JPH0563342A - Printed wiring board and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a printed wiring board of high reliability wherein solder does not flow via a through hole and high density mounting is possible, and the manufacturing method of said board. CONSTITUTION:In a printed wiring board provided with through holes 2 which are formed in land parts 3 so as to be in a unified body, a solder resist layer composed of photo-setting solder resist 5 is formed. By using the same photo- setting resist 5 as the above solder resist layer, the through holes 2 are closed. When land parts 3 for mounting chip parts 4 and land parts 3 for mounting discrete parts mixedly exist, only the through holes 2 in the land parts 3 for mounting the chip parts 4 are selectively closed by using the photo-setting solder resist 5. The solder resist layer and the photo-setting solder resist 5 for closing the through hole 2 are formed by selective exposure from the surface and the rear of the board 1.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In the field of printed wiring boards, high-density mounting has been promoted along with miniaturization of electronic devices.
So-called double-sided printed wiring boards and the like are widely used.
The double-sided printed wiring board is one in which arbitrary wiring patterns are provided on both sides of the substrate, and in order to establish continuity between the wiring patterns provided on both sides, as shown in FIG. Through holes 101 are provided at the portions so as to penetrate the substrate 102.

By the way, a chip component (chip resistor, chip capacitor, etc.) 104 as a mounting component is mounted on the printed wiring board by soldering to the land portion 103 with cream solder or the like. Then, during this soldering, the melted solder may flow from the land portion 103 into the through hole 101 and unexpectedly contact (conduct) with the wiring pattern on the back surface side, which may interfere with normal operation. ..

Therefore, conventionally, in order to prevent such a problem, the through hole 101 and the land portion 103 are slightly separated from each other and electrically connected to each other through the connection pattern 103a. However, when the through hole 101 and the land portion 103 are arranged apart from each other,
These occupy a large space on the substrate 102,
It is disadvantageous in increasing the density of the printed wiring board.

[0005]

In order to deal with such a problem, printed wiring boards as shown in FIGS. 10 and 11 have also been proposed. That is, in this printed wiring board, as shown in FIG. 9, the through hole 105 is integrally provided so as to be located in the land portion 106, the shape of the land portion 106 is reduced, and as shown in FIG.
A solder resist 107 for closing the through holes 105 is provided on the back surface side of the substrate 102.

With such a structure, when the chip component 104 is soldered to the land portion 106, even if the solder flows into the through hole 105, the solder does not flow out to the back surface side.

However, when the solder resist 107 is provided on the back surface side of the substrate 102 as described above, there is a problem that the chip component cannot be mounted on the back surface side due to the existence of the solder resist 107. As a result, the number of parts that can be mounted is reduced,
After all, the problem that the density of the printed wiring board cannot be increased cannot be solved.

Therefore, the present invention has been proposed in view of such conventional circumstances, and provides a highly reliable printed wiring board which can be mounted at high density and which is free from inadvertent short circuits due to solder flow. It aims at providing, and also aims at providing the manufacturing method. Further, the present invention is applicable not only to chip components but also to components such as discrete components in which leads are inserted into through holes and soldered, and the printed wiring board can be used for various purposes. And a method for manufacturing the same.

[0009]

In order to achieve the above-mentioned object, the present invention provides a printed wiring board having through holes integrally formed in a land portion, which is photocurable depending on the wiring pattern on the surface. A solder resist layer made of a solder resist is formed, and at least a part of the through hole is closed by the same photocurable solder resist as the solder resist layer in the middle part, Furthermore, the through hole integrally provided in the chip component mounting land part is blocked by the photo-curable solder resist in the middle part, and the through hole integrally provided in the discrete component mounting land part is opened. It is a feature.

Further, in the method for manufacturing a printed wiring board according to the present invention, a liquid photo-curable solder resist is applied to one surface of the printed wiring board having through holes integrally formed in the land portion, and the through wiring is applied. The step of filling the hole with the photo-curable solder resist, the step of performing selective exposure from the one surface side to form a solder resist layer on the one surface according to the wiring pattern, and the other of the printed wiring board. From the surface side of the through hole through a mask provided with a light transmitting portion corresponding to the through hole, to cure the photocurable solder resist in the through hole. is there.

[0011]

The lead portion of the chip component as a mounting component to be mounted on the printed wiring board is soldered to the land portion. Here, the through hole penetrating the substrate is closed by a photocurable solder resist formed at the same time as the solder resist layer. Therefore, when soldering the lead portion of the chip component to the land portion of the printed wiring board, even if the solder flows into the through hole, it is blocked by the photocurable solder resist and does not flow out to the back surface side.

Further, if all the through holes are closed by the photo-curable solder resist, there is a possibility that the insertion of the leads of the discrete parts may be hindered when the chip parts and the discrete parts are mixed. On the other hand, in the present invention, by selective exposure, it is possible to close only the through holes provided in the lands where the chip parts are mounted by the photo-curable solder resist and open the others. There is no problem when mounting discrete components.

On the other hand, in the manufacturing method of the present invention, the solder resist layer and the photo-curable solder resist for closing the through holes are formed of exactly the same material and process by one coating step and selective exposure from both sides. .. Therefore, there is almost no need to change the process from the normal solder resist layer forming process, and the number of processes can be slightly increased.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments to which the present invention is applied will be described in detail below with reference to the drawings.

In the printed wiring board of this embodiment, as shown in FIG. 1, a land 3 is provided at an arbitrary position on a substrate 1, and a through hole 2 is integrally formed in the land portion 3. It is a thing. The substrate 1 has a thickness of about 0.8 m, for example.
m is an insulating substrate, and its material is arbitrary as long as it is used for this type of printed wiring board. For example, a glass-epoxy resin laminated board etc. are mentioned.

An arbitrary wiring pattern is provided on the surface of the substrate 1, and a solder resist layer (not shown) made of a photocurable solder resist is formed in accordance with these wiring patterns. ..

The through hole 2 is formed in the substrate 1
Is a through hole having a diameter of about 0.3 mm that penetrates from the front surface (one surface) to the back surface (the other surface) of the substrate 1. The inner wall surface is plated with a conductive metal such as copper. It serves to electrically connect the provided land portion 3 and the land 3 provided on the back surface. A photocurable solder resist 5 is filled and cured in the middle of the through hole 2 at the same time as the formation of the solder resist layer, and the photocurable solder resist 5 is closed. ..

The through hole 2 is integrally provided in the land portion 3 as described above. Therefore, the through hole 2 is not separated from the land portion 3 and is located in the land portion 3. Is located in.

In such a printed wiring board, the land portion 3 has a chip component 4 mounted on the printed wiring board.
Lead portions provided at both end positions of (not shown)
Solder with cream solder. Here, a photocurable solder resist 5 which is an insulating resin composition is filled in the middle of the through hole 2. Therefore, when soldering the lead portion of the chip component 4 to the land portion 3, even if the solder flows into the through hole 2 from the front surface side of the substrate 1, the solder is blocked by the photocurable solder resist 5 and the back surface side Is prevented from flowing out.

Next, a method of manufacturing the printed wiring board having the above structure will be described. In order to manufacture the above-mentioned printed wiring board, first, as shown in FIG. 3, a through hole 2 and a land portion 3 plated with a conductive metal such as copper are patterned on the substrate 1. At this time, the through hole 2 is integrally provided in the land portion 3.

Next, as shown in FIG. 4, a liquid photo-curable solder resist 5 (for example, product name H59K manufactured by Taiyo Ink Co., Ltd.) is applied on the surface side of the substrate 1 by screen printing to a thickness of 15 to 25 μm. To coat. At this time, the photocurable solder resist 5 is also filled in the through holes 2. Then, hot air at 80-90 ° C is applied for 20
The liquid photocurable solder resist 5 is brought into a semi-cured state by spraying for 30 minutes and solvent drying (semi-cure).

Subsequently, as shown in FIG. 5, the photomask 6 having the through holes 6a formed in accordance with the desired resist pattern is provided at a slight interval on the surface side of the substrate 1, that is, the photocurable solder resist 5. A 5 kW UV (ultraviolet) lamp 7 (for example, a metal halide lamp) is arranged on the photomask 6 so as to face it. Then, ultraviolet rays from the UV lamp 7 are 100 to 1000 mJ / cm.
^{About 2 is} irradiated to selectively expose the photo-curable solder resist 5 in the portion corresponding to the portion where the through holes 6a are formed.

As a result, the semi-cured photo-curable solder resist 5 is completely cured at the portion corresponding to the through hole 6a, and as a result, a solder resist layer is formed on the surface of the substrate 1 according to the wiring pattern. Will be formed.

Next, as shown in FIG. 6, a photomask in which a light transmitting portion (through hole) 8a is formed on the back side of the substrate 1 corresponding to the through hole 2 to be closed by the photocurable solder resist 5. 8 is arranged, and further the UV lamp 7 is arranged thereunder. Similarly, the UV lamp 7 irradiates ultraviolet rays to selectively expose the photo-curable solder resist 5 in the through hole 2 for a predetermined period of time to cure it to some extent.

At this time, if the curing proceeds too much, the photo-curable solder resist 5a coated on the through holes 2 may be cured, so that it is necessary to appropriately adjust the intensity of the ultraviolet rays and the exposure time. Is. It is also possible to omit the photomask 8 during the exposure, but this is not preferable from the viewpoint of preventing the show-through phenomenon.

That is, in a thin printed wiring board having a thickness of about 0.8 mm or less, when exposure is performed from the surface opposite to the surface on which the solder resist is formed, the ultraviolet ray that has passed through the substrate 1 causes the show-through phenomenon (copper). (Phenomenon in which a thin film of solder resist is formed on the substrate 1 at a portion where the land is not formed and the solder resist does not need to be formed.). If such a show-through phenomenon occurs, it becomes an obstacle when performing position detection or the like due to the contrast between the copper pattern and the substrate.

After the exposure from the front side of the substrate 1 and the exposure from the back side as described above, the photocurable solder resist 5 is developed. For the development, the substrate 1 is coated with a developer (for example, 0.
5-2% sodium carbonate solution. ), So that the semi-cured portion of the photocurable solder resist 5 (that is, the portion that was not irradiated with ultraviolet light in any of the above exposures) is dissolved and removed, and as shown in FIG. On the surface of the substrate 1, a solder resist layer 5b having a desired pattern corresponding to the wiring pattern and a photocurable solder resist 5c for closing the through holes 2 remain.

Thereafter, the substrate 1 is turned upside down, and similarly, the back side of the substrate 1 is coated with a photo-curable solder resist, and then selective exposure is performed from the back side using a photomask having through holes corresponding to a desired pattern. For example, a printed wiring board having solder resist layers on both surfaces of the substrate 1 can be obtained.

Although the embodiment to which the present invention is applied has been described above, the present invention is not limited to this embodiment. For example, the order of exposure is arbitrary, and it is possible to perform the exposure from the back surface side of the substrate 1 first and the exposure from the front surface side later. Alternatively, it is possible to perform the exposure from the front surface side and the exposure from the back surface side of the substrate 1 simultaneously.

Further, as shown in FIG. 9, land portions 3 and through holes 2 (so-called via holes) on which chip components are mounted and land portions 9 and through holes 10 on which discrete components are mounted are mixed. It is also possible to apply to such a printed wiring board.

In this case, the through hole 2 provided in the land portion 3 on which the chip component is mounted only serves to establish conduction between both surfaces, and no lead or the like is inserted. Therefore, the photo-curable solder resist 5c is filled and cured in the middle part at the same time as the formation of the solder resist layer 5b by the same method as in the previous embodiment. On the other hand, the lead of the discrete component is inserted and soldered into the through hole 10 provided in the land 9 on which the discrete component is mounted. Therefore, the photocurable solder resist 5c is not filled and is in an open state. ..

As described above, in order to selectively fill and harden the photo-curable solder resist 5c only in the through holes 2 provided in the lands 3 on which the chip parts are mounted, refer to FIG. 6 of the previous embodiment. In the step shown, the through hole 2
The exposure may be performed using a photomask provided with through holes corresponding to That is, as shown in FIG. 10, a through hole 11a is provided corresponding to the through hole 2 provided in the land portion 3 where the chip component is mounted, and a through hole provided in the land portion 9 where the discrete component is mounted. A photomask 11 serving as a light-shielding portion is arranged at a portion corresponding to 10, and the photocurable solder resist 5 in the through hole may be selectively exposed from the back surface side of the substrate 1.

The reason why such an embodiment is possible is that the exposure from the back side is selective exposure using a photomask. For example, a through hole 2 provided in a land portion 3 where a chip component is mounted and a through hole 1 provided in a land portion 9 where a discrete component is mounted.
In a printed wiring board in which 0s are mixed, if the photocurable solder resist 5 in the through holes is exposed from the back surface side without using a photomask, not only the through holes 2 but also the through holes 10 are photo-cured. It is blocked by the conductive solder resist 5. If even the through holes 10 are blocked by the photocurable solder resist 5 in this manner, it becomes impossible to insert and solder the leads of the discrete component.

[0034]

As is clear from the above description, in the present invention, since the through hole is closed by the photo-curable solder resist, the lead part of the chip component is soldered to the land part of the printed wiring board. Even when the solder flows into the through hole at this time, it can be blocked by the photocurable solder resist, and an accidental short circuit or the like can be prevented. Moreover, since the land portion on the back surface side is not covered with the photocurable solder resist, the mounting density of chip components can be secured.

Therefore, it is possible to provide a highly reliable printed wiring board which enables high-density mounting.

Further, the photo-curable solder resist for closing the through holes is formed simultaneously with the solder resist layer formed on the surface of the substrate, which is advantageous in manufacturing as well, and moreover, the mounting portion of the chip component is selectively exposed. Since it can be formed only in the through-holes, it can be used not only for chip parts, but also for mixed parts such as discrete parts where leads are inserted into the through-holes and soldered, and various applications are possible. Can be applied to.

Further, according to the manufacturing method of the present invention, the photo-curable solder resist is formed in the through hole by adding only a few steps (selective exposure from the back surface side) to the usual solder resist layer forming step. It is possible, and it is very advantageous in manufacturing.

[Brief description of drawings]

FIG. 1 is a schematic plan view of an essential part showing an embodiment of a printed wiring board to which the present invention is applied.

FIG. 2 is a cross-sectional view taken along the line AA of FIG.

FIG. 3 is a schematic cross-sectional view of a main part showing an example of a method of manufacturing a printed wiring board to which the present invention has been applied in the order of steps and showing a through-hole forming step.

FIG. 4 is a schematic sectional view of an essential part showing a photo-curable solder resist coating step.

FIG. 5 is a schematic cross-sectional view of a main part showing a selective exposure step for forming a solder resist layer.

FIG. 6 is a schematic cross-sectional view of a main part showing a selective exposure step of a photocurable solder resist layer in a through hole.

FIG. 7 is a schematic cross-sectional view of essential parts showing a developing process of a photocurable solder resist layer.

FIG. 8 is a schematic cross-sectional view of an essential part showing another embodiment of the printed wiring board to which the present invention is applied.

FIG. 9 is a schematic cross-sectional view of a main part showing another example of the selective exposure step of the photocurable solder resist layer in the through hole.

FIG. 10 is a schematic plan view of an essential part showing an example of a conventional printed wiring board.

FIG. 11 is a main part schematic plan view showing another example of a conventional printed wiring board.

12 is a sectional view taken along line BB in FIG.

[Explanation of symbols]

 1 ... Substrate 2 ... Through hole 3 ... Land 5 ... Photocurable solder resist

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Yasuda 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (3)

[Claims] 1. A printed wiring board having a through hole integrally formed in a land portion, wherein a solder resist layer made of a photo-curable solder resist is formed in accordance with a wiring pattern on the surface, and at least the through hole. A part of the printed wiring board is blocked in the middle by the same photo-curable solder resist as the solder resist layer. 2. The through hole integrally formed in the chip component mounting land portion is closed by a photo-curable solder resist in the middle part, and the through hole integrally provided in the discrete component mounting land portion is opened. The printed wiring board according to claim 1, wherein: 3. A liquid photo-curable solder resist is applied to one surface of a printed wiring board having a through hole integrally formed in a land portion, and the photo-curable solder resist is filled in the through hole. And a step of performing selective exposure from the one surface side to form a solder resist layer on the one surface in accordance with a wiring pattern, and corresponding to the through hole from the other surface side of the printed wiring board. And a step of performing selective exposure through a mask provided with a light transmitting portion to cure the photocurable solder resist in the through hole.