JPH06302957A - Multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To shorten the distance between the centers of lands in a high-density wiring circuit. CONSTITUTION:In the wiring board in which lands on an inner- and other-layer substrates are electrically connected to each other by means of conductive paste filling up connecting holes formed in both substrate in a state where the holes are communicated with each other, the distance between the center of the land 17 of a blind via hole 11 and the center of the land 15 of a through via hole 12 is made shorter as compared with circular lands of the same areas by forming the lands 17 and 15 in rectangular shapes and so that the lands 17 and 15 can be brought nearer to each other.

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, and more particularly to a land for connecting via holes in a high density packaging multilayer printed wiring board.

[0002]

2. Description of the Related Art Multi-layer printed wiring boards are widely used in information processing equipment, electronic office equipment and household electric appliances which require high density signal lines and suppression of electromagnetic radiation. And
The multilayer printed wiring board is provided with via holes for connecting required circuits of each layer.

This via hole includes a plated via hole in which a hole wall is plated, and a conductive paste is pressed into the hole without plating so that a required circuit of each layer is electrically connected through the conductive paste. .

FIG. 11 shows an example of a conventional multilayer printed wiring board for connecting required circuits between layers by using a conductive paste. In this multilayer printed wiring board, a circuit 54 is formed on both sides of an inner layer board 51 having circuits 53 formed on both sides.
The outer layer board 52 on which the layers are formed is laminated, a blind via hole 61 for connecting a required circuit of each layer and an access-like through via hole 62 are provided, and each layer is connected by a conductive paste 63. A solder resist 55 is applied to the surface of the outer layer except for the connection portion of the circuit conductor.

In this case, the connection lands 64, 65, 66, 67 of the via holes 61, 62 for connecting the circuits of the respective layers.
Has a circular shape, and in the through via hole 62, the inner diameter of the outer layer land 65 is larger than the inner diameter of the inner layer land 64 to form a large area where the conductive paste is connected to the inner layer land.

[0006]

However, when the density of the signal lines of the printed wiring board becomes higher and higher due to the high integration of electronic equipment, the signal lines formed on the substrate surface should be extremely close to each other. In order to solve this problem, the circuit pattern has been thinned, and the diameter of the land for connecting the circuit of each layer has been reduced with a conductive paste. However, as with the conventional multilayer printed wiring board, the land 64 , 65, 6
When 6, 67 have a circular shape, the land diameter B needs to be large in order to secure the connection area with respect to the hole diameter A as shown in FIG. 12, and the land diameters B are formed close to each other. In this case, even if the shortest distance of the outer circumference is C, the center-to-center distance P between lands is P = B + C, which is the limit in the case of a circular land.

Further, if the land interval is further reduced, insulation failure due to deterioration of the insulator at the land boundary portion and insulation failure due to the conductor paste overcoming the insulator (solder resist 55) provided between the lands will occur. There are manufacturing problems such as easy occurrence.

Therefore, the present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a printed wiring board capable of further reducing the conventional center-to-land distance.

[0009]

In order to achieve the above object, the present invention makes the lands of both substrates conductive by a conductive paste filled in a connection hole formed in a state of communicating with the inner substrate and the outer substrate. In the multilayer printed wiring board, the lands of both conducting boards are formed in a shape in which at least two opposing sides are parallel straight lines.

[0010]

According to the printed wiring board of the present invention, since the lands are formed in a shape in which at least two opposite sides are parallel straight lines, the land areas for connection are not reduced at least and the land mutual connection is reduced. The center-to-center distance can be made closer than that of a conventional circular land.

[0011]

EXAMPLE 1 FIG. 1 shows an example of a multilayer printed wiring board according to the present invention. This multilayer printed wiring board has circuits 3 on both sides beforehand.
The outer layer board 2 is formed by heating and laminating the insulating layer side of the copper clad insulating sheet on both surfaces of the inner layer board 1 on which the outer layer board 1 is formed, and the outer layer board at positions corresponding to the specific conductor patterns 14 and 16 of the inner layer board 1. The copper foil 2 is selectively removed by etching.

Since the insulating layer constituting the copper clad insulating sheet is made of a resin layer having a property of being dissolved in an alkaline aqueous solution, the resin layer portion exposed by etching away the copper foil is dissolved in the alkaline aqueous solution. By removing and exposing the conductor patterns 14 and 16 on the inner layer side, the blind via hole 11 and the access-like through via hole 12 are formed. Then, the resin layer is cured to form the circuit 4 on the outer copper foil surface.

[0013]

By applying a conductive paste to the blind via hole 11 and the access through via hole 12 formed as described above, the land 1 of the inner and outer layers is formed.
4, 15, and 16, 17 are brought into conduction. In this case, the connecting lands 14, 15, 16, 17 of the via holes 11, 12 for connecting the circuits of the respective layers.
In place of the conventional circular shape, is a square shape in the present invention.

First, the merits of forming a rectangle by replacing the land shape with a circle will be described. As shown in FIG. 2, the square land and the conventional circular land are compared with each other. As shown in FIG. 2, in the square land T having a side length equal to the outer diameter of the circular land S, the square is about 27 times larger than the circle.
% Large area.

Therefore, the contact area of the conductive paste is 27%.
For example, the land of the blind via hole is circular and the outer diameters of the inner layer and the outer layer are each 0.
When the conductive paste is applied to each of the 5 mm and 0.8 mm lands and the lands formed in a square shape having 0.5 mm and 0.8 mm on one side of the inner and outer layer lands, the former connection resistance value is obtained. Is 3.6 mΩ, whereas in the latter case it is 2.6 mΩ. Therefore, it can be seen that the exposed area of the square land can be reduced by 27% when the same resistance value is sufficient for the circular shape and the square shape.

Comparing the shapes of the circular land and the square land when the circular land and the square land have the same area in this way, one side of the square land T is smaller than the diameter of the circular land S as shown in FIG. . When these two lands are brought close to each other, as shown in FIG. 4, when the shortest distance between the outer peripheries of the circular lands S is C, the center-to-center distance is P, and the relative distance of the square lands T at that time. The distance between the two sides is D. Therefore, the center-to-center distance P in the case of a square land can be made closer by the difference between D and C.

5 to 8 show the case where a rectangular land is formed in the through via hole 12, and FIG. 5 shows a state in which the inner layer land 14 and the outer layer land 15 form a square so as to surround the through via hole 12. It is a thing.

FIG. 6 shows that the land connecting area is made equal to that of the circular shape, and the two exposed sides of the inner layer land 14 are formed in a rectangular shape so as not to contact the diameter of the through via hole 12. In this case, the length of the two sides is shorter than that in the case of forming a square, and thus the center-to-center distance between the lands can be made closer.

In FIG. 7, a land is formed so that two sides of the exposed portion of the rectangular inner layer land 14 are in contact with the diameter of the through via hole 12, and the outer layer land 15 is formed along the extension of the width of the inner layer land 14. It was done. In this case, the land is divided into two parts with the through via hole 12 as the center, and the center-to-center distance between the lands can be further reduced as compared with the case of the rectangle of FIG.

In FIG. 8, the exposed portion of the inner layer land 14 is formed in a square shape, and the outer layer land 15 is formed only on one side of the via hole 12. In this case, it is suitable as a shape in the case where it has to be irregularly formed depending on the high-density arrangement in the vicinity of the land. For reference, FIG. 9 is a cross-sectional view showing a state in which the conductive paste 13 is applied to the land shown in FIG. 8, and the conductive paste 13 is provided between the inner layer land 14 and one outer layer land 15. Shows the connected state.

Although the land formation of the through via hole 12 has been described as an example, the blind via hole 11 has been described above.
The shape, function, and effect of the land are also the same, and thus the description thereof is omitted.

The land shape described above is not limited to the rectangular shape, and both ends of the two parallel sides facing each other may be formed by arcs or the like as shown in FIG. If square lands are provided close to each other, the conductive paste easily crosses between the lands to cause insulation failure due to a short circuit. In such a case, a dam 6 (FIG. 1) is provided between the lands to prevent the short circuit. It is desirable to do.

According to the present embodiment, by forming the land shape in a slender shape, it is possible to adapt to the arrangement of high-density circuits, and by extending the shape appropriately in the longitudinal direction, sufficient connection can be achieved. The area can be secured and the connection resistance can be reduced. Further, by making the land shape square, the center-to-center distance between the lands can be shortened as compared with a circular land.

[0025]

As described above, according to the printed wiring board of the present invention, since the land shape is a straight line in which at least two opposite sides are parallel to each other, the land mutual shape can be improved as compared with the circular land. The center-to-center distance of can be shortened. Further, since the land connection area can be arbitrarily increased, the conductivity between layers can be improved. As described above, it is possible to achieve higher circuit density and improved performance.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing an example of a multilayer printed wiring board according to the present invention.

FIG. 2 is a diagram showing a comparison of areas of a circular land and a rectangular land.

FIG. 3 is a diagram in which circular lands and square lands have the same area.

FIG. 4 is a diagram comparing a limit of a proximity distance between a circular land and a rectangular land.

FIG. 5 is a diagram showing a square land.

FIG. 6 is a view showing a rectangular land shape.

FIG. 7 is a diagram showing a rectangular land shape divided into two.

FIG. 8 is a view of a land in which a square outer layer land is formed on one side of a square inner layer land.

9 is a cross-sectional view showing a state in which a conductive paste is applied to the land of FIG.

FIG. 10 is a diagram showing another land shape.

FIG. 11 is an enlarged cross-sectional view of a conventional multilayer printed wiring board.

FIG. 12 is a diagram showing center distances of adjacent circular lands.

[Explanation of symbols]

 1 inner layer board 2 outer layer board 3,4 circuit 5 insulating layer 6 dam 11 blind via hole 12 through via hole 13 conductive paste 14,16 inner layer land 15,17 outer layer land

Claims (1)

[Claims] 1. A multilayer printed wiring board in which lands of both boards are electrically connected by a conductive paste filled in a connection hole formed in a state of communicating with the inner board and the outer board,
A multi-layer printed wiring board in which lands of both conducting boards are formed in a shape in which at least two opposite sides are parallel straight lines.