JPS61154096A - Manufacture of multilayer printed wiring board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an improved method of manufacturing multilayer printed wiring boards.

Conventionally, the manufacturing method for multilayer printed wiring boards (hereinafter referred to as multilayer boards) has been to stack an etched inner layer circuit board of a copper-clad laminate and a prepreg, heat and press them using a lamination press to form an integrated unit, and then form a double-sided printed wiring board. Drill a hole in the same way as
A common manufacturing method is to perform panel plating and then form an outer layer circuit to obtain a multilayer board.

In recent years, in order for information processing equipment such as computers to process large amounts of information at high speed, it is required that large-scale integrated circuit elements (LSI) and very large-scale integrated circuit elements (VLSI) be mounted in high density on multilayer boards. It's starting to look like this.

In order to transmit signals between these circuit elements at high speed, the multilayer board must have certain electrical characteristics.

An important electrical property is the characteristic impedance (ZO), and in order to keep this property constant, it is necessary to keep the thickness of the insulating layer between the signal layer and the power/ground layer of the multilayer board constant.

As a method for dealing with this problem, methods such as adjusting the resin content of the prepreg and adjusting the resin content of the prepreg to 70% have been conventionally used.

However, the above-mentioned conventional method has its own limitations because the circuit densities of the inner layer circuits are essentially different and the prepreg is required to have a moderate thickness of 70 mm in order to completely embed the circuit.

Furthermore, in order to reduce power supply loss, there is a tendency for thicker circuit copper foils to be required, and it is also true that conventional methods have reached a point where this cannot be achieved at all.

An object of the present invention is to provide a method for manufacturing a multilayer board that solves the problems of the prior art.

That is, when manufacturing a multilayer board, the circuit part on the surface of the circuit board constituting the inner layer and the level difference based on the thickness of the copper foil on the board surface are filled with a composition whose main component is a thermosetting resin, and the surface is smoothed. After that, the composition is heated and cured to form a B-stage state, and then a prepreg to be formed as an insulating layer is laminated on the treated surface and heated and pressure molded to form insulation between inner layer circuits. The present invention relates to a method for obtaining a multilayer printed wiring board with uniform layer thickness.

The details of the present invention will be described below.

The circuit boards used in the present invention are mainly glass-epoxy resin circuit boards and lath polyamino bismaleimide resin circuit boards, but other circuit boards are also applicable.

However, the present invention is applied to multilayer boards that require high performance, and the main target is lath polyamide/bismaleimide resin circuit boards.

The thermosetting resin composition used in the present invention may be in the form of a face or paste, but it is preferable to use as little solvent as possible in order to reduce the decrease in thickness after embedding. B of the embedding resin composition
In order to adjust the staging, a solvent that is easy to remove is preferred.

Further, the thermosetting resin used can be selected as appropriate, and in special cases, resins that can be cured by radiation such as ultraviolet rays can also be applied.

However, the resin composition constituting the prepreg is preferred in order to ensure the properties required for a multilayer board, such as smear resistance, interlayer adhesion, drill workability, and heat resistance.

That is, epoxy resins, imide resins, and epoxy resin-imide resin compositions are generally preferred.

In particular, in multilayer boards using imide-based substrates and imide-based prepregs, poly7minobismaleimide resin is used as a solvent that is a poor solvent for liquid epoxy resins or polyamino bismaleimide resins, and a good solvent for epoxy resins. Uniformly dispersed resin pastes are particularly preferred in the sense that they comply with the above-mentioned restrictions.

These pastes or pastes are applied onto the inner layer circuit board, and there are several methods for this, such as a roll coater, doctor knife coater, screen printing applicator, and wheeler. Printing gives favorable results.

Of course, in this case, so-called solid printing is performed on the entire surface of the circuit.

Next, the circuit board embedded between the circuits with these resin compositions is heated until the resin compositions are in a B-stage state.

After B-stage formation, the circuits on the back side are also treated in the same manner to obtain a circuit board in which the circuits on both sides are smoothed with resin.

In this case, it is ideal that the resin thickness is zero on the circuit and that the area between the circuits is buried to the same level as the circuit surface, but if the conventional step is reduced, even if it is thick, it can be applied thinly. Even if there is, there is a certain contribution to the accuracy of the insulating layer thickness.

The method is exactly the same as the conventional method in that a plurality of circuit boards thus obtained are used, a prepreg is inserted between the eyebrows, and a multilayer board is obtained by lamination molding.

Examples are shown below.

Example 1 Bisphenol type epoxy resin (Nipifu manufactured by Shell)
#828) 70 parts by weight of polyamino bismaleimide resin powder was dispersed in 30 parts by weight and passed through three ink rolls three times to ensure uniform dispersion of the powder to obtain a paste composition.

Next, one side of the 35μ copper foil lath polyimide double-sided circuit board on which the circuit was formed was coated with an applicator to a thickness of 40μ.

After curing at 130° C. for 0.5 hours, the back circuit was treated in the same manner and cured in a dryer at 150° C. for 0.5 hours.

The surface of the obtained circuit board was measured with a roughness meter and had a roughness of 2.5 .mu.m.

For comparison, when the same measurement was performed on an unprocessed circuit, a 30 μm difference in level between the board surface and the circuit surface was observed.

Therefore, the step difference on one side was reduced from 30μ to 5μ.

Next, two pieces of epoxy resin lath cloth prepreg were laminated on polyamide 7-bismaleimide to a thickness of 100μ after laminating between two of the treated circuit boards and 112 outer layers of 35μ, and heated at 170°C for 2 hours. , laminated molding was performed at a pressure of 40 kg/cta2.

The obtained multilayer board was cut, and the circuit thickness between the third and fourth layers was measured at 10 locations using micrographs.

As a result, the thickness of the circuit insulating layer was 210±10μ, and the thickness variation could be suppressed to within ±5%.

Furthermore, when the smear resistance, interlayer adhesion strength, perforation property, and post-boiling solder heat resistance were measured using established test methods, the multilayer board was found to have no inferiority compared to conventional products.

Comparative Example 1 Using the same inner layer circuit board used in Example 1, a multilayer board was produced in exactly the same manner as in Example 1 without treating the circuit surface, and the circuit thickness was measured.

As a result, the thickness between the circuits was 193±35μ, and the thickness variation was 20%.

The effects obtained by the method of the present invention are as follows.

1. Because the embedding method uses resin jlI material, it was possible to completely embed the circuit surface.

2. Even if the circuit density differs depending on the thickness of the board, smoothing can be achieved.

3. Because the smoothing treatment has been applied in advance, there is no need to consider the embedding of resin in the prepreg as in the conventional method, and the role of the prepreg is only layer opening and adhesion, allowing flow with a low resin content. It is possible to use a prepreg with a small amount.

Therefore, adjustment of thickness accuracy becomes extremely easy.

4. The thickness of the copper foil can be increased without being affected by the circuit thickness.

5. If a resin composition having the same composition as that of the circuit board and prepreg is applied, a multilayer board with the same performance as the conventional one can be obtained.

Patent applicant: NEC Corporation Sumitomo Bakelite Co., Ltd.

Claims (4)

[Claims] (1) In a method for manufacturing a multilayer printed wiring board, a composition containing a thermosetting resin as a main component is embedded between the circuit on the surface of the inner layer circuit board and the level difference between the board surface and subjected to surface smoothing treatment, and then heated and cured. A method for manufacturing a multilayer printed wiring board, comprising: bringing the composition into a B-stage state, and then laminating a prepreg to be formed into an insulating layer on the treated surface and thermocompression bonding. (2) The method for producing a multilayer printed wiring board according to claim 1, wherein the composition containing the thermosetting resin as a main component comprises a polyamino bismaleimide resin and an epoxy resin. (3) The composition containing the thermosetting resin as a main component is a liquid epoxy resin or a paste composition in which polyamino bismaleimide resin powder is uniformly dispersed in an epoxy resin solution using a poor solvent for polyamino bismaleimide resin. A method for manufacturing a multilayer printed wiring board according to claim 1, characterized in that: (4) The method for producing a multilayer printed wiring board according to claim 1, wherein the composition containing the thermosetting resin as a main component comprises an epoxy resin and a phenol novolak resin.