JPH03230591A - Flexible printed circuit board for bend - Google Patents

Abstract

PURPOSE:To prevent a crack from being generated in a film when its bend is repeated by making the outside film from the one with a specific property. CONSTITUTION:A film with the property that an elongation based on ASTM D 882-80 is not less than 150% is used as a base film 5. A metallic foil such as a copper foil is adhered to the base film 5 by an adhesive 4 made of an epoxy resin. A circuit pattern 3 is formed by etching a resultant adherent. On the other hand, an adhesive 2 made of an epoxy resin is applied to one side surface of a film which becomes a film for cover coat to make a cover coat film 1 with an adhesive layer. This flexible printed circuit board for bend is used when the base film is positioned outside when bent. Since the base film 5 which is the outside film has the property of not less than 150% elongation in the bend even when the cover coat film 1 is bent or used as bent inside in a U-shape, no crack is generated in the base film 5.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a flexible printed circuit board with excellent bending properties used in hard disk drives (HDDs), floppy disk drives (FDDs), printers, etc. be.

[Conventional technology]

Conventionally, flexible printed circuit boards with high flexibility have been used in HDDs, FDDs, printers, and the like. The flexible printed circuit board is equipped with an HDD.
With the miniaturization of FDDs, printers, etc., higher reliability in flexibility is required. That is,
The above-mentioned flexible printed circuit board is produced by attaching a metal foil such as copper foil to a base film and etching it to form a circuit pattern, and then laminating a cover coat film via an adhesive. The whole thing bends smoothly.

[Problem that the invention seeks to solve]

However, the flexible printed circuit board with the above structure has the disadvantage that if the above-mentioned bending is repeated many times, the outer film will crack during bending, and the circuit pattern formed by the metal foil will break as a result. There is. For this reason, there is a strong demand for a highly reliable and highly flexible printed circuit board that does not cause cracks in the film even after repeated 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 for bending that does not cause cracks in the film layer even if it is repeatedly bent.

[Means for Solving the Problems] In order to achieve the above object, the flexible printed i-board for bending of the present invention includes first and second synthetic resin film layers, and a metal disposed between the two film layers. A flexible printed circuit board that includes a foil circuit pattern and an adhesive layer that adheres both film layers with the metal foil circuit pattern interposed therebetween, and is bent into a substantially U-shape, the outer film being bent when bent. Layer is ASTM D 8
The composition is a synthetic resin film having an elongation of 150% or more based on 8280.

[Effect]

That is, the inventor conducted a series of studies to prevent film cracking as described above.

As a result, it was found that in the two synthetic resin film layers described above, the elongation characteristics of the outer film greatly influenced the cracking of the film during bending. As a result of numerous tests on the elongation characteristics of the film provided on the outside during bending, the inventor found that the above film has a property of elongation of 150% or more based on ASTM D 882-80. The inventors have discovered that when a synthetic resin film having the above-mentioned structure is used, the film does not crack and the circuit pattern does not break.

In addition, "bending" of the above-mentioned flexible printed circuit board for bending
This does not simply mean a static state of bending, but a state of dynamically repeating bending and extension.

In the bending flexible printed circuit board of the present invention, the first and second synthetic resin films and the metal foil forming the circuit pattern are arranged in a state where the circuit pattern is interposed between the first and second synthetic resin films and the metal foil forming the circuit pattern.
and an adhesive for bonding the second synthetic resin film.

Among the first and second synthetic resin films, the one located on the outside when the flexible pudding + 1 board is bent has an elongation of 150% or more based on ASTM D 882-80. There is a need. Although the film is not particularly limited as long as it has the above-mentioned properties, polyimide films having excellent properties such as heat resistance, electrical properties, flame retardance, and chemical resistance are usually preferably used. Furthermore, among the synthetic resin films described above, the synthetic resin film located on the inside when bent may be a film having the above-mentioned characteristics, or may be a commonly used synthetic resin film. Further, the thickness of the synthetic resin film is usually preferably set in the range of 12.5 to 125 μm, particularly preferably 25 to 125 μm.
It is 75 μm.

Copper foil is usually used as the metal foil forming the circuit pattern, but is not limited thereto.

Moreover, as the adhesive, an adhesive made of epoxy resin is generally used.

The flexible printed circuit board of the present invention is manufactured, for example, as follows. That is, among the first and second synthetic resin films, A as the base film
150% elongation based on STM D 882-80
A circuit pattern is formed by pasting a metal foil such as copper foil onto a film having the above characteristics using an adhesive made of epoxy resin, and etching it. on the other hand,
An adhesive made of epoxy resin is applied to one side of a film to be used as a cover coat film to produce a cover coat film with an adhesive layer. Next, it is manufactured by overlapping and integrating the adhesive-formed surface of the adhesive-attached cover coat film onto the foil surface of the metal foil on which the circuit pattern is formed on the base film. The flexible printed circuit board for bending obtained by the above manufacturing method is used when the base film is located on the outside during bending.

The flexible printed circuit board 6 for bending obtained in this way can be used, for example, as shown in FIG. base film 5 is AS
Since it is formed of a film having an elongation of 150% or more based on TMD 88280, cracks do not occur in the base film 5. Therefore, breakage of the circuit pattern 3 due to cracking of the base film 5 does not occur. In the figure, 2 is the adhesive layer of the cover coat film 1, and 4 is the adhesive layer of the base film 5.

However, when the cover coat film 1 is located on the outside when bent, on the contrary, a film having an elongation of 150% or more based on ASTM D 882-80 is used as the cover coat film 1.

[Effects of the Invention] As described above, the flexible printed M board for bending of the present invention has an outer film that meets the ASTM D standard during bending.
The film is made of a film having an elongation of 150% or more based on 8B2-80, so that the film does not crack due to repeated bending and bending, and the resulting breakage of the metal foil circuit pattern is prevented.

Next, examples will be described together with comparative examples.

〔Example〕

A polyimide film (Corpilex R1 manufactured by Ube Industries, Ltd.) with a thickness of 75 μm and an elongation of 150% was prepared as a base film and a film for cover coating, and at the same time, a 107 rolled copper foil with a thickness of 35 μm was prepared. Then, the rolled copper foil was adhered onto the base film using a rubber-modified epoxy resin adhesive, and a circuit pattern was formed by applying a conventional photoetching method. In forming the above circuit pattern, the pattern width was 150 μm, and the pattern interval was 15 μm.
Ten test patterns were formed at 0 μm. On the other hand, the same rubber-modified epoxy resin adhesive as above was applied to one side of the cover coat film. Next, the adhesive-formed surface of the adhesive-backed cover coat film is placed on the metal foil surface on which the circuit pattern is formed on the base film, and the adhesive is cured at a temperature of 140 to 170°C for 1 to 3 hours. A flexible printed circuit board for bending was obtained.

The structure of the flexible printed circuit board thus obtained is shown in FIG. In the figure, 1 is a cover coat film, 2 is a cover coat film adhesive layer, 3 is a circuit pattern, 4 is a base film adhesive layer, and 5 is a base film. The thickness of the cover coat film 11 foil 3 and the base film 5 is the same as the thickness described above, and the total thickness is about 2.
The thickness was 00 to 230 μm.

[Comparative Example 1] Polyimide film with elongation of 30% instead of polyimide film with elongation of 150%
% polyimide film (Corpilex S, manufactured by Ube Industries, Ltd.) was used. A flexible printed circuit board for bending was obtained in the same manner as in Example 1 except for the above.

[Comparative Example 2] Polyimide film with elongation of 90% instead of polyimide film with elongation of 150%
% polyimide film (Kapton H1 East, manufactured by DuPont) was used. A flexible printed circuit board for bending was obtained in the same manner as in Example 1 except for the above.

The flexible printed circuit boards obtained in the above Examples and Comparative Examples were subjected to a bending test to evaluate their bending reliability. The results are shown in the table below. In addition, as shown in FIG. 3, the above-mentioned bending test was carried out in accordance with the bending test method of IPC240B. The flexible printed circuit board 7 for bending was placed on the support stand 8, and the bending flexible printed circuit board 7 was placed in a U-shape (curvature radius R: 3 , Onun). Then, a bending test was conducted under the conditions of a stroke of 12 strokes in the direction of arrow A and a speed of 30 Hz. As a result, the number of times cracks occurred in the outer polyimide film was measured.

As is clear from the above table, the number of bending breaks of the example product is significantly improved compared to the comparative product, and it can be seen that high reliability can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the flexible printed circuit board for bending of the present invention in a bent state, FIG. 2 is a cross-sectional view of the flexible printed circuit board for bending of the present invention, and FIG. 3 is a configuration diagram showing the state of the bending test method. be. l...Film for cover coat 2...Adhesive layer for film for cover coat 3...Circuit pattern 4.
...Adhesive layer for base film 5...Base film

Claims (1)

[Claims] (1) First and second synthetic resin film layers, a metal foil circuit pattern disposed between the two film layers, and an adhesive that adheres the two film layers with the metal foil circuit pattern interposed therebetween. A flexible printed circuit board that is bent into a substantially U-shape, and that the outer film layer when bent is a synthetic resin film having an elongation of 150% or more based on ASTM D 882-80. Features a flexible printed circuit board for bending.