JPH06120667A - Multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To obtain a multilayer printed wiring board having reliable through holes in which the generation of crack or blowhole is retarded even when the printed board is produced through desmear step. CONSTITUTION:The multilayer printed wiring board 12 comprises inner and outer layer patterns 5a, 10. A plated through hole T connects the inner and outer layer patterns 5a, 10 electrically. The plated through hole T penetrates a nonconductive layer, i.e., an inner layer permanent resist 4. A land L is provided around the through hole T. The land L is provided with desmear liquid resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer printed wiring board.

[0002]

2. Description of the Related Art Conventionally, there has been known a multilayer printed wiring board in which an inner layer pattern and an outer layer pattern are formed with an insulating layer interposed therebetween. Usually, these patterns are connected by a plated through hole or the like penetrating the wiring board.

However, when the holes for plating through holes are formed in the insulating substrate, smear may occur on the inner wall surface of the insulating substrate due to frictional heat between the drill and the resin.
Since such smear causes a decrease in connection reliability of the plated through hole, it is generally removed by desmearing before plating. A so-called Desmear solution (an oxidizing solution such as an aqueous solution of permanganate or an aqueous solution of chromic acid) is used for such treatment.

[0004]

By the way, in recent years, a so-called full additive method has been proposed in which the conductor pattern of the inner layer is formed only by electroless plating. This method is shown in FIGS. 4 (a) and 4 (b). 1 shows an example of the multilayer printed wiring board 20 according to.

In the full additive method, first, the insulating substrate 2
2 has an adhesive layer 23 and a permanent resist 24 formed thereon,
Inner layer patterns 25a and 25b are formed on the non-formed portion of the permanent resist 24 by electroless plating. Figure 4
As shown in (a), the inner layer pattern 25a later becomes a conductive layer for the plated through hole T. On the other hand, the inner layer pattern 25b becomes a non-conductive layer for the plated through hole T. A prepreg 26 is provided on the front and back surfaces of the inner layer plate 21.
Are laminated, and then this multilayer printed wiring board 20
Has a hole 2 which will be a plated through hole T in a later step.
8 is transparently installed.

However, the permanent resist 24 containing acrylic resin is generally inferior in desmear resistance to the insulating substrate 22 and the epoxy resin forming the prepreg 26. Therefore, if the desmear process is performed here, there arises a problem that the permanent resist 24 swells or cracks. Therefore, even if the plating through-hole T is formed, the plating solution easily penetrates into the cracked portion.

[0007] Then, such a multilayer printed wiring board 2
When 0 encounters a heat cycle, a crack is generated in the plated through hole T portion, and the reliability of the plated through hole T deteriorates. Further, when the inner wall of the plated through hole T is largely torn and becomes a blow hole, the reliability is further deteriorated.

The present invention has been made in view of the above circumstances, and an object thereof is to prevent cracks and blow holes even when manufactured through desmear treatment and to improve the reliability of plated through holes. Another object is to provide an excellent multilayer printed wiring board.

[0009]

In order to solve the above problems, in the present invention, at least one of the inner layers is patterned by a full additive method, and the plating resist used when forming the inner layer pattern is left. In a multilayer printed wiring board that is stacked as it is and has a plated through hole that connects an inner layer pattern and an outer layer pattern, in this plated through hole that penetrates the inner layer formed by the full additive method, A land made of a substance having a higher desmear liquid resistance than the permanent resist is provided around the non-conductive plated through hole.

Further, it is desirable to form the land at the same time when the inner layer pattern is formed by the full additive method.

[0011]

With this structure, the land resistant to the desmear liquid prevents the desmear liquid from entering the permanent resist side.
The desmear solution does not come into direct contact with the permanent resist during processing. Therefore, even when the multilayer printed wiring board is manufactured through the desmear treatment, the permanent resist does not deteriorate and cracks and blowholes hardly occur.

The reason why the land is formed at the same time when the inner layer pattern is formed by the full additive method is as follows.
It is possible to simplify the process and shorten the manufacturing time,
This is because it is suitable.

[0013]

EXAMPLE A multilayer printed wiring board (four-layer board) according to the present invention, in which both the inner layer and the outer layer are manufactured by the full additive method
Materialized in 12. One example thereof will be described in detail with reference to FIGS.

In this embodiment, first, an inner layer plate 1 having inner layer patterns 5a, 5b and 5c was manufactured according to a conventional method (see FIG. 1). That is, after the adhesive layer 3 is formed on both front and back surfaces of the insulating substrate 2 made of glass epoxy, a permanent resist 4 as a plating resist is formed at a predetermined position on the adhesive layer 3.
a and 4b were formed. The former 4a is a permanent resist of a conductive layer for the plated through hole T formed later.
On the other hand, the latter 4b is a plated through hole T formed later.
The non-conductive layer is a permanent resist.

At this time, in the latter 4b, a permanent resist is formed on a portion for forming a circular inner layer pattern 5c to be the land L of the inner layer in the periphery of the penetrating portion of the plated through hole T later. Not not. Around the inner layer pattern 5c, other patterns 5 in the same layer are formed.
circular permanent resist 4b to avoid connection with
Are arranged. As described above, the layer serving as the non-conducting layer for each plated through hole T includes the inner layer pattern 5c.
The permanent resists 4a and 4b are formed so that the circles have a circular shape. The permanent resists 4a and 4b are made of acrylic modified epoxy.
The dissolved amount of a and 4b in permanganic acid is larger than that of epoxy.

Then, copper was deposited by chemical copper plating to form inner layer patterns 5a, 5b and 5c on the portions where the permanent resists 4a and 4b were not formed. 5
a is a pattern of the inner layer of the conductive layer with respect to the plated through hole T formed later. On the other hand, 5b is a pattern of the inner layer of the non-conductive layer with respect to the plated through hole T formed later. Then, the central portion of the inner layer pattern 5c is finally removed at the time of punching, and the remaining peripheral portion of the inner layer pattern 5c becomes the inner layer land L. The land L of the inner layer is copper deposited by chemical copper plating and has desmear liquid resistance. The land L of the inner layer is formed at the same time when the other inner layer patterns 5a and 5b are formed.

Subsequently, the obtained inner layer plate 1 is subjected to blackening treatment with a strong alkaline solution or the like to form inner layer patterns 5a, 5b, 5
The copper surface of c was oxidized. Two 0.1 mm thick prepregs 6 were laminated on each of the front and back surfaces of the inner layer board 1. At that time, the molding pressure was set to 20 kgf / cm ² .

Further, an adhesive was applied to the outer surface of the prepreg 6 and cured, and the surface was roughened with an aqueous solution of chromic acid to form an adhesive layer 7 having a thickness of 25 μm. Then, as shown in FIG. 2, holes 8 to be plated through holes T were formed in the inner layer plate 1 through a drill. The inner diameter D2 of the hole 8 was 0.35 mm, and the number of holes 8 per inner layer plate 2 was about 10,000. Since the land L is formed in the non-connection layer of the inner layer of each plated through hole T, the permanent resists 4a and 4b are formed in the plated through hole T.
Is not exposed on the inner wall surface of the.

Here, desmear treatment was performed using permanganate to remove the smear formed on the inner wall surface of the hole 8. Further, after forming the outer layer permanent resist 9 on the adhesive layer 7, chemical copper plating is performed again to deposit copper on the inner wall surface of the hole 8 and the outer surface of the adhesive layer 7 where the permanent resist 9 is not formed. It was By this copper plating, the plated through hole T and the outer layer pattern 10 were formed. At this time, the land 11 of the outer layer is simultaneously formed in the opening portion of the plated through hole T. Through the above steps, the multilayer printed wiring board 12 in which the inner layer patterns 5a and 5b and the outer layer pattern 10 were connected by the plated through holes T was manufactured (see FIG. 3 (a)).

The insulating substrate 2 has a thickness of 1.0 mm, and the adhesive layer 3 has a thickness of 25 μm. Further, the inner and outer layers of the permanent resists 4a, 4b, 9 both have a thickness of 40.
μm, and the inner and outer layer patterns 5a, 5b, 10
Both have a thickness of 35 μm.

Then, as shown in FIG. 3B, in this embodiment, the finished diameter D1 of the plated through hole T is about 0.3 mm. The outer diameter D3 of the land L of the inner layer is 0.7 mm, and the outer diameter (clearance diameter) D4 of the permanent resist 4 of the inner layer is 1.7 mm. The difference between D4 and D3 is designed to be about 1.0 mm in order to secure the insulation gap.

On the other hand, another multilayer printed wiring board was manufactured basically according to the full additive method similar to the above-mentioned embodiment. However, unlike the wiring board 12 of the above-mentioned embodiment, the land of the inner layer is not formed in the permanent resist of the inner layer of this wiring board. Therefore, when a hole to be a plated through hole is opened, the inner layer permanent resist is exposed on the inner wall surface side of the hole. Such a multilayer printed wiring board was used as a comparative example with respect to the embodiment (see FIGS. 4 (a) and 4 (b) above).

In order to compare the characteristics of the multilayer printed wiring boards of Examples and Comparative Examples, a heat cycle test was conducted according to the method of JIS C5024. In this test, each wiring board was first immersed in hot oil at 260 ° C. for 10 seconds and then left at room temperature. Next, make each wiring board 1 at 25 ℃
After holding for 5 seconds, they were soaked in hot oil again. After performing this cycle 30 times, the plated through holes of each wiring board were investigated.

As a result of investigating 100 plated through holes each, no particular abnormality was found in the relevant portions in the examples. As described above, in the example, it was possible to secure high reliability in the plated through hole T. This is because the land L of the inner layer prevents the desmear liquid from entering the inner layer of the permanent resist 4 side, so that the alteration of the permanent resist 4 is avoided.

On the other hand, in the comparative example, about 80% of the plated through holes had abnormalities such as cracks and blow holes. The present invention is not limited to the above-mentioned embodiment, and the number of laminated layers of the multilayer printed wiring board 12 is 6 for example.
It is possible to change the configuration, such as using eight layers or eight layers. Further, it is of course possible to change the clearance diameter and the like to values different from those in the above embodiment.

Further, instead of the above-mentioned embodiment in which the chemical copper plating layer is selected as the substance having the desmear liquid resistance, a metal different from that may be selected. Moreover, since the land L of the inner layer is not intended for conduction, it is not always necessary to select a metal as the substance. Therefore, it is possible to use a resin such as glass epoxy which is resistant to the desmear liquid.

[0027]

As described above in detail, according to the multilayer printed wiring board of the present invention, even if it is manufactured through desmear treatment,
Since no cracks or blow holes are generated, the plated through holes can be highly reliable, which is an excellent effect.

[Brief description of drawings]

FIG. 1 is a partial front cross-sectional view showing a process of manufacturing a multilayer printed wiring board according to an example.

FIG. 2 is a partial front cross-sectional view showing a process of manufacturing a multilayer printed wiring board according to an example.

FIG. 3A is a partial front sectional view of the multilayer printed wiring board of the embodiment, and FIG. 3B is a sectional view taken along the line AA.

FIG. 4A is a partial front sectional view of a conventional type multilayer printed wiring board, and FIG. 4B is a sectional view taken along line BB thereof.

[Explanation of symbols]

5a, 5b, 5c inner layer pattern, 10 outer layer pattern, 12 multilayer printed wiring board, T 2 plated through hole, 4 inner layer permanent resist, L 2 inner layer land.

Claims (2)

[Claims] 1. A pattern of at least one of the inner layers is formed by a full additive method, the layers are laminated with the plating resist used at the time of forming the inner layer pattern left, and the inner layer pattern and the outer layer pattern are connected. In a multilayer printed wiring board having a plated through hole formed therein, among the plated through holes penetrating the inner layer formed by the full-additive method, around the plated through hole that is non-conductive with this layer, more desmear-resistant than the permanent resist is formed. A multi-layer printed wiring board having a land made of a highly liquid substance. 2. The multilayer printed wiring board according to claim 1, wherein the land is formed at the same time when the pattern of the inner layer is formed by a full additive method.