JPH0732301B2 - Manufacturing method of embedded printed wiring board - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an embedded printed wiring board which particularly requires a high-density fine pattern.

[Background technology]

In recent years, electronic devices have become smaller and have higher performance, and printed wiring boards used in these devices are required to have higher density wiring. The densification of the printed wiring is usually done by making the wiring fine and laying the wiring under multiple layers. However, when the wiring is miniaturized, there is a problem that the adhesion between the conductive circuit on the wiring board and the substrate tends to be insufficient, and the reliability as the wiring board is reduced.

Conventionally, a conductive circuit has been created by etching a copper foil laminated on an insulating substrate according to a predetermined pattern. However, this method is not suitable for forming a fine pattern because the conductive circuit is side-etched during etching, and the conductive circuit is prone to damage from protruding from the substrate surface. Since the contact between the conductive circuit and the substrate is only on one side, there is a drawback that the contact force between the conductive circuit and the substrate is weak in the case of a fine conductive circuit pattern.

The following method has been considered as a method of manufacturing a printed wiring board for improving the above drawbacks. That is, a predetermined conductive circuit is formed by performing chemical plating on the insulating substrate. After forming the necessary conductive circuit on the conductive substrate by electroplating, the conductive circuit is transferred to the insulating substrate.

The printed wiring board formed by these methods has an advantage that the conductive circuit hardly projects from the substrate surface. However, the printed wiring board formed by the method of
There is a problem that the adhesion between the plating layer forming the conductive circuit and the substrate is weak. On the other hand, also in the printed wiring board formed by the method, the conductive circuit formed by electroplating is embedded in the resist film, but since the adhesion between the two is weak, the conductive circuit is also easily peeled off. The problem remains.

[Object of the Invention]

In view of the above points, it is an object of the present invention to provide a method for manufacturing an embedded printed wiring board that has high adhesion between an insulating substrate and a conductive circuit, and therefore has high reliability even when patterned with high density. To do.

[Disclosure of Invention]

To achieve the above object, the present invention provides a step of forming a photosensitive resin layer on the surface of a conductive substrate, a step of bringing a negative film and a diffusion plate into close contact with the photosensitive resin layer, and the diffusion plate and the negative film. A step of exposing the photosensitive resin layer to ultraviolet light through a film to perform photo-curing, and removing an unexposed portion of the photosensitive resin layer so that the width of the conductive substrate becomes narrower toward the conductive substrate. A step of forming a photosensitive cured insulating resin layer having a trapezoidal cross-section removed portion, and an inverted trapezoidal cross-section whose width becomes narrower toward the conductive substrate by filling the removed portion with a conductive metal. And the step of forming the conductive circuit, the insulating substrate is adhered to the surface of the insulating resin layer on which the conductive circuit is formed, and the conductive circuit and the insulating resin layer are transferred onto the insulating substrate. A step of, the gist of the method of embedding a printed wiring board comprising the step of separating the conductive substrate from the insulating resin layer after transfer.

Hereinafter, this will be described in detail with reference to the drawings showing an embodiment thereof.

FIG. 1 shows a cross-sectional structure of an embedded printed wiring board (hereinafter referred to as “printed wiring board”) 1 obtained by the present invention. This printed wiring board 1 has a structure in which a conductive circuit 5 is embedded in an insulating resin layer 4 on the surface of an insulating substrate 2 such as a glass epoxy plate. An adhesive layer 3 is interposed between the substrate 2 and the surface structure portion as needed. As shown in the figure, the conductive circuit 5 has a substantially trapezoidal cross section, and the circuit width becomes wider from the surface toward the inside so that the surface is flush with the surface of the insulating resin layer 4. Has been formed. Since the conductive circuit 5 has such a shape, the contact area with the substrate 2 is wide. In addition, it is adapted to be locked to the insulating resin layer 4. Therefore, it is difficult for the substrate 2 to be easily peeled off. That is, since the circuit width of the conductive circuit 5 becomes wider from the surface toward the inside, the insulating resin layer 4 in contact with the conductive circuit 5 on both sides thereof serves as resistance against peeling. . Therefore, the printed wiring board 1 having such a conductive circuit 5 has high reliability even if minute circuits are formed with high density.

The cross section of the conductive circuit does not necessarily have to be trapezoidal as long as the width of the circuit increases from the surface toward the inside. For example,
The circuit width may be wider in a curved shape from the surface toward the inside, or may be wider in a step shape.

Next, an example of a method for manufacturing a printed wiring board according to the present invention will be described with reference to FIG.

First, a conductive substrate 6 such as a stainless plate, an aluminum plate, and a support plate plated with chromium is prepared, and a photosensitive resin layer 7 is formed on one surface of the conductive substrate 6, as shown in FIG. This formation is performed by applying a photosensitive resin to the surface of the substrate 6 by a roll coater method, a dipping method, or the like. Then, as shown in FIG. 2B, a negative film 8 having a pattern opposite to the desired conductive circuit pattern is adhered to the resin layer 7. That is, in this film 8, the light-shielding portion 8a has a conductive circuit pattern. Further, a diffusion plate 9 is arranged on the surface of the film 8. The diffusion plate 9 has a function of spreading the incident light from the exposure source (not shown), and thus substantially spreads the photosensitive portion of the resin layer 7. In other words, the originally formed unexposed portion becomes narrower toward the inside. As the diffusion plate 9, a glass plate or the like whose surface is polished to have an appropriate roughness is used. Ultraviolet exposure is performed from this surface, development is performed to remove the unexposed portion, and a relief image 4a that is a cured photosensitive layer having a substantially trapezoidal cross section is formed as shown in FIG.

When exposed and developed without using such a diffusion plate,
In general, side etching proceeds on the photosensitive layer 4 ', and the photosensitive layer 4'has an inverted trapezoidal shape as shown in FIG. 3 (a). When the cured photosensitive layer 4'has such a shape, when the substrate 6 is plated to form a conductive circuit 5'and the conductive circuit 5'is transferred to the insulating substrate 2, it is shown in FIG. As can be seen, the cross-sectional shape of the conductive circuit 5'is an inverted trapezoid. Such a conductive circuit 5'has a small contact area with the substrate 2 and, unlike the conductive circuit 5 shown in FIG. The adhesion is weak.

Then, the surface of the conductive substrate 6 is electroplated, and the second
As shown in FIG. 3D, the conductive metal is electrodeposited only on the conductive metal exposed portion of the substrate 6 to form the conductive circuit 5.
After forming the circuit 5, an insulating substrate such as an insulating substrate (or a prepreg impregnated with a thermosetting resin) previously coated with the adhesive 3 is formed on this surface as shown in FIG. The material 2'is brought into close contact. When this is heated and pressed, the cured photosensitive layer 4a and the conductive circuit 5 are transferred to the insulating substrate 2. Then, when the conductive substrate 6 is peeled off, the printed wiring board 1 as shown in FIG.

Next, examples will be described together with comparative examples.

(Example) A DPR (trade name) manufactured by Asahi Kaken Co., Ltd. as a liquid solder resist was applied on a 2.0 mm thick aluminum plate by a roll coater method to form a photosensitive layer having a thickness of 30 μm. A negative film having a circuit pattern including a 1.5 mm square pad shape was adhered to this surface, and a 1 mm-thick polishing glass (# 200), which is a diffusion plate, was placed on the surface and exposed to ultraviolet light. At this time, a 500 mJ / cm ² ultra high pressure mercury lamp was used as a light source. Then, the unexposed portion was removed using a developing solution. The cross-sectional shape of the relief image obtained at this time was a trapezoid in which the angle between the side surface of the relief and the aluminum substrate was 70 °. Then, electroplating was carried out in a copper pyrophosphate solution under the condition of 2.5 A / 100 cm ² to obtain a copper plating pad having almost the same height as the relief image. Eight glass epoxy prepregs were overlapped with each other so as to face the plated surface on the aluminum substrate and press-molded to bond them together. The press molding at that time was carried out by applying a pressure of 60 kg / cm ^{2 at} a temperature of 170 ° C. for 60 minutes. Then, the aluminum plate was peeled and removed from this laminate.

(Comparative Example) A glass epoxy printed wiring board on which a copper plating pad was formed was obtained in the same manner as in Example except that ultraviolet exposure was performed on the surface of the photosensitive layer without using a diffusion plate. The cross-sectional shape of the relief image obtained in this process was an inverted trapezoid in which the angle between the relief side surface and the aluminum substrate was 85 °.

The adhesion of the conductive circuit to the substrate was measured for the above examples and comparative examples. The results are shown in Table 1. The adhesion was measured by soldering an aluminum wire (1 mm in diameter) to the copper-plated pad and pulling it vertically.

[Effects of the Invention] In the method for manufacturing a printed wiring board according to the present invention, a diffusion plate is used during ultraviolet exposure to form a conductive circuit having an inverted trapezoidal cross section and a narrow width, and this is transferred onto an insulating substrate. A printed wiring board having a conductive circuit firmly locked in the insulating resin layer can be easily obtained. Therefore,
According to the present invention, it is possible to increase the density of circuit patterns and easily realize a highly reliable printed wiring board. Therefore, it is possible to realize a printed wiring board with high reliability even when patterned with high density.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an embedded printed wiring board according to the present invention, and FIGS. 2 (a) to (f) are sectional views showing an example of a method for producing an embedded printed wiring board according to the present invention. FIGS. 3A and 3B are explanatory views of the conductive circuit formed when exposure is performed without using the diffusion plate. 1 ... Embedded printed wiring board, 5 ... Conductive circuit

Claims (1)

[Claims] 1. A step of forming a photosensitive resin layer on the surface of a conductive substrate, a step of bringing a negative film and a diffusion plate into close contact with the photosensitive resin layer, and the photosensitive resin through the diffusion plate and the negative film. A step of subjecting the layer to ultraviolet exposure to photo-curing, and removing an unexposed portion of the photosensitive resin layer to remove a trapezoidal cross section on the surface of the conductive substrate, the width of which becomes narrower toward the conductive substrate. Forming a photosensitive cured insulating resin layer having a portion, and filling the removed portion with a conductive metal to form a conductive circuit having an inverted trapezoidal cross section whose width becomes narrower toward the conductive substrate. And a step of adhering an insulating substrate to the surface of the insulating resin layer on which the conductive circuit is formed, and transferring the conductive circuit and the insulating resin layer onto the insulating substrate. Preparation of embedded printed wiring board comprising the steps of separating the conductive substrate from the insulating resin layer.