JPH06132630A - Manufacture of flexible circuit board - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a flexible circuit board having excellent economy by conducting all circuit conductor layers between layers in a high density flexible circuit board having both sides or a multilayer structure used for a wide electronic apparatus to be mutually connected, enhancing reliability of connecting interlayer circuit conductor layers and a density of circuits and simplifying manufacturing steps. CONSTITUTION:One main surface of a metal foil 6 is covered with an ultraviolet ray curable flexible insulating resin film 7, viaholes 8 are simultaneously formed at necessary positions by an optically processing method, a conductive metal layer 9 made of metallic copper is formed on the surface of the film 7, then the foil 6 and the layer 9 to be unnecessary are melted to be removed by a photoetching method, etc., thereby forming necessary circuit conductor layers on front and rear surfaces of the film 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a fusible wiring board used in a wide variety of electronic devices.

[0002]

2. Description of the Related Art In recent years, as the need for smaller and lighter electronic devices and higher performance has increased, the demand for full-flexible wiring boards for higher density has increased remarkably.

A conventional high-density flexible wiring board is manufactured by various methods. As a typical manufacturing method thereof, a manufacturing process of a double-sided flexible wiring board is shown in FIG.
It shows in (a)-(e).

In FIG. 3, 1 is a flexible insulating film, 2 is a metal copper foil, 3 is a through hole, 4 is a conductive metal layer (circuit conductor layer), and 5 is an etching resist layer.

The double-sided flexible wiring board having the above-described structure generally has a heat-resistant flexible insulating film 1 made of polyimide resin as shown in FIG. Using a so-called copper-clad film material adhered to the above, first through holes 3 are formed at the required positions as shown in FIG. 3 (b), and then electroless copper plating is performed as shown in FIG. 3 (c). And electro copper plating are used together to form a conductive metal layer 4 made of metallic copper on the entire surface of the metallic copper foil 2 including the through holes 3, and as shown in FIG. 3D, a screen printing method, a photo method, or the like. The conductive metal layer 4 is covered with a resist layer 5 having an etching resistance on the front surface and the back surface of the conductive metal layer 4, and then, the resist layer is immersed in an etching solution composed of ferric chloride solution. Exposed 5 uncoated Conductive metal layer 4 was dissolved and removed, FIG. 3
As shown in (e), by forming a wiring circuit conductor layer 4 of necessary conductive metal layers on both front and back surfaces of the flexible insulating film 1 and electrically interconnecting the circuit conductor layers 4 by the through holes 3. It was made.

On the other hand, in order to form a multilayer flexible wiring board, a plurality of flexible wiring boards in which a required circuit conductor layer is formed of copper foil on at least one main surface of an insulating film having flexibility. Is laminated and integrated by a heat roll press with an adhesive sheet sandwiched therebetween, a through hole is formed at a predetermined position, and thereafter, the steps shown in FIGS. 3 (b) to 3 (e) are performed.

[0007]

However, the double-sided and multi-layered high-density flexible wiring board according to the conventional example has a single-layered or multi-layered circuit conductor layer formed on both sides of the flexible insulating film. The through holes are connected by performing through-hole plating, and such a through-hole connection has a problem of poor reliability of interlayer connection of a multilayer circuit, and a through hole exposed on the surface. Since the occupied area is large, the degree of freedom in circuit design is restricted, and the capacity of wiring patterns per unit area is reduced, which makes it difficult to increase the circuit density.

On the other hand, in the conventional example, not only the manufacturing equipment becomes large-scaled, but especially in the hole drilling process, one hole is usually drilled by using a numerically controlled drill. However, there is a problem in that the man-hours are increased and the economy is lacking.

The present invention solves the problems of the conventional example, and provides a method for manufacturing a double-sided or multi-layered high-density fusible wiring board which is excellent in economy by increasing the circuit density and simplifying the manufacturing process. The purpose is to do.

[0010]

In order to solve this problem, a fusible wiring board according to the present invention covers at least one principal surface of a metal foil with a flexible insulating resin film, After removing a part of the film to form a via hole so that a part of the metal foil is exposed, and after providing a conductive metal layer on the insulating resin layer including the via hole, a metal foil layer which is unnecessary And the conductive metal layer are dissolved and removed to form a desired wiring circuit conductor layer on the front and back surfaces of the flexible insulating resin film, and the above-mentioned flexibility on both front and back surfaces using this double-sided flexible wiring board. Insulating resin layers and circuit conductor layers made of conductive metal are alternately formed to form a multi-layer wiring.

[0011]

As a result, a double-sided or multi-layered flexible wiring board in which the interlayer circuit conductor layers are connected by a blind through-hole which does not rely on a through-hole is constructed, so that the circuit density is increased and By eliminating the process of drilling through holes, a high-density flexible wiring board that is economical and has a simplified manufacturing process can be realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a flexible wiring board according to the present invention will be described below with reference to the drawings.

FIGS. 1A to 1E are process sectional views for explaining a manufacturing process of a double-sided flexible wiring board in the first embodiment of the present invention.

In FIG. 1, 6 is a metal foil (circuit conductor layer), 7 is a flexible insulating resin film, 8 is a via hole, 9 is a conductive metal layer (circuit conductor layer), and 10 is an etching resistant resist layer. is there.

The manufacturing process of the double-sided flexible wiring board having the above structure will be described in detail below.

In this embodiment, first, as shown in FIG. 1A, an electrolytic or rolled copper foil having an arbitrary thickness is used as the metal foil 6, and one surface of these metal copper foils 6 is subjected to an oxidation treatment or the like. The surface is densely roughened, and the insulating resin 7 having flexibility is applied to the entire surface thereof, and the metal copper foil 6 on the opposite side is provided at a predetermined position of the insulating resin film 7 as shown in FIG. 1B.
A fine hole having an arbitrary diameter was opened so that a part of the via hole was exposed to form a via hole 8.

In this case, as the insulating resin material forming the flexible insulating resin film 7, not only the coating film has excellent flexibility, but also the heat resistance, the electrical insulation characteristic, and the chemical resistance. It is desirable that it has excellent properties such as properties, and that it has the ability to easily remove a part of the coating film to easily form a via hole.

In this embodiment, an ultraviolet curable epoxy resin is used as an insulating resin material which can satisfy such characteristics.

As a method of forming the via hole 8 using this ultraviolet-curable epoxy resin, a photomask is designed so that the via can be opened at a predetermined position and light is not partially transmitted. This mask is brought into close contact with the dried flexible insulating resin film 7 and irradiated with ultraviolet rays, and the insulating resin film 7 in the unexposed portion (via diameter) is dissolved and removed by solvent development to remove the via hole 8. Formed.

Then, as shown in FIG. 1C, a conductive metal made of metallic copper is used on the surface of the flexible insulating resin film 7 having the via holes 8 opened by electroless copper plating or electrolytic copper plating. Layer 9 was formed.

In this case, in order to form the conductive metal film 8 having excellent adhesion on the surface of the flexible insulating resin film 7, the surface of the insulating resin film 7 is mechanically polished by sandblasting or the like in this embodiment. The surface of the resin was roughened by a chemical method in which a part of the surface layer of the resin was finely etched by immersing it in a potassium permanganate solution.

As a method for forming the conductive metal layer 9 on the surface layer of the roughened insulating resin film 7, first, the conductive metal layer 9 is first dipped in a hydrochloric acid acidic solution of stannous chloride and palladium chloride, and then fine particles of palladium metal. After the nuclei are uniformly adsorbed on the roughened insulating resin layer, they are immersed in an electroless copper plating solution consisting of an alkaline solution of a copper complex salt and formalin to thinly coat the metal copper (1 μm or less), and the metal copper foil 6 After masking the entire surface of the above, electrolytic copper plating was performed in a copper sulfate bath to form a conductive metal layer 9 having a thickness approximately the same as that of the metal copper foil 6 only on the insulating resin film 7.

Then, as shown in FIG. 1 (d), the surface of the metal foil 6 made of metallic copper and the conductive metal layer 9 is made to have a desired wiring circuit diagram shape by a screen printing method or a photo method so as to have etching resistance. The resist 10 is covered, and then an unnecessary conductive metal layer 9 exposed by performing an etching process is dissolved and removed. As shown in FIG. 3E, metal is formed on the front and back surfaces of the insulating resin film 7 having flexibility. A double-sided wiring board having required circuit conductor layers 6 and 9 made of copper was produced.

In the double-sided flexible wiring board obtained by the above method, the wiring circuit conductor layers 6 and 9 provided on both front and back surfaces of the flexible insulating resin film 7 are provided on the insulating resin film 7 instead of the through holes. Since they are electrically connected to each other through the via hole 8, the reliability of interlayer connection by surface connection is improved, and a double-sided wiring board without through holes is obtained, so that the degree of freedom in circuit design is improved. As a result, the density of the circuit can be increased, and the via holes having a minute diameter can be collectively formed by light processing, so that the manufacturing process can be simplified.

In this manufacturing method, as the metal foil 6 other than the metal copper foil, for example, a copper-zinc alloy foil, an iron-nickel alloy foil, or a tin-nickel alloy foil can be used. A flexible double-sided wiring board having a circuit conductor layer made of a dissimilar metal composed of alloy foil and metallic copper was prepared.

As described above, the flexible wiring board having a circuit made of different kinds of metals can be used as a flexible wiring board integrated with a lead terminal capable of directly bonding the semiconductor IC chip by utilizing the rigidity of the alloy foil. There is something.

Next, a method of manufacturing a multilayer flexible wiring board will be described as a second embodiment of the present invention.

2 (a) to 2 (d) are sectional views showing a manufacturing process of a flexible wiring board having a multilayer structure in the second embodiment of the present invention.

In FIG. 2, 6 to 9 show the same structure as in FIG. 1, 11a and 11b are flexible insulating resin layers between layers, and 12a and 12b are via holes provided in the interlayer insulating resin layers. Reference numerals 13a and 13b are conductive metal layers (outermost circuit conductor layers) provided on the interlayer insulating resin layer.

With respect to the multilayer flexible wiring board having the above structure, the details of the embodiment of the manufacturing method will be described below.

In this embodiment, the double-sided flexible wiring board obtained in the first embodiment described above is used, and first, as shown in FIG. 2 (a), a metal foil 6 and a conductive metal layer 9 are formed on the entire front and back surfaces thereof. The insulating resin 11a, 11b having flexibility is used so as to completely insulate the formed circuit conductor layer.
The insulating resin layer is coated to a desired thickness by a ten coat method, a screen printing method, a roller coat method or the like, and then, as shown in FIG. 2 (b). Circuit conductor layer 6 as a lower layer at a predetermined position of 11a, 11b
And fine holes, that is, via holes 12a and 12b, are formed so that parts of Nos. 9 and 9 are exposed.

In this case, as the interlayer insulating resins 11a and 11b, the same ultraviolet curable flexible resin as that used in the first embodiment is used, and the via holes 12a and 12b are also collectively formed by the light processing method. .

Then, as shown in FIG. 2 (c), the insulating resin films 11a, 11 having the via holes 12a, 12b are formed.
The surface of b is finely roughened by the same method as in Example 1, and electroconductive copper plating and electrolytic copper plating are used together to form conductive metal layers 13a and 13b made of metallic copper.
The required circuit conductor layers 13a and 13b are formed by dissolving and removing the unnecessary conductive metal layers by a known method such as a photo egg method, and the circuit conductor layers 6 and 9 between the layers are formed.
13a and 13b are replaced by insulating resin films 7, 11a and 11 respectively.
A multilayer flexible wiring board was produced in which the via holes 8, 12a, 12b provided in b were electrically connected to each other and electrically connected to each other.

In the multilayer flexible wiring board obtained by the above method, the circuit conductor layers between layers are interconnected by via holes provided in all insulating resin films between layers, not through holes. Thus, a multi-layer flexible wiring board without through holes and having many advantages can be obtained.

[0035]

As is apparent from the above description, in the high-density flexible wiring board having the double-sided or multi-layer structure obtained by the present invention, the connection of the circuit conductor layers between the layers is conducted through the through holes as in the conventional example. Unlike the so-called through-hole connection, the via-holes provided in the flexible insulating resin film between layers are interconnected by a so-called blind through-hole, which connects the via holes.

Therefore, a double-sided or multi-layered flexible wiring board with through-hole connection in the prior art causes corner cracks in through-hole connection due to thermal shock, which is a problem with multilayer wiring, and multi-layers due to smear generated by drilling. It is possible to obtain the effect that the reliability of the connection between the interlayer circuit conductor layers is significantly improved by eliminating any defective interlayer connection of the circuit.

On the other hand, in the present invention, the surface layer can be effectively utilized due to the structure in which the through hole is not exposed at all on the surface, so that the degree of freedom in circuit design is improved and the wiring accommodability per unit area is increased. Accordingly, the effect of dramatically increasing the circuit density can be obtained.

Further, in the present invention, since the via processing for connection is collectively formed by the light processing, the working time in the manufacturing process can be greatly shortened and the manufacturing cost can be reduced. I was able to.

[Brief description of drawings]

FIG. 1 is a sectional view of a manufacturing process of a flexible wiring board having a double-sided structure for explaining a first embodiment of the present invention.

FIG. 2 is a sectional view of a manufacturing process of a flexible wiring board having a multilayer structure for explaining a second embodiment of the present invention.

FIG. 3 is a sectional view of a manufacturing process of a conventional double-sided flexible wiring board.

[Explanation of symbols]

6 Metal Foil (Circuit Conductor Layer) 7 Flexible Insulating Resin Film 8 Via Hole 9 Conductive Metal Layer (Circuit Conductor Layer) 10 Etching Resistant Layer 11a, 11b Interlayer Insulating Resin Film 12a, 12b Interlayer Insulating Resin Film Provided via holes 13a, 13b Circuit conductor layer formed on insulating resin film between layers

Claims (4)

[Claims] 1. A via-hole in which at least one main surface of a metal foil is coated with a flexible insulating resin and a part of the insulating resin layer film is removed to expose a part of the metal foil. After forming a hole and providing a conductive metal layer on the insulating resin film including the via hole, the unnecessary metal foil and the conductive metal layer are dissolved and removed to obtain desired ones on both sides of the insulating resin film. A method for manufacturing a flexible wiring board provided with a circuit conductor layer. 2. The double-sided flexible wiring board according to claim 1 is used to cover the front and back both sides with an insulating resin having flexibility, and one of the circuit conductor layers as a lower layer is formed at a required position. A via hole is formed so that the portion is exposed, a desired circuit conductor layer is provided on the insulating resin layer to form a multilayer wiring, and the via hole provided on the insulating resin layer is electrically connected to the interlayer circuit conductor layer. Method for manufacturing interconnected flexible wiring boards. 3. The method of manufacturing a flexible wiring board according to claim 1, wherein the metal foil is made of a material different from that of the conductive metal layer formed on the surface of the insulating resin film. 4. The method for manufacturing a flexible wiring board according to claim 1, wherein an ultraviolet curable resin is used as the flexible insulating resin film.