JPH10126043A - Three-layer adhesive film and printed wiring board using the same - Google Patents

Abstract

(57) [Problem] To manufacture a rigid-flex printed wiring board provided with an IVH with good yield and at low cost. A three-layer adhesive film is laminated on both sides of a base film on which conductive circuits are formed. In the rigid part, a rigid plate 31 provided with an IVH 31a is laminated on the upper surface of the three-layer adhesive film 10 laminated on the conductor circuit 21. Similarly, a rigid plate 32 provided with 32a is laminated on the lower surface of the three-layer adhesive film 10 laminated on the conductor circuit 22. At the time of press working, the first adhesive layer 12 of the three-layer adhesive film 10 adheres to the base film 20 and the second adhesive layer 1
3 flows into the IVH 31a and the IVH 32a and hardens. The three-layer adhesive film 10 is an adhesive member for bonding the upper and lower layers in the rigid part and is used as a coverlay in the flex part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive film mainly used for rigid-flex printed wiring boards.

[0002]

2. Description of the Related Art Conventionally, a sheet such as a coverlay film is attached to a flex portion of a rigid-flex printed wiring board through an adhesive such as acrylic or epoxy.
It is laminated on a base film having conductor circuits formed on both sides, and a coverlay for insulating and protecting the conductor layers is formed. That is, the cover lay has a two-layer structure of a sheet such as a cover lay film and an adhesive layer.

However, when manufacturing a printed wiring board using such a coverlay, an adhesive layer is laminated on a polyimide sheet and pressed to form a coverlay.
Since the coverlay, prepreg, sheet with through-holes, etc. must be laminated and pressed again on a base film with conductor circuits formed on both sides, the pressing process is required twice, which increases the manufacturing cost. Had become.

Further, since the prepreg is used, a blackening treatment for increasing the degree of adhesion between the prepreg and the inner copper foil layer and a haloless treatment (oxidation) for removing the effect of a halo phenomenon caused by the blackening treatment. Reduction treatment), and these treatments also increase the production cost.

Further, at the time of the second batch laminating press, the prepreg is filled in the through holes to form IVH. When a through-hole is formed through this laminating step, a positional shift occurs at a connection portion between layers, resulting in a decrease in yield.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and when used as a coverlay, manufactures a rigid-flex printed wiring board having an IVH with good yield and at low cost. It is intended to provide an adhesive film that can be used.

[0007]

The three-layer adhesive film according to the present invention comprises a polyimide resin film as a base and a semi-cured polyimide resin adhesive applied to both surfaces thereof to form first and second adhesive films. The second adhesive layer is formed.

A rigid-flex printed wiring board according to the present invention is characterized in that the three-layer adhesive film according to claim 1 is used as a coverlay.

Preferably, the first adhesive layer is in close contact with the base film having the conductor circuit formed on the surface, and the second adhesive layer is a layer having a through hole for an IVH (interstitial via hole). It is used as a coverlay of a printed wiring board by being laminated so as to be in close contact.

[0010] Preferably, the through hole is filled with a part of the second adhesive layer.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of the three-layer adhesive film according to the present embodiment. 3 layer adhesive film 10 is 3
It has a layered structure. That is, an adhesive made of a polyimide-based resin is applied to the upper surface of the base film 11 made of a polyimide-based resin to form a first adhesive layer 12. Similarly, an adhesive made of a polyimide resin is applied to the lower surface to form a second adhesive layer 13. The first adhesive layer 12 and the second adhesive layer 13 are not in a single sheet but in a semi-cured state. The thickness of the first and second adhesive layers is variable, and it is sufficient that the first and second adhesive layers have a thickness sufficient to fill and adhere through holes as described later. Also,
The resin compositions of the base film 11 and the first and second adhesive layers are the same. When such a three-layer adhesive film is laminated and pressed between a base film and another printed wiring board in a rigid-flex printed wiring board, the first adhesive layer 12 and the second adhesive layer 13 are cured,
It can be used as a coverlay. A rigid-flex printed wiring board using a three-layer adhesive film as a coverlay and a manufacturing process thereof will be described below.

FIG. 2 is a sectional view showing a layer structure of a rigid-flex printed wiring board using the three-layer adhesive film of this embodiment as a coverlay. Conductive circuits 21 and 22 are formed on both sides of the base film 20.
The three-layer adhesive film 10 is laminated on the surface of the base film 20 on which the conductive circuit 21 is formed. Similarly, the three-layer adhesive film 10 is also laminated on the surface of the base film 20 on which the conductive circuit 22 is formed.

In the rigid part, an IVH 31a is provided on the upper surface of the three-layer adhesive film 10 laminated on the conductor circuit 21.
The rigid plate 31 provided with is laminated. Similarly, a rigid plate 32 provided with 32a is laminated on the lower surface of the three-layer adhesive film 10 laminated on the conductor circuit 22. The second adhesive layer 13 of the three-layer adhesive film 10 flows into the IVHs 31a and 32a and hardens during lamination pressing. Thereby, the insides of the IVHs 31a and 32a are filled with a part of the second adhesive layer 13. The upper surface of the rigid plate 31 is coated with a solder resist 41 to insulate the IVH 31a from other IVHs. Further, mounting pads 40 for mounting electronic components are formed on the IVH 31a. Similarly, the lower surface of the rigid plate 32 is coated with a solder resist 42, and a pad 43 is formed on the IVH 32a. Further, a through hole 51 penetrating each layer is provided in another portion of the rigid portion, and the through hole 51 is plated with copper. On the other hand, in the flex portion, the second adhesive layer 13 of the three-layer adhesive film 10 is the outermost layer, that is, the coverlay. As described above, the three-layer adhesive film 10 is an adhesive member for bonding the upper and lower layers in the rigid part, and is used as a coverlay in the flex part.

First adhesive layer 12 of three-layer adhesive film 10
The rigid plate 31 is disposed on the upper surface of the base film 20 with the three-layer adhesive film 10 interposed therebetween so that the base plate 20 adheres to the base film 20 and the second adhesive layer 13 adheres to the rigid plate 31. Similarly, on the lower surface of the base film 20, the first adhesive layer 12 of the three-layer adhesive film 10 is
0 so that the second adhesive layer 13 is in close contact with the rigid board 32 via the three-layer adhesive film 10.
2 is arranged. Further, the rigid plate 3 is positioned such that the position of the opening of the rigid plate 31 and the position of the opening of the rigid plate 32 match.
1, 32 are provided.

As described above, the base film 20 and the rigid plates 31 and 32 are provided and laminated and pressed. At this time, the second adhesive layer 13 is provided with the plated through holes 31a and 32a.
The second adhesive layer 13 flows into the plated through holes 31a and 32a because the second adhesive layer 13 has a thickness sufficient to fill a. Next, a hole constituting the through-hole 51 is formed, and copper plating is performed on the front surface. Further, a circuit is formed on the outermost layer to form pads 40 and 43 for mounting electronic components, and the outer layer is coated with solder resists 41 and 42. Thus, a rigid-flex printed wiring board having the layer structure shown in FIG. 2 is obtained.

As described above, if the three-layer adhesive film of the present embodiment is used as a coverlay of a rigid-flex printed wiring board, a single pressing step is required, so that the manufacturing cost can be reduced.

Further, since no prepreg is used for the rigid portion, the blackening process and the haloless process are not required, so that the manufacturing process is shortened, and the manufacturing cost is further reduced.

Further, in the three-layer adhesive film of this embodiment, since a semi-cured adhesive is used for the adhesive layer instead of the prepreg, extreme expansion due to heating and pressing in the pressing step can be suppressed. Also, since the resin composition of the base film and the adhesive layer is the same, the thermal expansion coefficient is the same and the thermal shrinkage does not change. Therefore, displacement between the layers of the through-hole connection portion is prevented, and a rigid-flex printed wiring board with a good yield can be obtained.

Furthermore, since the three-layer adhesive film of this embodiment uses a polyimide resin film for the base film 11, when used as a coverlay of a rigid-flex printed circuit board, the bending strength at the flex portion is reduced. Can be stronger.

In the present embodiment, the three-layer adhesive film is used as a coverlay of a rigid-flex printed wiring board, but is not limited to this, and may be used for other electronic components.

[0021]

As described above, according to the present invention, the IVH
Rigid-flex printed wiring boards provided with a high yield can be manufactured with good yield and at low cost.

[Brief description of the drawings]

FIG. 1 is a sectional view of a three-layer adhesive film of the present invention.

FIG. 2 is a sectional view of a layer structure of a rigid-flex printed wiring board using a three-layer adhesive film of the present invention as a coverlay.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Three-layer adhesive film 11 Base film 12, 13 Adhesive layer 21, 22 Conductor circuit 31, 32 Rigid board 31a, 32a IVH 40, 43 Pad

Claims (4)

[Claims] 1. A semi-cured polyimide resin adhesive is applied to both surfaces of a polyimide resin film as a base to form first and second adhesive layers. Three-layer adhesive film. 2. A rigid-flex printed wiring board using the three-layer adhesive film according to claim 1 as a coverlay. 3. The first adhesive layer is in close contact with a base film having a conductor circuit formed on the surface, and the second adhesive layer has a through hole for an IVH (interstitial via hole). The printed wiring board according to claim 2, wherein the printed wiring board is used as a coverlay of the printed wiring board by being laminated so as to be in close contact with the layer. 4. The semiconductor device according to claim 3, wherein said through hole is filled with a part of said second adhesive layer.
A printed wiring board according to claim 1.