JPH0290592A - Multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To restrain the thermal shrinkage and its variability of prepreg so as to enable a highly dense wiring by a method wherein the glass cloth of the prepreg is partially cut off. CONSTITUTION:A copper foil 1 18mum in thickness is provided to the outermost sides of both the faces of a wiring board, a number of inner substrates 3 provided with inner conductor patterns 2 formed on their front and rear sides are provided inside the copper foils 1, and a pair of glass cloth-polyimide resin prepregs 4 are interposed between the copper foil 1 and the inner board 3 respectively. The prepreg 4 composed of warps 5 and wefts 6 which are plain-woven is impregnated with semi-cured polyimide, where the warp and weft are formed of 200 or so of monofilaments 7mu in diameter collected together. Here, holes are irregularly bored in the prepreg per length of 10mm of warp and weft by a drill with diameter of 0.4mm to form cutoff points 7 in the prepreg. And, the prepregs 4 and others are formed into a multilayer structure, which is press- heated at a temperature of 170-200 deg.C under a pressure of 30kg/cm<2> to form a multilayer board.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a multilayer printed wiring board, and particularly to a prepreg used in multilayer molding.

[Conventional technology]

Conventionally, a method for manufacturing multilayer printed wiring (hereinafter abbreviated as multilayer PWB) is generally as follows. As a substrate material,
An inner conductor pattern is formed on a copper-clad laminate using a glass cloth as a base material and a thermosetting resin (epoxy resin, polyimide resin, etc.) as a T-binder, and this is then formed into multiple sheets of prepreg. (A sheet made of glass cloth impregnated with semi-hardened thermosetting resin.) An outer layer substrate (one-sided copper-clad laminate (copper foil) is placed on the outermost side) and heated and pressurized to integrate. It is molded into a multilayer substrate. Through-holes to be connected to the inner layer conductor pattern and through-holes for mounting components are drilled in this multilayered substrate, and then the insides of the through-holes are plated with metal to form through-holes.

Furthermore, an outer layer conductor pattern is formed by etching or the like to complete the multilayer PWB.

[Problem that the invention seeks to solve]

Since the conventional multilayer PWB described above uses glass cloth-based laminates and prepregs as substrate materials, dimensional changes are inevitable in the inner layer conductor pattern forming process and the multilayer molding process.

For this reason, a method has been adopted in which the dimensional changes of the inner layer substrate in each process are quantified, a certain dimensional correction is made to the mask film for forming the inner layer conductor pattern, and the desired constant inner layer conductor pattern dimensions are obtained after multilayer molding. There is.

Furthermore, in order to reduce the dimensional change and width of variation in the inner layer substrate, the copper-clad laminate used for the inner layer substrate is heated in advance to a temperature that exceeds the temperature conditions during multilayer molding to reduce the inherent strain in the substrate. Attempts have been made to reduce and control the heat treatment 9 mechanical polishing conditions in the inner layer conductor pattern forming process.

In addition, during multilayer molding, the inner layer substrate undergoes dimensional changes that far exceed the dimensional changes during the inner layer conductor pattern formation process due to thermal contraction of the prepreg in contact with the top and bottom surfaces, so it is necessary to control heating and pressure during multilayer molding. is becoming important.

However, it is difficult to quantify the thermal shrinkage of the prepreg itself, and the strain that occurs during the process of weaving the nine warps and wefts of the glass cloth, which is the raw material for the prepreg, and the strain that occurs during the process of impregnating the glass cloth with resin. There is no way to release the strain that occurs.

In recent years, in large-scale systems such as computers, in order to improve the performance of the layers (increasing the calculation speed, etc.), there has been a demand for higher density and higher multilayer multilayer PWBK. For this reason, a multilayer PW of 10 to 20 layers
In B, the thickness of the inner layer substrate is required to be 0.1 to 0.2 mm in order to suppress the thickness of the multilayer substrate after multilayer molding as much as possible.

In addition, with the demand for higher density inner layer conductor patterns, a large number of wiring patterns are formed between through holes, so the insulation gap between the through holes and the inner layer conductor patterns is becoming narrower.

As a result, as the thickness of the inner layer substrate becomes thinner, the effect of heat shrinkage of the prepreg during multilayer molding becomes more pronounced as a dimensional change, and the variation becomes larger.As a result, we can manufacture high-density, high-multilayer PWBs that satisfy the system requirements. It is becoming difficult to do so.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a multilayer printed wiring board that is free from distortion due to heat shrinkage of the prepreg and allows for high-density wiring.

[Means for solving problems]

The structure of the present invention is a multilayer printed wiring board formed by laminating and molding an inner layer substrate and an outer layer substrate via a prepreg made of glass cloth, in which the warp and weft of the glass cloth are each cut at a predetermined position. It is characterized by

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view showing a multilayer structure of a multilayer PWB according to a first embodiment of the present invention. In the same figure, the multilayer PWB of this example is made of a glass cloth with a thickness of Q, 1 mm, with copper of 18 μm thick disposed on the outermost sides of the front and back, and inner layer conductor pattern 2 formed on both the front and back sides. - A large number of inner layer substrates 3t made of a polyimide resin base material are arranged, and the copper foil 1. Inner layer substrate 3
Two glass cloth-polyimide resin prepregs 4 each having a thickness of 0.1 mm were inserted between the two sheets.

FIG. 2 is an enlarged plan view of the prepreg 4 shown in FIG. 1. In the same figure, the prepreg 4 of this example is made by converging approximately 200 monofilaments with a thickness of 7μ to form warp yarns 5 and weft yarns 6, and is plain woven at a density of 50 yarns in the warp and 60 yarns in the weft per square inch. After that, the warp yarn is impregnated with B-stage (semi-cured) polyimide resin.5. Only one place per 10mm length of each weft thread 6,
As shown in Figure 2, holes are drilled irregularly with a drill of 9.4 mm in diameter, and cutting point 7 (portion marked x in the figure) is made.
form.

Next, it was assembled into the multilayer structure shown in Fig. 1 and heated to a temperature of 170°C.
The multilayer substrate is completed by heating and pressing at a temperature of 200° C. and a pressure of 30 kg/cm’ for 90 minutes to 150 minutes.

FIG. 3 is an enlarged plan view showing a prepreg portion of a multilayer printed wiring board according to a second embodiment of the present invention.

In the figure, the prepreg 4 of this example has warp yarns 5.
A cutting point (X mark) 7 is provided for each of the weft threads 6, which has the advantage of further improving productivity compared to the first embodiment.

The first of these aspects of the present invention. The effects of the second embodiment will be shown. The following table compares the dimensional changes before and after multilayer molding of the inner layer conductor pattern of a glass cloth-polyimide resin laminate with a thickness Q of 1 mm with that of a conventional prepreg.

As shown in this table, the dimensional changes according to the present invention.

Both variations can be suppressed to 172 to 1/3 of the conventional level, and a high-density, high-precision multilayer PWB can be obtained.

〔Effect of the invention〕

As explained above, the present invention has the effect of suppressing the amount of heat shrinkage and variation in the prepreg by partially cutting the glass cloth of the prepreg.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the multilayer structure of a multilayer PWB according to the first embodiment of the present invention, FIG. 2 is a plan view of the prepreg shown in FIG. 1, and FIG. It is an enlarged plan view of the prepreg of multilayer PWB.L... Copper foil, 2.
...Inner layer conductor pattern, 3...Inner layer substrate, 4...Prepreg, 5...Warp thread (of glass cloth), 6... glass cloth)
Weft thread, 7... Cutting point (of glass cloth). Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] A multilayer printed wiring board formed by laminating and molding an inner layer substrate and an outer layer substrate via a prepreg made of glass cloth, characterized in that the warp and weft of the glass cloth are each cut at a predetermined position. multilayer printed wiring board.