JPH07135393A - Rigid flexible multilayer printed board - Google Patents

Abstract

PURPOSE:To eliminate the need for arranging accurately at a predetermined position by laminating a rigid circuit board and a flexible intermediate layer circuit sheet integrally through an interlayer adhesive prepreg or a protective layer, i.e., a prepreg, and an adhesive sheet. CONSTITUTION:A groove 7 is made at a predetermined position of a rigid circuit board 3, i.e., a double side copper clad laminate, and a photosensitive film is applied while filling the groove. A copper foil 4 is applied to the opposite side. The rigid circuit boards 3 are then applied to the surface and rear of a flexible intermediate layer circuit sheet 1 through a prepreg or a laminate of the prepreg and an adhesive thermosetting film 2. Since the rigid and flexible sheets are formed substantially in same size, accurate arrangement is not required resulting in the simplification of production process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called rigid / flexible multi-layer printed circuit board which is a multi-layer printed circuit board and is used for mounting components in a higher density and in a narrower space.

[0002]

2. Description of the Related Art A rigid / flexible multi-layer printed circuit board is composed of at least two rigid multi-layer printed circuit boards physically and physically connected by at least one flexible (flexible) circuit sheet. It is a structure. The rigid / flexible multilayer printed board can function as one printed board as a whole, and can be folded at the flexible circuit sheet part. As a result, by folding the rigid (hard) multilayer printed board with components mounted, A multilayer printed board that can be mounted in a narrower space. The exposed portion of the flexible circuit sheet, that is, the front and back of the portion other than the rigid multilayer printed board, is generally protected by a flexible insulating layer.

In the method of manufacturing a rigid-flexible multilayer printed board, there are the following methods for producing a rigid multilayer printed board part and a flexible circuit sheet part. First, a rigid circuit board is provided above and below a predetermined position of a part of the flexible circuit sheet.
This is a method in which a prepreg of substantially the same size as a rigid circuit board is laminated and molded to be integrated, and the rigid circuit board portion is electrically connected to the front and back sides. Secondly, a flexible circuit sheet and a rigid circuit board having substantially the same size as the flexible circuit sheet are made, and both are laminated and molded using a prepreg having substantially the same size as the rigid circuit board, Integrate only the positions that should be rigid multi-layer printed circuit boards, and after processing as multi-layer printed circuit boards, the flexible circuit sheet is finally exposed. For example, a method of forming a groove of a mold by selectively removing the groove may be used.

In the conventional method, the prepreg of
It is necessary to remove only the portion corresponding to the flexible intermediate layer circuit sheet in advance, or to prevent the resin from flowing out to the intermediate layer circuit sheet surface during the pressing process of the prepreg, or the same as the rigid circuit board. There are many problems in the manufacturing process, such as the prepreg cut into a size having to be arranged at a precise position on the flexible intermediate layer circuit sheet.

[0005]

SUMMARY OF THE INVENTION The present invention is intended to solve the drawbacks of the conventional manufacturing method and manufacture a highly reliable and inexpensive rigid flexible multilayer printed board material. In the conventional method, it is necessary to previously remove only a portion corresponding to the flexible intermediate layer circuit sheet in the prepreg, or prevent the resin from flowing out to the intermediate layer circuit sheet surface during the pressing step of the prepreg. However, there are many problems in the manufacturing process, such as the prepreg cut to the same size as the rigid circuit board and having to be placed in the correct position on the flexible intermediate layer circuit sheet. It was

Further, when a film obtained by forming an adhesive layer on a polyimide film is used as the cover layer,
There is a problem that the cover layer of the rigid portion has a large thermal expansion, so that the through hole reliability of the rigid portion is impaired, and delamination is likely to occur during soldering after absorbing moisture. Also,
As an improved method, a method has been proposed in which a cover lay of a polyimide film is adhered only to a portion where the flexible circuit sheet is exposed and is not used on the front and back sides of the flexible circuit sheet formed in the rigid multilayer printed board. However, this improved method has a problem in that the cover lay that has been cut in advance to a size corresponding to the exposed portion of the flexible circuit sheet must be accurately placed at a predetermined position, which makes the manufacturing process complicated. was there.

The present invention is an invention of a method for solving the above problems, in which a flexible intermediate layer circuit sheet is provided with an insulating protective layer on at least the circuit surface of the intermediate layer. In a rigid flexible multilayer printed circuit board in which two or more rigid circuit boards are connected by different layers, it should be part of a flexible intermediate layer circuit sheet and a rigid multilayer circuit of substantially the same size. Rigid circuit boards and / or prepregs for interlayer adhesion, and / or prepregs or adhesive sheets that should serve as insulating protective layers, and / or insulating laminated boards are laminated and then finally placed in positions where flexible circuit sheet parts are to be formed. To remove metal foils and laminates other than existing, flexible interlayer circuit sheets and / or insulating protective layers A multi-layer printed circuit board to be manufactured, in which a groove is formed at least at a boundary between a portion to be integrated as a rigid portion and a portion to be removed, which is located in the flexible circuit sheet portion, of the rigid circuit board located in the outermost layer. A resin film having a releasable surface is formed on at least the surface opposite to the outermost surface of the entire surface of the removed portion that is formed so as to close the groove. The present invention relates to a rigid flexible multilayer printed board in which a circuit board and a flexible intermediate layer circuit sheet have a structure in which they are integrally molded by laminating with a prepreg for interlayer adhesion and / or a prepreg or an adhesive sheet to be a protective layer. .

In the present invention, the flexible intermediate layer circuit sheet means a metal foil-clad plastic film such as copper foil, a glass woven or non-woven fabric-based flexible thermosetting resin impregnated prepreg and a metal foil. A metal foil sheet made by heating and pressing, an organic fiber woven fabric such as polyester fiber, aramid fiber, non-woven fabric and a flexible thermosetting resin impregnated prepreg and a metal foil made by heating and pressing are A tension sheet or a sheet obtained by bonding a metal foil to a thermoplastic resin such as a fluororesin, using a glass woven or non-woven fabric base material as a reinforcing base material, is used. The thickness of the insulating layer is 0.0
3 to 0.20 mm is suitable, and the thickness of the metal foil is 5 to 5.
70 μm is preferable.

Flexible and thermosetting resins include thermosetting resins such as epoxy resins, cyanate resins, polyimide resins, unsaturated polyester resins, polybutadiene resins, and rubbers such as nitrile butadiene rubber, acrylic rubber, epichlorohydrin rubber and the like. A composition obtained by mixing 5 to 40% by weight of a flexible component such as a resin and a thermoplastic resin elastomer is preferable.

The rigid circuit board of the present invention is a known metal-clad glass woven cloth / epoxy resin laminated board, polyimide resin laminated board or the like, and has an insulating layer thickness of 0.05 to 2.00.
mm laminate is preferred, and the metal foil thickness is preferred to be 5 to 70 μm. The metal foil sheet is etched by a known method to form a circuit. When used as the outermost layer, the outermost surface is left as a metal foil and a circuit is formed on the surface to be the inner layer, or a single-sided metal-clad laminate is used. The outermost surface is formed into a circuit after being multilayered.

The insulating protective layer formed on the surface of the flexible intermediate layer circuit sheet is a plastic film with an adhesive such as a photo-curable and / or thermosetting solder resist film and a polyimide film with an adhesive; A prepreg similar to that used for the production of such intermediate layer circuit sheets is exemplified.

The thickness of the insulating protective layer is 0.03 to 0.2.
mm is preferred. At least, a groove is formed in advance in the outermost layer of the rigid circuit board at a boundary between a portion to be integrated and left as a rigid portion and a portion to be removed located in the flexible circuit sheet portion. The groove has a perforation shape or a slit shape, and a small hole having a diameter of 0.5 to 2.0 mm is formed using a known drilling machine so that the distance between the hole walls is 0.3 mm or less, and the groove is almost linear or corrugated. Perforating or forming perforated holes overlap each other,
It does not matter if the hole wall is lost. Alternatively, a slit having a groove width of about 0.5 to 3.0 mm is formed by a known method. There is no particular limitation on the slit width.

At the time of laminating and molding each of the layers using a prepreg, at least a rigid circuit board and a flexible circuit sheet are adhered to each other in order to prevent the resin of the prepreg from melting and flowing into the small holes or slits. A resin film having a releasable surface is formed on the surface of the rigid circuit board which is in contact with the prepreg for adhesion and / or the prepreg or the adhesive sheet to be the protective layer. The resin film is formed on the entire surface of the part to be finally removed so as to close the groove. The edge of the resin film is slightly inserted into the rigid circuit board.
That is, the resin film is formed wider than the edge of the groove by about 1 to 5 mm. The releasable resin film is specifically a film made of a known photo / thermosetting or photocuring resin such as an acrylic epoxy resin having a thickness of 10 to 200 μm known by the name of dry film. A method of thermocompression-bonding the photosensitive resist in a strip shape is preferable.

For example, a groove is formed at a predetermined position on the double-sided copper-clad laminate, and then a photosensitive resist is thermocompression-bonded to one side, and one side is entirely adhered with an adhesive film. The photosensitive film resist is selectively exposed to form a circuit at a position where a rigid circuit board is formed, and a copper foil is left at a position to be removed by an etching process. Again, a photosensitive film-like resist is thermocompression-bonded to the entire surface of the circuit formation surface, and exposed and developed so that the photosensitive film remains on the copper foil surface corresponding to the removed portion including the groove surface. When manufacturing a four-layer rigid flexible multilayer printed circuit board consisting of the outer layer circuit and the flexible circuit sheet front and back, use a single-sided copper clad board, and after forming the groove, remove the copper foil-free surface including the grooved surface. It is exposed and developed so that a photosensitive film is formed on the part.

In addition to the film-like resist, a method of applying a liquid resist by a known curtain coating method and drying it, or a method of cutting a plastic film such as a polyester film with an adhesive into a predetermined size and sticking the same. It can also be taken. The prepreg for interlayer adhesion, which is used to integrally bond a flexible circuit sheet and a rigid circuit board, is a publicly known prepreg in a semi-curable resin state such as a glass cloth base material epoxy resin. 0.0
6 to 0.20 mm is suitable.

The rigid flexible multi-layer board of the present invention is formed by laminating and forming a multi-layer printed board. In the construction, a void is formed in the inner layer located at the boundary to be split, and stress is applied from the outside of the multi-layer printed board. ,easily,
It has a feature that the cured laminated plate located at the boundary can be broken, and the flexible intermediate layer circuit sheet can be removed from the releasable resin film, leaving it at a significantly lower cost than the conventional method. It enables a rigid flexible multilayer printed board.

A specific manufacturing method will be described with reference to the drawings.

[Example 1] A hole diameter of 0.9 mm and a hole wall distance of 0.05 mm at a predetermined position of a double-sided copper-clad laminate to be a rigid circuit board 3.
Grooves were formed. Next, one side of the photosensitive resist is thermocompression-bonded, and the other side is entirely adhered with an adhesive film. The photosensitive resist is selectively exposed to form a circuit at a position where a rigid circuit board is formed, and an etching process is performed so that a copper foil is left at a position corresponding to a removed portion.
Further, a photosensitive resist was thermocompression-bonded to the entire surface on which the circuit was formed, and exposed and developed so that the photosensitive resist remained on the surface including the grooves and remaining as the above-mentioned copper foil, to obtain a rigid circuit board 3.

A plain woven glass cloth having a thickness of 60 μm was impregnated with an epoxy resin composition in which 20% by weight of nitrile butadiene rubber was mixed and dried, and a 35 μm copper foil was laminated on the prepreg to form a laminate (170 ° C., 2 hours). Then, a predetermined circuit is formed by a known etching method, an adhesive thermosetting film is laid on the front and back of a flexible intermediate circuit sheet 1, and a rigid circuit board 3 having grooves is stacked to obtain a thickness. It is sandwiched between 2mm stainless steel plates, 17
Laminate molding was performed at 0 ° C. for 2 hours at 30 kg / cm ² . The integrated multi-layer board had grooves 7 at the positions to be split. The multilayer board having this groove was perforated by a known method, through-hole plated, and surface circuits were formed to obtain a multilayer printed board. Finally, unnecessary rigid portions were removed to obtain a rigid flexible multilayer printed board.

[0019]

[Example 2] The same procedure as in Example 1 was carried out except that the surface-releasing resist was screen-printed on the flexible intermediate layer circuit sheet 1 of Example 1 at a position where the rigid portion was finally removed and then cured.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a layer structure used for manufacturing a rigid-flexible multilayer printed board of the present invention.

FIG. 2 is a cross-sectional view schematically showing a groove portion of an integrated multi-layer plate with emphasis.

FIG. 3 is a perspective view schematically showing a layer structure used for manufacturing the rigid-flexible multilayer printed board of the present invention.

FIG. 4 is a cross-sectional view schematically showing a groove portion of an integrated multi-layer plate with emphasis.

[Explanation of symbols]

 1 Flexible intermediate layer circuit sheet 2 Adhesive thermosetting film for interlayer adhesion 3 Rigid circuit sheet 4 Copper foil 5 Photosensitive film 6 Copper foil circuit 7 Groove 8 Surface release resist

Claims (1)

[Claims] 1. A flexible intermediate layer circuit sheet, and an insulating protective layer formed on at least a circuit surface of the intermediate layer, wherein the flexible layer connects two or more rigid circuit boards. Rigid flexible multilayer printed circuit board of substantially the same size, the flexible intermediate layer circuit sheet and the rigid circuit board to be a part of the rigid multilayer circuit, and / or the prepreg for interlayer adhesion, and / or insulation protection A flexible intermediate layer circuit sheet and / or an insulating protective layer, which is present at a position where a prepreg or an adhesive sheet to be a layer and / or an insulating laminate is finally formed into a flexible circuit sheet portion after being laminated and molded. Other than the above, it is a multilayer printed board made by removing the metal foil and the laminated board, and at least the final position. A groove is formed at a boundary between a portion of the rigid circuit board to be integrated as a rigid portion and a portion to be removed, which is located in the flexible circuit sheet portion,
A resin film having a mold releasable surface is formed on at least a surface opposite to the outermost surface of the entire surface of the removed portion so as to close the groove. Rigid flexible multilayer printed board characterized in that the intermediate circuit sheet has a structure in which a prepreg for interlayer adhesion and / or a prepreg to be a protective layer or an adhesive sheet is laminated and formed into an integrated structure.