JP3599487B2 - Flexible printed circuit board - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a structure of a flexible printed circuit (hereinafter, referred to as FPC).
[0002]
[Prior art]
The first method of manufacturing an FPC is to first form a copper-clad plate in which copper foil is bonded to both sides of a base film made of polyimide or the like, open through holes, perform through-hole plating, and etch into a desired circuit shape. In another step, the land shape is punched out of the polyimide film with a mold to produce 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]
The 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 sides, 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]
[Problems to be solved by the invention]
However, the above conventional example has the following problems. First, in the case of the sticking type cover lay of the first method, since the cover lay having the opening is manually stuck, it is inevitably troublesome, and as a result, the cost is increased. In addition, an adhesive is used to attach the adhesive coverlay and the copper adhesive plate. For this reason, the adhesive oozes out from the sticking-type coverlay opening, and the substantial coverlay opening is reduced. In addition, during the above-described process procedure, it is unavoidable that the pattern of the FPC and the position of the opening of the cover lay deviate from each other in order to bond the adhesive cover lay film having the opening formed to the etched copper adhesive plate. Therefore, the opening of the adhesive coverlay must be large enough to allow some adhesive to protrude, and the copper foil pattern of the adhesive coverlay opening must be large enough to allow the adhesive displacement of the adhesive coverlay. become. Therefore, a large area is required for the land, which hinders the recent demand for high density mounting.
[0005]
Further, in the case of the photosensitive coverlay of the second conventional technique, sufficient mechanical strength cannot be obtained due to its characteristics. For this reason, 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 the adhesive coverlay film and the photosensitive coverlay film, but each has its own advantages and disadvantages. When high-density mounting is required, the mechanical strength of the FPC decreases. However, there was a dilemma that high-density mounting was not possible if mechanical strength was pursued.
[0006]
[Means for Solving the Problems]
In order to solve the above problem, in the first embodiment of the present invention, a circuit is protected by a photosensitive coverlay film in a place where dimensional accuracy is required for a coverlay opening such as an element mounting portion, and the coverlay is bent. At locations where mechanical strength is required, such as the parts, the circuit is protected with a stick-on coverlay film. With this configuration, it is possible to achieve both high density mounting and high reliability of a circuit formed on the FPC.
[0007]
Next, according to the second embodiment of the present invention, the component mounting portion is concentrated on one surface of the FPC, the coverlay film on that surface is unified with a photosensitive coverlay film, and the other surface is a folded circuit. And the coverlay film on this surface is used as a sticking type coverlay 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】
(Example 1)
A first embodiment 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 adhesive coverlay. Reference numeral 3 denotes a copper foil pattern formed by etching a copper plate. Reference numeral 4 denotes a through hole (hereinafter, referred to as TH) which is formed by drilling, plating, and electrically connecting the front and back patterns of the FPC. 5a and 5e are sensor-integrated ICs, 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 this FPC is covered with a photosensitive cover lay 1, and the other portions are covered with a stick-on type cover lay 2. As shown in FIG. 1, in the FPC of the present embodiment, a circuit is protected and a land is formed on a device mounting portion by a photosensitive coverlay film 1. 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. Further, 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 wavy line 7 in a portion other than the element, and is folded 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.
[0011]
When a portion requiring high density and a portion requiring high strength are continuous, and when protection of the coverlay is required, the photosensitive coverlay 1 and the sticking type coverlay 2 like the overlap portion 6 are used. They are designed 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.
[0012]
(Example 2)
Embodiment 2 of the present invention will be described with reference to FIG. 2 which is a cross-sectional view of an FPC on which an element is mounted, and FIG. 3 which is a mounting view of an FPC of this embodiment on which an element is mounted. First, FIG. 2 will be described. Reference numeral 21 denotes an FPC base film made of a polyimide film. Reference numeral 22 denotes an adhesive, and reference numeral 23 denotes a surface side (element mounting surface side) copper foil. The copper foil 23 is attached to the base film 21 by the adhesive 22.
[0013]
Reference numeral 24 denotes a photosensitive coverlay film, which 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 coverlay, which is attached to the FPC to protect the circuit on the back surface. 29 is a chip element and 30 is solder. A cover lay 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.
[0014]
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 an adhesive coverlay film 32 (corresponding to 28 in FIG. 2).
[0015]
Further, 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 the strong sticking type coverlay film 32, so that it is difficult to press down with a small radius. The copper foil pattern 33 is not cut even by bending. 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 can be reduced.
[0016]
The FPC having such a configuration has the following advantages in addition to the advantages shown in the first embodiment of the present invention. Since one type of coverlay film is unified for one surface of the FPC, the structure is simplified, the manufacturing process can be omitted, and the FPC can be manufactured quickly and cheaply.
[0017]
【The invention's effect】
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 sticky coverlay film is used in a place where a high strength is required. By using the FPC, a high-density and highly reliable FPC can be provided.
[0018]
According to the second embodiment, mounting requiring high precision 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 bent by bending or the like. In addition, by concentrating the places where strong protection is required, and by adopting a structure in which the circuit is protected only with the adhesive coverlay, the structure of the FPC can be simplified, and a short delivery time and low cost FPC can be provided. .
[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 cross-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 coverlay film 2, 28, 32 Sticky coverlay film 5, 29, 35 Electric element

Claims (1)

In a flexible printed circuit board having at least two pattern layers,
One surface exposed on the surface of the flexible printed circuit board is a mounting portion of the element, and the circuit pattern is protected and covered with a coverlay film for insulation, after being bonded to a copper bonding plate on which the circuit pattern is formed. A photosensitive coverlay film is used that exposes and cures the portions other than the coverlay opening and removes the uncured portions to form a coverlay opening to expose the copper foil, on the surface of the flexible printed circuit board. On the other exposed surface, a circuit pattern subjected to mechanical stress, which is used by bending the flexible printed circuit board, is concentrated and disposed, and a cover opening film for protecting and insulating the circuit pattern is provided with a land opening beforehand. Opening by processing, laminating cover lay film with land opening on copper paste board with circuit pattern formed A flexible printed circuit board, characterized in that with that patch type cover lay film.

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