JPH0750487A - Multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To prevent the deterioration of electric characteristics of blind via holes by constituting the sidewall of each via hole of a through hole formed through outer-layer substrates and adhesive layers and constituting the adhesive layers of non-flow type prepregs. CONSTITUTION:A multilayer printed wiring board is constituted of inner-layer substrates 7 provided with inner-layer conductor patterns 12 on their surface sides and outer-layer substrates 5 which are integrally joined to the surfaces of the substrates 7 with adhesive layers (adhesive sheets 4 composed of non-flow type prepregs). The substrates 5 have blind via holes 14 opened to the patterns 12. Each hole 14 has a chemically plated copper film 10 which integrally and electrically connects one pattern 12 and an outer-layer conductor pattern 11 to the internal surface of the hole 14 and its sidewall is constituted of a through hole 6 formed through the substrates 5 and layers 4. The adhesive layers 4 are formed of non-flow type prepregs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer printed wiring board used for mounting electronic parts of various electronic devices, and particularly to a multilayer printed wiring having a non-through hole (hereinafter referred to as a blind via hole). Regarding the board.

[0002]

2. Description of the Related Art In a conventional printed wiring board, it is general that a conductor layer is formed on the inner wall of the hole by passing through a hole for inserting a component or a via hole and plating. However, in recent years
Due to the performance and economic needs of electronic equipment, higher density packaging is being made, and there is an increasing demand for even higher density in printed wiring boards.

However, in the conventional multilayer printed wiring board in which the via holes are provided as through holes, there is a problem in that the via holes significantly impede the wiring density for high density. In addition, as a result of increasing the number of layers,
The aspect ratio (ratio between the thickness of the outer layer base material and the diameter of the hole drilled in the outer layer base material) increased, and the reliability and economical efficiency of the through hole were not always satisfactory.

On the other hand, a design for improving the wiring density by using blind via holes has been proposed.
Considering this from the viewpoint of manufacturing blind via holes, the following two attempts have been made.

That is, the first attempt is a method of forming blind via holes by a drill, and this method is to form a necessary blind via hole by a drill after forming a multilayer substrate. In this case, it is necessary to control the depth of the drill in the thickness direction of the multilayer board. However, when manufacturing a multi-layered board, it is inevitable that the thickness of the board varies from lot to lot, and the distance between the bottom of the blind via hole and the conductor circuit of the next layer varies, resulting in a large variation in electrical characteristics. There is. Also,
It was not suitable for mass production because it had to be drilled on each side and then through holes.

The second attempt is a method of laminating printed wiring boards, which are provided with via holes in advance, through prepregs. However, this method uses a printed wiring board having a via hole in the outermost layer, which increases the thickness of the copper plating in the outermost layer, making it unsuitable for fine patterns. I was not satisfied.

Also, when the adhesive layer of the prepreg is used, when the substrates are laminated and thermocompression bonded, the adhesive layer flows out into the through hole for the blind via hole, and the conductor pattern immediately below the through hole is formed. Sometimes became dirty (covered) with the adhesive layer.

When the above-mentioned conductor pattern is contaminated with the adhesive layer that has flowed out, when chemical copper plating for blind via holes is applied to the through hole and the conductor pattern immediately below it,
This causes a portion where the chemical copper plating is not formed. As a result, the electrical connectivity between the conductor pattern on the inner layer substrate and the blind via hole is degraded, and the electrical characteristics of the blind via hole are deteriorated.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and it is an object of the present invention to provide a multilayer printed wiring board having a blind via hole excellent in electrical characteristics.

[0010]

The present invention comprises an inner layer substrate having an inner layer conductor pattern provided on the front surface side and an outer layer substrate integrally bonded to the front surface side of the inner layer substrate via an adhesive layer. Has a blind via hole opened in the inner layer conductor pattern, and the blind via hole integrally and electrically has its inner surface, the inner layer conductor pattern, and the outer layer conductor pattern on the outer layer substrate. In the multilayer printed wiring board having the chemical copper plating connected to, the blind via hole has a sidewall formed by a through hole formed through the outer layer substrate and the adhesive layer, and the adhesive layer is The multilayer printed wiring board is characterized by using a non-flow type prepreg.

Next, the multilayer printed wiring board of the present invention will be described in detail with reference to the drawings together with its manufacturing method. FIG. 1 is a partially enlarged view showing an outer layer base material 5 in which a non-flow type adhesive sheet 4 is temporarily adhered to a resin base material 2 side of a single-sided copper clad laminate 3 and then a hole is drilled. FIG. What is important here is that a non-flow type prepreg was used as the adhesive layer. The through holes 6 are holes that form blind via holes, and are holes that electrically connect the outermost conductor pattern 11 of the outermost layer and the inner conductor pattern 12 of the next layer.

FIG. 2 shows that the outer layer base material 5 is aligned and stacked on a desired conductor pattern on the inner layer substrate 7 formed by a known method, and then heated and pressed to bond the layers. FIG. 6 is a partially enlarged cross-sectional view showing a step of forming a laminated substrate 8. FIG. 3 shows the laminated substrate 8 according to a known method.
FIG. 3 is a partially enlarged cross-sectional view of a target multilayer printed wiring board in which through holes 9 are drilled and copper plating 10 is performed to form outer layer conductor patterns. The inner layer substrate 7 shown in the present invention means a substrate having at least one conductor circuit.

[0013]

In the present invention, a non-flow type prepreg is used as the adhesive layer when joining the outer layer base material and the inner layer substrate. Therefore, when the inner layer substrate and the outer layer base material are heat-pressed, they do not flow out unlike the conventional adhesive. Therefore, the adhesive layer does not flow out into the inside of the through hole where the adhesive layer opens to the conductor pattern of the inner layer substrate, that is, onto the conductor pattern of the inner layer substrate immediately below the through hole.

Therefore, the chemical copper plating in the through hole is continuously formed not only on the side wall surface of the through hole but also on the conductor pattern immediately below the through hole. Therefore, blind via holes have excellent electrical characteristics. Therefore, according to the present invention, it is possible to provide a multilayer printed wiring board having a blind via hole having excellent electrical characteristics.

[0015]

Embodiments of the present invention will be described below with reference to FIGS. The multilayer printed wiring board of this example is shown in FIGS.
As shown in FIG. 5, an inner layer substrate 7 having an inner layer conductor pattern 12 provided on the surface side, and an outer layer substrate integrally bonded to the surface side of the inner layer substrate 7 via an adhesive layer (adhesive sheet 4 of a non-flow type prepreg). 5, the outer layer substrate 5 has a blind via hole 14 opened to the inner layer conductor pattern 12.

The blind via hole 14 has a chemical copper plating 10 for integrally and electrically connecting the inner surface thereof, the inner layer conductor pattern 12 and the outer layer conductor pattern 11 on the outer layer substrate 5. It should be noted that the blind via hole 14 has a side wall formed by a through hole 6 formed by penetrating the outer layer substrate 5 and the adhesive layer, and the adhesive layer is not formed. That is, the adhesive sheet 4 made of a flow type prepreg is used.

The manufacturing method of the above multilayer printed wiring board will be described. First, a glass epoxy single-sided copper clad laminate (0.
1 mm thick, copper foil thickness 18 μm) 3, and on the resin base material 2 side, a non-flow type prepreg with a thickness of 4
0 μm adhesive sheet 4 (manufactured by Nikkan Kogyo, trade name: SA
One piece of F) was temporarily bonded at a temperature of 50 ° C. and a pressure of 10 kg / cm ² for about 20 minutes. As a result, the adhesive layer made of the adhesive sheet 4 was temporarily adhered to the resin base material 2 side of the single-sided copper-clad laminate 3.

Then, a through hole 6 having a diameter of 0.4 mm was drilled at a predetermined position in the outer layer base material 5 by a drill to obtain the outer layer base material 5 shown in FIG. In FIG. 1, reference numeral 1 is a copper foil. On the other hand, the inner layer conductor pattern 12 (FIG. 3) was formed on the glass epoxy copper clad laminate having a thickness of 0.4 mm (copper foil thickness of 18 μm) by the tenting method.
The substrates 7a were laminated on each other with the glass epoxy prepreg 7b interposed therebetween and thermocompression bonded to obtain an inner layer substrate 7 having a thickness of 1.2 mm.

Next, a pin is erected in the reference hole, the through hole 6 of the outer layer base material 5 and the desired inner layer conductor pattern 12 of the inner layer substrate 7 are aligned and laminated, and then at a temperature of 150 ° C. A pressure of 20 kg / cm ² was applied and thermocompression bonding was performed for 20 minutes to obtain a laminated substrate 8 (FIG. 2). After that, as shown in FIG. 3, through holes 9 were drilled at predetermined positions in the laminated substrate 8. Then, known chemical copper plating 10 and electrolytic copper plating 10 were applied, and an outermost conductor pattern 11 of the outermost layer of the laminated substrate 8 was formed by etching.

As a result, a 6-layer multilayer printed wiring board (FIG. 3) according to the present invention was obtained as described above. As described above, in this example, the adhesive sheet 4 made of a non-flow type prepreg is used as the adhesive layer. Therefore, the adhesive layer does not flow onto the blind via hole and the conductor pattern of the inner layer substrate immediately below the blind via hole during the above-mentioned thermocompression bonding. Therefore, chemical copper plating for blind via holes can be formed continuously and uniformly. Therefore, it is possible to provide a multilayer printed wiring board having a blind via hole having excellent electrical characteristics.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a manufacturing process of a multilayer printed wiring board in an example.

FIG. 2 is an explanatory view of a process following FIG.

FIG. 3 is a cross-sectional view of a multilayer printed wiring board obtained in an example.

[Explanation of symbols]

 3 ... Single-sided copper clad laminate, 4 ... Adhesive sheet, 5 ... Outer layer base material, 6 ... Blind via hole, 7 ... Inner layer substrate, 8 ... Laminated substrate, 10. ..Copper plating, 11 ... Outer layer conductor pattern, 12 ... Inner layer conductor pattern,

Claims (1)

[Claims] 1. An inner layer substrate having an inner layer conductor pattern provided on the front surface side, and an outer layer substrate integrally joined to the front surface side of the inner layer substrate via an adhesive layer, wherein the outer layer substrate has the inner layer conductor. Chemical copper having a blind via hole opened in the pattern and integrally and electrically connecting the inner surface of the blind via hole with the inner conductor pattern and the outer conductor pattern on the outer substrate. In a multilayer printed wiring board having a plating, the blind via hole has a sidewall formed by a through hole formed through the outer substrate and the adhesive layer, and the adhesive layer is a non-flow type prepreg. A multilayer printed wiring board, characterized by comprising: