JP2001110487A - Connection structure of flexible printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connection structure of a flexible printed board, which is highly reliable, having holding force and contact force which do not decreased even under a server usage environment. SOLUTION: A bent beam 4 which elastically presses a flexible printed board 1 against a circuit board 2 is provided at a position, where an anisotropic conductive material 3 is arranged, and both ends of the bend beam 4 are stopped at a rear side of the circuit board 2. Thus, a wire film 1b of the flexible printed board 1 and a wire layer 2a of the circuit board 2 conduct electrically owing to the anisotropic conductive material 3. The bend beam 4 always presses against the flexible printed board, vibration resistance can be improved, and stable contact (electrical connection) corresponding to creep compression of the two substrates 1 and 2 can be maintained for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connection structure of a flexible printed circuit board which can be securely connected and fixed to a circuit board. In particular, it is most suitable for use in automobiles and the like that have a lot of vibration and a wide temperature range. For example, it is used for connecting a flexible printed circuit board provided with a pressure-sensitive sensor for detecting the weight of an occupant in a protection device of an automobile to a circuit board.

[0002]

2. Description of the Related Art Heretofore, there has been a device using an anisotropic conductive material to electrically connect a wiring film formed on a flexible printed board and a wiring layer formed on a circuit board. The anisotropic conductive material is obtained by mixing conductive particles into a resin adhesive. Since the conductive particles exist between the pair of contacts sandwiching the anisotropic conductive material, current flows between the contacts, but the conductive particles are discretely provided in the plane direction of the anisotropic conductive material. Therefore, no current flows in the lateral direction. Utilizing this property, a plurality of wiring films on a flexible printed circuit board and a plurality of corresponding wiring layers on a circuit board are electrically connected to each other while being insulated and separated from other wiring layers. is there.

As a method not using an anisotropic conductive material, as shown in FIG. 4, a wiring formed on a circuit board 2 by using a cylindrical clip ring 5 having a cross section of “C” shape. There is known one in which a layer 2a and a wiring film 1b formed on a flexible printed board 1 are mechanically and electrically contacted by elastic force.

[0004]

However, simply,
The method of obtaining electrical contact using an anisotropic conductive material is such that when the use environment temperature is 100 ° C. or higher, or when used for a long time, the adhesive property of the anisotropic conductive material changes or deteriorates. As a result, the bonding strength was reduced. As a result of the lowering of the bonding force, there is a problem that poor electrical contact occurs or the flexible printed circuit board cannot sufficiently withstand the tensile force, and the bonded portion is separated. For this reason, in a severe use environment such as a wide temperature range of the use environment and a large amount of vibration, it has not been possible to obtain an electrical contact that ensures reliability for a long period of time.

As shown in FIG. 4, a method of mechanically obtaining electrical contact by the elastic force of the clip spring 5 is as follows.
Since the connecting portion is inserted into the opening of the clip spring 5 and sandwiched, the assembling work is difficult. In addition, there is a problem that the alignment between the wiring film 1b and the wiring layer 2a is displaced at the time of insertion, or that both resin substrate surfaces are damaged. In addition, since the flexible printed circuit board 1 and the circuit board 2 are sandwiched by the clip spring 5, the disposition direction of the flexible printed circuit board 1 and the circuit board 2 is limited to one direction in which the clip spring 5 is open. There is also the problem of being done. Further, since the cross section of the clip spring 5 cannot be increased, the spring constant increases, and the clip spring 5 cannot be displaced following the creep compression of the flexible printed circuit board 1 and the circuit board 2, and the holding force and the contact force are reduced. There is a problem. Further, the flexible printed circuit board 1 is held at both edges of the clip spring 5.
And the circuit board 2, the shear force acts when vibration is applied, and the flexible printed board 1 may be damaged.

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable connection structure for a flexible printed circuit board which does not reduce the holding force and the contact force even in a severe use environment. . Another object of the present invention is to facilitate the assembly of a flexible printed circuit board on a circuit board. Still another object of the present invention is to provide a structure in which the holding force does not decrease even when vibration is applied. Still another object of the present invention is to improve the durability against vibration by providing a structure in which a shearing force does not act on a flexible printed circuit board even when vibration is applied.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, both ends are locked to a circuit board, and a central anisotropic conductive material is provided. A fixing member for elastically pressing the flexible printed board against the circuit board at the position was provided. As a result, conduction between the wiring film of the flexible printed board and the wiring layer of the circuit board is obtained by the anisotropic conductive material, and the pressing state is always maintained by the fixing member, so that the vibration resistance is improved, and the creep of both boards is improved. Following the compression, stable contact is ensured for a long period of time. In particular, this fixing member is smaller and lighter than a conventional tubular elastic member, and the connecting portion can be made compact.
Since only a small number of elastic members are required, the cost can be reduced. Further, since both sides of the fixing member are open, the direction in which the flexible printed circuit board is disposed with respect to the circuit board can be selected from the convenient direction.

According to the second aspect of the present invention, a through hole is provided in the circuit board, and both ends of the fixing member penetrate through the through hole and are locked on the surface of the circuit board on the side to which the flexible printed circuit board is not connected. You. Accordingly, the fixing member need only be pressed in from the pressing direction, and the mounting becomes easy. Further, there is no problem that the alignment between the wiring film and the wiring layer is displaced at the time of assembling or that both resin substrate surfaces are damaged.

According to the third aspect of the present invention, a through hole is provided in the circuit board, and both ends of the fixing member are press-fitted and fixed in the through holes provided in the circuit board. Accordingly, in addition to having the same operation and effect as in claim 2, the locking portions at both ends of the fixing member do not protrude to the surface side of the circuit board on the side where the flexible printed circuit board is not connected, so that the connection portion is more space-saving. And can be.

According to the fourth aspect of the present invention, both ends of the fixing member pass through the side surface of the circuit board and are locked to the surface of the circuit board to which the flexible printed circuit board is not connected. Accordingly, in addition to having the same operation and effect as in claim 2, through-holes of the circuit board for inserting the locking portions at both ends of the fixing member are not required, so that the processing of the circuit board is reduced and the cost is reduced. it can.

According to the fifth aspect of the present invention, the fixing member has a pressing portion for pressing the flexible printed circuit board at the center side, locking portions at both ends for locking to the circuit board, and a bent shape between them. And an elastic generating portion for generating a spring elastic force, and they are integrally formed. Thereby, the fixing member can be processed from one spring material,
Cost can be reduced.

According to the sixth aspect of the present invention, the fixing member has a pressing portion formed in a convex shape to the side pressing the flexible printed circuit board. This prevents the central portion of the pressing portion from floating when the both ends are locked, and prevents the pressing force from being applied, thereby ensuring the pressing state over the entire pressing portion.

According to the seventh aspect of the present invention, the fixing member is made of metal, and the hardness of the pressing portion is higher than other portions. Thereby, the rigidity of the pressing portion is increased and deformation of the pressing portion when both ends are locked is prevented, and a stable pressing state can be secured.

According to the eighth aspect of the present invention, the fixing member has a groove formed on the back side of the pressing surface of the pressing portion, and the pressing surface is formed in a semi-cylindrical shape.

According to the ninth aspect of the present invention, the fixing member has a rib formed on the back side of the pressing surface of the pressing portion, and the pressing surface is formed in a semi-cylindrical shape.

According to the tenth aspect of the present invention, the width of the pressing portion is made wider than other portions of the fixing member, and the pressing surface side is formed in a semi-cylindrical shape.

In any one of the eighth, ninth and tenth aspects, the rigidity of the pressing portion is increased, so that the pressing portion is prevented from being deformed when both ends are locked, and a stable pressing state can be ensured. In addition, since the contact surface with the flexible printed circuit board has a cylindrical shape, a shear force is not applied to the flexible printed circuit board with respect to forces in the insertion direction and the detachment direction, which are the longitudinal directions of the flexible printed circuit board, so that high reliability is achieved. Connection method.
In addition, because of the cylindrical shape, it is possible to make a small rotational displacement in the insertion direction and the detachment direction of the flexible printed circuit board. Since displacement is possible, stable contact is ensured without a decrease in pressing force, and vibration resistance is improved.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings. (First Embodiment) A first embodiment will be described with reference to FIG. FIG. 1A is a perspective view showing a structure of a connecting portion,
(B) is sectional drawing of the A section.

The flexible printed circuit board 1 is made of PET
(Polyethylene terephthalate) and PI (polyimide)
And the like, and a wiring film 1b formed on the lower surface thereof. As a method of forming the flexible printed board 1, a metal foil such as copper is formed on the resin film 1a, and the metal foil is etched into a predetermined shape to form the wiring film 1b, or a conductive ink is formed on the resin film 1a. Is printed to form the wiring film 1b. The flexible printed circuit board 1 is used, for example, to detect whether an occupant is present on a seat or to detect pressure based on weight distribution or gross weight on the seat when activating an airbag device of an automobile. It is used to derive the detection signal of the pressure switch to the outside.

A hard circuit board 2 made of resin or the like is arranged in a case (not shown). On the upper surface of the circuit board 2, a wiring layer 2a made of a metal film such as a copper film, a copper-based conductor, or an aluminum film is formed. At the connection between the circuit board 2 and the flexible printed board 1,
An anisotropic conductive material 3 is provided between the two. The anisotropic conductive material 3 is obtained by dispersing conductive particles such as nickel (Ni) in a resin adhesive or an adhesive sheet. FIG.
As shown in (b), since the conductive particles 3a exist between the wiring film 1b and the wiring layer 2a, a current flows in the thickness direction. However, in the plane direction of the anisotropic conductive material 3 (the direction parallel to the plane), an insulating base material 3b exists between adjacent conductive particles 3a, and the conductive particles 3a are not continuous.
No current flows.

A flexible beam 4 having elastic force is provided on the upper surface of the flexible printed circuit board 1 as an example of a fixing member.
Are pressed and held by the circuit board 2. In this state, stable electrical contact between the wiring film 1b and the wiring layer 2a is realized.

The bent beam 4 is made of a metal having high hardness such as spring steel, and is formed in a rod shape or a plate shape. This curved beam 4
In addition, two elastic generating portions 4c whose both ends are bent to generate a desired spring elastic force are provided at two positions on both ends.
Both ends (locking portions 4a) of the bent beam 4 are locked in the back surface 2d of the rigid circuit board 2 or in the through holes 2c. Also,
A pressing portion 4b designed to press the flexible printed circuit board 1 as uniformly as possible is provided at the center side of the bending beam 4, and the bending portion 4 is fixed by the locking portion 4a of the bending beam 4 and the elasticity generating portion 4c. The restoring force when elastically deformed is
b and the circuit board 2.

Further, due to the elastic force of the bent beam 4, even if there is a relatively large displacement at the electrical connection portion between the two substrates 1 and 2, the pressing force can be held and the response capability is high. Therefore, even if the flexible printed circuit board 1 and the circuit board 2 are plastically deformed by long-term pressing force, the bending beam 4 hardly attenuates the pressing force, and the flexible printed circuit board 1
Can be pressed. As a result, the electrical contact between the wiring film 1b and the wiring layer 2a is stabilized for a long period.

The assembly of the electrical connection between the substrates 1 and 2 is as follows. Anisotropic conductive material 3 is provided on the upper surface connecting portion of circuit board 2.
Is arranged. Next, the flexible printed circuit board 1 is overlapped while aligning the wiring layer 2a of the circuit board 2 and the wiring film 1b of the flexible printed circuit board 1 by using the positioning stud 2b provided on the circuit board 2. Then, it is bonded to the circuit board 2 by the anisotropic conductive material 3. Next, the bent beam 4 is connected to the back surface (anti-connection surface) 1 of the flexible printed circuit board 1.
The bent beam 4 is pressed from the c side to the circuit board 2 side.
Are locked through the through holes 2c provided in the circuit board 2 to the back surface 2d of the circuit board 2. Thereby, the restoring force of the elasticity generating portion 4c, which is the bent portion of the bent beam 4, becomes the pressing force of the pressing portion 4b, and the flexible printed circuit board 1 can be pressed toward the circuit board 2. (Second Embodiment) A second embodiment will be described with reference to FIG.

The locking portions 4a at both ends of the bent beam 4 are formed by press working or the like so as to be wider than other portions. In the same assembly as in the first embodiment, the locking portions 4a are formed.
May be pressed into the inner surface of the through hole 2c provided in the circuit board 2 and locked. (Third Embodiment) A third embodiment will be described with reference to FIG.

The longitudinal direction of the bent beam 4 is longer than the lateral width of the circuit board 2, and the locking portions 4 a on both sides of the bent beam 4 are locked to the back surface 2 d of the circuit board 2 via both side surfaces of the circuit board 2. May be. (Fourth Embodiment) A fourth embodiment will be described with reference to FIG.

The bending beam 4 has a pressing portion 4b for pressing the flexible printed circuit board 1 near the center, locking portions 4a at both ends for locking to the circuit board 2, and a spring elastic force in a bent shape between them. And a functional part with an elasticity generating portion 4c that generates the elastic force, and these are integrally formed with a single spring material.

In particular, in the example shown in FIG. 3A, the pressing portion 4b of the bent beam 4 has a convex shape toward the side of pressing the flexible printed circuit board 1, and the material of the bent beam 4 is a metal spring material. The hardness of the pressing portion 4b is increased with respect to other portions by heat treatment or the like. (Modification of Pressing Section 4b) In order to press the flexible printed circuit board 1 as uniformly as possible, for example, as shown in FIG.
The pressing portion 4b is formed with a groove 4d on the back side of the pressing surface by pressing or the like.
And the pressing surface side may be formed in a semi-cylindrical shape. Further, as shown in FIG. 3C, the pressing portion 4b of the bent beam 4
Alternatively, a rib 4e may be formed on the back side of the pressing surface by pressing or the like to form the pressing surface side in a semi-cylindrical shape. FIG.
As shown in (d), in the bent beam 4, the pressing portion 4b may be formed to have a semi-cylindrical shape on the pressing surface side by increasing the radial width of the pressing portion 4b with respect to other portions by press working or the like.

[Brief description of the drawings]

FIGS. 1A and 1B show a first embodiment of the present invention, wherein FIG. 1A is a perspective view showing a structure of a connecting portion, and FIG.

FIG. 2A is a cross-sectional view of a main part showing a second embodiment of the present invention, and FIG. 2B is a cross-sectional view of a main part showing a third embodiment of the present invention.

FIG. 3A shows a bent beam 4 according to a fourth embodiment of the present invention.
FIGS. 4B, 4C, and 4D are perspective views showing a modification of the pressing portion 4b of the bending beam 4. FIGS.

FIG. 4 is a perspective view showing a conventional connection structure.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 flexible printed board 1a resin film 1b wiring film 2 circuit board 2a wiring layer 2b stud 2c through hole 3 anisotropic conductive material 3a conductive particle 3b base material 4 fixing member (curved beam) 4a locking portion 4b pressing portion 4c elasticity Generating part 4d Groove part 4e Rib 5 Clip ring

Claims (10)

[Claims] A flexible printed circuit board on which a wiring film is formed, a circuit board on which a wiring layer is formed, and a circuit board disposed between the wiring film of the flexible printed board and the wiring layer of the circuit board; An anisotropic conductive material that conducts in the thickness direction but does not conduct in the plane direction, and both ends are locked to the circuit board, and the anisotropic conductive material at the center is provided at a position where the anisotropic conductive material is disposed. A connection structure for a flexible printed circuit board, comprising a fixing member for elastically pressing the flexible printed circuit board against the circuit board. 2. A circuit board, wherein a through-hole is provided in the circuit board, and both ends of the fixing member penetrate through the through-hole and are fixed to a surface of the circuit board on a side to which the flexible printed circuit board is not connected. The connection structure for a flexible printed circuit board according to claim 1. 3. The flexible printed circuit board according to claim 1, wherein a through hole is provided in the circuit board, and both ends of the fixing member are press-fitted and fixed in the through holes provided in the circuit board. Connection structure. 4. The flexible device according to claim 1, wherein both ends of the fixing member are engaged with a surface of the circuit board on a side to which the flexible printed circuit board is not connected through a side surface of the circuit board. Connection structure of printed circuit board. 5. The fixing member includes a pressing portion that presses the flexible printed circuit board at a center side, locking portions provided at both ends to lock the circuit board, and a spring elastic force in a bent shape interposed therebetween. 2. An elastic generating portion for generating the elastic force, wherein the elastic generating portion is formed integrally.
A connection structure for a flexible printed circuit board according to claim 4. 6. The flexible printed circuit board connection structure according to claim 5, wherein the fixing member has a shape in which the pressing portion is convex toward the side that presses the flexible printed circuit board. 7. The connection structure for a flexible printed circuit board according to claim 5, wherein the fixing member is made of metal, and the hardness of the pressing portion is higher than other portions. . 8. The fixing member according to claim 5, wherein a groove is formed on the back side of the pressing surface of the pressing portion, and the pressing surface is formed in a semi-cylindrical shape. The connection structure of a flexible printed circuit board according to the above. 9. The fixing member according to claim 5, wherein a rib is formed on the back side of the pressing surface of the pressing portion, and the pressing surface side is formed in a semi-cylindrical shape. The connection structure of a flexible printed circuit board according to the above. 10. The fixing member according to claim 5, wherein a width of the pressing portion is made wider than other portions, and a pressing surface side is formed in a semi-cylindrical shape. A connection structure for a flexible printed circuit board according to claim 1.