JP4318554B2 - Flexible printed circuit board - Google Patents

Description

  The present invention relates to a flexible printed circuit board, and more particularly to a flexible printed circuit board used for a hinge portion of a mobile phone or the like.

  The case of a foldable mobile phone is usually provided with a receiving unit including a display unit, a transmitting unit including a keypad unit, and a hinge unit that rotatably supports these units. The talking part is connected via a hinge part so as to be opened and closed.

  In addition, a flexible printed circuit board for transmitting an electrical signal or supplying power between the receiver unit and the transmitter unit passes through the hinge unit from the receiver unit inside the housing. It is installed to reach the talk section.

  As the flexible printed circuit board installed in this way, for example, a lower part located in the transmitting part, a central part located in the hinge part, and an upper part located in the receiving part are formed and formed in a crank shape. The thing is known (for example, refer patent document 1).

Japanese Patent Laid-Open No. 2002-300247 (FIG. 6)

  However, the above-described crank-shaped flexible printed circuit board has a bent portion that bends at right angles between the lower portion and the central portion and between the upper portion and the central portion, and the hinge portion of the receiving portion and the transmitting portion. By repeating the opening and closing operation via the conductor, a large bending stress is intermittently applied to the bent portions, and the conductor patterns such as signal lines and power lines arranged in the flexible printed circuit board in the bent portions are fatigued. This causes the problem of disconnection.

  An object of the present invention is to provide a flexible printed circuit board capable of reducing damage such as fatigue disconnection and extending the bending life significantly even by repeated bending operations.

In order to achieve the above object, a flexible printed circuit board according to the present invention includes a belt-like central portion, a direction substantially perpendicular to the longitudinal direction of the central portion from both ends of the central portion, and the A flexible printed circuit board that is integrally provided with strip-shaped connecting portions extending in opposite directions with respect to the central portion, and at least one of the bent portions in which the central portion and the connecting portions are continuous An inner side where the width direction end portion of the central portion and the width direction end portion of the connection portion are opposed to each other in a direction inclined toward the direction in which the connection portion extends with respect to the longitudinal direction of the central portion A reinforcing portion that bulges so that an end in the width direction of the central portion and an end in the width direction of the connecting portion are continuous, and the reinforcing portion is substantially isosceles in a plan view. Formed in a triangle, front The reinforcing portion, the length of substantially equal sides, the percentage of the value obtained by dividing the width direction length of the central portion is characterized by 20 to 90%.
In the flexible printed circuit board of the present invention, the percentage of a value obtained by dividing the length of substantially equal sides in the reinforcing portion by the length in the width direction of the central portion is 45 to 70%.
Is preferred.

  In the flexible printed circuit board of the present invention, it is preferable that the reinforcing portion is provided on both of the bent portions.

  According to the flexible printed circuit board of the present invention, the reinforcing portion that bulges so that the width direction end portion of the center portion and the width direction end portion of the connection portion are continuous is provided inside the bent portion. Therefore, the bending stress generated in the bent portion by the bending operation can be reduced by the reinforcing portion. As a result, even when the bending operation is repeated, damage such as fatigue disconnection can be reduced, and the bending life can be greatly extended.

  FIG. 1 is a plan view showing an embodiment of a flexible printed circuit board according to the present invention.

  In FIG. 1, this flexible printed circuit board is used to electrically connect two members, such as a foldable mobile phone, that are rotatably supported via a hinge portion.

  The flexible printed circuit board has a flat plate band shape having flexibility, and is formed in a crank shape in a plan view having two bent portions that are bent in a right angle direction.

  More specifically, the flexible printed circuit board includes a belt-like central portion 1 and a belt-like first connecting portion 2 extending from one longitudinal end of the central portion 1 in a direction perpendicular to the longitudinal direction of the central portion 1. From the other end in the longitudinal direction of the central portion 1, a band-shaped second connection portion 3 extending in a direction orthogonal to the longitudinal direction of the central portion 1 and opposite to the direction in which the first connection portion 2 extends. Integrated.

  The central portion 1 has a substantially rectangular shape in plan view, and has a longitudinal length L1 of, for example, 5 to 30 mm, preferably 10 to 25 mm, and its width direction (a direction orthogonal to the longitudinal direction, hereinafter the same). .) The length W1 is 2 to 15 mm, preferably 5 to 10 mm.

  The first connection portion 2 has a substantially rectangular shape in plan view, is continuous from one longitudinal end portion of the central portion 1 and extends in a direction perpendicular to the longitudinal direction of the central portion 1, and its longitudinal length L2 is For example, it is formed to 10 to 50 mm, preferably 20 to 30 mm, and its width direction length W2 is formed to 2 to 15 mm, preferably 5 to 10 mm.

  The second connection portion 3 has a substantially rectangular shape in plan view, is continuous from the other longitudinal end portion of the central portion 1, and is opposite to the direction in which the first connection portion 2 extends with respect to the longitudinal direction of the central portion 1. It extends in a right angle direction, and its longitudinal length L3 is, for example, 10 to 50 mm, preferably 20 to 30 mm, and its width direction length W3 is 2 to 15 mm, preferably 5 to 10 mm. ing.

  Note that the width direction length W2 of the first connection portion 2 and the width direction length W3 of the second connection portion 3 are substantially equal, and the width direction length W1 of the central portion 1 is the first connection. It is preferable that the width direction length W2 of the portion 2 and the width direction length W3 of the second connection portion 3 are substantially equal to or slightly shorter than the width direction length W3.

  In the flexible printed circuit board, a first reinforcing portion 5 is formed in a first bent portion 4 where the central portion 1 and the first connecting portion 2 are continuous, and the central portion 1 and the second connecting portion 3 are formed. A second reinforcing portion 7 is formed in the second bent portion 6 where the and are continuous.

  The first reinforcing portion 5 has an inner side 10 of the first bent portion 4, that is, a side surface 8 at one end in the width direction of the central portion 1 and a side surface 9 at one end in the width direction of the first connecting portion 2. On the inner side 10 (in FIG. 1, the outer side 11 of the first bent portion 4 is also shown) facing in the inclined direction D1 inclined in the direction in which the first connecting portion 2 extends with respect to the longitudinal direction. Is provided.

The first reinforcing portion 5 is formed to bulge from the first bent portion 4 so that the side surface 8 at one end in the width direction of the central portion 1 and the side surface 9 at one end in the width direction of the first connecting portion 2 are continuous. They are substantially isosceles triangles in plan view.

More specifically, the length L4 of the side surface 8 at one end in the width direction of the central portion 1 where the first reinforcing portion 5 is continuous, and the width direction one end portion of the first connecting portion 2 where the first reinforcing portion 5 is continuous. the length L5 of the side surface 9, the actual qualitatively equal properly, that is, the first reinforcing portion 5, in plan view, isosceles length L4 and L5 are substantially equal, i.e., at a right angle isosceles triangle that has been formed.

A first reinforcing portion 5, in plan view, be formed as an isosceles triangle, while achieving a reliable reinforcement, it can be efficiently produced a flexible printed circuit board.

  Note that the lengths L4 and L5 are substantially equal, for example, the percentage of the value obtained by dividing the difference between L4 and L5 by L4 or L5 is within 20%, that is, (L4-L5) / L4 ( Or L5) × 100 = ± 20% difference is included.

The length L4 is percentage 2 0% to 90% of the value obtained by dividing the width length W1 of the central portion 1, good Mashiku the range 45-70% i.e., L4 / W1 × 100 = 2 It is preferable that it is 0 to 90% or 45 to 70%. If it is less than 20 % or more than 90 %, it may not be possible to extend the life of a sufficient bending life.

The length L5, similarly to the above, percentages are 2 0% to 90% of the value obtained by dividing the width direction length W2 of the first connecting part 2, good Mashiku the range 45-70% i.e., It is preferable that L5 / W2 × 100 = 2 to 90% or 45 to 70%. If it is less than 20 % or more than 90 %, it may not be possible to extend the life of the bending life as described above.

Further, the first reinforcing portion 5, opposite end face 12 of the first bent section 4 that are formed in a linear shape in a flat plane view. By forming the end surface 12 of the first reinforcing portion 5 in a straight line in a plan view, it is possible to improve the production efficiency and the reinforcement.

  The second reinforcing portion 7 includes an inner side 15 of the second bent portion 6, that is, a side surface 13 at the other end in the width direction of the central portion 1 and a side surface 14 at the other end in the width direction of the second connecting portion 3. The inner side 15 (in FIG. 1, the outer side 16 of the second bent portion 6 is also shown) facing in the inclined direction D2 inclined in the direction in which the second connecting portion 3 extends with respect to the longitudinal direction of 1. ).

The second reinforcing portion 7 bulges from the second bent portion 6 so that the side surface 13 at the other end in the width direction of the central portion 1 and the side surface 14 at the other end in the width direction of the second connecting portion 3 are continuous. It is formed and is formed in an isosceles triangle substantially in plan view.

More specifically, the length L6 of the side surface 13 of the other end in the width direction of the central portion 1 where the second reinforcing portion 7 continues, and the other end in the width direction of the second connecting portion 3 where the second reinforcing portion 7 continues. the length L7 of parts of the side surface 14, the actual qualitatively equal properly, that is, the second reinforcing portion 7, in a plan view, the length L6 and L7 are substantially equal isosceles triangles, i.e., a right angle isosceles that it has been formed in a triangle.

The second reinforcing portion 7, in plan view, be formed as an isosceles triangle, while achieving a reliable reinforcement, it can be efficiently produced a flexible printed circuit board.

  Note that the lengths L6 and L7 are substantially equal, for example, the percentage of the value obtained by dividing the difference between L6 and L7 by L6 or L7 is within 20%, that is, (L6-L7) / L6 ( Or L7) × 100 = ± 20% difference is included.

The length L6 is percentage 2 0% to 90% of the value obtained by dividing the width length W1 of the central portion 1, good Mashiku the range 45-70% i.e., L6 / W1 × 100 = 2 It is preferable that it is 0 to 90% or 45 to 70%. If it is less than 20 % or more than 90 %, it may not be possible to extend the life of a sufficient bending life.

The length L7, similarly to the above, percentages are 2 0% to 90% of the value obtained by dividing the width length W3 of the second connecting part 3, good Mashiku the range 45-70% i.e., It is preferable that L7 / W3 × 100 = 2 to 90% or 45 to 70%. If it is less than 20 % or more than 90 %, it may not be possible to extend the life of the bending life as described above.

Further, the second reinforcing portion 7, the second bent portion 6 opposite to the end surface 17, that are formed in a linear shape in a flat plane view. By forming the end face 17 of the second reinforcing portion 7 in a straight line in plan view, it is possible to improve production efficiency and reinforcement.

  Next, a method for manufacturing such a flexible printed circuit board will be briefly described with reference to FIG.

  2, in this method, first, as shown in FIG. 2A, a base insulating layer 21 is prepared. The base insulating layer 21 is not particularly limited as long as it has insulating properties and flexibility. For example, polyimide resin, acrylic resin, polyether nitrile resin, polyether sulfone resin, polyethylene terephthalate resin, polyethylene naphthalate resin It consists of a resin film such as polyvinyl chloride resin. Preferably, it consists of a polyimide resin film. The insulating base layer 21 has a thickness of 5 to 30 μm, for example.

  Next, in this method, as shown in FIG. 2B, the conductor layer 22 is formed on the insulating base layer 21 as a wiring circuit pattern. The conductor layer 22 is not particularly limited as long as it has conductivity. For example, a metal such as copper, chromium, nickel, aluminum, stainless steel, copper-beryllium, phosphor bronze, iron-nickel, and alloys thereof. Formed from foil. Preferably, it forms from copper foil. Moreover, the thickness of the conductor layer 22 is 3-25 micrometers, for example.

  Moreover, in order to form the conductor layer 22 as a wiring circuit pattern, well-known patterning methods, such as an additive method and a subtractive method, are used.

  Next, in this method, as shown in FIG. 2C, a cover insulating layer 23 is formed on the base insulating layer 21 so as to cover the conductor layer 22 formed as a wiring circuit pattern. The insulating cover layer 23 is made of the same resin film as described above, and is preferably made of a polyimide resin film. The insulating cover layer 23 is formed by, for example, applying or printing a resin solution, drying and curing, or attaching a resin film. Furthermore, after applying the photosensitive resin solution, it can be formed simultaneously with patterning by exposure and development. The insulating cover layer 23 has a thickness of 2 to 15 μm, for example.

  In forming the insulating cover layer 23, the conductor layer 22 formed as a wiring circuit pattern is exposed at the free end portion of the first connection portion 2 and the free end portion of the second connection portion 3 in the flexible printed circuit board. Thus, the connection terminal portions 24 and 25 are respectively formed (see FIG. 1). The connection terminal portions 24 and 25 may be formed at the same time as the cover insulating layer 23 is formed, for example, by printing a resin solution or patterning a photosensitive resin. When a resin film is attached, the opening is formed by a known method such as drilling, punching, laser processing, or etching.

  And in this method, as shown in FIG.2 (d), it forms in the above-mentioned planar view crank shape. Although it does not restrict | limit in particular in forming in a planar view crank shape, For example, well-known processing methods, such as punching, are used.

  In the flexible printed circuit board thus formed, the side surface 8 at one end in the width direction of the central portion 1 and the side surface 9 at one end in the width direction of the first connecting portion 2 are continuous inside the first bent portion 4. The first reinforcing portion 5 bulging out is formed, and the side surface 13 at the other end in the width direction of the central portion 1 and the width direction of the second connecting portion 3 are formed on the inner side 15 of the second bent portion 6. The 2nd reinforcement part 7 which bulges so that the side surface 14 of an other end part may continue is formed. Therefore, the bending stress generated in the first bent portion 4 and the second bent portion 6 by the bending operation can be reduced by the first reinforcing portion 5 and the second reinforcing portion 7. As a result, even when the bending operation is repeated, damage such as fatigue disconnection of the conductor layer 22 formed as the wiring circuit pattern can be reduced, and the bending life can be greatly extended.

  Therefore, even if this flexible printed circuit board is placed on a member that repeatedly bends, such as a hinge portion of a folding mobile phone, damage such as fatigue breakage is reduced, and good connection reliability is achieved over a long period of time. Can be maintained.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the examples and comparative examples.

Preparation of flexible printed circuit board A base insulating layer made of polyimide having a thickness of 13 μm was prepared (see FIG. 2A), and a conductor layer made of copper foil having a thickness of 10 μm was formed on the base insulating layer by an additive method. The wiring circuit pattern was formed (see FIG. 2B).

  Thereafter, a cover insulating layer made of polyimide having a thickness of 13 μm was formed on the base insulating layer so as to cover the conductor layer formed as the wiring circuit pattern. In forming the insulating cover layer, do not form the insulating cover layer at positions corresponding to the free end of the first connection portion and the free end of the second connection portion in the punched flexible printed circuit board. The conductor layer formed as a wiring circuit pattern was exposed to form a connection terminal portion (see FIG. 2C).

Thereafter, it is substantially the same shape as the crank shape in a plan view shown in FIG. 1, and the width direction lengths W1, W2, and W3 of the central portion, the first connection portion, and the second connection portion are all 5 mm, and
1) The length L4 of the side surface of one end in the width direction of the central portion where the first reinforcing portion continues,
2) The length L5 of the side surface of one end in the width direction of the first connecting portion where the first reinforcing portion is continuous,
3) The length L6 of the side surface of the other end in the width direction of the central portion where the second reinforcing portion is continuous,
4) The length L7 of the side surface of the other end in the width direction of the second connecting portion where the second reinforcing portion is continuous.
Were set to various lengths shown in Table 1 and punched out to obtain flexible printed circuit boards of Examples 1 to 5 and Comparative Example 2 (see FIG. 2D).

  In the flexible printed circuit board of Comparative Example 1, the first reinforcing portion and the second reinforcing portion were not formed in this punching.

Evaluation (flexural properties)
By the finite element method, the stress applied to the conductor layer arranged in the first bent portion and the second bent portion generated at the time of 180 ° bending was calculated.

  The relative stress magnitude (%) when the comparative example in which the first reinforcing portion and the second reinforcing portion were not formed was set to 100 was obtained and used as a criterion for evaluation. The results are shown in Table 1.

FIG. 1 is a plan view showing an embodiment of a flexible printed circuit board according to the present invention. It is a manufacturing process figure which shows the manufacturing method of the flexible printed circuit board shown in FIG. 1, Comprising: (a) is a process which prepares a base insulating layer, (b) is a wiring circuit on a base insulating layer and a conductor layer. (C) is a step of forming a cover insulating layer on the base insulating layer so as to cover the conductor layer formed as a wiring circuit pattern, and (d) is a crank shape in plan view. The process of forming is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Center part 2 1st connection part 3 2nd connection part 4 1st bending part 5 1st reinforcement part 6 2nd bending part 7 2nd reinforcement part 10 Inside of 1st bending part 15 Inside of 2nd bending part

Claims (3)

A band-shaped central portion and a band-shaped connecting portion extending in opposite directions to the central portion in a direction substantially perpendicular to the longitudinal direction of the central portion from both ends of the central portion are integrated. A flexible printed circuit board,
Among the bent portions in which the central portion and the connection portions are continuous, at least one of the bent portions includes a width direction end portion of the central portion and a width direction end portion of the connection portion. Bulges so that the widthwise end of the central portion and the widthwise end of the connecting portion are continuous on the inner side facing each other in a direction inclined toward the extending direction of the connecting portion with respect to the longitudinal direction There is a reinforcement part ,
The reinforcing part is substantially formed in an isosceles triangle in plan view,
The percentage of the value obtained by dividing the length of substantially equal sides in the reinforcing portion by the width direction length of the central portion is 20 to 90%.
A flexible printed circuit board characterized by the above.   The percentage of the value obtained by dividing the length of substantially equal sides in the reinforcing portion by the width direction length of the central portion is 45 to 70%.
The flexible printed circuit board according to claim 1, wherein: The reinforcing portion is characterized in that provided on both of each of the bent portions, the flexible wired circuit board according to claim 1 or 2.

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