JP4816724B2 - Shielded flat cable - Google Patents

Description

  The present invention relates to a shield flat in which a plurality of conductors are arranged in parallel and covered with an insulating film, and the outside is covered and shielded by a common shield film, and at least one end thereof is provided with a terminal portion for connector connection. Regarding cables.

  Flexible flat cable (FFC) is a space-saving and easy connection in many fields such as AV equipment such as CD and DVD players, OA equipment such as copiers and printers, and internal wiring of other electronic and information equipment. It is used as. Further, since the influence of noise increases as the operating frequency of the device increases, shielded shielded flat cable cables are used. The cable shield is formed, for example, by covering the outside of the FFC with a shield film (see, for example, Patent Document 1).

  Moreover, the shield flat cable has a terminal portion that forms a connection with a connector at at least one end of the cable in order to simplify wiring. For example, the terminal portion is formed by removing the insulating film on one side of the cable end, exposing one side of a plurality of flat conductors arranged in parallel to form a contact connection portion, and a contact terminal of the connector. Electrically connected. At this terminal portion, a structure for electrically connecting the shield film to the ground is required.

  In addition, a conductor for electrical wiring such as a flat cable is made of copper having good conductivity, high ductility, suitable strength, and easy coating with other metals. The conductor using copper is generally tin-plated for the purpose of corrosion resistance and ease of soldering. Tin plating is usually formed by electroplating, and it is known that acicular crystals (hereinafter referred to as whiskers) are generated on the surface of the electrotin plating.

  This is because when a copper-based metal material is tin-plated, copper atoms diffuse during the tin-plating process, creating a copper-tin intermetallic compound with a crystal structure different from that of tin, which can strain the interstitial distance. Compressive stress is generated in the film. It is said that when this compressive stress becomes a driving force for whisker growth and tin plating is applied on a copper-based material, whiskers are likely to occur. It has also been found that whiskers are likely to occur specifically at the contact portion using an insertion / extraction type electrical connector. This is attributed to external stress applied to the surface of the tin plating by the contact terminals of the connector. This whisker generation causes an electrical short circuit between the conductors. Has been proposed.

For example, by applying a thin tin plating of less than 1.0 μm to the electrical connection portion of the electric conductor and further forming a tin alloy layer, the amount of the tin layer that is a substantial source of whisker generation is reduced. Thus, whisker generation is reduced (see, for example, Patent Document 2). In addition, there is a method of suppressing whisker generation by applying nickel plating to the entire copper conductor of the flat cable in order to enhance corrosion resistance and solderability and applying gold plating only to the connection terminal portion (for example, Patent Document 3). reference).
JP 2005-93178 A JP 2006-127939 A JP 2006-49185 A

  Assuming that the shielded flat cable has a constant characteristic impedance for use at a high frequency and has a shielding function, for example, a shielded flat cable having a structure as shown in FIG. 4 is assumed. As shown in FIG. 4 (A), the shield flat cable 1 has a plurality of flat conductors 3 for signal transmission arranged in parallel, and both surfaces (upper and lower surfaces) are sandwiched between insulating films 4 and covered with insulation. The upper film 4a of the insulating film 4 is removed at the end portion, and the portion that becomes the contact terminal is exposed to form the cable terminal portion 2. In addition, the lower film 4b that has not been removed by the cable terminal portion 2 has a form in which a reinforcing tape 6 is attached to provide strength that allows insertion into and removal from the electrical connector.

  On the upper film 4a of the insulating film 4, a ground portion 5 for ground connection is attached to a rear position separated from the flat conductor 3 so as not to cause an electrical short circuit. Next, the outer surface of the cable is shielded by using a shield film 7 (for example, a film having a three-layer shape of an insulating layer, a metal layer, and a conductive adhesive layer) so as to be electrically connected to the ground portion 5. . The ground portion 5 is exposed from the front end of the shield film 7 by a predetermined amount in order to connect to the ground connection terminal on the connector side.

In the cable terminal portion 2, the exposed contact terminal portion of the flat conductor 3 is tin-plated for the various purposes described above. In addition, in order to suppress the above-described whisker generation on the terminal portion, gold plating or the like can be taken or other various measures can be taken.
On the other hand, the ground portion 5 is also tin-plated to ensure electrical contact with the shield film 7 and prevent oxidation and corrosion. As a result, the ground contact terminal on the connector side also comes into contact with the ground portion 5, so that whiskers may occur due to external stress due to this contact.

  Whisker generated in the ground portion 5 is not particularly problematic in the ground portion 5 itself, but this whisker may fall on the exposed flat conductor 3 located in the vicinity and cause a problem in signal transmission. In order to prevent whisker generation at the ground portion 5, it is conceivable to apply gold plating in the same manner as the flat conductor 3. However, the surface area of the conductor of the ground portion 5 is relatively large, and gold plating is expensive. is there.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a shielded flat cable that can prevent a failure due to whisker generation at a ground portion where a shield film is grounded and connected at low cost.

In the shielded flat cable according to the present invention, a plurality of flat conductors are arranged in parallel and covered with an insulating film, one side of the flat conductor is exposed at at least one end to form a cable end, and the outer surface of the insulating film is A cable covered with a shield film. In the vicinity of the exposed flat conductor portion of the cable, another insulating film having a conductor width of 0.15 mm to 1.0 mm is attached on the insulating film, and the ground conductor is electrically connected to the shield film. And at least a portion exposed from the shield film is gold-plated.

Also, as one side of both ends of the other ground conductor affixed to the insulating film is exposed, it may be an intermediate portion of the ground conductor is covered with another cover film.

  According to the present invention, since the ground conductor for connecting the shield film to the ground is a narrow conductor and the gold plating is applied to the exposed portion of the predetermined area, the cost can be reduced and the generation of whiskers can be prevented. It can be reduced efficiently.

  An embodiment of the present invention will be described with reference to FIGS. 1A is a diagram for explaining the outline of a shielded flat cable according to the present invention, FIG. 1B is a diagram showing a cross section of the cable, and FIGS. 2A and 2B show examples of forming a ground conductor. FIG. In the figure, 11 is a shield flat cable, 12 is a cable terminal, 13 is a flat conductor, 14 is an insulation film, 14a is an upper film, 14b is a lower film, 15 is a ground conductor, 16 is a reinforcing tape, and 17 is a shield film. , 19 is a gold-plated portion, 20 is another insulating film, 21 is a covering film, and 22 is an adhesive layer.

  As shown in FIG. 1, the shielded flat cable 11 according to the present invention is, for example, arranged in parallel with a plurality of flat conductors 13 having a flat cross section and sandwiched between both surfaces (upper and lower surfaces) with an insulating film 14. A flat cable is used. At at least one end of the flat cable, the upper film 14a of the insulating film 14 is removed, and a portion that becomes a contact connecting portion is exposed to form the cable terminal portion 12. The lower film 14b that has not been removed by the cable terminal portion 12 is provided with a reinforcing tape 16 so that it can be inserted into and removed from the connector (female edge connector).

On the upper film 14a of the insulating film 14, for example, a narrow ground rectangular short conductor 15 is connected to the flat conductor 13 exposed in the longitudinal direction of the cable with a distance L (0. 2 mm to 10 mm) are provided at rearward positions. The ground conductor 15, of providing to the upper film 14a through the other insulating film 20 to the rear predicate is manufacturing preferred. By providing the ground conductor 15 on the outer surface of the insulating film 14, all the flat conductors 13 arranged in a row can be assigned for signals. As a result, the number of signal line conductors can be increased without increasing the lateral width of the cable.

  The outer surface of the insulating film 14 is shielded by covering almost the entire surface with a shield film 17. As the shield film 17, for example, a film having a three-layer shape of an insulating layer, a metal layer, and a conductive adhesive layer is used, and the shield film 17 is attached to the outer surface of the insulating film 14 with the conductive adhesive layer inside. The shield film 17 is attached so that the end portion thereof overlaps a part of the ground conductor 15, and the shield film 17 and the ground conductor 15 are electrically connected via the conductive adhesive layer, thereby The shield function is given to the shield film 17. The ground connection of the ground conductor 15 is realized by bringing a ground connection terminal on the connector side into contact with a portion exposed from the tip of the shield film 17.

  The signal flat conductor 13 is made of, for example, a conductive metal foil such as a copper foil or a tinned annealed copper foil, and depends on the signal transmission current value. t is 12 μm to 50 μm, the width W is about 0.3 mm, and the pitch P is 0.5 mm. The arrangement state of the flat conductors 13 is held between the upper and lower films 14 a and 14 b of the insulating film 14.

  The upper and lower films 14a and 14b have adhesive layers (not shown) on their inner surfaces (joint surfaces). For the upper and lower films 14a and 14b themselves, a resin material having excellent flexibility is used. For example, a versatile resin film such as a polyester resin, a polyphenylene sulfide resin, or a polyimide resin can be used. The resin film has a thickness of 9 to 50 μm. Examples of the polyester resin include resin materials such as polyethylene terephthalate resin, polyethylene naphthalate resin, and polybutylene naphthalate resin. Of these resin films, polyethylene terephthalate resin is preferably used from the viewpoints of electrical characteristics, mechanical characteristics, cost, and the like.

  In addition, what consists of resin materials is used for said adhesive layer, For example, the adhesive agent etc. which added the flame retardant to the polyester-type resin and the polyolefin-type resin are mentioned. This adhesive layer is formed with a thickness of 10 μm to 100 μm. The upper film 14a and the lower film 14b of the insulating film 14 are bonded and integrated by facing the adhesive layer across the flat conductor 13 and joining them while applying heat with a heating roller.

  The shield film 17 is formed of, for example, a resin layer serving as a film base material and a conductive metal such as silver deposited on the resin layer or a metal foil (aluminum foil or copper foil) bonded to the resin layer. And a three-layer structure in which a conductive adhesive is applied on the shield layer. For the resin layer, a resin film having a thickness of about 9 μm such as polyethylene terephthalate is used. The conductive adhesive layer is not only attached to the insulating film 14 but also provides electrical continuity with the ground conductor 15 to produce a shield function. For example, a silver paste or the like is applied to the silver vapor deposition surface of the shield layer Formed.

  The entire thickness of the shield film 17 is about 30 μm. As shown in FIG. 1B, the shield film 17 is wrapped so as to be wrapped in a single wide film to shield the whole. In addition, the insulating film 14 may be sandwiched from above and below by two thin shield films, and the ears may be adhered to electrically close the outer surface of the flat cable, and the cable side surface may be completely covered and shielded. .

The ground conductor 15 is formed of a conductive metal foil, for example, tin-plated annealed copper foil, similar to the flat conductor 13, and is a short rectangular conductor having a thickness of 12 μm to 50 μm and a conductor width of about 0.15 mm to 1.0 mm. Is used. As shown in FIG. 2, two or several ground conductors 15 are previously provided on another insulating film 20 by bonding or the like, and an adhesive layer 22 (for example, a double-sided adhesive tape is used on the back surface of the other insulating film 20. formed) set only by a previously formed as a ground conductor member 23a or 23b. By sticking the ground conductor member 23a or 23b on the insulating film 14, the ground conductor 15 can be easily provided at a predetermined position.

Ground conductor member 23a shown in FIG. 2 (A), paste the two ground conductors 15 on the other insulating film 20 is intended to adhesive layer 22 digits set on the back. In order to reliably form the ground connection of the ground conductor member 23a, the contact length with the shield film 17 is set to 2.5 mm or more, and the ground conductor member 23a is exposed to 2.5 mm or more from the tip of the shield film 17 to be an external ground member. Need to be connected. Therefore, the ground conductor member 23a is formed with a length of 5.0 mm or more.

The ground conductor member 23b shown in FIG. 2 (B) has two to several ground conductors 15 attached on another insulating film 20, an adhesive layer 22 is provided on the back surface, and both ends of the ground conductor 15 are exposed. the intermediate portion is obtained by coating with the covering film 21. In order to reliably form the ground connection of the ground conductor member 23b, the contact length with the shield film 17 is set to 2.5 mm or more, and the contact length with the external ground conductor is exposed to 2.5 mm or more. It is necessary to make the length of the covering film 21 at the intermediate portion 15 mm or more in production. Therefore, the ground conductor member 23b is formed with a length of 20 mm or more.

In the cable terminal portion 12, the flat conductor 13 is tin-plated for various purposes as described above. In addition, various measures such as applying gold plating can be taken on the exposed contact terminal portion to suppress whisker generation as required.
The ground conductor 15 is also tin-plated to ensure electrical contact with the shield film 17 and prevent oxidation and corrosion. In this case, when an external stress is received by bringing the connector-side ground connection terminal into contact, whisker generation is expected as described above.

  In the present invention, the ground conductor 15 is formed of a narrow conductor having an electrical contact surface necessary for ground connection of the shield film 17 and is exposed to a connecting member such as a ground terminal on the connector side. The above-described whisker generation is suppressed by applying gold plating 19 to the surface. As shown in FIGS. 2A and 2B, the gold plating 19 is applied to a predetermined region on at least one end side in a state where the ground conductor 15 is provided on the other insulating film 20. The entire ground conductor 15 may be gold-plated 19 as long as it is gold-plated at least in the above-described region, which can effectively prevent whisker generation and reduce the cost for that. The price can be kept low.

FIG. 3 is a diagram illustrating an example of a manufacturing method of the ground conductor member 23b illustrated in FIG. As shown in FIG. 3 (A), another insulating film 20 in the form of a tape is arranged on one side (lower surface side) of a long ground conductor 15 having a flat cross-sectional angle that is continuously supplied, and the other side (upper surface). The other insulating film 21 in the form of a tape having an opening window 24 is disposed on the side) and laminated and integrated by a heating roller 25 or the like. Alternatively, a double-sided adhesive tape may be applied to the lower surface side of the other insulating film 20 as an adhesive layer 22 and laminated simultaneously.

Another insulating film 20, the ground conductor 15, after piece laminate to be covered film 21, as shown by a chain line in FIG. 3 (B), by cutting at the center of both side edge portions and the opening window 24, Fig. Thus, the ground conductor member 23b having the form shown by 2 (B) is obtained. Alternatively, the ground conductor 15b may be continuously fed into the gold plating tank before being divided into the ground conductor member 23b, and the ground conductor 15 exposed from the opening window 24 may be plated with gold. It should be noted that a portion other than the gold plating is partially masked on the opening window 24 so that the extra area is not plated.

It is a figure explaining the outline of the shield flat cable by this invention. It is a figure which shows the structural example of the ground conductor member used for this invention. It is a figure which shows the manufacture example of the ground conductor member used for this invention. It is a figure explaining a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Shield flat cable, 12 ... Cable terminal part, 13 ... Flat conductor, 14 ... Insulating film, 14a ... Upper film, 14b ... Lower film, 15 ... Ground conductor, 16 ... Reinforcement tape, 17 ... Shield film, 17a ... Ear part, 18 ... grounding bar member, 19 ... gold plating, 20 ... other insulating film, 21 ... covering film, 22 ... adhesive layer , 23a, 23 ... ground conductor member.

Claims (2)

A plurality of flat conductors are arranged in parallel and covered with an insulating film, one side of the flat conductor is exposed at at least one end to be a cable end, and the outer surface of the insulating film is covered with a shield film A shielded flat cable,
Another insulating film in which a ground conductor having a conductor width of 0.15 mm to 1.0 mm is attached on the insulating film in the vicinity of the exposed flat conductor portion, and the ground conductor is the shield film. A shielded flat cable characterized in that gold plating is applied to at least a portion exposed from the shield film. 2. The shielded flat cable according to claim 1 , wherein an intermediate portion is covered with a covering film so that one side of both ends of the ground conductor attached to the other insulating film is exposed.