number of coatings to the same surface of a printed-wiring board 1, a low-viscosity ink is coated on a first ink-coating portion 15a and a high-viscosity ink is coated on a second ink-coating portion 15b. A low- viscosity liquid ink is coated without any gap on a side surface of a conductor pattern 3 between the high-density conductor patterns 3 and an insulation substrate 2 and a high-viscosity and low fluidity liquid ink can be coated on the second ink-coating portion 15b, thus forming a solder resist with a uniform film thickness on the high-density conductor pattern 3, a corner portion, a side surface of the conductor pattern 3, or the insulation substrate 2.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing printed wiring boards used in various electronic devices.

0002

2. Description of the Related Art In recent years, printed wiring boards, which are widely used in various electronic devices, are becoming more densely wired due to the miniaturization and multifunctionalization of electronic devices. For this reason, the conventional screen printing method is being replaced by a photographic method with excellent resolution for forming conductor patterns and solder resists.

However, compared to the screen printing method, the photographic method has many steps and is low in productivity, raising manufacturing costs.As one means of solving this problem, spray coating methods, static Electrocoating method,
Application methods of liquid solder resist ink for photographic methods, such as roll coater application method and curtain coater application method, are being studied, and among them, the roll coater application method and curtain coater application method, which have high coating efficiency, are attracting attention.

[0004] Below, a method of forming a solder resist using a conventional curtain coater coating method for a printed wiring board will be explained.

FIG. 2 shows a conventional manufacturing process for forming a solder resist using a photographic method for printed wiring boards. FIG. 2(a) shows a conventional printed wiring board manufacturing apparatus. FIGS. 2(b) and 2(c) show the manufacturing process of a conventional printed wiring board. Figure 2(a),(b),
In (c), 1 is a printed wiring board, 2 is an insulating substrate,
3 is a conductor pattern, 4 is liquid solder resist ink, 5 is
6 is a liquid solder resist ink application section, and 6 is a conveyor.

[0006] Formation of solder resist on the printed wiring board constructed as above will be explained below.

First, an etching resist is formed on a copper-clad laminate (not shown) cut to a predetermined size using a photographic method, and then etching is performed using a solution such as cupric chloride to form a conductor pattern. 3 is formed, and the etching resist is peeled off.

Next, as shown in FIG. 2(a), the printed wiring board 1 with the conductor pattern 3 formed on the insulating substrate 2 is conveyed by the conveyor 6 of the curtain coater device, and is coated with liquid solder resist ink. In section 5, liquid solder resist 4 falls vertically onto the surface of printed wiring board 1 in the form of a film, and is applied as printed wiring board 1 advances.

[0009] Thereafter, the mask film is dried to the touch with hot air, etc., the mask film is adhered, and after exposure to ultraviolet rays, the unexposed areas are developed with a specified developer and hardened again with hot air, etc., to form the solder resist on the printed wiring board. Form.

0010

[Problems to be Solved by the Invention] However, as the density of the conductor patterns 3 increases, as shown in FIG. 4 is not completely applied, and the solder resist is formed with air bubbles 7, etc., causing problems such as poor insulation between the conductor patterns 3 and blistering and peeling when mounting and soldering electronic components.

[0011] For this reason, a method is used in which liquid solder resist ink is adjusted to a low viscosity and coated on the side surface of the conductor pattern 3 or on the insulating substrate 2. However, when the liquid solder resist ink is adjusted to a low viscosity, Although it is easy to apply liquid solder resist on the side surfaces of the conductor patterns 3 between the conductor patterns 3 and on the insulating substrate 2, as shown in FIG. 2(c), after applying the liquid solder resist ink 4, the conductor patterns The liquid solder resist ink 4 on the insulating substrate 2
The liquid solder resist ink 4 gradually flows upward, and the film thickness of the liquid solder resist ink 4 at the upper corner of the conductor pattern 3 becomes extremely thin, several micrometers or less. This causes problems such as poor adhesion and peeling of solder resist, which reduces the process yield of printed wiring board manufacturing.

[0012] Furthermore, when electronic components are soldered and mounted in the manufacturing process of electronic devices, the solder causes short circuits between conductor patterns and deterioration of insulation properties due to adhesion of solder balls, causing problems in the functions of electronic devices. There was a problem.

[0013] The present invention solves the above-mentioned conventional problems, and improves the consistency and uniformity of the solder resist film thickness of printed wiring boards having high-density conductor patterns, and significantly improves the yield of the manufacturing process. It is an object of the present invention to provide a method for manufacturing a printed wiring board that also improves reliability.

[0014]

[Means for Solving the Problems] In order to achieve this object, the method for manufacturing a printed wiring board of the present invention involves dropping liquid solder resist ink in the form of a film, and holding the printed wiring board in a horizontal position while passing through the falling film. When the liquid solder resist ink is applied to the printed wiring board by passing through the solder resist ink, the viscosity of the liquid solder resist ink is increased according to the number of times of application to the same side of the printed wiring board.

[0015]

[Operation] With this configuration, a low viscosity liquid solder resist ink is applied in the first application section, and a high viscosity liquid solder resist ink is applied in the second application section in the subsequent process, thereby forming a printed wiring board. Low viscosity liquid solder resist ink is applied without gaps on the conductor pattern side surfaces between high-density conductor patterns and on the insulating substrate. It becomes possible to apply a liquid solder resist ink with low fluidity, and it is possible to form a solder resist with a uniform thickness on the high-density conductor pattern, the corner portion, the side surface of the conductor pattern, and the insulating substrate.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1(a) shows a printed wiring board manufacturing apparatus according to an embodiment of the present invention. Figure 1 (
b) and FIG. 1(c) show the manufacturing process of a printed wiring board according to an embodiment of the present invention, and the same parts as those shown in FIG. 2 are given the same numbers.

In FIG. 1(a), 1 is a printed wiring board, 2 is an insulating substrate, 3 is a conductor pattern, 14a is a low viscosity liquid solder resist ink, 14b is a high viscosity solder resist ink, and 15a is a first solder resist ink. An ink application section, 15b is a second ink application section, 16a is a first conveyor, 1
6b is a second conveyor.

A method of forming a solder resist on a printed wiring board constructed as described above will be explained with reference to FIG. First, a printed wiring board 1 on which a conductor pattern 3 is formed on an insulating substrate 2 using a method similar to the conventional method is transported by a transport conveyor 16a of a curtain coater device, and is coated in a first ink application section 15a for about 70 to 90 m. passes at a speed of /min. At this time, the viscosity is approximately 0.10 to 0.25 Pa・s
The alkaline-developable liquid solder resist ink 14a, which has been adjusted to A viscous liquid solder resist 14a is applied.

Next, this printed wiring board 1 is transported by a transport conveyor 16b and passed through the second ink application section 15b at a speed of about 60 to 120 m/min depending on the desired coating thickness. At this time, the viscosity is approximately 0.25 to 0.40 Pa・
The liquid solder resist ink 14b adjusted to s is similarly falling in the form of a film, and as it passes through the printed wiring board 1, the high viscosity liquid solder resist ink 14b is applied onto the printed wiring board, and as shown in FIG. ), a printed wiring board is obtained in which the liquid solder resist ink is applied relatively uniformly on the conductor pattern 3 and the corners of the conductor pattern 3. After that, dry to the touch in a hot air circulation tank or the like at an ambient temperature of 60 to 80 degrees Celsius and a processing time of about 15 to 30 minutes to make the mask film adhere, and then use ultraviolet rays with a wavelength suitable for curing the liquid solder resist ink. Exposure is performed at an exposure amount of approximately 500 to 700 mJ/cm2, and the unexposed areas are developed and removed using a developer containing sodium carbonate as a main component. Final curing is performed for about 30 to 60 minutes, and the formation of the solder resist on the printed wiring board 1 is completed.

In the conventional manufacturing method, the thickness of the formed solder resist is several micrometers, especially at the corners of the conductor pattern.
However, in the printed wiring board according to the embodiment of the present invention, the thickness was more than 10 μm, and on the conductor pattern it was 25 μm.
It was possible to ensure a film thickness of at least m, and all problems with conventional solder resist forming methods were solved.

[0021] In the embodiments of the present invention, the number of repeated coatings on the same side of the printed wiring board was set to two, but since high reliability is required for applications such as aerospace and medical equipment, the film thickness of the solder resist is For printed wiring boards, etc., which have strict regulations, a third ink application section and a fourth ink application section may be provided as necessary, so that the liquid solder resist ink 14a of the second application section and the third application section The liquid solder resist ink 14b may be coated using a liquid solder resist ink having a higher viscosity than the liquid solder resist ink 14b. Further, although the liquid solder resist inks 14a and 14b were of an alkali-developed type, the liquid solder resist inks 14a and 14b may be of a solvent-developed type, and the printed wiring board 11 was a single-sided printed wiring board, but the printed wiring board 11 Needless to say, a double-sided printed wiring board or a multilayer printed wiring board may also be used.

[0022]

As described above, the present invention provides a curtain coater application method for liquid solder resist ink, in which the viscosity of the liquid solder resist ink is increased in accordance with the number of times of application to the same surface of a printed wiring board. By ensuring the thickness and uniformity of the solder resist film on printed wiring boards with high-density conductor patterns, it is possible to realize printed wiring boards that significantly increase the yield of the manufacturing process and improve the reliability of electronic devices. be. Furthermore, by adjusting the ink application area, the viscosity of the liquid solder resist ink, and the speed of the conveyor, it is possible to control the solder resist film thickness as desired, making it possible to control the solder resist film thickness as desired for applications such as space and medical applications where solder resist film thickness regulations are strict. This makes it possible to configure a production line that can handle everything from equipment to general consumer equipment, and to stably produce high-quality printed wiring boards.

[Brief explanation of drawings]

FIG. 1 (a) is a schematic diagram showing an apparatus for applying liquid solder resist ink to a printed wiring board according to an embodiment of the present invention; FIG. The cross-sectional view (c) showing the applied state is a cross-sectional view showing the state where high viscosity liquid solder resist ink is also applied at the second ink application part.

[Fig. 2] (a) is a schematic diagram showing a conventional coating device for liquid solder resist ink for printed wiring boards; (b) is a cross-sectional view showing a state in which low-viscosity liquid solder resist ink is applied; Cross-sectional view showing the state in which high viscosity liquid solder resist ink is applied

[Explanation of symbols]

1 Printed wiring board 2 Insulating substrate 3 Conductor pattern 14a Low viscosity liquid solder resist ink 14b
High viscosity liquid solder resist ink 15a First ink application section 15b Second ink application section 16a First conveyor 16b Second conveyor

Claims (1)

[Claims] [Claim 1] When applying the liquid solder resist ink to a printed wiring board by dropping the liquid solder resist ink in the form of a film and passing the printed wiring board horizontally through the falling film, the viscosity of the liquid solder resist ink is determined. A method for manufacturing a printed wiring board, comprising increasing the number of times of application on the same side of the printed wiring board.