JP7373703B2 - Cable joining method - Google Patents

Description

The present invention relates to a cable joining method for joining a cable, in which a plurality of wiring lines are adhered to a base material with an adhesive, to a substrate.

2. Description of the Related Art In recent years, electronic devices in which rigid substrates (hereinafter simply referred to as "substrates") made of hard base materials with low flexibility are connected with highly flexible cables have been widely used. Patent Document 1 discloses that FPC (Flexible Printed Circuits), in which multiple wirings are formed by etching a metal foil formed on the surface of a thin and highly flexible insulating base material, are bonded to electrodes of a substrate by thermocompression bonding. It is disclosed that

Additionally, as a highly flexible cable, FFC (Flexible Flat Cable), which has thin, highly flexible insulating base material bonded to the top and bottom of the wires arranged in parallel with adhesive, is also frequently used. . A flexible flat cable is connected to a board by removing the base material on one side of the tip end to expose one side of the wiring, and attaching the exposed part to a socket mounted on the board. In addition, flexible flat cables are sometimes connected (joined) to the board by removing the base material on both sides of the tip to expose the upper and lower surfaces of the wiring, and then thermocompressing the entire exposed part to the electrodes of the board. .

International Publication No. 2010/070779

However, in the conventional technology, when connecting the flexible flat cable to the board, it is necessary to use a dedicated socket, which has the problem of increasing costs. Additionally, when thermocompression bonding all exposed parts of a flexible flat cable to electrodes on a board without using a socket, an additional processing step is required to insulate the exposed part of the flexible cable wiring after crimping, which is costly. There was a problem in that the number increased.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a cable joining method that can connect a flexible flat cable to a board at low cost.

The cable joining method of the present invention is a cable joining method in which a cable having a plurality of wirings bonded to the base material with a first adhesive is joined to a substrate having a plurality of electrodes formed on the surface thereof, the cable joining method comprising: With the second adhesive positioned between the substrate and the substrate, the exposed portion of the plurality of electrodes is exposed from the first adhesive on the opposite side of the surface where the plurality of wires of the cable are bonded to the substrate. aligning and thermocompression bonding the cable to the substrate, the first adhesive having a thermoplastic property and the second adhesive having a thermoplastic or thermosetting property; , the first adhesive is applied between the plurality of electrodes by the thermocompression bonding, and the second adhesive is left on the side surfaces of the plurality of electrodes by the thermocompression bonding, and the first adhesive is applied between the plurality of electrodes by the thermocompression bonding. The first adhesive is introduced in between .

According to the present invention, a flexible flat cable can be connected to a substrate at low cost.

(a) Plan view (b) Bottom view (c) Cross-sectional view near the center (d) Cross-sectional view of the exposed portion of a flexible flat cable according to an embodiment of the present invention (a) (b) Process explanatory diagram for joining a flexible flat cable according to an embodiment of the present invention to a board (a) (b) Process explanatory diagram for joining a flexible flat cable according to an embodiment of the present invention to a board (a) (b) Process explanatory diagram for joining a flexible flat cable according to an embodiment of the present invention to a board (a) (b) (c) Cross-sectional views illustrating the process of joining a flexible flat cable according to an embodiment of the present invention to a substrate (a) (b) Cross-sectional views illustrating the process of joining a flexible flat cable according to an embodiment of the present invention to a board (a) Cross-sectional view (b) Enlarged cross-sectional view of a connected structure according to an embodiment of the present invention (a) Cross-sectional view (b) Enlarged cross-sectional view of another example of the connection structure according to one embodiment of the present invention

An embodiment of the present invention will be described in detail below with reference to the drawings. The configuration, shape, etc. described below are examples for explanation, and can be changed as appropriate depending on the specifications of the flexible flat cable, substrate, adhesive, etc. Hereinafter, corresponding elements in all drawings will be denoted by the same reference numerals, and redundant explanation will be omitted.

First, with reference to FIG. 1, the configuration of a flexible flat cable (hereinafter simply referred to as "cable 1") to be connected to an electrode of a substrate will be described. Figure 1 (a) is a plan view of the cable 1 seen from above, Figure 1 (b) is a bottom view of the cable 1 seen from below, and Figure 1 (c) is the vicinity of the center of the cable 1 shown in Figure 1 (b). 1(d) is a BB sectional view of the exposed portion 1a formed at both ends of the cable 1 shown in FIG. 1(b).

The cable 1 has a structure in which a plurality of (six in this case) wirings 2 arranged in parallel are bonded to an upper base material 4 and a lower base material 5 with a first adhesive 3. The first adhesive 3 has thermoplasticity, and the upper base material 4 and the lower base material 5 are flexible insulators. At both ends of the cable 1, exposed parts 1a are formed where the lower base material 5 is removed and a plurality of wiring lines 2 are exposed. As shown in FIG. 1D, in the exposed portion 1a, in addition to the lower base material 5, the first adhesive 3 adhering to the lower surface of the plurality of wirings 2 is also removed. That is, in the exposed portion 1a, the side opposite to the surface on which the plurality of wires 2 of the cable 1 are bonded to the upper base material 4 is exposed from the first adhesive 3. Note that the exposed portion 1a may be formed at an intermediate position of the cable 1.

Next, the substrate 10 to which the cable 1 is bonded will be described with reference to FIG. 2(a). The substrate 10 is a printed circuit board in which conductor wiring (not shown) is formed on or inside a hard insulating base with low flexibility, and components 11 such as chip resistors and integrated circuit components are mounted on the surface. ing. Further, on the surface of the substrate 10, a plurality of electrodes 12 to be connected to the wirings 2 of the cable 1 are formed in correspondence with the intervals between the wirings 2 of the cable 1.

Next, with reference to FIGS. 2(b) to 6(b), a cable joining process (joining method) for joining a plurality of wires 2 of a cable 1 to a plurality of electrodes 12 of a substrate 10 will be described in order. 5(a) to FIG. 6(b) schematically represent the cross section of the vicinity of the plurality of electrodes 12 of the substrate 10 and the exposed portion 1a formed on the cable 1 connected to the electrodes 12.

In FIG. 2B, first, the second adhesive 14 stored in the dispenser 13 is applied to the plurality of electrodes 12 of the substrate 10 held on a substrate holding stage (not shown) using the dispenser 13. . FIG. 5A shows the state after the second adhesive 14 is applied to the plurality of electrodes 12 of the substrate 10. The second adhesive 14 is thermoplastic or thermosetting, and includes conductive metal particles 15 containing solder or the like that melts by thermocompression bonding.

The second adhesive 14 may be in the form of a fluid liquid or in the form of a sheet. The second adhesive 14 formed in a sheet shape is attached to the plurality of electrodes 12 on the substrate 10 . In this way, the second adhesive 14 is attached to the plurality of electrodes 12 on the substrate 10. Further, the second adhesive 14 may be attached to the plurality of wiring lines 2 in the exposed portion 1a of the cable 1. That is, when placing the cable 1 to be described later on the board 10, the second adhesive 14 may be located between the wiring 2 of the cable 1 and the electrode 12 of the board 10.

In FIG. 3A, the camera 16 then recognizes the positions of the substrate 10 held on the substrate holding stage and the cable 1 held on the holding head (not shown). Next, based on this recognition result, the substrate holding stage and the holding head are moved relatively to align the substrate 10 and the cable 1. That is, the surface where the plurality of wires 2 of the cable 1 are bonded to the plurality of electrodes 12 on the base material (upper base material 4) with the second adhesive 14 positioned between the cable 1 and the substrate 10. The cable 1 is placed on the substrate 10 by aligning the exposed portion 1a with the opposite side exposed from the first adhesive 3 (FIGS. 3(b) and 5(b)).

In FIG. 4A, next, using the crimping tool 17 and the substrate lower support member 18, pressure is applied for a predetermined period of time while heating the vicinity of the plurality of electrodes 12 of the substrate 10 and the exposed portion 1a of the cable 1. 12 and the plurality of wirings 2 in the exposed portion 1a are bonded by thermocompression. For example, the crimping tool 17 and the substrate lower support member 18 heat the electrode 12 to 150 degrees and apply a pressure of 2 MPa for 15 seconds to bond the electrode 12 and the wiring 2 by thermocompression (FIGS. 5(c) to 6(b)). b)).

During the thermocompression bonding process, the first adhesive 3 and the second adhesive 14 heated by the compression bonding tool 17 gradually soften. Then, due to the pressure applied from the crimping tool 17, the distance between the electrode 12 of the substrate 10 and the wiring 2 of the cable 1 gradually narrows while the conductive metal particles 15 contained in the second adhesive 14 are sandwiched between them ( Figure 5(c)). When the first adhesive 3 and the second adhesive 14 are further softened by further heating, the first adhesive 3 enters between the electrodes 12 while pushing away the second adhesive 14 (see FIG. 6). a)).

In FIG. 6(b), when further heated, the conductive metal particles 15 (solder) between the electrode 12 and the wiring 2 are melted, and a solder joint 19 that joins the electrode 12 and the wiring 2 is formed. Furthermore, a convex portion 3a into which the first adhesive 3 has entered is formed between the plurality of electrodes 12 on the substrate 10 by thermocompression bonding. Further, the thermosetting second adhesive 14 undergoes a curing reaction and changes from a liquid state to a cured product 14a (solid).

In the example of FIG. 6(b), the first adhesive 3 enters between the plurality of electrodes 12 while leaving the second adhesive 14 that has changed into a cured material 14a on the side surfaces of the plurality of electrodes 12. A convex portion 3a is formed. That is, the second adhesive 14 (cured material 14a) is placed on the side surface of the plurality of electrodes 12 after bonding, and the first adhesive 3 forming the convex portion 3a is the second adhesive 14. It enters between the plurality of electrodes 12 via. In this way, the cable 1 is thermocompression bonded to the substrate 10.

Next, with reference to FIGS. 7(a) and 7(b), a structure of a connection structure C including a plurality of electrodes 12 of a substrate 10 and a plurality of wirings 2 of an exposed portion 1a formed by thermocompression bonding. I will explain about it. FIG. 7(b) is an enlarged view of the chain line portion D shown by the one-dot chain line in FIG. 7(a). A solder joint 19 is formed between the electrode 12 and the wiring 2 by conductive metal particles 15 (solder) melted during thermocompression bonding. That is, the electrode 12 and the wiring 2 are electrically connected to each other by the solder joint 19 .

Note that if the conductive metal particles 15 are made of a minute metal that does not melt during thermocompression bonding, the conductive metal particles 15 pierce the electrode 12 and the wiring 2 by thermocompression bonding, so that the electrode 12 and the wiring 2 are electrically connected. Connected. Further, by bringing the electrode 12 and the wiring 2 into close contact during thermocompression bonding, it is also possible to ensure electrical connection between the electrode 12 and the wiring 2 without using the solder joint 19 or the conductive metal particles 15.

In FIG. 7B, between the plurality of electrodes 12 of the substrate 10, a convex portion into which the first adhesive 3 has penetrated is formed with a cured material 14a formed on the side surface of the electrode 12 and the surface of the substrate 10. 3a is formed. That is, the connection structure C includes a convex portion 3 a formed between the plurality of electrodes 12 by the first adhesive 3 . Furthermore, the connection structure C includes an adhesive part (cured material 14a) between the plurality of electrodes 12, which adheres the convex part 3a and the substrate 10. In this way, by forming the convex portions 3a, the area in which the first adhesive 3 contacts the plurality of electrodes 12 directly or via the cured product 14a in which the second adhesive 14 is changed is increased. The strength with which the cable 1 is bonded to the plurality of electrodes 12 on the substrate 10 can be increased.

Note that if the amount (thickness) of the first adhesive 3 that adheres the upper base material 4 of the cable 1 and the wiring 2 is sufficient to bond the cable 1 and the board 10, the second adhesive The cable 1 may be joined to the substrate 10 without using the cable 14. In that case, the electrical connection between the electrode 12 and the wiring 2 can be ensured by bringing the electrode 12 and the wiring 2 into close contact with each other by thermocompression bonding.

Next, another example of the connected structure C (hereinafter referred to as "connected structure C1") will be described with reference to FIGS. 8(a) and 8(b). FIG. 8(b) is an enlarged view of the chain line portion E indicated by the one-dot chain line in FIG. 8(a). The connection structure C1 differs from the connection structure C shown in FIG. 7 in that the tip of the convex portion 3a is directly adhered to the surface of the substrate 10 without using an adhesive portion (cured material 14a). Such a connection structure C1 is formed by continuing thermocompression bonding until the first adhesive 3 that has entered between the plurality of electrodes 12 reaches the surface of the substrate 10. By bonding the tip of the convex portion 3a directly to the surface of the substrate 10, the bonding strength between the cable 1 and the substrate 10 can be increased.

As explained above, in the cable joining method of this embodiment, with the second adhesive 14 positioned between the cable 1 and the substrate 10, the plurality of wires 2 of the cable 1 are attached to the plurality of electrodes 12. The cable 1 is thermocompression bonded to the substrate 10 by aligning the exposed portion 1a exposed from the first adhesive 3 with the surface opposite to the surface bonded to the base material (upper base material 4). In addition, the connection structure C formed by this cable connection method has a plurality of electrodes 12 formed on the surface of the substrate 10 and a plurality of wiring lines 2 on the exposed portion 1a of the cable 1, and a plurality of A convex portion 3 a formed by the first adhesive 3 is provided between the electrodes 12 .

Thereby, the flexible flat cable (cable 1) can be joined to the board 10 without using a dedicated socket. Further, since the upper part of the joint between the wiring 2 of the flexible flat cable and the plurality of electrodes 12 of the substrate 10 is covered with the upper base material 4 which is an insulator, an additional step of insulating treatment after joining is not necessary. In this manner, the cable joining method of this embodiment allows the flexible flat cable to be connected to the board 10 at low cost.

Furthermore, in the present invention, since the first adhesive used to construct the cable is used as an adhesive for bonding to the substrate, the amount of the second adhesive that is additionally used can be reduced. As a result, the cost required for the cable joining method can be reduced.

The cable joining method of the present invention has the effect that a flexible flat cable can be connected to a board at low cost, and is useful in the field of mounting components on a board.

1 Cable 1a Exposed part 2 Wiring 3 First adhesive 3a Convex part 4 Upper base material (base material)
5 Lower base material (base material)
10 Substrate 12 Electrode 14 Second adhesive 14a Cured product (adhesive part)
15 Conductive metal particles C, C1 connected structure

Claims (5)

A cable joining method in which a cable having a plurality of wirings bonded to a base material with a first adhesive is joined to a substrate having a plurality of electrodes formed on the surface thereof, the method comprising:
an exposed portion where the opposite side of the surface of the plurality of electrodes where the plurality of wires of the cable are bonded to the base material is exposed from the first adhesive with the second adhesive being positioned between the cable and the substrate; Align the position of
thermocompression bonding the cable to the substrate ;
The first adhesive has thermoplasticity,
The second adhesive has thermoplastic or thermosetting properties,
entering the first adhesive between the plurality of electrodes by the thermocompression bonding;
A cable joining method, wherein the first adhesive is introduced between the plurality of electrodes while the second adhesive is left on the side surfaces of the plurality of electrodes by the thermocompression bonding. The cable joining method according to claim 1 , wherein thermocompression bonding is continued until the first adhesive that has entered between the plurality of electrodes reaches the surface of the substrate. The cable joining method according to claim 1 or 2 , wherein the second adhesive contains conductive metal particles. 4. The cable joining method according to claim 3 , wherein the conductive metal particles include solder that melts by the thermocompression bonding. 5. The cable joining method according to claim 1 , wherein the second adhesive is in liquid form or sheet form.

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