JPH09199811A - Flexible printed circuit board and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an FPC(flexible printed circuit board) which can be made small in size by narrowing the pattern width. SOLUTION: A band-like base film 1 is divided into left and right bases 1a and 1b pinching a bend line 2 at the center of widthwise direction, circuit patterns 3a and 3b, which make a left and right symmetrical shape, are formed thereon, and a pair of substrate constituent members 9a and 9b are formed. Both substrate constituent members 9a and 9b are bent at the bend line 2, the surface of both substrate constituent members 9a and 9b are superposed while both circuit patterns 3a and 3b are being aligned. 'When both superposed substrate constituent members 9a and 9b are press-molded under the state of heating, both substrate constituent members 9a and 9b are integrally formed in the state wherein the opposing parts of both circuit patterns 3a and 3b are superposed with each other. Lastly, external shape is punched out, and an FPC 10, having each pattern 4 in double thickness, is completed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a flexible printed circuit board and a method for manufacturing the same.

[0002]

2. Description of the Related Art Flexible printed circuit boards (hereinafter simply referred to as F
A general manufacturing method of (PC) is as follows.
First, a conductor foil is laminated on the surface of a synthetic resin base film via an adhesive, the surface of the conductor foil is covered with a resist film corresponding to a circuit pattern, and the conductor foil is subjected to a predetermined circuit by etching. Form in a pattern. Next, after removing the resist film, the surface is covered with a protective film (insulating resin) or protective film called a coverlay, and then the circuit pattern is sandwiched between the coverlay and the base film by pressing in a heated state. It is manufactured through the process of.

The thickness of the conductor foil used in such an FPC is generally of three types of 18, 35 and 70μ.
Each pattern width of the circuit pattern formed on the PC is determined by the current flowing therethrough and the thickness of the conductor foil. Here, as the width of each pattern becomes wider, the entire circuit pattern becomes larger, which in turn leads to a larger FPC.
There is a circumstance that we want to keep the width of each pattern to the minimum necessary.

[0004]

Generally, the design standard of the pattern width of the FPC is said to be 1 mm / A in the case of a conductor foil of 35 μ. For example, in order to pass a current of 10 A, the pattern width needs to be 10 mm. Becomes Where the thickness is doubled 7
By using a conductor foil of 0 μ, the pattern width can be narrowed to half, that is, 5 mm, and by using a thicker conductor foil, the pattern width can be further narrowed.

However, when the unnecessary portion of the conductor foil is removed by etching to form the circuit pattern, the thicker the conductor foil, the longer the etching process becomes.
When the etching process is incorporated in the line, the line speed becomes slow, so that the manufacturing cost becomes high and the product price rises. Further, as the thickness of the conductor foil increases, the possibility of over-etching in the etching process (a phenomenon in which the pattern width is reduced to be narrower than the original pattern width) increases, and the precision of the circuit pattern deteriorates.

When forming a circuit pattern, in addition to the above-mentioned etching method, a die stamp method is used.
By cutting the conductor foil using a mold having a blade corresponding to the circuit pattern, a method of forming a circuit pattern is also adopted, but from the problem of accuracy when manufacturing a blade for cutting, Similarly, there is a limit to narrowing the pattern width.

The present invention was completed in view of the above circumstances, and an object of the present invention is to provide a flexible printed circuit board that can be reduced in size by narrowing the pattern width and a manufacturing method thereof.

[0008]

As a means for achieving the above object, in a flexible printed circuit board according to the invention of claim 1, circuit patterns made of a conductive material are formed symmetrically on the surface of an insulating film. The present invention is characterized in that a pair of substrate constituents formed in 1 is provided, and both circuit patterns are superposed on each other so that both substrate constituents are integrated.

A second aspect of the invention is characterized in that, in the first aspect of the invention, the pair of substrate constituent members are connected so as to be bendable. The invention of claim 3 is characterized in that, in the invention of claim 1 or 2, a conductive adhesive layer is formed on the surface of the circuit pattern.

According to a fourth aspect of the present invention, there is provided a method for manufacturing a flexible printed circuit board, wherein circuit patterns made of a conductive material are formed on the surfaces of a pair of insulating films so as to have symmetrical shapes, and the surfaces of both insulating films are formed. Both insulating films are overlapped while facing each other and matching both circuit patterns,
It is characterized in that the laminated insulating films are press-formed in a heated state to be integrated.

A fifth aspect of the present invention is characterized in that, in the fourth aspect of the invention, the pair of insulating films are formed by being connected to each other, and both insulating films are bent from the connecting portion and overlapped with each other. Have.

According to a sixth aspect of the present invention, in the invention according to the fourth or fifth aspect, a conductive adhesive layer is formed on the surface of at least one of the circuit patterns, and the conductive adhesive is applied. It is characterized in that both circuit patterns are adhered to each other. In the above description, both circuit patterns having a symmetrical shape include the case where they have the same shape and the case where only a part thereof has a symmetrical shape.

[0013]

Function and Effect of the Invention

<Invention of Claims 1 and 4> Since the thickness of each pattern is increased by superposing a pair of circuit patterns, the circuit pattern formed on each substrate structure has a narrow pattern width and The required capacity can be obtained while keeping the thickness thin. That is, since the pattern width is narrow, each substrate structure can be made small, and the flexible printed circuit board on which the patterns are stacked can be compactly assembled.

Further, when the etching method is used to form the circuit pattern, the processing time can be shortened by keeping the thickness of the conductive material thin during the etching processing.
The line speed can be increased and the manufacturing cost can be reduced. In addition, over-etching can be prevented, and a highly accurate circuit pattern can be obtained.

<Inventions of Claims 2 and 5> Since the pair of substrate constituent members are preliminarily connected to each other and the flexible printed circuit board is formed by bending and superimposing them, a circuit pattern is formed. Can be performed efficiently, and the work of matching the two circuit patterns can be easily performed, so that the manufacturing cost can be further reduced as a whole.

<Inventions of Claims 3 and 6> Since both circuit patterns are adhered to each other via a conductive adhesive,
The final circuit pattern can be manufactured more firmly.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings. <First Embodiment> FIGS. 1 to 6 show a first embodiment of the present invention. In the first embodiment, the case where the FPC is used as a harness of an automobile is illustrated, and an etching method is used for forming a circuit pattern.

In FIG. 1, reference numeral 1 is polyester,
A wide base film made of a synthetic resin material such as polyimide, which is divided into left and right regions 1a and 1b (hereinafter, referred to as a left base and a right base) with a folding curve 2 at the center in the width direction. There is. Circuit patterns 3a and 3b are formed on the surface of each of the bases 1a and 1b, which are symmetrical with respect to the folding curve 2 as a center. In each of the circuit patterns 3a and 3b, for example, four patterns 4 are arranged at regular intervals on the connection end side (lower end in the same figure) of the terminal fitting 11, and two patterns 4 on the inner side of the patterns are arranged in the middle. It has a single shape.

Next, the procedure for forming the circuit pattern and manufacturing the FPC will be described. Circuit patterns 3a, 3
b is formed by an etching method. First, as shown in FIG. 2 (A), over the surfaces of the left and right bases 1a and 1b,
A conductor foil 7 having a thickness of, for example, 70 μ is laminated via the adhesive 6. Subsequently, as shown in FIG. 3B, the surface of the conductor foil 7 is covered with a resist film 8 corresponding to the shapes of the left and right circuit patterns 3a and 3b. The width of each pattern is 5 mm.

Then, the resist is subjected to an etching treatment, so that only the conductor foil 7 corresponding to the shapes of the circuit patterns 3a and 3b is left, as shown in FIG. Finally, when the remaining resist film 8 is removed, as shown in FIG.
As shown in (A), a pair of left and right board constituent members 9a and 9b having circuit patterns 3a and 3b having a symmetrical shape are formed on the bases 1a and 1b, respectively.

Then, both of the above-mentioned board constituents 9a and 9b are bent from the bending curve 2, and both circuit patterns 3a and 3b are aligned and aligned as shown in FIG.
The surface sides of a and 9b are overlapped. Subsequently, when the two substrate constituents 9a and 9b that have been overlapped with each other are press-molded in a heated state, as shown in FIG.
Are integrally joined via the adhesive 6, and both circuit patterns 3
Corresponding parts of a and 3b overlap and are integrated. Finally, the outer shape is punched to complete the FPC 10 as shown in FIG. The FPC 10 thus formed has a thickness of each pattern of 70 μm.
Which is twice that of 140 μ.

As described above, according to this embodiment, since the thickness of each pattern is increased by superposing the pair of circuit patterns 3a and 3b, each substrate structure 9 is formed.
With respect to the circuit patterns 3a and 3b formed on a and 9b, the pattern width can be narrowed to 5 mm, and the thickness can be kept to a usual value of 70 μ to obtain a large capacity. That is, since the pattern width can be narrowed, each of the substrate constructing bodies 9a and 9b can be made small, and the FPCs in which they are stacked are stacked.
The whole 10 can be compactly integrated.

Further, since the thickness of the conductor foil 7 forming the circuit patterns 3a and 3b is kept to a normal thickness, the etching process time can be shortened, the line speed can be increased, and the manufacturing cost can be reduced. It can contribute to the reduction.
Also, over-etching can be prevented and a highly accurate circuit pattern can be obtained.

The terminal fitting 11 is connected to the end of the FPC 10 as follows. The terminal fitting 11 is
As shown in FIG. 4, a mounting plate 13 is provided so as to extend at the rear end of the main body 12, and a pair of front and rear projecting pieces 14 are formed upright at the leading end and the middle of the mounting plate 13.

On the base film 1 side, as shown in FIG. 1, one base (left base 1a in this embodiment) is provided with a pair of front and rear mounting holes 15 at each position where the end of each pattern 4 is formed. Are pre-opened by pressing. The mounting holes 15 are formed at the same intervals as the intervals of the projecting pieces 14 of the terminal fitting 11 described above.

Then, through the above manufacturing process, FIG.
When the FPC 10 as shown in (D) is manufactured,
The end of the FPC 10 on the connection side of the terminal fitting 11 is formed in a cross-sectional shape as shown in FIG. That is, the mounting hole 15 is opened on the upper surface side of the FPC 10 and the pattern 4 is exposed at the bottom thereof.

Then, as shown in FIG.
From the lower surface side of the terminal 10, the protrusion 14 of the terminal fitting 11 is concentric with each mounting hole 15 and communicates with the mounting hole 15.
An insertion hole 16 that can be inserted is opened. Next, the terminal fitting 11 is turned upside down from FIG. 4, and the front and rear projecting pieces 14 are inserted from the corresponding mounting holes 15 into the insertion holes 16.
Then, as shown in FIG. 3C, the projecting end portions of the projecting pieces 14 are caulked, and the base end portions of the projecting pieces 14 located in the mounting holes 15 and the exposed patterns 4 are formed. To solder.

As a result, as shown in FIG.
Pattern 4 corresponding to the terminal fitting 11 along the edge of 0
A product electrically connected to the connection end of the product and mounted in a line at a predetermined interval is obtained.

Further, as shown by the chain line in FIG. 3A, when the surface of the conductor foil 7 forming the circuit patterns 3a and 3b is plated with metal such as tin or solder,
When both of the above-mentioned substrate constituents 9a and 9b are bent and press-formed in a heated state, the overlapping patterns 4 are adhered to each other via the molten metal plating 18, so that the final pattern becomes stronger. Is formed.

<Second Embodiment> A second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, the die stamp method is used to form the circuit pattern. In this method, an adhesive 6 made of a thermosetting or thermoplastic resin is applied on a strip-shaped base film 1 made of a synthetic resin material such as polyester or polyimide, and then a conductor foil 7 is superposed thereon. As shown in FIG. 7, a pair of heat rollers 20 are passed between them, or as shown in FIG. Similar to the first embodiment, the base film 1 is divided into left and right bases 1a and 1b with a folding curve 2 at the center in the width direction interposed therebetween.

Then, the circuit patterns 3a and 3b having a symmetrical shape as shown in FIG. 1 are formed.
Therefore, as shown in FIG. 9 (A), a lower mold 22 on which the base film 1 to which the conductor foil 7 is temporarily adhered is placed and an upper mold 23 installed above the lower mold 22 so as to be capable of being lifted and lowered are provided. On the lower surface of the upper mold 23, the circuit patterns 3a, 3
A cutting blade 24 corresponding to the shape of b is formed.

That is, when the upper die 23 descends, only the conductor foil 7 is cut along the shape of the circuit patterns 3a and 3b by the cutting blade 24 of the upper die 23 as shown in FIG. As shown in FIG. 6C, after the upper mold 23 is raised and retracted to remove the base film 1 from the lower mold 22, when the unnecessary conductor foil 7 is peeled and removed as shown in FIG. , A pair of left and right substrate constituting bodies 9a and 9b having circuit patterns 3a and 3b having a symmetrical shape are formed on the respective bases 1a and 1b.

After that, as in the first embodiment, FIG.
As shown in (A), both board constituents 9a and 9b are bent from the bending curve 2, and the circuit boards 3a and 3b are aligned and the surface sides of both board constituents 9a and 9b are overlapped. By press-molding the two superposed substrate constituents 9a and 9b in a heated state, as shown in FIG. 7B, the two circuit constituents 9a and 9b are overlapped with each other in corresponding portions of the circuit patterns 3a and 3b. , 9b are integrated, and finally the outer shape is punched to complete the FPC 10 in which the thickness of each pattern 4 is doubled as shown in FIG.

FPC1 obtained by the second embodiment
0 also has a structure in which the thickness of each pattern is increased by superimposing a pair of circuit patterns 3a and 3b. Therefore, the width of the circuit patterns 3a and 3b formed on the respective substrate constructing bodies 9a and 9b should be narrow. The FPC 10 can be formed, and similarly, each of the substrate constructing bodies 9a and 9b can be made small, and the FPC 10 can be compactly assembled.

Further, the die stamp method does not have the adverse effect of over-etching in the etching method and is suitable for forming a circuit pattern having a large thickness from the beginning. Therefore, the circuit pattern as in this embodiment is used. By stacking the layers, it becomes possible to obtain a circuit pattern having a larger thickness.

<Other Embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings. For example, the following embodiments are also included in the technical scope of the present invention. In addition, various changes can be made without departing from the scope of the invention. (1) In the above-described embodiment, the case where the pair of substrate constituent members are formed in a state of being foldably connected has been described as an example. However, both substrate constituent members may be formed as separate members and stacked together. Good.

(2) The present invention can be widely applied not only to the case of being used as the harness of the automobile illustrated in the above-mentioned embodiment but also to the FPC generally used for other purposes such as connecting to the JB. Further, like the terminal fitting, it is possible to attach and use a connector or other electronic component.

[Brief description of drawings]

FIG. 1 is a plan view showing a state where a circuit pattern is formed on a base film according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a step of forming a circuit pattern by an etching method.

FIG. 3 is a cross-sectional view showing a manufacturing process of an FPC.

FIG. 4 is a perspective view of a terminal fitting.

FIG. 5 is a partial cross-sectional view illustrating a procedure for attaching a terminal fitting.

FIG. 6 is an external perspective view of a state in which a terminal fitting is attached to the end of the FPC.

FIG. 7 is a cross-sectional view showing a method of bonding a conductor foil according to the second embodiment of the invention.

FIG. 8 is a cross-sectional view showing another bonding method.

FIG. 9 is a sectional view showing a step of forming a circuit pattern by a die stamp method.

FIG. 10 is a cross-sectional view showing the manufacturing process of the FPC.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Base film (insulating film) 2 ... Folding curve 3a, 3b ... Circuit pattern 7 ... Conductor foil (conductive material) 9a, 9b ... Substrate structure 10 ... FPC (flexible printed circuit board) 18 ... Metal plating (conductive adhesion) Agent)

Claims (6)

[Claims] 1. A pair of board constituents, each of which has a circuit pattern made of a conductive material and formed in a symmetrical shape with each other, are provided on the surface of an insulating film, and both circuit patterns are superposed to integrate the two board constituents. Flexible printed circuit board characterized by. 2. The flexible printed circuit board according to claim 1, wherein the pair of substrate components are connected so as to be bendable. 3. The flexible printed board according to claim 1, wherein a conductive adhesive layer is formed on the surface of the circuit pattern. 4. A pair of insulating films are formed with circuit patterns made of a conductive material so as to be symmetrical with each other, and the surfaces of both insulating films are opposed to each other to align the circuit patterns with each other. And a method of manufacturing a flexible printed circuit board, characterized in that the two insulating films thus laminated are pressed together in a heated state to be integrated. 5. The method for manufacturing a flexible printed circuit board according to claim 4, wherein the pair of insulating films are formed by connecting the insulating films to each other, and the insulating films are bent from the connecting portion and overlapped with each other. 6. The method according to claim 4, wherein a conductive adhesive layer is formed on the surface of at least one of the circuit patterns, and both circuit patterns are attached via the conductive adhesive. Item 6. A method for manufacturing a flexible printed circuit board according to item 5.