JP2003133728A - Multi-layer wiring substrate and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high bonding strength, and to prevent the peeling of a boundary face at a high temperature. SOLUTION: This multi-layer wiring substrate is provided with a flexible print circuit 10 where first wiring patterns 21a and 21b are formed on one face of a flexible base film 11, and a plurality of through-holes 13 are formed, insulating resin layers formed on the both faces of the flexible print circuit 10 so as to be integrated through those through-holes, and a second wiring pattern formed on at least one face of the insulating resin layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer wiring board using a flexible printed circuit and a method for manufacturing the same.

[0002]

2. Description of the Related Art Flexible printed circuits (hereinafter referred to as FP
C) is formed by using a thin resin film in order to ensure flexibility. Therefore, in the case of FPC, it is essentially difficult to mount electronic components. However, in recent years, the number of components mounted on the FPC has increased and multilayer wiring of the FPC has been required due to demands for miniaturization, weight reduction, and space saving of various devices.

When electronic components are mounted on the FPC,
A certain degree of rigidity is required at the mounting location. Therefore,
Multiple FPCs with a circuit pattern formed on one side are attached with an adhesive, all layers are punched with a laser at one time, and interlayer connection is performed using through-hole plating, etc., to form multilayer wiring, and rigidity FPCs with a flex-rigid structure are being manufactured. A build-up structure in which a thin insulating layer is formed by further coating or laminating an insulating resin on such a multi-layered FPC having increased rigidity, and then a conductor is sputtered, electroless plated, and copper foil is laminated on the conductor. Sometimes.

In addition to this, a rigid substrate (hereinafter referred to as RPC) is attached to the FPC, or the RPC is attached.
A reinforcing plate having a rigidity equivalent to that of the above is bonded with an adhesive for reinforcement. When FPC and RPC are bonded together, a component structure called flex rigid or rigid flex is used in which the FPC and RPC are electrically connected by through-hole connection, and the component joint surface has strength.

[0005]

However, in the above-mentioned conventional multi-layer wiring board based on FPC, there is a problem that it is difficult to secure the adhesive strength between the respective layers that can be practically used. Particularly, when the temperature is about 240 ° C., which is the component mounting temperature, there is a problem that the bonded portion between the base film of the FPC and the rigid substrate is distorted due to the difference in linear expansion coefficient, and peeling occurs at the bonded portion. .

In order to satisfy the above points, conventionally, a method of increasing the heat resistance of the adhesive and performing interface modification including roughening of the interface between the base film and the adhesive layer has been adopted.
However, even if such interface modification is performed, the multilayer wiring board is eventually formed by joining different materials. Therefore, it is necessary to select the material such as matching the linear expansion coefficient of different layers and matching the elongation when absorbing moisture. Has the problem that there are considerable restrictions.

The present invention has been made in order to solve the above problems, and provides a multilayer wiring board and a method for producing the same, which provides high adhesive strength and does not cause peeling of the interface even at high temperature. The purpose is to provide.

[0008]

A multilayer printed wiring board according to the present invention is a flexible printed board in which a first wiring pattern is formed on at least one surface of a flexible base film and a plurality of through holes are formed. A circuit, an insulating resin layer formed on both surfaces of the flexible printed circuit and integrated through the plurality of through holes, and a second wiring pattern formed on at least one surface of the insulating resin layer. It is characterized by that.

According to the present invention, a plurality of through holes are formed in the flexible printed circuit on which the first wiring pattern is formed, and insulating resin layers integrated by the through holes are formed on both surfaces of the flexible printed circuit. At the same time, a second wiring pattern is further formed on the insulating resin layer to form a multilayer wiring board, so that the flexible printed circuit and the insulating resin layer are insulated from each other by the through holes. By integrating the resin layers, they are firmly fixed to each other, and peeling does not occur even at high temperatures. Further, according to the present invention, the resin is integrated through the through holes, and since the through holes are independent, the characteristics of the flexible printed circuit board as a film are not impaired. Therefore, according to the multilayer wiring board of the present invention, it is possible to maintain a good bending resistance.

In a preferred embodiment of the invention,
A through hole is formed in the insulating resin layer, and the first wiring pattern and the second wiring pattern are electrically connected through the through hole. As a result, the first and second wiring patterns can be interconnected.

In order to further increase the interlayer connection strength, it is desirable that the area of the flexible printed circuit where the through holes are formed is set larger than the area of the portion where the through holes are not formed. In addition, the flexible printed circuit board
It is desirable that the through-holes are formed so that no gap is formed between the through-holes when the inside is viewed parallel to the main surface from all directions of the peripheral edge portion. With such a structure, even if peeling occurs, it does not propagate due to bending of the multilayer wiring board.

When the second wiring pattern is formed on both sides of the insulating resin layer, it is preferable that through holes be formed in the insulating resin layer and that both sides of the insulating resin layer be formed through the through holes. The second wiring patterns are electrically connected to each other. In this case, the through hole that connects the second wiring patterns to each other can be formed in the through hole portion of the insulating resin layer. In this way, the through hole also has a function of ensuring a space for forming the through hole.

The method of manufacturing a multilayer wiring board according to the present invention is
A step of forming a flexible printed circuit by forming a first wiring pattern on at least one surface of a flexible base film; a step of forming a plurality of through holes in the flexible printed circuit; Forming insulating resin layers on both surfaces and integrating the insulating resin layers on both surfaces of the flexible printed circuit through the plurality of through holes; and forming a second wiring pattern on at least one surface of the insulating resin layer. And a step of forming.

As the step of forming the plurality of through holes in the flexible printed circuit, for example, any one step of laser processing, plasma processing, press processing, drill processing and roll processing can be applied. In addition, as the process of forming the insulating resin layers on both sides of the flexible printed circuit and integrating the insulating resin layers on both sides, any one of the insulating resin coating process by roll or spray, the printing process and the vacuum impregnation process is applied. It is possible.

In a preferred aspect of the present invention, the first wiring pattern is formed on the insulating resin layer between the step of forming and integrating the insulating resin layer and the step of forming the second wiring pattern. And a step of forming a through hole connecting the second wiring pattern with each other and a step of forming a conductor inside the through hole.

When the step of forming the second wiring pattern is the step of forming the second wiring pattern on both surfaces of the insulating resin layer, the step of forming and integrating the insulating resin layer is performed. Between the step of forming the second wiring pattern and the step of forming the second wiring pattern, a step of forming a through hole connecting the second wiring patterns on both surfaces of the insulating resin layer, and a conductor inside the through hole. The step of forming may be further provided.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a structure of a multilayer wiring board according to an embodiment of the present invention.
The figure (a) is the AA 'cross section figure of the figure (b), and the figure (b).
Is a plan view with a part cut away. The multilayer wiring board 1 is FP
It is mainly composed of C10. The FPC 10 includes a first wiring pattern 12 made of, for example, copper foil on both sides of a base film 11 made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or the like.
a, 12b are formed, and the first wiring patterns 12a, 12a,
A plurality of through holes 13 are formed in a portion where 12b is not formed. An insulating resin layer 21 is provided on both sides of the FPC 10.
a, 21b are formed, and these insulating resin layers 21a, 21b
b is connected and integrated at the through hole 13. As the insulating resin layer, for example, a polyolefin-based thermoplastic resin (however, a resin that does not soften at a component mounting temperature of 240 ° C.), an epoxy-based thermosetting resin, or the like can be used. On the insulating resin layers 21a and 21b, second wiring patterns 22a and 22 made of, for example, copper foil are provided.
b is formed. The insulating resin layers 21a and 21b have
A through hole 23 is formed at a predetermined position, and a conductor 24 is formed in the through hole 23 by plating, filling with a conductive paste or the like, and the first wiring patterns 12a, 12 are formed.
b and the second wiring patterns 22a and 22b are interlayer-connected, or between the second wiring patterns 22a and 22b are interlayer-connected. In particular, the through hole 23 between the second wiring patterns 22a and 22b is formed in a larger through hole formed in the FPC 10 to reduce the wiring space.

The through-hole 13 is formed in all directions a, b, c, on the peripheral portion of the FPC 10, as shown in FIG.
When viewed from the inside of the FPC 10 in parallel with its main surface, the through holes 13 are formed as densely as possible so that no gap is formed between the through holes 13. In order to obtain a stronger adhesive strength, for example, the total area of the through holes 13 is FPC0.
It is desirable that the through hole 13 be formed so as to have a larger area than other areas. The size of the through hole 13 may be changed depending on the place as illustrated. The through hole 13 in which the through hole 23 is formed is the through hole 23.
It has a larger diameter.

According to the multilayer wiring board 1 thus constructed, the insulating resin layers 21 formed on both sides of the FPC 10 are formed.
Since a and 21b are connected and integrated at the through hole 13 of the FPC 10, the FPC 10 and the insulating resin layer 21
The adhesive strength with a and 21b is remarkably improved, and there is no problem such as peeling of both due to the influence of heat or the like. In addition, FPC10
Since the insulating resin layers 21a and 21b are formed on both surfaces, the planarity of the upper surfaces of the insulating resin layers 21a and 21b is improved, and a base surface suitable for component mounting can be provided.

Next, a method of manufacturing the above-mentioned multilayer wiring board 1 will be described. 2 and 3 are cross-sectional views showing the multilayer wiring board 1 in the order of manufacturing steps. First, FIG. 2 (a)
As shown in (1), the copper-clad laminated FPC 10 in which the copper foils 12 are pasted on both sides of the base film 11 is subjected to processing such as photoetching and stamping to form the desired first wiring patterns 12a and 12b. The same figure (b)].
Then, as shown in FIG. 3C, a plurality of through holes 13 are formed in the FPC 10 at the positions where the first wiring patterns 12a and 12b are not formed. 100 through holes 13
In the case of a fine hole of μm or less, the through hole 13 may be formed by laser, plasma or the like. Also, the through hole 1
If 3 is a larger hole, machine it,
The through hole 13 can be formed by using at least one of press working, drill working, and roll working.

Next, as shown in FIG.
Resin is applied to both surfaces of 0 to form insulating resin layers 21a and 21b. The resin can be applied by a roll method, a spray method, a printing method, a vacuum impregnation method, or the like. In the process of applying the resin, the upper and lower insulating resin layers 21 are formed through the through holes 13.
Since a and 21b are integrated, a sufficient connection strength for the FPC 10 is secured.

Then, as shown in FIG. 3A, through holes 23 are formed in the insulating resin layers 21a and 21b. The through hole 23 can be formed by laser, plasma, press, drill or the like. Next, as shown in FIG. 3B, a conductor 24 is formed in the formed through hole 23 by a method such as plating or filling with a conductive paste. Further, copper foil 22 is formed on both surfaces of the insulating resin layers 21a and 21b.
Are attached by, for example, the RCC (Resin Coated Copper) method or the like, and the second wiring patterns 22a and 22b are formed by photoetching, stamping or the like.

As another method, before the through hole 23 is formed in FIG. 3A, the additive method, R
The second wiring patterns 22a and 22b are formed by the CC method or the like, and then the second wiring patterns 22a and 22b are formed.
The through hole 13 is drilled from the land portion of b to plate copper, or a via hole reaching the connection destination copper foil is formed by laser irradiation using the land portion as a mask, and the copper is plated to form the conductor 24. May be formed.

A plurality of the multilayer wiring boards 1 formed as described above are further laminated with an insulating resin layer interposed therebetween, or an insulating resin layer is further laminated on the insulating resin layers 21a and 21b, and the same is formed thereon. If the wiring pattern is formed by the above method, it is possible to form a multilayer wiring board.

FIG. 4 shows an RPC (rigid printed circuit board) 2a, 2b, on the multilayer wiring board 1 formed as described above.
FIG. 3 is a cross-sectional view showing a printed circuit board having a flex-rigid structure in which 2c and 2d are laminated via an adhesive layer 31. RP
C2a to 2d are composed of a hard substrate 32 made of epoxy or the like and a wiring pattern 33 formed thereon.
Even in this case, the adhesive layer 31 and the insulating resin layers 21a and 21b
When and are partially connected, they are integrated and the joint strength between them is improved. Then, by appropriately connecting the RPCs 2a to 2d and the multilayer wiring board 1 by through holes 34,
It is possible to connect the multilayer wiring board 1 and the RPCs 2a to 2d.

Thus, the multilayer wiring board 1 of this embodiment
As a result of integrating the insulating resin layers 21a and 21b through the through holes 13 formed in the base film 11, the peeling strength is not only the interface strength but also the insulating resin layers 21a and 21b integrated through the through holes 13. The tensile strength is added, and the peel strength is greatly improved. Especially when the thickness of the base film 11 is thin, the effect is great.

The insulating resin layers 21a and 21b formed on both sides of the FPC 10 can be formed symmetrically.
In this case, the thermal characteristics of both can be made uniform. With these, it is possible to form the multilayer wiring board 1 without warping.

Further, the insulating resin layers 21a and 21b are formed until the strength required for the components mounted on the multilayer wiring board 1 is obtained.
It is also possible to stack the layers, and it is possible to realize a multi-layer wiring board that can meet all requirements from thin ones on which small and lightweight components are mounted to thick ones on which heavy components are mounted.

Further, when the arrangement of the through holes 13 is viewed horizontally from the respective faces a, b, c as shown in FIG. 1 (b), the through holes 13 are overlapped at any place. Thirteen
It is possible to prevent the peeling from propagating inside by forming the.

The present invention is not limited to the above embodiment. For example, when an electronic component is mounted on the above-mentioned multilayer wiring board, a more compact electronic circuit can be configured by embedding the FPC including the electronic component in the insulating resin layer.

[0031]

As described above, according to the present invention, a plurality of through holes are formed in the flexible printed circuit on which the first wiring pattern is formed, and the through holes are integrally formed on both sides of the flexible printed circuit. The multilayer printed wiring board is formed by forming the insulating resin layer that has been converted into the insulating resin layer and further forming the second wiring pattern on the insulating resin layer. By integrating the insulating resin layers on both sides of the flexible printed circuit with each other, they are firmly fixed to each other, and peeling does not occur even at high temperature. Further, according to the present invention, the resin is integrated through the through holes, and since the through holes are independent, the characteristics of the flexible printed circuit board as a film are not impaired. Therefore, according to the multilayer wiring board of the present invention, it is possible to maintain the excellent bending resistance.

[Brief description of drawings]

FIG. 1A of a multilayer wiring board according to an embodiment of the present invention
-A 'sectional drawing (a) and a partially cutaway plan view (a).

FIG. 2 is a cross-sectional view showing the same multilayer wiring board in the order of steps.

FIG. 3 is a cross-sectional view showing the same multilayer wiring board in the order of steps.

FIG. 4 is a cross-sectional view of a flex-rigid structure printed circuit board to which the multilayer wiring board is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Multilayer wiring board, 2a-2d ... Rigid printed circuit board (RPC), 10 ... Flexible printed circuit (FP)
C), 11 ... Base film, 12a, 12b ... First wiring pattern, 13 ... Through hole, 21a, 21b ... Insulating resin layer, 22a, 22b ... Second wiring pattern, 23 ... Through hole, 24 ... Conductor , 31 ... Adhesive layer.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05K 3/00 H05K 3/00 N

Claims (11)

[Claims] 1. A flexible printed circuit in which a first wiring pattern is formed on at least one surface of a flexible base film and a plurality of through holes are formed, and the flexible printed circuit is formed on both surfaces of the flexible printed circuit. An insulating resin layer integrated via a plurality of through holes, and a second resin formed on at least one surface of the insulating resin layer.
And a wiring pattern. 2. A through hole is formed in the insulating resin layer, and the first wiring pattern and the second wiring pattern are electrically connected through the through hole. Item 1. The multilayer wiring board according to Item 1. 3. The multilayer wiring board according to claim 1, wherein the area of the flexible printed circuit in which a through hole is formed is set larger than the area of a portion in which the through hole is not formed. . 4. The flexible printed circuit board is formed with the through holes so that no gap is formed between the through holes when the inside is viewed parallel to the main surface from all directions of the peripheral edge portion. Claims 1-3 characterized by the above.
A multilayer wiring board substrate according to any one of 1. 5. The second wiring pattern is formed on both sides of the insulating resin layer, a through hole is formed in the insulating resin layer, and a second hole is formed on both sides of the insulating resin layer through the through hole. 5. The multilayer wiring board according to claim 1, wherein the wiring patterns are electrically connected to each other. 6. The multilayer wiring board according to claim 5, wherein the through hole connecting the second wiring patterns to each other is formed in a through hole portion of the insulating resin layer. 7. A step of forming a first wiring pattern on at least one surface of a flexible base film to form a flexible printed circuit, and a step of forming a plurality of through holes in the flexible printed circuit. Forming insulating resin layers on both sides of the flexible printed circuit and integrating the insulating resin layers on both sides of the flexible printed circuit through the plurality of through holes; and a step of forming an insulating resin layer on at least one surface of the insulating resin layer. And a step of forming a wiring pattern of 2. 8. The first wiring pattern and the second wiring pattern are formed on the insulating resin layer between the step of forming and integrating the insulating resin layer and the step of forming the second wiring pattern. 8. The method for manufacturing a multilayer wiring board according to claim 7, further comprising: a step of forming a through hole connecting with the through hole; and a step of forming a conductor inside the through hole. 9. The step of forming the second wiring pattern is a step of forming the second wiring pattern on both surfaces of the insulating resin layer, and the step of forming and integrating the insulating resin layer, Between the step of forming the second wiring pattern and the step of forming a through hole connecting the second wiring patterns on both surfaces of the insulating resin layer, and forming a conductor inside the through hole. 9. The method for manufacturing a multilayer wiring board according to claim 7, further comprising: 10. The step of forming a plurality of through holes in the flexible printed circuit is one of laser processing, plasma processing, press processing, drill processing and roll processing. 10. The method for manufacturing a multilayer wiring board according to any one of items 9 to 10. 11. The step of forming insulating resin layers on both sides of the flexible printed circuit and integrating the insulating resin layers on both sides is one of an insulating resin applying step by a roll or a spray, a printing step and a vacuum impregnation step. It is one, The manufacturing method of the multilayer wiring board of any one of Claims 7-10.