JP2002033554A - Flexible printed wiring board capable of being bent by 180 degrees - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible wiring board which has connection reliability even when used by bending by 180 deg. at a very-small diameter. SOLUTION: Cover lays 3 are adhered to both the sides of the folding line of a 180 deg. folded part except a width of several mm. After an anisotropic conductive film 4 is mounted by the folded part avoiding the adhesion of the cover lays 3, a guide is applied to the folding line and the base material 1 with wiring patterns 2 is folded. In a state (c) of Fig.1 bent by 180 deg., the part of the anisotropic conductive film 4 is heated and pressed to make a mutual electric connection between wiring patterns brought into contact with both the surfaces of the anisotropic conductive film 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the design of a flexible printed wiring board, and more particularly to a flexible printed wiring board that can be bent 180 degrees.

[0002]

2. Description of the Related Art Although flexible printed wiring boards have been used only for a limited number of times, demand has been increasing again due to the explosion of portable terminal electronic devices in recent years. The features of the flexible printed wiring board are that it is thin, bendable, moves locally, can change the relative position between connections, and can be folded and stacked in multiple layers. In order to take advantage of its features, a polyimide film or polyester film having a thickness of 25 μm to 100 μm (typically 40 to 50 μm) is used for the base material,
As the copper foil for forming a wiring pattern adhered to the base material, a rigid printed wiring board is a copper foil made of plated copper, whereas a rolled copper foil is used to ensure strength against bending.

[0003]

As described above, although some measures have been taken to endure bending, there are operating conditions that must be observed in order to avoid disconnection of the wiring pattern due to bending fatigue. This is one of the usages where it is desired to avoid bending at an extremely small radius by 180 degrees. On the other hand, for a small electronic device, bending at an extremely small radius at 180 degrees is also one of the most desirable uses. The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a flexible printed wiring board which does not impair connection reliability even when used by being bent at an extremely small radius by 180 degrees.

[0004]

According to a first aspect of the present invention, there is provided a flexible printed wiring board having a 180-degree bendable flexible wiring board having a continuous wiring pattern on at least one surface thereof. An anisotropic conductive film is arranged perpendicular to the pattern, the flexible printed wiring board is folded and overlapped so as to sandwich the anisotropic conductive film, and the sandwiched anisotropic conductive film portion is thermocompressed to face each other. The wiring patterns to be connected are electrically connected.

According to the flexible printed wiring board of the first aspect, the wiring patterns on both sides of the 180-degree bent portion are electrically connected by the anisotropic conductive film. It is formed.

According to a second aspect of the present invention, the wiring pattern of the flexible printed wiring board is divided at the predetermined bending position.

According to the flexible printed wiring board which can be bent by 180 degrees according to the second aspect, since there is no wiring pattern at the bent portion by 180 degrees, the bending process is easy.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a flexible printed wiring board bent at an extremely small radius of 180 degrees showing an embodiment according to the present invention. FIG. 1A is a plan view, and FIG. FIG. 1 (c) is a cross-sectional view of a state of being bent at an extremely small radius of 180 degrees as viewed from the side. In FIG. 1, 1 is a base material such as a polyimide resin film, 2 is a wiring pattern on the base material 1, 3 is a coverlay of a polyimide resin film or the like adhered on the base material 1 and the wiring pattern 2, and 4 is anisotropic. It is a conductive film.

In the figure, the back surface pattern and the through holes are omitted, but first, the base material 1 to which the copper foil has been adhered.
, Through-hole drilling, copper plating, resist treatment,
The wiring pattern 2 is formed through etching. Then
The cover lay 3 is adhered to the 180-degree bent portion while leaving a width of several mm on both sides of the folding line. First, the anisotropic conductive film 4 is placed on the bent portion where the coverlay 3 is not bonded, and then the base 1 with the wiring pattern 2 is bent by applying a guide to the fold line portion. By making the state of FIG. 1 (c) bent by 180 degrees and thermocompression bonding the portion of the anisotropic conductive film 4,
Wiring patterns in contact with both surfaces of the anisotropic conductive film 4 are electrically connected to each other.

FIG. 2 is a cross-sectional view of the embodiment in which the wiring pattern is divided at the predetermined bending position as viewed from the side in a bent state. Regarding the bending and thermocompression bonding using the anisotropic conductive film 4,
It is the same as FIG.

Here, assuming that the thickness of the anisotropic conductive film 4 is 100 μm, the bending radius of the wiring pattern portion is 50 μm from FIG. 1C. If the thickness of the wiring pattern is 30 μm, the expansion and contraction of the bent outer and inner wiring patterns are approximately ± 23%. It is not normal that the wiring pattern made of rolled copper foil and copper plating is broken by this one-time bending. However, if the pattern is too thin, the copper plating is too thick, or if there is an unnoticeable scratch on the pattern, a crack will occur in the conductor at the bent portion, making it impossible to guarantee reliability. The anisotropic conductive film 4 disposed at the bent portion is a means for compensating for breakage of the bent portion wiring pattern. Even if the bent portion wiring pattern is cracked or broken, the connection by the anisotropic conductive film 4 can be made. An established state can be maintained.

[0012]

According to the present invention, even when the flexible printed wiring board is designed to be used by bending it 180 degrees with a very small radius, the connection of the bent portion is anisotropic with the wiring pattern itself. Because it is doubled from the conductive film, even if the wiring pattern breaks at the bent part, the connection is maintained, so the flexible printed wiring board that is used by bending it 180 degrees with a very small radius is used Sex design can be possible.
Further, in the method of dividing the bent portion wiring pattern according to another embodiment, there is no redundant system of the bent portion pattern, but the bending process is easy because there is no pattern in the bent portion.

[Brief description of the drawings]

FIG. 1 is a schematic view of a flexible printed wiring board showing an embodiment according to the present invention, FIG. 1 (a) is a plan view, FIG. 1 (b) is a cross-sectional view seen from a side, FIG. (C) is a cross-sectional view as viewed from the side, in a state of being bent at a minimum radius of 180 degrees.

FIG. 2 is another embodiment of the present invention in which a wiring pattern is divided at a predetermined bending position, and is a cross-sectional view of a folded state viewed from a side.

[Explanation of symbols]

 Reference Signs List 1 base material such as polyimide resin film 2 wiring pattern 3 coverlay such as polyimide resin film 4 anisotropic conductive film

Claims (2)

[Claims] 1. A flexible printed wiring board having a continuous wiring pattern on at least one side, an anisotropic conductive film is disposed at a predetermined bending position of the wiring pattern so as to be orthogonal to the wiring pattern. The flexible printed wiring board is folded and overlapped so as to sandwich a film, and the sandwiched anisotropic conductive film portion is thermo-compressed to electrically connect opposed wiring patterns. Flexible printed wiring board. 2. The flexible printed wiring board according to claim 1, wherein the wiring pattern of the flexible printed wiring board is divided at the predetermined bending position.