JPH0832194A - Flexible printed board for thermal fusion, and its connection mechanism - Google Patents

Abstract

PURPOSE:To enable a worker to judge whether the thermal fusion between wiring patterns is good or bad, and enhance the resistance to separation by providing a small hole through a wiring pattern exposed part, where a cover film at one end of a flexible printed board is removed, and a base film. CONSTITUTION:A wiring pattern 3 is printed on the surface of a base film 2 made of polyimide, and a cover film 4 made of polyester is bonded on it. The end of the cover film 4 is removed, and small holes 5 are provided at specified pitches through the exposed wiring pattern 3a and the base film 2 vertically. Next, a hot melt adhesive is applied in belt shape to the vicinity of the exposed part 3a of the wiring pattern so as to form a hot melt layer 6. Next, a solder layer is formed by pressure-welding the wiring patterns to the layer 6 and heating them. The remainder of the fused solder solidifies within the small hole 5, and firmly connects the wiring pattern of the printed board with the wiring pattern 3a of FPC for thermal fusion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed board used for connecting internal units and parts of an electronic device to each other, for example, a rigid printed board and a connector of an external cable. The present invention relates to the above-mentioned flexible printed board characterized by the structure of the connecting portion and its connecting structure.

[0002]

2. Description of the Related Art A flexible printed circuit board (hereinafter referred to as "FPC") having a large number of wiring patterns printed in the longitudinal direction of a band-shaped insulating flexible film, particularly for connection between internal units and parts of electronic devices. ) Is widely used.
The FPC is extremely thin and can provide a large number of wiring patterns on a single base film. Therefore, the FPC is particularly effective when a complicated electronic circuit needs to be mounted in a narrow space.

Since the FPC is a type of cable, its end must be connected to an electric unit to be connected, for example, a rigid printed board (hereinafter simply referred to as "printed board"). A connector is usually used for the connection between the cable and the electric unit. In the case of FPC as well, it is basically connected to a printed board or the like via a connector, but since the connector is extremely thick compared to FPC, the mounting space for the connector is an obstacle to downsizing of the device. The situation occurs.

Therefore, in such a case, a connection structure is adopted in which the FPC and the printed board are connected by directly soldering the FPC wiring pattern and the printed board wiring pattern. When this connection structure is adopted, the structure shown in FIG.
Further, as shown in FIG. 6, the cover film 4 at the end portion of the FPC 15 is peeled off, the exposed wiring pattern 3a is overlapped with the wiring pattern 8 of the printed board 7 and heat-sealed with the solder layer 11.

In this case, the FP connected to the printed board 7
The hot melt layer 6 is provided in advance on the end portion of the cover film 4 of C, and when the wiring patterns 8 and 3a are heat-sealed to each other, the end portion of the cover film 4 and the printed board 7 are formed by the hot melt layer 6. It is performed by heat fusion to secure the mechanical strength of the connection between the FPC 15 and the printed board 7. That is, even when an external force is applied to the FPC when the device is assembled or used, the external force is prevented from directly acting on the heat-sealed portion (solder layer) 11 of the wiring patterns 8 and 3a.

[0006]

However, the heat-sealed portion 11 between the wiring patterns 8 and 3a by soldering and the heat-sealed portion 6 between the FPC 15 and the printed board 7 formed by the hot-melt layer 6 are both in the peeling direction. Since the resistance is relatively weak, when an external force is applied to the FPC 15 in the direction of peeling the heat-sealed portions 11 and 6, the wiring patterns 8 and 3a are peeled from each other, resulting in poor connection or poor connection. There was a risk of a wire breakage accident. Therefore, at the connection portion where such a problem may occur, the end portion of the FPC 15 is connected to the printed board 7.
The fixing component 16 that is sandwiched between and is provided. For example, as shown in FIG. 7, the fixing component 16 is fixed by soldering legs 17 protruding from both ends thereof to the printed board 7, and the fixing component 16 is pressed from above and soldered. By doing so, when the peeling direction force is applied to the FPC 15 by sandwiching the end portion of the FPC 15, the fixing component 16 receives the force.

The fixing component 16 is usually made of a metal plate or a resin molded product provided with an insulating sheet 18 at the contact portion with the FPC 15. However, if the fixing component is bent by an external force. Since the anti-stripping effect cannot be expected, a corresponding rigidity is required, so the mounting space becomes large as in the case where the thickness becomes thick and a connector is provided. Has become a factor that inhibits. Further, when such a fixing component 16 is used, there is a problem that the component cost and the number of assembling steps increase, leading to an increase in the cost of the apparatus.

Further, since the heat-sealing portion 11 between the wiring patterns 8 and 3a is on the back surface side of the FPC 15, it is difficult to visually confirm whether or not the heat-sealing has been performed well. However, there is a problem in that it is impossible to confirm or make a decision.

An object of the present invention is to solve the above problems, and when the wiring pattern of the FPC is directly connected to the wiring pattern of the printed board or other electronic unit by soldering, the mechanical strength of the heat-sealed portion thereof. It is an object to improve the reliability of the connection portion of the FPC by increasing the size of the FPC and making it possible to confirm whether or not the connection is performed well.

[0010]

According to the present invention, a conventional FP is used.
The above problem is solved by providing the small hole 5 penetrating the base film 2 in the exposed portion 3a of the wiring pattern of C15. The small holes 5 can be formed by edging or laser processing. The FPC 1 of the main body in which such a small hole 5 is formed in the exposed portion 3a of the wiring pattern is obtained by positioning the wiring patterns 8 and 3a with respect to the wiring pattern 8 of the mating unit 7 that has been subjected to paste solder or solder plating. They are superposed and preferably heated and heat-sealed in a state where a pressing force is applied to the contact surfaces of the both 8 and 3a.

In the state where the FPC 1 of the present invention is connected to the counterpart unit 7, the molten solder enters the small holes 5 of the FPC and solidifies to form the solder fillet 12.

[0012]

The exposed portion 3a of the wiring pattern of the FPC having the above structure
Is superposed on the wiring pattern 8 of the electric unit such as the printed board 7 to be connected, and both patterns 3a and 8 are soldered, the melted solder enters the small hole 5 to form the solder fillet 12. When the solder fillet 12 meshes with the small hole 5, the FP
A large resistance force against the force of peeling C1 is generated.

Since the small hole 5 also penetrates the cover film 4, the fillet 12 that has penetrated into the small hole 5 and solidified.
The penetration state of the head can be easily viewed with a loupe or the like, and the quality of heat fusion between the wiring patterns 8 and 3a can be determined.

Since the small holes 5 penetrate the base film 2, the molten solder is not prevented from entering the small holes 5. If the FPC 1 and the wiring patterns 3a and 8 of the electric unit 7 on the opposite side are heated while being pressed against each other at the time of heat fusion, the penetration of the molten solder into the small holes 5 becomes more reliable.

[0015]

1 and 2 show an embodiment of the present invention. The FPC 1 for heat fusion of the present invention has a structure in which a wiring pattern 3 made of tin-plated annealed copper foil is printed on the surface of a base film 2 made of polyimide in the longitudinal direction, and a cover film 4 made of polyester is adhered thereon. The end portions of the cover film 4 are peeled off, and the exposed wiring patterns 3a and the base film 2 are provided with small holes 5 vertically penetrating at a predetermined pitch. A hot melt layer 6 formed by applying a hot melt adhesive in a strip shape is provided on an end portion of the cover film, that is, in the vicinity of the exposed portion 3a of the wiring bun.

3 and 4 show the connection structure of the present invention. The wiring pattern 8 of the printed board 7 which is an internal unit of the electronic device is plated with solder, and the exposed portion 3a of the wiring pattern of the FPC 1 for heat fusion of the above-described embodiment is brought into contact with the wiring pattern 8 and the wiring patterns 3a.
They are pressed against each other and heated at 240 degrees Celsius for a predetermined time. The heating causes the solder plating to melt and become molten solder, and a part thereof becomes the solder layer 11 connecting the wiring patterns 8 and 3a.
Since the FPC of the present invention has the small hole 5 penetrating the base film 2 in the wiring pattern 3a and opening on the upper surface thereof, the remainder of the molten solder smoothly rises and solidifies in the small hole 5. To form the fillet 12 in the small hole 5. Since the fillet 12 firmly connects the wiring pattern 8 of the printed board and the wiring pattern 3a of the FPC for heat fusion, the resistance to the peeling direction is improved.

After the soldering is completed, the penetration state of the fillet 12 in the small hole 5 is visually confirmed using a loupe or the like,
When the heat fusion between the wiring patterns 8 and 3a is considered to be insufficient or when a particularly high peel strength is required, the hot melt layer 6 previously attached to the cover film 4 is provided on the upper surface of the printed board 7. It is preferable that the cover film 4 and the printed board 7 are welded to each other by being pressed against and heated to 120 degrees Celsius to increase the resistance in the peeling direction of the FPC 1.

[0018]

INDUSTRIAL APPLICABILITY As described above, the FPC for heat fusion of the present invention
Can form a solder fillet in the small hole of the FPC by superposing the wiring pattern of the exposed part on the wiring pattern of the solder-plated electric unit and heating it, and the formed solder fillet becomes the wiring pattern of the FPC. Since it is caught, the FPC can be prevented from peeling off. Also, since the small holes penetrate the base film,
Molten solder can penetrate quickly. Since the infiltration state of the fillet formed in the small hole can be easily visually confirmed using a loupe or the like, it is possible to determine the quality of heat fusion between the wiring patterns. As a result of the judgment, if it is considered that the resistance to peeling is insufficient, the FP in the hot melt layer is
The resistance to peeling can be reinforced by heat-sealing C and the printed board.

[Brief description of drawings]

FIG. 1 is a back view of an FPC for heat fusion of the present invention.

FIG. 2 is a sectional view of the FPC for heat fusion of the present invention.

FIG. 3 is a plan view showing a connection structure.

FIG. 4 is a cross-sectional view showing a connection structure.

FIG. 5 is a plan view showing a conventional FPC and its connection structure.

FIG. 6 is a sectional view showing a conventional FPC and its connection structure.

FIG. 7 is a side view showing a conventional FPC and its connection structure.

[Explanation of symbols]

 1 FPC for heat fusion 2 Base film 3 Wiring pattern 3a Exposed part 4 Cover film 5 Small hole 6 Hot melt layer 7 Printed board 11 Solder layer 12 Fillet

Claims (3)

[Claims] 1. A plurality of wiring patterns (3) are provided between the insulating base film (2) and the insulating cover film (4) along the longitudinal direction of the two, and the cover film is provided at one end thereof. The exposed part (3) of the wiring pattern (3) where the (4) is peeled off
In a flexible printed board provided with a), each of the wiring patterns of the exposed portion (3a), a small hole (5) penetrating the exposed portion (3a) of the wiring pattern and the base film (2)
A flexible printed board for heat fusion, which is provided with. 2. The flexible printed board for heat fusion according to claim 1, wherein a hot melt layer (6) is provided at an end of the insulating cover film (4) on the exposed side of the wiring pattern. 3. The wiring pattern (3a) of the flexible printed board (1) for heat fusion according to claim 1 or 2 and the wiring pattern (8) of the electric unit (7) connected thereto are soldered. Layer (1
A connection structure for a flexible printed board, characterized in that the solder fillet (12) is heat-sealed in (1) and the molten solder penetrates into the small hole (5) and is solidified.