JPH0870176A - Manufacture of foldable multilayer circuit board - Google Patents

Abstract

PURPOSE: To obtain a foldable multilayer circuit board having less moisture absorption and less thermal expansion coefficient at low cost by a method wherein a circuit board with a prescribed bored part is provided on one side of a semi-cured thermoset resin on a flexible circuit board, a crosslinked polyolefin sheet having a specified thickness is put on the surface on the outer edges of the circuit board and lamination is performed. CONSTITUTION: A sheet 1 with an internal layer circuit, which is formed of glass-cloth epoxy resin double-sided copper-clad plates 2 with an internal layer formed on one side, glass-cloth base material flexible thermosetting prepregs 3 and a glass-cloth base material flexible thermosetting copper-clad sheet 4, is put and moreover, a crosslinked polyethylene sheet 1 of a thickness of 0.1 to 2.0mm is superposed on the sheet 1. Here, a position, which is finally used as the position of a flexible circuit sheet, is previously bored in the plates 2 using an NC router or the like. Stainless plates are respectively put on the upper and lower surface of the stacked materials, lamination is performed, the sheets 1 are removed and perforation plating is applied to a rigid multilayer circuit board to obtain a flexible multilayer printed board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foldable multilayer circuit board in which two or more rigid circuit boards are connected by a flexible intermediate layer circuit sheet.

[0002]

2. Description of the Related Art A rigid flexible multi-layer circuit board is a flexible part, and is used by being folded, and has come to be widely used as a multi-layer circuit board advantageous for a limited device space. The exposed portion of the flexible circuit sheet, that is, the front and back surfaces of the portion other than the rigid multilayer circuit 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 position that should be a rigid multilayer printed board, make a multilayer printed board, and after processing, finally expose the flexible circuit sheet, so the rigid circuit board covering the surface is in the position where it should be broken For example, a V-shaped groove may be formed by selectively removing it.

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. Also, as a press pad, there was a method of pressing a material with steps using a pad having a release film such as a thin polyester film on both sides of a crosslinked polyolefin sheet, or a method of using a silicone rubber sheet. , Both were expensive. In addition, a method for adhering a flexible intermediate layer circuit sheet of a rigid flexible multilayer circuit board and a polyimide film with an adhesive such as an acrylic type, an epoxy type, or a polyimide type to the cover layer on the circuit surface of the intermediate layer. Was common. In the rigid flexible multilayer circuit board using such a cover layer, the coefficient of thermal expansion in the thickness direction is large and the through hole reliability is poor. It has a drawback that it has a high moisture absorption rate and is likely to cause interlayer swelling during soldering.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of conventional rigid flexible multilayer circuit boards and is highly reliable and inexpensive, and relates to a method of manufacturing a foldable multilayer circuit board. It is a thing.

[0006]

That is, according to the present invention, a flexible intermediate layer sheet and a flexible insulating layer protective layer are adhered to the entire circuit surface of the intermediate layer, and two or more sheets are formed by the flexible layer. In a foldable multi-layer circuit board having a rigid circuit board connected, at least the entire surface of the flexible circuit board on which the circuit is formed is integrated with a thermosetting resin layer and protected. A method of manufacturing a foldable multi-layer circuit board, which is characterized in that However, in order to expose a finally flexible portion, a special device for removing an unnecessary rigid plate and a processing step are required.

The present invention is an invention of a method for solving the above problems, in which all of the copper-clad insulating material forming a circuit is composed of a glass cloth base thermosetting resin copper-clad laminate. And at least two rigid multilayer circuit boards,
Integrated with at least one flexible circuit board,
In a foldable multi-layer circuit board in a connected form, at least the entire surface of the flexible circuit board on which the circuit is formed is integrated with a thermosetting resin and protected, In the production of a foldable multilayer circuit board, a flexible circuit board, at least over the entire surface where the circuit is formed, after a semi-cured thermosetting resin sheet or a semi-cured prepreg is overlaid,
A circuit board for forming a rigid circuit board, and / or a copper-clad laminate, in which a portion corresponding to the position of the flexible circuit board to be exposed is hollowed out on one surface of the semi-cured thermosetting resin. , And / or laminates, and / or prepregs are arranged on the outer surface of which the thickness is 0.
A 1 mm to 2.0 mm cross-linked polyolefin sheet is placed and laminated by heating and pressing. The cross-linked polyolefin sheet used at this time is softened and deformed during lamination molding and becomes a convex shape that follows the hollowed portion, and pressure is applied to the non-planar portion, that is, the hollowed portion. effective. Further, the polyolefin sheet which is used for lamination molding and is deformed into a convex shape can be repeatedly used. The present invention relates to a method for producing a foldable multilayer circuit board, which comprises forming a multilayer circuit board after finally removing the crosslinked polyolefin sheet.

In the present invention, the flexible thermosetting resin means epoxy resin, cyanate resin, polyimide resin,
Examples thereof include unsaturated polyester resins, polybutadiene resins, and the like. Further, those obtained by imparting flexibility to these thermosetting resins are preferable. As a method of imparting flexibility, a method of selecting a thermosetting resin having flexibility in its molecular structure (epoxy resin having a large epoxy equivalent, epoxy dimer acid, etc.) and flexibility are used. Examples of the method include adding a property imparting component (rubber-based resin such as acrylonitrile butadiene rubber, acrylic rubber, epichlorohydrin rubber, thermoplastic elastomer, etc.). The flexibility-imparting component may be one that reacts with the thermosetting resin to bond with it or may be simply mixed.

In the present invention, the glass fiber cloth refers to a glass cloth used for a known copper clad laminate or the like, and is preferably a cloth having a thickness of 0.03 mm to 0.2 mm.

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.
A 70 μm rolling foil is preferred.

In the present invention, the rigid circuit board means a copper-clad laminate such as a known glass cloth base material epoxy resin, polyimide resin, cyanate resin, etc., a hard double-sided board or a multilayered printed board using a laminate, a prepreg, etc. as appropriate. Say

The crosslinked polyolefin in the present invention means low density polyethylene, linear low density polyethylene, high density polyethylene, medium density polyethylene and low molecular weight polypropylene produced by a known method by chemical crosslinking with organic peroxide. Method or the method of radiation by radiation energy is used. Further, it is a water-crosslinking type polyolefin that has an active silane group in the side chain of polyolefin and is produced by contacting with water. Examples of the organic peroxide used for crosslinking include benzoyl peroxide, dicumyl peroxide, perhexane, lauroyl peroxide, capryl peroxide, acetyl peroxide, parachlorobenzoyl peroxide, and the like. The organic peroxide can be used and is not particularly limited. The organic peroxide is preferably 0.1% by weight or more and 10% by weight or less, and when it is 0.1% by weight or less, crosslinking is insufficient. If it exceeds 10% by weight, there is adhesiveness and it becomes difficult to release it. The thickness of the crosslinked polyolefin sheet is preferably 0.1 mm to 2.0 mm.

[0013]

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

Example 1 In FIG. 1, a glass cloth epoxy resin double-sided copper clad plate 2 (thickness 0.6 mm, copper foil, inner layer 35 μm, outer layer 18 μm) having an inner layer formed on one side, and a glass cloth substrate flexible heat Inner layer circuit is formed with curable prepreg 3 (thickness 0.08 mm), glass cloth base material flexible thermosetting resin copper clad sheet 4 (thickness 0.08 mm, glass cloth # 1080, copper foil, 35 μm both sides) A supporting sheet was placed, and a cross-linked polyethylene sheet 1 (thickness 1 mm) was further laminated. As the flexible thermosetting resin, a cyanate resin composition obtained by mixing 20% by weight of nitrile butadiene rubber with a plain woven glass cloth having a thickness of 60 μm was used. The glass cloth epoxy resin double-sided copper clad board of No. 2 is hollowed out in advance by using an NC router or the like at a position where it finally becomes a flexible circuit sheet. The cross-linked polyethylene sheet of No. 1 was prepared by using low-density polyethylene and 1% by weight of dicumyl peroxide as an organic peroxide of a cross-linking agent at 130 ° C. and 30%.
A sheet that was kneaded for 2 seconds and crosslinked at 170 ° C. for 5 minutes was used. A stainless plate having a thickness of 2 mm was placed on the upper and lower surfaces of the stacked materials, and laminated molding was performed at 180 ° C. and 40 kg / cm ² for 2 hours.

Example 2 Example 1 was repeated except that the cyanate resin flexible thermosetting film prepreg was used in the glass cloth substrate flexible thermosetting prepreg 3 in Example 1.
Same as.

Example 3 Example 1 was repeated except that water-crosslinked polyethylene (trade name; LINKRON: XF-800, manufactured by Mitsubishi Yuka Co., Ltd.) was used in the crosslinked polyethylene sheet 1 in Examples 1 and 2. Same as.

[Example 4] The same procedure as in Example 1 was carried out except that crosslinked polypropylene was used in the crosslinked polyethylene sheet 1 in Examples 1 and 2.

[Example 5] Example 1 was repeated except that water-crosslinked polypropylene (trade name; LINKRON: XPF-800H, manufactured by Mitsubishi Petrochemical Co., Ltd.) was used in the crosslinked polyethylene sheet 1 in Examples 1 and 2. Same as above.

FIG. 2 is a cross-sectional perspective view schematically showing an integrated laminated plate after laminating and molding, and a polyolefin sheet having convex portions that are softened and deformed into concave portions. FIG. 3 shows a rigid flexible multilayer printed board in which the polyolefin sheet is removed after lamination molding, and the rigid multilayer circuit board is perforated and plated to form an outer layer circuit. When completed, the rigid multilayer circuit board has the same level of through-hole reliability as the ordinary rigid multilayer circuit board, the level of heat resistance after moisture absorption, and the excellent dimensional stability. It is possible to form circuits with high density. In addition, since the rigid part of the part that will be the flexible layer is hollowed out in advance,
Alternatively, there is no need for a processing step for removing a rigid portion that becomes unnecessary after component mounting and a special device for removing the rigid portion.

Conventionally, the flexible circuit sheet and the insulating protective layer of the rigid flexible multilayer board can only be formed by a plastic film or an adhesive, which makes high density and high reliability impossible, and is economical. There was a defect that it was inferior in sex. In addition, by removing beforehand the rigid portion of the portion that will eventually become the flexible sheet, special measures and processing steps for removing it have been required. INDUSTRIAL APPLICABILITY According to the present invention, it is possible to economically mass-produce a rigid flexible multilayer circuit board having the same level of high density and high reliability as an ordinary rigid multilayer board, that is, a foldable multilayer circuit board, which is highly practical. It is the invention of the method.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional perspective view schematically showing an integrated multilayer plate and a polyolefin sheet which is softened and deformed and has convex portions.

FIG. 3 is a sectional perspective view schematically showing an integrated multilayer printed board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polyolefin sheet 2 Rigid circuit board 3 Flexible thermosetting resin film prepreg 4 Glass cloth base material Flexible thermosetting resin circuit sheet 5 Polyolefin sheet 6 having a convex portion 6 Integrated multi-layer board

Claims (1)

[Claims] 1. A copper-clad insulating material forming a circuit is entirely composed of a glass cloth base thermosetting resin copper-clad laminate, and at least two rigid multilayer circuit boards are made up of at least one. A foldable multi-layer circuit board integrated and connected by a flexible circuit board, at least the entire surface of which the circuit of the flexible circuit board is formed is integrated with a thermosetting resin. In manufacturing a foldable multilayer circuit board having a protected structure, a thermosetting resin sheet in a semi-cured state or a semi-cured resin sheet is formed on at least the entire surface of the flexible circuit board on which the circuit is formed. After stacking the prepregs in the state, a rigid circuit board in which only the portion corresponding to the position of the flexible circuit board to be exposed is hollowed out on one surface of the semi-cured thermosetting resin. Circuit board for construction, and / or copper clad laminate, and / or laminate, and / or
Alternatively, a prepreg is placed and the outer surface thereof has a thickness of 0.1.
Place a cross-linked polyolefin sheet of ~ 2.0 mm,
A method for producing a foldable multilayer circuit board, which comprises laminating and molding by heating and pressing, and finally removing the crosslinked polyolefin sheet, and then forming a multilayer circuit board.