JPH04277695A - Printed wiring board - Google Patents

Abstract

PURPOSE:To provide a printed wiring board which dissolves the halation of a photosensitive solder resist and sharply improves the yield rate in the manufacturing process and also improve the reliability on the electric apparatus as well, concerning the printed wiring board used for various kinds of electric apparatus. CONSTITUTION:An inner layer pattern 6 of the same area as the nonformation part or more is formed inside the insulating layer 1 right below the part where photosensitive resist 3 being made on the body of a printed wiring board is not formed, whereby even if the ultraviolet rays entering from the solder resist formation part, that is, the exposure part at the time of exposure of photosensitive solder resist ink 3a is reflected at the bottom of the insulating layer 1, since the inner layer pattern 6 of the same area as the solder resist pattern nonformation part exists right below the solder resist nonformation part, the ultraviolet rays never reach the solder resist nonformation part, and the solder resist ink at the solder resist nonformation part can be prevented from photopolymerizing.

Description

[Detailed description of the invention]

0001

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

0002

[Prior Art] In recent years, printed wiring boards have been widely used in various electronic devices, and as electronic devices become smaller and more multifunctional, they are required to have higher wiring densities and higher reliability. It's coming.

[0003] A conventional printed wiring board will be explained below.

FIG. 2 shows a conventional manufacturing process for forming a solder resist for a printed wiring board. In FIG. 2, 1 is an insulating layer, 2 is a conductive pattern, 3 is a photosensitive solder resist, 3a is a photosensitive solder resist ink, 4 is a mask film, 5 is an insulating substrate for an inner layer, and 6 is an inner layer pattern.

[0005] The formation of the solder resist for the printed wiring board constructed as described above will be explained below. First, the prepreg or bonding sheet that will become the insulating layer 1 and the copper foil that will become the base of the outer layer conductor pattern 2 are set in predetermined positions on the inner layer insulating substrate 5 on which the inner layer pattern 6 is formed, and then After heating and pressurizing, and cooling, a copper-clad laminate (not shown) having an inner layer pattern is obtained. The resulting copper-clad laminate is subjected to through-hole drilling and copper plating, and then an etching resist is formed using a screen printing method or a photographic method, and then etching is performed using a solution such as cupric chloride. , a conductor pattern 2 is formed, and the etching resist is peeled off. Next, as shown in FIG. 2(a), a photosensitive solder resist ink 3a is applied to the printed wiring board on which the conductor pattern 2 is formed, and the ink is dried to the touch using hot air or the like. Next, as shown in FIG. 2(b), the mask film 4 is brought into close contact with the surface of the photosensitive solder resist ink 3a which has been dried to the touch, and after exposure to ultraviolet rays,
As shown in (c), the unexposed areas are developed with a predetermined developer, and after drying with hot air or the like, a photosensitive solder resist 3 is formed.

[0006]

[Problems to be Solved by the Invention] In order to form a high-resolution solder resist that corresponds to higher wiring densities, the conventional screen printing method has been replaced with a method for forming solder resists for multilayer printed wiring boards that have many high-density wirings. Photographic methods such as those described above are often used.

However, in the conventional manufacturing method, when exposing the photosensitive solder resist ink 3a that is dry to the touch, the ultraviolet light incident through the mask film 4 passes through the photosensitive solder resist ink 3a and is insulated. The light enters from the surface of layer 1, is reflected by the opposite surface of insulating layer 1, reaches areas that should not be exposed, and polymerizes the photosensitive solder resist ink in areas where solder resist is not formed (hereinafter referred to as halation). After development, ink remained in areas where solder resist was not formed. This phenomenon is particularly noticeable in the case of solder resist inks with high exposure sensitivity and in printed wiring boards with thin insulating layers where the attenuation of reflected light is relatively low, resulting in a significant deterioration of yield in the printed wiring board manufacturing process. Furthermore, when external forces or vibrations are applied in the manufacturing process or market of electronic devices, the solder resist in the halation area may peel off, impeding solderability or impairing the functionality of precision parts. had.

The present invention solves the above-mentioned conventional problems, and provides printed wiring that eliminates halation in solder resist of printed wiring boards, significantly improves the yield of the manufacturing process, and improves the reliability of electronic equipment. The purpose is to provide a board.

[0009]

[Means for Solving the Problems] In order to achieve this object, the present invention has a photosensitive solder resist formed on a printed wiring board main body, and an insulating substrate directly under a portion where the photosensitive solder resist is not formed. It has a structure in which a conductor pattern having an area equal to or larger than that of the non-forming portion is formed therein.

0010

[Function] With this configuration, even if the ultraviolet light incident from the solder resist forming part, that is, the exposed part, is reflected by the bottom surface of the insulating substrate during photosensitive solder resist ink exposure, the solder resist will not be left directly under the solder resist non-forming part. Since there is an inner layer pattern with an area equal to or greater than the area where the solder resist is formed, ultraviolet light does not reach the areas where the solder resist is not formed, and the solder resist ink in the areas where the solder resist is not formed can be prevented from being photopolymerized. .

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Figure 1(a), Figure 1(b), Figure 1(c)
) is a sectional view showing the manufacturing process of a printed wiring board in an embodiment of the present invention. Note that in FIG. 1, the same parts as in FIG. 2 are given the same numbers, and their explanations will be omitted. First, a mask film having a diameter larger on one side by about 0.2 mm than the diameter of the solder resist-free portion of a mask film for solder resist exposure is prepared, and a mask film for forming an inner layer pattern based on this mask film is prepared. Generally, the inner layer pattern has a large pattern width because it is used as a power supply circuit or a ground circuit, and the copper foil of the inner layer pattern remains directly under most of the portions where no solder resist is formed. Therefore, this mask film for forming an inner layer pattern can be designed relatively easily. Etching resist is formed on the copper-clad laminate for inner layer by screen printing or photography based on the mask film for inner layer formation, inner layer pattern is formed by the same method as before, and prepared prepreg and copper foil are formed. After heating and pressurizing, it is cooled to obtain a copper-clad laminate, which is subjected to through-hole drilling, copper plating, etc., and a conductor pattern 2 is formed in the same manner as in the conventional method to form a printed wiring board main body.

In FIG. 1(a), an alkali-developable photosensitive solder resist ink 3a is applied to a printed wiring board on which a conductor pattern has been formed using a method such as screen printing, a roll coater or a curtain coater, and hot air circulation is applied. Dry to the touch in a furnace or the like at a temperature of 60 to 80°C for about 15 to 30 minutes.

Next, as shown in FIG. 1(b), the mask film 4 is attached tightly, and the amount of ultraviolet light is about 500 to 700 mJ.
/cm2. Then, as shown in FIG. 1(c), the unexposed areas are developed and removed using a developer containing sodium carbonate as a main component. Thereafter, the formed solder resist 3 is dried using hot air or the like, if necessary. Thereafter, final curing is performed in a hot air circulation oven or the like at a temperature of 130 to 160° C. for about 30 to 60 minutes. After development, we confirmed that there was no residual ink in areas where solder resist was not formed, and as a result of sequentially changing the diameter of the inner layer pattern,
It was also confirmed that it is effective to make the diameter 0.1 mm or more larger than the diameter of the solder resist-free portion.

In the embodiments of the present invention, the photosensitive solder resist ink 3a was of an alkali-developable type, but
The photosensitive solder resist ink 3a may be of a solvent-developable type, and the same effect can be obtained even with a design in which a ring-shaped inner layer pattern with a width is formed along the outer periphery of the non-solder resist area. Needless to say.

[0015]

As described above, the present invention has a structure in which a conductor pattern having an area equal to or larger than the non-forming part is formed in the insulating substrate directly under the non-forming part of the photosensitive solder resist formed on the printed wiring board. By doing so, it is possible to create a printed wiring board that eliminates halation in the solder resist of printed wiring boards, significantly improves the yield of the manufacturing process, and improves the reliability of electronic devices. In a multilayer printed wiring board with a thickness of 1.0 mm or less, simultaneous exposure of the front and back sides of the photosensitive solder resist was impossible due to the generation of halation, but this structure also has the effect of making it possible to expose the front and back sides simultaneously. It is something.

[Brief explanation of the drawing]

FIG. 1 (a) is a cross-sectional view showing the process of applying and drying the photosensitive solder resist ink on a printed wiring board according to an embodiment of the present invention; FIG. Cross-sectional view (c) is a cross-sectional view showing the steps of developing, curing, and forming the photosensitive solder resist.

[Figure 2] (a) is a cross-sectional view showing the process of applying and drying to the touch a photosensitive solder resist ink for a conventional printed wiring board (b).
) is a cross-sectional view showing the exposure process of the photosensitive solder resist ink; (c) is a cross-sectional view showing the developing, curing, and forming process of the photosensitive solder resist.

[Explanation of symbols]

1 Insulating layer 2 Conductor pattern 3a Photosensitive solder resist ink 3 Photosensitive solder resist 4 Mask film 5 Insulating substrate for inner layer 6 Inner layer pattern

Claims (1)

[Claims] 1. A photosensitive solder resist formed on a printed wiring board main body, and an area of the insulating substrate immediately below the non-formed part of the photosensitive solder resist that is the same as or larger than the non-formed part. A printed wiring board with a conductor pattern formed on it.