JPH0365910B2 - - Google Patents

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) involves stacking an etched inner layer circuit board of a copper-clad laminate and a prepreg, heating and pressing them using a lamination press to form an integrated structure, and then pressing both sides together. A common manufacturing method is to drill holes in the same way as printing plates, plate the panels, and then form outer layer circuits to obtain a multilayer board.

In recent years, information processing devices such as computers process large amounts of information at high speed, and large-scale integrated circuit devices (LSI) have been replaced by very large-scale integrated circuit devices (VLSI).
There is a growing demand for high-density mounting of devices on multilayer boards.

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

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.

Conventionally, methods such as adjusting the resin content of the prepreg and adjusting the flow of the resin in the prepreg have been used to deal with this problem.

However, since the circuit densities of the inner layer circuits essentially differ from each other and the prepreg is required to have a moderate flow in order to completely embed the circuit, the above-mentioned conventional method has its own limitations.

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 heat and pressure molding is performed to create 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 glass-polyaminobismaleimide resin circuit boards, but other circuit boards are also applicable.

However, the present invention is applied to multilayer boards that require high performance, and glass-polyamino bismaleimide resin circuit boards are the main targets.

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

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

In multilayer boards using imide-based substrates and imide-based prepregs, polyamino bismaleimide resin is uniformly dispersed in a solvent that is a poor solvent for liquid epoxy resin or polyamino bismaleimide resin and a good solvent for epoxy resin. A resin paste is particularly preferred in that it overcomes the above-mentioned limitations.

These varnishes or pastes are applied onto the inner layer circuit board using a roll coater,
There are methods using a doctor knife coater, screen printing applicator, wheeler, etc., but screen printing, which allows easy adjustment of the coating thickness, gives preferable 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 the B-stage, the circuits on the back side are treated in the same way to obtain a circuit board in which the circuits on both sides are smoothed with resin.In this case, the resin thickness is zero on the circuit and the thickness between the circuits is the same as that between the circuits. Ideally, it would be buried, but if the conventional level difference is reduced, whether it is thickly coated or thinly coated, it will make a certain contribution to the accuracy of the insulating layer thickness.

It 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 layers, and a multilayer board is obtained by lamination molding.

Examples are shown below.

Example 1 70 parts by weight of polyamino bismaleimide resin powder was dispersed in 30 parts by weight of bisphenol type epoxy resin (Epicoat #828 manufactured by Ciel Co., Ltd.) and passed through three ink rolls three times to ensure uniform dispersion of the powder. A paste composition was obtained.

Next, use an applicator to apply 40μ to one side of the 35μ copper foil glass polyimide double-sided circuit board with the circuit formed.
I applied a coat to make it look like this.

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 ±2.5μ.

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

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

Next, two of the treated circuit boards and 35μ outer layer copper foil 2
Two sheets of polyamino bismaleimide epoxy resin-glass fabric prepreg with a thickness of 100 μm after lamination were laminated between each layer, and heated at 170℃ for 2 hours for 40 minutes.
Lamination molding was carried out at a pressure of Kg/cm ² .

The obtained multilayer board is cut into 3 to 3 layers.
The circuit thickness between the four layers was measured at 10 locations using micrographs.

As a result, the thickness of the insulating layer between the circuits was 210±10μ,
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 processing the circuit surface, and the inter-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 Since the embedding method uses a resin composition, it was possible to completely embed the circuits.

2. Smoothness can be achieved even if the circuit boards are different within the board.

3. Because the smoothing process has been applied in advance, there is no need to consider embedding with resin in the prepreg as in the past, and the role of the prepreg is only interlayer adhesion, making it possible to use prepreg with a low resin content and low flow. can.

Therefore, adjustment of thickness accuracy becomes extremely easy.

4. Copper foil thickness can be increased without being affected by 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.

Claims (1)

[Claims] 1. In a method for manufacturing a multilayer printed wiring board, a composition containing a polyamino bismaleimide resin and an epoxy resin as main components is embedded between the circuit on the surface of the inner layer circuit board and the step between the substrate surface, and after surface smoothing treatment, heat curing is performed. A method for manufacturing a multilayer printed wiring board, which comprises at least 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.