JPH03230595A - Flexible printed circuit board - Google Patents

Abstract

PURPOSE:To prevent the breakage of a wire from being generated even by repeating a bend or a stretch by positioning the peak portion or the through portion of a waveform in the end portion of the approximate boundary of the waveform of a film-like insulator on the terminal portions of a band-like conductor. CONSTITUTION:A metallic foil such as a copper foil is adhered to a film 1 which is a base film by using an epoxy resin adhesive and, by applying etching thereto, a prescribed conductor circuit 3 formed. On the other hand, a semicircular projected portion 16 is formed by processing a portion wherein the boundary end portion 11 of a film which is used as a cover lay film to which the epoxy resin adhesive is applied in advance overlaps the upper surface of a linear conductor terminal portion 3a laminated on a board 2 to be adhered. Then, a flexible printed circuit board is manufactured by laminating the cover lay film 5 with the adhesive on the base film 1. At this time, a positioning is conducted so that the semicircular projected portion 16 of the cover lay film 5 is laminated on the upper surface of the linear conductor terminal portion 3a. Thus, the concentration of stress is dispersed and the conductor circuit 3 can be prevented from being broken.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a flexible printed M board used in high-precision electronic equipment and the like.

[Conventional technology]

Flexible pudding)! Boards are used in a wide range of fields, including office equipment such as word processors. This type of flexible printed circuit board 6 is usually made of polyester, as shown in FIG.

A conductor circuit 3 is formed by pasting a metal foil such as copper foil or aluminum foil through an adhesive layer 2 to a base film 1 made of a plastic insulating film such as polyimide, and etching it. It is formed by laminating a coverlay film 5b made of a polymer film on the coverlay film with an adhesive layer 4 for coverlay film interposed therebetween. In this substrate 6, the end of the coverlay film 5b is removed so that the end of the conductor circuit 3 is exposed. 3a is a linear conductor terminal portion extending in a strip shape from the conductor circuit 3 to the exposed portion. Such a flexible printed circuit board 6 is usually used by bending the linear conductor terminal portion 3a in order to connect it to another flexible printed circuit board.

[Problem to be solved by the invention]

By the way, in recent years, as electronic devices have become smaller and lighter,
The flexible printed circuit boards used in these electronic devices are also being used under harsh conditions (minimization of bending angles).

However, in the flexible printed circuit board 6 having the above structure, as shown in FIG. 4, the boundary edge of the coverlay film 5b is formed in a straight line. When 3a is bent in the direction of arrow Y, the boundary edge of the coverlay film 5b is bent at a sharp angle; stress is concentrated on the bent portion 7 of the linear conductor terminal portion 3a (the boundary edge of the coverlay film 5b). However, there is a problem in that wire breakage occurs. In addition, in the above-mentioned flexible printed circuit board, even if there is no disconnection during mounting, the flexible printed circuit board 6 may bend over time during operation of an electronic device using the flexible printed circuit board 6.
Repeated stretching causes stress to concentrate on the bent portion 7 of the flexible printed circuit board 6, causing an inconvenient situation in which the wire breaks due to metal fatigue. As a result of such disconnection, the reliability of electronic equipment is significantly reduced. In order to prevent the conductor circuit 3 from breaking due to such bending,
Proposals as shown in a) and (b) have been made. That is, the adhesive layer 2 is laminated on both sides of the base film 1, and the conductor circuit 3 is formed on either side of the negative side. The surface of this conductor circuit 3 and the base film 1
Insulating coatings N8 and 9 are provided on the other surface, and a portion of the insulating coating layer 8 on the surface on which the conductor circuit 3 is not formed is removed to expose a portion of the base film l. In this case, the insulation coating layer 8
The boundary end 8a, which is a part of the removal trace, is formed in a sawtooth shape. In this way, when the boundary end 8a of the insulating coating layer 8 is formed in a sawtooth shape, even if the sawtooth part is bent in the direction of arrow Z in FIG. 5(b), it will not be bent linearly. Since stress is not concentrated on the conductor circuit 3, breakage of the conductor circuit 3 can be prevented.

However, even if the flexible printed M board 10 in which the boundary edge 8a of the insulating coating layer 8 is formed into a sawtooth shape is used, if it is bent during mounting, the conductor circuit 3 may actually break near the boundary edge 8a. It is also difficult to effectively prevent the conductor circuit 3 from breaking due to bending.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a flexible printed circuit board that does not cause disconnection due to bending.

[Means for Solving the Problems] In order to achieve the above object, the flexible printed circuit board of the present invention has a plurality of strip-shaped conductors arranged in parallel on the board surface at a predetermined interval, and the board surface has an end portion. In a flexible printed circuit board that is covered with a film-like insulator, the ends of a plurality of strip-shaped conductors are exposed in parallel on the edge of the board surface, and the boundary end of the film-like insulator is exposed. , are formed to cross the ends of those strip conductors and are set in a substantially waveform shape, and the peak portion or each valley portion of the waveform is positioned on the exposed end of each strip conductor. It is structured as follows.

[Function] That is, the flexible printed circuit board of the present invention, unlike the above-mentioned proposal, has a wave-shaped boundary of a film-like insulator on each end of each band-shaped conductor exposed at the end of the board surface. Each peak or valley of the waveform at the end is located. In other words, each end of the band-shaped conductor corresponds to the peak portion (or each valley portion) of the waveform of the film-shaped insulator. Therefore, the boundary edge of the film insulator does not bend at a steep angle when the board is bent.
Stress is not concentrated at the bent part. Therefore, the flexible printed circuit board of the present invention has a stronger resistance to bending than the one according to the above proposal, and does not cause wire breakage not only by bending during mounting but also by repeated bending and stretching after mounting.

Next, the present invention will be explained in detail based on examples.

FIG. 1 is a cross-sectional perspective view showing one embodiment of the present invention. In this flexible printed circuit board, the coverlay film 5 is laminated so that the end of the base film 1 and the upper end of the linear conductor terminal part 3a are exposed, and the boundary end 11 of the coverlay film 5 is A semicircular convex portion 16 is formed so as to cross the terminal portion 3a.

The semicircular convex portion 16 is positioned on the exposed linear conductor terminal portion 3a. The flexible printed circuit board basically has the same structure as that shown in FIG. 4, and the same parts are given the same reference numerals.

This flexible printed circuit board is manufactured, for example, as follows. That is, a metal foil such as a copper foil is adhered onto a film 1 serving as a base film using an epoxy resin adhesive and etched to form a predetermined conductor circuit 3. On the other hand, a mold is formed on the boundary end 11 of a film used as a coverlay film coated with an epoxy resin adhesive in advance, in a portion that overlaps with the upper surface of the linear conductor terminal portion 3a laminated on the substrate 1 to be adhered. ,
A semicircular convex portion 16 is formed by Thomson processing. Next, the base film 1 on which the conductor circuit 3 is formed
It is manufactured by laminating an adhesive-backed coverlay film 5 on which a semicircular convex portion 16 is provided at the boundary end portion 11. At this time, it is necessary to position the semicircular curved portion 16 of the adhesive-backed coverlay film 5 so that it is laminated on the upper surface of the linear conductor terminal portion 3a.

The flexible printed circuit board obtained in this way is
A semicircular convex portion 16 provided at the boundary end portion 11 of the coverlay film 5 with adhesive on the upper surface of the plurality of linear conductor terminal portions 3a.
is positioned, so even if the coverlay film 5 with adhesive is bent from the boundary edge 1■ during mounting, it will not bend at a steep angle, and the semicircular convex portion 16 of the boundary edge 11 and other parts It bends gently at two places. Therefore, concentration of stress is dispersed and breakage of the conductor circuit 3 can be prevented.

FIG. 2 shows another embodiment of the flexible printed circuit board of the present invention. This flexible printed circuit board is
A semicircular notch 12 is provided at the boundary end 11a of the adhesive-backed coverlay film 5C, and the semicircular notch 12 is positioned over the linear conductor terminal 3a. Note that in the above embodiments, the same parts are given the same reference numerals.

FIG. 3 shows still another embodiment of the flexible pudding M board of the present invention. In this flexible printed circuit board, the boundary end 1 of the coverlay film 5a with adhesive is
5 is formed in a wavy shape, and the peak portion of the wavy shape is positioned on the linear conductor terminal portion 3a.

Note that the shape of the boundary end of the coverlay film with adhesive is one having a semicircular convex part as shown in Fig. 1 above, and one having a semicircular notch part as shown in Fig. 2. , and is not limited to the waveform shape as shown in FIG. 3, but includes, for example, a waveform, sawtooth shape, rectangular shape, etc. as shown in FIG. 3, and a boundary formed with such a substantially waveform shape Effects similar to those of the above embodiment can be obtained by using a coverlay film having edges and positioning the troughs or peaks of the boundary edges over the linear conductor terminals 3a.

〔Effect of the invention〕

As described above, in the flexible printed circuit board of the present invention, since each peak (or trough) of the waveform at the substantially waveform boundary end of the film insulator is positioned on the strip conductor terminal portion, the film Even if it is bent at the boundary edge of the insulator, it will not bend at a sharp angle, and the concentration of stress at the bent part will be dispersed.For this reason, it has strong resistance to bending, and only bends during mounting. Moreover, even after repeated bending and stretching after mounting, wire breakage does not occur.

Next, a specific example will be explained.

[Specific Example 1] Polyimide film with a thickness of 25 μm (Kapton 100
H, manufactured by DuPont) as the base film and coverlay film material, and at the same time, a film with a thickness of 17.5μ
m copper foil (1/20Z electrolytic copper foil) was prepared. On the other hand, the boundary edge of the polyimide film with adhesive used as the above-mentioned coverlay film material was treated with a first layer by Thomson processing.
A semicircular convex portion 16 as shown in the figure was provided. Then, the copper foil was adhered onto the base film 1 using an epoxy resin adhesive and etched in that state to form a predetermined conductor circuit 3. Next, the coverlay film 5 with adhesive is positioned so that the semicircular convex portion 16 of the boundary end 11 overlaps the linear conductor terminal 3a, the coverlay film 5c with adhesive is laminated, and the temperature is It was cured at 150°C for 1 hour to obtain a flexible printed circuit board as shown in FIG.

[Specific Example 2] As shown in FIG.
2 is provided with an adhesive-backed coverlay film 5c, and the adhesive-backed coverlay film 5c is placed so that the semicircular notch 12 at the boundary end of the coverlay film 5c overlaps the upper surface of the linear conductor terminal portion 3a. The film 5c was positioned and stacked.

A flexible printed circuit board as shown in FIG. 2 was obtained in the same manner as in Example 1 except for the above.

[Comparative Example 1] An adhesive-attached coverlay film 5b having a straight boundary edge portion was used. Other than that, a flexible printed circuit board as shown in FIG. 4 was obtained in the same manner as in Example 1.

[Comparative Example 2] As shown in FIGS. 5(a) and 5(b), a conductor circuit 3 is formed on one side of the base film 1, and a coverlay film is formed on the surface of the conductor circuit 3 and the other side of the base film 1. A flexible printed circuit board was obtained using 8.9 using an adhesive. At this time, the boundary edge of the coverlay film 8 provided on the surface where the conductor circuit 3 is not formed is formed in a sawtooth shape. The sawtooth-like unevenness of this boundary end portion and the linear conductor terminal portion 3a do not match as shown in the figure.

Using the specific examples 1 and 2 and comparative examples 1 and 2 obtained as described above, in the direction of the coverlay film forming surface, in the direction of arrow P in FIG. 1, in the direction of arrow X in FIG. A bending rupture test was performed by bending the coverlay film from the boundary edge in the direction of arrow Y in FIG. 4 and in the direction of arrow Z in FIG. 5(b).
The fracture resistance properties of each were evaluated. The results are shown in the table below. The above-mentioned breakage resistance was evaluated by conducting a test in which bending was repeated at bending angles of 0.38R and 135° under a load of 500g, and by indicating the number of times the linear conductor terminal portion broke.

As is clear from the results in the table above, the number of bending breaks in all of the implemented height measurements was significantly improved compared to the comparative height measurements, indicating that high reliability was obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of this invention, FIG. 2 is a block diagram showing another embodiment of this invention, FIG. 3 is a block diagram showing still another embodiment of this invention, and FIG. 5(a) is a top view showing a conventional flexible printed circuit board, and FIG. 5(b) is a top view showing a conventional flexible printed circuit board.
) is this AA' sectional view. 1...Base film 3...Conductor circuit R3a...
Linear conductor terminal portion 5... Coverlay film with adhesive 11... Coverlay film boundary end portion 16... Semicircular convex portion

Claims (1)

[Claims] (1) In a flexible printed circuit board in which a plurality of band-shaped conductors are arranged in parallel on a board surface at predetermined intervals, and the board surface is covered with a film-like insulator except for the ends, the ends of the board surface are covered with a film-like insulator. The ends of the plurality of strip conductors are exposed in parallel, and the boundary end of the film insulator is
It is formed to cross the ends of these strip conductors and is set in a substantially waveform shape, and each peak or valley of the waveform is positioned on the exposed end of each strip conductor. A flexible printed circuit board characterized by: