JPH05347480A - Manufacture of multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To reduce the number of holes by realizing conduction between upper and lower surfaces by shaping a hole in a multilayer printed wiring board and then cutting off the conduction. CONSTITUTION:A hole 3 of a small diameter is made to pass through a multilayer printed wiring board 1 and a hole 4 whose diameter is larger than that of the hole 3 is shaped up to a specified depth of the wiring board 1 in the same position. Then, after upper and lower surfaces of the wiring board 1 are made conductive by a method such as plating, a bottom of the hole of the large diameter is cut with a drill whose diameter is larger than the small diameter of the hole 4 and smaller than the large diameter thereof; thereby, conduction between up and down of the wiring board is cut off. Since two or more conductions are thereby possible by one through-hole 6, the number of holes 3, 4 of the printed wiring board 1 can be reduced and troubles such as adhesion defective of plating metal can be prevented.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is a method of reducing the number of holes in a multilayer printed wiring board to obtain a high density wiring board.

[0002]

2. Description of the Related Art A conventional multilayer printed wiring board is formed with a large number of small-diameter drill holes to form through holes. Each of these through holes transmits a signal. In order to increase the wiring density, it is necessary to increase the number of the small diameter holes, which causes various problems such as accuracy in manufacturing a multilayer printed wiring board. Also,
In the plating process for small-diameter holes, since the hole diameter is smaller than the thickness of the multilayer printed wiring board, plating defects often occur. Further, for example, when it is necessary to insulate one surface side from the other surface side, there is a drawback that the positions of the corresponding circuit patterns and holes are restricted, and the number of holes increases.

[0003]

SUMMARY OF THE INVENTION The present invention is intended to eliminate such drawbacks, and to reduce the number of holes and also to reduce plating defects, thereby making it possible to reduce the number of circuit patterns and holes in each multilayer circuit. It is possible to reduce the restriction on the position of.

[0004]

According to the present invention, a hole having a small diameter is penetrated through a multilayer printed wiring board, a hole having a diameter larger than the hole is made at the same position to a predetermined depth of the wiring board, and then plating or the like is performed. After connecting the upper and lower surfaces by a method, by cutting the large-diameter bottom part with a drill having a diameter larger than the small diameter and smaller than the large diameter to remove the conduction between the upper and lower surfaces. A method for manufacturing a characteristic multilayer printed wiring board.

The present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of an example of a four-layer printed wiring board (hereinafter referred to as a four-layer board). Reference symbols a, b, c, and d respectively indicate a surface layer circuit or an inner layer circuit. FIG. 2 shows the four-layer plate of FIG. 1 provided with small-diameter through holes (2). The two through holes conduct the circuits c and d and the circuits a and b, respectively. FIG. 3 illustrates the process of the present invention using the 4-layer board of FIG. First, a small-diameter hole (3) penetrating each circuit of a, b, c, d is opened in the four-layer plate (FIG. 3A), and the circuits of a and b are cut to form a concentric circle with the small-diameter hole (3). Drill a hole (4) with a larger diameter than this (Fig. 3B). Plating is performed on the entire inner surfaces of these small diameter holes and large diameter holes (FIG. 3C). (5) indicates a plated hole. Then, the bottom portion of the large diameter hole is cut with a drill having a diameter intermediate between the small diameter hole and the large diameter hole to remove the plated portion to form the through hole (6) (FIG. 3).
D). (7) shows a plated portion and (8) shows a non-plated portion.
By such a process, the circuit of a and b and the circuit of c and d are respectively conducted through one hole, and an insulated through hole is formed between b and c. FIG. 4 shows an example in which the present invention is applied to a 6-layer printed wiring board (11). Through hole (1
In 2), holes with different diameters are formed in three steps, and after plating, the bottom of each is cut to remove the plating on that part. The through hole (13) is obtained by performing the process shown in FIG. 3 from both upper and lower sides. In FIG. 4, (14) shows a plated portion and (15) shows a non-plated portion. In both cases, the circuits a and b, the circuits c and d, and the circuits e and f are electrically connected, and the portions b and c and the portions d and e are insulated from each other.

[0006]

According to the method of the present invention, since one through hole can conduct electricity at two or more places, the number of holes can be reduced. Further, various types of conduction and insulation can be performed by changing the diameter of the hole and the position of the hole. Furthermore, since the small diameter portion is short, troubles such as poor adhesion of the plated metal can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view of a four-layer printed wiring board (four-layer board).

FIG. 2 is a cross-sectional view of the four-layer board of FIG. 1 with through holes.

3 is a cross-sectional view showing each step of providing a through hole according to the present invention in the four-layer board of FIG. 1, A: a state of penetrating a small-diameter hole, B: a state of forming a large-diameter hole in the middle of the four-layer board, C: hole is plated, D: large diameter hole bottom is cut

FIG. 4 is a sectional view when the method of the present invention is applied to a six-layer printed wiring board (six-layer board).

[Explanation of symbols]

 1 Multilayer board (4 layer board) 2 Through hole 3 Small diameter hole 4 Large diameter hole 5 Plated hole 6 Through hole 7 Plated part 8 Non-plated part 11 Multi-layer plate (6 layer plate) 12 Through hole 13 Through hole 14 Plated part 15 Non-plated part

Claims (1)

[Claims] 1. A multilayer printed wiring board having a small-diameter hole penetrating through it, and a hole having a larger diameter than that at the same position is drilled to a predetermined depth of the wiring board, and then the upper and lower surfaces are electrically connected by a method such as plating. After that, by using a drill having a diameter larger than the small diameter and smaller than the large diameter of the hole to cut and remove the large-diameter bottom portion, the conduction between the upper and lower sides of the multilayer printed wiring board is blocked. Production method.