JPH021391B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a multilayer printed wiring board, and more particularly to a multilayer printed wiring board having a thick conductive layer as an inner layer capable of supplying a large current.

In general, a multilayer printed wiring board (hereinafter abbreviated as multilayer board) has a copper layer in its inner layer for supplying power, etc., and a conductive pattern has conventionally been formed on the copper layer by photo-etching.

In recent years, in information processing equipment such as large computers, as semiconductor elements have become more highly integrated and faster, the wiring capacity of printed wiring boards (hereinafter referred to as wiring boards) on which these devices are mounted has of course improved. However, due to the need to supply a large amount of current through the wiring board, the number of layers has been increasing as the board has become multilayered.

On the other hand, with high-density packaging, the number of input/output pins on wiring boards has also increased, and although through-holes were previously provided on a grid spacing of 100 mils, the grid spacing has also increased to 75 mils.
It has been reduced to a mill.

As a result, the volumes of the copper layers of the power supply layer and ground layer provided in the inner layer of the multilayer board are reduced, making it difficult to supply a large amount of current.

Therefore, wiring boards for large computers that have been put into practical use in recent years have become increasingly multi-layered, with multilayer configurations of around 20 layers now common, with the power supply layer and ground layer accounting for more than half of the board. Generally, conductive patterns are formed on these power supply layers and ground layers by photo-etching on a copper-clad laminate, so the thickness of the copper layer is limited to 2 to 3 ounces of copper foil. Therefore, as shown in Figure 1, if a thick copper foil is used, the amount of side etching will increase during etching, making it difficult to improve the precision of the conductive pattern.
The distance accuracy between the through hole 8 shown in the figure and the inner copper layer 1a of the power supply layer or the ground layer deteriorates, and the insulation property is significantly impaired.

Therefore, in order to supply a large current, the number of layers such as power supply layers has to be increased, and the number of layers in multilayer boards is increasing, making it difficult to manufacture them. One way to solve this problem is to use a thick copper plate and mechanically remove the through holes and non-connecting parts, but when this copper plate is placed on the inner layer of a multilayer board, the inner layer Since the layers 1a and 1b are exposed at the edge of the board and come close to or short-circuited to the inner copper layers 1a and 1b or to the conductive pattern 99, there is a drawback that the insulation properties of the multilayer board are significantly impaired.

An object of the present invention is to provide a method for manufacturing a multilayer board that eliminates such conventional drawbacks.

According to the present invention, clearance holes that are not connected to through holes are formed with high precision in a copper foil that is approximately 2 to 20 times thicker than the copper foil used for the inner layer of a multilayer board, regardless of the thickness of the copper layer. A method for manufacturing a multilayer board is obtained, which is characterized in that the copper layers are not exposed at the ends of the multilayer board.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 3A to 3H. Clearance holes 2a-1, 2a-2 are bored in a copper plate 10a with a thickness of about 0.1 to 1.6 mm by drilling with an N/C drilling machine, punching with a press, etc. at positions that are not connected to the ground layer (third Figure A).

Next, the copper plate 10a having the clearance holes 2a-1, 2a-2 and the copper plate 10b having the clearance holes 2a-1, 2a-2 manufactured by the same method are stacked via the pre-preg 3a (FIG. 3B),
By pressurizing and heating with a press or the like, a laminate 3 having conductive patterns of thick copper layers on the upper and lower sides is formed (FIG. 3C). Next, the copper layer corresponding to the outer edge of the wiring board, that is, the upper and lower copper plates 10a and 10b of the laminate 3, is removed by photo-etching until the prepreg 3a is exposed, forming a groove-shaped outer contour pattern 4.
a, 4b are formed (Fig. 3D). Next, the outer contour patterns 4a, 4b of the laminate 3 removed by this etching and the clearance holes 2a-1, 2a-2 formed by mechanical processing using a drill or the like,
2b-1 and 2b-2 are filled with a paste composition in which polyamide bismaleimide resin powder is uniformly dispersed in an epoxy resin solution using a poor solvent for liquid epoxy resin using a roll coater, a doctor knife coater, or the like. After being discontinued, the temperature is 150℃.
The filled resin portion 5 is formed by drying for 30 minutes to obtain a B-stage state or by drying at a temperature of 150° C. for 90 minutes to obtain a C-stage state (FIG. 3E).

Next, the prepreg layers 3a and 3b of the single-sided copper-clad laminates 6a and 6b are inserted above and below the laminate 3 on which the filled resin portion 5 has been formed, with the copper-clad surfaces facing outward (FIG. 3F). Next, this is pressurized and heated to be integrated to form a laminate 7 having a conductive pattern of a thick copper layer on the inner layer. (Figure 3G).

Next, using the usual manufacturing method for through-hole wiring boards, through-holes 8 and conductive patterns 9a and 9 are formed by drilling, through-hole plating, and photo-etching.
b is formed in a predetermined position, the outer shape is finished by cutting at the outer contour patterns 4a and 4b on the groove by mechanical processing so that the inner conductor is not exposed at the end, and the inner layer according to the present invention is made of thick copper. A multilayer board 17 having a conductive pattern of layers is obtained (FIG. 3H).

As described above, the following effects can be obtained by the present invention.

(i) Since the inner layer has a thick conductive pattern, side etching will not occur due to etching.

(ii) Moreover, even if the thickness of the conductor layer is changed in terms of design, the accuracy of the conductive pattern does not change, and a method for manufacturing a multilayer board that is compatible with higher accuracy can be provided.

(iii) Since the inner conductor layer is not exposed at the edge of the board, there is no reduction in insulation resistance. Therefore, a multilayer board with excellent interlayer insulation properties can be provided.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views of a multilayer printed wiring board manufactured by a conventional manufacturing method. 3A to 3H are cross-sectional views showing the manufacturing process of the multilayer printed wiring board of the present invention. 1a, 1b...inner copper layer, 10a, 10b...
Copper plate, 2a-1, 2a-2, 2b-2...Clearance hole, 3,7...Laminated body, 3a...Pre-preg, 4a, 4b...Outline contour pattern, 5...
Filled resin layer, 6a, 6b... laminate, 8... through hole, 9a, 9b... conductive pattern, 17...
...Multilayer board.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a multilayer printed wiring board, characterized by including the following steps. (b) A process of forming holes in the through-holes of the conductive sheet forming the conductive pattern and the portions forming the non-connecting parts; (b) Preparing the conductor layer consisting of one or more conductive sheets in which the holes are formed; (c) Forming a groove-shaped outer outline in which the prepreg is exposed in the conductor layer of the laminate; (d) Applying heat to the outer outline. A process of embedding a curable resin and then heating and curing it to form a B-stage state; (e) The laminate in which the thermosetting resin is embedded, the laminate on which a normal conductor pattern is formed, and the conductor layer are made of prepreg. A process of forming a molded body by inserting. (F) A step of cutting the molded body along the groove-like outer contour line so that the conductive sheet is not exposed at the end. 2. The method of manufacturing a multilayer printed wiring board according to claim 1, wherein the conductive sheet is a copper foil or a copper plate having a thickness of 0.1 to 1.6 mm.