JPH0424983A - Flexible printed board for bending - Google Patents

Abstract

PURPOSE:To prevent the disconnection of a belt type circuit part for an earth line when bending and stretching are repeated, by branching the belt type circuit part for an earth line of the part to be bent in a U-type, into a plurality of a narrow belts. CONSTITUTION:A wide belt circuit part 2 for an earth line in a metal foil circuit pattern is branched into a plurality of narrow belts, at a bending part A, thereby forming a branching circuit 3, whose width is set nearly equal to the width of a belt type circuit part 1 for a signal line. In this case, in order to keep electric characteristics as the earth line, the sectional area of the total branching circuit 3 is set nearly equal to the sectional area of the belt type circuit part 2 for an earth line which is not branched. Hence the stress concentration on the bending part of the belt type circuit part 2 for an earth line is dissolved, and the stress is dispersed on the whole part of the metal foil circuit pattern, so that the generation of the situation that disconnection concentrates on the belt type circuit part 2 for an earth line can be evaded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a flexible printed circuit board for use in hard disk drives, printers, and the like.

[Conventional technology]

2. Description of the Related Art Flexible printed circuit boards with high flexibility have been used in hard disk drives (HDDs), printers, and the like. This kind of flexible printed circuit board is
As shown in Fig. 3 (cross-sectional view) and Fig. 4 (plan view of the circuit forming surface), it has a plurality of band-shaped circuit parts for signal lines and a band-shaped circuit part wider than the band-shaped circuit parts for ground wires. A base film is bonded to the negative side of the metal foil circuit pattern via a base adhesive layer, and a cover 1/if film is bonded to the other side of the metal foil circuit pattern via a coverlay adhesive layer. There is. In FIGS. 3 and 4, 1 is a signal line strip circuit part, 2 is a ground wire strip circuit part, A is a bent part, 4 is a base film, 5 is a base adhesive, 6 is a coverlay film, and 7 is a coverlay adhesive.

[Problem to be solved by the invention]

A flexible printed circuit board with this structure is
It is bent approximately at right angles to the longitudinal direction from the bent portion shown by the solid line A in FIG. 4, and repeats the bent state and the extended state as shown in FIG. 5. However, in a bendable flexible printed circuit board with such a structure, the ground wire in the metal foil circuit pattern is set wider than the signal wire in order to maintain the characteristics of the device, which causes bending and bending. By repeating the stretching, there is a problem that the wire breaks due to stress concentration at the bent portion A.

The present invention has been 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 disconnection in a band-shaped circuit portion for a ground wire even after repeated bending and stretching.

[Means for Solving the Problems] In order to achieve the above object, the flexible printed circuit board for bending of the present invention has a band-shaped circuit part for a signal line and a band-shaped circuit part for a ground line that is wider than the band-shaped circuit part. In a flexible printed circuit board in which a metal foil circuit pattern is tightly sandwiched between a pair of upper and lower synthetic resin film layers, the strip-shaped circuit portion for the ground wire that is bent into a substantially U-shape is formed into multiple narrow strips along the longitudinal direction. It has a branched configuration.

[Effect]

That is, in this invention, 1. By branching the strip circuit part for the ground wire at the bend into multiple narrow strips,
The width of each branch portion is approximately the same as the width (thickness) of the signal line. As a result, stress concentration on the band-shaped circuit portion for the ground wire is avoided, and bending stress is uniformly applied to the entire metal foil circuit pattern. Therefore, disconnection of the band-shaped circuit portion for the ground wire due to stress concentration does not occur.

Next, examples will be described.

〔Example〕

FIG. 1 (cross-sectional view) and FIG. 2 (plan view of the circuit forming surface) show an embodiment of the present invention. That is, this flexible printed circuit board for bending has a wide width in a metal foil circuit pattern. The ground wire strip circuit portion 2 is branched into a plurality of narrow strips at the bent portion A to form a branch circuit 3. The width of this branch circuit 3 is set to the width of the band-shaped circuit portion 1 for the signal line and the width of the path. In this case, in order to maintain the electrical characteristics of the ground wire, the cross-sectional area of the branch circuit 3 as a whole is set to be equal to the cross-sectional area of the strip circuit portion 2 for the unbranched ground wire. The other parts are the same as those in FIGS. 3 and 4, and the same or equivalent parts are given the same reference numerals.

As a result of this configuration, stress concentration on the ground wire strip circuit portion 2 at the bent portion is eliminated and is dispersed over the entire metal foil circuit pattern. therefore,
The occurrence of a situation in which disconnections occur intensively in the band-shaped circuit portion 2 for the ground wire can be avoided.

Next, a specific example will be explained.

〔Concrete example〕

A polyimide film (manufactured by DuPont, Kapton 300) 1) having a thickness of 75 μm was prepared as a base film and a coverlay film material. Then, an epoxy adhesive was applied to the base film, and a rolled copper foil having a thickness of 35 μm was bonded to the base film to form a base substrate. Next, a metal foil circuit pattern as shown in FIG. 2 was formed on this base material. In this case, the width of the band-shaped circuit portion 1 for the signal line is 1
In the belt-shaped circuit portion 2 for the ground wire, the convergence (thickness) of each branch circuit at the bent portion was set to 150 μm, and the width of the other portions was set to 500 μm. Next, a coverlay film was bonded to the base material using an epoxy adhesive to obtain a flexible printed circuit board as shown in FIGS. 1 and 2.

[Comparative example]

The metal foil circuit pattern was as shown in FIG. Other than that, flexible printed circuit boards as shown in FIGS. 3 and 4 were obtained in the same manner as in the above specific example.

The bending characteristics of the flexible printed circuit boards of the above specific examples and comparative examples were evaluated, and the results are shown in the table below.

(Left below) MIT folding resistance: Based on JISP8115, load 2kg
The bending angle was 2R, 135°, and the number of times was 3/sec.

Bending resistance: Based on IPC-FC-240B, bending radius was 1.5R, stroke was 25mm, and the number of cycles was 2 views/second.

As is clear from the above results, it can be seen that the MIT bending resistance and bending resistance of the specific height measurement are significantly improved compared to the comparative example.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, FIG. 2 is a plan view of its circuit forming surface, FIG. 3 is a cross-sectional view of a conventional example, and FIG.
The figure is a plan view of the circuit forming surface, and FIG. 5 is a view of the circuit in a bent state. 1... Band-shaped circuit part for signal line 2... Band-shaped circuit part for ground wire

Claims (1)

[Claims] (1) In a flexible printed circuit board in which a metal foil circuit pattern having a band-shaped circuit part for a signal line and a band-shaped circuit part wider than the band-shaped circuit part for a ground wire is tightly sandwiched between a pair of upper and lower synthetic resin film layers, approximately U 1. A flexible printed circuit board for bending, characterized in that a band-shaped ground wire circuit portion of a portion bent in a character shape is branched into a plurality of narrow band-shaped circuits along the longitudinal direction.