JPH104256A - Flexible printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make feasible of the high density packaging and the enhancement of a circuit reliability by a method wherein a circuit is protected by a photosensi tive cover lay film for the position requiring of the dimensional precision for the cover lay aperture part while the circuit is protected by a bonding cover lay film for the position requiring the mechanical strength. SOLUTION: The circuit in an element packaging part of FPC is protected by a photosensitive cover lay film so as to form a land. The land is formed in high precision for the pattern and configuration of FPC for packaging the element. On the other hand, the parts excluding the FPC elements are bent to be assembled into a product along the broken lines 7 to be covered with a bonding cover lay film to increase the protecting capacity to a copper foil pattern 3. When the parts required of high density and high strength are connected so as to be required of the protection by the cover lays, the sensing cover lay 1 and the bonding cover lay 2 are to be overlapped not to expose the copper foil pattern 3. Through these procedures, the high density and high performance FPC can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a flexible printed circuit (hereinafter referred to as "FPC").

[0002]

2. Description of the Related Art A first method of manufacturing an FPC is to first form a copper-clad plate made by bonding a copper foil to both sides of a base film made of polyimide or the like, open a through-hole, and perform through-hole plating to obtain a desired circuit shape. Etch. In another step, a land shape is punched out of a polyimide film with a mold to form an adhesive coverlay film. Then, an adhesive type cover lay film is manually attached to both sides of the etched copper adhesive plate, and the outer shape of the FPC is formed by punching out a die. After that, an appropriate surface treatment such as gold plating or cream solder printing may be performed on the exposed portion of the copper foil.

[0003] A second method of manufacturing the FPC is to prepare a copper-clad plate that has been completely etched by the same method as the first method. Then, a photosensitive coverlay film made of an acrylic resin or the like is laminated on both surfaces, a necessary portion of the coverlay is exposed, and the remaining coverlay opening is removed to form a land. Then, the outer shape of the FPC is completed by die processing.

[0004]

However, the above-mentioned prior art has the following problems. First, in the case of the sticking type cover lay of the first method, it takes time and effort to stick the cover lay with openings formed by hand,
As a result, costs increase. In addition, an adhesive is used for attaching the adhesive coverlay and the copper adhesive plate. For this reason, the adhesive oozes out from the sticking-type cover lay opening, and the substantial cover lay opening is reduced. In addition, during the above-described process steps, it is inevitable that the pattern of the FPC and the position of the opening of the cover lay deviate from each other in order to attach the adhesive cover lay film having the opening formed to the etched copper plate. Therefore, the opening of the adhesive coverlay must be large enough to allow some adhesive to stick out, and the copper foil pattern of the adhesive coverlay opening needs to be large enough to allow the adhesive slippage of the adhesive coverlay. become. Therefore, a large area is required for the land, which hinders the recent demand for high density mounting.

Further, in the case of the conventional photosensitive coverlay of the second method, sufficient mechanical strength cannot be obtained due to its characteristics. Therefore, the pattern may be cut due to severe bending of the FPC, or the FPC may be deformed (warped) when the element is reflowed, resulting in poor soldering. As described above, the conventional FPC mainly uses two types of cover-lay film and photosensitive cover-lay film, but each has its own advantages and disadvantages. However, there is a dilemma that high-density mounting cannot be achieved if mechanical strength is pursued.

[0006]

In order to solve the above-mentioned problems, in the first embodiment of the present invention, a photosensitive coverlay is provided at a place where dimensional accuracy is required for a coverlay opening such as an element mounting portion. The circuit is protected by a film, and the circuit is protected by a stick-on coverlay film in places where mechanical strength is required, such as a bent part. With this configuration, it is possible to achieve both high density mounting and high reliability of a circuit formed in the FPC.

Next, according to the second embodiment of the present invention, the FPC
The component mounting part is concentrated on one side, the coverlay film on that side is unified with a photosensitive coverlay film, the other side is a circuit that can be folded, and the coverlay film on this side is attached with a cover Ray film. In this way, the manufacturing process of the FPC can be simplified, the manufacturing process can be omitted, and the FPC can be manufactured quickly and inexpensively.

[0008]

【Example】

(Embodiment 1) An embodiment 1 of the present invention will be described with reference to FIG. In the figure, black portions 1a to 1d are portions where the circuit is protected by the photosensitive coverlay, and hatched portions 2a to 2d are portions where the circuit is protected by the sticking type coverlay. Reference numeral 3 denotes a copper foil pattern formed by etching a copper paste plate. Reference numeral 4 denotes a through hole (hereinafter, referred to as TH) that is formed by drilling, plating, and electrically connecting the front and back patterns of the FPC. 5a,
5e is a sensor-integrated IC, 5b and 5c are chip capacitors, and 5d and 5f are optical elements. Reference numeral 6 denotes an overlapping portion between the photosensitive coverlay 1 and the sticking type coverlay 2. The dashed lines 7a to 7r indicate locations where the FPC is bent when the FPC is incorporated into a product.

[0009] The element mounting portion of the FPC is covered with a photosensitive cover lay 1, and the other portions are covered with a sticking type cover lay 2. As shown in FIG.
In the PC, a circuit is protected by a photosensitive coverlay film 1 in an element mounting portion to form a land. For this reason,
The lands can be formed very accurately with respect to the pattern and the outer shape of the FPC, and each element can be mounted with high accuracy. In addition, the required land size is reduced, and the pattern for the land is also reduced. As a result, a dense layout of elements such as the chip capacitors 5b and 5c is possible.

[0010] In addition, the FPC is complicatedly bent along the dashed line 7 at a portion other than the element and is incorporated into a product. Since such a place is covered with the adhesive coverlay, the protection ability against the copper foil pattern 3 is high, and in most cases, the copper foil pattern 3 is not cut and disconnected.

When a portion requiring high density and a portion requiring high strength are continuous and the protection of the coverlay is required, the photosensitive coverlay 1 and the adhesive cover are provided like the overlap portion 6. The rays 2 are designed so as to overlap each other, so that the copper foil pattern 3 thereunder is not exposed in any case due to tolerances. As described above, in the present invention, it is possible to provide a highly accurate and highly reliable FPC by using a photosensitive coverlay film in a place where accuracy is required and a sticky coverlay in a place where strength is required. it can.

(Embodiment 2) FIG. 2 is a cross-sectional view of an FPC on which elements according to Embodiment 2 of the present invention are mounted, and the FP of this embodiment.
A description will be given based on FIG. 3 which is a mounting diagram in which elements are mounted on C. First, FIG. 2 will be described. 21 is an FPC base film made of a polyimide film. 2
2 is an adhesive, 23 is a surface side (element mounting surface side) copper foil, and the copper foil 23 is bonded to the base film 21 by the adhesive 22.
Attached to.

Reference numeral 24 denotes a photosensitive coverlay film,
It is attached to the surface of the FPC by vacuum lamination. 25 is an adhesive, 26 is a back surface copper foil, and is attached to the back surface of the FPC. Reference numeral 27 denotes an adhesive, and reference numeral 28 denotes an adhesive cover lay, which is attached to the FPC to protect the circuit on the back surface. 29 is a chip element, and 30 is solder. A coverlay opening 24a is formed on the surface of the FPC shown in FIG. 2, and a chip element 29 is connected and attached thereto via a solder 30.

Next, FIG. 3 will be described. 31 is a photosensitive coverlay film, 32 is a sticking type coverlay film, 33 is a copper foil pattern, 34 is TH, 35 is an electric element such as a capacitor or a transistor, and 37 is a wavy line. This is a bent portion of the FPC. As can be seen from FIG. 3a (surface view), the surface of the FPC is a mounting portion of the element, and the circuit protection on the surface is unified by a photosensitive coverlay film 31 (corresponding to 24 in FIG. 2). Therefore, a high-density element as shown in FIG. 3 can be mounted. The circuits on the back side are all protected by a stick-on coverlay film 32 (corresponding to 28 in FIG. 2).

As shown in FIG. 3B (back view), since the copper foil pattern 33 of the bent portion 37 is concentrated on the back surface, it is protected by a strong adhesive coverlay film 32, so that it is pressed with a small radius. Even under such severe bending, the copper foil pattern 33 does not break. Furthermore, although the circuit of this FPC is a considerably complicated circuit, the pattern distribution is almost completed on the surface on which the high-density mounting is performed due to the photosensitive coverlay film 31, and the rear surface has a sufficient thickness. The copper foil pattern 33 and the ground pattern having a large area can be patterned, so that the noise generated by this circuit can be reduced, and the received noise is also reduced.

The FPC having such a configuration has the following advantages in addition to the advantages shown in the first embodiment of the present invention. Because one type of coverlay film is integrated on one side of the FPC, the structure is simplified, the manufacturing process can be omitted, and the FPC can be quickly and inexpensively.
Can be manufactured.

[0017]

As described above, according to the first embodiment of the present invention, a photosensitive coverlay is required in a place where a high precision is required for a coverlay opening, and a photosensitive coverlay is required in a place where a high strength is required. By using the adhesive coverlay film, a high-density and highly reliable FPC can be provided.

According to the second embodiment, mounting requiring high accuracy is concentrated on one side of the double-sided FPC, the circuit is protected only by the photosensitive coverlay, and the other side is mechanically folded or the like. The FPC is concentrated on the areas where strong protection is required, and the circuit is protected only by the stick-on coverlay, which simplifies the structure of the FPC and provides a short delivery time and low cost FPC. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a mounting diagram of an FPC showing a first embodiment of the present invention.

FIG. 2 is a sectional view of an FPC showing a second embodiment of the present invention.

FIG. 3 is a mounting diagram of an FPC showing a second embodiment of the present invention.

[Explanation of symbols]

 1, 24, 31 Photosensitive cover lay film 2, 28, 32 Sticky cover lay film 5, 29, 35 Electric element

Claims (6)

[Claims] In a flexible printed circuit board, a coverlay film for insulating and protecting a circuit pattern is attached to a copper adhesive plate on which a circuit pattern is formed, and then exposed to light except for the coverlay opening and cured. A photosensitive coverlay film exposing the copper foil by forming a coverlay opening by removing the uncovered portion, and a land opening of the coverlay film previously formed by machining, and the coverlay film is formed with a circuit pattern. A flexible printed circuit board, characterized by using a combination of an adhesive cover lay film to be attached to a copper adhesive plate and 2. The flexible printed circuit board according to claim 1, wherein the circuit pattern is insulated and protected by using a photosensitive coverlay film for the element mounting portion. 3. The flexible printed circuit board according to claim 1, wherein the circuit pattern is protected and insulated by using an adhesive coverlay film for a portion of the flexible printed circuit board which is to be used by bending. Flexible printed circuit board. 4. A flexible printed circuit board having at least two pattern layers, wherein a coverlay film for protecting and insulating a circuit pattern is attached to a copper-clad board on which a circuit pattern is formed, and then the coverlay film other than the coverlay opening is formed. A photosensitive coverlay film that exposes the copper foil by forming a coverlay opening by exposing the uncured portion and exposing the copper foil; A flexible printed circuit board, comprising: an adhesive coverlay film for attaching a coverlay film having an opening to a copper adhesive plate having a circuit pattern formed thereon. 5. The flexible printed circuit board according to claim 4, wherein a photosensitive coverlay film is provided on a coverlay film for protecting and insulating a circuit pattern on one surface exposed on a surface of the flexible printed circuit board. A flexible printed circuit board, characterized in that an adhesive coverlay film is used as a coverlay film for protecting and insulating the circuit pattern on the other surface exposed on the surface of the flexible printed circuit board. 6. The flexible printed circuit board according to claim 5, wherein elements to be mounted are concentrated on the surface using the photosensitive coverlay film, and mechanical stress is not applied on the surface using the sticking type coverlay film. A flexible printed circuit board in which added circuit patterns are concentrated.