JP2000299563A - Method for forming via hole in printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fine boring method comparable to ordinary photo-via method or laser-via method by boring a wiring layer and an insulation layer through press. SOLUTION: A wiring board comprises a core board 10 arranged, on the surface thereof, with a wiring layer 11 of copper foil serving as the inner layer pattern of a multiplayer wiring board, an insulation layer 12 of thermosetting resin being applied onto the core board 10, and a wiring layer 13 of copper foil applied onto the surface of the insulation layer 12. Via holes are bored in the wiring board by press. Boring by press means boring by deformation processing comprising shearing or shaping and it is distinguished from ordinary boring, i.e., drilling with rotary drill. Boring is performed by driving a male die corresponding to the shape to be obtained into the wiring board down to a required depth with a strong pressure.

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, and more particularly, to a method of forming a via hole when manufacturing a printed wiring board by a build-up method.

[0002]

2. Description of the Related Art A build-up method is known as a method for manufacturing a multilayer printed wiring board for increasing the mounting density. In this manufacturing method, an insulating layer made of resin and a wiring layer made of a conductor are sequentially stacked on a core substrate having a wiring layer (circuit pattern) disposed on the surface.
That is, several methods have been proposed for forming via holes for connecting wiring layers sandwiching an insulating layer.

The first is a method called a photo via method, in which a core substrate is coated with a photosensitive resin as an insulating layer, holes are formed by a photographic method, and then copper plating is performed to form a via hole conductor.

The second is a method called a laser via method, in which a thermosetting resin is coated on a core substrate or a copper foil coated with a thermosetting resin is laminated as an insulating layer, and holes are formed by laser processing. After that, copper plating is performed to form a via-hole conductor.

The third is a method called a bump method.
A conductive paste is printed and dried on the core substrate to form a bump, and an insulating layer made of FR-4 material or the like is laminated thereon. By connecting the tip of the bump penetrating the insulating layer to the wiring layer, a via hole is formed. Configure the conductor.

[0006]

Among the above-mentioned methods, the photo via method has an advantage that a plurality of holes can be formed collectively in a short time by the photographic method. The width is small, and there is a problem in water absorption and adhesion strength of the resin surface due to the characteristics of the resin, and there is a problem in that the thickness of the resin applied by coating is not uniform, resulting in excessive or insufficient exposure.

The laser via method has the advantages of good processing accuracy and a wide range of resin choices. However, in addition to the high cost of the laser machine, it is necessary to individually irradiate laser light for each hole. Further, there is a problem that it is difficult to set the conditions of the laser beam because the thickness of the resin applied by the coating is uneven. On the other hand, in the case of a copper foil coated with a thermosetting resin, the laser beam is reflected by the copper foil surface and cannot penetrate the copper foil, and the outer copper foil must be etched corresponding to a via hole to be processed. There was a problem to be had.

Further, the bump method has an advantage that copper plating for forming a via hole conductor is unnecessary, but there is a limit in reducing the size of the bump, and further, it is difficult to secure the positional accuracy between the bump and the land of the circuit pattern. There was a problem.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has a via hole for connecting circuits of different layers in manufacturing a printed wiring board by a build-up method. In forming the wiring layer, a hole is formed in the wiring layer and the insulating layer by press working.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In this embodiment, a four-layer wiring board is illustrated, but the number of layers is not limited to this, and the materials of the core substrate, the insulating layer, and the wiring layer are also illustrated. Of course, it is not limited.

FIGS. 1 to 4 are views showing steps of a method of forming a via hole according to the present invention. In the figure, reference numeral 10 denotes a core substrate on which a wiring layer 11 made of copper foil serving as an inner layer pattern of a multilayer wiring board is disposed, 12 denotes an insulating layer made of a thermosetting resin coated on the core substrate, and 13 denotes a core substrate. This is a wiring layer made of copper foil applied to the surface of the insulating layer.

A hole for a via hole is formed in the wiring board by press working. Here, punching by press working refers to punching by plastic working such as shearing or forming, and is distinguished from drilling by cutting of a conventionally known rotary drill tooth. Specifically, this hole is formed by driving a male mold corresponding to the shape of the hole to be obtained into the wiring board with a strong pressure to a required depth.

In the figure, reference numeral 1 denotes a male type used in the present invention, which is formed in a conical shape. This male type makes a plurality of holes by sequentially moving one thing in the X and Y directions,
It can be assumed that a plurality of male molds arranged in advance in accordance with the arrangement of the holes are prepared and the holes are punched collectively. It is desirable that the male mold has a high hardness, and in addition to this, when preparing a plurality of male molds for making a hole in a lump, it is preferable that the male mold be made of an inexpensive material. I have.

FIG. 6 is a view showing the shape of the male mold 1 in this embodiment. Here, a conical shape in which the tip of the driving portion 2 is cut off is employed, but the shape is not limited to this. May be sharply converged without cutting off
Further, as shown in FIG. 7, it goes without saying that the shape may be a polygonal pyramid or a pyramid. In the figure, reference numeral 3 denotes a hole which is opened toward the tip of the male driving portion, and has a function of releasing chips generated on the wiring board during plastic working. The hole 3 is not always a requirement of the present invention. For example, in the case of a polygonal pyramid or a pyramid-shaped male type shown in FIG. A gap is formed between the tip of the driving portion and the surface portion, and it can be expected that the gap has a function of releasing chips.

The above-mentioned male mold 1 is a wiring layer 1 on the surface of a multilayer wiring board.
The via-hole is driven in the Z direction of the wiring board at a location where the third via hole is to be formed (specifically, a connection land location) (see FIGS. 1 and 2).

The above-described implantation must be performed at a depth where the tip of the male mold 1 reaches a location (specifically, a connection pad location) corresponding to the via hole of the inner wiring layer 11, but in this embodiment. In order to enhance the driving accuracy in the Z direction, a flange 4 for regulating the driving depth of the male die by contacting the lower end surface with the surface of the printed wiring board is provided on the peripheral side of the male die. After the above-mentioned implantation, the wiring layer 13 and the insulating layer 1 outside the wiring board were placed at the locations where the male mold was pulled out.
A hole H penetrating through 2 and reaching the inner wiring layer 11 appears (see FIG. 3).

The wiring layer 11 (land portion), the hole H, and the wiring layer 13 (pad portion) are plated with copper 13 to connect them by a known means, thereby forming a via-hole conductor (see FIG. 4). .

Incidentally, in the present invention, the depth of the hole H obtained is determined by the depth of the driving of the male mold 1, and there is no other restriction. Therefore, the hole H is not limited to between the two wiring layers as in the embodiment,
And three or more wiring layers as shown in FIG.

[0019]

The via hole forming method according to the present invention having the above-described structure has the following specific effects. Unlike drilling with rotary drill teeth, which must form cutting teeth on the circumferential side, the diameter of the male mold can be made as small as possible. Fine drilling comparable to the laser or laser via method is possible. Since the mechanical drilling process is used, drilling can be performed for the entire outer wiring layer without making the drilling impossible depending on the material to be drilled. Therefore, it is not necessary to provide an opening in the wiring layer in advance. For the same reason, there is no restriction on the type of resin constituting the wiring board, so that various resins can be used. In addition to the same reason, since the depth of the hole is determined by the depth of the male implantation, it is possible not only to form the hole between the two layers in the related art but also to form the hole between the multilayers. Since the depth of the hole is determined by the depth of the male implantation, it is possible to always obtain a hole having a constant depth irrespective of the unevenness of the surface of the wiring board due to the uneven thickness of the insulating layer. Compared with the conventional laser via method, the equipment for drilling is extremely inexpensive, and the male mold can be configured at low cost.Therefore, prepare multiple male molds that are arranged in advance according to the hole arrangement and collectively Drilling can be performed, thereby shortening the working time and improving the positional accuracy at the same time.

[Brief description of the drawings]

FIG. 1 is a sectional view of a printed wiring board showing a step of forming a via hole according to the present invention.

FIG. 2 is a cross-sectional view of a printed wiring board showing a step of forming a via hole according to the present invention.

FIG. 3 is a cross-sectional view of a printed wiring board showing a step of forming a via hole according to the present invention.

FIG. 4 is a sectional view of a printed wiring board showing a step of forming a via hole according to the present invention.

FIG. 5 is a cross-sectional view of a printed wiring board showing a step of forming a via hole according to another embodiment.

FIG. 6 is a perspective view of a main part of a male mold.

FIG. 7 is a perspective view of a main part of a male mold according to a different embodiment.

[Explanation of symbols]

 Reference Signs List 1 male type 12 insulating layer 13 wiring layer H hole

Claims (7)

[Claims] 1. A printed wiring, characterized in that in forming a via hole for connecting circuits of different layers in the manufacture of a printed wiring board by a build-up method, a hole is formed in a wiring layer and an insulating layer by press working. A method of forming a via hole in a plate. 2. A method of forming a via hole in a printed wiring board according to claim 1, wherein the hole is formed by driving a conical male mold into the wiring layer and the insulating layer to a required depth. 3. The method for forming a via hole in a printed wiring board according to claim 2, wherein the male mold has a shape in which the implanted portion has a conical shape. 4. The method for forming a via hole in a printed wiring board according to claim 2, wherein the male mold has a shape in which a driving portion is formed into a pyramid or a polygonal pyramid. 5. The method for forming a via hole in a printed wiring board according to claim 3, wherein the tip of the male-type driving portion is cut off. 6. The method for forming a via hole in a printed wiring board according to claim 2, wherein a hole opened toward the tip of the driving portion is provided in a male form. 7. The male die according to claim 2, wherein a flange for regulating a driving depth of the male die by contacting a lower end surface with a surface of the printed wiring board is provided on a peripheral side of the male die. A method of forming a via hole in a printed wiring board.