JPH0677662A - Printed circuit board - Google Patents

Abstract

PURPOSE:To apply plating perfectly onto the inner face of a blind hole by facilitating removal of residual bubbles from the hole and intrusion of pretreatment liquid and plating liquid into the blind hole in the plating step on the inner face of the blind hole made in a multilayer printed circuit board. CONSTITUTION:A blind hole 3 for connecting an outer layer circuit pattern with an inner layer circuit pattern at an appropriate depth is made in a multilayer printed circuit 1. The blind hole 3 is made through laser boring method or the like to have elliptical cross section. Outer layer circuit pattern, i.e., a line 4 and a land 2, is formed by applying a copper plating layer onto the outer layer copper foil and then performing baking and etching using photosensitive resist and plating on the inner face of the hole 3 is also performed simultaneously. Since the blind hole 3 has elliptical cross section, residual bubbles can be removed easily during plating process resulting in perfect plating in the hole.

Description

Detailed Description of the Invention

[0001]

[Industrial application] The structure of printed circuit boards, especially
The present invention relates to a multilayer printed circuit board having blind holes for electrically connecting an outer conductor layer and an inner conductor layer.

[0002]

2. Description of the Related Art In general, a multilayer printed circuit board is constructed by using through-holes, through-holes called interstitial via holes, etc. for connecting conductors of the respective layers. Further, recently, a printed circuit board configured by adopting a blind via hole having a blind hole structure has been used.

FIG. 3 is a plan view showing the structure of a conventional printed circuit board, and FIG. 4 is a sectional view of the conventional printed circuit board. 3 and 4, 1 is a printed circuit board, 2 is a land, 3 is a blind hole, 4 is a line, 5 is an inner layer circuit pattern, 6 is a copper foil, and 7 is a copper plating layer.

Normally, the printed circuit board 1 is constructed so as to connect the layers by using through-holes.
The prior art shown in FIG. 4 is configured by using a dead end hole 3 called a bride via hole. The printed circuit board 1 has a blind hole 3 to connect the outer layer circuit pattern of the printed circuit board 1 and the inner layer circuit pattern 5 to each other. And the inner surface of the dead-end hole 3 is plated, and thereafter, the circuit pattern of the outer layer such as the land 2 and the line 4 is formed by the baking and etching technique to which the printing technique is applied. Since the dead-end hole 3 is usually formed by using a drill or the like, its cross-sectional shape is circular as shown in FIG.

The blind hole 3 called a bridging via hole is often adopted to realize a high-density printed circuit board. Therefore, the shape of the blind hole 3 is required to be as small as possible. Is. However, as the diameter of the holes becomes smaller, the drilling technology and the plating technology inside the holes become difficult.

For the small-diameter hole drilling, a laser drilling technique has been developed in recent years, which makes it possible to make a small-diameter blind hole.

Further, it is necessary to apply plating to the inner surface of the bridging via hole thus drilled in order to electrically connect the wiring layers.

Generally, the plating process of the printed circuit board is performed by a wet method (liquid), and therefore, when the plating is applied to the inner surface of the dead end hole having a reduced diameter, it is necessary to remove the air bubbles remaining in the hole. If the removal of the air bubbles is insufficient, the plating pretreatment liquid and the plating liquid cannot penetrate into the holes, resulting in plating voids and incomplete plating.

For this reason, normally, during the plating pretreatment, the plating treatment, or the like, the printed circuit board to be processed is subjected to vibration, impact, or the like to expel air bubbles in the holes.

As a conventional technique relating to this type of printed circuit board, for example, the technique described in Japanese Patent Publication No. 4-3676 is known.

[0011]

Since the printed circuit board according to the prior art described above has a blind hole having a circular cross section with a reduced diameter, vibration and impact are applied to the printed circuit board during pre-plating treatment and during plating treatment. There is also a problem that it is difficult to remove air bubbles inside, and thus it is difficult to completely plate the inner wall of the dead end hole.

The object of the present invention is to solve the above-mentioned problems of the prior art, to have a blind hole having a reduced diameter, and to allow the pretreatment liquid for plating and the plating liquid to easily enter into the hole having the reduced diameter.
It is an object of the present invention to provide a printed circuit board that can be completely plated without plating voids.

[0013]

According to the present invention, the above object is achieved by making a cross-sectional shape of a blind via hole having a blind hole structure an elliptical shape.

[0014]

In general, when the inner surface of a hole having a dead-end hole structure is plated, whether or not bubbles existing inside can be easily removed depends on the shape of the dead-end hole, that is, the depth and the hole. It is related to the diameter. The removal of bubbles
It is easier as the depth of the blind hole is smaller and the hole diameter is larger.

It is considered that this is influenced by the size of the bubbles, the easiness of the bubbles to come into contact with the surface inside the hole of the printed circuit board to be processed, the movement of the liquid on the surface of the circuit board, and the like. Also, the bubbles are
It is stable in a spherical shape due to the balance of surface tension in the liquid. And since spherical bubbles are distributed in various sizes, bubble shapes that match the hole shape will also occur, and in some cases most of the bubbles will fit inside the circular dead-end holes. It can be estimated that removal will be difficult. In particular, when the bubbles contact the circumference of the inner wall of the hole and the bottom of the dead-end hole, the bubbles are semi-fixed in the hole and are difficult to remove.

According to the present invention, since the cross-sectional shape of the dead end hole is oval, it is possible to reduce the contact area between the air bubble and the inner surface of the hole and reduce the contact area. Therefore, the spherical air bubble is formed in the hole. Even if it remains, a gap is created between the bubble and the wall surface of the hole, and the plating solution can enter there, so the bubble can be easily generated by the vibration, shock, and rocking of the printed circuit board during the plating process. Can be removed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a printed circuit board according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a plan view showing the structure of a printed circuit board according to an embodiment of the present invention, FIG. 2 is a sectional view showing the structure of a printed circuit board according to the embodiment of the present invention, and the reference numerals in FIG. Figure 4
Is the same as

One embodiment of the present invention, as shown in FIG.
The blind hole 3 is different from the prior art described with reference to FIGS. 3 and 4 in that the cross-sectional shape of the blind hole 3 is an ellipse.

Since the oblong blind hole 3 according to the embodiment of the present invention can be formed by the laser drilling method, the short side and the long side have the same dimensions.
The optimum value may be determined in consideration of the pattern size, the hole diameter, etc., and the removal degree of bubbles in the dead-end hole 3 at the time of manufacturing.

Further, the dead end hole is usually provided at the position of the land 2, but it may be provided on the line 4 as shown in FIG.

According to the above-described embodiment of the present invention, since the dead-end hole 3 of the printed circuit board 1 has an oval cross-section, bubbles remaining in the hole during the plating process become holes. The area in contact with the inner surface can be reduced,
Bubbles can be easily removed. Therefore, it is possible to completely perform plating on the inner surface of the blind hole without the plating void, and it is possible to improve the yield at the time of manufacturing.

Further, according to one embodiment of the present invention, it is possible to surely remove bubbles even if the depth is large and the diameter is small as compared with a conventional blind hole having a circular cross section.

[0024]

As described above, according to the present invention, it is possible to easily remove the air bubbles remaining in the dead-end holes and make it easier for the pretreatment liquid for plating and the plating liquid to enter the dead-end holes with a reduced diameter. This allows for complete plating of the inner surface of the dead end hole.

[Brief description of drawings]

FIG. 1 is a plan view showing a printed circuit board structure according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a printed circuit board structure according to an embodiment of the present invention.

FIG. 3 is a plan view showing a structure of a printed circuit board according to the related art.

FIG. 4 is a cross-sectional view of a printed circuit board according to the related art.

[Explanation of symbols]

 1 Printed circuit board 2 Land 3 Dead end hole 4 Line 5 Inner layer circuit pattern 6 Copper foil 7 Copper plating layer

Claims (1)

[Claims] 1. A printed circuit board having a blind hole provided for electrically connecting an outermost conductor layer and an inner conductor layer, wherein the blind hole has an oval cross section. Printed circuit board characterized by.